The Proposed Dredging of the Navigation Channel at Sligo Harbour Vol. 1: Environmental Appraisal Report
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Sligo Harbour Dredging Environmental Appraisal Report Contents
CONTENTS
VOLUME 1 – ENVIRONMENTAL APPRAISAL REPORT
1.0 INTRODUCTION ...... 1-1 1.1 PROJECT SUMMARY ...... 1-1 1.2 EXISTING PORT FACILITIES ...... 1-2 1.3 STRATEGIC POLICY DRIVERS ...... 1-4 1.3.1 National Policy ...... 1-4 1.3.2 Regional/Local Policy...... 1-9 1.3.3 Other Relevant Policies ...... 1-15 1.4 PROJECT JUSTIFICATION ...... 1-17 1.4.1 Background ...... 1-17 1.4.2 Sligo Port ...... 1-19 1.4.3 Customers ...... 1-22 1.4.4 Economic Impact ...... 1-24 1.4.5 The Economic Impact arising from Construction ...... 1-27 1.4.6 The Positive Impact of Development ...... 1-28 1.4.7 Conclusion ...... 1-29 1.5 CONSIDERATION OF ALTERNATIVES ...... 1-31 1.5.1 Alternative Locations...... 1-31 1.5.2 Alternative Designs ...... 1-32 1.5.3 Alternative Processes ...... 1-34 1.6 THE CONSENTING PROCESS ...... 1-44 1.6.1 Required Permissions ...... 1-44
2.0 CONSULTATIONS ...... 2-1 2.1 STATUTORY CONSULTATIONS ...... 2-1 2.2 DUMPING AT SEA CONSULTATIONS ...... 2-2 2.3 PUBLIC CONSULTATION ...... 2-5 2.4 ADDITIONAL OFFSHORE FISHERIES CONSULTATION ...... 2-7 2.5 LOCAL AQUACULTURE ...... 2-8 2.6 RESPONSE TO ISSUES RAISED DURING CONSULTATION ...... 2-8 2.7 CONCLUSIONS ...... 2-8
3.0 SITE DESCRIPTION ...... 3-1 3.1 INTRODUCTION ...... 3-1
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3.2 SITE CONTEXT AND EXISTING LAND USE ...... 3-3 3.2.1 Sligo Harbour Development ...... 3-3 3.3 NATURE CONSERVATION DESIGNATIONS ...... 3-4 3.3.1 Natura 2000 ...... 3-4 3.3.2 Other Designations ...... 3-9
4.0 PROJECT DESCRIPTION...... 4-1 4.1 EXISTING CONDITIONS ...... 4-1 4.2 WATER INJECTION MAINTENANCE DREDGING AT JETTIES TO -2.0M CD ...... 4-2 4.3 DESIGN OF PROPOSED CAPITAL & MAINTENANCE DREDGING WORKS TO -3.0MCD ...... 4-2 4.3.1 Channel Depth ...... 4-2 4.3.2 Channel Width ...... 4-5 4.3.3 Channel Side Slopes ...... 4-5 4.3.4 Channel Alignment ...... 4-5 4.3.5 Dredging Quantities ...... 4-5 4.4 PROPOSED DISPOSAL METHOD ...... 4-6 4.5 DREDGING METHODOLOGY ...... 4-6 4.5.1 Equipment ...... 4-6 4.5.2 Dredging Programme...... 4-7 4.5.3 Personnel ...... 4-8 4.5.4 Navigation...... 4-8 4.5.5 Waste ...... 4-8
5.0 BIRDS ...... 5-1 5.1 BACKGROUND...... 5-1 5.1.1 Description of Proposed Works ...... 5-1 5.1.2 Previous Information ...... 5-1 5.2 ASSESSMENT METHODOLOGY ...... 5-2 5.2.1 Legislation and guidance ...... 5-2 5.2.2 Consultations ...... 5-2 5.2.3 Desktop review ...... 5-3 5.3 FIELD SURVEYS ...... 5-3 5.4 ECOLOGICAL EVALUATION AND IMPACT SIGNIFICANCE ...... 5-4 5.5 BASELINE ENVIRONMENT...... 5-5
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5.5.1 Designated Areas for Nature Conservation ...... 5-5 5.5.2 Cummeen Strand SPA (Site Code 004035)...... 5-6 5.5.3 Cummeen Strand/Drumcliff Bay candidate SAC (site code 0627) .....5-7 5.6 DESCRIPTION OF EXISTING BIRD POPULATIONS AND USAGE OF THE AREA ...... 5-8 5.6.1 General description of the study area ...... 5-8 5.6.2 Bird populations of the entire area of Sligo Harbour ...... 5-8 5.6.3 Bird usage of the area within 1km of the shipping channel ...... 5-10 5.6.4 Bird usage of the shipping channel and immediate banks only ...... 5-11 5.7 PREDICTED IMPACTS OF THE PROPOSED DREDGING ...... 5-14 5.7.1 Potential impacts on birds ...... 5-14 5.7.2 Likely direct impacts on birds ...... 5-14 5.7.3 Impacts on the Tidal Regime of Sligo Harbour ...... 5-16 5.8 LIKELY INDIRECT IMPACTS ON BIRDS...... 5-17 5.9 MITIGATION MEASURES ...... 5-22 5.9.1 Mitigation by Reduction/Remedy ...... 5-22 5.10 RESIDUAL IMPACTS ...... 5-22
6.0 INTERTIDAL AND SUBTIDAL FLORA AND FAUNA, MARINE MAMMALS ...... 6-1 6.1 INTRODUCTION ...... 6-3 6.2 INTERTIDAL AND SUBTIDAL FLORA & FAUNA – DREDGING AREA ...... 6-4 6.2.1 Introduction ...... 6-4 6.2.2 Desktop Study ...... 6-4 6.2.3 Field Survey – Aquafact 2010 ...... 6-13 6.2.4 Sligo Harbour Intertidal and Subtidal Flora and Fauna - Predicted Impacts ...... 6-40 6.3 SUBTIDAL FLORA AND FAUNA – OFFSHORE DUMP SITE ...... 6-51 6.3.1 Introduction ...... 6-51 6.3.2 Results ...... 6-58 6.3.3 Proposed Dumpsite Baseline Conditions - Conclusions ...... 6-69 6.3.4 Predicted Impacts at the Proposed Offshore Dump Site ...... 6-71 6.3.5 Mitigation of the Potential Impacts at the Dump Site and Residual Impacts ...... 6-74 6.4 MARINE MAMMALS ...... 6-75 6.4.1 Legislation pertaining to Marine Mammals in Irish waters ...... 6-75 6.4.2 Desktop Study of Marine Mammals in the Area ...... 6-75 6.4.3 Site visit ...... 6-80
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6.4.4 Potential Impacts of Dredging on Marine Mammals and Identification of Sensitive Receptors...... 6-82 6.4.5 Direct, Indirect and Cumulative Impacts of Proposed Dredging and Dumping of Dredged Material on Pinnipeds...... 6-84 6.4.6 Direct, Indirect and Cumulative Impacts of Proposed Dredging and Dumping of Dredged material on Cetaceans ...... 6-86 6.4.7 Assessment of impact magnitude and significance ...... 6-86 6.4.8 Marine Mammals - Mitigation Measures...... 6-87 6.4.9 Marine Mammals - Residual Impacts ...... 6-87
7.0 FISHERIES AND AQUACULTURE ...... 7-3 7.1 INTRODUCTION ...... 7-3 7.2 COMMERCIAL FISHERIES ...... 7-3 7.2.1 Irish Brown Crab Fishery ...... 7-3 7.2.2 The North West Crab Fishery ...... 7-5 7.2.3 Other Inshore Fisheries ...... 7-9 7.3 AQUACULTURE ...... 7-12 7.3.1 Introduction ...... 7-12 7.3.2 Shellfish Production ...... 7-13 7.3.3 Annual Production ...... 7-15 7.4 Shellfish Waters Directive ...... 7-15 7.4.1 Classification of Shellfish Production Waters ...... 7-16 7.5 SALMONID MIGRATIONS ...... 7-17 7.5.1 Life Cycle ...... 7-17 7.5.2 Salmon Conservation...... 7-17 7.5.3 Local salmon/sea trout rivers ...... 7-18 7.5.4 RECREATIONAL SEA ANGLING ...... 7-19 7.5.5 Shore Angling ...... 7-19 7.5.6 Boat Angling ...... 7-20 7.6 EEL & LAMPREY MIGRATIONS ...... 7-20 7.6.1 Eel (Anguilla anguilla) ...... 7-20 7.6.2 Lamprey...... 7-20 7.7 IMPACT ASSESSMENT ...... 7-22 7.7.1 Potential Effects of Dredging and Disposal of Dredged Materials at Sea ...... 7-22 7.7.2 Socio-Economic and Conservation Aspects ...... 7-22
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7.7.3 Impact Hypotheses ...... 7-24 7.7.4 Potential Impacts of the Scheme ...... 7-25 7.8 MITIGATION MEASURES ...... 7-28 7.8.1 Dredging Area...... 7-28 7.8.2 Dredge Disposal Site ...... 7-28
8.0 AIR AND CLIMATE ...... 8-1 8.1 CLIMATE ...... 8-1 8.1.1 Wind ...... 8-1 8.1.2 Temperature ...... 8-2 8.1.3 Precipitation ...... 8-2 8.1.4 Potential Impacts on Climate ...... 8-4 8.1.5 Potential Impacts on Air Quality ...... 8-4 8.2 NOISE ...... 8-4 8.2.1 Existing Environment ...... 8-4 8.2.2 Evaluation Criteria ...... 8-4 8.2.3 Assessment of Temporary Construction Noise Impact ...... 8-5 8.2.4 Comment on Noise Associated with Dredging ...... 8-6 8.2.5 Mitigating Measures for Temporary Construction Works ...... 8-8 8.2.6 Conclusions ...... 8-8
9.0 MATERIAL ASSETS ...... 9-1 9.1 INFRASTRUCTURE ...... 9-1 9.1.1 Water Supply ...... 9-1 9.1.2 Sewerage Infrastructure ...... 9-2 9.1.3 Surface Water ...... 9-3 9.1.4 Mechanical and Electrical Services ...... 9-5 9.2 TRAFFIC ...... 9-6 9.2.1 Background ...... 9-6 9.2.2 Existing Baseline Conditions ...... 9-6 9.2.3 Existing Flows taken from Model ...... 9-8 9.2.4 Predicted Impacts During Dredging ...... 9-9 9.2.5 Mitigation Measures ...... 9-9 9.2.6 Conclusions ...... 9-10 9.2.7 Percentage Increase ...... 9-11
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10.0 GEOLOGY AND SOILS ...... 10-1 10.1 SOLID GEOLOGY ...... 10-1 10.1.1 Regional Geology ...... 10-2 10.2 HYDROGEOLOGY ...... 10-3 10.2.1 Potential Impacts to Groundwater ...... 10-4 10.2.2 Predicted Impacts to Groundwater...... 10-5 10.3 GROUND CONDITIONS ...... 10-5 10.3.1 Dredging Area Sediment Physical Properties ...... 10-5 10.4 OFFSHORE DISPOSAL SITE ...... 10-8 10.4.1 INFOMAR Survey ...... 10-8 10.4.2 Field Surveys ...... 10-11 10.4.3 Dumpsite Sediments Properties Conclusions ...... 10-14
11.0 HYDRODYNAMIC MODELLING ...... 11-1 11.1 COMPUTATIONAL MODEL OF WATER INJECTION DREDGING OPERATIONS (5,500M³) ...... 11-1 11.1.1 Modelling Software ...... 11-1 11.1.2 Hydrodynamic Flow Model ...... 11-1 11.1.3 Bathymetry ...... 11-2 11.1.4 Model Calibration ...... 11-3 11.1.5 Model Simulations ...... 11-3 11.1.6 Dredging Plume Simulation Modelling ...... 11-5 11.1.7 Results of the Dredging Simulations ...... 11-9 11.1.8 Suspended Sediments, pH and Dissolved Oxygen ...... 11-13 11.1.9 Sensitive Areas ...... 11-16 11.1.10Conclusion ...... 11-20 11.2 COMPUTATIONAL MODEL OF CONVENTIONAL DREDGING OPERATIONS (250,000M³) ...... 11-22 11.2.1 Introduction ...... 11-22 11.2.2 Computational Models ...... 11-22 11.2.3 Model simulations ...... 11-23 11.2.4 Impacts of Dredging on Sensitive Habitats ...... 11-34 11.3 DUMPSITE PLUME MODELLING ...... 11-43 11.3.1 Disposal Site Dispersion ...... 11-43 11.3.2 Modelling System ...... 11-44 11.3.3 Ambient Tidal and flow Conditions ...... 11-46 11.3.4 Modelling Results ...... 11-48
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11.3.5 Wave induced Sediment Transport ...... 11-56 11.3.6 Dumping at Sea Impacts Summary & Conclusions ...... 11-57
12.0 CULTURAL HERITAGE ...... 12-1 12.1 INTRODUCTION ...... 12-1 12.2 ASSESSMENT METHODOLOGY ...... 12-1 12.2.1 Limitations ...... 12-2 12.2.2 Classification of Impacts/Effects ...... 12-2 12.3 THE RECEIVING ENVIRONMENT ...... 12-3 12.3.1 Overview...... 12-3 12.3.2 Placenames ...... 12-5 12.3.3 Topographic files, National Museum of Ireland ...... 12-6 12.3.4 Record of Monuments and Places ...... 12-6 12.3.5 Intertidal Survey ...... 12-8 12.3.6 National Inventory of Architectural Heritage ...... 12-8 12.3.7 Cartographic Sources ...... 12-9 12.3.8 Shipwreck Inventory ...... 12-9 12.3.9 Licensed archaeological work ...... 12-11 12.3.10 Conclusion ...... 12-11 12.4 ARCHITECTURAL SITE ASSESSMENT ...... 12-12 12.5 MARINE GEOPHYSICAL SURVEY ...... 12-12 12.5.1 Nature of record ...... 12-13 12.5.2 Harbour ...... 12-13 12.5.3 Marine Disposal Area...... 12-15 12.5.4 Conclusion ...... 12-16 12.6 PREDICTED IMPACTS ...... 12-17 12.7 RECOMMENDATIONS ...... 12-17 12.7.1 Pre-construction Measures ...... 12-17 12.7.2 Construction Phase Measures ...... 12-17 12.7.3 Archaeological/Cultural Heritage Management ...... 12-17 12.8 FIGURES ...... 12-19
13.0 HUMAN BEINGS ...... 13-1 13.1 INTRODUCTION ...... 13-1 13.2 SOCIO-ECONOMIC PROFILE ...... 13-1 13.3 ECONOMIC PROFILE ...... 13-2
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13.3.1 Labour Force ...... 13-2 13.3.2 Fisheries and Aquaculture ...... 13-4 13.3.3 Sligo Port ...... 13-4 13.4 TOURISM...... 13-5 13.4.1 Bathing Waters ...... 13-8 13.4.2 Sailing ...... 13-8 13.5 CONCLUSIONS ...... 13-9 13.5.1 Predicted Impacts ...... 13-9 13.5.2 Mitigation Measures ...... 13-9 13.5.3 Residual Impacts ...... 13-9
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14.0 WATER QUALITY AND SEDIMENT ...... 14-1 14.1 OVERVIEW OF EXISTING LEGISLATION ...... 14-1 14.1.1 Bathing Waters ...... 14-1 14.1.2 Shellfish Waters ...... 14-2 14.1.3 The Water Framework Directive ...... 14-3 14.2 EXISTING WATER QUALITY...... 14-5 14.2.1 Bathing Waters ...... 14-5 14.2.2 Shellfish waters...... 14-6 14.2.3 The Water Framework Directive ...... 14-7 14.3 SEDIMENT QUALITY ...... 14-10 14.3.1 Dredging Area – Sediment Chemical Properties ...... 14-10 14.3.2 Dredged Sediments Properties Conclusions ...... 14-14 14.4 POTENTIAL IMPACTS DURING DREDGING ...... 14-14 14.4.1 Short term increase in Suspended Sediment and Turbidity ...... 14-14 14.4.2 Potential for the Spread of Contaminated Dredged Material ...... 14-16 14.4.3 Potential for impacts to Dissolved Oxygen and Nutrients ...... 14-16 14.4.4 Potential for impact on Water Quality in the wider Sligo Bay Area. 14-16 14.4.5 Accidental Spillages during Dredging Operations ...... 14-17
15.0 SUMMARY OF IMPACTS AND MITIGATION MEASURES ...... 15-1 15.1 INTRODUCTION ...... 15-1 15.2 TECHNICAL DIFFICULTIES ...... 15-1 15.3 INTERACTIONS AND CONCLUSIONS ...... 15-18
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LIST OF FIGURES
CHAPTER 1 - INTRODUCTION Figure 1.1: Border Region Relationships in terms of the NSS ...... 1-7 Figure 1.2: Irish Port Traffic ...... 1-19 Figure 1.3: Sligo Port Traffic ...... 1-21 Figure 1.4:Former Finisklin Landfill ...... 1-38 Figure 1.5: Suggested Reclamation Area ...... 1-40
CHAPTER 2 – CONSULTATIONS Figure 2.1 Dumpsite Consulted Sites ...... 2-3 Figure 2.2 Pot Fishing area as indicated in Public Consultations ...... 2-7
CHAPTER 3 – SITE DESCRIPTION Figure 3.1 Site Location (Regional Context) ...... 3-1 Figure 3.2 SAC Designated Areas ...... 3-7 Figure 3.3 SPA Designated Areas ...... 3-9 Figure 3.4 pNHA and Ramsar Designated areas ...... 3-10 Figure 3.5 EU Shellfish Waters ...... 3-11
CHAPTER 4 – PROJECT DESCRIPTION Figure 4.1 : Dredging Area ...... 4-3 Figure 4.2 : Dumpsite ...... 4-4 Figure 4.3: Example of a Trailing Suction Dredger ...... 4-6 Figure 4.4:Example of a Backhoe Dredger ...... 4-7
CHAPTER 5 - BIRDS Figure 5.1: Area of the shipping channel surveyed as part of the bird surveys over the period December 2009 – November 2010 ...... 5-4 Figure 5.2: Cummeen Strand SPA boundary (updated February 2012) ...... 5-5
CHAPTER 6 – INTERTIDAL AND SUBTIDAL FLORA & FAUNA, MARINE MAMMALS Figure 6.1: Map showing the location of the 30 intertidal stations surveyed by ASU in 2007 ...... 6-8 Figure 6.2: Figure showing location of transects surveyed by ASU in Sligo Bay, 2007...... 6-9 Figure 6.3: Location map for the sites surveyed by BIOMAR and OPW teams in Sligo Bay 1996 ...... 6-12 Figure 6.4: Map showing recent intertidal survey effort, Sligo Harbour...... 6-15 Figure 6.5: Location of observations made during the walkover survey, October 2010. .... 6-15 Figure 6.6: Trestles, clam farm site, Sligo Harbour, 07th October 2010...... 6-16 Figure 6.7: Commercial clam park. South west Sligo Harbour, 07th October 2010...... 6-17 Figure 6.8: Mussel bed, Sligo beach, 07th October 2010...... 6-17 Figure 6.9: Mussel bed, close view. A mix of blue mussel and clams...... 6-18
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Figure 6.10: Algae (primarily fucoids) on mussel bank, Sligo Harbour, October 2010...... 6-18 Figure 6.11: Lugworm feeding casts, near mussel bank, Sligo harbour, October 2010. .... 6-19 Figure 6.12: Seagrass and lugworm feeding casts, Sligo Harbour, October 2010...... 6-19 Figure 6.13: Vaucheria sp. mat over intertidal muddy fine sand flat, Sligo Harbour, 07th October 2010...... 6-20 Figure 6.14: Gooses feeding on the intertidal sand flat, 07th October 2010...... 6-21 Figure 6.15: Fyke net on pole, Sligo Harbour, 07th October 2010 ...... 6-21 Figure 6.16: Mussel bank, Sligo Harbour, 07th October 2010...... 6-22 Figure 6.17: Mussel bank Sligo Harbour, 07th October 2010...... 6-22 Figure 6.18: Commercial clam park (Noel Carter’s)...... 6-23 Figure 6.19: Clam cultivation hardware, Sligo Harbour, 07th October 2010...... 6-23 Figure 6.20: Rippled fine sand surrounding clam cultivation site, 07th October 2010...... 6-24 Figure 6.21: Intertidal area with filamentous algal growth, Sligo Harbour, October 2010 .. 6-24 Figure 6.22: Points of interest near the navigation channel walkover area 7th October 2010...... 6-25 Figure 6.23: Rippled fine sand with some algae, 08th October 2010...... 6-26 Figure 6.24: Channel marker, Sligo harbour, 08th October 2010...... 6-26 Figure 6.25: Base of channel marker & training wall, Sligo harbour, 08th October 2010. ... 6-27 Figure 6.26: Intertidal sand flat, Sligo Harbour, 08th October 2010...... 6-27 Figure 6.27: View towards Sligo along navigation channel, 08th October 2010...... 6-28 Figure 6.28: Encrusting flora and fauna on the northern Sligo harbour navigation channel training wall, Sligo Harbour, 08th October 2010...... 6-29 Figure 6.29: Muddy sand flat adjacent to training wall, Sligo harbour approach channel, 08th October 2010...... 6-29 Figure 6.30: Map showing subtidal sampling locations ...... 6-31 Figure 6.31: Dendrogram showing the natural grouping of each station sampled in Sligo Harbour...... 6-37 Figure 6.32: MDS ordination showing the natural grouping of each station sampled in Sligo Harbour...... 6-37 Figure 6.33: Sediment grain size data ...... 6-40 Figure 6.34: Sediment type according to Folk (1954)...... 6-40 Figure 6.35: Location of Proposed Offshore 1km² Dump Site ...... 6-52 Figure 6.36: Sampled stations at proposed dump site, Donegal Bay, Jan/Feb 2011...... 6-54 Figure 6.37: Locations of Faunal Stations, Donegal Bay, Jan/Feb 2011 ...... 6-56 Figure 6.38: Video transect locations in the vicinity of the proposed dumpsite, Donegal Bay, January 2011...... 6-59 Figure 6.39 Current and tide measurements, Donegal Bay, Jan & Feb 2011...... 6-60 Figure 6.40 Ebb drogue tracks, Donegal Bay, 27.1.2011 ...... 6-61 Figure 6.41: Flood drogue tracks, Donegal Bay, 27.1.2011 ...... 6-62 Figure 6.42 Flood drogue tracks, Donegal Bay, 17.2.2011 ...... 6-63 Figure 6.43 Ebb drogue tracks, Donegal Bay, 17.2.2011 ...... 6-63 Figure 6.44 Dendrogram showing the natural grouping of each station sampled in Donegal Bay...... 6-66 Figure 6.45: MDS plot of all stations sampled in Donegal Bay...... 6-67 Figure 6.47: Survey Area ...... 6-82 Figure 6.48: Vantage point for marine mammal survey on south shore of Sligo Harbour . 6-83
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Figure 6.49: North shore of Sligo Harbour at low tide, scanned for hauled-out pinnipeds.6-83 Figure 6.50: Proposed dredging area showing main environmental designations ...... 6-86
CHAPTER 7 – FISHERIES AND AQUACULTURE Figure 7.1: National landings of brown crab between 1952 and 2004 (from Tully et al, 2006; reproduced by permission of BIM) ...... 7-3 Figure 7.2:Probable distribution of the northwest crab stock (from Tully et al, 2006; reproduced by permission of BIM) ...... 7-5 Figure 7.3: Annual landings of crab into Donegal and Mayo, 1990-2004 (from Tully et al, 2006; reproduced by permission of BIM) ...... 7-5 Figure 7.4: Landings of crab by statistical rectangle by the Mayo and Donegal <12m fleets in 2004 (from Tully et al, 2006; reproduced by permission of BIM) ...... 7-6 Figure 7.5: Size composition of male and female crab in the inshore landings 1996/97 (from Tully et al, 2006; reproduced by permission of BIM) ...... 7-7 Figure 7.6:Distribution of fishing in the <12m and vivier crab fisheries in 1997 (from Tully et al, 2006; reproduced by permission of BIM) ...... 7-9 Figure 7.7: Distribution of fishing in the <12m and vivier crab fisheries in 2004-2005 (from Tully et al, 2006; reproduced by permission of BIM) ...... 7-10 Figure 7.8: Sites licensed for shellfish production in the Sligo area ...... 7-12 Figure 7.9: Map of region showing principal salmonid rivers draining to Sligo Bay...... 7-17 Figure 7.10: Annual salmon catch from principal local rivers, 2001-10 (Source: IFI) ...... 7-18 Figure 7.11: The potential environmental impacts of marine dredging - a conceptual model 7- 22 Figure 7.12: The potential environmental impacts of marine dredged material disposal - a conceptual model ...... 7-22
CHAPTER 8 – AIR AND CLIMATE Figure 8.1: Windrose for Belmullet Meteorological station 1957-2010 ...... 8-1 Figure 8.2: 30 year monthly average temperatures (Belmullet) and sea temperatures (Malin) ...... 8-2 Figure 8.3: Met Éireann 1961-1990 mean annual average rainfall ...... 8-3 Figure 8.4: Met Éireann Average Monthly Rainfall for 5km² containing Sligo Harbour ...... 8-3 Figure 8.5: Location of Dredging Area ...... 8-5
CHAPTER 9 - MATERIAL ASSETS Figure 9.1: Sligo WWTP at Finisklin ...... 9-2 Figure 9.2: Junctions in Vicinity of Port ...... 9-7
CHAPTER 10 – GEOLOGY AND HYDROGEOLOGY Figure 10.1: Site Location ...... 10-1 Figure 10.2: Local Geology, from GSI 100k mapping ...... 10-2 Figure 10.3: Bedrock Aquifers ...... 10-3 Figure 10.4: Groundwater Status (2010)...... 10-4 Figure 10.5: Vibrocore sample stations...... 10-5 Figure 10.6: Vibrocorer ...... 10-7 Figure 10.7 GSI/Marine Institute INFOMAR Moraine Shaded Relief Image ...... 10-9
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Figure 10.8 GSI Backscatter Image of Dumpsite ...... 10-10 Figure 10.9 Grab Sample Stations January/February 2011 ...... 10-11
CHAPTER 11 - COASTAL PROCESSES - HYDRODYNAMIC MODELLING Figure 11.1: Extent of 30 and 10 metre grid nested flow model ...... 11-2 Figure 11.2: Extent of LiDAR Bathymetry and 2011 Bathymetric Survey ...... 11-3 Figure 11.3: Tidal curve for 1 month simulation period...... 11-4 Figure 11.4: Typical flow patterns in Sligo harbour - flood tide ...... 11-4 Figure 11.5: Typical flow patterns in Sligo harbour - ebb tide ...... 11-5 Figure 11.6: Target areas (A-E) for maintenance dredging by Water Injection Dredging . 11-7 Figure 11.7: Peak sediment deposition depths in Sligo Harbour during water injection dredging operations ...... 11-11 Figure 11.8: Final sediment deposition depths on completion of water injection dredging operations ...... 11-12 Figure 11.9: Mean suspended sediment concentrations during water injection dredging operations (for bottom 0.5m of water column)...... 11-15 Figure 11.10: Location of Identified Sensitive Areas and Timeseries Locations ...... 11-16 Figure 11.11: Time series showing peak Suspended Sediment Concentration in bottom 0.5m and Sedimentation for Carton Marsh Area during dredging campaign (Point Mon-1)...... 11-17 Figure 11.12: Time series showing peak Suspended Sediment Concentration in bottom 0.5m and Sedimentation for Southern part of Cummeen Strand during dredging campaign (Point Mon-2) ...... 11-18 Figure 11.13: Time series showing peak Suspended Sediment Concentration in bottom 0.5m and Sedimentation near commercial shellfish farm during dredging campaign (Point Mon-3) ...... 11-19 Figure 11.14: Time Series showing peak Suspended Sediment Concentration in bottom 0.5m and Sedimentation for commercial clam farm during dredging campaign (Point Mon-4) ...... 11-20 Figure 11.15: Extent of 30 and 10 metre grid nested flow model ...... 11-22 Figure 11.16 ...... 11-23 Figure 11.16: Comparison of existing and dredged channel tidal curves at Sligo (neap tide) ...... 11-24 Figure 11.17: Comparison of existing and dredged channel tidal curves at Sligo (overall average) ...... 11-25 Figure 11.18: Comparison of existing and dredged channel tidal curves at Sligo (extreme spring tide) ...... 11-25 Figure 11.19 ...... 11-26 Figure 11.19: Difference in mean spring flood tide velocity - proposed minus existing ... 11-26 Figure 11.20: Difference in mean spring ebb tide velocity - proposed minus existing..... 11-27 Figure 11.21 ...... 11-27 Figure 11.21: Difference in peak spring flood tide velocity - proposed minus existing .... 11-27 Figure 11.22: Difference in peak spring ebb tide velocity - proposed minus existing ...... 11-28 Figure 11.23: Tidal curve for hydrodynamic regime used in the dredging simulations .... 11-29 Figure 11.24 ...... 11-31 Figure 11.24 Peak sediment deposition depths during dredging of lower channel ...... 11-32 Figure 11.25 Peak sediment deposition depths during dredging of upper channel...... 11-32
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Figure 11.26 Sediment deposition depths on completion of all dredging operations ... 11-33 Figure 11.27: Location of potentially vulnerable areas ...... 11-34 Figure 11.28: Lower channel dredging - mean suspended sediment concentration in Area 1 – Cartron/Standalone Point ...... 11-35 Figure 11.29: Lower channel mean suspended sediment concentration in Area 2 – seagrass habitat in southern part of Cummeen Strand ...... 11-35 Figure 11.30: Lower channel mean suspended sediment concentration in Area 3 – commercial shellfish farm ...... 11-36 Figure 11.31: Mean suspended sediment concentration in lower 0.5m of water column during dredging of the upper section of the channel ...... 11-36 Figure 11.32: Upper channel dredging - mean suspended sediment concentration in Area 1 –Cartron Marsh/Standalone Point...... 11-37 Figure 11.33: Upper channel dredging - mean suspended sediment concentration in Area 2 – Seagrass habitat in southern part of Cummeen Strand ...... 11-37 Figure 11.34: Upper channel mean suspended sediment concentration in Area 3 – commercial and natural shellfish beds ...... 11-38 Figure 11.35: Mean suspended sediment concentration in bottom 0.5m at location of 4 points in potential vulnerable areas ...... 11-40 Figure 11.36: Time series showing Suspended Sediment Concentration in Cartron Marsh Area during dredging (Point 1) ...... 11-40 Figure 11.37: Time series showing Suspended Sediment Concentration in Southern part of Cummeen Strand during dredging (Point 2) ...... 11-41 Figure 11.38: Time series showing Suspended Sediment Concentration near commercial shellfish farm during dredging (Point 3) ...... 11-41 Figure 11.39: Time Series showing Suspended Sediment Concentration near commercial clam farm during dredging (Point 4) ...... 11-41 Figure 11.40: Extents of sediment dumping hydrodynamic model (blue square) and proposed dump site location (red square)...... 11-43 Figure 11.41: Flexible mesh model base model ...... 11-45 Figure 11.42: Flexible mesh model – zoomed extents ...... 11-46 Figure 11.43: Extent of 45m grid with deposition area marked by yellow square ...... 11-46 Figure 11.44: Tidal elevations at the dump site over simulation period ...... 11-47 Figure 11.45: Tidal flow around deposition site - Mid flood spring tide ...... 11-47 Figure 11.46: Tidal flow around deposition site - Mid ebb spring tide ...... 11-48 Figure 11.47: Measured and modelled current speed – site of drogue release 1 spring Tide ...... 11-49 Figure 11.48: Measured and modelled current direction – site of drogue release 2 spring tide ...... 11-49 Figure 11.49: Measured and modelled current speed – site of drogue release 1 neap tide 11- 50 Figure 11.50: Measured and modelled current speed – site of drogue release 2 neap tide 11- 50 Figure 11.51: Drogue track at neap tide in mid layer (drop at high water) and particle track from the model ...... 11-51 Figure 11.52: Drogue track at Spring tide - mid layer (drop at low water) and particle track from the model ...... 11-51
IBE00440/EAR/September ‘12 14 Sligo Harbour Dredging Environmental Appraisal Report Contents
Figure 11.53: Drogue track at mid layer (mid flood drogue drop) and particle track from the model ...... 11-52 Figure 11.54: Drogue track at mid layer (mid ebb drogue drop) and particle track from the model ...... 11-52 Table 11.11.5: Grain diameter occurrence used in modelling ...... 11-53 Figure 11.55: Track of suspended sediment over a month of tides ...... 11-54 Figure 11.56: Maximum suspended sediment concentration in the water column ...... 11-55 Figure 11.57: Mean suspended sediment concentration in the water column ...... 11-55 Figure 11.58: Final Deposition of sediment at the end of dredging operations ...... 11-56 Figure 11.59: Significant wave height Donegal Bay ...... 11-57 Figure 11.60: Mean wave period Donegal Bay ...... 11-57
CHAPTER 12 – CULTURAL AND ARCHITECTURAL HERITAGE Figure 12.1: Admiralty Chart showing Harbour area and proposed dredging works ... 12-19 Figure 12.2: Admiralty Chart showing proposed marine disposal site...... 12-19 Figure 12.3: Distribution of RMP sites in Harbour area...... 12-20 Figure 12.4: Distribution of NIAH sites in Harbour area...... 12-20 Figure 12.5: Extract from 1859 sea chart showing the location of the Fancy...... 12-21 Figure 12.6: Extracts from OS First Edition 1838 Sheet 14 and Third Edition ...... 12-22 Figure 12.7: Map of known wrecksites in the vicinity of the marine disposal site...... 12-23 Figure 12.8: The Hans Broge, before she wrecked, c. 1907...... 12-23 Figure 12.9: Marine geophysical survey tracklines within the Harbour area...... 12-24 Figure 12.10: Seabed images from the sonar data, Harbour area...... 12-24 Figure 12.11: Sonar trace showing the terminal perch, ss5...... 12-25 Figure 12.12: Sonar trace showing anomaly ss25 within its local context...... 12-26 Figure 12.13: Distribution of marine geophysical anomalies observed within the Harbour area...... 12-27 Figure 12.14: Distribution of marine geophysical anomalies observed within the Harbour area, East side...... 12-27 Figure 12.15: Distribution of marine geophysical anomalies observed within the Harbour area, central zone...... 12-28 Figure 12.16: Distribution of marine geophysical anomalies observed within the Harbour area, West side...... 12-28 Figure 12.17: Marine geophysical survey tracklines at the marine disposal site...... 12-29 Figure 12.18: Sonar trace showing nature of seabed imaged at the marine disposal site. . 12- 30 Figure 12.19: Distribution of marine geophysical anomalies observed at the marine disposal site...... 12-31
CHAPTER 13 – HUMAN BEINGS Figure 13.1 Population pyramids (2011 census) for State and Sligo County ...... 13-2 Figure 13.2 Composition of Working Labour Force in Co. Sligo and State (2006) ...... 13-3 Figure 13.4 North West Region Overseas Visitor Numbers 1999-2009 ...... 13-6
CHAPTER 14 – SEDIMENT AND WATER QUALITY
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Figure 14.1: Designated Bathing Water ...... 14-1 Figure 14.2: Sligo Bay and Drumcliff Bay EC Designated Shellfish Waters ...... 14-2 Figure 14.3: Water Framework Directive Water Body Boundaries and Overall Status ..... 14-4 Figure 14.4: Bathing Water Quality Status ...... 14-6 Figure 14.5: Sligo Sediment Chemical Sampling Stations ...... 14-11
CHAPTER 15 – SUMMARY OF IMPACTS AND MITIGATION MEASURES (no figures)
IBE00440/EAR/September ‘12 16 Sligo Harbour Dredging Environmental Appraisal Report Contents
LIST OF TABLES
CHAPTER 1 – INTRODUCTION Table 1.1: Irish Port Traffic ...... 1-21 Table 1.2: Sligo Port Traffic ...... 1-22 Table 1.3: Sligo Port 2008 - 2011 Traffic Details ...... 1-22 Table 1.4: Sligo Port 2010 and 2011 Traffic Details ...... 1-23 Table 1.5: Employment associated with Harbour Activity ...... 1-26 Table 1.6: Comparison of Navigable Period with Dredged Depth ...... 1-34
CHAPTER 2 – CONSULTATIONS Table 2.1 Organisations/Agencies consulted as part of the Appraisal Process ...... 2-1
CHAPTER 3 – SITE DESCRIPTION Table 3.1 Cummeen Strand/Drumcliff Bay SAC Summary ...... 3-6 Table 3.2 Sligo Harbour and Drumcliff Bay SPA Summary ...... 3-8
CHAPTER 4 – PROJECT DESCRIPTION (no tables)
CHAPTER 5 – BIRDS Table 5.1:Irish Wetlands Bird Survey (IWeBS) peak counts in Sligo Harbour (entire estuary)...... 5-8 Table 5.2: Summary of peak and mean numbers of water birds within 1km of the shipping channel in Sligo Harbour over ten months, December 2009-November 2010...... 5-11 Table 5.3: Summary of peak and mean numbers of water birds on the shipping channel and its immediate banks in Sligo Harbour over ten months, December 2009-November 2010.5-12 Table 5.4: Tolerance thresholds of Zostera spp. to turbidity levels...... 5-20 Table 5.5: Tolerance thresholds for Zostera spp. to sedimentation...... 5-20
CHAPTER 6 – INTERTIDAL AND SUBTIDAL FLORA & FAUNA, MARINE MAMMALS Table 6.1: Subtidal station co-ordinates...... 6-31 Table 6.2: The classification of sediment particle size ranges into size classes ...... 6-32 Table 6.3: Diversity indices for the 15 stations sampled in Sligo Harbour...... 6-35 Table 6.4: SIMPER Results ...... 6-38 Table 6.5: Granulometry results for the 14 stations sampled in Sligo Harbour (as percentage weight of the total sample)...... 6-39 Table 6.6: Sediment organic carbon results for the fourteen stations surveyed off Sligo, 6th October, 2010...... 6-41 Table 6.7: Summary of critical thresholds for mussel (Mytilus edulis) beds...... 6-49 Table 6.8: Tolerance thresholds of Zostera spp. to turbidity levels...... 6-50 Table 6.9: Tolerance thresholds for Zostera spp. to sedimentation...... 6-50 Table 6.10: Locations of the sediment sampling stations in Donegal Bay...... 6-54 Table 6.11 Diversity indices for the 4 stations sampled in Donegal Bay...... 6-65 Table 6.12 Descriptions of the video transects, Donegal Bay, January 2011...... 6-68
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CHAPTER 7 – FISHERIES AND AQUACULTURE Table 7.1: Total landings of brown crab into Irish ports, 2001-10 (Source: SFPA) ...... 7-3 Table 7.2: Clam and oyster production in the Sligo Bay area, 2006-11 (Source: BIM) ..... 7-14 Table 7.3: Classification of designated bivalve mollusc production areas, 2012 ...... 7-15 Table 7.4: Summary of migrations/presence of eel and lamprey in local estuaries at different times of year ...... 7-20
CHAPTER 8 – AIR AND CLIMATE Table 8.1: Example Threshold of significant impact at dwellings 8-6
CHAPTER 9 - MATERIAL ASSETS Table 9.1: Docking Pattern at Sligo Harbour ...... 9-6 Table 9.2: Existing Traffic Flows along Primary Route ...... 9-8 Table 9.3: Percentage increase during dredging operations ...... 9-11
CHAPTER 10 – GEOLOGY AND HYDROGEOLOGY Table 10.1: Summary of Sediment Conditions ...... 10-7 Table 10.2 Results of the granulometric analysis on the dump site sediments ...... 10-12 Table 10.3 Physical properties of the dump site sediments ...... 10-12 Table 10.4 Proposed Dumpsite Baseline Sediment Testing Results ...... 10-13
CHAPTER 11 - COASTAL PROCESSES - HYDRODYNAMIC MODELLING Table 11.1: Dredging Area Sediment Samples – Descriptions ...... 11-7 Table 11.2: Dredging Area Sediment Samples – Granulometry Results ...... 11-8 Table 11.3: Measured suspended sediment in Sligo Harbour ...... 11-13 Table 11.4: Water Quality Measurements in Sligo Harbour ...... 11-39
CHAPTER 12 – CULTURAL AND ARCHITECTURAL HERITAGE Table 12.1 Townlands and placenames identified within the Sligo study area...... 12-5 Table 12.2 Side-scan sonar anomalies identified within the harbour area* ...... 12-14 Table 12.3 Magnetometer anomalies identified within the harbour area* ...... 12-15 Table 12.4 Side-scan sonar anomalies identified on marine disposal area survey* . 12-16
CHAPTER 13 – HUMAN BEINGS (no tables)
CHAPTER 14 – SEDIMENT AND WATER QUALITY Table 14.1: Site Area Transitional and Coastal Waterbody Status ...... 14-8 Table 14.2: Site Area River water body status ...... 14-8 Table 14.3: Dredging Area Sediment Samples - Descriptions ...... 14-11
CHAPTER 15 – SUMMARY OF IMPACTS AND MITIGATION MEASURES Table 15.1 Summary of Potential Impacts and Proposed Mitigation Measures ...... 15-2 Table 15.2 Interactions ...... 15-15
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VOLUME 2 - LIST OF APPENDICES
APPENDIX 1 - INTRODUCTION Appendix IA: Harbour Office Submission In Relation To The Docklands Local Area Plan
APPENDIX 2 – CONSULTATIONS Appendix 2A: Summary of Consultee Responses Appendix 2B: Public Consultation Display Information Appendix 2C: Copy of Written Consultee Responses
APPENDIX 3 – BIRDS Appendix 3A: Bird Field Survey Counts Appendix 3B: Screening For Appropriate Assessment
APPENDIX 4 – INTERTIDAL AND SUBTIDAL FLORA & FAUNA, MARINE MAMMALS Appendix 4A: Biomar Survey Data – Sligo Bay Appendix 4B: SAC Site Synopses Appendix 4C: Benthic Fauna Species List Appendix 4D: Ecological Site Evaluation Criteria Appendix 4E: Dump Site Current Metering and Drogue Tracking Results Appendix 4F: Dump Site Area Infaunal Sampling Species List Appendix 4G: Dumpsite ROV Video 163 Appendix 4H: Dumpsite Benthos Simper Similarity Percentages
APPENDIX 5 – FISHERIES APPENDIX 5 - ICES Areas and Atlas Of Commercial Fisheries
APPENDIX 6 – GEOLOGY AND HYDROGEOLOGY APPENDIX 6A: Vibrocore Report Appendix 6B: Dump Site Granulometric Testing Results
APPENDIX 7 – CULTURAL HERITAGE APPENDIX 7A: Known Archaeological And Architectural Heritage Records for the Sligo Harbour and Marine Disposal Areas APPENDIX 7B: Observation Of Marine Geophysical Survey Anomalies. APPENDIX 7C: Architectural Heritage Assessment APPENDIX 7D: Marine Geophysical Survey
APPENDIX 8 - SEDIMENT AND WATER QUALITY APPENDIX 8A: Report on Dredging Sediment Testing APPENDIX 8B: Dumpsite Grab Sample Chemical Testing Results [Data DVD-ROM]
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VOLUME 3 – NATURA IMPACT STATEMENT
1. INTRODUCTION ...... 1 1.1. The requirement for an assessment under Article 6 ...... 1 1.2. The aim of this report ...... 2 1.3. Background – an overview of the Sligo Harbour Dredging project ...... 2 1.4. Consultation ...... 3 1.4.1. Government Departments ...... 3 1.4.2. Other Bodies ...... 3 1.5. Constraints ...... 4 2. THE APPROPRIATE ASSESSMENT PROCESS ...... 4 2.1. Introduction ...... 4 2.2. Stages ...... 6 2.3. Alternatives ...... 7 2.3.1. Introduction ...... 7 2.3.2. Alternative dredging methods ...... 7 2.3.3. Alternative timing of works ...... 8 2.3.4. Alternative dredge spoil disposal methods ...... 8 2.3.5. Alternative sea disposal sites ...... 8 3. THE ECOLOGICAL IMPACT ASSESSMENT ...... 9 3.1. Introduction ...... 9 3.1.1. Description of the project ...... 10 4. NATURA 2000 SITES ...... 11 4.1. Areas and Species of Scientific Interest – Sligo Harbour ...... 12 4.1.1. Areas of Scientific Interest (ASI) ...... 13 4.1.2. Special Areas of Conservation (SAC) ...... 15 4.1.3. Special Protection Area (SPA) ...... 16 4.1.4. Natural Heritage Area (NHA) ...... 16 4.1.5. Designations under the Wildlife Act, 1976 ...... 17 4.1.6. Proposed Nature Reserve in private ownership ...... 17 4.1.7. County Geological Sites ...... 17 4.1.8. International Reserves/Conventions ...... 17 4.2. Designated sites in the vicinity of the project ...... 18 4.2.1. Sligo Harbour ...... 19 4.3. Characteristics of the designated sites ...... 20 4.3.1. Cummeen Strand/Drumcliff Bay SAC (Site code: 000627) ...... 20 4.3.2. Cummeen Strand SPA (Site code: 004035) ...... 24
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4.3.3. Lough Gill SAC (Site code: 001976) ...... 27 4.4. Desk Study ...... 31 4.4.1. Intertidal habitats ...... 31 4.5. Field Survey – AQUAFACT 2010 ...... 52 4.5.1. Intertidal survey 2010...... 52 5. ASSESSMENT OF LIKELY EFFECTS ...... 85 5.1. Consideration of significance ...... 85 5.2. Potential impacts on Natura 2000 sites – impacts prediction ...... 87 5.2.1. Potential impacts on Cummeen Strand/Drumcliff Bay SAC ...... 87 5.2.2. Potential impacts on Cummeen Strand SPA ...... 93 5.2.3. Indirect Impacts on Natura sites in the wider locality, including Lough Gill SAC ...... 98 5.2.4. Cumulative Impacts ...... 98 6. MITIGATION MEASURES ...... 103 6.1. Habitats in Cummeen Strand/Drumcliff Bay SAC ...... 103 6.1.1. The removal of estuarine sediments ...... 103 6.1.2. Deposition of sediments on mudflats and sandflats ...... 103 6.2. Species in the Cummeen Strand/Drumcliff Bay SAC ...... 104 6.2.1. Marine mammal species listed for the SAC – Annex II species (EU Habitats Directive) ...... 104 6.2.2. Fish species (Annex II) ...... 104 6.2.3. Otter (Lutra lutra) (Annex II and IV) ...... 104 6.2.4. Marine mammals (Annex II and Annex IV) ...... 104 6.2.5. Other fish species ...... 105 6.3. Mitigation for Cummeen Strand SPA ...... 105 6.3.1. Macrobenthos - food source for SPA bird species ...... 105 6.3.2. Indirect Impacts on Natura sites in the wider locality, including Lough Gill SAC ...... 107 6.4. Qualifying Species and Listed Species of Importance for the SPA ...... 107 7. CONCLUSIONS ...... 108 7.1. Cummeen Strand/Drumcliff Bay SAC (Site code: 000627) ...... 108 7.2. Cummeen Strand SPA (Site code: 004035) ...... 108 7.3. Lough Gill SAC (Site code: 001976) ...... 109 8. ACKNOWLEDGEMENTS ...... 112 9. REFERENCES ...... 113
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IBE00440/EAR/September ‘12 24 Sligo Harbour Dredging Environmental Appraisal Report Introduction
1.0 INTRODUCTION
1.1 PROJECT SUMMARY
Sligo Harbour is the only working port, apart from Killybegs Fishery Harbour, between Galway and Derry. It located in the estuary of the Garavogue River (sometimes written as Garvogue or Garvoge) in Sligo Bay on the north west coast of Ireland.
At present, the harbour can accommodate ships with a maximum draft of 5.2 metres and length of 100 metres, however the larger vessels that use the port can only pass through the harbour to the quays at high spring tides, due to the shallow bathymetry of the navigation channel and the harbour berths. At low spring tide, laden cargo vessels sit on the seabed even at Deepwater Quay.
A training wall, the upstream 1,500m of which was recently refurbished 2007, reduces the movement of sediment into the channel. Despite this, the shipping channel and jetty areas have to be regularly maintenance dredged to remove siltation.
Within the Irish National Spatial Strategy 2002-2020, Sligo has been selected as a gateway town because of its strategic location, physical capacity, infrastructure and its amenities including water services. Sligo County Council is now proposing to dredge the harbour and its channel with the aim of: x Meeting the present and future demands of the tourism and transport industry. x Promoting and improving facilities for marine leisure sector. x Allowing the port to take account of business opportunities and increase marina berthage. x Enhancing the viability and environmental well-being of the area.
Sligo County Council is proposing to undertake a combination of maintenance dredging and capital dredging within the harbour and its approach channel. Maintenance dredging from Barytes Jetty to the Red Light is required to preserve the minimum required depth for current vessels using Sligo Harbour. Capital dredging along the channel is also proposed to generate new business, thereby securing the future viability of the harbour. A feasibility study prepared by RPS Consulting Engineers in 2009 found that a depth of 3m below Chart Datum was necessary to give a vessel of 4,500 dwt and a draft of 5.9m a 3 hour window of opportunity for a 1 hour passage time to navigate the channel per tide, thereby securing Sligo Harbour’s viability as a working port. In order to achieve this minimum requirement, dredging a quantity of approximately 250,000m3 of material along the channel is considered to be necessary.
This report documents the Environmental Impact Assessment (EIA) of the harbour dredging scheme. The EIA has been carried out to ensure that the dredging is properly integrated with the overall development of Sligo Harbour and that safeguards are put in place to protect and maintain the natural environment.
IBE0440/EAR/September ‘12 1-1 Sligo Harbour Dredging Environmental Appraisal Report Introduction
1.2 EXISTING PORT FACILITIES
The Port of Sligo extends from the Timber Jetty at Hyde Road Bridge for a distance of 1.3km and formerly comprised a number of quays and jetties, namely: x Sligo Jetty, x Liverpool Jetty, x Barytes Jetty, x Deepwater Jetty, x Lynn’s Dock; and x Ballast Quay.
Only the Timber Jetty, the Barytes Jetty and the Deepwater Jetty have remained in service to the present day. The main docking jetty is Deepwater Jetty, at the most westerly end of the port. It and the Barytes jetty handle cargoes of coal, timber, fish meal and scrap metal and at present around 25 ships per year dock in the harbour.
1.2.1.1 Improvement Works Sligo County Council took over responsibility for Sligo Harbour from Sligo Harbour Commissioners in June 2006. Since then Sligo County Council has embarked on a series of improvement works which have included the refurbishment of the Deepwater Jetty in the form of fendering and installation of safety items and the reinstatement of the Barytes Jetty, which has been effectively rebuilt and which now functions as a much needed second commercial facility. Improvements have also been made to the shipping channel training wall.
The Deepwater Jetty is 77m long, the Barytes Jetty is 55m long and the harbour can currently accommodate vessels of up to 3,500 DWT. The maximum draught for vessels is currently 5.2m and the maximum length that can be accommodated is 100m.
The largest vessels that use the port can only pass through the harbour to the quays at high spring tides due to the shallow water depths in the channel. At low spring tide, laden cargo vessels sit on the seabed, even at Deepwater Quay.
Consequently, the shipping channel and jetty areas have to be regularly dredged to prevent siltation. A training wall was constructed in order to hold back and reduce the movement of sediment into the channel.
In the 1970s, problems regarding the storage of the silt led to the construction of a large holding pond/bunded area (circa 6 hectares), westward of the Deepwater Jetty.
This area was filled with sediment in a major dredging operation (in 1985) and subsequent maintenance dredging. The area is now completely filled and was developed in the late 2000s into the site for Sligo’s main wastewater treatment plant. As all of the remaining intertidal area of Sligo Harbour has been designated as both a Special Area of Conservation
IBE0440/EAR/September ‘12 1-2 Sligo Harbour Dredging Environmental Appraisal Report Introduction and a Special Protection Area, bunding a further area of the foreshore for the containment of dredged sediments is not considered to be a feasible option in the present day.
Maintenance dredging adjacent to the jetties is ideally required every year, and the disposal of the dredged material will soon become a problem, as the former disposal area is no longer available. Major capital dredging of the channel is urgently required.
In 2008 the Council also refurbished the Timber Jetty and installed pontoons for mooring leisure craft. The new berthing pontoon installation at the Timber jetty is attracting small fishing vessels and visiting yachts as their shallower draft allows them to navigate the harbour entrance channel with fewer tidal restrictions.
The navigation channel upstream of Barytes Jetty is no longer used for commercial shipping and so maintaining its depth is less critical. This section of the channel is therefore not included in the current proposed dredging plans. However, the recently installed pontoon berthing facility at the Timber Jetty is attracting visiting yachts and an acceptable minimum depth will continue to be required in the future.
In the longer term, further improvement works are envisaged. These include: x further extensions of the Timber Jetty pontoons; x repairs to the bulk of the harbour wall from Deepwater Jetty to Silver Swan development (city centre), to be done in sections; x probable removal of Liverpool Jetty, which is broken; x maintenance of the shipping channel and training wall; x maintenance dredging of the shipping channel, as necessary.
A full description of the proposed dredging extents and depths is provided in Chapter 4 “Project Description”.
IBE0440/EAR/September ‘12 1-3 Sligo Harbour Dredging Environmental Appraisal Report Introduction
1.3 STRATEGIC POLICY DRIVERS
Ireland has a planning policy framework that operates at European, National, Regional and Local level. Planning authorities must recognise the key elements of the parent documents in all decision making. The proposed dredging at Sligo is entirely consistent with the strategic objectives at national, regional, county and local level as outlined in the review of the following strategic policy drivers below:
1.3.1 National Policy
1.3.1.1 National Ports Policy Statement
The Government published the National Ports Policy Statement; the framework within which the State’s commercial ports are expected to operate, in 2005. The core objective of the National Ports Policy is to ensure investment in ports meets port capacity requirements and to facilitate the availability of commercial port services which are effective, competitive and cost efficient. The Harbours (Amendment) Act 2009 enacted many of the legislative changes proposed by the Policy Statement. A review of the policy framework is currently being undertaken, with a consultation document launched in September 2010.
The National Ports Policy Statement recognised that ports are essential pieces of national infrastructure and as such have a strategic role in facilitating both national and regional economic development.
When the 2005 report was published, there were 10 ports operating as commercial State port companies and a further 13 harbour authorities (including Sligo) operating under the Harbours Act 1946. The National Ports Policy Statement acknowledged that these smaller harbours range from those with some commercial traffic to those that have experienced gradual decline in terms of commercial and seaborne trade and exist only to service the local economies that depend on them for seafishing and marine leisure. The Harbours Act 1946 was considered to be no longer appropriate governing legislation for these regional harbours and a policy was put forward to transfer them to local control, where maximum utilisation and benefit for the local regions can be realised. This is likely to be achieved by fully developing the amenity value of these maritime facilities. To this end, the responsibility for Sligo Harbour transferred from Sligo Harbour Commissioners to Sligo County Council in 2006 (S.I. No. 316/2006 — Harbours Act, 1996 (Transfer of Sligo Harbour to Sligo County Council) Order 2006). A number of improvements in the harbour have been carried out by the Council since then to enhance its commercial and amenity value.
From 2005, Ireland’s ports as a whole have experienced both record traffic volumes, peaking in 2007 and, more recently, sharp declines. The Ports Policy Statement focuses most of its attention on the larger ports in Ireland and the challenges they face in light of a worldwide shift towards containerised transport with larger ships requiring deep-water ports and the reduced availability of smaller ships to serve local ports. There has also been a movement from multi-cargo common user ports to specialist terminal-based ports such as Lift On-Lift Off and Liquefied National Gas terminals. Whilst Sligo Port will never be able to receive large
IBE0440/EAR/September ‘12 1-4 Sligo Harbour Dredging Environmental Appraisal Report Introduction container vessels, there are a number of markets such as sea tourism charters and support for the expanding energy industries such as wind energy, tidal current energy and gas exploration and supply on the west coast which it may be able to expand.
The 2010 review provides insight into the role that smaller ports can play in transporting goods. With increasing European trends towards charging for road use (e.g. tolls, congestion charges) and increasing pressure on governments to implement policies to reduce the amount of road freight transportation, the development and use of short sea shipping routes is becoming increasingly important. Compared to road and air transport, rail and sea transport are both regarded as being more sustainable modes. Sligo Harbour has retained its rail link to the quays and as such has a significant advantage over several other ports who have, over the years, removed their railway links. This makes the port ideally placed to capitalise on EU investment programmes such as the Trans-European Transport Network (TENs) and Marco Polo which provide funding for projects which shift freight transport from the road to sea, rail and inland waterways.
1.3.1.2 National Development Plan 2007-2013
The National Development Plan Transforming Ireland – A Better Quality of Life for All (hereafter NDP) was published in 2007. This document supersedes the National Development Plan of 2000 to 2006 and notes that the Irish economy and society will undergo a transformation almost as radical as the changes experienced in the past decade of growth and development. This will be driven largely by the continuing increase in the population which is projected to reach over five million by 2021.
One of the main aims of the NDP is developing the Gateways (see National Spatial Strategy below). The key objective is to build on current trends and maintain strong and sustainable growth in each of the Gateways over the period of the Plan with particular emphasis on those with lower populations. Each Gateway therefore needs a clear vision of: x Its future development strategy; x The mechanisms to implement the strategy; x Effective prioritisation of investment, both locally and centrally; and x Accelerated delivery of critical elements of such investments.
The Plan provides for some €32.9 billion investment in transport generally. National and international access will be central to the competitiveness of the Gateways. Key priorities will be completion of the major interurban routes, the upgrade and enhancement of the public transport network, improved port and airport access and investment in key secondary and non-national roads between and within the Gateway regions.
By the end of the Plan, all the inter-urban routes between Dublin and the Gateways will have been completed and many of the key inter-urban routes between Gateways, such as the Atlantic Corridor, will also have been significantly upgraded. Investment in strategic non- national roads within and between Gateways and their immediate hinterlands will also play a key role in improving connectivity, circulation and facilitating the development of strategically placed landbanks.
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Under the transport programme, some €481 million has been set aside for the ports sub- progamme.
Of this, €450 will be spent on the major commercial ports; however €31 million has been included in the Plan for investment in Regional Harbours. Following the establishment of the commercial port companies, under the Harbours Act 1996, there remained thirteen regional harbour authorities operating under the Harbours Act 1946. The Ports Policy Statement stipulates that these regional harbours would best achieve their potential through transfer to local authority or port company control and indeed by 2010 seven harbours had transferred to relavant local control and one further harbour, Dingle, has been designated as a fishery harbour centre. The Department continues to pursue the policy to transfer the five remaining harbours to relevant local authority or port company control. These proposed transfers are at various stages.
Sligo Harbour was transferred by Ministerial Order to Sligo County Council in June 2006. In order to enhance the harbours during their transfer phase, a programme of remedial works will continue to be funded, as appropriate, under this NDP. Exchequer funding has been allocated for these remedial works over the period 2006-2009. These will be prioritised on the basis of the protection of the fabric of the harbours. This expenditure is designed to ensure that any undue financial burden is not placed on local authorities or ports companies arising from the transfer of harbours. As part of the NDP and ports policy mid-term review in 2010 (Department of Transport, 2010) the issue of further funding for these harbours over the remainder of the Plan was being considered. As of the time of writing, the Department of Transport are still reviewing the submissions during made during the consultation period – the revised policy statement will have to have regard to the changed economic and business climate within which Irish ports currently operate.
1.3.1.3 The National Spatial Strategy 2002-2020
The Government’s ‘National Spatial Strategy’ (NSS) is intended to set a national context for spatial planning which will inform Regional Planning Guidelines and strategies, as well as County and City Development Plans and strategies. It is a twenty year planning framework designed to achieve a better balance of social, economic, physical development and population growth between regions. It aims to ensure high quality urban environments as well as vibrant rural communities by strategically informing future investment to enable each part of Ireland to achieve its potential.
It is a key infrastructural principal of the NSS that achievement of a spatial balance by developing the potential of areas will depend on enhancing capacity for the movement of people, goods, energy and information between different places.
In addition to initiating the process of preparing the National Spatial Strategy, the National Development Plan (NDP) 2000-2006 identified the five main cities, Dublin, Cork, Limerick, Galway and Waterford, as ‘Gateways’, or engines of regional and national growth. The NDP
IBE0440/EAR/September ‘12 1-6 Sligo Harbour Dredging Environmental Appraisal Report Introduction set the NSS the task of further developing the Government’s approach to achieving more balanced regional development, including the identification of a limited number of additional gateways. The National Spatial Strategy identified a further four national level gateways to support the original five gateways; namely Dundalk, Sligo, and the "linked" gateways of Letterkenny/Derry, and Athlone/Tullamore/Mullingar (Figure 1.1).
Figure 1.1: Border Region Relationships in terms of the NSS
The NSS states that critical mass in the West and North West “can be strengthened by developing Sligo as a gateway to capitalise on its strategic location and energise its associated hinterland. Building up the national role and scale of Sligo will require, as a first step, the development of a planning, land use and transportation framework. This will provide a focus around which local authorities, business and community interests can reach consensus on the future development of Sligo and utilise its substantial physical capacity for development, while safeguarding its outstanding natural setting.”
The NSS continues: the critical factor [for revitalising the West] is “underpinning the sustainable development of strategically placed medium-sized towns to reinforce dynamic rural economies. These economies will be based on the sustainable use of natural resources such as scenic landscapes for tourism, the sea for fisheries and marine–based aquaculture, the land for agriculture, forestry, inland aquaculture (in rivers and lakes) and renewable energy. Appropriate investment in enterprise and local services will also be required to sustain these economies.”
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The Strategy recognises an overdependence on Dublin Port inconsistent with the NSS policy to promote balanced regional development. In accordance with this general policy, the NSS identifies the ‘suggested solution [of] promoting alternative locations for some current and future Dublin port activities, such as transit and storage of petrochemicals, bulk goods and cars. More port business to and from various parts of the country through other nationally strategic ports could be encouraged. This may require substantial investment in facilities at alternative ports’ (p. 63).
Balanced regional development across the entire nation is central to the objectives of the NSS. This means supporting the economic and social development of all regions in their efforts to achieve their full potential by integrating strategic development frameworks for regional development, rural communities, all-island co-operation, and for protection of the environment with common economic and social goals.
Section 2 states that ‘marine and natural resources, including inland fisheries, sea fisheries, aquaculture, forestry and mining, have an important role to play in providing sustainable alternative sources of employment in rural areas’ (p. 19). It is considered that the strengths of all rural areas must be identified and supported by an appropriate level of infrastructure provision whilst ensuring a balanced approach to their potential for economic activity. The Strategy considers that developments in marine and natural resources sectors offer significant advantages for stable, long term economic activity in rural areas and coastal communities, providing work for which many of the skills required are available locally.
The proposed dredging at Sligo harbour will safeguard the port’s future in terms of commercial trade for further ten years or more. Sligo can capitalise on its existing strengths as an employment centre for other towns in the surrounding area by building on the existing facilities. Enhancement of the port’s navigability will therefore support the concept of balanced regional development which is central to national policy objectives. The scheme may enhance the employment opportunities in Sligo by providing better transport links for the movement of goods and materials. This could have wider repercussions for the surrounding rural hinterland thus improving the performance of the economy in Co. Sligo and the northwest region as a whole.
1.3.1.4 Sustainable Development – A Strategy for Ireland (1997) The National Sustainable Development Strategy, published in 1997, includes a number of measures and actions relating to the conservation of the natural environment and the protection of air and water quality. It aims to provide a comprehensive analysis and framework which will allow sustainable development in Ireland. Although this document is over ten years old, it remains relevant. A five-year review of the National Sustainable Development Strategy entitled “Making Ireland's Development Sustainable”, was produced by the Department of the Environment, Heritage and Local Government in 2002. A further “Statement of Strategy 2008-2010” was published by the Department of Environment, Heritage and Local Government in 2008.
Whilst cautioning that marine natural resource exploitation should be operated in a manner which respects the environment, the Strategy notes that industry in Ireland has grown
IBE0440/EAR/September ‘12 1-8 Sligo Harbour Dredging Environmental Appraisal Report Introduction substantially since the 1960s. It is strongly export oriented with some 68% of manufacturing jobs dependent upon exports at the time of the Strategy’s publication. The Strategy also notes that at the time of publication it was estimated that ‘some 80% of all goods produced in the world are transported by sea’ (p. 66). While the Strategy highlights that all modes of ‘transport have an extensive impact on the environment… there is no real alternative to road transport for the vast bulk of goods movement’ (p. 106).
Additionally, it states that ‘sustainable industrial development must allow industry to pursue its primary functions of generating wealth and employment while minimising impacts on the environment’ (p. 87). While our natural assets are recognised as highly important especially in terms of competing on an international scale, there is also recognition that industrial development in a sustainable manner is needed in order to ensure continued economic growth in areas.
Measures to mitigate any potential impact on the environment as a result of the proposed development are outlined in the relevant sections of this Report.
1.3.2 Regional/Local Policy
1.3.2.1 Regional Planning Guidelines for the Border Region
The Border Regional Authority covers the counties of Cavan, Donegal, Leitrim, Louth, Monaghan and Sligo, situated along the southern side of the border with Northern Ireland. It is one of eight Regional Authorities established in 1994 to provide a regional tier of government level in Ireland. The aim of the Authority is to achieve sustainable, balanced regional growth and development whilst ensuring that quality of life, the environment and the unique culture and heritage of the area are protected and enhanced. The function of the Authority is to promote the co-ordination of the provision of public services at regional level.
The 2nd Regional Planning Guidelines 2010-2022 were adopted on the 29th September, 2010. The Guidelines form a long term strategic planning document which aims to direct the future growth of the Border Region and seeks to implement the planning framework set out in the National Spatial Strategy (NSS) published in 2002.
The new Guidelines also provide a more integrated model for the growth and development of the Region, as spatial planning has been closely aligned with the economy and proposed infrastructure within all relevant sectoral areas. This new approach has been complimented by more detailed consideration given to areas such as climate change, environmental management and flood risk management, all of which pose significant challenges for policy makers.
The Guidelines state: “all ports within the Region are a significant asset and provide for the efficient movement of goods for import and export.... the Border Regional Authority considers it necessary that a ports strategy is developed for all ports on the island of Ireland, and in particular, for the entire eastern seaboard of the island. The development and promotion of
IBE0440/EAR/September ‘12 1-9 Sligo Harbour Dredging Environmental Appraisal Report Introduction port activities will contribute to a modal shift from cars and decrease reliance on imported fossil fuel.”
The guidelines further recognise that “Sligo Port has significant potential along the western seaboard, but all options and proposed land uses should be considered with respect to its future existence”.
The aims of Policy INFP14 are to “Support the provision of adequate port facilities for commercial, fishing and amenity purposes within the Region, subject to compliance with the Habitats Directive”
1.3.2.2 Sligo and Environs Development Plan 2010 - 2016 On 2nd November 2009, Sligo Borough Council and Sligo County Council adopted the Sligo and Environs Development Plan 2010–2016. The Plan covers the Borough of Sligo together with its urban and rural environs located outside the Borough, under the jurisdiction of Sligo County Council. The SEDP 2010–2016 became operational on 30 November 2009 and will remain in force for six years.
The Sligo and Environs Development Plan 2010 - 2016 includes a range of policies and objectives that take into account the operations of and activities at Sligo Port.
As part of its Spatial Strategy, the Plan indicates that the Zoning Objective PF – Port Facilities and Related Uses is to “Retain the port as a viable infrastructural and commercial entity, supported by port-related industries and/or business activities”.
The Sligo and Environs Development Plan 2004-2010 also includes a range of policies and objectives relating to an area obviously larger than the lands transferred from the Harbour Commissioners. This area was referred to as “the Docklands”, “the Port” or “the Harbour”.
In 2006-2007 it became evident that piecemeal development was not a good option. Instead, a comprehensive redevelopment framework should be prepared for a clearly defined area, which would encompass the Port/Docklands/Harbour as well as other lands that are underutilised, derelict, possibly contaminated, or are critical for the future provision of essential infrastructure and various other facilities.
The Sligo and Environs Development Plan 2010-2016 (SEDP) identifies five areas suitable for planned urban extensions, one of which is the Docklands and surrounding area located between the Inner Relief Road, Strandhill Road and the sea shore.
The Spatial Strategy (Chapter 5 of the SEDP) makes provision for the preparation of a local area plan for the Docklands, while the detailed policy sections include a variety of policies and objectives directly or indirectly applicable to the Docklands area. The main specific proposals included in the SEDP are:
x retention of the Port as a valuable piece of commercial/industrial infrastructure; x reduction in the area reserved for port-related activities;
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x remediation of the former landfill and other potentially contaminated lands; x revised street/road layout and improved connectivity with the city centre via pedestrian-friendly crossings of the Inner Relief Road; x extended mixed-use zoning, including both retail and non-retail uses; x more land reserved for housing and a relocated neighbourhood centre; x enhanced provision of open space in the form of linear parks and cycle/pedestrian routes; x support for the regeneration of the Sligo Docklands through the provision of a cultural landmark building and the innovative reuse of former industrial buildings located in the area as workspace for creative enterprises and new community uses. x In relation to Effective Transport and Movement, the Development Plan notes that, while the significance of the Port in national terms is relatively low, it remains important in the local and regional economy, supporting local industry and providing a sustainable transport mode for imports and exports.
The Docklands “proper” area, i.e. lands immediately adjoining the waterfront, is currently a run-down, visually unattractive enclave in one of the most visible locations of Sligo City. It is considered that the redevelopment of the former docks should be undertaken in conjunction with that of adjoining areas
It is the aim of the local authorities to encourage a significant shift from travelling by car to other modes of transport and, in this respect, sets out their public transport policies that include: Encourage the maximization of freight transport by rail and through the port (P-PT- 6).
1.3.2.3 Proposed Docklands Local Area Plan (LAP) In February 2008, the DoEHLG recommended that the Sligo local authorities “harness all the powers” of the new SEDP to secure the redevelopment of key areas such as the Docklands.
Having recognised the strategic nature of the Harbour and surrounding lands in their Sligo and Environs Development Plan 2010-2016, Sligo Local Authorities indicated that they wished to plan the redevelopment of this key area of the Gateway on the basis of a detailed Local Area Plan (LAP). The formal LAP preparation has now commenced, with a pre-draft consultation document having been released in 2011.
This paper has set out the broad scope of what could be achieved at Sligo and gives examples of other coastal cities which have undergone significant regeneration of their docklands. The purpose of the paper is to provide the public and other stakeholders with sufficient information and suggestions to stimulate a debate on the future of the area. The paper offers background information relating to the docklands and outlines the main challenges that the LAP must address, such as meeting the requirements of the Habitats Directive, in order to help transform the area into a vibrant urban quarter. The consultation period ended in April 2011 and Sligo Council are now considering the submissions for inclusion into the plan.
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The pre-draft consultation notes that the proximity to the city centre, the waterfront along the Garavogue Estuary, the unparalleled views of Benbulben, Knocknarea and the sea, the variety of greenfield and brownfield lands with development potential all confer a special character to the wider Docklands area.
It also argues that the Docklands LAP needs a clear vision of what it hopes to achieve, and how this will bring benefits in the long term, if it is to be effective in regenerating the area.
A key issue raised within the draft consultation paper is the future vision of the port in the context of its location at the centre of the city. The consultation paper asks whether the commercial port operations need to be retained and enhanced or are best moved away from their traditional location to an area where cargo handling would be more efficient. These issues will be discussed further later in this Chapter and it is clear that retaining and enhancing the port’s trade is of utmost importance to the economy of the area and that there are no viable alternative locations for these activities.
Almost 40 submissions were received in response to the consultation paper, including one from the Harbour Office which is reproduced in Appendix 1A.
The key port-related points raised in the submissions included: x The container railhead is a major landholding and strategic land bank. Its future development is important for the overall area (IDA) x There should be provision for cargo transhipment zone within the docklands. Need to think of a ship/rail/road freight hub as well as a train/bus hub. A tidal lock gate, like at Kilrush, should be constructed for a marina (Des McConville) x Seek the protection and promotion of Sligo’s maritime heritage (Auriel Robinson) x Marine leisure should not be the only use for the port. Dredging of the port channel can increase capacity at a cost of €5m. Silt-bed pollution test results support dredging (Johnny Gogan) x More traffic could be generated if port dredging and widening took place. Either way, commercial traffic would not constrain other uses and should be retained. Mooring rings should be provided and rocks on the sea bed removed to eliminate possible damage as boats fall with the tide. Expansion of the pontoon facility and the provision of services should be a main feature of any redevelopment (Bryan Armstrong) x Commercial port activity must be retained and enhanced, as stated in the SEDP. There is a complete lack of appreciation of the historical importance of Sligo Port. There appears to be an agenda by Sligo County Council now the port has been taken over to cease to fully recognise the importance of the port as a facility and generator of trade. SPBA fully supports the proposed capital and maintenance dredging of sections of the navigation channel as being essential for the port’s ongoing viability (Sligo Port Business Alliance) x A total of 150 plus persons are directly employed in the port area. It is estimated that between 150 and 300 additional jobs rely on these businesses. There is clearly an identifiable business community here, as demonstrated by the level of trade at Margarets’ Café on Finisklin Road. Any LAP must acknowledge this community. Sligo Port has also evolved into a hub for the people of Sligo and includes activities such as refuelling
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vehicles, purchasing bulk fuels, bringing scrap metal and shopping for homeware. This trade must be enhanced. Greenstar and Erin Recyclers Ltd. take exception to the manner in which their businesses have been presented in the consultation paper. The brief statement on ‘waste management’ is the only mention of the huge contribution that these two companies make to Sligo Port in terms of services, trade and employment. Any policies or objectives must take into account these existing land uses and protect these businesses. Incompatible developments must not be allowed to locate adjacent to these facilities (i.e. housing or office). (Existing Business Community) x Sligo Fuels Ltd. business plan envisages an increase in importation and distribution of oil in bulk together with diversification into the importation, offloading, packaging and distribution of solid fuels. Medium to long term strategy envisages an increased proportion of these materials will be imported by sea. The company’s present road delivery set up is expensive, disruptive and unsustainable. This will result in port usage and also a larger storage depot. It is considered that the maintenance of the port and its activity is a fundamental requirement of the proposed LAP. (Sligo Fuels Ltd) x The Chamber encourages a feasibility study for commercial rail linkage between the railway station and the port prior to this link being severed. A rail corridor should be preserved within the plan as there are too many examples where rail facilities were removed only to be later regretted. Consideration should be afforded to the provision of a marina within the plan. These have proven to be very popular in other locations and are typically self-financing. They add to the ambience of an area and provide commercial activity. (Sligo Chamber of Commerce)
As can be seen, the residents of communities connected or close to the Docklands, the business people operating in the area and their customers, the potential users of future amenities, the wider community, the artists and students of Sligo - all had the unique opportunity to make a valuable input into the shaping of the Docklands’ future. Infrastructure and service providers, state/semi-state bodies and funding agencies were also called to contribute to the creation of a shared vision.
The extent of the LAP boundary will be decided following pre-draft consultation with the public and the main stakeholders
1.3.2.4 Sligo County Development Plan 2005-2011 The role of the County Development Plan is to regulate, control and effectively promote sustainable development in County. The Plan states the County Council's policies for land use and for development control in its area.
Section 8.1.6. of the plan acknowledges that while the significance of Sligo Port in national terms is quite low, it remains important in the regional and local economy, supporting local industry and providing a sustainable import and export transportation facility.
As such, it outlines a number of key ports and harbours objectives: x Continue to support the development and operation of Sligo Port.
IBE0440/EAR/September ‘12 1-13 Sligo Harbour Dredging Environmental Appraisal Report Introduction x Improve road and rail access to the Port, in order to boost its viability as an international freight port. x Assist Rosses Point Yacht Club and the local community in the development and management of a local yacht haven facility, as resources become available. x Carry out improvement works on Coney Island Pier and at Raghly Harbour and maintain and improve other piers and harbours, as resources allow. x Support the role of harbours, piers and shipways in facilitating fishing, marine leisure, recreation and other activities.
However, the ports and harbours objectives must be set into the wider context of the Plan’s coastal zone management and environmental objectives.
The plan recognises that the coastline is a finite resource that provides environmental, economic, recreational and aesthetic benefits and access to marine resources such as fisheries and aquaculture. It also contains many sensitive ecosystems, ranging from sand dune systems to salt marshes and estuaries rich in marine and bird life and is significant in terms of cultural and archaeological heritage. The plan acknowledges that the coastal zone is under increasing pressure from issues such as coastal erosion, pollution and conflicting user groups (eg fishermen, shellfish farmers, conservationists and tourism developers).
The objectives for fishing (6.2.2.1) include: x Support and facilitate the development of the existing fishing industry. x Encourage the expansion of sport fishing.
The objectives for mariculture (6.2.2.2) include: x Encourage and facilitate mariculture development associated with job creation, in a manner that is compatible with other uses of the Sligo coast. x Work with the mariculture industry to increase environmental sustainability.
The objectives for nature conservation in the coastal areas (6.2.6.1) x Support the management of sites of conservation importance, including pNHAs, cSACs and SPAs. x Take into account the potential conservation of all sites of interest within the coastal zone when assessing development proposals. x Promote the natural interest of the Sligo Coast as a sustainable tourism, conservation and educational asset.
These are in addition to the more specific “Objectives for designated nature conservation sites” (7.2.2.4) of which Sligo Harbour is one. x Maintain, and where possible enhance, the conservation value of all pNHAs, cSACs and SPAs, as identified by the Minister for the Environment, Heritage and Local Government, as well as any other sites that may be proposed for designation during the lifetime of this Plan.
IBE0440/EAR/September ‘12 1-14 Sligo Harbour Dredging Environmental Appraisal Report Introduction x Discourage development that would destroy or damage any sites of international or national importance, designated for their wildlife/habitat significance, including pNHAs, cSACs and SPAs.
The dredging scheme has been designed to maintain the aims of the development plan by supporting local industry and boost viability as an international freight port whilst safeguarding the interests of the local fishermen, shellfish producers and tourism developers whilst providing the minimum possible impacts on the local conservation and heritage designations. These aspects are discussed in more detail in Part III of this Report.
1.3.3 Other Relevant Policies The proposed development would also support the objectives of the following national and EU policies.
1.3.3.1 Transport Emissions The EU’s climate and energy package contains specific measures aimed at addressing emissions from transport. This reflects the fact that transport is responsible for around a quarter of all EU greenhouse gas emissions, making it the second biggest greenhouse gas emitting sector after power generation. Road transport alone contributes about one-fifth of the EU's total emissions of carbon dioxide (CO2), and while emissions from other sectors are generally falling, those from transport have increased 36% since 1990.
In addition to the legally binding target of 10% for renewable transport fuels in each member state contained in the climate and energy package, the EU has also put in place a range of policy instruments that are aimed at reducing GHG emissions from the road transport sector in recent years. This includes targets to improve the fuel efficiency of vehicles, targets to reduce the GHG intensity of transport fuels and the CO2 labelling of cars.
1.3.3.2 Irish Government Policy Initiatives Climate change has also become a primary driver of policy in Ireland. The National Climate Change Strategy 2007-2012, for example, contains a target to reduce greenhouse gases by 3% per year in an effort to meet Ireland’s commitments under the Kyoto Protocol, and of course, Ireland is now legally obliged to meet the more stringent targets contained in the EU’s climate and renewable package.
Recent estimates from the EPA indicate that after several years of very significant growth, Ireland’s emissions actually declined in the last two years. However, it is also evident that the majority of this decline is due to the economic downturn and it is expected that once economic activity picks-up again, emissions will once again start rising. For this reason, it is clear that concerted action will continue to be needed to “de-carbonise” the economy if Ireland is to meet its international commitments.
In March 2007, the Government’s Energy White Paper was published. It sets out the energy policy directions and targets for Ireland to 2020. It sets a target to achieve 20% savings in energy end use across the electricity, transport and heating sectors by 2020, in
IBE0440/EAR/September ‘12 1-15 Sligo Harbour Dredging Environmental Appraisal Report Introduction line with EU targets, and an indicative target of 30% by 2020 to surpass the EU ambition. It also sets a target for the penetration of renewable energy in transport – to account for 5.75% of road transport by 2010 and 10% by 2020.
1.3.3.3 The Transport Sector – Irish Policy Initiatives The transport sector will be expected to make a significant contribution to meeting EU and national emission reduction targets. In 2009, the sector was responsible for over 21% of Ireland’s total emissions and until recently, had seen amongst the fastest increase in emissions of all sectors.
The National Climate Change Strategy 2007-2012 committed to changing the basis for assessing Vehicle Registration Tax (VRT) and Motor Tax from 2008 so that they would be more closely aligned with CO2 emissions and send the right “signals” to drivers. As a result, both taxes are now levied on the basis of the CO2 emission rating of the car rather than engine size as was the case in the past.
In line with the general shift in policy to ensure that motor taxes take greater account of CO2 emissions, in Budget 2010 the Government also announced the introduction of a carbon levy on fossil fuels to change the relative price of fuels based on CO2 emissions in order to change consumption patterns, encourage fuel efficiency and lead to an improvement in environment quality. It is anticipated that the levy, which was introduced in December 2009 at a rate of €15 per tonne of carbon, will steadily increase in the coming years.
Sligo’s commercial port provides a net positive impact in terms of CO2 by reducing the road haulage of goods handled at the port due to their bulk transport by shipping to and from the North West region.
The Government’s Smarter Travel policy document, Smarter Travel: A Sustainable Transport Future, was published in February 2009, which covers the period 2009-2020, highlights a number of key steps to ensure that people choose more sustainable transport modes, to minimize the impact of transport on the environment and to improve Ireland’s security of energy supply by reducing dependency on imported fossil fuels.
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1.4 PROJECT JUSTIFICATION
1.4.1 Background
With a population of 17,568 (expanding to c.35,500 living within 10km of the city centre) in 2011 (CSO, 2012), Sligo is the largest urban centre in the North-West.
During the 17th and 18th centuries, Sligo Port established itself as an important focus of trade, with good quantities of cattle, hides, butter, barley, oats, and oatmeal being exported and with the city’s linen exports well established. Imports included wood, iron, maize and coal. The town prospered due to the trade with wealthy merchants setting up homes along the fashionable Castle Street and Radcliffe Street (later renamed Grattan Street). This wealth is demonstrated by the construction of the Cathedral of John the Baptist, which was completed as early as 1730. It was designed by Richard Cassels, the architect of many important buildings at the time, such as Leinster House in Dublin and Russborough House in County Wicklow. The most notable ship companies who operated out of Sligo included Sligo Steam Navigation Company who introduced the first steamer in 1857, Messrs Middleton & Pollexfen, Harper Cambell Ltd and the former Sligo Harbour Commissioners who owned a number of dredgers used for maintenance of the Channel (McTernan, 1992).
Sligo Harbour is the most northerly commercial port on the west coast of Ireland. There are two working jetties, Deepwater and Barytes which handle cargoes of coal, timber, fish meal and scrap metal. Sligo County Council took over responsibility for Sligo Harbour from Sligo Harbour Commissioners in June 2006. Since then Sligo County Council has embarked on a series of improvement works including refurbishment of the Deepwater Jetty, reinstatement of Barytes Jetty and improvements to the shipping channel training wall. The Deepwater Jetty is 77m long and the Barytes Jetty is 55m long, allowing the harbour to accommodate vessels of 3,500 DWT. The maximum draught for vessels is currently 5.2m and the maximum length that can be accommodated is 100m. Most recently, the Council refurbished the old Timber Jetty and installed pontoons for mooring leisure craft. The facility became operational in November 2008.
Sligo County Council, in the interest of ensuring continued use of the existing facilities and to improve operational opportunities in the port, now wishes to undertake the following works within the harbour and its approaches:
x Maintenance Dredging of the berths and navigation channel from the Barytes Jetty to the Red Light is required in order to maintain the minimum required depth for current vessels using Sligo Harbour. The siltation of the channel has begun to pose a significant threat to navigational safety.
x Capital dredging along lengths of the channel in order to generate new business and thereby secure the future viability of Sligo Harbour as a destination for commercial vessels.
In the operation phase, the dredging will permit vessels with a draft of up to 5.9m to access the Barytes and Deepwater Jetties and improve the window for access. Additionally with the
IBE0440/EAR/September ‘12 1-17 Sligo Harbour Dredging Environmental Appraisal Report Introduction refurbishment of the Barytes jetty in 2008 the Port has increased the capacity of the facility by being able to unload two vessels simultaneously which will contribute to an increase in trade. The primary purpose of the dredging is to safeguard the existing trade at the port, allow for its future expansion and to comply with health and safety requirements.
Sligo Harbour holds a number of important environmental designations including Special Area of Conservation and Special Protection Area and therefore the EIA studies must include an Appropriate Assessment which will fulfil the requirements of the Habitats Directive.
1.4.1.1 Works to Date Following the Review of Regional Harbours and Ports carried out by KPMG Management Consultants in 1999, which recommended the transfer of ownership of certain harbours to local authorities, Sligo Port was transferred to Sligo County Council under Ministerial Order in 2006. There were approximately 90 acres of land under the control of the Harbour Commissioners, most of which had been reclaimed from the sea since the 19th Century. In 2006 it was estimated that approximately 75 acres (36 properties) were leased for both port- related and non-port-related purposes.
Funding was made available by the Department of Marine and Natural Resources specifically for the takeover and was directed at Safety and Remedial issues. A total grant of €1.85M was provided to carry out essential works. The works included the design and construction of replacement commercial berthage at Barytes Jetty, new access and safety facilities at Timber Jetty and substantial improvements to the training wall which helps maintain the shipping channel to the port. In addition, the new pontoon facility at the Timber Jetty gives opportunities to strengthen the recreational fishing and sea tourism activities in Sligo, such as the establishment of a sea bus between Sligo and Rosses Point.
Maintenance dredging of the channel took place in 1998, while maintenance dredging of the berths took place in May 2010.
A 60 metre pontoon was recently provided that can handle up to 10 vessels alongside if some are tied up in parallel with each other.
1.4.1.2 Approach The approach adopted for the business case study commissioned for this Report was as follows:
x A site visit was made and discussions with were held with the Harbour Master and other officials in relation to commercial, marine tourism and other business related activities, employment, ship movements and trends at Sligo Port
x Telephone discussions were held with the Port’s principal commercial customers
x All relevant traffic, financial and commercial data including port charges and operating and maintenance costs were collected and analysed
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x A report was prepared demonstrating the socio-economic importance of Sligo Port to the city and region, excerpts of which have been incorporated into this Chapter.
1.4.2 Sligo Port In this section, we examine the current activities in Sligo Port and present brief profiles of the Port’s customers.
1.4.2.1 Port Volumes Table 1.1 provides details of traffic volumes (‘000 Tonnes) for the major Irish ports including Sligo Port for selected years between 1990 and 2010.
Figure 1.2 provides a graphic representation of national traffic volumes (‘000 Tonnes) for the major Irish ports including Sligo Port for selected years between 1990 and 2010.
Figure 1.2: Irish Port Traffic
80 60,000 70 50,000 ) 60 40,000 50 40 30,000 30 20,000
Sligo (000 Tonnes) (000 Sligo 20
10,000 Tonnes (000 Republic 10 0 0 1987 1994 1997 2000 2003 2006 2009
Sligo Republic
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Table 1.1: Irish Port Traffic
‘000 Tonnes 1990 1995 2000 2005 2006 2007 2008 2009 2010
Belfast 7,757 10,144 12,484 13,500 13,514 13,416 13,040 12,050 12,827
Larne 4,001 4,673 4,508 5,496 5,488 5,464 5,166 4,297 4,609
Warrenpoint 1,413 1,683 1,676 2,436 2,307 1,999 2,118 1,841 2,327
Londonderry 730 1,044 1,189 1,150 1,689 1,934 1,840 1,619 1,757
Other NI 2,485 2,491 1,634 1,471 1,487 1,055 1,334 979 1,387
N IRELAND 16,386 20,035 21,491 24,053 24,485 23,868 23,498 20,786 22,907
Dublin 6,384 8,899 15,892 19,227 20,795 21,801 21,127 18,606 19,548
Shannon Foynes 5,933 8,061 10,282 11,355 11,393 11,072 10,819 7,577 9,134
Foynes 1,084 1,362
Cork 5,857 7,104 9,732 9,919 9,709 10,098 9,633 7,968 8,466
Waterford 1,328 1,776 1,943 2,257 2,376 2,253 2,082 1,631 1,451
New Ross 1,021 1,056 1,121 966 831 729 694 515 444
Rosslare 807 1,130 1,913 3,118 2,744 2,926 2,722 2,328 2,502
Drogheda 1,004 673 1,015 1,402 1,279 1,035 664 555 499
Greenore 491 300 444 649 869 790 700 390 503
Arklow 275 270 88 0 0 0 0 0 0
Dun Laoghaire 261 n/a 225 156 82 61 49 14 2
Dundalk 321 232 285 337 436 371 217 222 140
Wicklow 205 154 151 282 297 221 85 73 89
Galway 429 456 727 1,019 946 945 838 723 671
Sligo 32 32 37 35 43 46 41 53 54
Bantry 1,198 1,142 1,191 1,402 1,009 933 1,224
Other R of I 641 875 220 282 327 389 401 292 344
REPUBLIC 26,073 32,380 45,273 52,146 53,318 54,139 51,081 41,880 45,071
ISLAND 42,459 52,415 66,764 76,199 77,803 78,007 74,579 62,666 67,978
Source: CSO
1.4.2.2 Tonnage and Vessel Numbers
Table 1.2 and Figure 1.3 present details of vessel numbers and tonnage per vessel between 2000 and 2011. It can be seen that tonnage per vessel has been growing steadily such that it
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was 2,344 tonnes per vessel in 2011. Table 1.3 provides a more detailed breakdown for the period 2008 – 2011 based on the harbour’s own records.
Table 1.2: Sligo Port Traffic
2000 2002 2004 2005 2006 2007 2008 2009 2010 2011 Tonnage 37,000 57,000 72,000 35,000 43,000 46,000 41,000 53,000 52,000 49,000 Vessel Numbers 28 37 35 21 22 24 22 25 24 21 Tonnes/Vessel 1,321 1,541 2,057 1,667 1,955 1,917 1,864 2,120 2,183 2,344 Sources: CSO and Sligo Port (2011)
Figure 1.3: Sligo Port Traffic
80 2,500
70 2,000 60
50 1,500 40
30 1,000 Tonnes per Vessel 20 500
Tonnage ('000) & Vessel Numbers Vessel & ('000) Tonnage 10
0 0 2000 2001 2002 2003 2004 2005 2006 2007 2008 2009 2010 2011
Tonnage Vessel Numbers Tonnes/Vessel
Table 1.3: Sligo Port 2008 - 2011 Traffic Details
Company Product Import/Export 2008 2009 2010 2011 Hunter Coal Import 12,724 20,700 15,361 14,150 Arigna Fuels Coal Products Import 4,814 9,117 15,301 14,281 Erin Recyclers Scrap Export 21,203 13,752 19,021 20,796 Fish Industries Fish Meal Import 5,119 7,204 2,697 0 Brooks Timber Import 4,098 0 0 0 Emerald Salvage Scrap Export 4,475 2,673 0 0 Coillte Logs Export 0 1,793 0 0 TOTAL 52,433 55,239 52,380 49,227 Source: Sligo Harbour It can be seen that timber was last imported in October 2008 and that there were no fishmeal imports in 2011.
1.4.2.3 Freight Traffic Analysis - 2010
Table 1.4 provides more detail on the Port’s traffic in 2010 and 2011 respectively.
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Table 1.4: Sligo Port 2010 and 2011 Traffic Details 2010 Freight Type Customer No of Ships Tonnage Tonnage per Vessel Hunters, Arigna Coal 12 30,662 2,555 Fuels Scrap Erin Recyclers 10 19,021 1,902 United Fish Fishmeal 2 2,697 1,349 Industries Total 24 52,380 2,183
2011 Freight Type Customer No of Ships Tonnage Tonnage per Vessel Hunters, Arigna Coal 11 28,431 2,584 Fuels Scrap Erin Recyclers 10 20,796 2,080 Total 21 49,227 2,344 Source: Sligo Harbour
1.4.2.4 Financial Performance - 2011 The Port charges €1,300 for Tonnage and €1 per tonne cargo dues for all good other that scrap that is charged at €0.90 per tonne.
The estate is about 90 acres in size with much of the property leased out on long-term leases with no rent reviews.
Total revenue in 2011 was of the order of €250,000 comprising €65,000 from shipping tonnage and cargo dues, €185,000 from leases and the balance from earnings from the pontoon.
Budgeted income in 2012 is estimated at €285,000.
Costs include an annual charge of €4,800 for the foreshore lease as well as the salaries of the Harbour Master, part-time secretary and Council engineering staff allotted to port activities.
1.4.3 Customers
1.4.3.1 Arigna Fuels Arigna Fuels is located in Carrick-on-Shannon in the valley of Arigna on the border of the counties Leitrim and Roscommon some 26 miles from Sligo. Arigna Fuels was established to focus on the development of low smoke and smokeless fuels (coals), with the aim of protecting the environment in Ireland.
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Slack is imported from Swansea and is processed into smokeless fuels.
While not employing any staff at Sligo, the company employs 50 in bagging and there would be 20 hauliers engaged in collecting the slack and in transporting the end product to customers. Some of the product is exported to Scotland and elsewhere in Britain.
Total imports in 2010 were some 70,000 tonnes of which about 20,000 tonnes came through Sligo. The reduction in water depth and weather concerns have resulted in the loss of a number of cargoes, of the order of 9,000 tonnes, to Sligo because of the reduced window for docking with diversions to Belfast and Derry. These diversions resulted in an extra cost to Arigna of some €3 per tonne.
The company sees the importance of Sligo Port being able to take 3,500 tonne vessels safely.
1.4.3.2 Hunters (Bord na Mona) Ltd Hunters import coal from Poland, Rotterdam and Scotland, with nuggets from Germany through Rotterdam. The product is distributed locally to wholesalers and co-ops.
The company acts as agent and stevedore, and employs about nine in total including a crane operator and with five staff in the yard. There would also be a number of hauliers that would transport the coal to customers.
Should Sligo Harbour close, then the local facility would also close.
1.4.3.3 Erin Recyclers Ltd Erin Recyclers Ltd. is one of Ireland's leading independent Scrap Metal Recycler providing collection, sorting, processing and crushing services on a nationwide all-Ireland basis for all types of scrap metal waste including ferrous and non-ferrous metal, End of Life Vehicles (ELVs), Car Shells, Lead Acid Batteries, Electrical Cables and WEEE.
The company has two modern fully waste permitted scrap yard facilities strategically positioned at Sligo Harbour and its sister company Foyle Recyclers located at Derry Port.
In 2010, almost 17,000 tonnes of scrap steel were exported through Sligo while an additional 12,000 tonnes of car bales were exported through Belfast at an extra transport cost of some €300,000. It is expected that the car bales will be exported through Sligo Harbour in 2011 with a potential eight extra ship movements.
The company uses 2,500 tonne vessels.
The company employs 30 directly and 40 indirectly.
1.4.3.4 United Fish Industries Ltd United Fish Industries Ltd. located at Killybegs, imported fishmeal into Sligo from Rotterdam for Skretting in Westport. Unfortunately, this company closed in late 2010. In addition, with
IBE0440/EAR/September ‘12 1-23 Sligo Harbour Dredging Environmental Appraisal Report Introduction the reduction in fish quotas, including those for blue whiting, these events will now impact on future imports through Sligo. In 2011, there were no loads imported through Sligo.
Employing some 20/25 on a seasonal basis at Killybegs, the company does not employ any staff at Sligo but would send some of their workers down to Sligo when a ship unloads its product there that would be stored at the Gallaghers site. Any other imports are imported through Larne.
1.4.3.5 Sea Angling There are three charter vessels operating primarily from Sligo Harbour and Rosses Point that are available for hire for sightseeing, sea angling, eco-tourism, seal watching trips etc and trips to Inishmurray Island, Coney island and elsewhere. Tourists come from all around Ireland, the UK and mainland Europe. The charterers also provide any necessary tackle.
All-day trips as well as evening trips are offered during the summer at a cost of the order of up to €40/€50 per head.
At least 5,000 visitors have used this service in recent years, although there has been a reduction in visitor numbers due to the economic recession.
Two of the charterers are members of Irish Angling Charters/North West Charter Skippers Association, http://www.irishanglingcharters.ie/ - this site gives additional details of the services offered. One of the charter skippers is also the Harbour Pilot.
While the pontoon at Sligo Harbour is welcomed, it is suggested that there should be another pontoon at Rosses Point as it would reduce the travel time off the sea journeys. It would also address possible safety issues in accessing boats that are moored off other boats at the Harbour pontoon.
1.4.3.6 Fishing Boats No fishing boats operate from Sligo Port.
1.4.4 Economic Impact In this section the economic impact of Sligo Harbour will be considered.
The overall impact of Sligo Harbour’s activities may be separated into three parts as follows: x The Direct Impacts give the total expenditure on the purchase of goods and services by Sligo Harbour and other businesses at the Port x Indirect Impacts are those which occur when local suppliers in receipt of expenditure, in turn purchase goods and services. This in turn results in further production and employment in businesses located in the country. x Induced Impacts relate to the re-spending of household incomes derived from the additional employment generated through the indirect impacts described above. This expenditure in turn accrues to households, businesses and the government and some leaks out as imports. Thus, the knock-on impacts throughout the economy arising from
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the direct expenditures result in a higher overall impact than is suggested by the initial round of direct expenditures.
The overall impact is the sum of the direct, indirect and induced impacts. These impacts may be quantified in terms of expenditure and employment. This overall impact can then be measured as a multiple of the direct impact of business. Thus, expenditure and employment "multipliers" encapsulate the impact of the business in the country, and is estimated to be of the order of 1.8 for port-related business.
1.4.4.1 Employment associated with Harbour Activity The total employment, full-time and part-time, associated with the Harbour’s activity is of the order of 180 made up as follows (Table 1.5):
Table 1.5: Employment associated with Harbour Activity Sligo Harbour Elsewhere Indirect Sligo Harbour Company 4 Hunters 9 Arigna 0 50 20 Erin Recyclers 30 40 Fish Industries 0 25 Marine Tourism 3 TOTAL 46 75 60
According to the submission by the Existing Business Community in relation to the Docklands LAP (refer to Section 1.3.2.3), a total of 150 plus persons are directly employed in the port area and that between 150 and 300 additional jobs rely on these businesses. Many of these jobs could be impacted by the closure of the Harbour.
1.4.4.2 Disposable Income Applying the average industrial salary of €36,000 to the FTEs based in the Harbour (46) and applying an Employment Multiplier of 1.8 to take account of indirect and induced employment effects, the total gross salary income is of the order of €3 million.
The net disposable income, after tax, PRSI and Universal Social Charge deductions totalling some 30 per cent, is €2.1 million.
This sum is likely to be under-estimated as it is probable that the average income is greater that the average industrial wage and the numbers overall benefiting from harbour activity is larger than that estimated.
1.4.4.3 Gross Value Added Gross Value Added (GVA) is a measure of the value of the goods and services produced in a region and, as such, it represents the overall contribution to the Gross Domestic Product (GDP) of the Irish economy.
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Its determination can be used to estimate the value of the economic output linked to jobs directly associated with Sligo Harbour.
The CSO publishes GVA values per employee and was of the order of €58,000 per worker for the Border Region in 20081.
Using that value per worker, the GVA associated with Sligo Harbour is of the order of €4.8 million.
1.4.4.4 Value of Throughput The value at cost of the freight through the port in 2011, nett of taxes and freight costs, is estimated at some €8.5 million.
1.4.4.5 Maritime Tourism There is general consensus that harbours and marinas have a tourism and economic benefit for the towns where they are sited: x Maritime tourism is a major instrument of regional development. Many tourism enterprises are situated in areas where other employment options are limited. x Local communities benefit from investment in facilities for tourists such as leisure and sporting facilities and in associated infrastructure including access transport and roads. x A vibrant tourism industry contributes to the viability and sustainability of a wide range of local enterprises. x Tourism promotes an enhanced awareness and positive appreciation of local traditions, way of life and cultural heritage
Specifically, tourist expenditure creates both temporary employment and income from the purchase of local goods and services. Service-type jobs are created in shops, gift production, and restaurants and hotels. There is also a multiplier effect where the income or wages generated from tourism is spent by residents on local services.
Research suggests that the average visitor to an Irish marina contributes about €140 to the local economy. Whether the marina is occupied by a yacht owner, a visitor or a berth owner, local businesses will benefit from the purchases of fuel, supplies and gifts. Chandler purchases and any repairs carried out will also contribute to the local economy. Most users of a marina will spend money in a town on visitor attractions, golf, meals, drink and other day-to-day requirements, and all of this spend will boost the local economy which will have a significant impact on employment and local disposable income.
The British Marine Federation estimates that visiting boats to UK marinas contribute on average £150 each per night to the local economy. The BMF has also reported that for every £ spend on boating, there is an associated spend of £6 onshore.
1 County Incomes and Regional GDP, CSO, 17 February 2011
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In the Republic of Ireland, it is estimated that for every Euro spent by an out-of-state tourist, 26 cent eventually ends up with the government through VAT, excise duty, PAYE etc. For every €1 million of foreign and domestic tourism revenue, there is generated an overall GNP impact of almost €680,000. Over 80 cent in every Euro of tourism spend remains in Ireland.
A survey of businesses in Dún Laoghaire and Malahide carried out by an Irish Sea Interreg project found that marinas in both towns had a positive impact on 37 per cent of respondents. At Kilmore Quay, some 67 per cent of businesses surveyed believed that their local marina contributed to their success.
Whether the marina is occupied by a yacht owner, a visitor or a berth owner, local businesses benefit from the purchases of fuel, supplies and gifts. Chandler purchases and any repairs carried out will also contribute to the local economy. Most users of the marina will spend money in the town on visitor attractions, golf, meals, drink and other day-to-day requirements, and all of this spend will boost the local economy which will have a significant impact on employment and local disposable income.
1.4.5 The Economic Impact arising from Construction Construction is one of the most labour-intensive forms of economic activity in the Irish economy. In 2006, it was estimated by Government that one quarter of all small and medium sized enterprises (SMEs) in Ireland were in the construction industry.
There are many economic benefits that will arise from the construction of the new harbour development. The benefits can be considered under three separate impacts: x the direct addition to economic output generated by the output of the industry; this can be measured by the earnings of those employed in construction, i.e. payroll plus profits earned. This comprises the employment generated by all jobs created by construction firms that work directly on projects x the indirect employment generated by the firms that provide the inputs to the project in question plus the employment generated by those firms who supply the firms providing the inputs and so on. These are sometimes called ‘second generation’ suppliers and include, for example, persons employed in concrete manufacturing, joinery workshops and steel fabrication. Estimates of indirect employment in construction are typically estimated at 40 per cent of direct employment, implying that for every ten persons directly employed on a construction project there are a further four ‘indirectly’ employed in supporting industries x the induced employment impacts which include all of the jobs created by those directly and indirectly employed in construction spending their wages and profits throughout the wider economy. These would include the additional jobs (and income) in retail and other sectors that are created as a result of the various consumer purchases made by those households employed at the direct and indirect stages. Our estimate for the induced multiplier is 1.4
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In a submission2 to Government prepared by DKM for the Construction Industry Council, the authors found that of the order of nine direct and indirect jobs were created for each €1 million of construction spend in 2007. With reduced tender prices now prevailing, DKM suggests that the number of construction jobs per €1 million is of the order of eleven excluding the induced multiplier effect. The actual labour intensity of construction projects, of course, varies depending on the type of constructed being carried out.
According to the CIF, every €10 million invested in construction projects returns over €3 million to the Exchequer in VAT and Income Tax, excluding any Corporation Tax receipts.
1.4.6 The Positive Impact of Development The proposed dredging will avoid a number of consequences. Some of those are listed below.
1.4.6.1 Retention of Local Employment The closure of the Port would result in a reduction in the number of people employed in port- related activities and probably the closure of a number of local companies.
Based on our estimates above, if all of the directly related employment were to cease, at least €2 million of disposable income would be lost to Sligo Town and its environs that would have a major impact on local retailers, restaurants and the like. Further, given the current levels of unemployment, it is likely that not all of those made redundant would find alternative employment.
Those who could not find employment would be entitled to social assistance that would be a cost to the Exchequer which, ultimately, will be funding the dredging.
1.4.6.2 Maintenance of Port Revenues and Lease Income Closure of the Port would mean that the Council would no longer generate harbour income for tonnage and cargo dues. In addition, a likely result would be a number of tenants leaving the harbour site, which would impact on the Council’s lease income.
1.4.6.3 Avoidance of Extra Transport Costs The diversion of freight to alternative ports, e.g., Galway, Derry and Killybegs, would result in extra freight traffic on our roads in bringing the goods to Sligo. The extra transport costs are estimated at almost €2 per mile,
1.4.6.4 Reduction in Carbon Footprint The additional road traffic would add to the carbon footprint from the additional transport emissions, would lead to increased health risks and the incidence of accidents and fatalities, and generate greater traffic congestion and extra travel times. Already, over 30 per cent of transport greenhouse gas emissions are from the freight sector. Statistics from the UK
2 Submission To The Government by the Construction Industry Council: Jobs and Infrastructure – A Plan For National Recovery, DKM Economic Consultants and Goodbody Corporate Finance, March 2009
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Department of Energy and Climate Change indicate that every extra kilometre of travel by a
Heavy Goods Vehicle generates 0.9 kilograms of Greenhouse Gas in terms of CO2, CH4 and
NO2. The consequences of the additional road traffic run contrary to Government objectives laid down in its document “Smarter Travel – A Sustainable Future; A New Transport Policy for Ireland 2009 – 2020”. 1.4.6.5 Growth in Marine Tourism A failure to maintain the harbour and provide a working environment would affect its attractiveness for marine tourism.
1.4.6.6 An Improved Image A working harbour can be a major attraction. A closed harbour can be an eyesore. It is probable that a failure to maintain the port area would result in it becoming a derelict site with all of the consequent problems that such a site can become.
1.4.7 Conclusion The city of Sligo has been designated as one of four National Level Gateways under the National Spatial Strategy and, as such, plays an important role in the economic life of the region and country. As a Gateway, it is important that it offers and provides transport links for all modes of transport.
The Regional Planning Guidelines for the Border Region note that Sligo Port has significant potential along the western seaboard. This support is echoed in the Sligo and Environs Development Plan 2010 - 2016 that points out that, while the significance of the Port in national terms is relatively low, it remains important in the local and regional economy, supporting local industry and providing a sustainable transport mode for imports and exports. The Development Plan has as a Zoning Objective ‘Retain the port as a viable infrastructural and commercial entity, supported by port-related industries and/or business activities’.
Sligo Harbour enables the movement of bulk cargo by sea direct to and from Sligo and the loss of such a facility would be a loss to the city, county and region given that Sligo Port is the only commercial working harbour between Galway and Killybegs and Derry.
We argue that the proposed maintenance and capital dredging should proceed. Not only will it facilitate the retention of existing business and be the basis for potential new harbour business such as off-shore energy servicing, it will also protect local employment and retain port revenue. In addition, it will also avoid: x the loss of employment that would arise, possibly up to 80 jobs x reduction in consequent spend in the city and environs – up to € 2 million annually x loss of tax income to the State and payment of social welfare to those who cannot find alternative employment x loss of economic benefits arising from the construction phase in terms of employment and local spend x loss of port revenues and certain lease income currently €250,000 in total per annum
IBE0440/EAR/September ‘12 1-29 Sligo Harbour Dredging Environmental Appraisal Report Introduction x extra transport costs and journey times for those industries remaining x increased carbon emissions x higher incidence of accidents and fatalities x additional travel that would not be in accordance with the Government’s Policies on Sustainable Transport and Climate Change x reduction in maritime tourism activity and spend x negative impact on image and profile of the city
The proposed development supports the Council’s own Public Transport Policy that states ‘Encourage the maximisation of freight transport by rail and through the port’.
Further, many of the submissions in relation to the Docklands Local Area Plan support the development of the Port.
Our analysis suggests that the cost of the proposed dredging, some €5 million, would be recouped by the State in a short number of years.
It is vitally important that maintenance dredging is carried out in the short term which would have a cost estimate of €80,000 for 2012.
At a broader level, we therefore conclude that there is a business case for proceeding with the proactive dredging of the channel.
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1.5 CONSIDERATION OF ALTERNATIVES
The consideration of alternatives in an important requirement of the Environmental Impact Assessment (EIA) process. For the purposes of the EIA Regulations, alternatives may be described at three levels: x Alternative Locations; x Alternative Designs; x Alternative Processes.
1.5.1 Alternative Locations
The port at Sligo Harbour is well established and has a long history of being a hub of activity within the city. Indeed, Sligo began its development as a port of consequence for agricultural goods to Britain and the Europe in the 13th century. Official records in the fifteenth century mention ‘Fish Quay’ under Henry VI reign. Customs duties under the Harbour Commissioners can be traced back to George II, in 1689. At that time and for two hundred years thereafter, Sligo was the most important Port in the Northwest (Sligo County Council, 2008). During the time of the Great Famine, around 1847-1850, it is estimated that more than 30,000 people emigrated through Sligo Port, mainly to Canada and the United States.
Sligo Harbour is sheltered from the storms of Donegal Bay and the Atlantic by the headlands at Strandhill and Rosses Point and by Coney Island and Oyster Island. As a consequence, the sand flats within the harbour have become important areas for bird life and the entire harbour holds the European-level designations of Special Protection Area and Special Area of Conservation. There is no feasible means of relocating the port elsewhere within the harbour and although the container gantries at the port were removed in 2006, the port is still capable of receiving bulk materials and general cargo and provides a valuable service to its hinterland area.
The nearest harbour to Sligo capable of accepting commercial port traffic is Killybegs, Co. Donegal, some 100km northwest by road. Killybegs is primarily a fishing port, although its recent upgrade and redevelopment in 2006 have allowed it to expand its trade into the import and export of dry bulk, break bulk, fuels and general cargo including containers. Most of the trade through Killybegs is directly related to the fishing industry, e.g. fishmeal. Killybegs is constrained in the amount of goods it can distribute to its hinterland by its poor road connections. Most of the industry at Killybegs is centred around processing of raw materials landed on site and re-exporting the goods by sea. Up to two thirds of the fishmeal produced at Killybegs is exported by sea.
Sligo County Council have stated that it is their intention to continue with the programme of developing and enhancing the commercial and amenity value of the port which began when
IBE0440/EAR/September ‘12 1-31 Sligo Harbour Dredging Environmental Appraisal Report Introduction they took over responsibility for the port from Sligo Harbour Commissioners. In this respect there are no suitable alternative locations where this development may take place.
1.5.2 Alternative Designs
The alignment and width of the proposed dredging have largely been determined by the existing channel depths, the characteristics of the vessels which will use the port and current guidelines on navigational safety.
The tide levels for Sligo Harbour (Oyster Island) are as follows:
Highest Astronomical Tide HAT 4.6m CD Mean High Water Spring Tide MHWS 4.1m CD Mean High Water Neap Tide MHWN 3.0m CD Mean Low Water Neap Tide MLWN 1.5m CD Mean Low Water Spring Tide MLWS 0.5m CD Lowest Astronomical Tide LAT -0.2m CD
Tide levels are established in relation to the Standard Port, Galway.
1.5.2.1 Channel Alignment The alignment of the navigation channel is largely determined by existing physical constraints. These include the training walls extending from Ballyweelin Point to the Barytes Jetty, Oyster Island and various rock outcrops between Ballyweelin Point and Sligo Bay.
Field surveys undertaken during summer 2010 and winter 2010-11 have observed that the training walls are important roosting areas for the bird life within Sligo Harbour SPA and disturbance of the training walls might adversely impact the species which use them. Realigning the navigation channel would also create increased dredging quantities and might potentially cause changes to the tidal currents within the harbour, therefore alteration of the route of the navigation channel is not being considered for this scheme.
The alignment of the proposed dredging of the channel will therefore follow the alignment of the existing channel.
1.5.2.2 Vessel Characteristics Through consultation with the Harbour Master from Sligo County Council the vessel characteristics for the current and anticipated users of the port have been reviewed and the following criteria will apply:
Vessel Characteristic Design Criteria Length overall 100m Beam 17m Draft 5.9m Dead Weight Tonnage 4,500 tonne
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1.5.2.3 Channel Width The design criteria for the channel cross section were based on the requirements of Sligo County Council and the design guide produced by PIANC (The World Association for Waterborne Transport Infrastructure).
The bottom width of the channel has been determined from the sum of the basic manoeuvring lane plus the additional width to account for vessel speed, cross winds, cross currents, longitudinal currents, wave height, aids to navigation, bottom surface, depth of waterway plus an allowance for bank clearance. Having regard to the foregoing, a bottom channel width of 50m is recommended.
The bed material is predominantly a fine silty sand with a relatively uniform grading. This material is typically stable at side slopes of approximately 1 in 5 in still water conditions and approximately 1 in 11 in active water conditions.
A stability analysis of the channel side slopes undertaken as part of RPS’ 2010 Feasibility Study concluded that a slope of 1 in 7 should be provided which maintains a compromise of pragmatic gradient whilst not over-stretching the dredging footprint.
1.5.2.4 Channel Depth
The following table (Table 1.6) illustrates the navigable period which will be available for a range of dredged depths. Given the length of channel and the anticipated vessel speed, a 3 hour window of opportunity for a 1 hour passage time is considered to be adequate. The costs of dredging to the various depths were also examined.
The bed level which has been chosen to accommodate the required size of vessel in the port, allowing it sufficient navigation time whilst retaining cost effectiveness, is 3 metres below Chart Datum.
Table 1.6 Comparison of Navigable Period with Dredged Depth
Vessel Draft 3.0 m 4.0 m 5.0 m 6.0 m Dredged Quantity Allow +10% for squat, draught & sounding Depth (approx) uncertainties and initial siltation 3.3 m 4.4 m 5.5 m 6.6 m m CD m3
-0.5 m CD 0 2.8 hrs N/A N/A N/A -1.0 m CD 0 5.7 hrs N/A N/A N/A -1.5 m CD 25,000 7.3 hrs 2.0 hrs N/A N/A -2.0 m CD 50,000 Navigable period in 8.6 hrs 5.1 hrs N/A N/A -2.5 m CD 125,000 hours per tide (of 12.4 10.2 hrs 7.1 hrs 0.7 hrs N/A -3.0 m CD 250,000 hours) 12.4 hrs 8.3 hrs 4.6 hrs N/A -3.5 m CD 400,000 12.4 hrs 9.9 hrs 6.9 hrs N/A -4.0 m CD 550,000 12.4 hrs 12.4 hrs 8.1 hrs 4.0 hrs -4.5 m CD 700,000 12.4 hrs 12.4 hrs 9.5 hrs 6.7 hrs
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1.5.2.5 Dredging Methodology
The material to be dredged is predominantly a silty sand which is expected to be suitable for removal by a trailer suction dredger. Trailer suction dredging produces large quantities of water with the dredged material. This excess water is either allowed to overflow the vessel and return to the main body of water or it can be taken out to the disposal site together with the dredged material. It is costly to take an excessive quantity of water to sea but this may be necessary if dispersal of overspill creates undesirable levels of turbidity.
Dredging with hydraulic excavators is a slower process but reduces the amount of excess water which is extracted. The slower rate of dredging with this system provides greater time for the dispersal of supernatant water and reduces the level adverse affect there may be on adjacent areas of seabed.
The dispersal of sediment plumes from the potential range of dredging activities is discussed in Chapter 11 “Coastal Processes”.
1.5.3 Alternative Processes
As the port is located on an estuary, siltation of the berths and navigation channel is a constant process, although construction of the training walls and their subsequent refurbishment in 2007 has helped to reduce the annual rate of sedimentation. In the past, large-scale maintenance dredging of the channel has taken place approximately once every ten years with the most recent dredging taking place in 1998.
In the 1970s, problems regarding the disposal of the dredged material from maintenance dredges led to the construction of a large holding pond/bunded area (circa 6 hectares), westward of the Deepwater Jetty. This area was filled with sediment in a major dredging operation (in 1985) and was used again during maintenance dredging in 1998. Now full, this area was subsequently developed as the site for Sligo’s main wastewater treatment plant, which was commissioned in 2009.
Small-scale dredging of the harbour berths takes place every two to four years, mainly by plough dredging which redistributes the sediment rather than removing it, thus avoiding the requirement to find an off-site disposal area. However, plough dredging is only a temporary solution in between the larger scale maintenance dredging as it does not remove the excess sediment from the area.
A Feasibility Study, prepared by RPS Consulting Engineers in 2010 (RPS, 2010), examined the various options for disposing of or reusing the dredged material from this scheme.
In total, five disposal options of the dredged material were considered, in addition to the “do nothing” scenario:
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i) Beneficial Re-use ii) Disposal on Land iii) Incineration iv) Reclamation within Sligo Harbour v) Disposal at Sea
1.5.3.1 The “Do Nothing” Scenario
In the “do nothing” scenario, the natural process of siltation will continue within the navigation channel. At present, commercial trade vessels can only enter the harbour on a spring tide and when berthed the vessels rest on the bed for much of the tide. With continued siltation, the harbour will become inaccessible even at spring tides and will no longer be able to be served by commercial vessels. This trade will be lost to other ports and the businesses which rely on the imports and exports into and out of the harbour will be forced to find alternative means of transporting their goods. For this reason, the “do nothing” scenario is not considered to be a viable option at Sligo Harbour.
1.5.3.2 Beneficial Re-use
The options for beneficial uses of fine materials are fairly limited. Historically, the main uses for marine sediments from capital and maintenance dredging are: x land raising as part of port development; x land raising for other projects, for example housing; x land reclamation/capping; x flood and coast protection (above the level of mean high water springs).
Other potential uses such as brick manufacture and the addition of dredged materials as aggregate filler in concrete or a raw material in cement manufacture have been investigated. However, these uses are not currently considered to be viable markets for large volumes of marine sediments from dredging, such as would be required at Sligo.
In order for the dredged sediment to fully meet the category for “beneficial reuse” (as opposed to finding an alternative use for a waste product), a clear need for the sediment must be demonstrated in advance of the project being progressed.
In the case of reuse for engineering projects or aggregate purposes, the sediment needs to exhibit the correct geotechnical properties such as grain size, permeability and strength. At Sligo, the proposed material to be dredged generally comprises a fine silty sand. Whilst this material is chemically “clean”, the significant silt fraction makes the material physically unsuitable for use on land as an engineering fill material, e.g. for raising land for housing or for flood protection. The viability of using the sediments in other uses such as land reclamation or capping is discussed in more detail in the sections below.
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In terms of coastal protection, in some areas dredged sediments can be used for beach nourishment. Beach nourishment has occurred at a few locations within Ireland, but it remains a relatively new concept. However, as with beneficial reuse on land, the physical properties of the sediment are the key consideration in the sediment’s ability to be reused as a resource. In general, it is a requirement for the grain size of the dredged sediments to match the grain size on the beach to be renourished (CIRIA, 2010). Occasionally, slightly coarser sediments are used, as these may stabilise the beach for longer periods of time.
At Sligo, the material to be dredged is too fine to be of any practical use as beach nourishment. Fine material can sometimes be used for habitat creation purposes, such as mudflat recharge or salt marsh restoration. However, these types of projects typically require small quantities of sediment (e.g. 1,000m³-5,000m³) (UKMSAC, 2001) and there are no areas near to the site which could accommodate anything approaching the volume of sediment required to be removed at Sligo Harbour. Due to the diversity and abundance of species which they support, mudflats and salt marsh areas are very often awarded European-level environmental designations such as Special Protection Areas and Special Areas of Conservation which creates additional levels of restriction on what sort of works can take place in these areas. For these reasons there are no viable alternative beneficial uses of the dredged sediment at Sligo Harbour.
1.5.3.3 Disposal on Land
General Landfill Option This disposal option would require the dredger to bring the dredge spoil ashore, either by barge or by pumping. The material would then be temporarily stored in a designated hardstanding or lagoon area to allow for dewatering/drying, material classification and leachate testing before subsequent transfer by road to a landfill site.
Even following a period of settlement, the dredged sediment would be likely to be considered a wet material for the purposes of land-filling. Landfill space is in very short supply and it is often the case that landfill sites are only licensed to receive relatively small volumes of wet waste (e.g. 500m³) per week. At these rates, even if three landfill sites were to accept the dredged material, it would still take over three years to transport all the material to landfill.
With an approximate specific gravity of 1.41t/m³ for 25% saturated silty sand, there would be about 352,500 tonnes of dredge material to dispose of.
In order to be transported to a landfill, the material would be loaded into tipper trucks (capacity 15 tonnes) or articulated lorries (capacity 30 tonnes). Assuming 100% loading, this would generate the following number of return HGV trips: x 30 tonne capacity 11,750 trips x 15 tonne capacity 23,500 trips
There are no currently operating landfills that would be potentially able to accept all of this material and the nearest landfill that could accommodate any of the material is approximately
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52km from Sligo. The four next nearest landfills with the potential to accommodate the waste range from 70 to 130km one way distance from Sligo Harbour.
In addition to the transport costs, the waste material will be subject to Landfill Tax. In May 2011 the Minister for Environment announced that Landfill Tax will rise from €30 to €50 per tonne from September 2011, increasing to €65 per tonne from July 2012 and €75 per tonne from July 2013.
The material would also require a waste licence to permit disposal, which can take upwards of a year to acquire, therefore it is realistic to assume that the 2013 tax rate will apply. In this event, the tax alone to dispose of the material at landfill would be in excess of €26,000,000. The gate fees and transportation costs would likely equal the tax costs to dispose of the material at landfill, creating a total disposal cost in excess of €50million, an entirely prohibitive cost.
For these reasons, disposal of the dredged sediments in landfill is not considered to be a viable option.
Finisklin Option A variation to the landfill option which has also been examined was the feasibility of placing the material on the site of the former landfill at Finisklin, adjacent to the port. This option seems attractive as the lands are immediately adjacent to the dredging area and the dredged sediment could be pumped directly into a bunded lagoon on to the site where the supernatant water would be able to drain back into the sea.
The landfill at Finisklin was in operation from 1958 to 1994. Following its closure, it was covered and the site has largely remained disused since then. The precise boundary of the landfill and the area filled as part of previous reclamation works is not fully known, however the site is conservatively estimated as covering approximately 13 hectares (Malone O’Regan, 2011). The access road to the new Sligo waste water treatment works crosses the former landfill (Figure 1.4).
Following the closure of the landfill, the site was capped using imported fill, which varies in thickness from a few centimetres to 2 metres. No specific capping design was undertaken for the landfill at the time. It is estimated that approximately 625,000 tonnes of municipal waste was placed in the landfill and a further 250,000 tonnes of capping material was accepted.
At the time the landfill was initiated, none of the infrastructure that would be a compulsory requirement under today’s legislation was installed, e.g. no landfill liner, leachate collection system or gas collection, flaring or venting systems. The land reclamation process was completed by depositing waste material directly on top of the existing mudflats and progressively filling the estuary parallel to the shore.
In order to create a containment area for the dredged spoil, bunds would need to be constructed around the edges of the two areas of the landfill shown in Figure 1.4. To
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Figure 1.4 Former Finisklin Landfill
Aerial photograph ESRI/Bing Maps © Microsoft Corporation 2012 Due to its central location in Sligo, the former landfill has the potential to be a valuable commercial site. However, there are potential risks from landfill gas and escape of leachate due to the lack of a formal engineering design at the time the landfill was commenced. These issues must be addressed prior to any development being allowed to take place. Sligo County Council recently commissioned consultants Malone O’Regan to undertake an Environmental Assessment of the landfill which includes a risk assessment of the landfill. The report makes a series of recommendations to reduce the risk to acceptable levels.
As part of the option evaluation, RPS met with engineers from Sligo County Council’s Environmental Services Section and discussed the feasibility for the dredged material to be placed on top of the landfill as additional capping with engineers from Malone O’Regan.
The Environmental Assessment Project (Malone O’Regan, 2011) has identified that the greatest risk posed by the landfill is migration of landfill gas, which is currently unable to escape in a controlled manner from the landfill. The report makes recommendations for the construction of venting wells and trenches.
As already discussed, the landfill does not have a liner and the waste has been placed directly on the original foreshore. A large (30m width crest) porous rock bund was constructed to function as the outermost boundary of the former landfill (into Sligo Harbour). The bund was designed to allow the free flow of the tide to and from the landfill at the time to dilute and disperse the leachate. Leachate continues to visibly drain from the landfill into
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Sligo Harbour, however monitoring results from the Environmental Assessment Project (Malone O’Regan, 2011) and Sligo County Council indicate that the leachate contents do not currently exceed published leachate discharge guidelines and that the available assimilative capacity within the receiving water is such that the leachate is not currently impacting the water quality. However, the threat of contamination remains a high risk.
The placement of c.250,000m³ of dredged material from Sligo Harbour onto the former landfill site at Finisklin is therefore considered to be unfeasible for the following reasons: x The lack of an engineered cap means that the landfill gas is currently venting through the capping layer in a diffuse manner, thus reducing its potential to migrate to the surrounding commercial and residential premises. Placement of c. 250,000m³ of material on top of the former landfill will pose a barrier to the gas, thus preventing it from venting and greatly increasing the risk of dangerous levels of gas migrating laterally to the areas surrounding the landfill. This would pose an unacceptable safety risk and it is unlikely the risk would be able to be mitigated without significant additional gas venting works. x Placing the dredged sediment, which will be wet material, on top of the landfill will both compress the material within the landfill and increase the amount of water passing through the landfill contents. This poses a risk of leaching contaminants from previously undisturbed portions of the landfill which could drain onto the foreshore or into the underlying water table and cause an adverse impact on the neighbouring SAC and SPA designated foreshore. x There is no current requirement for any additional capping material on the former landfill, and if there were, the dredged material does not possess the necessary physical properties of normal landfill capping material. Therefore, if the dredged material were to be placed on the site, it would have to be placed there as a “waste material”. Disposing of “waste” requires a waste licence from the EPA which would necessitate a separate EIA and planning permission. In order for this scenario to be facilitated, the former landfill would effectively have to be re-licensed as a landfill. Such permission is very unlikely to be acquired due to the environmental and safety risks outlined above. In addition, as described above in the general landfill option, the disposal of waste on land will attract landfill tax which renders this option highly uneconomical. x The site of the former landfill, once it becomes available for development, will be a valuable commercial site, particularly since it has excellent infrastructural connections arising from electricity network, fresh water, drainage and high speed telecommunications upgrades constructed in support of the new waste water treatment works in the adjacent site. The dredged material would not have the structural properties to provide a stable foundation for any future development and would require piling and the significant increase in ground level would also pose a significant negative impact on the site’s potential for development.
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Whilst the use of the former Finisklin landfill site initially appeared to be an option for the disposal of the dredged sediments, this option is unable to be progressed due to the environmental and safety reasons outlined above.
1.5.3.4 Incineration There are no suitable incineration facilities in Ireland capable of accepting the proposed type or quantity of dredge spoil. The dredge spoil would therefore need to be transported to mainland Europe.
This option can therefore be ruled out due to prohibitive cost.
1.5.3.5 Reclamation within Sligo Harbour
Reclamation of the foreshore has been the traditional method for disposal of dredged spoil arising from maintenance dredging in Sligo Harbour. The area of foreshore reclaimed from this activity has been recently used to construct Sligo city’s new Waste Water Treatment Plant (WWTP) and consequently there is no further space available within this area to dispose of further material.
The examined option would be to reclaim a further part of Sligo Bay (3.17 hectares), within an area known as Cummeen Strand. A suitably sized semi-enclosed location lies immediately west of the previously reclaimed site of the new WWTP (Figure 1.5).
Figure 1.5 Suggested Reclamation Area
Aerial photograph ESRI/Bing Maps © Microsoft Corporation 2012
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Cummeen Strand holds a number of nature conservation designations including SAC, SPA, Ramsar and pNHA. It is therefore an important site of high conservation value and includes a number of habitats and species listed on Annex I and II of the EU Habitats Directive.
The option of reclamation does not present an adequate long term solution for the disposal of dredged sediments from Sligo Harbour. Although the amount of sediment to be removed would keep the channel operational for several years, maintenance dredging would still be required and the reclamation area would be entirely filled by the 250,000m³, thus requiring a new means of disposal to be identified for any future works.
Under the Habitats Directive, a plan or project may not proceed unless it is demonstrated to have no significant impact on the integrity of a Natura 2000 site. Reclaiming 3.17ha of intertidal sandflats and mudflats from the SAC/SPA area would pose a significant and permanent negative impact to the footprint, altering it from its status as an Annex I habitat. Under these circumstances, the project would not be given consent to proceed unless no alternative was found to be available and imperative reasons of overriding public interest could be demonstrated. In addition, an equivalent area of compensatory habitat would also have to be designated in its place. Since virtually all of Sligo Harbour and the surrounding coastline has already been designated as a SAC or SPA, the opportunities are very limited in providing compensatory habitat for a direct loss of habitat at the proposed reclamation site in Cummeen.
As there are alternatives which exist which do not require the loss of SAC and SPA habitat, this option must therefore be ruled out on conservation grounds.
1.5.3.6 Water Injection/Plough Dredging
Water injection is relatively new method of dredging which operates by injecting water into certain fine-grained sea bed materials, reducing their density to the point where they act as a fluid and flow over the bed through the action of gravity to lower levels. Although the sediments are not raised from the surface of the water, this technique still requires a dumping at sea licence under the Dumping at Sea Act:
“dumping” means— (a) any deliberate disposal in the maritime area (including side-cast dredging, plough dredging, water injection dredging and other such dredging techniques) of a substance or material from or in conjunction with a vessel or aircraft or offshore installation.
This type of dredging can create significant amounts of turbidity at the bottom of the water column which would have the potential to cause adverse impacts including smothering of the intertidal and benthic species within the SAC and consequently the SPA species which would feed on these.
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Water injection dredging is mainly used to remove small amounts of sediment quantities (less than 5,000m³) although in certain areas it has been used for quantities up to 25,000m³ (Sullivan, 2000). Typically it tends to be used most often to move sediments in difficult to access areas (such as beneath marina finger berths) into the path of a conventional dredger. The major limitation of water injection dredging techniques is a loss in effectiveness with increasing quantities of material removed. It would be unfeasible to attempt to relocate 250,000m³ of sediments from the navigation channel at Sligo Harbour using this method as the amount of turbidity generated would be unacceptable. Furthermore, as the harbour is an enclosed area, the displaced sediments would merely resettle elsewhere in the harbour and would most likely be returned to the navigation channel within a short time scale.
Plough dredging is a more basic method of this type of dredging, where sediments are physically pushed aside from the area to be dredged. This type of dredging is suitable for clearing small areas, however as the sediment is not actually removed from the system it is often a very temporary measure, particularly where the grain size is fine, as the sediment can rapidly migrate back to the dredge pocket. Plough dredging would not be a suitable means of removing the 250,000m³ of sediment in Sligo Harbour, particularly as the training walls would provide a physical barrier constraining the area in which the sediment could be redistributed.
1.5.3.7 Dumping at Sea
The dumping at sea option would require transporting the dredged material directly from the dredging area to an agreed offshore location where it would be discharged from the vessel (e.g. by bottom-opening hopper) for disposal.
The OSPAR Convention 1992 (The Convention for the Protection of the Marine Environment of the North-East Atlantic) regulates international cooperation on environmental protection in the North-East Atlantic. It updates the 1972 Oslo Convention on dumping waste at sea and the 1974 Paris Convention on land-based sources of marine pollution.
In Ireland, dumping at sea is only permitted at an authorised dump site and a dumping at sea licence must be sought by the applicant. There are currently no operational dump sites within Donegal Bay (a dumpsite was formerly licensed for the disposal of dredged material from the upgrading of Killybegs Fishery Harbour in 2003; however this dump site was subsequently closed upon completion of the scheme).
Therefore, as part of this scheme, a suitable location for a new dump site must be identified. The process of identifying a new dump site has been described in more detail in Section 2.2 of Chapter 2, “Consultations”.
The Foreshore and Dumping at Sea (Amendment) Act 2009 amends the Dumping at Sea Acts 1996 to 2006. This has transferred responsibility for functions relating to dumping at sea from the Minister for Agriculture, Fisheries and Food to the Environmental Protection Agency (EPA).
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In accordance with Section 5 (2) of the Dumping at Sea Acts 1996-2009 (as amended) the dumping of substances or material at sea is only acceptable when the Agency is satisfied that there is no suitable alternative means of disposal of the material concerned. The applicant must also demonstrate that all necessary steps have been taken to minimise the quantity of material to be dumped or render the material less harmful for dumping at sea.
The feasibility of the other various means of disposal or reuse of the dredged sediments has been examined in detail in the sections above. Owing to the environmental constraints within Sligo Harbour and the physical composition of the sediments, dumping at sea is considered to be the only viable disposal mechanism available for the disposal of the dredged material.
Sediment quality analysis has been undertaken on the sediments to be dredged, under the supervision of the Marine Institute. The results of the analysis are described in more detail in Chapter 10 “Geology and Soils”. The results demonstrate that the sediments are clean in terms of the guidance valies set by the Marine Institute (Cronin et al, 2006), and do not pose any known environmental threat, should they be disposed of at sea.
The predicted impacts of the dumping the dredged sediments at sea in terms of marine ecology, fisheries and archaeology are described in more detail in Chapter 6, Chapter 7 and Chapter 12 respectively. These impacts are considered to be insignificant and the disposal of the dredged material at an offshore dump site, subject to licensing, is considered to be the most appropriate means of disposing of the dredged material from the capital and maintenance dredging of Sligo Harbour.
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1.6 THE CONSENTING PROCESS
The proposed dredging is beneath the thresholds for EIS as set out in Schedule 5 of the Planning and Development Regulations 2001-2011. However, where a sub-threshold development is proposed within a conservation area such as a European site (e.g Special Protection Area or Special Area of Conservation), a local authority may request the Board to determine the question of whether a development would be likely to have significant effects on the environment, in which case an EIS must be prepared.
A request for a direction from An Bord Pleanàla as to whether an environmental impact statement is required for the proposed dredging scheme was issued by RPS on behalf of Sligo County Council on 2nd August 2011. On 30 May 2012 the Board issued their decision that an EIS would not be required.
As the project has been evaluated as not requiring an EIS, it does not fall under the remit of any of the Planning categories in Part XV of the Planning and Development Act (2000) (as amended).
Instead, however, the scheme will require consent through the Foreshore Licensing process.
In addition, as there are no currently licensed dump sites in operation in Donegal Bay, permission must be sought for the creation and use of a new dumping at sea disposal area.
1.6.1 Required Permissions
1.6.1.1 Foreshore Licensing
The key legislation relating to offshore marine developments are the Foreshore Acts 1933 – 2009. This relates to a collective series of Acts, comprising the following: x The Foreshore Act 1933 x The Foreshore (Environmental Impact Assessment) Regulations, 1990 x The Foreshore (Amendment Act) 1992 x Section 5 of the Fisheries and Foreshore (Amendment) Act 1998 x Fisheries (Amendment) Act 2003 (Part 5) x Maritime Safety Act 2005 No. 11 (Part 6) x Foreshore and Dumping at Sea (Amendment) Act 2009
Before the commencement of any works or activity on State-owned foreshore, a lease or license must be obtained from the relevant Minister. This relates to the carrying out of works or placing of structures or materials on, or for the occupation of or removal of material from State-owned foreshore which represents the greater part of the foreshore. Developments on privately owned foreshore also require the prior permission of the Minister under the Foreshore Acts. All the foreshore of Ireland is presumed state-owned unless valid alternative title is provided.
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The foreshore is the seabed and shore below the line of high water of ordinary or medium tides and extends outwards to the limit of 12 nautical miles (or 22.224 km).
Applications for foreshore licences or leases are separate from terrestrial planning applications; are granted subject to the payment of fees; and the relevant Minister has absolute discretion to accept or reject a proposal to use state-owned foreshore.
x A Foreshore Lease is generally required for the long term construction and operation of an intended project that requires exclusive occupation of the foreshore (e.g., piers, marinas, bridges, roads, and offshore wind farms). Such structures would generally preclude the use of that part of the foreshore for other purposes;
x A Foreshore License is generally required to investigate the suitability of a site for an intended project or for other works (e.g., laying of submarine pipelines and cables) and purposes (e.g., aquaculture) i.e., for development that does not require exclusive occupation of the foreshore. Such activities/development would not generally preclude the use of that part of the foreshore for other purposes.
A foreshore licence application will therefore be made to the Department of Environment, Community and Local Government (formerly known as the Department of Environment, Heritage and Local Government prior to May 2011)
1.6.1.2 Dumping at Sea Licensing
Prior to 15th February 2010, dumping at sea was regulated under the Dumping at Sea Acts, 1996 and 2006. The Coastal Zone Management Division (CZMD) of the Department of Agriculture, Fisheries and Food was charged with implementing the provisions of these Acts i.e., permitting of dumping at sea operations. The Dumping at Sea (Amendment) Act, 2009, transferred the responsibilities for controlling dumping at sea from the CZMD to the Environmental Protection Agency (EPA). All permit applications are now processed by the Environmental Licensing Programme of the Agency.
The purpose of a Dumping at Sea permit is to regulate the dumping of material at sea. The Dumping at Sea Acts, 1996 to 2009, provide for the implementation of the requirements of international Conventions regulating the disposal of dredged materials at sea: the London Convention of 1972 (including the 1996 Protocol) and the OSPAR Convention for the Protection of the Marine Environment of the North-East Atlantic), adopted in 1992. The aforementioned Acts prohibit the dumping at sea of a substance or material unless permitted by the Agency.
Disposing of a substance or material at sea without a permit, or contravening the conditions of a Dumping at Sea permit, are offences under the Dumping at Sea Acts, 1996 to 2009. Offenders are liable upon conviction to a fine or imprisonment or both.
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Dumping at Sea Permits are only granted for the disposal of dredge material from ports, harbours and marinas in the absence of suitable alternative reuse and disposal methods.
A Dumping at Sea Licence application for a new dump site will therefore be made to the Environmental Protection Agency
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2.0 CONSULTATIONS
The consultation phase of the project timeline is of key importance, as it enables all concerned and interested parties to voice their opinions on the development during the initial stages of the project. This enables changes to be made during the design phase of the development, incorporating comments and ideas from the consultation process.
Consultation meetings were held with the principal consultees such as the Department of Agriculture, Fisheries and Food, the Department of Environment, Community and Local Government (formerly the Department of Environment, Heritage and Local Government) and the Environmental Protection Agency at the outset of the project. This consultation with statutory bodies continued throughout the Environmental Appraisal and particularly when potential issues were arising during the impact assessment phase. In addition, meetings were also held with key non-statutory consultees including the Killybegs Fishermen’s Organisation and the Sea Fisheries Protection Authority.
In November 2009, the Department of Agriculture, Fisheries and Food, then the authority responsible for Foreshore Licensing, advised that a full Environmental Impact Assessment was required for the proposed dredging and an Environmental Impact Statement (EIS) would be necessary, therefore consultations and impact studies were undertaken on this basis. This direction to prepare an EIS was subsequently over-ruled by An Board Pleanàla, who overtook responsibility for Local Authority development on the Foreshore in 2010 and who issued a determination that the project would not require an EIS to be prepared in May 2012.
Letters were sent out to all relevant stakeholders and consultees, informing them of the extent of the dredging, the proposed dumpsite location and inviting their comments on the scheme. The consultees who were contacted about the proposed development are listed below in Table 2.1. A summary of the written responses received from those consultees is provided in Appendix 2A. Copies of the written responses are included in Appendix 2C.
Table 2.1 Organisations/Agencies consulted as part of the Appraisal Process
Office of Climate, Licensing and Resource Use Fáilte Ireland North West Development Applications Unit Federation of Irish Fishermen Department of Communications, Energy and Natural Foreshore Unit, Department of the Environment, Resources Heritage and Local Government Department of Transport Geological Survey of Ireland Sligo County Council Health and Safety Authority An Taisce The National Trust for Ireland Heritage Ireland Aquaculture and Foreshore Management Division, Iarnrod Eireann Department of Agriculture, Fisheries and Food Birdwatch Ireland Irish Coast Guard Blue Flag Beaches Irish Federation of Sea Anglers (Connaught) Bord Gais Eireann Irish Whale and Dolphin Group Bord Iascaigh Mhara Marine Institute Central Fisheries Board Maritime Safety and Environment, Department of
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Transport National Monuments Section, Department of the Coastwatch Environment, Heritage and Local Government Coillte National Parks and Wildlife Service Commissioners of Irish Lights National Roads Authority Department of Education and Science North Western Regional Fisheries Board Department of Enterprise, Trade and Innovation Northern Regional Fisheries Board Department of Finance Office of Environmental Assessment Department of Health and Children Office of Public Works Donegal Bay Sea Angling Club RNLI Eircom Sligo Harbour Commissioners Tourism Development Policy Division, Department of Electricity Supply Board Tourism, Culture and Sport Engineering Division, Department of Agriculture, Underwater Archaeology Unit, Department of the Fisheries and Food Environment, Heritage and Local Government Inland Fisheries Ireland
2.1 DUMPING AT SEA CONSULTATIONS
A feasibility study undertaken for the dredging scheme by RPS in 2010 (see also “Consideration of Alternatives” (Chapter 1.5) of this Environmental Appraisal) concluded that the only viable means of disposing of the waste material arising from the dredging project was by dumping at sea at an offshore dump site.
An offshore dumpsite previously existed within Donegal Bay which was used for the disposal of sediments arising from the upgrading of Killybegs Harbour in 2002. However, this dumpsite is closed to new applications and it was necessary to choose a location for a new dump site.
Consultation on a suitable dump site location was subsequently held with the Environmental Protection Agency, the Sea Fisheries Protection Authority, the regional Fisheries Board, Bord Iascaigh Mhara, the Department of Agriculture, Fisheries and Food and the Marine Institute. Opinions were also sought from the Killybegs Fishermen’s Organisation (KFO) and the Irish Fish Producer’s Organisation (IFPO).
Three potential dump site locations within Donegal Bay were presented to these consultees (Figure 2.1).
The initial site proposed during initial scoping was located approximately 15 nautical miles from the port, due west of Ballyconnell Point in approximately 50 metres water depth. This site was advised as being unsuitable by BIM and the Sea Fisheries Protection Agency as there are known spawning areas nearby and the site is also within the migration route for salmon species.
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At a meeting with the Department of Agriculture, Fisheries and Food and representatives of the KFO in February 2010, the KFO strongly objected to any dumping at sea activities taking place within the confines of Donegal Bay and stated that any potential dump site should be located west of a theoretical line marking the entrance to Donegal Bay, stretching between Malin More Head and the Broadhaven Stags (Figure 2.1).
Figure 2.1 Dumpsite Consulted Sites Extract from Admiralty Chart 2725 © Crown copyright UKHO. Not for Navigation Use The second site proposed was located approximately 25 nautical miles from the port, due north of Rathlee Head in approximately 60 metres water depth. This site was also considered to be unsuitable by BIM and the KFO as it is within a highly productive fishing area and the local tidal currents would potentially sweep the sediment east in to Donegal Bay. The KFO expressed their support for the dredging project, however they reiterated their objections to any dumping taking place inside the Malin More Head – Stags line and added that the site should also be in excess of 100 metres water depth.
RPS subsequently undertook some preliminary tidal current modelling to locate a potential dump site where residual tidal currents would not sweep any of the dumped sediments east. The site finally chosen as the proposed dump site is west of the Malin More Head – Stags line and is in water depths of 92-93 metres. Examination of the tidal current modelling of the site shows that the residual tidal currents travel in a northerly direction and so would not transport the dumped sediment back into Donegal Bay. The site is approximately 34 nautical miles from the berths at Sligo Harbour. Published Admiralty charts have poor coverage of this area of seabed, showing the area as “unsurveyed” and there is an inferred 100m contour
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5nm west of the proposed dump site. Accurate bathymetry information was therefore instead obtained from the GSI/Marine Institute InfoMar project. At the proposed dump site location, the seabed is relatively flat and the true 100m depth contour is some 30km west of the 90m contour. This is beyond the viable range of a small dredger.
It should also be noted that the area around the 100 metre contour is shown in the Atlas of Commercial Fisheries Around Ireland (Marine Institute, 2009) as being a much more heavily fished area in terms of hours effort per square nautical mile, based on data recorded in the VMS (Vessel Monitoring System) database.
Details of this revised dump site were issued to Bord Iascaigh Mhara (BIM), the Marine Institute, the Killybegs Fishermen’s Organisation, the Irish Fish Producer’s Organisation, the Geological Survey of Ireland, the North West Regional Fisheries Board and the Sea Fisheries Protection Agency in June 2010 as well as being included within the EIA consultation package sent to the consultees outlined in Table 2.1.
BIM responded that the site appeared to avoid the main fishing areas. The Marine Institute responded that they could see no issues with this site, especially given that the material is clean. No immediate response was received from the Regional Fisheries Board or the Sea Fisheries Protection Agency.
GSI reviewed information provided by the Infomar project and from the confirmed that the proposed dumping site is located west of an important moraine, approximately running NE- SW, which, along with the identified tidal currents, would act as a natural barrier to the re- deposition of any dredged material towards Donegal Bay and Sligo Bay. GSI also confirmed that no particularly important forms of life (e.g. cold water corals and others) were identified in that area on the seabed during the Infomar survey. Backscatter information from the survey indicated that the substrate is likely to be coarse sand and gravel, although the bed is a mosaic of substrate types in this area. The nearest areas of uniformly sandy substrate west of the moraine are 10-12 kilometres further from the port and beyond the range of the dredger. East of the moraine ridge is a large sandy area which would have potentially been suitable, but this area is a heavily fished and would not be acceptable to fishermen as the sediments would be confined inside Donegal Bay.
The KFO and IFPO stated their continued concerns regarding the choice of dumping at sea as being the preferred disposal method. Although the site is west of the theoretical Malin More Head – Stags line both groups expressed fears that the plume of dumped material will spread widely into Donegal Bay and may affect juvenile and spawning grounds. Both groups are opposed to any dumping at sea proposal and feel that alternative disposal methods on land should have been examined in more detail. IFPO also indicated that there are pot fishermen fishing within the proposed site and that the presence of any heavy metals in the dredged spoil could contaminate the crabs or lobsters and subsequently result in the catch being excluded from the market.
RPS have taken the responses from the various consultees on board during the site selection process. A further assessment of alternative disposal sites on land or involving
IBE0440/EAR/September ‘12 2-4 Sligo Harbour Dredging Environmental Appraisal Report Consultations reclamation of the foreshore was undertaken (See Section 1.5 of Chapter !, Introduction) to ensure that dumping at sea was being undertaken as a last resort. However, no more suitable locations were able to be identified for the disposal of the material.
It will be clearly demonstrated within this Environmental Appraisal that the dredged spoil is free of harmful contaminants (Chapter 14 Sediment and Water Quality) and that there will be no significant impacts to marine flora and fauna arising from disposing of this material offshore (Chapter 6 Marine Intertidal and Subtidal Flora and Fauna). Detailed modelling of the dispersal plume is shown in Chapter 11, Coastal Processes.
2.2 PUBLIC CONSULTATION
Public consultation is an important part of the EIA process, as it allows stakeholders outside the statutory and non-statutory consultee bodies to have an opportunity to become involved in the EIA and offer their views on the proposed scheme.
A public consultation event was held on 9th February 2011. The event involved open afternoon/evening sessions in the Sligo County Council offices at Market Yard in Sligo.
The proposal was exhibited in a display, showing the dredging and proposed dumpsite locations as well as summarising the key issues being examined in the Environmental Appraisal (Appendix 2B). Present to answer questions were Gary Salter of Sligo County Council, Dr Alan Barr and Sophie Gilloway of RPS and Dr Paul Johnson, independent fisheries consultant.
The public consultation sessions were advertised in the local newspaper and a notice was placed on the Sligo County Council website. Additionally, local stakeholders who had been identified as potentially having an interest in the scheme, such as shellfish cultivators, local conservation groups, boat charter operators and fishermen, were also issued direct invitations.
The afternoon session was held between 2pm and 4pm. This was well attended by in excess of 25 visitors, including the main local shellfish cultivators, Inland Fisheries Ireland, Co. Sligo based pot fishermen, Bord Iascaigh Mhara, local boat charter companies and other harbour users.
Key issues raised during this session were: x Impact of suspension of sediments during dredging activities on salmonid species travelling through Sligo Harbour to Lough Gill. Visitors seemed to be reasonably satisfied that the methodology and mitigation measures would reduce this impact to insignificant levels. x Impact of suspension of sediments during dredging activities on shellfish cultivation areas. Cultivators seemed to be reasonably satisfied that the methodology and mitigation measures would reduce this impact to insignificant levels.
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x Impact of disposing of dredged sediments at offshore dumpsite on crab, lobster and demersal fisheries. Fishermen are concerned that if crustaceans ingest or inhale suspended sediments the value of their catch will be reduced as contamination with sand or grit will lower the prices paid per crab. Crabs prefer the sandy substrate, lobsters prefer rocky substrate and all these habitats are present at the dumpsite. The fishermen were not satisfied that mitigation measures would prevent impacts.
It was recognised by the fishermen that the dumpsite had been moved outside the main pelagic fishing and spawning areas in Donegal Bay, which has helped to reduce some concerns about the impact of dumping at sea. However, some concern was raised that although outside Donegal Bay, the proposed dumpsite area is regarded as a popular and productive area for crab and lobster potting, as well as other species such as dogfish. Further consultation was recommended with the fishermen who fish this area.
The evening session was held between 5:30pm and 7:30pm. This session was again well attended with a large group of pot fishermen from Sligo, Mayo and Donegal present. Also present was a local councillor.
The pot fishermen held very strong concerns about the dumping of the dredged spoil offshore. Their key concerns were: x The dredged material may potentially contain substances harmful to crustaceans, as until 2009 the city’s sewage was discharged without any treatment into the river channel. Although the sediments have been tested under the supervision of the Marine Institute and found to be clean, the fishermen continue to have concerns. x A large area in the outer reaches of Donegal Bay west of 9°W was highlighted by the fishermen as being a very productive area for both crab and lobster fishing and probably spawning (Figure 2.2). The fishermen estimate that over 40,000 pots are laid around this area. The fishermen are concerned that the tidal and wave driven currents in the area will disperse the dumped sediments over a very wide area, thus causing a widespread impact footprint. Fishermen estimate current speeds of 2.5 knots (1.3 m/s) at the dump site during spring tides. x The fishermen also hold concerns that if this area becomes a licensed dumpsite, other ports will make applications to dispose of spoil here and the issues arising from dumping at sea will continue on a longer term basis. x The fishermen concluded that they would oppose any dumping at sea application and that the council should re-examine all alternative methods of disposing of the sediments on land. The fishermen are not satisfied that environmental designations within the harbour should mean that this area is protected from having the material disposed of there, when in their opinion the dump site area is just as important to them.
At the time of the public consultation, no information on the fate of the dredged material following its disposed was available as model studies had not been completed. It was
IBE0440/EAR/September ‘12 2-6 Sligo Harbour Dredging Environmental Appraisal Report Consultations agreed that once the dump site plume modelling and benthic impact hypothesis had been completed (in the absence of an alternative land-based dump site being located), RPS would re-engage with the fishermen to discuss the potential impacts to the pot fisheries.
Figure 2.2 Pot Fishing area as indicated in Public Consultations Extract from Admiralty Chart 2725 © Crown copyright UKHO. Not for Navigation Use
2.3 ADDITIONAL OFFSHORE FISHERIES CONSULTATION
Following the public information day in February 2011, further consultation was held with representatives of the crab fishing industry. These included the local BIM Fisheries Officer, Declan Nee and a local crab fisherman who attended a meeting with the project fisheries representative on 17th February 2011. Further consultation was undertaken by telephone with the following: x Oliver Tully – Marine Institute x Owen Doyle - local BIM Fisheries Officer – Donegal/Sligo x Grainne O’Brien – BIM Environmental Officer x John Dennis – BIM x Ben Dallaghan – BIM x Aisling Donegan – IFI Ballina – Environmental Officer x Lesley McCaffrey – SFPA Killybegs x Anthony Keohane – SFPA Clonakilty x Daryl Ewing – charter boat operator x Kevin Barber – Sea Angling
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Ongoing consultation and liaison with the commercial pot fishermen within the region is expected to continue throughout the duration of the proposed project.
2.4 LOCAL AQUACULTURE The main local aquaculture producers met with the project’s fisheries representative on 17th February 2011 to discuss the potential issues relating to their commercial interests. These were: x Noel Carter – Coney Island Shellfish Ltd x Charles Kelly – Atlantic clams Ireland Ltd x Paul Leydon – Armada Shellfish Co
2.5 RESPONSE TO ISSUES RAISED DURING CONSULTATION
Following the comments made during the public consultations, RPS undertook a thorough re- examination of the alternative disposal methods, including more detailed research into the options at Finisklin landfill and the reclamation of an area of foreshore. These are described in Chapter 1.3 “Consideration of Alternatives”.
RPS also re-engaged with the Marine Institute to verify the potential for the sediment to contain elements harmful to crustaceans. The Marine Institute have confirmed that the chemical testing of the sediments indicates that all concentrations of potential contaminants are below the lower guidance level threshold. This threshold is set at a level below which no ecological risk is associated. Full recognition has been taken of the history of the sediments during the testing regime, i.e. that prior to 2009 untreated sewage was being discharged into the main channel and that the site is working port.
Current metering and drogue tracking has taken place at the dump site during both spring and neap tides. Video footage and grab samples have also been taken. This information has been be used to model the dispersion footprint of the dumped sediments and quantify how widespread the impacted area is likely to be and whether the impacts are likely to be significant, discussed in detail in Chapter 6 “Intertidal and Subtidal Flora and Fauna”.
2.6 CONCLUSIONS
The issues raised during both the public consultation and the stakeholder consultation period have been addressed and, where possible, mitigated for to reduce the environmental impact of the development. It will be seen that the impact to the environment from the dredging , in particular to the designated SAC and SPA areas at Cummeen Strand in addition to the EU. Shellfish Water have been addressed in full in the Environmental Appraisal Report (Chapters 5, 6, 7 and 11) and Natura Impact Statement (Volume 3).
The decision to dispose of the dredged material at an offshore dump site has been taken after careful and detailed consideration of all other potential options. Detailed studies have taken place to quantify the risk of adverse ecological impacts occurring at the dump site and
IBE0440/EAR/September ‘12 2-8 Sligo Harbour Dredging Environmental Appraisal Report Consultations these studies have concluded that the disposal of c. 250,000m³ of dredged sediments will pose no significant impacts to marine benthic and fish species, including crustaceans.
The various submissions and comments made in relation to the proposed dredging Sligo Harbour have been fully considered by the consultants in the preparation of the Environmental Appraisal and in the design of the scheme. Every effort has been made to address all concerns raised and, where possible, mitigation measures have been proposed to minimise the environmental impact of the proposed development.
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3.0 SITE DESCRIPTION
3.1 INTRODUCTION
Sligo Harbour is a large, shallow bay stretching from Sligo city westwards to Coney Island, in County Sligo on the west coast of Ireland. It is one of three enclosed estuaries which make up Sligo Bay, with Drumcliff Bay to its north and Ballysadare Bay to its south. The Garavogue River (sometimes written as Garvoge, Garavoge or Garvogue) flows into the harbour, forming a permanent channel. Sligo Bay is part of Donegal Bay which opens into the Atlantic Ocean.
Sligo Harbour and Sligo city are surrounded by a mountainous skyline, with the ridges of Slieve Daeane and Killery Mountain to the south-east, Cope’s and Keelogyboy Mountains to the northeast, the highly-distinctive Knocknaree to the west and Benbulbin to the north.
© Ordnance Survey Ireland. All rights reserved. Licence number 2010/20 CCMA/ Sligo County Council
Figure 3.1 Site Location (Regional Context)
The northern boundary of Sligo Harbour is the peninsula of Rosses Point. Rosses Point, approximately 6km in length, divides Sligo Bay from Drumcliff Bay. Rosses Point hosts the popular County Sligo Golf Course and has two west-facing fine sandy beaches, stretching for more than 1.5km. These beaches, popular because of their safety and proximity to the city of Sligo, hold a Blue Flag award. The largest settlement on Rosses Point peninsula, Rosses Point village, lies on its southern shore at the entrance to Sligo Harbour. At the last census
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(CSO, 2012a) the Rosses Point peninsula had a population of 1,517. Immediately south of Deadman’s Point and south west of Rosses Point village, the “Metal Man” navigation beacon marks the entrance to the navigation channel into Sligo harbour.
To the south of Sligo Harbour lies the Coolera peninsula (sometimes called Strandhill peninsula) which separates Sligo Harbour from Ballysadare Bay. The main settlement on the Coolera Peninsula is Strandhill (CSO 2012a population 1,210), which is the location of Sligo’s regional airport and is a popular surfing beach. On the north western corner of the Coolera peninsula is Killaspugbrone townland, which holds an ecclesiastical complex comprising a church, enclosure, graveyard and shrine, parts of which date from the 11th – 12th century.
Sligo city has developed at the mouth of the Garavogue River, which is a short river (4.3 km long) connecting Lough Gill with the sea. The Garavogue, despite its short length, is popular with canoeists and is also reputed for its excellent fishing. Lough Gill, which is nearly six and a half miles long and two and a half miles wide, is also a popular fishing and tourist area and was the subject of several poems by W.B. Yeats such as “The Lake Isle of Innisfree”.
Sligo's Irish name Sligeach - meaning shelly place - allegedly originates in the abundance of shellfish found in the river and its estuary, and from the extensive 'shell middens' or Stone Age food preparation areas in the vicinity. Although Sligo is not an especially large city in the national context, with a population of 19,452, it is the largest town in the province of Connaught (CSO, 2012b), making it important in a regional context. Due to its status as a regional growth centre and gateway to the North-West, its daily population expands to over 42,000 (Sligo Chamber of Commerce, 2011).
Sligo is an historic, cultural, commercial, industrial, retail and service centre of regional importance. Served by a regional airport and established rail, port and road links, Sligo city exerts significant influence on its immediate hinterland. This hinterland, comprising the county of Sligo and beyond is essentially rural in character. The county is characterised by relatively small towns and villages providing local commercial, retail and support services with sparsely populated environs depending largely on agriculture and tourism related business.
At the entrance to Sligo Harbour lies Coney Island. The island is accessed by a causeway across the beach by car or foot when the tides are low. The island has few permanent residents but is a popular tourist destination, especially in the summer months. The island’s name derives from the large rabbit population it formerly hosted.
Extending west from Coney Island is a training wall which connects the island with Black Rock and the Blackrock lighthouse. This training wall is named the Cluckhorn and was constructed from rock armour between 1908 and 1912. The aim of the training wall was to remedy the navigational difficulties in accessing Sligo Harbour, by enhancing the tidal flows through the entrance channel and thus keeping the entrance clear of sediments.
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Whilst this training wall has been largely effective in maintaining navigable depths into Sligo Harbour, passage through the Bungar Bank, which is highly mobile, can be difficult and pilotage into Sligo Harbour is compulsory for commercial vessels.
3.2 SITE CONTEXT AND EXISTING LAND USE
3.2.1 Sligo Harbour Development
Under the 1996 Harbour Act, the government proposed the transfer of control of a number of regional ports and harbours to local authorities, Sligo Port was one such harbour where a transfer to Sligo County Council has taken place by Ministerial Order. A grant of €1.85m was obtained from the Department of Transport - Marine Section to carry out essential works.
Approximately 90 acres of land under the control of the Harbour Commissioners, most of which had been reclaimed from the sea since the 19th century, including the site of the former landfill, were transferred to Sligo County Council (SBC/SCC, 2011).
Finisklin Landfil Timber Jetty Sligo WWTP Barytes Jetty Deepwater Jetty
Cartron Marsh
Plate 3.1 Sligo Docklands Photo: Sligo County Council Plate 3.1 shows the majority of the docklands area. The roughly square bunded area formerly used for the disposal of dredged sediment and which now hosts the city’s new main drainage waste water treatment works is visible on the lower right of the image. Adjacent to this can be seen the Barytes and Deepwater jetties which were refurbished with part of the
IBE00440/EAR/September ‘12 3-3 Sligo Harbour Dredging Environmental Appraisal Report Site Description grant awarded by the Department of Transport. Also included within this programme of works was the refurbishment of the training wall.
South west of the waste water treatment works is the site of a former landfill at Finisklin. The formerly filled area comprises approximately 13ha (Malone O’Regan, 2011). The landfill was closed in 1994, however it continues to produce methane gas as a byproduct of the breakdown of organic products contained within it.
Further south east along the navigation channel, within the inner part of Sligo Docklands is the new access and safety facilities at Lynn’s Place - the Timber Jetty. This new facility, opened in 2008, allows leisure vessels to tie alongside the pontoons at any tide level and visitors to access the quay top via the articulating ramp.
Plate 3.2 and 3.3. Timber Jetty
North east of the Deepwater and Barytes Jetties is a lagoon area, enclosed between Cartron Point and Standalone Point, known as Cartron Marsh. This site forms a highly important area for birdlife in Sligo Harbour and is included within the SPA and SAC designations.
3.3 NATURE CONSERVATION DESIGNATIONS
Sligo Harbour supports a diversity of natural and semi-natural habitats and a wide range of flora and fauna. There are four environmentally designated sites within the dredging area: x Cummeen Strand/Drumcliff Bay Special Area of Conservation (SAC) (Figure 3.2) x Cummeen Strand Special Protection Area (SPA) (Figure 3.3) x Cummeen Strand/Drumcliff Bay proposed Natural Heritage Area (pNHA) (Figure 3.4) x Cummeen Strand Ramsar wetland (Figure 3.4)
A brief summary of the designations surrounding the proposed dredging area is given below. More detailed examination on how the proposed dredging will affect these designated areas will be given in Chapter 5 “Birds” and Chapter 6 “Intertidal and Subtidal Flora and Fauna”
3.3.1 Natura 2000 Sites holding the SAC (Special Area of Conservation) and SPA (Special Protection Area) designations are known as Natura 2000 sites. The Birds and Habitats Directives set out
IBE00440/EAR/September ‘12 3-4 Sligo Harbour Dredging Environmental Appraisal Report Site Description various procedures and obligations in relation to nature conservation management in Member States in general, and of the Natura 2000 sites and their habitats and species in particular. A key protection mechanism is the requirement to consider the possible nature conservation implications of any plan or project on the Natura 2000 site network, before any decision is made to allow that plan or project to proceed. Not only is every new plan or project captured by this requirement but each plan or project, when being considered for approval at any stage, must take into consideration the possible effects it may have in combination with other plans and projects when going through the process known as “Appropriate Assessment”.
The Habitats Directive states: “Any plan or project not directly connected with or necessary to the management of the site but likely to have a significant effect thereon, either individually or in combination with other plans or projects, shall be subject to appropriate assessment of its implications for the site in view of the site’s conservation objectives. In the light of the conclusions of the assessment of the implications for the site and subject to the provisions of paragraph 4, the competent national authorities shall agree to the plan or project only after having ascertained that it will not adversely affect the integrity of the site concerned and, if appropriate, after having obtained the opinion of the general public.”
3.3.1.1 Special Areas of Conservation Special Areas of Conservation (SAC) are among the most important areas of wildlife habitat in Ireland and throughout the European Union. The legal basis on which SACs are selected and designated is the EU Habitats Directive, transposed into Irish law in the European Union (Natural Habitats) Regulations, 1997 as amended in 1998 and 2005. SACs are selected for the conservation of Annex I habitats (including priority types, which are in danger of disappearance) and Annex II species (other than birds). Protected Irish habitats include raised bogs, blanket bogs, turloughs (seasonal lakes in limestone areas), sand dunes, machair (flat sandy plains on the north and west coasts), heaths, lakes, rivers, woodlands, estuaries and sea inlets.
The aim of the Habitats Directive is to ensure the protection of biodiversity through the conservation of natural habitats of wild flora and fauna and consequently 26 Irish species (6 mammals, 8 fish, 7 invertebrates, and 5 plants) which must be afforded protection are also named in Annex II.
Other species are listed for protection measures on Annex IV and V, and some species (such as the otter) are included on more than one annex. The annexed habitats and species for which each site is selected correspond to the qualifying interests of the sites; from these the conservation objectives of the site are derived. The Directive is binding on the Member States and its agencies and the National Parks and Wildlife Service of the Department of Arts, Heritage and the Gaeltacht is the statutory agency responsible for the selection and designation of SACs.
Dredging works may have impacts on the intertidal and subtidal habitats and species which use them for breeding, food and shelter.
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A summary of the features of the Cummeen Strand/Drumcliff Bay SAC is given below in Table 3.1
Table 3.1 Cummeen Strand/Drumcliff Bay SAC Summary Name Code Summary Description This large coastal site extends from Cullamore in the north- Cummeen Strand/Drumcliff Bay 000627 west to Killaspug in the south-west, and from Sligo town in SAC the south-east to Drumcliff village in the northeast.
It encompasses two large, shallow bays (Drumcliff Bay and Sligo Harbour), Ardboline and Horse Islands, sand dunes and sand hills at Rosses Point, Killaspug, Yellow Strand and Coney Island, grassland at Ballintemple and Ballygilgan (Lissadell) and a variety of other habitats (woodland, salt marsh, sandy beaches, boulder beaches, shingle, fen, freshwater marshes, rocky sea cliffs, lakes). The site is largely underlain by Carboniferous limestone, but acidic rocks are also found on the Rosses Point peninsula. The dominant habitats on the site are estuaries and intertidal sand and mud flats.
Qualifying Habitats x Estuaries x Mudflats and sandflats not covered by seawater at low tide x Shifting dunes along the shoreline with Ammophila arenaria (white dunes) x Fixed coastal dunes with herbaceous vegetation (grey dunes) x Embryonic shifting dunes x Petrifying springs with tufa formation (Cratoneurion) Juniperus communis formations on heaths or calcareous grasslands
Qualifying Species Phoca vitulina (harbour seal) Vertigo angustior (narrow mouthed whorl snail
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Figure 3.2 SAC Designated Areas
3.3.1.2 Special Protection Areas Special Protection Areas (SPAs) are designated because they are important habitats for birds. The legal basis for the SPA is the European Birds Directive (79/409/EEC) which was transposed into Irish Law mainly by the Wildlife Act and the Wildlife (Amendment) Act, 2000 and the European Communities (Conservation of Wild Birds) Regulations, 1985. The EU Birds Directive (79/409/EEC) requires designation of SPAs for: x Annex I listed rare and vulnerable species. x Regularly occurring migratory species, such as ducks, geese and waders. x Wetlands, especially those of international importance, which attract large numbers of x migratory birds each year. (Internationally important means that 1% of the population of a species uses the site, or more than 20,000 birds regularly use the site.)
Annex I birds are those that require special conservation measures because they are rare, in danger of extinction, or vulnerable to habitat changes in the EU. Ireland supports populations of 33 Annex I bird species. The SPA network includes important seabird colonies, wintering waterfowl sites, and sites supporting rare species (e.g. the corncrake).
A judgment delivered by the European Court of Justice in December 2007 (C-418/04) found Ireland to have been in breach of the requirements of the Birds and Habitats Directives in a number of areas. This included a finding that the designation of Ireland’s original suite of Special Protection Areas (SPAs) was inadequate and did not meet the full requirements of
IBE00440/EAR/September ‘12 3-7 Sligo Harbour Dredging Environmental Appraisal Report Site Description the Directives. The Court also found that some of Ireland’s SPAs were not sufficiently extensive to include all important habitat for the birds in question.
A summary of the features of the SPAs at Cummeen Strand and Drumcliff Bay is given below in table 3.2
Table 3.2 Sligo Harbour and Drumcliff Bay SPA Summary Name Code Summary Description Cummeen Strand is a large shallow bay stretching from Cummeen Strand SPA 004035 Sligo town westwards to Coney Island. The Garavogue River flows into the bay and forms a permanent channel. At low tide, extensive sand and mud flats are exposed. These support a diverse macro-invertebrate fauna which provide the main food supply for the wintering waterfowl. Areas of salt marsh fringe the bay in places and provide roosting sites for birds during the high tide periods. There are sand dunes at Killaspug Point and Coney Island, with a shingle spit at Standalone Point near Sligo town.
Qualifying Species Brent Goose, Oystercatcher, Redshank, Golden Plover, Bar- tailed Godwit and Whooper Swan
Both Drumcliff Bay and Cummeen Strand are important for Drumcliff Bay SPA 004013 the large numbers of waterfowl which use them in autumn/winter, including Ringed Plover, Redshank, Lapwing, Knot, Bar-tailed Godwit, Oystercatcher, Curlew, Golden Plover, Dunlin, Turnstone, Brent Goose, Grey Heron, Teal, Wigeon, Mallard, Shelduck and Redbreasted Merganser.
The fields at Lissadell and Ballintemple support one of the largest populations of Barnacle Goose in the country (c2000 in winters of 1995/96 and 1996/97). The important feeding site for Barnacle Geese at Lissadell is a Statutory Nature Reserve
Qualifying Species Barnacle Goose, Chough, Golden Plover and Bar-tailed Godwit.
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© Ordnance Survey Ireland. All rights reserved. Licence number 2010/20 CCMA/ Sligo County Council
Figure 3.3 SPA Designated Areas
3.3.2 Other Designations
3.3.2.1 Proposed Natural Heritage Area The Natural Heritage Area (NHA) designation was created for the protection of Irish natural habitats. NHAs are selected by having special scientific significance for one or more species, communities, habitats, landforms or geological features, or for a variety of natural attributes and encompass 1,246 sites in Ireland. The NHA regulation has evolved from the Area of Scientific Interest (ASI) designation and NHAs have statutory protection under the 1976 Wildlife Amendment Act. The statutory body responsible for NHAs is the National Parks and Wildlife Service of the Department of Arts, Heritage and the Gaeltacht.
There are 630 proposed Natural Heritage Areas (NHAs), comprising 65,000 ha, which were published on a non-statutory basis in 1995. These and other sites of biodiversity significance may be designated as NHAs in the coming years. Under the Wildlife Amendment Act (2000) NHAs are legally protected from damage from the date they are formally proposed for designation; however these protections are recognised as being more limited than those for SACs or SPAs. Nonetheless Planning and Licensing Authorities must recognise the ecological value of pNHAs and ensure that they are protected.
3.3.2.2 Ramsar Wetlands The Convention on Wetlands of International Importance, especially as waterfowl habitat, was adopted at Ramsar, Iran in 1971, and is commonly referred to as the Ramsar
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Convention. The Convention provides a worldwide framework for the conservation and wise use of wetlands. Wetlands are areas where water is the primary factor controlling the environment and the associated plant and animal life. They occur where the water table is at or near the surface of the land, or where the land is covered by shallow water. Wetlands are important ecosystems which improve water quality, provide storm protection, provide flood mitigation, stabilise shorelines, maintain biodiversity, and provide natural products such as fish and shellfish.
Ireland has designated 45 sites as Wetlands of International Importance pursuant to the Ramsar Convention. This includes one site within Sligo Harbour, namely Cummeen Strand.
In all cases the Ramsar Wetlands lie within areas designated as Statutory Nature Reserves or Special Protection Areas (SPAs).
© Ordnance Survey Ireland. All rights reserved. Licence number 2010/20 CCMA/ Sligo County Council Figure 3.4 pNHA and Ramsar Designated areas
3.3.2.3 EU Designated Shellfish Water
Sligo Harbour supports a regionally important aquaculture industry, with mussels, clams and oysters being commercially produced. Part of Sligo Harbour has been designated as a Shellfish Cultivation Designated Area (Figure 3.5), one of sixty four such areas around Ireland. The aim of the EC Shellfish Waters Directive is to protect or improve shellfish waters in order to support shellfish life and growth, therefore contributing to the high quality of shellfish products directly edible by man. It sets physical, chemical and microbiological water quality requirements that designated shellfish waters must either comply with (‘mandatory’ standards) or endeavour to meet (‘guideline’ standards). Any proposed dredging at Sligo
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Harbour should therefore carefully consider the impacts on local water quality in shellfish producing areas.
© Ordnance Survey Ireland. All rights reserved. Licence number 2010/20 CCMA/ Sligo County Council Figure 3.5 EU Shellfish Waters
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4.0 PROJECT DESCRIPTION
This chapter of the Environmental Appraisal Report describes the main elements and methodology of the capital and maintenance dredging scheme at Sligo Harbour. The activities associated with the works and operational characteristics following the completed dredging are also described.
4.1 EXISTING CONDITIONS
Siltation has taken place in the navigation channel since previous large scale dredging was carried out in 1998 and the soundings displayed on the Admiralty Charts no longer represent the current bed level of the channel.
Hydrographic surveys of Sligo Harbour were undertaken in 2007. In May-June 2008 a LiDAR (Light Detection And Ranging) and multi-beam hydrographic survey of Sligo Harbour, Drumcliff Bay and Ballysadare Bay was undertaken by the Geological Survey of Ireland and the Marine Institute in under the INFOMAR project (Integrated Mapping for the Sustainable Development of Ireland's Marine Resources).
The hydrographic survey carried out for the Sligo Western Bypass has also provided information on the harbour bed. The current level of hydrographic information is considered to be adequate for broad assessment of the quantity of dredging that will be required to achieve the specified depth.
In 2007 renovation of the upstream 1500m of the training wall was carried out and this work has provided improved definition of the channel. The natural process of siltation continues and the channel depth is reducing. The most recent surveys indicate that the average bed depth is now typically in the range -2.2 to -2.8m Chart Datum, although some shallower areas exist.
The channel widens locally at the Deepwater Jetty to provide a ship turning area. Water depth in this area has also reduced since previous dredging was carried out. The tide levels for Sligo Harbour (Oyster Island) are as follows:
Highest Astronomical Tide HAT 4.6m CD Mean High Water Spring Tide MHWS 4.1m CD Mean High Water Neap Tide MHWN 3.0m CD Mean Low Water Neap Tide MLWN 1.5m CD Mean Low Water Spring Tide MLWS 0.5m CD Lowest Astronomical Tide LAT -0.2m CD
Tide levels are established in relation to the Standard Port, Galway.
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4.2 WATER INJECTION MAINTENANCE DREDGING AT JETTIES TO -2.0m CD
The purpose of the maintenance dredging within the harbour is primarily to facilitate immediate safe docking and berthing of boats and ships in Sligo Harbour (see Figure 1 Attachment B.2). Currently, the build up of sediment within some areas of the harbour is resulting in Health and Safety issues associated with docking, with ships observed tilting or listing when berthed.
This maintenance dredging is required as a result of the natural siltation of the navigation channel and berths from estuarine sediments. A minimum depth of -2.0m CD at the target areas is required to reinstate safe berthing. Depths within the dredging area boundary currently range from +0.5m to -2.5m CD (see see bathymetric survey shown on Drawing 3 and Drawing 3c).
At present, the area immediately downstream of the Deepwater Jetty has only a narrow channel c. 4 metres wide in which depths achieve -2.0mCD. It is proposed to clear this small section of the approach channel back to c. 35m in breadth and also to remove small pockets of siltation immediately in front of the berths. This is the minimum amount of dredging required to maintain operations at the berths.
4.3 DESIGN OF PROPOSED CAPITAL & MAINTENANCE DREDGING WORKS TO -3.0mCD
4.3.1 Channel Depth During a feasibility study prepared by RPS in 2010, it was determined through consultation with the Harbour Master and Sligo County Council that the proposed dredging works should be designed to allow vessels with the following criteria a three hour “window of opportunity” to complete the one hour passage into the port during each tide:
Vessel Characteristic Design Criteria
Length overall 100m Beam 17m Draft 5.9m Dead Weight Tonnage 4,500 tonnes
At present, the innermost portion of the navigation channel, the area in greatest need of dredging, between Ballyweelin Point and the Deepwater Jetty, is approximately 30m wide with a depth generally of 2.2m at LAT. This section of the navigation channel is bounded on its southern side by a training wall.
The bed level chosen to accommodate a suitable size of vessel in the port is 3 metres below Chart Datum.
. .
IBE0440/EAR/September 12 4-2 Figure 4.1: Dredging Area Ex t r act fr o m A d mir a l yC ty h a r t 272 5©C r o wn wn copy ri g h tU KH O . N ot f o r N a vi gat i o n Use
IBE00440/EIS01/June 11 4-3 Figure 4.2 Dumpsite
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4.3.2 Channel Width The dredging design criteria for the channel cross section have been based on the requirements of Sligo County Council and the design guide produced by PIANC (1995).
The bottom width of the channel has been determined from the sum of the basic manoeuvring lane, plus the additional width to account for vessel speed, cross winds, cross currents, longitudinal currents, wave height, aids to navigation, bottom surface, depth of waterway plus an allowance for bank clearance. Having regard to the foregoing, a bottom channel width of 50m has been determined.
4.3.3 Channel Side Slopes Within the majority of the section of the navigation channel between Ballyweelin Point and the Barytes Jetty, the bed material is predominantly a fine silty sand. However, the silt fraction generally decreases and the gravel fraction increases with increasing distance from the port area. This bed material is typically stable at side slopes of approximately 1 in 5 in still water conditions and approximately 1 in 11 in active water conditions.
A stability analysis of the channel side slopes undertaken during the 2010 Feasibility Study indicated that a slope of 1 in 7 should be provided along this section, which maintains a compromise of pragmatic gradient whilst not over-stretching the dredging footprint
Channel Cross Section Summary
Channel Depth -3.0m CD Channel bottom width 50m Channel width at direction changes 50m Channel side slopes 1 in 7
Further details on the composition of the bed sediments are presented in Chapter 10, Geology and Soils.
4.3.4 Channel Alignment The alignment of the navigation channel is largely determined by existing physical constraints. These include the training walls extending from Ballyweelin Point to the Barytes Jetty, Oyster Island and various rock outcrops between Ballyweelin Point and Sligo Bay.
The alignment of the proposed dredged channel will therefore follow very closely the alignment of the existing channel.
4.3.5 Dredging Quantities The quantity of dredging required to achieve the stated -3.0m CD depth has been estimated to be 250,000m³. Figure 4.1 shows the layout of the area proposed for dredging in the channel, including the turning circle at Deepwater Jetty.
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The greater part of this quantity, at approx 55%, lies in the easterly 1500m of channel nearest the town quays starting from the Barytes Jetty.
The bulk of the remaining 45% lies in the westerly length of channel, approx 2200m long, from the bend at Old Mill No 14 buoy to Ballyweelin Point. This variation reflects the increasing depth and width of existing seabed in the outer reaches of the channel. Relatively small amounts of dredging will also be required to level the section from Ballyweelin Point to Oyster Island.
4.4 PROPOSED DISPOSAL METHOD
Detailed studies were undertaken to review the alternative means of disposal of the dredged material (see Section 1.5 of Chapter 1, “Introduction”). Following these studies and extensive consultation, it was concluded that the only viable solution available for the disposal of this quantity of material is dumping at sea.
The licensed dump site used to dispose of dredged spoil during the upgrading of Killybegs in 2003 has been closed and no other currently licensed dump site is in operation in or near Donegal Bay. Therefore an application will be made to the EPA to licence a new offshore dumpsite for this scheme. The proposed dump site is located some 34 nautical miles (63 kilometres) from the deepwater jetty, approximately 17 nautical miles southwest of Malin More Head (Figure 4.2). Water depths at the site are between 92 and 93 metres Chart Datum.
4.5 DREDGING METHODOLOGY
In European terms, the proposed dredging volumes are not considered to be particularly great and as such the scheme is likely to be undertaken by a small scale local dredging company. The specific type of dredger which will undertake the work will therefore not be known until a contractor has been appointed. There are two types of dredger which could undertake this work; a suction dredger or a backhoe dredger.
4.5.1 Equipment
4.5.1.1 Suction Dredger
Suction dredgers essentially are suction pumps operating on the seabed which draw in seabed material along with water and pump the resultant mixture into hoppers on the dredging vessel or a transport barge (Figure 4.3). This form of dredging therefore draws up substantial quantities of excess water as well as the sediments. This excess water is either allowed to overflow the vessel and return to the main body of water, causing a temporary increase in suspended sediments, or it can be taken out to the disposal site together with the dredged material. However, it is costly to take an excessive quantity of water to sea.
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4.5.1.2 Backhoe Dredger
A backhoe or mechanical dredger involves the use of hydraulic grab or bucket to loosen the in situ material, then raise and transport it to the surface (Figure 4.4). Dredging with hydraulic excavators is a slower process, but reduces the amount of excess water which is extracted. A backhoe dredger will sometimes transfer the dredged sediments into a transporting barge, rather than carrying the sediment itself.
Figure 4.3 Example of a Trailing Suction Dredger
Figure 4.4 Example of a Backhoe Dredger
4.5.2 Dredging Programme
The water depths in the existing channel are such that it is likely that the dredger will have to dig its way upstream and that it will only be able to dredge during the upper half of the tidal cycle.
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The dredger size will be limited by the constraints within the channel and economies of scale. It is likely that a dredger with a laden capacity of up to 1,500m³ would be suitable for this scheme. Dependent on how much of the supernatant water is allowed to overspill from the dredger, between 500m³ and 1050m³ of sediments could be transported to the dumpsite per dredging cycle. It is assumed that the dredger will rotate personnel in shifts and operate on a 24hr basis, as this would be the most economic option, allowing between 1,000m³ and 2,100m³ to be dredged per day. The dredging operations could therefore take between 4 and 8 months, dependent on the dredger. Adverse weather conditions would increase the length of time taken.
For each tide (approx 12.4 hours) the dredger will only be able to dredge for around 70-80 minutes. The rest of the time it will be steaming to and from the dump site. A typical dredger would travel at an average speed of 6.5 knots laden and 8 knots unladen, therefore taking around 10 hours in normal conditions to for a return trip to the dump site, including the time taken to discharge the sediments.
4.5.3 Personnel
During the dredging it is anticipated that operations will occur on a 24hr basis. Typically, a dredging project of this scale would have a total of seven personnel in total crewing the dredger, working in shifts with four or five personnel on board at any one time and two or three on shore. Those on board would live on the ship. In line with best practice, at all times at least one of the personnel on board should be a qualified marine mammal observer (MMO).
4.5.4 Navigation
As the dredging will occur within the existing navigation channel, no amendments or additions to the existing navigation markers in Sligo Harbour are envisaged.
4.5.5 Waste All rubbish to be disposed of from the dredger vessel will be handled and disposed by a licensed waste disposal contractor. Waste awaiting disposal will not be permitted to be stored on the quayside.
Discharges from the vessel to the harbour waters will not be permitted
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5.0 BIRDS
5.1 BACKGROUND
Maintenance dredging of the berths and navigation channel in Sligo Harbour, from the Barytes Jetty to the eastern end of Oyster Island, is required in order to maintain the minimum required depth for current vessels using Sligo Harbour. Capital dredging along lengths of the channel is required in order to generate new business and thereby secure the future viability of Sligo Harbour as a destination for commercial vessels.
Natura Environmental Consultants Ltd was commissioned to undertake baseline surveys, in the winter 2009/10 and summer/autumn 2010, of non-breeding birds likely to be affected by the proposed dredging of the shipping channel along the northern edge of the estuary. The entire area of Sligo Harbour, below Mean High Water Mark (MHWM) is designated as a Special Protection Area (SPA) under the terms of the EU Birds Directive (79/409/EEC) and as a Special Area of Conservation (SAC) under the EU Habitats Directive (92/43/EEC). This chapter covers the impacts of the scheme on birds and includes an Appropriate Assessment under Article 6(3) of the Habitats Directive.
5.1.1 Description of Proposed Works
The area to be dredged represents in total a 5.3km length of the navigation channel from Oyster Island to the Barytes Jetty. The greatest proportion of dredging activity will take place in the easternmost section of the navigation channel, the 1.5km stretch between the Old Mill and the Barytes Jetty.
The bottom sediments within the navigation channel comprise of fine sand and silt and no rock breaking or blasting activities are envisaged. Sediment testing has been undertaken which has confirmed that the dredged sediment is free of contaminants and is suitable for dumping at sea, and the dredger is expected to take one load to the dump site per tide.
In the operation phase, the dredging will permit vessels with a draft of 5.2m to access the Barytes and Deepwater Jetties for a greater portion of the tidal cycle. A detailed description of the proposed works is provided in Chapter 4 of this Appraisal Report, “Project Description”.
5.1.2 Previous Information
Sligo Harbour has been covered by regular counts of wintering birds since the 1970s. Hutchinson (1979) reported that very large flocks of wigeon and brent geese appear at times in September and October on Cummeen Strand, on the south side of the Harbour. In the 1970s this was considered the best wader area in Sligo Bay with the most numerous species being oystercatcher (up to 700 in late autumn), ringed plover (up to 200), curlew (up to 300), bar-tailed godwit (up to 180), redshank (up to 160) and dunlin (up to 200) (Hutchinson 1979).
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Since the mid 1990s, the bay has been continuously monitored as part of the national IWeBS survey (Crowe 2005). Up to 2000/01 numbers of water birds overall had remained consistent since the mid 1980s (Sheppard 1993) with a marginal 6% decline. However, there had been several changes at species level. Substantial declines were reported in the numbers of wintering brent geese and ringed plover while grey heron, red-breasted merganser and bar-tailed godwit had also declined. Increases had occurred in this period in shelduck, mallard, golden plover, lapwing, curlew, redshank and turnstone (Crowe 2005). The total area of Sligo Harbour is still regularly counted for IWeBS and the peak counts for each species for the last five available winters are given in Table 5.1.
More applied studies of birds in Sligo Harbour were undertaken in connection with the proposed reconfiguration of Sligo Airport Runway (RPS Consulting Engineers). This study covered the winter of 2007/08 and counts were conducted in the area of Dorrins Strand (at the south-west of Cummeen Strand) at intervals of 2 weeks over the period 22 November 2007 to 16 March 2008. During each visit, counts were conducted at hourly intervals between first light and dusk. In addition to the above, counts of the whole of Sligo Harbour were carried out at monthly intervals from November 2007 to March 2008 inclusive. Sub- sites used during the visits were identical to those used by IWeBS (Crowe 2005).
5.2 ASSESSMENT METHODOLOGY
5.2.1 Legislation and guidance
Flora and fauna in Ireland are protected at a national level by the Wildlife Act, 1976 and Wildlife (Amendment) Act, 2000 and the Flora (Protection) Order, 1999 (SI 94/1999). They are also protected at a European level by the EU Habitats Directive (92/43/EEC) and the EU Birds Directive (79/409/EEC) which are transposed into Irish law by the European Communities (Birds and Natural Habitats) Regulations, 2011 (S.I. No 477 of 2011).
5.2.2 Consultations Consultations were undertaken with the Development Applications Unit (DAU) of the Department of the Environment, Heritage and Local Government in 2009 (now part of the Department of Arts, Heritage and the Gaeltacht). The response received from the DAU (G2009/591) noted that the proposed works were to take place within the Natura 2000 sites Cummeen Strand SPA and Cummeen Strand/Drumcliff Bay cSAC and identified the following potential impacts: x Direct loss of habitat due the excavation and removal of material from the Special Area of Conservation; x Risks from inappropriate disposal of dredge material; x Direct disturbance to wildfowl.
The response also recommended that special consideration be given to a number of issues in the Environmental Impact Assessment, summarised as follows (the full consultation response is included as Appendix 2C);
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x The intertidal and sub-tidal habitats that may be affected by the scheme. x Disturbance to wildfowl within Sligo Harbour. x The storage site for the dredged material, if it is to be re-used in future building projects. x The reclamation of land within Cummeen Strand and the disposal of dredged material. x Beach nourishment and the possibility of disposing of suitable dredge material within the Sligo Bay coastal system.
The response considered that appropriate assessment, as outlined in Article 6(3) of the EU Habitats Directive 92/43/EEC, would be required as part of this proposal. The Screening for Appropriate Assessment in relation to Cummeen Strand SPA is included as Appendix 3B to this Environmental Appraisal Report.
Consultations were also undertaken with BirdWatch Ireland in relation to Irish Wetland Bird Survey (IWeBS) bird count data for Sligo Harbour/Cummeen Strand.
5.2.3 Desktop review
A desktop review was carried out of all available bird count data for the study area in the most recent 5-year period, 2003/04 to 2007/08. These counts were provided by BirdWatch Ireland and form part of the Irish Wetland Bird Survey (IWeBS). In addition, the counts carried out on behalf of RPS Consulting Engineers for the proposed reconfiguration of Sligo Airport Runway were reviewed. These covered the winter of 2007/2008. The National Parks and Wildlife Service was consulted in relation to the proposed project and the conservation objectives of the designated areas.
5.3 FIELD SURVEYS
The methodology for the field surveys was as follows: the area of the proposed dredging was surveyed at monthly intervals from December 2009 to March 2010 inclusive and from June to November 2010. On each visit, counts were conducted within 2 hours either side of low tide and within 2 hours either side of high tide. The area covered coincided with sub- sites 3, 4 and 6 of the IWeBS survey sites (Crowe 2005) and essentially covered the shipping channel and any intertidal areas within 1km of its boundaries (Figure 5.1). This included the areas known as the inner harbour, Cartron Strand, Standalone Point, the northern part of Cummeen Strand and the shoreline from Ballincar to Rosses Point, including the channel north of Oyster Island. In addition to the monthly counts on the shipping channel, a single low tide count of the entire Sligo Harbour was undertaken in January 2010 to provide an overall context for the regular monitoring. All counts were undertaken in reasonable to good visibility using a 34x telescope.
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Figure 5.1: Area of the shipping channel surveyed as part of the bird surveys over the period December 2009 – November 2010 Extract from Admiralty Chart 2852 © Crown copyright UKHO. Not for Navigation Use
5.4 ECOLOGICAL EVALUATION AND IMPACT SIGNIFICANCE
The prediction of impacts/impact significance is based upon the guidance provided in the EPA guidance document Guidelines on the information to be contained in Environmental Impact Statements (2002), and considers such factors as the character of the impact, its magnitude, extent, and duration and the probability of such an impact occurring. From these criteria the significance of the impact is determined on the basis of the factors which characterise the site/receptor and take into account the effects on the conservation status or integrity of the site resulting from the proposed development. The integrity of a site can be regarded as the coherence of ecological structure and function, across the entirety of a site, which enables it to sustain all of the ecological resources for which it has been valued. The following impact significance criteria (EPA, 2002) are used where applicable:
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Significance of Significance Criteria Impact Imperceptible An impact capable of measurement but impact without noticeable consequences An impact which causes noticeable changes Slight impact in the character of the environment without affecting its sensitivities An impact that alters the character of the Moderate impact environment in a manner that is consistent with existing and emerging trends An impact which, by its character, Significant impact magnitude, duration or intensity alters a sensitive aspect of the environment An impact which obliterates sensitive Profound impact characteristics
5.5 BASELINE ENVIRONMENT
5.5.1 Designated Areas for Nature Conservation
In 1995, the entire intertidal area of Sligo Harbour, from Sligo town to beyond Coney Island, was designated as a Special Protection Area (SPA) under Article 4 of the EU Birds Directive (79/409/EEC) (Statutory Instrument 31/1995). The area covered by the Special Protection Area designation has increased in the interim according to a notice issued on 12th March 2010 by the Department of the Environment, Heritage and Local Government and the existing Cummeen Strand SPA boundary is shown below (Figure 5.2).
© Ordnance Survey Ireland. All rights reserved. Licence number 2010/20 CCMA/ Sligo County Council Figure 5.2: Cummeen Strand SPA boundary (updated February 2012)
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5.5.2 Cummeen Strand SPA (Site Code 004035).
Cummeen Strand is a large shallow bay stretching from Sligo town westwards to Coney Island. It is one of three estuarine bays within Sligo Bay, with Drumcliff Bay to the north and Ballysadare Bay to the south. The Garavogue River flows into the bay and forms a permanent channel.
At low tide, extensive sand and mud flats are exposed. These support a diverse macro- invertebrate fauna which provide the main food supply for the wintering waterfowl. Invertebrate species such as lugworm (Arenicola marina), ragworm (Hediste diversicolor), cockles (Cerastoderma edule), sand mason (Lanice conchilega), Baltic tellin (Macoma balthica), spire shell (Hydrobia ulvae) and mussels (Mytilus edulis) are frequent. Of particular note is the presence of eelgrass (Zostera noltii and Z. angustifolia) beds, which provide a valuable food stock for herbivorous wildfowl. The estuarine and intertidal flat habitats are of conservation significance and are listed on Annex I of the EU Habitats Directive. Areas of salt marsh fringe the bay in places and provide roosting sites for birds during the high tide periods. There are sand dunes at Killaspug Point and Coney Island, with a shingle spit at Standalone Point near Sligo town.
Cummeen Strand is of ornithological importance as it supports important concentrations of wintering waterfowl. The site supports an Internationally Important flock of Brent Geese (peak of 232 individuals in the winter of 1999/00, with the mean of peak monthly counts in the period 1996/99 (except 1998) being 228, peaking at 309) and Nationally Important populations of a further two species – Oystercatcher 891 and Redshank 501 (all figures are average peaks for the period). Other species which occurred in significant numbers included Shelduck 80, Wigeon 178, Teal 70, Mallard 170, Red-breasted Merganser 17, Golden Plover 567, Lapwing 734, Knot 18, Sanderling 18, Dunlin 601, Bar-tailed Godwit 57, Curlew 546, Greenshank 18 and Turnstone 80. Whooper Swans also occurred (9), though they are not regular visitors. The presence of Golden Plover, Bar-tailed Godwit and Whooper Swan is of particular note as these species are listed on Annex I of the EU Birds Directive.
This site is of high ornithological importance, with one species having a population of International Importance and two having populations of National Importance. In addition, there are three species that are listed on Annex I of the Birds Directive. The site is also important as a component of the much larger Sligo Bay complex.
Qualifying Interests: x Light-bellied Brent Goose (Branta bernicla hrota) [A046] Wintering x Oystercatcher (Haematopus ostralegus) [A130] Wintering x Redshank (Tringa totanus) [A162] Wintering x Wetlands & Waterbirds [A999]
Conservation Objective: To maintain or restore the favourable conservation condition of the bird species listed as Special Conservation Interests for this SPA.
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5.5.3 Cummeen Strand/Drumcliff Bay candidate SAC (site code 0627)
The entire intertidal area of Sligo Harbour, together with Drumcliff Bay, is also designated as a candidate Special Area of Conservation (cSAC). A description of the cSAC and the potential impacts of the proposed dredging works on it, are discussed in Chapter 6 of the Environmental Appraisal Report and in the Natura Impact Statement for Cummeen Strand/Drumcliff Bay cSAC (Appendix 4A).
5.5.3.1 Implications of the SPA and cSAC designations for any development
In order to protect ecologically important sites, certain potentially harmful works are restricted within SPAs and cSACs. These works (known as activities requiring consent, damaging activities or operations requiring consent) are works liable to destroy or to significantly alter, damage or interfere with the ecology of the site. Among the activities requiring consent are: x Altering watercourses or wetlands, including changing the height of the water table, blocking or altering the flow of water or deepening any channel.
In respect of the activities requiring consent, there is no requirement to obtain the consent of the Minister, if the said activity is licensed by or subject to the permission of another Minister, Public Body, State of Local Authority or specified as permitted in an approved farm plan for the land in question (from Notice of Intention to designate Cummeen Strand (Site code 004035) County Sligo as a Special Protection Area (SPA).
As the entire area of the shipping channel is covered by the SPA and cSAC designations (which are part of the Natura 2000 network of protected sites) there is a requirement for Appropriate Assessment of the likely impacts of the proposed dredging works. This is in accordance with Article 4 of the European Directive 2009/147/EC on the conservation of wild birds, known as the “Birds Directive” and Article 6(3) of the European Directive 92/43/EEC, known as the “Habitats Directive”. The Appropriate Assessment process follows the guidance published by the Department of the Environment, Heritage and Local Government (2009).
A Screening for Appropriate Assessment was carried out for the proposed development. The screening report concluded that there will be no risk of significant negative effects on Cummeen Strand SPA, either alone or in combination with other plans or projects, and therefore, no adverse effect on the integrity of the Natura 2000 site or on its conservation objectives as a result of the proposed works. Therefore, Stage 2 of the Appropriate Assessment process (Natura Impact Statement] is not required. The full Screening for Appropriate Assessment report is included in Appendix 3B.
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5.6 DESCRIPTION OF EXISTING BIRD POPULATIONS AND USAGE OF THE AREA
5.6.1 General description of the study area
Sligo Harbour lies in the centre of a group of three estuaries that comprises Sligo Bay. Also known as Cummeen Strand, it forms the estuary of the Garavogue River. It is protected from the open sea by Coney Island at the western end and by the smaller Oyster Island, which lies in the mouth of the main channel near Rosses Point. The existing shipping channel runs along the northern edge of Sligo Harbour, while to the south of the estuary there are large undivided areas of sand and mudflats. There is a natural shingle spit at Standalone Point between Cartron and Ballincar. This protects an area of finer muds in Cartron Bay.
Bird populations and their usage of the estuary are described below in relation to three different units as follows: 1. The entire area of Sligo Harbour (also known as Cummeen Strand); 2. The shipping channel and all intertidal areas within 1km of the channel; 3. The shipping channel and its banks only.
5.6.2 Bird populations of the entire area of Sligo Harbour
The best available information on the bird populations of the entire area of Sligo Harbour is provided by the Irish Wetland Bird Survey (IWeBS), organised by BirdWatch Ireland. Table 5.1 gives the peak counts for a series of five winters (2005/06 to 2009/10), the latest complete information available. This shows that Sligo Harbour is of international importance for light-bellied brent goose and of national importance for three species of wader (oystercatcher, knot and bar-tailed godwit).
The most significant low tide feeding areas are on the intertidal mudflats which extend south from the shipping channel to the southern shoreline of the bay and west as far as Coney Island. Another important concentration of feeding birds occurs in Cartron Bay to the north of the shipping channel.
Table 5.1:Irish Wetlands Bird Survey (IWeBS) peak counts in Sligo Harbour (entire estuary). (Mean is the average of the peak counts in the last 5 winters) Species 2005/06 2006/07 2007/08 2008/09 2009/10 Peak Mean Mute Swan 20 26 38 36 14 38 27 Whooper Swan 0 0 0 1 0 1 0 Brent Goose 331 663 331 543 433 663 460 Ruddy Shelduck 0 0 0 0 1 1 0 Shelduck 60 45 94 118 120 120 87 Wigeon 84 153 337 108 62 337 149 Gadwall 0 0 0 1 0 1 0 Teal 75 22 108 73 15 108 59
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Species 2005/06 2006/07 2007/08 2008/09 2009/10 Peak Mean Mallard 156 202 185 301 148 202 198 Scaup 0 0 0 6 0 6 1 Long-tailed duck 0 0 0 0 1 1 0 Eider 10 0 0 2 0 10 2 Common Scoter 120 1 0 0 0 120 24 Goldeneye 6 8 9 15 3 15 8 Red-breasted Merganser 23 13 35 37 23 37 26 Ruddy Duck 0 0 0 0 1 1 0 Red-throated Diver 3 2 4 1 6 6 3 Great Northern Diver 14 1 10 13 15 14 11 Little Grebe 0 3 3 2 3 3 2 Great Crested Grebe 2 2 20 6 7 20 7 Cormorant 23 16 26 16 16 26 19 Shag 21 2 15 19 4 21 12 Little Egret 0 0 0 1 3 3 1 Grey Heron 18 23 24 25 11 25 20 Oystercatcher 759 684 1011 678 987 1011 824 Ringed Plover 165 173 157 93 127 173 143 Golden Plover 350 0 363 654 9 654 275 Grey Plover 67 0 20 11 80 80 36 Lapwing 59 438 216 341 111 438 233 Knot 700 346 1400 523 950 1400 784 Sanderling 98 41 10 110 0 110 52 Dunlin 601 477 2079 945 662 2079 953 Snipe 9 0 0 0 8 9 3 Black-tailed Godwit 2 40 0 8 1 40 10 Bar-tailed Godwit 960 277 236 233 438 960 429 Curlew 479 297 292 529 480 480 415 Greenshank 8 9 16 10 9 16 10 Redshank 191 74 335 482 376 482 292 Turnstone 72 12 96 32 191 191 81 Unidentified wader sp. 0 0 0 35 0 35 7 Mediterranean Gull 0 0 0 1 0 1 0 Black-headed Gull 554 452 500 717 234 717 491 Ring-billed Gull 1 1 0 1 0 1 1 Common Gull 373 298 338 370 122 373 300 Lesser Black-backed Gull 0 3 0 0 0 3 1 Herring Gull 55 118 160 135 168 168 127 Iceland Gull 0 0 0 1 1 1 0 Glaucous Gull 0 0 0 7 0 7 1 Great Black-backed Gull 4 21 13 26 11 26 15 (data supplied by BirdWatch Ireland on behalf of National Parks and Wildlife Service). * If the 5-year mean peak exceeds 1% of the national or international populations of a species, the site is classified as of either national or international importance (Boland and Crowe 2012). Significant population figures are underlined.
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5.6.3 Bird usage of the area within 1km of the shipping channel
Intertidal areas within 1km of the shipping channel, including the inner harbour, east of Barytes Quay, and the channel north of Oyster Island were included in the regular monthly counts carried out from December 2009 to November 2010. This area was included to enable assessment of possible indirect effects of dredging on the shipping channel.
On either side of the shipping channel, there are extensive intertidal mudflats and sandflats exposed at low tide. The area to the south-east of the channel, known as Cummeen Strand, holds large flocks of brent goose, shelduck, bar-tailed godwit, curlew and dunlin. The sheltered mudflats within Cartron Bay, north-east of the harbour, are also important at low tide for a range of wildfowl and waders, particularly brent goose, curlew, redshank, oystercatcher and lapwing. In the inner harbour, between the shipping quay and the N15 road bridge, a small number of waders are found with moderate numbers of gulls and a resident flock of mute swan.
The most important high tide roosts on the northern side of the channel are on the southern and eastern sides of Standalone Point. This area, opposite the existing port, is particularly used by birds in strong westerly winds when it provides a degree of shelter. The main species roosting here include grey heron, oystercatcher, lapwing, bar-tailed godwit, curlew, redshank, greenshank and turnstone. There are also other smaller high tide roosts on the east side of Cartron Bay, along the northern shore of the channel between Ballincar and Rosses Point and occasionally on the training wall south of the channel.
A total of 27 species of waterbirds was recorded within this count area over the period of December 2009 to November 2010. This includes ten species of wildfowl (and allies), ten species of waders, five species of gull, together with cormorant and grey heron. Tables 1 and 2 in Appendix 3A, give the full counts of this area while Table 5.2 below gives a summary of the mean and peak numbers of each species occurring at low tide and high tide. The peak figure represents the maximum number of birds recorded at any one time during the winter counts. The peak counts for each species occurred on different dates. The highest total count of all species at low tide was 3,295, recorded in November 2010. The highest total count of all species at high tide was 716, also recorded in November 2010.
For most species of wildfowl and waders, numbers are greater at low tide as more of the intertidal area is exposed. At high tide the birds move to a few key roost sites and some leave the area of the channel completely. For diving species such as cormorant, red- breasted merganser and great crested grebe, some birds were present on all states of the tide as they are mainly confined to the channel.
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Table 5.2: Summary of peak and mean numbers of water birds within 1km of the shipping channel in Sligo Harbour over ten months, December 2009-November 2010.
Low tide High tide Number of counts 10 10 Species Peak Mean Peak Mean Mute Swan 50 14 45 15 Brent Goose 225 78 155 22 Shelduck 48 8 2 0 Wigeon 62 20 53 15 Teal 70 11 40 4 Mallard 155 64 94 56 Goldeneye 4 1 2 0 Red-breasted Merganser 14 3 17 2 Great Northern Diver 1 0 2 0 Great Crested Grebe 11 2 3 1 Cormorant 31 8 16 7 Grey Heron 18 8 14 3 Oystercatcher 212 102 222 54 Grey Plover 1 0 0 0 Lapwing 40 12 50 12 Black-tailed Godwit 4 0 0 0 Bar-tailed Godwit 280 39 83 9 Dunlin 20 152 0 0 Curlew 432 134 271 85 Greenshank 5 2 13 2 Redshank 511 173 200 89 Turnstone 6 1 124 28 Black-headed Gull 380 128 90 26 Common Gull 32 7 14 5 Lesser Black-backed Gull 3 1 7 1 Herring Gull 70 30 52 16 Great Black-backed Gull 5 2 9 3
5.6.4 Bird usage of the shipping channel and immediate banks only
In order to assess the direct disturbance effects of dredging on the birds using the shipping channel, an analysis was made of species and numbers using only the channel and its immediate banks. A summary of this information is given in Table 5.3.
The central part of the channel is permanently covered by water even at low tide. It is used by a few cormorant, great northern diver, red-breasted merganser and great crested grebe, which are all fish-eating species. The edges of the channel are used for swimming and feeding by various wildfowl including light-bellied brent goose, shelduck, wigeon, teal and
IBE00440/EAR/September ‘12 5-11 Sligo Harbour Dredging Environmental Appraisal Report Birds mallard. Gulls are also generally present including black-headed, common, herring and great black-backed gulls.
The edges of the shipping channel are marked (in the eastern part in particular) by a line of rocks creating a breakwater along the sides of the channel. This is exposed at low tide and at neap high tides but largely covered at high spring tides. It provides an important roost site on some dates for significant flocks of redshank, oystercatcher and turnstone. The birds are sometimes present at low tide as well as high tide. Isolation from ground predators and other disturbance, together with proximity to intertidal feeding areas are the principal attractions of this breakwater for birds.
Table 5.3: Summary of peak and mean numbers of water birds on the shipping channel and its immediate banks in Sligo Harbour over ten months, December 2009- November 2010.
Low tide High tide Number of counts 10 10 Species Peak Mean Peak Mean Mute Swan 50 9 31 5 Brent Goose 184 33 25 4 Shelduck 2 0 0 0 Wigeon 62 11 28 6 Teal 70 8 0 0 Mallard 37 9 48 13 Goldeneye 10 0 2 0 Red-breasted Merganser 10 2 8 1 Great Northern Diver 1 0 0 0 Great Crested Grebe 2 1 3 0 Cormorant 13 3 10 3 Grey Heron 6 3 2 1 Oystercatcher 164 49 222 32 Lapwing 10 1 0 0 Bar-tailed Godwit 10 1 80 8 Curlew 19 6 42 9 Greenshank 5 1 0 0 Redshank 230 24 106 14 Turnstone 6 1 120 27 Black-headed Gull 0 0 1 3 Common Gull 0 0 14 1 Lesser Black-backed Gull 0 0 2 0 Herring Gull 24 5 3 1 Great Black-backed Gull 1 0 3 0
The following species are of particular note, in the area of the shipping channel and its banks.
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Mute swan: A flock of mute swan regularly feeds in winter in the inner harbour area where they benefit from artificial food sources. In later summer they appear to disperse into the estuary and a peak of 50 birds was recorded in July 2010 in the mid-channel area near Ballincar.
Brent goose: A significant part of the brent goose flock uses the northern part of the bay on both sides of the shipping channel. A peak of 184 was recorded in this area in November 2010. They occasionally use Cartron Bay and have been recorded in the channel north of Oyster Island. Small flocks of brent geese feed along the northern shore of the channel throughout the winter, especially where minor freshwater streams enter the bay.
Wigeon: A peak of 62 wigeon was recorded in the immediate area of the shipping channel. These regularly feed in the area south of Standalone Point and at various locations along the northern shore of the channel in smaller numbers.
Teal: A peak count of 70 teal in the shipping channel area was recorded at low tide. At high tide the birds often move into vegetated areas and become difficult to see and identify. The main feeding areas are around Standalone Point.
Mallard: Mallard are generally scattered in small flocks all along the northern bank of the shipping channel. The principal feeding areas are at the mouth of Cartron Bay and at Ballincar.
Red-breasted merganser: A small number of merganser use the shipping channel for feeding.
Great crested grebe: A small number of grebe use the shipping channel for feeding.
Cormorant: Cormorant are usually present in small numbers throughout the channel. They roost on the training walls, on the navigation marks and on the eastern end of Oyster Island.
Grey Heron: Herons are widely distributed in small numbers along the banks of the channel. The main high tide roost is on Standalone Point.
Oystercatcher: This common wader species is normally present along the channel in higher numbers at low tide. Unusually large roosts were recorded at the southern end of Standalone Point (220 in October 2010) and on the southern training wall (83 in March 2010).
Curlew: The highest numbers of curlew are found near the shipping channel at high tide when they roost on the southern end of Standalone Point.
Redshank: Small numbers of redshank feed along the channel at low tide. Significant numbers are usually present in Cartron Bay and they use the training walls on the south side of the shipping channel as a roosting site.
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Turnstone: Turnstone are often well camouflaged in the more gravely areas of the channel banks. They use the training walls on either side of the shipping channel and the southern end of Standalone Point as roosting sites (peak of 120 recorded in October 2010).
5.7 PREDICTED IMPACTS OF THE PROPOSED DREDGING
5.7.1 Potential impacts on birds
The following are the individual elements of the proposed development which could potentially give rise to adverse effects on waterbirds within Sligo Harbour/Cummeen Strand; x The physical act of dredging by the dredging vessel and its crew has the potential to cause some temporary disturbance to waterbird populations in Sligo Harbour. x The dredging will result in the removal of sediments from the estuary along the shipping channel. This will result in the loss of some sub-tidal and intertidal habitat and has the potential to impact on the training walls along the shipping channel, which are an important roost site for waterbirds. x The dredging will result in the removal of sediments from the estuary along the shipping channel. This will impact directly on the benthic environment and has the potential to negatively impact on the infaunal macrobenthos which acts as important food source for waterbird species in the estuary. x The dispersion and settlement of sediment released during the dredging works has the potential to cause impacts directly on the intertidal environment (habitats and fauna) within Sligo Harbour and also may have associated indirect impacts on waterbird species within the SPA. x The disposal of the dredged material has the potential to impact on the intertidal environment (habitats and fauna) within Sligo Harbour.
5.7.2 Likely direct impacts on birds
Dredging activities have the potential to cause some temporary disturbance to waterbird populations in Sligo Harbour.
There is potential for the disturbance of waterbirds as a result of noise, vibration and dredging activity associated with the construction phase of the project. However, waterbirds within Sligo Harbour/Cummeen Strand are unlikely to be significantly disturbed by the dredging activities as the disturbance will be localised and short-term in nature. For each tidal cycle (approx 12.4 hours) the dredger will only be able to dredge for around 70-80 minutes. The rest of the time it will be travelling to and from the proposed dump site (approximately 50km away, offshore). A typical dredger would travel at an average speed of 6.5 knots laden and 8 knots unladen, therefore taking around 10 hours in normal conditions to for a return trip to the dump site, including the time taken to discharge the sediments (for a full description of the proposed works, see Chapter 4, Section 4.4.2 of this document).
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Bird species in the harbour are already subject to disturbance from recreation, transport (shipping movements in the harbour and low flying aircraft in the area of Sligo Airport) and other activities and appear to be habituated to current levels of disturbance.
Given the factors discussed above, disturbance to waterbird species as a result of the proposed dredging activities (either alone or in combination with existing disturbance levels) will result in an imperceptible impact. It is extremely unlikely to have a significant negative effect on waterbirds within Sligo Harbour/Cummeen Strand, even in the short term.
The dredging will result in the removal of sediments from the estuary along the shipping channel. This will result in the loss of some sub-tidal and intertidal habitat. This also has the potential to impact on the tidal regime in Sligo Harbour.
Direct loss of habitat The proposed works will require the removal of predominantly sub-tidal substrate within the existing deep water channel in Sligo Harbour. However, the proposed works will also require the removal of a small area (c. 31,811m² or 0.07% of the overall cSAC area1) of intertidal material (fine silts and sands) inside the training wall between Ballyweelin Point and the Deepwater Jetty. A total estimated volume of 250,000m3 of sediment will be removed from the estuarine environment in Sligo Harbour during the course of the proposed work. This material will be removed from an area that has been the subject of previous large scale dredging works (in 1998) and exists as a maintained channel at this location, which is delineated by man-made training walls at its outer edges. The removal of this material will not have a significant negative effect on the estuary and will not destabilise the structure or functioning of the estuary relative to existing conditions. From observations made during the field surveys, the intertidal area between the training walls along the deep water channel is not of great importance for birds within the estuary as a whole. The volume of sediment to be removed is not significant in the context of the total available sediment within the SPA and will not have any significant effect on the habitats, or on the waterbirds, within the estuary. The training walls along the shipping channel are an important roost site for waterbirds in Sligo Harbour. However, the training walls will not be directly impacted by the proposed dredging works.
A literature review was undertaken as part of this assessment to find any examples of recorded impacts of dredging activity on estuarine birds elsewhere. An assessment of potential impacts of both capital and maintenance dredging on birds in the Tamar Estuary, south-west England was published (Widdows et al. 2007). Maintenance dredging in the lower Tamar typically accounts for the annual removal of between 5,000 and 200,000 tonnes of dry sediment per year. During periods of capital dredging, the amount of sediment dredged increased significantly to between 500,000 and 700,000 tonnes per year. The study reviewed population data for ten bird species, including mallard, shelduck, teal, wigeon, curlew, dunlin, oystercatcher and redshank, over a 30-year period from 1971 to 2002. None of the wildfowl or wader species studied showed any correlation between bird numbers and
1 The area of the cSAC (48,541,373 m²) has been calculated using the geodatabase file of the Cummeen Strand/Drumcliff Bay (Sligo Bay) SAC polygon (v1.04) as published on the National Parks and Wildlife Service data maps viewer http://webgis.npws.ie/npwsviewer/ on 21 June 2012
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dredging activity in the Tamar. There were no marked changes in numbers during the year of peak dredging or during the following winters. Declines in teal and wigeon were considered to be related to a series of milder winters reducing their need to migrate as far as south-west England.
Given the factors discussed above, the removal of intertidal and sub-tidal material as a result of the proposed dredging activities will result in a slight impact in the short-term in the immediate area. However, the impact will reduce to an imperceptible impact within a short period, particularly when taken in the context of the estuary as a whole and the wider complex of estuarine habitats that make up Sligo Bay. It is extremely unlikely to have a significant negative effect on waterbirds within Sligo Harbour/Cummeen Strand, even in the short term.
5.7.3 Impacts on the Tidal Regime of Sligo Harbour
Hydrodynamic modelling was undertaken as part of the study to investigate the impact of the dredging on the hydraulic regime of Sligo Harbour and on the sedimentation in the harbour area during the dredging operations (Chapter 11, Coastal Processes). The modelling was used to examine the effect of:
x The change in channel bathymetry on the tidal flows and water levels, and x The dispersion and fate of material spilled during the period of the dredging operations.
Dredging works will involve some temporary suspension of fine sediments in the water column within Sligo Bay (refer to Chapter 11.1 and 11.2).
The results of the tidal flow modelling indicate that while the proposed dredging will lower the level of the low water spring tides in the channel at Sligo (caused by the removal of the bar within the shipping channel by the proposed dredging) the high spring tide level will be unaffected by the proposed dredging works. At present, this bar slows down the passage of water exiting the channel at low tide, causing some water be retained or pooled behind it. If the bar is dredged, the water will be able to drain more freely at low tide, thus causing lower water levels and possible drying out of the channel upstream of the bar at extreme low spring tides. As can be seen on Figure 11.18 of Chapter 11 of this document, this drying will last for a maximum of 2 hours. It is not considered that this will result in any significant negative effect on waterbird populations in Sligo Harbour or have an adverse affect on the structure and functioning of the estuary.
The impact of the proposed dredging on the flow regime in Sligo Harbour has been assessed by comparing the mean and peak flow velocities for both flood and ebb tides. Figures 11.19 and 11.21 of this report show the difference in the mean tidal velocity for both flood and ebb spring tides. In these diagrams, the difference in the tidal velocity is calculated by comparing the average tidal velocity over the flood or ebb period for the model with the dredged channel in place and subtracting the equivalent flows for the model with the existing bathymetry. These diagrams show that the difference in the mean velocities is generally very
IBE00440/EAR/September ‘12 5-16 Sligo Harbour Dredging Environmental Appraisal Report Birds small (less than 0.1 m/s) and the changes are restricted to the area around the channel and the northern section of the harbour area. As such, the impact of the dredging will have an imperceptible effect on the current flows in the harbour area except in the area of the channel itself, where increases of up to 0.4m/s may be experienced in localised areas, and the area north of the navigation channel may be slightly decreased by around 0.1m/s.
Given the factors discussed above, the removal of intertidal and sub-tidal material as a result of the proposed dredging activities will result in an imperceptible impact on the tidal regime of Sligo Harbour. It is not considered that this will result in any significant negative effect on waterbird populations in Sligo Harbour or have an adverse affect on the structure and functioning of the estuary.
5.8 LIKELY INDIRECT IMPACTS ON BIRDS
The dredging will result in the removal of sediments from the estuary along the shipping channel. This will impact directly on the benthic environment and has the potential to negatively impact on the infaunal macrobenthos which acts as an important food source for waterbird species in the estuary.
There will be a loss of benthic habitat along the navigational channel as a result of sediment removal. All of the mobile non-sessile species have the ability to vacate the area during dredging. Along the channel, where dredging will occur, the removal of the surface sediment and any associated fauna, will occur over a relatively short time frame.
Once dredging ceases, recovery of the dredged area follows. In a harbour navigation channel, where both maintenance and capital dredging are routinely carried out, this cycle of regular disturbance and subsequent recovery has played out as long as the channel has existed and will continue to do so for as long as the channel is maintained and used. The benthic environment surrounding the Sligo Harbour navigation channel exists in its current form after a long history of similar periodic disturbance. The typical phases of recovery following dredging disturbance are outlined below.
Recovery begins with the colonization of the defaunated area by small opportunistic species adapted to survive in areas of physical disturbance. This colonization occurs either from neighbouring sites or via larval settlement or both. Few organisms follow this life style strategy so there is a tendency for a limited number of species to reach extremely high densities in the presence of pollutants. The bioturbatory activities of the infauna start to significantly modify the physical, chemical and biological nature of the deposit. The macrofaunal assemblage enters a ‘transitory’ phase of succession when the sedimentary changes allow further colonization of a larger variety of species. This stage is unfavourable for the ‘pioneer’ population to persist. Species that characterise the transitory sere include suspension and deposit feeding bivalves, ‘conveyor belt’ polychaetes and relatively immobile holothurians. Here again the physical and chemical properties of the sediment are further modified by the new infaunal dominants making way for additional species to take hold. A more complicated and persistent faunal assemblage now forms and evolves towards an ‘equilibrium’ or ‘climax’ community status.
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What is described above is typical of recovery from a physical disturbance like dredging. This recovery sequence is applicable if there is no subsequent disturbance to the site. While there will be a loss of infaunal habitat due to the removal of sediment from an area of up to 27.2ha, or 0.56% of the overall cSAC area, recolonisation of denuded habitat will occur quickly and the floral and faunal communities inhabiting the SPA will not be permanently impacted.
Impacts on benthos from noise in the vicinity of the dredging operation are expected to be localised and temporary in nature. The fact that the proposed dredging will take place in an already operational port navigation channel suggests that the additional, temporary noise loading of a dredger at work would be of minimal significance to the infaunal macrobenthos in the vicinity of the dredged area.
It is considered that given the factors discussed above, direct impacts on the benthic environment as a result of the proposed dredging activities will result in a moderate impact in the short-term in the immediate area. However, the impact will reduce to a slight and then imperceptible impact within a short period. It is extremely unlikely to have a significant negative effect on waterbirds within Sligo Harbour/Cummeen Strand, even in the short term.
The dispersion and settlement of sediment released during the dredging works has the potential to cause impacts directly on the intertidal environment within Sligo Harbour and as a result, may impact on the macrobenthos. This may have associated indirect impacts on waterbird species within the SPA which feed on the subtidal infaunal macrobenthos.
As discussed above, the removal of a small area (up to 27.2ha or 0.56% of the overall cSAC area) of intertidal material (fine silts and sands) between Ballyweelin Point and the Deepwater Jetty, within the area delineated by the training walls, will not result in a significant impact on waterbirds. From observations made during the field surveys, this area is not of great importance for birds within the estuary as a whole.
5.8.1.1 Potential impacts of sediment dispersion and settlement on the macrobenthos (food source for waterbirds in Sligo Harbour)
Intertidal macrobenthos is of greatest value to bird species as a food source (due to accessibility). The subtidal infaunal macrobenthos along the floor of the navigation channel will be subject to the greatest level of impact (complete removal, though with potential for rapid recolonisation). Impacts to the intertidal macrobenthos are likely to be imperceptible, localised and temporary, as the continued movement of the dredger along the navigation channel will ensure that any given area will not be impacted for a protracted period.
The hydrodynamic modelling presented in Chapter 11 shows that the sediment put into suspension by the dredger during water injection dredging will be dispersed around the northern portion of Sligo Harbour. The sediment will be redistributed during periods of higher current velocities during successive spring tides, before eventually coming to rest in
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small deposits around the fringes of Sligo Harbour and Cartron Marsh (see Figure 11.8 in Chapter 11). Some of the material will be successfully transported out of the harbour and will settle out on the nearby sand banks in depths of a few mm.
During subsequent conventional dredging, small amounts of sediment put in to suspension by the dredger during dredging operations will be temporarily deposited along the sides of the navigation channel and in sheltered areas along the north shore of the harbour area.
The areas that will experience the greatest amount of temporary sedimentation occur along the north shoreline of Sligo Harbour (peak sedimentation during dredging of 20-70mm). These peak values are typically of a short duration (a matter of hours) and the material may then be re-suspended and transported elsewhere as the tidal currents pick up during the subsequent tide. The residual pattern of sedimentation following completion of all conventional dredging operations is shown in Figure 11.26 in Chapter 11. This shows that the maximum final deposition depth following completion of operations does not exceed 1mm in the majority of the harbour area and exceeds 25mm only in very localised areas around the navigation channel and the northern shore of the harbour. Overall, the amount of sediment deposited in the harbour area as a result of the dredging will be insignificant. No residual impact is expected.
Potential impacts of sediment dispersion and settlement on seagrass beds (food source for waterbirds in Sligo Harbour) – background information from Chapter 6 of this report and Section 6.3.1.3 of the separate Natura Impact Statement for the Cummeen Strand/Drumcliff Bay SAC.
Marine seagrasses (especially eelgrass, Zostera spp.) are a key food resource for waterbirds, especially Brent Geese and Wigeon (Mathers et al., 1998). Small areas of this seagrass occur at the southern edge of Cummeen Strand (Nairn and Robinson, 2003).
Light is one of the key environmental resources imperative for the growth and survival of seagrasses (Hemminga & Duarte, 2000). The degree of water transparency (which determines the depth-penetration of photosynthetically active radiation of sunlight) is the primary factor determining the maximum depth at which seagrasses can occur. Reduction in light due to turbidity has been identified as a major cause of the loss of seagrasses worldwide (Shepherd et al., 1989; Green & Short, 2003). The amount of light that reaches a seagrass leaf is determined by the natural water colour, concentration of suspended solids, phytoplankton concentration and the epiphyte cover of the leaf. There are various reports of sublethal and lethal effects on seagrass meadows due to prolonged exposure to high turbidity and siltation associated with dredging activities (Erftemeijer & Lewis, 2006). Laboratory experiments have shown that some seagrasses can survive in light intensities below their minimum requirements for periods ranging from four weeks to several months. However, widespread seagrass mortality was observed in Chesapeake Bay (USA) following a month-long (seasonal) pulse of increased turbidity (light extinction coefficient (k)>3.0 m-1) (Moore et al., 1997).
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The minimum light requirements of Zostera marina (eelgrass) have been extensively studied in a range of locations and environments. The values for the minimum light requirements of this species, as reported in literature, vary between 11 and 37 % of Surface Irradiance (SI). For the survival of seagrasses, the lowest value of 11%SI is the most critical level below which widespread mortality surely occurs. Some of the higher values (up to 37%SI) reported for eelgrass appear to refer to the minimum light levels required to enable and sustain lateral shoot development, meadow expansion and flowering. Levels below 37%SI but above 11%SI do affect these processes, but may not cause substantial eelgrass mortality. There has been only 1 detailed study of the minimum light requirements for Zostera noltii: Peralta et al. (2002) reported a minimum light requirement of 2% of SI for Zostera noltii in Spain. According to the same study (also reported in: MarLIN Database, 2006), Zostera noltii plants can tolerate acute light reduction below 2% SI for up to two weeks, and thus appear tolerant of short-term events of very high turbidity. A recent monitoring study into the effects of a dredging plume on intertidal eelgrass (Zostera marina) in the Ems Estuary (The Netherlands) during (day-time) periods of low tide exposure (Ochieng & Erftemeijer, 2009). This implies that intertidal eelgrass plants are relatively tolerant to further turbidity increases such as may be caused by a dredging plume (Ochieng and Erftemeijer, 2009). Based on the above information, the tolerance thresholds of seagrass beds to turbidity is summarised in Table 5.4.
Table 5.4: Tolerance thresholds of Zostera spp. to turbidity levels.
Seagrass Minimum Tolerated Optimum Species Range Zostera marina 11-37% SI >37% SI Zostera noltii 2% SI can tolerate acute light reduction below 2% SI for 2 weeks
Several studies have documented deterioration of seagrass meadows by smothering due to excessive sedimentation (Erftemeijer and Lewis, 2006). Seagrass species that develop vertical shoots may respond to fluctuations in sediment depth by modifying their vertical growth but there are limits to the level of sedimentation seagrasses can tolerate. Sedimentation rates of as much as 1013 cm yr-1 have been reported as maximum threshold of what some seagrass species can survive. Settlement of suspended material on leaf blades of seagrasses may interfere significantly with photosynthesis, and appears especially significant in low wave energy environments where fine sediments are present and can settle out. A maximum allowable sedimentation rate of 2 cm in 4 months was reported for Mediterranean Zostera noltii (Spain). Tolerance of Zostera noltii in the Dutch Wadden Sea was documented to range from minor erosion of 2 cmyr-1 to maximum sedimentation levels of 25 cm yr-1. Mortality of 75% was reported for Zostera marina meadows (USA) at burial with 4 cm (i.e. 25% of plant height), which demonstrates that this species is probably more sensitive to sedimentation than some of the other (taller) seagrass species. Vermaat et al. (1997) proposed an estimate of the annual sedimentation rates that can be survived or escaped by seagrasses, either vertically or horizontally, to be in the order of 5-10 cm yr-1.
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Based on the above information, the tolerance thresholds of seagrass beds to sedimentation is summarised in Table 5.5.
Table 5.5: Tolerance thresholds for Zostera spp. to sedimentation. Seagrass Minimum Tolerated Maximum Tolerated Species Zostera marina 75% mortality at 4cm/day (25% of plant height Zostera noltii -1 to -2 cm/yr (erosion) 2-5 cm/year (sedimentation) 2cm / 4 months Impacts of the dredging plume on the seagrass beds in Sligo Harbour are considered to be imperceptible; because the plumes of high turbidity and sedimentation do not reach the seagrass beds documented in the area (they are remote from the shipping channel and occur at the southern edge of Cummeen Strand). Intertidal seagrass is also likely to be unaffected by increased turbidity, since it obtains most of its light during (day-time) periods of low tide exposure (see Ochieng & Erftemeijer, 2009). Based on the final sediment deposition depth computed for the Cummeen Strand seagrass habitat, on completion of all dredging activities, no residual impact on this habitat is expected.
5.8.1.2 Indirect impacts on bird species As discussed above, significant deposition will only occur in small sheltered areas along the coastline, particularly along the north shoreline (refer to Figures 11.7 and 11.8 as well as 11.24, 11.25 an 11.26 of Chapter 11, Coastal Processes). Overall the amount of sediment deposition in the harbour area on completion of dredging is expected to be relatively small as both the deposition depths and the increase in the level of the suspended sediment concentrations in the greater part of the harbour area are not considered to be significant. As such, the dispersion and settlement of sediment released during the dredging works will have an imperceptible impact on waterbirds within Sligo Harbour/Cummeen Strand.
The disposal of the dredged material has the potential to impact on the intertidal environment (habitats and fauna) within Sligo Harbour. It is proposed to dispose of all of the dredged material at an offshore dumpsite (see Chapter 4, Project Description and Figure 4.2). The proposed dump site (subject to granting of a licence by the EPA) is located some 34 nautical miles (63km) from the deepwater jetty at Sligo, in waters that are 92 – 93m in depth. This element of the dredging works does not pose any risk of negative impacts to either the habitats or fauna of Sligo Harbour/Cummeen Strand.
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5.9 MITIGATION MEASURES
5.9.1 Mitigation by Reduction/Remedy
As the proposed dredging activities do not pose a risk of significant negative effects on waterbirds in Sligo Harbour/Cummeen Strand as a result of disturbance, no mitigation measures will be necessary.
As the physical act of dredging does not pose a risk of significant negative effects on waterbirds in Sligo Harbour/Cummeen Strand as a result of the removal of intertidal and sub- tidal material from the estuary, and the associated impacts on the benthic environment (either directly to the infaunal macrobenthos, or indirectly on the tidal regime of the estuary), no mitigation measures will be necessary.
The dispersion and settlement of sediment released during the dredging works does not pose a risk of significant negative effects on waterbirds in Sligo Harbour/Cummeen Strand, either through direct or indirect impacts. As a result no mitigation measures will be necessary.
5.10 RESIDUAL IMPACTS
As discussed under Section 5.8 above, none of the predicted impacts of the proposed capital and maintenance dredging in Sligo Harbour will result in significant negative effects on waterbirds. This is also discussed in detail in the Screening for Appropriate Assessment Report, the conclusions of which are provided below (for full Screening for Appropriate Assessment Report, refer to Appendix 3B). There are no residual impacts of the proposed capital and maintenance dredging works on waterbirds within Sligo Harbour.
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6.0 INTERTIDAL AND SUBTIDAL FLORA AND FAUNA, MARINE MAMMALS
This chapter provides an assessment of the likely impact on the marine ecological environment by the proposed dredging in Sligo Harbour and associated dumping at sea. The assessment focuses on ecological features of conservation significance and specific methodologies used for the individual sub-sections of this Chapter are provided below.
6.1 INTRODUCTION The principal focus of the impact assessment will be to consider the potential impacts of the dredging within Sligo Harbour itself, as the site holds SAC and SPA designations. A programme of marine intertidal and subtidal ecological surveys was drawn up, centred on the navigation channel but extending throughout Sligo Harbour and into Sligo Bay. These studies and the associated impact assessment are presented in section 6.2 of this chapter.
Further benthic studies have been undertaken at the proposed dump site, some 34 nautical miles west of the harbour quays. These studies included current meter recording (including deployment of drogues, ROV acquisition and benthic grabs. The results of these surveys and the associated impact assessment are presented in section 6.3 of this chapter.
A marine mammal survey covering Sligo Harbour and the surrounding waters in Sligo Bay/Dumcliff Bay has also been undertaken, incorporating a desktop assessment, field surveys and impact assessment. These surveys are presented in Section 6.4 of this chapter.
The proposed dredging area lies within the Cummeen Strand/Drumcliff Bay (Sligo Bay) Shore SAC, which forms part of the Natura 2000 site network established under the EC ‘Habitats’ Directive (92/43/EEC). The European Communities (Natural Habitats) Regulations 1997 (SI 94/1997) transpose the Habitats Directive into Irish Law. Under this legislation the proposed dredging requires an appropriate assessment under Article 6(3) and 6(4) of the Habitats Directive. Under Part IV of the Habitat Regulations, Planning and Development Matters, an EIA can be considered as an appropriate assessment. Notwithstanding this, the EC guidance states that the assessments required under Article 6 should be clearly distinguishable and identified within the Environmental Appraisal or reported separately. Therefore Sections 6.2 to 6.4 of this Chapter will discuss the individual impact assessments undertaken for the Environmental Appraisal whilst the Natura Impact Statement to support the Appropriate Assessment Process is presented separately in Volume 3 of this Report.
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6.2 INTERTIDAL AND SUBTIDAL FLORA & FAUNA – DREDGING AREA
6.2.1 Introduction
6.2.1.1 Project background
Aquafact International Ltd were commissioned to describe the intertidal and subtidal flora and fauna that exist in Sligo Harbour and evaluate the potential impact of the proposed work on the habitats and species present. An A3 figure showing the extents of the proposed dredging area is presented in Figure 4.1 (page 4-3) in Chapter 4 of this Environmental Appraisal.
6.2.1.2 Sligo Harbour Sligo Harbour is a large embayment located between Sligo City to the east and Rosses Point village to the west. It measures approximately 6 km in length (from West to East) and is approximately 3 km wide at its widest point. The Garavogue River discharges through Sligo Harbour and the main channel runs along the northern edge of the embayment. Extensive sand flats are present throughout the area, with large sand flats to the south of the embayment at Cummeen Strand and Dorrins Strand. Several mussel banks are present throughout these flats, in addition to commercial clam farming being undertaken close to the main channel at Cummeen Strand.
6.2.2 Desktop Study
6.2.2.1 Intertidal habitats The Aquatic Services Unit (ASU) of University College Cork (UCC) has carried out several intertidal studies in the Sligo Bay area and within Sligo Harbour. Recent intertidal work carried out by ASU in the Sligo Harbour area includes:
x A survey covering a small area in the south west corner of Dorrins Strand, 2005 (carried out as part of an EIS for a proposed extension of the Sligo airport site). 12 stations were sampled in a relatively small study area. Samples taken included faunal cores (x3) and samples for granulometric and organic carbon analysis.
x An assessment of the wider intertidal benthic community of Sligo Harbour, 2007 (carried out as part of an EIS for a proposed extension of the Sligo airport site). 30 stations were sampled over a large area of Sligo Harbour. The sampling regime included faunal cores (x5), 1 x 1m2 quadrat described physically and biologically, 1 x 0.25m2 quadrat was marked out and excavated to a depth of 20cm. Sediment was sieved in situ through a 5mm mesh sieve. Samples were taken for granulometric and organic carbon analysis.
x A survey of Mudflats and Sandflats in Ireland, 2007 (commissioned by the National Parks and Wildlife Service). This survey consisted of several shore transects in the Sligo Bay area. Three stations were investigated on each transect – a High, Mid and Low shore station. At each of these stations, faunal cores (x5), a 1 x 1m quadrat was
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excavated using a hand spade to a depth of 20cm and examined for macrofaunal content. A core was also taken for granulometric and organic carbon analysis.
6.2.2.1.1 Aquatic Services Unit, UCC – Dorrins Strand 2005 (Excerpt from ASU, 2005). The area of Sligo Bay surveyed at Dorrins Strand was dominated by an expansive sandy intertidal area ringed for the most part by a narrow saltmarsh fringe. This site was just to the east of Sligo Airport runway. Immediately below the saltmarsh fringe the shore was mainly comprised of sand right from the top of the shore. This was supplemented just east from where Sligo Airport runway comes closest to the shore around to Rinn Point by a narrow upper shore gravel / cobble fringe interspersed with muddy sand in places. This latter was dominated by the brown seaweed, spiral wrack (Fucus spiralis) with a locally heavy cover of the green seaweed, Enteromorpha sp., especially common close to where a small freshwater stream flows onto the shore running east. The stream joins the shore immediately east of where the small by-road (from the south) reaches the shore. At low tide, the small stream hugs the shore travelling east to ENE in a shallow channel on the surface of the sand, eventually joining the main eastwest tidal channel just off Rinn Point. The intertidal channel of the stream near where it joins the east-west tidal channel and the tidal channel itself, had significant numbers of loosely scattered clumps of Enteromorpha and to a lesser extent small clumps of filamentous brown and red algae (e.g. Ceramium nodulosum). In addition, numerous small gobies were visible in the shallow water of these channels during low water. A couple of smaller streams/drainage ditches drain to the shore closer to the airport runway and these join the main tidal channel via short shallow meandering channels.
The sandy or muddy sand habitats of the shore appear (in May) rather uniform to the eye with virtually no macroalgal (large seaweed) cover. The most obvious feature is the moderately dense lugworm (Arenicola marina) burrows which dominate most of the shore, particularly south of the east-west running low-tide channel. North of this channel the shore height is slightly higher, and the substrate slightly drier and sandier and so the lugworm densities are visibly lower. Around all the lower-lying and wetter areas of the flats e.g. stream channel edges, the lugworm cast density tends to be highest. During early August much of the soft-sediment intertidal area about 70m to the south of the east-west flowing tidal channel had a moderate to locally dense cover of the green filamentous alga Vaucheria sp.
The only area where there is a typical rocky shore community was on the short steep rock- armoured shore, which begins adjacent to the eastern end of the runway and runs north east along the shore for a short distance. This is a typical sheltered shore dominated by brown fucoid seaweeds. The upper shore boulders were virtually devoid of the yellow and grey lichen zones, which are sometimes evident on such substrates and the brown seaweed channel wrack is confined to a few scattered clumps at the top of the shore. This was followed by a better-defined, but narrow (~0.5m), band of Fucus spiralis and then by the main zone which is dominated by two more brown seaweeds: egg wrack (Ascophyllum nodosum) and bladder wrack (Fucus vesiculosus) forming a dense band of about 3m width and 100% cover. The lower shore and shallow subtidal were dominated by Fucus serratus (serrated wrack), Laminaria saccharina (strap weed or sugar wrack) and clumps of the
IBE00440/EIS01/June ‘12 6-3 Sligo Harbour Dredging Environmental Appraisal Report Intertidal and Benthic Flora and Fauna & Marine Mammals invasive brown seaweed Sarragassum muticum. Bootlace weed (Chorda filum) was present in the deeper (>1m) water of the sandy-bottomed channel adjoining the shore at this point. Most of the mid to lower shore brown algae had other finer seaweed growing as epiphytes on them including fine filamentous browns and fine red algae such as Polysiphonia lanosa, Aglaothamnion roseum and Ceramium pallidum. Other, very infrequent small reds included Hypoglossum hypoglossoides and Apoglossum ruscifolium on silted rock in the lower shore. Some Enteromorpha was also present on this shore.
The intertidal fauna was quite sparse and comprised scattered littorinid snails (including the edible periwinkle Littorina littorea and L. obtusata/mariae), frequent limpets (Patella vulgata), occasional dog whelks (Nucella lapilis), blue mussels (Mytilus edulis) and top shells (Gibbula cineraria). Barnacles were not common on the shore and included Semibalanus balanoides and Elminius modestus. The shore crab (Carcinus maenas) was also occasionally noted under stones. The lower boulders on the shore had coatings of silty sand on their surfaces. Small hydroids (Dynamena sp.) were noted as epizootic on fucoid algae, as was the Bryozoan Alcyonidium sp. The fine sponge Leucsolenia sp. was noted under stones in the mid-lower shore, while another sponge, Hymeniacidon perleve was occasionally found on the sides of silted boulders in the same locations. In the upper sub-tidal large clumps of the sea squirt (Tunicata) Ciona intestinalis (deep orange form) was present on brown algal covered boulders.
6.2.2.1.2 Aquatic Services Unit, UCC – Wider Sligo Harbour Intertidal Survey 2007 An assessment of the wider intertidal benthic community of Sligo Harbour, 2007 (carried out as part of an EIS for a proposed extension of the Sligo airport site). 30 stations were sampled over a large area of Sligo Harbour. The sampling regime included faunal cores (x5), 1 x 1m² quadrat described physically and biologically, 1 x 0.25m² quadrat was marked out and excavated to a depth of 20cm. Sediment was sieved in situ through a 5mm mesh sieve. Samples were taken for granulometric and organic carbon analysis.
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© Ordnance Survey Ireland. All rights reserved. Licence number 2010/20 CCMA/ Sligo County Council Figure 6.1: Map showing the location of the 30 intertidal stations surveyed by ASU in 2007.
6.2.2.1.3 Aquatic Services Unit, UCC - Intertidal Transect Survey 2007 The following section is taken from Aquatic Services Unit (2007). Aquatic Services Unit, University College Cork, was employed by the Department of Environment, Heritage and Local Government National Parks and Wildlife Service to carry out a survey of mudflats and sandflats across seven intertidal SACs (Special Areas of Conservation) around Ireland. As part of this survey, ASU undertook a detailed survey of intertidal habitats in Sligo Harbour – three transects were surveyed in Sligo Harbour itself. An additional four transects were surveyed in the adjoining SAC of Ballysodare Bay.
x Sligo Harbour Transect 1 Transect 1 (length 1930m) was located along the southern shore of Sligo Harbour. The shore was backed by a 2 – 3 meter high sea all, which connected directly to the main road. The upper section of the wall was characterised by the presence of lichens. At the base of the wall was a band of Enteromorpha ulva. This immediately gave way to a band of Fucus sp. attached to cobble within a sediment matrix. There was evidence of freshwater influence across the area, as a drain was present 10 metres from the start of the transect. The transect crossed a shallow channel approximately thirty metres from the start of the transect. The upper shore site was located within the intertidal from the sea wall to the shallow channel. The transect crossed an extensive mussel bank, which ran in a west-northwest direction across Cummeen Strand.
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This raised bank of mussels measured approximately 35 to 40m across at this point of the transect. The mid shore area of the transect was characterised by the presence of a significant amount of standing water (ranging from 50% to nearly 100% in places). Arenicola sp. casts were abundant at this shore height. A clam farm was present approximately 1½ km along he transect, and there was evidence of motorised vehicle use on the sediment. The low water site was taken immediately adjacent to the main channel. The strandline at Transect 1 returned 25 specimens of a single species, Orchestia gammarellus.
© Ordnance Survey Ireland. All rights reserved. Licence number 2010/20 CCMA/ Sligo County Council
Figure 6.2: Figure showing location of transects surveyed by ASU in Sligo Bay, 2007.
x 20m from the shoreline – T1 high shore station The sediment at this shore height has been classified as gravelly sand, with a significant amount of mud present. Standing water was evident at the site, covering 25% of the sediment surface. An anoxic layer was present just beneath the sediment surface, with evidence of a stone layer at a depth of 10cm. The station was located approximately 20 meters from a shallow channel which crossed the transect at the upper shore level. Macoma balthica shells were present on the sediment surface, and live specimens were
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recovered in the dig. Enteromorpha intestinalis and Fucus vesiculosus were present on the sediment surface. No Arenicola sp. casts were present within this shore height, although a single specimen was recovered in the 1m dig.
x 900m from the shoreline – T1, mid-shore station This sediment at this station was dominated by fine rippled sand. The anoxic layer was present at a depth of 2 cm, and presented as a black layer. A thick shell layer was present at a depth of 15cm. The sediment was under a significant amount of standing water (~85%). Fifteen Arenicola sp. casts were identified in the quadrat, although only two specimens were returned in the dig. In addition, large numbers of dead cockle shells were present on the sediment surface. Enteromorpha intestinalis and Fucus vesiculosus were present on the sediment surface. The station was located approximately 100m from the raised mussel bank.
x 1950m from the shoreline – T1, low shore station This station was taken immediately adjacent to the main channel at low water. Sediment at this site was characterised as rippled gravelly sand. There was no visible fauna present on the sediment surface, although the red algae Ceramium sp. was present. The depth of the anoxic layer at this site was 10cm. Approximately 30% of this site was under standing water, which was present between the ripples.
x Sligo Harbour Transect 2 Transect 2 (length 1990m) was located along the southern shore of Sligo Harbour running from the shoreline near Coney Island causeway in a north-northwest direction to the lighthouse on Oyster Island. The shore was backed by a narrow strip of saltmarsh and agrcultural land giving way to fine rippled sand with a layer of water over it. This gave way to an extensive area of rippled sand with extensive amounts of Cerastoderma edule and Arenicola marina casts on the sediment surface. At the low water site Lanice conchilega dominated. C. edule were also evident at low water.
The strandline at Transect 2 returned 9 specimens of Orchestia meditteranea and 5 specimens of Ligia oceanica.
x 185m from the shoreline – T2, upper shore station The sediment at this station was dominated by fine sand. The site was located in a water channel, with a very weak flow (100% cover). Dead cockle shells were present on the sediment surface. Arenicola casts were present on the sediment surface (3 per square meter) and 1 was returned in the dig. There was occasional Enteromorpha present at this shore height.
x 1460m from the shoreline – T2, mid-shore station The sediment at this station was characterised as rippled muddy sand. The anoxic layer was present at 4cm depth. There was a significant amount of standing water present within this area, with ~75% of the sediment covered with a thin layer of standing water. There were significant numbers of Cerastoderma edule on the sediment surface.
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Arenicola casts were present (2 per square meter) although none were returned in the dig. There were occasional clumps of Enteromorpha present at this shore height.
x 1990m from the shoreline – T2, low shore station This station was taken immediately adjacent to the main channel at low water. Sediment at this site was characterised as rippled fine sand. The anoxic layer at this site was 15cm deep. Standing water (10%) was present between the ripples on the sediment surface. Lanice conchilega and Cerastoderma edule were abundant and algae were present in significant numbers on the sediment surface (Enteromorpha and Ceramium).
x Sligo Harbour Transect 3 Transect 3 (length 135m) was located along the outer part of Sligo Harbour between the mainland, near Sligo Airport and Coney Island. There was a channel running between Coney Island and the mainland. The shore was backed by a dune system, giving way to a cobble/boulder with a large amount of algal drift at the uppermost part of this. This leads to a soft mobile sand area with occasional clumps of Fucus vesiculosus and Fucus serratus. At 50 meters this sand becomes more firm. Arenicola casts were present from this location to the low water site. At 60 meters, the sediment becomes wet, and Enteromorpha became more abundant. The bottom of the transect is characterised by shell and sand with large numbers of Enteromorpha. On both sides of this transect, the shoreline was dominated by a fucoid covered boulder shore, with limited soft sediment in evidence.
The strandline at transect 3 returned 94 specimens of a single species, Orchestia gammarellus.
x 20m from the shoreline – T3, upper shore station The sediment at this station was characterised as rippled gravelly sand. The sediment was very dry and there was no evidence of fauna on the sediment surface. The anoxic layer was not visible at this site.
x 60m from the shoreline – T3, mid-shore station The sediment at this station was dominated by wet sand. The anoxic layer was present just beneath the sediment surface. Enteromorpha was present on the sediment surface with occasional clumps of Fucus present along the shore height. Arenicola casts were present at this shore height (6 per square meter), although only 1 specimen was returned in the dig.
x 130m from the shoreline – T3, lower shore station This station as taken immediately adjacent to the main channel at low water. Sediment at this site was characterised as gravelly sand. The anoxic layer was present just below the sediment surface. The sediment surface was dominated by the fucoid algae Fucus serratus, F. vesiculosus, with Enteromorpha present in significant numbers. Arenicola casts were present (1 per square metre) and a single specimen was returned in the dig.
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6.2.2.1.4 BIOMAR and Office of Public Works intertidal surveys A number of intertidal areas were surveyed by the BIOMAR team and Office of Public Works in 1996 (Picton & Costelloe, 1998). These are shown in Figure 6.3. (Site two was a subtidal station surveyed using SCUBA equipment off Ballyconnell Point, South Donegal Bay). The data collected at these stations give a good indication of the variation of floral and faunal communities to be found along this stretch of coast. Sites were surveyed in detail with substrates, site exposures, habitats, biotopes and species present and abundance scales all recorded. Sediment cores were taken at several of the sites where sedimentary habitats dominated. (Detailed data for each of these stations are presented in Appendix 4A of the Environmental Appraisal).
Figure 6.3: Location map for the sites surveyed by BIOMAR and OPW teams in Sligo Bay 1996.
Sites 6, 7 and 8 are in closest proximity to the dredging work proposed for Sligo Harbour. Site 6 was located in an exposed area at Rosses Point on the western edge of the small peninsula separating Sligo Harbour from Drumcliff Bay. This is a gently sloping beach composed of fine, well-sorted sand backed by low dunes with little surface evidence of life. Sampling showed the presence of polychaetes (Angulus tenuis) and bivalves (juvenile Donax sp.). Brown shrimp (Crangon sp.) were present in a midshore runnel.
Site 7 was located in a very sheltered area at Dorrins Strand on the south shore of Sligo Harbour. It ran from the southern end of the roadway to Coney Island across the large sand flat to the edge of the main channel to the south of Oyster Island (approximately 2km). The
IBE00440/EIS01/June ‘12 6-9 Sligo Harbour Dredging Environmental Appraisal Report Intertidal and Benthic Flora and Fauna & Marine Mammals shore was backed by grassland and a narrow strip of salt marsh giving way to rippled fine sand with a shallow layer of standing water. A wide (100m) shallow channel (2-5cm), split by a sandbar, was located approximately 100m from the shore. The bed of the channel was soft rippled sand with frequent cockles, Arenicola sp. casts and frequent clumps of Enteromorpha sp. on the surface. To the north of this channel the sand was firmand, for the most part, covered with a layer of standing water and had an anaerobic layer 1-2cm below the surface. A. marina castings were visible on the surface at densities of 1-9 per metre squared with Cerastoderma edule present in the top 10-15 cm of sediment at densities of 1- 5 per metre squared. Fine tube worms were also common. At 1.75km out from the shore the surface rose gently to the top of a large sandbank running adjacent to the main channel. The sediment on the bank was coarse and dry with an ARPD layer greater than 25cm below the surface. At 2km out from the shore the sandbank sloped down to the main channel with a dense bed of Lanice conchilega and filamentous brown algae 50m from the channel. Ulva sp. was also present attached to worm tubes with an anoxic layer 10cm below the sediment surface in the coarse sand and broken shell at the channel edge.
Site 8 was located at Cummeen Strand in Sligo Harbour. It was taken from the sea wall next to Gibraltar Point on the southern shore to the main channel on the north side of the bay. This transect was approximately 2km long and crossed a small channel about 50m from the sea wall. It started with an area of mud, gravel and stone sloping gently to the shallow channel and was characterised by Enteromorpha spp., Ulva sp., Fucus ceranoides and Scrobicularia plana. Beyond the channel the beach had a short steep upward slope characterised by small burrows containing very small gastropods. The beach appeared flat for 600m and was characterised by Arenicola marina for the first 300m and then by a mixture of A. marina for the first 300m and then by a mixture of A. marina and Cerastoderma edule. Between 600m and 700m there was a dense mussel bed with mussel and dead cockle shells banded together on the shoreward side. Some F. vesiculosus and Enteromorpha sp. were present on the bed. Seaward of this the shore sloped very gently to the channel and was covered with standing water 1.5cm deep with small cockles present for the next 200m. After this, cockles were occasional as were A. marina casts. The sand was very flat with small tubes present. Close to the channel the sand became rippled and algae (in particular Polysiphonia sp. or Ceramium sp.) were attached to dead cockle shells. Close to the channel the sand became rippled and algae, in particular Polysiphonia sp. or Ceramium sp. were attached to dead cockle shells. Lanice conchilega were frequent sat the channel edge. Across most of the beach Enteromorpha spp. were present attached to dead shells. The anoxic layer varied from 1 to 10cm below the sediment surface but was generally 1cm to 5cm beneath the surface. Clam beds were present on the beach.
6.2.2.2 Subtidal habitats
6.2.2.2.1 BIOMAR and Office of Public Works subtidal surveys A single subtidal station in close proximity to the proposed work was surveyed by the BIOMAR team in 1996. This site was located off Ballyconnell Point and was adjacent to the very exposed headland near the entrance to inner Sligo Bay. The dive documented a large subtidal cliff with abundant jewel anemones (Corynactis viridis). This stretched from 13m to approximately 26m BCD. Stepped limestone bedrock was documented at the bottom of the
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Subtidal habitat in Sligo Harbour is very limited in areal extent when compared with intertidal habitat and is largely confined to the deeper channels present – the primary areas being the navigation approach channel along the northern shore of the harbour and the channel surrounding Oyster Island.
6.2.3 Field Survey – Aquafact 2010
Numerous intertidal surveys have been carried out in Sligo Harbour in recent years (see section 6.2.2.1). Field surveys were undertaken in Sligo Harbour by Aquafact in 2010 specifically for the proposed dredging scheme.
The objective of the intertidal survey was to carry out: x A general walkover of the harbour, incorporating: The shore of the navigation channel areas of mussel bank clam production areas areas of Zostera bed. x In addition to: Documenting existing habitats along the route with notes and photographs.
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Figure 6.4: Map showing recent intertidal survey effort, Sligo Harbour. (The route of the current intertidal walkover is shown in red. Survey stations & transects carried out by ASU in 2005 and 2007 are also shown. Orthorectified images © OSI
Figure 6.5: Location of observations made during the walkover survey, October 2010.
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6.2.3.1 Materials and Methods - 2010 The survey was carried out on 7th- 8th October, 2010. Cloud cover varied between 3/8ths and 7/8ths. The southern shore was accessed at the Scarden More landfall of the Coney Island causeway. A four wheel drive vehicle was used to transit the shore during the work. A Trimble® GeoXT™ handheld mapping unit was used to record the track followed during the survey work and to document various features encountered. This unit provides real time sub- metre accuracy. Digital photographs were taken during the survey. The camera time was synchronised with UTC to allow matching of images to their locations.
Bird species present on the shore were noted during the survey. Photographs and notes were taken throughout the survey work.
6.2.3.2 Results 2010
6.2.3.2.1 Anthony Lynch - Clam site - Northern Walkover This survey covered the area shown in Figure 6.5. Notes and photographs were taken during the walkover along with GPS coordinates at features of interest. For the most part the shoreline was characterised by the presence of clean fine-medium sand with a variable shell fraction.
The following sections (denoted by letters A-N) correspond with each point marked by the letters shown in Figure 6.5 showing the intertidal location of documented observations. A. The beach here was composed of fine sand. Numerous wheeled clam trestles were noted. Small stands of algae (primarily Enteromorpha sp.) were recorded attached to larger shell fragments on the shore. Small amounts of fucoid algae (Fucus vesiculosus) were found attached to the trolleys themselves.
Figure 6.6: Trestles, clam farm site, Sligo Harbour, 07th October 2010.
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Figure 6.7: Commercial clam park. South west Sligo Harbour, 07th October 2010.
B. Mussel bank 1. This area was characterised by a mussel bed. There was a mix of blue mussel and clams. Algal cover was noted around the margins of the bed.
Figure 6.8: Mussel bed, Sligo beach, 07th October 2010.
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Figure 6.9: Mussel bed, close view. A mix of blue mussel and clams.
Figure 6.10: Algae (primarily fucoids) on mussel bank, Sligo Harbour, October 2010.
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Figure 6.11: Lugworm feeding casts, near mussel bank, Sligo harbour, October 2010.
C. Seagrass bed. A seagrass bed was noted here. Some algal cover (primarily Enteromorpha sp.) and lugworm casts (Arenicola sp). were noted.
Figure 6.12: Seagrass and lugworm feeding casts, Sligo Harbour, October 2010.
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D. Filamentous algal mat over muddy sand flat. The intertidal was quite soft in this area. An extensive mat of filamentous algae was noted (primarily Vaucheria sp.). A shallow tidal channel ran through this area.
Figure 6.13: Vaucheria sp. mat over intertidal muddy fine sand flat, Sligo Harbour, 07th October 2010.
E. Geese feeding on intertidal flat. A flock of gooses was noted feeding in the intertidal zone. As well as supporting a seagrass bed of variable density this area had quite a high density of lugworm feeding casts.
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Figure 6.14: Gooses feeding on the intertidal sand flat, 07th October 2010.
F. Fyke net on pole in shallow tidal channel. A single fyke net on a pole was noted at the centre of a shallow tidal channel in the sand.
Figure 6.15: Fyke net on pole, Sligo Harbour, 07th October 2010
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G. Mussel bank 2. Another dense area of mussel bed was recorded in this area.
Figure 6.16: Mussel bank, Sligo Harbour, 07th October 2010.
H. Mussel bank 3. A third extensive area of mussel bank was recorded.
Figure 6.17: Mussel bank Sligo Harbour, 07th October 2010.
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I. Commercial clam park (Noel Carter’s). Clam cultivation frames and plots in clean, rippled fine sands. Some algae were present – Enteromorpha sp. attached to larger shell fragments etc. on the sand flat, and fucoids on any available hard surfaces (clam cultivation hardware for example).
Figure 6.18: Commercial clam park (Noel Carter’s). Sligo Harbour, 07th October 2010
Figure 6.19: Clam cultivation hardware, Sligo Harbour, 07th October 2010.
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Figure 6.20: Rippled fine sand surrounding clam cultivation site, 07th October 2010.
J. Intertidal sands with filamentous algal growth.
Figure 6.21: Intertidal area with filamentous algal growth, Sligo Harbour, October 2010
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6.2.3.2.2 Sligo Intertidal – Navigation Channel Area A walkover survey was conducted in the intertidal zone to the north of the navigation channel in Sligo Harbour at low water on 8th October 2010. This survey covered the area shown in Figure 6.22. Notes and photographs were taken during the walkover along with GPS coordinates at features of interest.
Orthophotography © Ordnance Survey Ireland. All rights reserved. Licence number 2010/20 CCMA/ Sligo County Council
Figure 6.22: Points of interest near the navigation channel walkover area 7th October 2010.
The following sections (denoted by letters K-N) correspond with each point marked by the letters shown in Figure 6.22 showing the intertidal location of each documented observation.
K. Intertidal sand flat with sparse algal cover. The sediment surface here was composed of quite firm, rippled fine sand. Occasional fragments of shell gravel were noted. Sparse algal cover (mostly Enteromorpha sp.) was recorded.
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Figure 6.23: Rippled fine sand with some algae, 08th October 2010.
Figure 6.24: Channel marker, Sligo harbour, 08th October 2010.
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Figure 6.25: Base of channel marker & training wall, Sligo harbour, 08th October 2010.
L. Clean rippled sand flat. An area of clean, rippled, tide-swept fine sands.
Figure 6.26: Intertidal sand flat, Sligo Harbour, 08th October 2010.
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M. View along navigation channel towards Sligo.
Figure 6.27: View towards Sligo along navigation channel, 08th October 2010.
N. A close up view of the harbour training wall. Species recorded included algae (primarily Fucus vesiculosus), barnacles (Semibalanus balanoides), limpets (Patella vulgata) and mussels (Mytilus edulis). The intertidal flat at the base of this wall sloped very gently towards the navigation channel. The sediments here were composed of muddy fine sand. Small, low ridges of stabilised sediment supporting filamentous algal growth were noted. Numerous lugworm (Arenicola sp.) feeding casts were noted.
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Figure 6.28: Encrusting flora and fauna on the northern Sligo harbour navigation channel training wall, Sligo Harbour, 08th October 2010.
Figure 6.29: Muddy sand flat adjacent to training wall, Sligo harbour approach channel, 08th October 2010.
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6.2.3.3 Infaunal survey – Marine benthos 2010
6.2.3.3.1 Sampling Procedure & Processing To carry out the infaunal survey of Sligo Harbour, Aquafact sampled a total of 15 stations. These stations can be seen in Figure 6.30. Table 6.1 shows the station coordinates.
Sampling was carried out on the 6th and 7th October 2010 from Aquafact’s RIB. Stations were located using DGPS and this positioning method is accurate to within ca. 1m. A 0.025m2 grab sampler was used to collect the benthic samples. Three replicate samples were taken at each of the 15 stations. Data on each sample, e.g. station number, date, time, depth of sediment, surface features and visible macrofauna were logged in a field notebook. The faunal returns were sieved on a 1mm mesh sieve, stained with Rhodamine dye, fixed with 10% buffered formalin and preserved in 70% alcohol. Samples were then sorted under a microscope (x 10 magnification), into four main groups: Polychaeta, Mollusca, Crustacea and others. The ‘others’ group consisted of echinoderms, nematodes, nemerteans, cnidarians and other lesser phyla. The taxa were then identified to species level where possible.
An additional sample was taken at Stations 1 to 14 for sediment granulometric analysis. The sediment samples were taken through the opening on the top of the grab. Samples were also taken for determination of total organic carbon content. All samples were stored immediately in a cold room on board the vessel and were frozen at –20oC on return to the lab.
Particle size analysis was carried out using the traditional granulometric approach. Traditional analysis involved the dry sieving of approximately 100g of sediment using a series of Wentworth graded sieves. The process involved the separation of the sediment fractions by passing them through a series of sieves. Each sieve retained a fraction of the sediment, which were later weighed and a percentage of the total was calculated.
Table 6.2 shows the classification of sediment particle size ranges into size classes. Sieves, which corresponded to the range of particle sizes, were used in the analysis.
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Extract from Admiralty Chart 2852 © Crown Copyright UKHO. Not for navigational use
Figure 6.30: Map showing subtidal sampling locations
Table 6.1: Subtidal station co-ordinates.
Station Easting Northing Longitude Latitude 1 163931.8 339745 -8.55414 54.3051 2 165748.2 339095 -8.52616 54.2994 3 167086.5 338473.6 -8.50553 54.2939 4 160270.5 341198.1 -8.61058 54.3179 5 165729 339486.9 -8.5265 54.3029 6 168453.5 337536.8 -8.48444 54.2856 7 162115.5 338540.5 -8.58189 54.2942 8 164677.5 339286.2 -8.54263 54.301 9 166369.5 339066.3 -8.51661 54.2992 10 167392.4 338339.8 -8.50082 54.2927 11 167946.9 337374.3 -8.4922 54.2841 12 165662.1 337278.7 -8.52727 54.2831 13 166057.4 338759.7 -8.52137 54.2964 14 165018.3 338818.4 -8.53734 54.2969 15 159843.2 340666.7 -8.61707 54.3131
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Table 6.2: The classification of sediment particle size ranges into size classes Range of Particle Size Classification Phi Unit <63µm Silt/Clay >4 Ø 63-125 µm Very Fine Sand 4 Ø, 3.5 Ø 125-250 µm Fine Sand 3 Ø, 2.5 Ø 250-500 µm Medium Sand 2 Ø, 1.5 Ø 500-1000 µm Coarse Sand 1 Ø, 1.5 Ø 1000-2000 µm Very Coarse Sand 0 Ø, -0.5 Ø >2000 µm Gravel -1 Ø, -1.5 Ø, -2 Ø, -3 Ø, -4 Ø (adapted from Buchanan, 1984)
6.2.3.3.2 Data Processing All replicates for each station were combined to give a total abundance for each station prior to analyses. A data matrix of all the combined faunal abundance data was compiled and used for statistical analyses. The faunal analysis was carried out using the PRIMER ® (Plymouth Routines in Multivariate Ecological Research) programme.
Univariate statistics in the form of diversity indices were calculated on the combined replicate data. The following diversity indices were calculated: 1) Margalef’s species richness index (D), (Margalef, 1958). S 1 D log2N where: N is the number of individuals S is the number of species
2) Pielou’s Evenness index (J), (Pielou, 1977). H' (observed) J = ' Hmax ' where: Hmax is the maximum possible diversity, which could be achieved if all species were
equally abundant (= log2S)
3) Shannon-Wiener diversity index (H'), (Pielou, 1977). H' = - S p (log p ) ¦i=1 i 2 i th where: pI is the proportion of the total count accounted for by the i taxa
Species richness is a measure of the total number of species present for a given number of individuals. Evenness is a measure of how evenly the individuals are distributed among different species. The diversity index incorporates both of these parameters. Richness ranges from 0 (low richness) to 12 (high richness), evenness ranges from 0 (low evenness) to 1 (high evenness), diversity ranges from 0 (low diversity) to 5 (high diversity).
The PRIMER ® manual (Clarke & Warwick, 2001) was used to carry out multivariate analyses on the station-by-station faunal data. It must be noted here that the species that were present only once or twice in the survey were excluded from the multivariate analysis.
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All species/abundance data were fourth root transformed and used to prepare a Bray-Curtis similarity matrix in PRIMER ®. The fourth root transformation was used in order to down- weigh the importance of the highly abundant species and allow the mid-range and rarer species to play a part in the similarity calculation. The similarity matrix was then used in classification/cluster analysis. The aim of this analysis was to find “natural groupings’ of samples, i.e. samples within a group that are more similar to each other, than they are similar to samples in different groups (Clarke & Warwick, loc. cit.). The PRIMER ® programme CLUSTER carried out this analysis by successively fusing the samples into groups and the groups into larger clusters, beginning with the highest mutual similarities then gradually reducing the similarity level at which groups are formed. The result is represented graphically in a dendrogram, the x-axis representing the full set of samples and the y-axis representing similarity levels at which two samples/groups are said to have fused. The CLUSTER programme was set to include a series of ‘similarity profile’ (SIMPROF) permutation tests, which look for statistical evidence of genuine clusters in samples which are a priori unstructured. SIMPROF performs tests at every node of a completed dendrogram, that the group being sub-divided has ‘significant’ internal structure. The test results are displayed in a colour convention on the dendrogram plot (samples connected by red lines cannot be significantly differentiated).
The Bray-Curtis similarity matrix was also subjected to a non-metric multi-dimensional scaling (MDS) algorithm (Kruskall & Wish, 1978), using the PRIMER ® program MDS. This programme produces an ordination, which is a map of the samples in two- or three- dimensions, whereby the placement of samples reflects the similarity of their biological communities rather than their simple geographical location (Clarke & Warwick, 2001). With regard to stress values, they give an indication of how well the multi-dimensional similarity matrix is represented by the two-dimensional plot. They are calculated by comparing the interpoint distances in the similarity matrix with the corresponding interpoint distances on the 2-d plot. Perfect or near perfect matches are rare in field data, especially in the absence of a single overriding forcing factor such as an organic enrichment gradient. Stress values increase not only with the reducing dimensionality (lack of clear forcing structure), but also with increasing quantity of data (it is a sum of the squares type regression coefficient). Clarke and Warwick (loc. cit.) have provided a classification of the reliability of MDS plots based on stress values, having compiled simulation studies of stress value behaviour and archived empirical data. This classification generally holds well for 2-d ordinations of the type used in this study and the threshold stress values are shown below:
x Stress value < 0.05: Excellent representation of the data with no prospect of misinterpretation. x Stress value < 0.10: Good representation, no real prospect of misinterpretation of overall structure, but very fine detail may be misleading in compact subgroups. x Stress value < 0.20: This provides a useful 2-d picture, but detail may be misinterpreted particularly nearing 0.20. Stress value 0.20 to 0.30: This should be viewed with scepticism, particularly in the upper part of the range, and discarded for a small to moderate number of points such as < 50. x Stress values > 0.30: The data points are close to being randomly distributed in the 2- d ordination and not representative of the underlying similarity matrix.
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Each stress value must be interpreted both in terms of its absolute value and the number of data points. In the case of this study, the moderate number of data points indicates that the stress value can be interpreted more or less directly. While the above classification is arbitrary, it does provide a framework that has proved effective in this type of analysis.
SIMPER analysis was then carried out on the transformed data to determine the dominant/characterising species within each group identified by the CLUSTER/SIMPROF analysis.
6.2.3.3.3 Results
FAUNA The taxonomic identification of the benthic infauna across all 15 stations sampled in Sligo Harbour yielded a total count of 110 species accounting for 2,303 individuals, ascribed to 8 phyla. A complete listing of these species abundance is provided in Appendix 4C, which is located on the accompanying data DVD-ROM.
Of the 110 species enumerated, 43 were annelida (segmented worms), 29 were crustaceans (crabs, shrimps, prawns), 32 were molluscs (mussels, cockles, snails etc.), 2 species were arthropods (insects, spiders), 1 species was a nematode (round worm), 1 was a nemertean (ribbon worm), 1 was a chelicerata (sea spider) and 1 species was a plathyhelminth (flatworm).
x Univariate Analyses Univariate statistical analyses were carried out on the combined replicate station-by- station faunal data. The following parameters were calculated and can be seen in Table 6.3: species numbers, number of individuals, richness, evenness and diversity. Species numbers ranged from 2 (Stations 5 and 15) to 35 (Station 1). Number of individuals ranged from 2 (Station 5) to 1073 (Station 7). Richness ranged from 0.25 (Station 15) to 6.97 (Station 4). Evenness ranged from 0.1 (Station 7) to 1.00 (Stations 5 and 10). Diversity ranged from 0.13 (Station 15) to 4.39 (Station 4).
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Table 6.3: Diversity indices for the 15 stations sampled in Sligo Harbour. Station Species Individuals Richness Evenness Diversity 1 35 139 6.89 0.84 4.29 2 5 11 1.67 0.86 2.00 3 28 320 4.68 0.54 2.58 4 31 74 6.97 0.89 4.39 5 2 2 1.44 1.00 1.00 6 11 170 1.95 0.39 1.36 7 8 1073 1.00 0.10 0.29 8 5 21 1.31 0.63 1.47 9 32 184 5.94 0.74 3.68 10 6 6 2.79 1.00 2.58 11 3 4 1.44 0.95 1.50 12 14 169 2.53 0.52 1.99 13 7 24 1.89 0.79 2.21 14 7 50 1.53 0.45 1.26 15 2 56 0.25 0.13 0.13
x Multivariate Analyses The dendrogram and the MDS plot can be seen in Figure 6.31 and Figure 6.32 respectively. Five groupings were identified through the SIMPROF programme. These are as follows: Group a: Stations 1, 3, 6, 7, 9, 11 and 12 Group b: Stations 2, 5 and 10 Group c: Station 15 Group d: Station 4; and Group e: Stations 8, 13 and 14.
Groups b and e consisted of sandy stations located within or close to the navigation channel in the harbour. Group a consisted of sand, gravelly muddy sand, sandy gravel and slightly gravelly muddy sand stations and all were located within the harbor area. Stations 4 (slightly gravelly sand) and station 15 (no granulometric data) were located outside the harbor and grouped separately from all the other stations.
Group a formed at a similarity level of 12.5%. The 7 stations in this group accounted for 80 different species comprising 2,059 individuals. Of the 80 species present, 37 were present more than twice. Five species accounted for 80% of the abundance in this group: the gastropod mollusc Hydrobia ulvae (1,326 individuals; 64.4%), the oligochaete Tubificoides benedii (162 individuals; 7.9%), the bivalve mollusc Parvicardium pinnulatum (3 individuals; 3.6%), the barnacle Balanus crenatus (65 individuals; 3.2%) and the oligochaete Tubificoides pseudogaster agg. (31 individuals; 1.5%). This group had an average within group similarity of 21.33% according to SIMPER analysis (See Table 6.4).
Group b formed at a similarity level of 50.36%. The 3 stations in this group accounted for 8 different species comprising 19 individuals. Of the 8 species present, 3 were
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present more than twice. Three species accounted for 74% of the abundance in this group: the polychaete Scoloplos armiger (6 individuals; 32%); the bivalve mollusc Tellina sp. (5 individuals; 26%) and the polychaete Eteone longa agg. (3 individuals; 16%). This group had an average within group similarity of 50.61% according to SIMPER analysis (See Table 6.4).
Group c consisted of station 15 only. This station contained 2 species and 56 individuals. The bivalve mollusc Donax vittatus accounted for 55 of the individuals (98% of the abundance). Within group similarity could not be calculated for this group because it only contained 1 station.
Group d consisted of station 4 only. This station contained 31 species and 74 individuals. Of the 31 species present, 14 were present more than twice. The bivalve mollusc Donax vittatus was also the dominant species at this station but in significantly lower numbers than at station 15 (Group c). Four species accounted for 46% of the abundance in this group: Donax vittatus (12 individuals; 16%), the polychaetes Nephtys cirrosa (9 individuals; 12%) and Scoloplos armiger (7 individuals; 9%) and the bivalve mollusc Tellina sp. (6 individuals; 8%). Within group similarity could not be calculated for this group because it only contained 1 station.
Group e formed at a similarity level of 49.22%. The 3 stations in this group accounted for 12 different species comprising 95 individuals. Of the 12 species present, 4 were present more than twice. These four species accounted for 88% of the faunal abundance: the bvivalve mollusc Tellina tenuis (64 individuals; 67%), the polychaete Nephtys cirrosa (13 individuals; 14%) and the molluscs Retusa obtusa (4 individuals; 4%) and Mytilidae sp. (3 individuals; 3%). This group had an average within group similarity of 55.88% according to SIMPER analysis (see Table 6.4). Table 6.4 also shows the characterizing species for each group.
These delineations were also preserved in the MDS plot. The stress value of the MDS ordination is 0.1; which results in a good representation with no real prospect of misinterpretation of the overall structure, but the very fine detail may be misleading in compact subgroups.
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Figure 6.31: Dendrogram showing the natural grouping of each station sampled in Sligo Harbour.
Figure 6.32: MDS ordination showing the natural grouping of each station sampled in Sligo Harbour.
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Table 6.4: SIMPER Results Group a Average similarity: 21.33 Species Av.Abund Av.Sim Sim/SD Contrib% Cum.% Hydrobia ulvae 2.23 3.99 0.76 18.69 18.69 Tubificoides benedii 1.34 3.04 0.79 14.23 32.92 Cardiidae sp. (juv) 0.95 2.62 0.79 12.3 45.22 Tubificoides pseudogaster agg 1.08 2.09 0.87 9.79 55.01 Parvicardium pinnulatum 1.03 1.55 0.49 7.27 62.27 Pygospio elegans 0.86 1.39 0.58 6.51 68.78 Capitella sp. 0.67 1.08 0.59 5.06 73.85 Macoma balthica 0.6 1.03 0.59 4.84 78.69 Cerastoderma edule 0.69 0.83 0.6 3.9 82.59 Eteone longa aggregate 0.64 0.56 0.39 2.62 85.21 Abra alba 0.29 0.49 0.22 2.32 87.53 Aoridae sp. 0.51 0.42 0.39 1.99 89.51 Platynereis dumerilii 0.57 0.34 0.4 1.59 91.11 Group b Average similarity: 50.61 Species Av.Abund Av.Sim Sim/SD Contrib% Cum.% Eteone longa aggregate 1 22.49 4.65 44.43 44.43 Scoloplos armiger 1.14 22.49 4.65 44.43 88.86 Tellina sp. (juv) 0.8 5.64 0.58 11.14 100 Group d - Less than 2 samples in group Group e Average similarity: 55.88 Species Av.Abund Av.Sim Sim/SD Contrib% Cum.% Tellina tenuis 2.09 23.42 10 41.91 41.91 Nephtys cirrosa 1.41 15.73 6.23 28.16 70.07 Mytilidae sp. (juv) 1 12.41 11.19 22.22 92.28 Group c - Less than 2 samples in group
SEDIMENT The results from the traditional granulometric analysis can be seen in Table 6.5. Figure 6.33 shows these data in graphical form. The sediment sampled during the survey was classified as sand, slightly gravelly sand, sandy gravel, slightly gravelly muddy sand and gravelly muddy sand according to Folk (1954). Figure 6.34 shows the sediment type according to Folk’s (1954) classification.
The majority of stations were classified as sand (Stations 2, 3, 5, 7, 8, 10, 12, 13 and 4) (See Figure 6.33 and Figure 6.34). All of the stations sampled within the harbour area (i.e. inside Oyster Island) were classified as sand with the exception of the two inner stations (stations 11 and 6) and station 1 located approximately 300m northeast of Oyster Island. Station 1 was classified as sandy gravel, station 6 as slightly gravelly muddy sand and station 11 as gravelly muddy sand. Outside the harbour area, Station 4 was classified as slightly gravelly sand.
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Station 1 contained the highest percentage of gravel (68.5%). Station 9 contained the highest percentage of very coarse sand (10.2%) and coarse sand (8.3%). Station 14 contained the highest medium sand fraction (33.5%). Station 12 contained the highest fine sand (89.3%). Station 2 contained the highest very fine sand (15.6%) and station 11 contained the highest silt-clay (16.8%).
Table 6.5: Granulometry results for the 14 stations sampled in Sligo Harbour (as percentage weight of the total sample).
Stn Gravel Very Coarse Medium Fine Very Fine Silt- Folk (1954) (%) Coarse Sand (%) Sand (%) Sand Sand (%) Clay Sand (%) (%) (%) 1 68.5 7.7 4.6 4 9.5 4.9 0.9 Sandy gravel 2 0.7 1.1 1.7 4.8 75 15.6 1 Sand 3 0.2 0.3 0.5 2.7 81.7 9.3 5.2 Sand 4 3.4 1.4 2.3 8.1 81.7 3.1 0.1 Slightly gravelly sand 5 0.5 0.6 1.5 3.8 77.3 14.1 2.1 Sand 6 1.3 1.4 1.5 3.6 58.4 20.9 13 Slightly gravelly muddy sand 7 0.1 0.3 0.4 6.1 85.3 7.2 0.5 Sand 8 0.8 2.4 6.4 26.8 60.2 3.2 0.1 Sand 9 51 10.2 8.3 9.8 15.4 4 1.2 Sandy gravel 10 0 0.1 0.3 5.1 89.2 5.3 0 Sand 11 6.8 2.9 2 3.1 46.5 22 16.8 Gravelly muddy sand 12 0.2 0.3 0.6 3.3 89.3 5.8 0.5 Sand 13 0.2 1.7 3.3 13.4 79.5 1.8 0 Sand 14 0.6 1.8 5.4 33.5 56.5 2.2 0 Sand *The particle size ranges for each classification (gravel, very coarse sand, coarse sand, medium sand, fine sand, very fine sand and silt clay) is adapted from Buchanan (1984) and can be seen in Table 6.2. The classifications according to Folk (1954) are based on varying percentages of gravel, sand and silt-clay.
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Extract from Admiralty Chart 2852 © Crown Copyright UKHO. Not for navigational use
Figure 6.33: Sediment grain size data
Extract from Admiralty Chart 2852 © Crown Copyright UKHO. Not for navigational use
Figure 6.34: Sediment type according to Folk (1954)
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ORGANIC CARBON Sediment samples were taken for organic carbon analysis. Samples were sent to SAL (Scientific Analysis Laboratories, Manchester, England – a UKAS and UK Environment Agency MCERTS accredited laboratory) for total organic Carbon (TOC) determination.
Table 6.6: Sediment organic carbon results for the fourteen stations surveyed off Sligo, 6th October, 2010.
Station
Determinand Units 1 2 3 4 5 6 7 8 9 10 11 12 13 14
TOC % 2.0 2.1 1.5 0.3 1.6 3.8 1.6 1.7 3.1 2.6 5.2 1.5 1.1 1.6
6.2.4 Sligo Harbour Intertidal and Subtidal Flora and Fauna - Predicted Impacts
The impact assessment has been undertaken with due regard to the EPA’s “Advice Notes on Current Practice” (2003); the EPA’s “Guidelines on the information to be contained in Environmental Impact Statements” (2003); with reference to the discipline-specific Institute of Ecology and Environmental Management’s “Guidelines for Ecological Impact Assessment“ (IEEM, 2006) and the National Roads Authority (NRA)’s “Guidelines for Ecological Impact Assessment”.
Criteria for assessing impact level have been derived from those set out in Appendix 4 of the NRA discipline specific EcIA Guidelines (2004), but expanded in order to be able to address issues such as habitat quality and are shown in Appendix 4D of this report. Terminology for impact significance and duration follows that set out by the EPA (2003) in its generic guidelines.
6.2.4.1 Consideration of Significance In terms of significance, the NPWS Guidance (2010 Rev) uses an EC definition as follows:..”any element of a plan or project that has the potential to affect the conservation objectives of a Natura 2000 site, including its structure and function, should be considered significant (EC, 2006)”. Other guidance documents also discuss significance criteria, some in more detail than others. The Dutch Guidance1 (2004) discusses a number of criteria in relation to habitats and species population.
In general, significance indicators might include: x impact on Annex I habitat (including loss or reduction in size - percentage relative to the overall area of the habitat in the Natura site; impairment of function); x fragmentation of habitat or population (depending upon the duration or permanence); x disturbance (noise, light etc. - distance, duration); x effect on species populations (direct or indirect damage to size, breeding patterns etc);
1 Translated from Publication of Dutch State Printers in book:’Praktijkboek Habitattoets’ , 2004 (F. Neumann en H. Woldendorp, SDU)
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x changes in water quality.
To summarise the significance issue, it is useful to quote from Morris (2008) who describes significance in the context of the Habitats Directive as follows: “...Within the Habitats Regulations, significance is quite different. It is used as a coarse filter and the test is a question over the possibility that there will be a significant effect on a key receptor that determines the conservation status of a European site. Thus, determining whether there will be a ‘likely significant effect’ does not imply that there will be such an effect or even that such an effect is more likely than not; it simply flags the need to test the issues and then make a judgement of the pathways and mechanisms imposed by a project on the designated wildlife interest. This test best equates to the screening and scoping opinions sought for an EIA but is confined to the Natura 2000 and Ramsar interest rather than wider environmental or nature conservation issues”.
In order to assess the likely impacts and ascertain whether a significant impact on the integrity of the Natura site(s) is likely to occur as a result of the proposed development, should the appropriate assessment process deemed to be required, it is necessary to consider what constitutes the integrity of a Site as referred to in Article 6(3). The document Managing Natura 2000 Site, The provisions of Article 6 of the ‘Habitats’ Directive 92/43/EEC (2000) gives clear guidance in this regard and states: “The integrity of the site involves its ecological functions. The decision as to whether it is adversely affected should focus on and be limited to the site’s conservation objectives”.
Integrity has been discussed and defined in various ways in guidance documentation and the literature. For example, Treweek (1999) discusses biological integrity and ecosystem health, and refers to three generally accepted criteria: systematic indicators of ecosystem functional and structural integrity; ecological sustainability or resilience (relating to the ability of a system to withstand “natural” or anthropogenic stresses); and absence of detectable symptoms of ecosystem disease or stress. A similar, but less academic, approach is adopted by the various guidance documents with a number of definitions proposed. The essence of the concept of ecological integrity is distilled in the following definition from Planning Policy Statement 9 (UK Department of Environment, 1994 – now superseded by PP9, 2005): “coherence of the site’s ecological structure and function, across its whole area, or the habitats, complex of habitats and/or populations of species for which the site is or will be classified”.
6.2.4.2 Potential impacts on Natura 2000 sites – impacts prediction Criteria for assessing impact level have been derived from those set out in Appendix 4 of the NRA EcIA Guidelines (2004) criteria and expanded in order to be able to address issues such as habitat quality. Terminology for impact significance and duration follows that set out by the EPA (2003). The potential impact magnitude described in the following sections, without mitigation, is negative unless otherwise stated as being positive or neutral. Where the impact is stated as being localised, it refers to the immediate area of impact.
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6.2.4.2.1 Potential impacts on Cummeen Strand/Drumcliff Bay SAC
Potential impacts on habitats in Cummeen Strand/Drumcliff Bay SAC
Qualifying marine habitats for the Cummeen Strand/Drumcliff Bay SAC: The proposed dredging scheme will have a direct impact on the Mudflats and Sand flats/Estuarine habitats in Sligo Harbour. This impact may be divided into two parts: a) The removal of sediments from the estuarine environment b) The suspension of sediments in the water column as a result of the dredging operation and the subsequent deposition of some of this material over parts of the mudflats and sandflats in Sligo Harbour
a) The removal of estuarine sediments There will be a loss of benthic habitat along the navigational channel as a result of sediment removal. Along the channel where dredging occurs, removal of all surface sediment and associated fauna will occur over a relatively short time frame. (The dredging will extend across an area of up to 271,910m², which is 0.56% of the SAC area (48,541,373m²).
b) Deposition of sediments on mudflats and sandflats
Based on the results of the hydrodynamic sediment transport model attached in Chapter 11, during the proposed dredging operations, sediment put into suspension by the dredger during water injection dredging will be dispersed around the northern portion of Sligo Harbour. The sediment will be redistributed during periods of higher current velocities during successive spring tides, before eventually coming to rest in small deposits around the fringes of Sligo Harbour and Cartron Marsh (see Figure 11.8 in Chapter 11). Some of the material will be successfully transported out of the harbour and will settle out on the nearby sand banks in depths of a few mm.
During conventional dredging small amounts of sediment put in to suspension by the dredger will be temporarily deposited along the sides of the navigation channel and in sheltered areas along the north shore of the harbour area.
The areas that will experience the greatest amount of temporary sedimentation occur along the north shoreline of Sligo Harbour (peak sedimentation during dredging of 20- 70mm). It should be noted that these peak values are typically of a short duration (a matter of hours) and tend to occur during slack tide. The material may then be re- suspended and transported elsewhere as the tidal currents pick up during the subsequent tide. The residual pattern of sedimentation following completion of all conventional dredging operations is shown in Figure 11.26 in Chapter 11. This shows that the maximum final deposition depth following completion of operations does not exceed 1mm in the majority of the harbour area and exceeds 25mm only in very localised areas around the navigation channel and the northern shore of the harbour. Post dredging, the modelled area in which there will be residual deposits of sediment in excess of 25mm is approximately 35,078m². These deposits will be mainly concentrated
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in the lee of the training wall. The area of habitat which will experience residual deposition in excess of 25mm represents approximately 0.18% of the SAC habitat “Mudflats and sandflats not covered by seawater at low tide” or 0.07% of the overall SAC area.
Potential impacts on qualifying species and listed species for the Cummeen Strand/Drumcliff Bay SAC
Once dredging ceases, recovery of the dredged area follows. In a harbour navigation channel where both maintenance and capital dredging are routinely carried out, this cycle of regular disturbance and subsequent recovery has played out as long as the channel has existed and will continue to do so for as long as the channel is maintained and used. The benthic environment surrounding the Sligo Harbour navigation channel exists in its current form after a long history of similar periodic disturbance. The typical phases of recovery following dredge disturbance are outlined below.
Recovery begins with the colonization of the defaunated area by small opportunistic species adapted to survive in areas of physical disturbance. This colonization occurs either from neighbouring sites or via larval settlement or both. Few organisms follow this life style strategy so there is a tendency for a limited number of species to reach extremely high densities in the presence of pollutants. The bioturbatory activities of these infauna start to significantly modify the physical, chemical and biological nature of the deposit. The macrofaunal assemblage enters a ‘transitory’ phase of succession when the sedimentary changes allow further colonization of a larger variety of species. This stage is unfavourable for the ‘pioneer’ population to persist. Species that characterise the transitory sere include suspension and deposit feeding bivalves, ‘conveyor belt’ polychaetes and relatively immobile holothurians. Here again the physical and chemical properties of the sediment are further modified by the new infaunal dominants making way for additional species to take hold. A more complicated and persistent faunal assemblage now forms and evolves towards an ‘equilibrium’ or ‘climax’ community status
What is described above is typical of recovery from a physical disturbance like dredging. This recovery sequence is applicable if there is no subsequent disturbance to the site. While there will be a loss of infaunal habitat due to the removal of sediment from an area of up to 271,910m² (which is 0.56% of the SAC area), recolonisation of denuded habitat will occur quickly and the floral and faunal communities inhabiting the qualifying habitats in the SAC will not be permanently impacted.
Qualifying plant species for the SAC No qualifying marine plant species listed for this SAC. Listed bird species for the SAC – Annex I species (EU Birds Directive) - Please refer to Chapter 6, “Birds”
Mammal species for the SAC – Annex II species (EU Habitats Directive) Please refer to Section 6.4 of this Chapter, “Marine Mammals”.
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Qualifying Annex II and listed fish species for the SAC
Cummeen Strand/Drumcliff Bay SAC Both the river lamprey (Lampetra fluviatilis) and the sea lamprey (Petromyzon marinus) are listed for the Cummeen Strand/Drumcliff Bay SAC. These two species both spawn in rivers and both occur in coastal and estuarine environments – though L. fluviatilis tends to remain closer to the coast than P. marinus. Additional detail on lamprey migration is presented in Chapter 7, “Fisheries and Aquaculture”.
On migrating through estuarine environments these species may frequently encounter high suspended sediment loads, which do not appear to impact on migrations.
Projected levels of suspended sediment during dredging operations are within recommended guidelines and will not have an adverse effect the upstream and downstream migrations of eels and lamprey.
Lough Gill SAC The adjoining Lough Gill SAC (Site Code: 001976) is of considerable importance for the presence of four Red Data Book fish species that are listed on Annex II of the E.U. Habitats Directive - Brook Lamprey (Lampetra planeri), River Lamprey (Lampetra fluviatilis), Sea Lamprey (Petromyzon marinus) and Atlantic Salmon (Salmo salar).
It is likely that the three migratory species of the above – salmon and river and sea lamprey – use the Sligo Harbour navigation channel during migrations to and from the Lough Gill SAC.
More detailed information on salmonids is presented in Chapter 7, “Fisheries and Aquaculture”.
Fish migrating through estuarine environments may frequently encounter high suspended sediment loads which do not appear to impede this behavioural activity. Atlantic salmon are known to move through the Severn Estuary where sediment concentrations in suspension can reach into several thousand mg/l for periods (Gibson, 1933). Simenstad (1988) suggests that salmonids are likely to have adapted physiologically to the turbid conditions that occur naturally within estuarine and harbour areas.
Suspended sediment concentrations in the lower 0.5m of water column are predicted to remain relatively low throughout dredging operations. Adult salmonids are most likely to move upstream via the navigation channel where the mean concentration be slightly higher but will remain within the Fish Directive recommended limit of 25 mg/l for salmonid waters. Moreover, suspended sediment concentrations are likely to be lower in the upper layers of the water column which salmon more commonly utilise when swimming through estuarine and coastal waters.
Projected levels of suspended sediment are within recommended guidelines and will not have an adverse effect the upstream and downstream migration of salmonids.
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Otter (Lutra lutra) (Annex II and IV) Otter are listed in the Conservation objectives for the adjoining Lough Gill SAC. Though not listed, this species also occurs in the Cummeen Strand/Drumcliff Bay SAC. The proposed dredging scheme will not have an effect on the type of substrate primarily used by otters for foraging i.e. the littoral and shallow sublittoral zones. Due to the adaptability and mobility of this species, it is unlikely that the intermittent temporary dredging works will have a significant negative effect on these animals.
Marine mammals (Annex II and Annex IV) No cetaceans are listed as qualifying species for the Cummeen Strand/Sligo Harbour SAC, or as being of special importance to the SAC. The dolphins and harbour porpoises recorded in the Cummeen Strand/Sligo Harbour SAC are highly mobile species. Due to the shallow depths that characterise this area it is likely that they use this site primarily at high water. They are able to detect noise and vibration at great distances and are unlikely to be impacted by either a plume of suspended sediment (as they rely primarily on hearing, as opposed to vision for navigation) or the physical presence and activity of a dredger. As they are air-breathing mammals, the presence of an elevated level of suspended matter in the water column is of no consequence to these species.
A full examination of the potential impacts on marine mammals is presented in Section 6.4 this chapter.
Other fish species Due to their mobility, impacts to fish species occurring subtidally in the Cummeen Strand/Sligo Bay SAC are likely to be negative, slight and short-term. Fish are very sensitive to vibration and disturbance in the water column and quickly relocate when disturbed. It is likely that demersal and pelagic fish species that become acclimatised to the dredging pattern will learn to avoid the dredge plume (relocating upstream of the tidal flow) and will enter the dredged area to scavenge on exposed, dead or moribund infauna left behind on the seafloor in the wake of the dredging operation (when dredging ceases as low tide is approaching). It is not uncommon that elevated numbers of scavenging fauna are noted in areas where the seafloor has been subject to physical disruption/disturbance.
Having undergone a sharp decline in recruitment from 1980, European eel (Anguilla anguilla) is now listed as CR – critically endangered on the IUCN (International Union for Conservation of Nature) Red Data List. A population of eel exists in Lough Gill and it is likely that they use the navigation channel area during migrations to and from their distant breeding grounds. All possible measures should be taken to minimise disturbance to this species during migration through the estuarine environment as the next classification level in the IUCN Red Data List is EW – extinct in the wild. On migrating through estuarine environments eels may frequently encounter high suspended sediment loads which do not appear to impact on migrations.
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Projected levels of suspended sediment during dredging operations are within recommended guidelines and will not have an adverse effect the upstream and downstream migrations of eels.
Potential impacts on the macrobenthos - food source for SPA bird species
Intertidal macrobenthos is of greatest value to bird species as a food source (due to accessibility). The subtidal infaunal macrobenthos along the floor of the navigation channel will be subject to the greatest level of impact (complete removal, though with potential for rapid recolonisation). Impacts to the intertidal macrobenthos are likely to be imperceptible, localised and temporary, as the continued movement of the dredger along the navigation channel will ensure that any given area will not be impacted for a protracted period.
The hydrodynamic modelling presented in Chapter 11 shows that the sediment put into suspension by the dredger during water injection dredging will be dispersed around the northern portion of Sligo Harbour. The sediment will be redistributed during periods of higher current velocities during successive spring tides, before eventually coming to rest in small deposits around the fringes of Sligo Harbour and Cartron Marsh (see Figure 11.8 in Chapter 11). Some of the material will be successfully transported out of the harbour and will settle out on the nearby sand banks in depths of a few mm.
During subsequent conventional dredging, small amounts of sediment put in to suspension by the dredger during dredging operations will be temporarily deposited along the sides of the navigation channel and in sheltered areas along the north shore of the harbour area.
The areas that will experience the greatest amount of temporary sedimentation occur along the north shoreline of Sligo Harbour (peak sedimentation during dredging of 20-70mm). These peak values are typically of a short duration (a matter of hours) and the material may then be re-suspended and transported elsewhere as the tidal currents pick up during the subsequent tide. The residual pattern of sedimentation following completion of all conventional dredging operations is shown in Figure 11.26 in Chapter 11. This shows that the maximum final deposition depth following completion of operations does not exceed 1mm in the majority of the harbour area and exceeds 25mm only in very localised areas around the navigation channel and the northern shore of the harbour. Overall, the amount of sediment deposited in the harbour area as a result of the dredging will be insignificant. No residual impact is expected.
Noise impact on benthos Impacts on benthos from noise in the vicinity of the dredging operation are expected to be localised and temporary. The fact that the proposed dredging will take place in an already busy port navigation channel suggests that the additional, temporary noise loading of a dredger at work would be of minimal significance to benthos in the vicinity of the dredged area.
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Bivalve Beds Blue mussels (Mytilus edulis) are filter-feeding bivalves that have a very high efficiency in removing particulate matter (phytoplankton, organic matter and suspended sediment) from the water column to an extent that food for the bivalves may become a limiting resource at the sediment-water interface. This high efficiency at removing particulate matter from the water column directly relates to the potentially adverse effects of dredging-induced sediment plumes on these filter feeding bivalves. Large quantities of suspended sediment in the water column can be detrimental due to clogging of the gills and impairment of proper respiratory and excretory functioning and feeding activity. Overall, research suggests that the degree of an impact on filter-feeding species depends on the extent of turbidity and sedimentation against background levels. Benthic shellfish in normally turbid environments (such as that found in the Cummeen Strand area) are probably able to survive smothering unless the rate of deposition is excessive. Studies also show that filter feeders, and bivalves in particular, are highly adaptable in their response to increased suspended sediment levels from, for example, periodic storms and dredging, maintaining their feeding activities over a wide range of particulate loads and suspended sediment concentrations (Newell et al., 1998).
Previous studies on effects of suspended sediments on adult mussels (Mytilus edulis) have shown that they are capable of coping with extreme high concentrations of suspended material (Kiørboe et al., 1980). In one recent study, a no effects level of 1,867 mg/L for Mytilus edulis has been reported (Anchor Environmental, 2003). In laboratory studies, lethal concentrations for adult bivalves exposed for as long as 3 weeks were in the realm of fluid mud, i.e. around 10,000 mg/L (Clarke & Wilbur, 2000). The ability for mussels to effectively utilize suspended food particles for growth is optimal at concentrations below 50 mg/L. Concentrations above 100 mg/L result in weight loss (Prins & Smaal, 1989). The growth rate of common mussels increased in a field experiment in Denmark, where mussels were regularly exposed to silt concentrations between 200-250 mg/L in a plume originating from dumping of dredged spoil during a period of five weeks (Birklund & Wijsman, 2005). The high concentrations did not affect the survival of the mussels. Mussels can protect themselves from overloading by temporarily closing the valves and the closing response depends on the size of the mussels. Widdows et al. (1979) demonstrated that maximum filtering rates by 3cm long mussels (Mytilus edulis) (from an area that had a natural range in suspended matter between 5 and 35 mg/L) were found at suspended matter concentrations of 125mg/L, 30% reduced at 225mg/L and negligible at concentrations >250 mg/L. Larger mussels (7 cm) stopped filtering and closed their valves at 350 mg/L. When mussels are given sufficient time (months), they can adapt their gills and palps to higher concentrations of suspended matter up to concentrations as high as 400 mg/L (Essink et al., 1989).
Suspended bottom material, which is always present in the natural habitats of the blue mussel Mytilus edulis, serves as an important additional food source for the mussels. Mytilus edulis depends on this suspended bottom material to exploit fully its clearance potential and reach the maximum growth rates observed in nature (Kiørboe et al., 1980). Field research in the Ems Estuary (The Netherlands) indicated that a 10-20% increase in turbidity did not have negative impacts on the growth and survival of mussels (Essink et al., 1990).
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In instances of incidental deposition, sessile benthic species such as mussels have a relatively low tolerance of sediment cover. Adult mussels in a mussel bed are not capable of moving upwards after deposition of layers of mud or sand and deposition of a layer of 1-2cm within a relatively short period can be considered fatal to mussels (Essink, 1999).
Based on the above information, the tolerance thresholds of mussel beds is summarised in Table 6.7.
Table 6.7: Summary of critical thresholds for mussel (Mytilus edulis) beds. Species Parameter Optimum Range Maximum Tolerated Mytilus Suspended <1867 mg/l <10,000 mg/k for 3 edulis sediment 50-100 mg/l weeks (adult) <250 mg/l (5 weeks) <400 mg/l (turbid estuaries) Sedimentation 1-2 cm (within short time)
Impacts of the dredging plume on mussel beds in Sligo Harbour are considered negligible. Mussels are very tolerant of extremely high turbidities (see Table 6.7).
The proposed dredging scheme will not have any impact on mussels (adults, larvae or spat). Neither suspended sediment levels nor sedimentation rates demonstrated in Chapter 11, “Hydrodynamic Modelling” reach lethal levels for mussels.
Zostera Beds Light is one of the key environmental resources imperative for the growth and survival of seagrasses (Hemminga & Duarte, 2000). The degree of water transparency (which determines the depth-penetration of photosynthetically active radiation of sunlight) is the primary factor determining the maximum depth at which seagrasses can occur. Reduction in light due to turbidity has been identified as a major cause of the loss of seagrasses worldwide (Shepherd et al., 1989; Green & Short, 2003). The amount of light that reaches a seagrass leaf is determined by the natural water colour, concentration of suspended solids, phytoplankton concentration and the epiphyte cover of the leaf. There are various reports of sublethal and lethal effects on seagrass meadows due to prolonged exposure to high turbidity and siltation associated with dredging activities (Erftemeijer & Lewis, 2006). Laboratory experiments have shown that some seagrasses can survive in light intensities below their minimum requirements for periods ranging from 4 weeks to several months. However, widespread seagrass mortality was observed in Chesapeake Bay (USA) following a month-long (seasonal) pulse of increased turbidity (light extinction coefficient (k)>3.0 m-1) (Moore et al., 1997).
The minimum light requirements of Zostera marina (eelgrass) have been extensively studied in a range of locations and environments. The values for the minimum light requirements of this species, as reported in literature, vary between 11 and 37 % of Surface Irradiance (SI). For the survival of seagrasses, the lowest value of 11%SI is the most critical level below which widespread mortality surely occurs. Some of the higher values (up to 37%SI) reported
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for eelgrass appear to refer to the minimum light levels required to enable and sustain lateral shoot development, meadow expansion and flowering. Levels below 37%SI but above 11%SI do affect these processes, but may not cause substantial eelgrass mortality. There has been only 1 detailed study of the minimum light requirements for Zostera noltii: Peralta et al. (2002) reported a minimum light requirement of 2% of SI for Zostera noltii in Spain. According to the same study (also reported in: MarLIN Database, 2006), Zostera noltii plants can tolerate acute light reduction below 2% SI for up to two weeks, and thus appear tolerant of short-term events of very high turbidity. A recent monitoring study into the effects of a dredging plume on intertidal eelgrass (Zostera marina) in the Ems Estuary (The Netherlands) during (day-time) periods of low tide exposure (Ochieng & Erftemeijer, 2009). This implies that intertidal eelgrass plants are relatively tolerant to further turbidity increases such as may be caused by a dredging plume (Ochieng and Erftemeijer, 2009). Based on the above information, the tolerance thresholds of seagrass beds to turbidity is summarised in Table 6.8.
Table 6.8: Tolerance thresholds of Zostera spp. to turbidity levels. Seagrass Species Minimum Tolerated Optimum Range Zostera marina 11-37% SI >37% SI Zostera noltii 2% SI can tolerate acute light reduction below 2% SI for 2 weeks
Several studies have documented deterioration of seagrass meadows by smothering due to excessive sedimentation (Erftemeijer and Lewis, 2006). Seagrass species that develop vertical shoots may respond to fluctuations in sediment depth by modifying their vertical growth but there are limits to the level of sedimentation seagrasses can tolerate. Sedimentation rates of as much as 1013 cm yr-1 have been reported as maximum threshold of what some seagrass species can survive. Settlement of suspended material on leaf blades of seagrasses may interfere significantly with photosynthesis, and appears especially significant in low wave energy environments where fine sediments are present and can settle out. A maximum allowable sedimentation rate of 2 cm in 4 months was reported for Mediterranean Zostera noltii (Spain). Tolerance of Zostera noltii in the Dutch Wadden Sea was documented to range from minor erosion of 2 cmyr-1 to maximum sedimentation levels of 25 cm yr-1. Mortality of 75% was reported for Zostera marina meadows (USA) at burial with 4 cm (i.e. 25% of plant height), which demonstrates that this species is probably more sensitive to sedimentation than some of the other (taller) seagrass species. Vermaat et al. (1997) proposed an estimate of the annual sedimentation rates that can be survived or escaped by seagrasses, either vertically or horizontally, to be in the order of 5-10 cm yr-1. Based on the above information, the tolerance thresholds of seagrass beds to sedimentation is summarised in Table 6.9.
Table 6.9: Tolerance thresholds for Zostera spp. to sedimentation.
Seagrass Species Minimum Tolerated Maximum Tolerated Zostera marina 75% mortality at 4cm/day (25% of plant height
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Zostera noltii -1 to -2 cm/yr (erosion) 2-5 cm/year (sedimentation) 2cm / 4 months
Impacts of the dredging plume on the seagrass beds in Sligo Harbour are considered negligible, because the plumes of high turbidity and sedimentation do not reach the seagrass beds documented in the area. Besides, intertidal seagrass is probably not affected much by increased turbidity anyway, since it obtains most of its light during (day-time) periods of low tide exposure (see Ochieng & Erftemeijer, 2009). Based on the final sediment deposition depth computed for the Cummeen Strand seagrass habitat, on completion of all dredging activities, no residual impact on this habitat is expected.
Indirect Impacts on sites in the wider locality, including Lough Gill SAC
The adjoining Lough Gill SAC (Site Code: 001976) is of considerable importance for the presence of four Red Data Book fish species that are listed on Annex II of the E.U. Habitats Directive - Brook Lamprey (Lampetra planeri), River Lamprey (Lampetra fluviatilis), Sea Lamprey (Petromyzon marinus) and Atlantic Salmon (Salmo salar). It is likely that the three migratory species of these, salmon and river and sea lamprey, use the navigation channel during migrations between the sea and the Lough Gill SAC. Timing of the works should take these migrations into account and, despite the fact that the Lough Gill SAC will not be directly impacted by the proposed dredging works, the link between freshwater and seawater habitats and species should not be ignored.
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6.3 SUBTIDAL FLORA AND FAUNA – OFFSHORE DUMP SITE
This section describes the baseline surveys undertaken at the proposed offshore disposal site, and presents an impact hypothesis for the predicted impacts of dumping the dredged sediment at this location, based on the baseline data acquired at the site and the dumpsite plume model and settlement pattern described in Chapter 11, “Coastal Processes”.
6.3.1 Introduction
The survey at the Sligo proposed dumpsite was conducted from the M/V Nomad, a multi- purpose tug boat out of Killybegs, on two sampling dates, 27th January and 17th February 2011, covering both neap and spring tide conditions respectively. Following consultation with The Marine Institute, it was recommended that the baseline study should involve a hydrodynamic survey, benthic community study and sediment chemistry analysis. The location of the proposed dump site is shown below in Figure 6.35.
Extract from Admiralty Chart 2725 © Crown Copyright UKHO. Not for navigational use
Figure 6.35: Location of Proposed Offshore 1km² Dump Site
6.3.1.1 Hydrodynamic Survey The hydrodynamic environment at the site was investigated by recording current speed and direction, drogue movements and tidal elevations at various stages of the tide on both spring and neap tidal conditions.
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6.3.1.2 Current and Tide Measurements Current speed and direction was recorded mid water (45-50m) by means of an Aquadopp current profiler every 10 minutes for an ebb and flood tide during both the neap (27th January) and spring (17th February) tide. Tidal elevation was also recorded at the same time. The meter was located on both occasions approximately in the centre of the site at 54° 35.800’ N, 9° 16.5879’ W on 27th January and 54° 36.0087’ N, 9° 16.5885’ W on 17th February.
6.3.1.3 Drogue Studies Drogues, designed to track currents at the surface, mid-water (45m) and off-bottom (90 m), were released from the centre of the dump site at high water, mid-tide and low water and tracked through to the following slack water when they were recovered on both sampling dates. Each drogue was fitted with a GPS tracking unit set to record every 5 minutes, a flashing beacon and a radar reflector for navigation alert and to aid recovery at night. Regular checks were made on their progress by means of a DGPS unit as a backup to track their progress and also aid recovery in this environment. Wind speed and direction was regularly checked by means of a hand held anemometer.
6.3.1.4 Sediment Sampling Sediment samples were taken at the locations outlined in Figure 6.36 and Table 6.1 by means of a 0.1 m2 Day grab. It was intended to take a single grab at three stations along the southwest-north east axis of the dumpsite and a fourth approximately 1 km from the dumpsite in the direction opposite to the residual current for sediment analysis. However, on site, the bottom type dictated where it was possible to take these grabs, which returned the locations as outlined in Figure 6.36. When samples were returned from each station, notes were logged on sediment type, amount, colour, smell and any other information that was considered relevant. A sample of surface sediment was taken from the centre of the grab and placed in a suitable cleaned container. All sampling jars were marked externally with date, station number, sample number and survey reference number and placed in a cooler box.
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Extract from Admiralty Chart 2725 © Crown Copyright UKHO. Not for navigational use
Figure 6.36: Sampled stations at proposed dump site, Donegal Bay, Jan/Feb 2011
Table 6.10: Locations of the sediment sampling stations in Donegal Bay.
STATION EASTING NORTHING St 1 117396 373288 St 2 116900 373170 St 3 117260 372202 St 4 116322 371258
On return to the laboratory, the samples for contaminant samples were sent to the UK Environment Agencies National Laboratory Service (NLS) facility at Llanelli for the following analysis:
Sample 1 - a), b), c), d), e), f) & g) Sample 2 & 3 - a), b) & c) Sample 4 - a), b), c), d), e), f) & g)
Where: a) total organic carbon b) carbonate c) mercury, arsenic, cadmium, copper, lead, zinc, chromium, nickel, lithium, aluminium.
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d) organochlorines including Ȗ-HCH (Lindane), and PCBs (to be reported as the 7 individual CB congeners: 28, 52, 101, 118, 138, 153, 180). e) total extractable hydrocarbons. f) tributyltin (TBT) and dibutyltin (DBT) g) Polycyclic aromatic hydrocarbons (PAH) - Acenaphthene, Acenaphthylene, Anthracene, Benzo (a) anthracene, Benzo (a) pyrene, Benzo (b) fluoranthene, Benzo (ghi) perylene, Benzo (k) fluoranthene, Chrysene, Dibenz (a,h) anthracene, Flourene, Fluoranthene, Indeno 1,2,3 – cd pyrene, Naphthalene, Phenanthrene, Pyrene.
The methodologies for each of the analysis are included in the results report sent by NLS and included as Appendix 8. Appropriate marine Certified Reference Material (CRM) were analysed with the samples and the results presented with the sample results.
Granulometric analysis was carried out on one aliquot of each sediment sample as described by Folk (1974). A 30-ml solution of aqueous sodium hexametaphosphate (6.2 g/l) was added to 100 g of oven-dried (100°C) sediment; the mixture was made up to 1 litre with distilled water, stirred mechanically for 15 min and allowed to stand overnight. This mixture was then re-stirred and washed through a 45-ȝm sieve. This material left on the sieve was oven-dried at 100°C and weighed, and the 45-ȝm fraction determined by subtraction. The dried remaining fraction was broken up with a mortar and pestle and graded through a nest of sieves of 4, 2, 1 mm and 500-, 250-, 125-, and 63-ȝm mesh. Each grade was weighed and the value expressed as a percentage of the total dry weight of the sample. Material passing through the 63 ȝm mesh was added to the 45-ȝm fraction and classified as the silt– clay fraction. Water content was taken as the percentage weight difference between the wet and dried sediment.
6.3.1.5 Benthic Communities
6.3.1.5.1 Faunal Samples AQUAFACT has in-house standard operational procedures for benthic sampling and these were followed for this project. A 0.1m2 Day grab was used to sample the grab stations. The grab was weighted at 70–100 kg for sandy sediments. On arrival at each prescribed sampling station, the vessel location was recorded using DGPS (Lat/Long & ING). Additional information such as date, time, site name, sample code, depth, sampler, anchorage, weather, sea state and exposure were recorded in a data sheet.
As for the sediment grabs, bottom type dictated the locations where grabs could be taken. A minimum of three grab samples were taken at four faunal grab locations for faunal content (Figure 6.37). The grab deployment and recovery rates did not exceed 1 metre/sec and <0.5 m/sec for the last 10m. Upon retrieval of the grab, penetration depth was measured and only grab samples that contained a depth of >7cm for sand and >10cm for mud were retained. Re-sampling occurred until a sufficient depth of sediment was collected in the grab (the vessel repositioned between grab samples). All additional relevant data (sediment type, texture, grain size, colour, odour, layering, volume, presence of fauna, algae, surface features) were recorded in the sample data sheets.
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Extract from Admiralty Chart 2725 © Crown Copyright UKHO. Not for navigational use
Figure 6.37: Locations of Faunal Stations, Donegal Bay, Jan/Feb 2011
The grab sampler was cleaned between stations to prevent cross contamination.
The contents of the grab sample were carefully and gently sieved on a 1mm mesh sieve as a sediment water suspension for the retention of fauna. Great care was taken during the sieving process in order to minimise damage to taxa such as spionids, scale worms, phyllodocids and amphipods. The sample residue was carefully flushed into a pre-labelled (internally and externally) container from below. Each label contained the sample code and date. The samples were stained immediately with Eosin-briebrich scarlet and fixed immediately in with 4% w/v buffered formaldehyde solution. These samples were ultimately preserved in 70% alcohol upon return to the laboratory.
All faunal samples were placed in an illuminated shallow white tray and sorted first by eye to remove large specimens and then sorted under a stereo microscope (x 10 magnification). Following the removal of larger specimens, the samples were placed into Petri dishes, approximately one half teaspoon at a time and sorted using a binocular microscope at x25 magnification. A full species list is presented in Appendix 4F on the accompanying data DVD-ROM.
The fauna was sorted into four main groups: Polychaeta, Mollusca, Crustacea and others. The ‘others’ group consisted of echinoderms, nematodes, nemerteans, cnidarians and other lesser phyla. The fauna were maintained in stabilised 70% industrial methylated spirit (IMS)
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following retrieval and identified to species level where practical using a binocular microscope, a compound microscope and all relevant taxonomic keys. 6.3.1.5.2 Statistical Analysis All replicates for each station were combined to give a total abundance for each station prior to analyses. A data matrix of all the combined faunal abundance data was compiled and used for statistical analyses. The faunal analysis was carried out using PRIMER ® (Plymouth Routines in Multivariate Ecological Research).
Univariate statistics in the form of diversity indices were calculated on the combined replicate data. The following diversity indices were calculated:
1) Margalef’s species richness index (D), (Margalef, 1958). S 1 D log2 N where: N is the number of individuals S is the number of species
2) Pielou’s Evenness index (J), (Pielou, 1977). H' (observed) J= ' Hmax ' where: H max is the maximum possible diversity, which could be achieved if all species were equally abundant (= log2S)
3) Shannon-Wiener diversity index (H'), (Pielou, 1977). S H' = - p(log p ) ¦ i=1 i 2 i th where: pI is the proportion of the total count accounted for by the i taxa
Species richness is a measure of the total number of species present for a given number of individuals. Evenness is a measure of how evenly the individuals are distributed among different species. The diversity index incorporates both of these parameters. Richness ranges from 0 (low richness) to 12 (high richness), evenness ranges from 0 (low evenness) to 1 (high evenness), diversity ranges from 0 (low diversity) to 5 (high diversity).
The PRIMER ® manual (Clarke & Warwick, 2001) was used to carry out multivariate analyses on the station-by-station faunal data. It must be noted here that the species that were present only once or twice in the survey were excluded from the multivariate analysis. All species/abundance data were fourth root transformed and used to prepare a Bray-Curtis similarity matrix in PRIMER®. The fourth root transformation was used in order to down- weigh the importance of the highly abundant species and allow the mid-range and rarer species to play a part in the similarity calculation. The similarity matrix was then used in classification/cluster analysis. The aim of this analysis was to find “natural groupings’ of samples, i.e. samples within a group that are more similar to each other, than they are similar to samples in different groups (Clarke & Warwick, loc. cit.). The PRIMER ® programme CLUSTER carried out this analysis by successively fusing the samples into
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groups and the groups into larger clusters, beginning with the highest mutual similarities then gradually reducing the similarity level at which groups are formed. The result is represented graphically in a dendrogram, the x-axis representing the full set of samples and the y-axis representing similarity levels at which two samples/groups are said to have fused. The CLUSTER programme was set to include a series of ‘similarity profile’ (SIMPROF) permutation tests, which look for statistical evidence of genuine clusters in samples which are a priori unstructured. SIMPROF performs tests at every node of a completed dendrogram, that the group being sub-divided has ‘significant’ internal structure. The test results are displayed in a colour convention on the dendrogram plot (samples connected by red lines cannot be significantly differentiated).
The Bray-Curtis similarity matrix was also subjected to a non-metric multi-dimensional scaling (MDS) algorithm (Kruskall & Wish, 1978), using the PRIMER ® program MDS. This programme produces an ordination, which is a map of the samples in two- or three- dimensions, whereby the placement of samples reflects the similarity of their biological communities rather than their simple geographical location (Clarke & Warwick, 2001). With regard to stress values, they give an indication of how well the multi-dimensional similarity matrix is represented by the two-dimensional plot. They are calculated by comparing the interpoint distances in the similarity matrix with the corresponding interpoint distances on the 2-d plot. Perfect or near perfect matches are rare in field data, especially in the absence of a single overriding forcing factor such as an organic enrichment gradient. Stress values increase not only with the reducing dimensionality (lack of clear forcing structure), but also with increasing quantity of data (it is a sum of the squares type regression coefficient). Clarke and Warwick (loc. cit.) have provided a classification of the reliability of MDS plots based on stress values, having compiled simulation studies of stress value behaviour and archived empirical data. This classification generally holds well for 2-d ordinations of the type used in this study. Their classification is given below:
x Stress value < 0.05: Excellent representation of the data with no prospect of misinterpretation. x Stress value < 0.10: Good representation, no real prospect of misinterpretation of overall structure, but very fine detail may be misleading in compact subgroups. x Stress value < 0.20: This provides a useful 2-d picture, but detail may be misinterpreted particularly nearing 0.20. Stress value 0.20 to 0.30: This should be viewed with scepticism, particularly in the upper part of the range, and discarded for a small to moderate number of points such as < 50. x Stress values > 0.30: The data points are close to being randomly distributed in the 2- d ordination and not representative of the underlying similarity matrix.
Each stress value must be interpreted both in terms of its absolute value and the number of data points. In the case of this study, the moderate number of data points indicates that the stress value can be interpreted more or less directly. While the above classification is arbitrary, it does provide a framework that has proved effective in this type of analysis.
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SIMPER analysis was then carried out on the transformed data to determine the dominant/characterising species within each group identified by the CLUSTER/SIMPROF analysis. These results are presented in Appendix 4H.
6.3.1.5.3 Video Survey Video footage of the seafloor and associated biota was recorded by means of a LH Camera professional colour video camera that was operated from the work vessel. Footage was recorded directly to a laptop for later analysis. Video transects were attempted at various locations across and outside the dumpsite in order to get footage of the various bottom types encountered at this location. However a significant swell and boat drift due to the moderate to strong wind hampered this operation. In total 6 video transects were achieved across the area during the January survey as indicated in Figure 6.38. Additional video transects were attempted during the February survey. However, the camera was damaged on the first transect attempted on the 17th February and no footage was recorded.
374000
373500 V2 V1
373000 V3 V4
372500
372000 V6
371500
V5 371000 116000 116500 117000 117500 118000 118500 119000
Figure 6.38: Video transect locations in the vicinity of the proposed dumpsite, Donegal Bay, January 2011.
6.3.2 Results
6.3.2.1 Hydrodynamic Survey
6.3.2.1.1 Current and Tide measurements
Figure 6.39 presents current (stick plots) and tide measurements from the dump site location on both a neap (27th January) and spring (17th February) tide.
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Figure 6.39 Current and tide measurements, Donegal Bay, Jan & Feb 2011.
The tidal range recorded during the neap was 2.0 m while the range during the spring was 3.0 m. Current velocities were relatively low with a maximum velocity of 0.15ms-1 recorded during the neap and 0.217 ms-1 recorded during the spring tide. Due to the low velocities recorded during the neap tide, the direction of the water movement was difficult to assess although in general, it was in a north west direction during the ebb tide and south east during the flood (see stick plot, Figure 6.39). With the increased velocities during the spring tide, the direction of water movement was more defined with an easterly current during the flood and west flow during the ebb.
6.3.2.2 Drogue Study
6.3.2.2.1 Neap Tide (27.1.2011) Track records of the drogues released on the ebb and flood tide on 27.1.2011 are presented in Figure 6.40 and Figure 6.41, respectively, and the track data included as Appendix 4E on the accompanying DVD along with the current measurements as detailed in the previous
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section. Mid-water and off-bottom drogues, released at the same time, remained close to each other while the surface drogue followed a different path. This was mainly due to the prevalent wind, which was predominantly easterly in direction and increased from approximately 3 ms-1 at the start of the study to 5 ms-1 towards the end of the study. This was particularly evident during the flood tide deployments when the mid-water and off- bottom drogues moved in a south-east direction following water movement as recorded by the current meter (see Figure 6.39) while the surface drogues moved in the opposite direction in a north-westerly direction under the influence of the 4-5 ms-1 north-westerly wind (Figure 6.41). The average speed of the surface drogue (Drop 1) over the full ebb tide was 0.39 km/h while the mid-water and off-bottom drogues recorded average speeds of 0.34 km/h and 0.33 km/h, respectively. This compared to average speeds of 0.15 km/h for the surface drogue and approximately 0.1 km/h for the mid water and off-bottom drogues.
375000 Drogue Drop 1 - 11:15 Drogue Drop 2 - 14:50 Recovery - 18:00 Wind 3-4 m/s 374500 High Wate r 11:40 Low Water 18:00
374000
373500
373000
372500
Surf ace Mid-water Off-bottom D Surf ace 2 M idwat er 2 Off-bottom 2
372000 116 0 0 0 116 50 0 1170 0 0 11750 0 118 0 0 0 118 50 0 119 0 0 0
Figure 6.40 Ebb drogue tracks, Donegal Bay, 27.1.2011
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375000 Drogue Drop 3 - 18:40 Drogue Drop 4 - 20:00 Recovery - 22:00 Wind 4-5 m/s 374500 High Wate r 11:40 Low Water 18:00
374000
373500
373000
372500
Surf ace Mid-water Off-bottom D Surf ace 2 Midwater 2 Off-bottom 2
372000 116000 116500 117000 117500 118000 118500 119000
Figure 6.41: Flood drogue tracks, Donegal Bay, 27.1.2011
6.3.2.2.2 Spring Tide (17.2.2011)
Track records of the drogues released on the ebb and flood tide on 17.2.2011 are presented in Figure 6.42 and Figure 6.43, respectively, and the track data included in Appendix 4F. The gps track of the off-bottom drogue released on the flood tide and drop 4 on the ebb tide was found to be corrupted and could not be used in the Figures. However, as noted in the neap tide study, the mid-water and off-bottom drogues, released at the same time, remained close to each other during the spring tide study and the mid-water track is representative of both. Unlike the neap study, the prevailing wind (2-5 ms-1 south easterly) did not have the same influence on the drogue tracks.
The average speed of the surface drogue (drop 1) over the full flood tide was 0.4 km/h while the mid-water and off-bottom drogues recorded average speeds of 0.36 km/h. This compared to average speeds of 0.69 km/h for the surface drogue and 0.57 km/h and 0.51 km/h for the mid water and off-bottom drogues, respectively.
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376000 Drogue Drop 1 - 10:50 Drogue Drop 2 - 13:00 Recove ry - 17:15 37550 0 Wind 2-3 m /s Low Water 11:00 High Water 17:10 375000 Low Water 23:00 Range 3 m
374500
374000
373500
373000
372500
Surface Mid-water Off-bottom D Surf ace 2 M idwat er 2 Off-bottom 2
372000 116 0 0 0 116 5 0 0 117 0 0 0 117 5 0 0 118 0 0 0 118 5 0 0 119 0 0 0 119 50 0 12 0 0 0 0
Figure 6.42 Flood drogue tracks, Donegal Bay, 17.2.2011
376000 Drogue Drop 3 - 17:40 Drogue Drop 4 - 19:30 Recovery - 23:00 3 75500 Wind 4-5 m /s Low Water 11:00 High Water 17:10 3750 00 Low Water 23:00 Range 3 m
374500
374000
373500
373000
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Surface Mid-water Off-bottom D Surf ace 2 M id wat er 2 Off-bottom 2
372000 114 5 0 0 115 0 0 0 115 5 0 0 116 0 0 0 116 5 0 0 117 0 0 0 117 50 0 118 0 0 0 118 5 0 0
Figure 6.43 Ebb drogue tracks, Donegal Bay, 17.2.2011
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6.3.2.3 Sediment Samples
The detailed report of the granulometric and chemical composition of the sediment samples recovered from the proposed dump site is reported in Section 10.4.2 of Chapter 10, “Geology”.
In general, the sediments collected in and around the dumpsite (Stations 1-3) were typically made up of fine sand with varying amounts of coarse sand and gravel. This corresponds well with the properties of the sediment to be dredged. The sediments were also subjected to chemical testing under the supervision of the Marine Institute as per the requirements of the Dumping at Sea Acts 1996-2006 (as amended 2009) and these results are also presented in that chapter.
6.3.2.4 Benthic Communities
The taxonomic identification of the benthic infauna across all 4 stations sampled in Donegal Bay yielded a total count of 77 taxa accounting for 262 individuals, ascribed to 8 phyla. A complete listing of the taxa abundance is provided as Appendix 4F, which is on the accompanying data DVD.
Of the 77 taxa enumerated, 43 were annelida (segmented worms), 11 were crustaceans (crabs, shrimps, prawns), 14 were molluscs (mussels, cockles, snails etc.), 4 were echinoderms (starfish, brittlestars, sea cucumbers), 2 were cnidarians (corals, jellyfish etc), 1 was aphoronid (horseshoe worm), 1 was a nematode (round worm) and 1 was a nemertean (ribbon worm).
6.3.2.4.1 Univariate Analysis Univariate statistical analyses were carried out on the combined replicate station-by-station faunal data. The following parameters were calculated and can be seen in Table 6.11; taxon numbers, number of individuals, richness, evenness and diversity. Taxon numbers ranged from 19 (Station 2) to 41 (Station 4). Number of individuals ranged from 29 (Station 2) to 81 (Station 1). Richness ranged from 5.35 (Station 2) to 9.29 (Station 4). Evenness ranged from 0.92 (Stations 1 and 3) to 0.95 (Stations 2 and 4). Diversity ranged from 4.02 (Station 2) to 5.10 (Station 4).
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Table 6.11 Diversity indices for the 4 stations sampled in Donegal Bay Station No. Taxa No. Individuals Richness Evenness Diversity Station 1 31 81 6.83 0.92 4.53 Station 2 19 29 5.35 0.95 4.02 Station 3 32 79 7.09 0.92 4.58 Station 4 41 74 9.29 0.95 5.10
6.3.2.4.2 Multivariate Analysis The dendrogram and the MDS plot can be seen in Figure 6.44 and Figure 6.45 respectively. SIMPROF analysis revealed that there was no significant difference between the 4 stations (hence the red line joining all stations in the dendrogram).
Faunal returns from the area in question were poor, with the maximum number of any taxon present at a station being 11 (the cnidarians Edwardsiidae sp. at Station1). Edwardsiidae sp. was also the dominant taxon at the other 2 stations located within the dumpsite (Stations 2 and 3). Of the 31 taxa found at Station 1, 19 were present twice or less, of the 19 taxa found at Station 2, 17 were present twice or less and of the 32 taxa found at station 3, 19 were present twice or less.
Station 1 was dominated by Edwardsiidae sp., the polychaete Chaetozone setosa, the polychaete Aonides oxycephala and the mollusc Thyasira flexuosa. Station 2 was dominated by Edwardsiidae sp. and the polychaete Scoloplos armiger. Station 3 was dominated by Edwardsiidae sp., Thyasira flexuosa, Chaetozone setosa and Scoloplos armiger.
The control station (Station 4) contained the highest number of taxa (41) and of those 29 were present twice or less. Station 4 was dominated by the polychaete Chaetozone setosa, the enchinoderm Echinocyamus pusillus, the polychaete Lumbrineris cf cingulata and the cnidarians Edwardsiidae sp.
SIMPER analysis revealed that the taxa responsible for the grouping of all stations as one group were Edwardsiidae sp., Harpinia sp., and the polychaete Owenia fusiformis. Appendix 4H contains the results of the SIMPER analysis.
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Figure 6.44 Dendrogram showing the natural grouping of each station sampled in Donegal Bay.
The MDS plot reflects the data in the dendrogram. The stress value of the MDS ordination is 0; which results in a good representation with no real prospect of misinterpretation of the overall structure, but the very fine detail may be misleading in compact subgroups.
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Figure 6.45: MDS plot of all stations sampled in Donegal Bay.
6.3.2.4.3 Video Survey Footage from each of the video transects (see Figure 6.38) are included as Appendix 4G on the DVD accompanying this report. It is noticeable that the seafloor is very variable with bottom type quickly changing composition across each transect indicating a mosaic of bottom types in the area. A summary of these features are included as Table 6.12. The seafloor along video transect 6 was similar to that seen in video transect 5. However, due to a power loss during recording of V6, the footage was lost and no images or recording is available for this transect.
Faunal presence across the transects was sparse, the only obvious biota noted during the transects being a number of starfish, Asterias rubens, and hydroid colonies (sp. ident.) and serpulids on the boulders.
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Table 6.12 Descriptions of the video transects, Donegal Bay, January 2011.
V1 Start 118018 E, 373358 N End 118089 E, 373229 N Transect length - 147 m Clean gravel formed in large waves, fine sand in small waves to bolder field
V2 Start 117818 E, 373351 N End 117979 E, 373307 N Transect length - 167 m Gravel with mud mix, fine sand in small waves
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V3 Start 117760 E, 373031 N End 117912 E, 372883 N Transect length - 212 m Boulder field with varying amounts of silt, sand and gravel. A single starfish, Asterias rubens, was imaged.
V4 Start 117298 E, 372791 N End 117486 E, 372716 N Transect length - 202 m Fine sand formed into small waves
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V5 & V6 Start 117352 E, 372791 N End 117094 E, 372136 N Transect length - 258 m Clean gravel formed in large waves, fine sand in small waves to bolder field and combinations each.
6.3.3 Proposed Dumpsite Baseline Conditions - Conclusions
Current velocities were relatively low at the site with a maximum velocity of 0.15ms-1 recorded during neap and 0.217 ms-1 recorded during spring tides. In general, water
IBE00440/EIS01/June ‘12 6-67 Sligo Harbour Dredging Environmental Appraisal Report Intertidal and Benthic Flora and Fauna & Marine Mammals movement was in a north west to west direction during the ebb tide and south east to east direction during the flood. The tidal range recorded during the neap was 2.0 m while the range during the spring was 3.0 m.
The track taken by drogues designed to follow water movement at different depths agreed with the direct current measurements with movement in a north west to west direction during the ebb tide and south east to east direction during the flood. Given the relatively low current velocities, wind speed and direction had a major influence on drogue movement.
The marine sediments collected in and around the potential dumpsite were typically made up of fine sand with varying amounts of coarse sand and gravel. The sediments were typically brown or grey/brown in colour with no particular smell.
In general, contaminant analysis of sediments taken from the four stations indicated that the marine sediments present at the dump site do not contain significant levels of contaminants and are within the guideline values for marine sediments from similar environments as proposed by The Marine Institute. However, copper levels at Stations 1, 2 & 3 and chromium and nickel at Station 3 were above the upper level guidance values as published by The Marine Institute (2006). The upper level guidance values are set at the lower end of the known range of effective concentrations i.e. lowest concentrations shown to have adverse effects on marine organisms. There are no obvious nearby sources of any potential source for elevated levels (e.g. a shipwreck) within the sampling area and it has never been previously used as a dump site.
The Marine Institute was consulted in relation to the elevated copper, chromium and nickel levels and the sampling laboratory, NLS, was asked to verify that the analysis was undertaken correctly. The laboratory has confirmed that the sampling was undertaken correctly and the results are accurate. As of June 2012 the Marine Institute are continuing their investigation into the sampling process undertaken at the laboratory to verify whether these results are correct.
The sediment samples obtained at the offshore disposal site are required as part of the dumping at sea licensing process to characterise the baseline of the sediments at the dump site. The nickel, copper and chromium levels measured in the sediment to be dredged are all substantially below the lower guidance level. All the other parameters tested in the dredged sediments are also below the Marine Institute’s guidance levels and the sediment is therefore confirmed as being clean and will pose no significant adverse impacts in terms of sediment chemistry at the dump site.
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6.3.4 Predicted Impacts at the Proposed Offshore Dump Site
Hydrodynamic modelling was undertaken as part of the study to investigate the impact of the dumping operation on sedimentation and suspended sediment loads in the area of the proposed dumpsite (see relevant section of model details). Results from the model simulation reported that:
x the suspended sediment values beyond the immediate vicinity of the dumping operation are minimal. x the majority of the dumped material will be deposited and remain within 2km on the dumping site with only a small amount of material being transported further offshore by the residual current. x material at the bed may be re-suspended however any subsequent transport will take place by advection on tidal currents. In the area of the dump site the tidal currents are weak and the material would not be transported significant distance before the current speeds reduce at slack water and the material is deposited, or if it remains in suspension it will be carried back to the site on the returning tide. x Based on the results of the hydrodynamic modelling study, the final settlement model (Figure 11. 58 in Chapter 11) shows that most of the dumped sediment will settle on the seabed close to the dump site. Some of the material will migrate towards the east under the influence of tidal action, but all particles will settle within 5.5km of the dump site. An area extending across approximately 2km to the east and south of the dumpsite will experience deposition in excess of 20mm. Within this, an area measuring approximately 0.5km² will experience deposition depths in excess of 130mm. It can be seen from the suspended sediment and deposition diagrams that the proposed dredging will not have a significant impact on bed sediments or water quality in a waters beyond the immediate vicinity of the dumping site. Sediment transport due to wave action is likely to be limited at the site due to the 90m water depth. In addition any material that may be re-suspended during extreme swell events will not be transported far from the site due to the weak tidal currents.
Potential impacts resulting from dumping the dredge spoil at the proposed dumpsite are discussed below.
6.3.4.1 Bottom Communities Bottom type and associated species composition in the vicinity of the dumpsite was very variable over such a small sampling area. Following dumping, all species covered by the dumped material will be lost. However, it was found that no unusual species or habitats were located within the proposed dump area and given the relatively small area of impact relative to the surrounding habitats, there should be no significant negative impact on the bottom communities from Donegal Bay.
Responses of benthic infauna to large scale disturbance by dredged material placement have been studied at numerous sites. Wilber et al (2008) monitored eight paired (placement and reference) areas in Corpus Christi Bay, Texas in 1995 and 1996. Total infaunal abundance, taxa richness, and the biomass of annelids and molluscs in placement areas no
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longer differed from that of reference areas approximately one year after placement. Differences in community structure between placement and reference areas returned to pre- placement levels one year after disturbance. The use of the term “recovery” with reference to recolonisation of dredging-related disturbance implies a return to pre-placement ecological conditions that are frequently neither a reality nor a practical expectation for areas that are subject to repeated disturbances. Wilber et al (Loc. cit.) characterisation of biological responses to dredged material disturbance targeted benchmarks that were linked to both pre-disturbance conditions and differences between disturbed and neighbouring undisturbed areas and indicate that impacts persisted less than one year. However, Wilber and Clarke (2008) point out that few generalisations can be made about typical recovery rates because biological responses are influenced by numerous factors, including site-specific bathymetry, hydrodynamics, depth of deposited material, the spatial scale of the disturbance, sediment type and timing and frequency of the disturbance. That being said, it is probable that following completion of the dumping operation, the impacted seafloor will be recolonised from the surrounding faunal community and will integrate as part of the overall habitat.
6.3.4.2 Fish and Crustaceans Suspended solids in the area will be temporarily increased during the dumping phase and the seafloor in the footprint of the dumped material will be smothered with the loss of burrow habitat for shrimp and food source for bottom feeding fish.
Local fishing interests have been concerned that the dumping of dredged spoil could negatively impact on the crab, lobster and prawn fishery. Given the relatively small footprint of the dumped material, the immediate loss of habitat to crustaceans is negligible and long term, could increase available soft sediment for burrowing. Results from the video survey (see Video Survey Section 6.3.1.5.3) would suggest that the predominant bottom type at the dumpsite of mixed gravel, boulders and sand is typical crab ground but unsuitable for Nephrops, which require soft substrate for burrowing, or lobster, which are normally found on rock that provides shelter. Burrows or individuals were not imaged in any of the video transects recorded in the vicinity of the dumpsite.
Dumping on the proposed dumpsite has the potential to kill a number of commercial crustaceans although most will escape. Those that escape undamaged will quickly recolonise the surrounding seabed and migrate to new habitats if necessary. Shelton (1973) reported that Cancer pagurus avoided areas of spoil dumping and suggested this may be due to increased suspended sediment or due to decreased macrofauna. Cancer pagurus relies on visual acuity to find prey so although mortality due to an increase in suspended sediment is unlikely, some perturbation is expected. The Marine Life Information Network (MarLin.ac.uk) suggest that smothering is unlikely to cause mortality in crabs, which are able to escape from under silt and migrate away from an area experience dumping. Given the crabs normal behaviour for “pit digging” in soft sediments (Hall et al, 1991), it is unlikely that any increase in fine sediment will have significant negative impacts on their health.
The turbidity caused by suspended solids can affect primary production by shading and increased sedimentation can disturb benthic communities. There is also the possibility of negative impact on shrimp, particularly if solids are suspended during the breeding season.
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In an assessment of tolerance to suspended sediment, the Marine Life Information Network (MarLin.ac.uk) assess Nephrops norvegicus as being probably tolerant of changes in suspended sediment. This is based on the fact that Nephrops are not dependent on increased suspended sediment for food availability as Nephrops is a carnivore and feeds by predation and scavenging. The species is also able to move to more suitable conditions if necessary. Therefore Nephrops has been assessed as tolerant to this factor. Nephrops norvegicus is also assessed as being tolerant of displacement, such as that caused by a passing trawl that does not kill the species but throws it into suspension, because it can reburrow into suitable substrata. Following displacement to suitable sediments Nephrops norvegicus are likely to commence burrowing immediately provided that individuals are not damaged.
Newcombe and MacDonald (1991) state that high levels of suspended solids (typically of the order of 20,000 mg/L or more for exposure periods of 24 to 96 hours for smolts of several species) can be lethal for salmonids. The same authors also detail sub-lethal responses (including cellular damage and physiological stress) and behavioural responses (e.g. avoidance behaviour and alarm responses) to suspended solids. The concentrations of suspended solids causing these responses were variable (from 6 to 650 mg/L for behavioural responses and from 14 to 1547 mg/L for sub-lethal responses) and are probably dependent on the duration of exposure of the fish to the suspended solids. Whitman et al. (1992) observed the effects on Pacific Chinook Salmon (Oncorhynchus tshawytscha) that were caused when volcanic ash was added to water under experimental conditions. When ash was added to a concentration of 350 mg/L the preference of the fish for home water (i.e. water from their natal river) was significantly reduced. This was apparently due to avoidance of the ash, rather than an inability to identify home water.
The avoidance behaviour of Cod and Herring to dredging-induced turbidity and the effects of sediment plumes on the buoyancy and mortality of Cod eggs and larvae have been studied as part of the Environmental Impact Assessment for the Öresund Link bridge-tunnel project between Denmark and Sweden (Westerberg et al., 1996). The avoidance threshold to suspended sediments of glacial clay of limestone origin was studied in an experimental saltwater flume and was found to be approximately 3 mg/l for both species. Adhering particles from sediment suspensions were shown to cause a loss of buoyancy for Cod eggs, while larvae showed increased mortality on exposure to sediment concentrations of 10 mg/l.
The adverse impacts of suspended solids of fish that have been recorded experimentally are generally at concentrations greater than 10 mg/l and often several orders of magnitude more than this. Results from the model sediment analysis predict that concentrations of suspended material in the dredge plume will fall to concentration of 3.5 mg/l or less within several hundred metres of the disposal site. It should be realized that negative impacts on fish from experimental data often followed prolonged periods of exposure, whereas fish in the vicinity of the site of the proposed development will have the opportunity to move away from areas affected by the dredge plume. It is therefore concluded that there will be no significant impact on fish species as a result of the dumping operation.
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6.3.5 Mitigation of the Potential Impacts at the Dump Site and Residual Impacts Given that the material is required to be dumped only within the limits of the proposed defined dumpsite, there are few mitigation measures that can be proposed to reduce the impact of the material on the seafloor and short term effects on the water column as predicted by the hydrodynamic model.
As the model predicts the fate of the material during slack water, optimum dumping to reduce far field effects should occur at high or low water when water currents are at their minimum to reduce dispersion of the material. However, given the relatively slack currents recorded at the site (see Section 6.3.1.2 Current and Tide Measurements); this mitigation measure would be limited in its effectiveness. Furthermore, as the dumpsite takes several hours to steam to, it will not be possible to arrive on site at a defined stage of the tide.
The proposed dump site has endeavoured to mitigate against impacts through site selection - it been chosen in an area where the residual currents will not transport sediment east into Donegal Bay and does not occur in a known spawning area.
No unusual species or habitats were found within the proposed dump site during the video and grab sampling studies. Given the relatively small area of impact relative to the surrounding habitats, there should be no significant negative impact on the bottom communities from Donegal Bay. Any areas affected by sedimentation will be quickly recolonised upon completion of dumping. No significant impact is predicted to occur on fish species as a result of the dumping operation.
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6.4 MARINE MAMMALS
This section of the Environmental Appraisal details the potential risks to marine mammals and makes recommendations for mitigation measures related to the proposed dredging of Sligo Harbour. It is based on a site visit by the author, information from published and unpublished literature and communication with local relevant authorities. This report is based on the information provided in Chapter 4.0 – “Project Description” which includes both dredging and dumping activities.
6.4.1 Legislation pertaining to Marine Mammals in Irish waters
Marine mammals are protected by national legislation and by a number of international regulations which the Republic of Ireland is signatory to. The main legislation that affords protection to marine mammals in Irish waters is the Wildlife Act (1976) and the Wildlife (Amendment) Act (2000), which prohibits wilful interference to wild mammals and disturbance of resting and breeding sites.
All cetacean species (whales, dolphins and porpoises) occurring in European waters are now afforded protection under the EC Habitats Directive. All cetaceans are included in Annex IV of the Directive as species “in need of strict protection”. Additionally, the harbour porpoise (Phocoena phocoena) and bottlenose dolphin (Tursiops truncatus) are designated Annex II species (those animals of community interest, whose conservation requires the designation of special areas of conservation). Ireland’s two pinniped (seals) species, the Harbour Seal (Phoca vitulina) and Grey Seal (Halichoerus grypus) are also designated Annex II species under the EC Habitats Directive.
The Republic of Ireland is also signatory to conservation orientated agreements under the Bonn Convention on Migratory Species (1983), the OSPAR Convention for the Protection of the Marine Environment of the northeast Atlantic (1992) and the Berne Convention on Conservation of European Wildlife and Natural Habitats (1979).
In light of the legislation and conservation status of marine mammals, careful consideration must be given during all anthropogenic activity with potential effect on the species and their habitat. Furthermore, Sligo Harbour holds a number of important environmental designations including the Cummeen Strand Special Area of Conservation and the Cummeen Strand/Drumcliff Bay Special Protection Area. Nearby Drumcliff Bay is also a Special Area of Conservation. Therefore, the EIA requires an Appropriate Assessment which will fulfil the requirements of the Habitats Directive.
6.4.2 Desktop Study of Marine Mammals in the Area
It is necessary to determine what marine mammals use the area and surrounding waters in order to estimate the likely significance of any impacts resulting from the proposed development.
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Figure 6.46 shows a map of cetacean sightings recorded by the members of the Irish Whale and Dolphin Group and public sightings reported to the group in the sea around County Sligo and Donegal between January 2010 and June 2012 (www.iwdg.ie). The map is a useful tool in gaining a broad overview of the species that may occur in the area, however it is limited in the sense that observations will mainly only occur from terrestrial vantage points and the results may be skewed towards sightings from more populated places. The figure shows that the species recorded in the Sligo Harbour area and adjacent areas are mainly dolphins and harbour porpoises.
Figure 6.46: Cetacean sightings in the County Sligo area. (All records are validated and available on www.iwdg.ie)
6.4.2.1 Cetaceans
Based on the species’ ecology and sighting records, cetacean species likely to use the area include minke whales (Balaenoptera acutorostrata), harbour porpoises (Phocoena phocoena) bottlenose dolphins (Tursiops truncatus), Risso’s dolphins (Grampus griseus) and common dolphins (Delphinus delphis) (Evans, 1992, Berrow et al., 2001; Ingram, 2000; Ingram et al., 2001 and 2003; Rogan et al., 2001; Ó Cadhla et al., 2004; O Brien et al., 2009; Anderwald et al., 2011).
Minke Whale The most common species of baleen whale found around Irish coasts, the minke whale is frequently recorded around all parts of the west coast (Pollock et al., 1997, Berrow et al., 2002; Ó Cadhla et al., 2004). Research conducted in UK waters suggest that the species
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moves southwards to inshore Atlantic Margin waters in spring and summer remaining until late autumn following which numbers decline (Pollack et al., 2000; Northridge et al., 1995). The minke whale has been sighted in near inshore waters in northwest, west and southwest Ireland (Ó Cadhla et al., 2004; Roycroft et al., 2007) and of all whale species that use Irish waters is the species with the most near-shore distribution, and therefore potentially the most vulnerable to anthropogenic noise resulting from coastal developments such as the proposed harbour works. It is unlikely, however, that there is a threat to individuals from the proposed dredging, as there are no records of this species within Sligo Harbour and therefore highly unlikely that the dredging work will impact on this species. Minke whales have been sighted in Donegal Bay (IWDG, 2011) and it is likely they use the proposed dumping area. Mitigation measures outlined in Section 6.4.8 will minimise potential impacts of the proposed works if there is occasional use of the harbour by this species.
Vocalisations of minke whales involve intense, low frequency, broadband (0.5-1 kHz bandwidth) and harmonic down-sweeps with maximum source level of 165 dB re 1 IPa (Edds, 1988).
Harbour Porpoise Sightings of Europe’s smallest cetacean species, the harbour porpoise, have been relatively common off all coasts of Ireland and in the Irish Sea (Northridge et al., 1995; Hammond et al., 1995; Pollack et al., 1997; Berrow et al., 2001; Ó Cadhla et al., 2004; Anderwald et al., 2011). The small size of harbour porpoises and their erratic surfacing behaviour make them difficult to detect. Information relating to the movements of this species around coastal areas is very limited but there have been occasional sightings of the species within Sligo Bay (IWDG, 2011) and this species is likely to visit Sligo Harbour particularly at mid-high water. It is also likely that they will use the proposed dump area west of Donegal Bay.
Harbour porpoises produce high-frequency sounds used for echolocation and communication, but do not make frequency-modulated whistles typical of many delphinids. The high frequency sounds are comprised entirely of click trains, produced in two narrow band frequency components, one between 1-20 kHz and the other between 120-160 kHz (peaking around 125-130 kHz) (Goodson et al., 1995). Maximum source level is estimated at between 149 and 177 dB re 1IPa at 1 m (Akamatsu et al., 1992).
Harbour porpoises are very sensitive to vessel noise and activity and are unlikely to approach areas of high activity and are therefore considered not likely to be impacted by the proposed works. However, mitigation measures outlined in Section 6.4.8 will minimise potential impacts of the proposed works if there is occasional use of the harbour by this species.
Bottlenose Dolphin A coastal species of cetacean commonly sighted in western Irish waters (Evans, 1992, Pollock et al., 1997) bottlenose dolphins are numerous on the south and west coasts (Ingram and Rogan, 2003; Ingram et al., 2001, 2003). There are resident communities in the waters of the outer Shannon Estuary (Ingram, 2000; Ingram and Rogan, 2003) and a transient population recorded off all Irish coasts (O Brien et al., 2009). Bottlenose dolphins
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have been recorded in the Sligo Harbour area and likely to be part of this transient population. Bottlenose dolphins are a wide-ranging species and individuals commonly travel between coastal regions especially during the summer months (Ingram et al., 2003).
The bottlenose dolphin makes a wide range of vocalisations. Echolocation clicks (used for orientation and foraging) are composed of intense short duration broadband clicks (40-130 kHz) (Au, 1993). Burst pulse vocalisations may have a variety of social functions (0.2-16 kHz). Whistles are pure tone frequency modulated calls ranging from 2-20 kHz. Clicks and whistle vocalisations can be made simultaneously.
Bottlenose dolphins may be attracted to vessel activity, making them potentially vulnerable to physical harm from industrial activities. It is considered unlikely that the proposed works will impact upon bottlenose dolphins in the area as they do not frequent the waters of the inner harbour, however mitigation measures outlined in Section 6.4.8 will minimise potential impacts of the proposed works if there is occasional use of the harbour by this species.
Common Dolphin Although a mainly oceanic species, common dolphins have been frequently observed in large schools around the coasts of Ireland (Pollock et al., 1997; Gordon et al., 2000) and it is the most commonly stranded cetacean around the Irish coast (Berrow & Rogan, 1997). The mobile schools of common dolphins seen in coastal waters tend to be foraging for shoaling fish species.
Vocalisations of common dolphins vary from whistles of 1-50 kHz frequency (mainly 6-12 kHz, max. source level 172dB) to echolocation clicks which may reach 150 kHz (max. source levels 170 dB) (Evans, 1973; Moore & Ridgway, 1995). Clicks and whistles may be given simultaneously.
Common dolphins are attracted to vessels and are easily sighted and identified. It is considered unlikely that the proposed dredging works will impact upon common dolphins in the area as they do not frequent the waters of the harbour; however it is possible they will use the area where the proposed dumping of dredged material will take place. Mitigation measures outlined in Section 6.4.8 will minimise potential impacts of the proposed works on this species.
Risso’s Dolphin In Ireland Risso’s dolphin have generally been recorded close to the coast with highest numbers of sightings between August and February (Pollack et al., 1997; 2000). A large and robust species, Risso’s dolphins are slow moving and often seen in small schools around the west coast (Berrow et al., 2002). Risso’s dolphins will not usually approach vessels but are readily recognised by their distinctive colouration patterns and large size.
Vocalisations include a variety of clicks, whistles, and pulsed calls. Whistles are rarely heard, but range over 2.5-20 kHz, maximum source level of 170 dB re 1IPa @ 1 m. Clicks have peak frequency at 65 kHz and durations of 40-100 secs (Au, 1993).
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It is considered unlikely that the proposed works will impact upon this species as there are no records of this species in the harbour or surrounding area, however mitigation measures outlined in Section 6.4.8 will minimise potential impacts of the proposed works if there is occasional use of the harbour by this species.
6.4.2.2 Pinnipeds
Harbour Seal Harbour Seals (also known as “Common Seals”) have established themselves at terrestrial colonies (or haul-outs) along all coastlines of Ireland, which they leave when foraging or moving between areas, for example, and to which they return to rest ashore, rear young, engage in social activity, etc. These haul-out groups of harbour seals have tended historically to be found among inshore bays and islands, coves and estuaries (Lockley, 1966; Summers et al., 1980), particularly around the hours of lowest tide. Harbour seals haul-out at terrestrial haul-out sites on the Aran Islands. A national aerial census of harbour seals in Ireland during 2003 identified haul-out sites in Ballysadare Bay Co. Sligo where over 250 harbour seals were recorded and in Killala Bay where approximately 110 seals were recorded (Cronin et al., 2004, 2007). These counts, which are conducted during the seals annual moult are considered to represent about 60-70% of the total number of seals using the area. Therefore there are approximately 500-600 harbour seals using haul-out sites within 40km of Sligo harbour, assuming the population has not changed since the 2003 census. Recent findings from tagging harbour seals in SW Ireland suggest that harbour seals are local foragers, generally staying within 20km of their haul-out sites (Cronin et al., 2008). It is highly likely that harbour seals from haul-out sites in Ballysadare Bay use the waters of Sligo Harbour.
Harbour seals are most vulnerable at their terrestrial haul-out sites during breeding and moulting periods. These events occur between June and September in Ireland. However the terrestrial haul-out sites in the Ballysadare area are not located in close proximity to Sligo Harbour and therefore there is no considered threat of physical disturbance at the haul-out sites by the proposed works.
In addition to the identified terrestrial sites, the surrounding waters are likely to be critical habitat for harbour seals, for feeding and/or for navigation to more offshore foraging areas. Results from a study by the Coastal and Marine Research Centre (CMRC) on the haul-out behaviour of harbour seals in southwest Ireland in recent years suggests that harbour seals spend up to 80% of their time at sea (Cronin, 2007; Cronin et al., 2008). Similar behaviour patterns have been seen in studies of harbour seals in Scotland (Sharples, SMRU pers comm, Thompson & Miller, 1990). Unlike grey seals harbour seal adults continue to forage during the breeding season (Bonnes et al., 1994). In addition the mating strategy is based on males diving and calling at aquatic display sites (Van Parijs et al., 1997, 2000, Hayes et al., 2004). Disturbance from anthropogenic noise during this period could potentially affect mating success.
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The hearing range of harbour and grey seals extends over wide frequencies, including the ultrasonic spectrum. The area of best hearing is between 8 and 25 kHz, with acute hearing also at lower frequencies (Møhl 1968; Terhune & Turnbull 1995)
Considering the relatively large population of harbour seals using waters in Sligo Bay and the proximity of haul-out sites to Sligo Harbour, there is high potential for harbour seal use of the waters in the vicinity of Sligo Harbour and therefore they are the marine mammal species most at risk to potential detrimental impacts of the proposed dredging and dumping. Mitigation measures outlined in Section 6.4.8 will minimise potential impacts of the proposed works.
Grey Seal Grey seals are distributed throughout Irish coastal waters and commonly seen hauled out on more exposed shores than the harbour seal (Kiely, 1998). Whilst there are no large colonies of grey seals on the coastline of Co. Sligo, the bordering counties provide haul-out sites for a significant proportion of the national population of grey seals. A national census of the grey seal population in 2005 estimated between 795-1022 grey seals use breeding sites in Co. Donegal and 1351-1737 use breeding sites in Co. Mayo (Ó Cadhla et al., 2007).
Grey seals use Inishmurray (54.433N 8.660W) and Rathlin O Birne Island (54.664N 8.827W) as breeding sites (Ó Cadhla et al., 2005) and Ballysadare Bay and Ardboline (54.346N 8.693W) as moult sites (Ó Cadhla & Strong, 2007), where approximately 50 seals haul-out to moult. Grey seals also use Inishmurray and Ballysadare Bay as haul-out sites outside of the breeding and moult seasons; over 110 grey seals were recorded on Inishtrahull and 20 in Ballysadare Bay in August 2003 during the harbour seal census (Cronin et al., 2003).
Grey seals are also most vulnerable at their terrestrial haul-out sites during breeding and moulting periods. These events occur between September and March in Ireland. There are no known terrestrial sites for grey seals in the immediate proximity of the proposed works however the surrounding waters are likely to be a critical habitat for grey seals, for feeding and/or for navigation to more offshore foraging areas. Grey seals have a wider offshore foraging distribution than harbour seals and as a result seals from large breeding colonies on the coasts of Mayo and Donegal will be likely to use the waters of Donegal Bay and Sligo Bay for foraging and/or navigation and therefore could potentially be affected by dredging and dumping. Mitigation measures outlined in Section 6.4.8 will minimise potential impacts of the proposed works.
6.4.3 Site visit
A visit to Sligo Harbour and adjacent coastal areas was made on March 18th and 19th 2011.
6.4.3.1 Methods: The waters in the Sligo Bay and harbour were surveyed from a vantage point on the south shore of the harbour using a telescope (equipped with a 30x eyepiece) mounted on a tripod and 10 x 50 leica binoculars for all marine mammals at sea between 15:00 and 19:00 on March 18th 2011 (2 hours either side of high tide) (Figure 6.47 to Figure 6.49).
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The shorelines of Sligo Bay and Drumcliff Bay were surveyed using 10 x 50 Leica binoculars for all marine mammals ashore during the low water period between 09:20 and 13:20 (2 hours either side of low water) on March 19th. The low water period was surveyed in order to maximise the likelihood of observing seals hauled out on rocks.
Observations of marine mammals at sea are affected by prevailing sea conditions with a decline in sighting probability in Beaufort sea-states of three or higher. The conditions on March 18th/19th were favourable for visual surveillance, with a Beaufort sea-state of one to two and a light variable NE breeze.
6.4.3.2 Results:
One seal (unidentified species) was observed approximately 200m east of Oyster Island on March 18th at 16:25.
One harbour seal was observed in the channel approximately 50m from the north shore near Rosses Point on March 19th at 10:10.
No cetaceans were observed during visual observations, but given the limited time available and the transient nature of cetacean movement patterns this does not indicate that the area is not visited by dolphins or porpoises.
Drumcliff Bay
Rosses Point
Sligo Bay
Figure 6.47: Survey Area ( denotes observation point for Sligo Bay marine mammal survey (source: ESRI topographical map)
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Figure 6.48: Vantage point for marine mammal survey on south shore of Sligo
Harbour Figure 6.49: North shore of Sligo Harbour at low tide, scanned for hauled-out pinnipeds.
6.4.4 Potential Impacts of Dredging on Marine Mammals and Identification of Sensitive Receptors.
The most likely impact of the proposed dredging activities in the harbour will be through sound disturbance and local habitat modification. Benthic dredging activity can result in significant modification to the biological environment. Destruction of benthic communities will displace many species of invertebrate and fish and subsequently affect the food chain and impact on marine predators. However, the effects of substrate removal will be determined by the extent of dredging activity. In addition to the physical act of sediment removal, dredging
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activities will result in potential disturbance to marine mammals through increases in vessel activity and increase local ambient marine noise levels.
Studies on the responses of marine mammals to anthropogenic noise have identified the following factors as influencing the degree of response given by animals: (i) source intensity levels, (ii) degree of background noise, (iii) distance to source, (iv) species involved, (v) behavioural state and season, (vi) prior degree of exposure and (vii) age, sex and time of day (Anguilar et al., 2004). The peak pressure, duration and the frequency spectrum of anthropogenic sound are important factors relating to potential biological impacts. Several studies have examined the direct and indirect impacts of underwater noise on marine mammals and in general have indicated that source levels of 180-200dB P-P re 1 ȝPa are sufficient to induce behavioural effects on marine mammals within a few kilometres of the sound source (Gausland, 2000).
Biological damage from high-level sound may be categorized as either direct injuries (lethal, sub-lethal or non-lethal) or indirect effects (changes in behavioural or distribution patterns). Considering the proposed works in Sligo Harbour there is no potential for direct injuries to marine mammals that could be caused by e.g. blasting. However there is potential impact from underwater noise resulting from dredging. The physiological effect of exposure to underwater noise can include temporary or permanent shifts in hearing thresholds, which degrade an animal’s ability to forage and carry out other activities that depend on auditory acuity such as communication, navigation and mating (Richardson et al., 1995).
There have been very few studies describing dredging noise from North America and the UK, covering a variety of dredger types. The sparse data available indicate the predicted vibration levels close to the source are relatively small and that dredging is not as noisy as seismic surveys, pile driving and sonar; but it is louder than most shipping, operating offshore wind turbines and drilling. Thompsen et al. (2009) suggest it should be viewed, therefore, as a medium impact activity and because of its continuous source which might last for extended periods, the potential adverse effects, especially in areas of high ecological sensitivity should not be overlooked.
Noise associated with dredging is predominantly of low frequency, below 1 kHz; estimated source sound pressure levels range between 168 and 186 dB re 1 ȝPa at 1 m. In most cases the noise is continuous in nature. Audibility of dredging noise is dependent on many factors (hearing sensibility of the species in question, prevalent ambient noise, transmission loss etc). Since dredging noise is predominantly of low frequency, it would potentially affect low frequency cetaceans such as minke whales to a greater extent than mid or high frequency cetaceans. The harbour porpoise is a potential exception as it has a relatively high sensitivity across most frequencies. There is also a potential issue with seals as both harbour and grey seals have relatively good underwater hearing at frequencies below 1 kHz (Thompsen et al., 2009)
Studies have shown that in shallow water, which would also characterise the situation at most dredging sites, received sound pressure levels were above 140 dB re 1 ȝPa, respectively at 1 km distance from the source; a value that is probably detectable for most
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marine mammals sensitive to sound pressure, depending on hearing abilities and local ambient noise conditions. Even at 10 km distance, sound pressure levels were well above 120 dB re ȝPa, a value which might exceed ambient noise levels in several areas (Thompsen et al., 2009).
The dumping of dredged material of fine sand and silt will likely affect water quality and create a plume effect which will travel according to local water currents. This may have a temporary impact on marine mammals’ visibility in the immediate vicinity of the vessel. The changes to the benthos in this region caused by accumulation of dredged material on the seabed will most likely invoke local changes in faunal assemblages and prey availability at higher trophic levels, potentially affecting marine mammals.
To summarise, the potential effects of dredging and dumping on marine mammals include;
1. Physical injury or death of individuals resulting from collisions with operator vessels. 2. Chronic hearing damage or disturbance/displacement as a result of noise. 3. Consumption of contaminated prey items resulting from contaminants entering the food chain (this is only a problem where contaminated substrates are disturbed). 4. Temporary impact on marine mammals’ visibility should they intersect the sediment plume during the dumping of dredged material. 5. Changes in prey availability due to local changes in benthic ecology caused by accumulation of dredge spoil on the seabed.
The likelihood and scale of each of these effects can be estimated and appropriate precautionary mitigation measures should be employed to reduce the estimated effects.
6.4.5 Direct, Indirect and Cumulative Impacts of Proposed Dredging and Dumping of Dredged Material on Pinnipeds.
The proposed dredging activities at Sligo Harbour are unlikely to cause detectable impacts on seals at the population level. The numbers of seals in the adjacent coastal areas represent a small fraction of local populations. There is a small possibility that impacts may be suffered by individual grey or harbour seals entering the works zone. Sightings during the field survey and local reports show that seals regularly enter the harbour area. However, risks to these animals will be small and with a degree of vigilance from operators collisions with seals and excessive disturbance will be avoided. Sediment plumes may present a small level of habitat disturbance to local seals foraging in the area. Acoustic disturbance can be a threat to marine mammals causing hearing damage however, noise levels from vessels or from the dredging process are highly unlikely to cause hearing damage to exposed seals provided they have the opportunity to leave the affected works area. As the received sound pressure levels can be 140 dB re 1 ȝPa at 1 km distance from the source, a
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value that is detectable for seals, and as the area is of ecological importance2 (Figure 6.50) it is suggested that appropriate mitigation measures be put in place to minimise acoustic disturbance to seals (see Section 6.4.8).
The dumping of dredged material of fine sand and silt will have a minor impact on water quality (discussed in more detail in Chapter 11). This may have a temporary impact on marine mammals’ visibility in the immediate vicinity of the vessel. However this effect will be temporary and as it is an open body of water 34 nautical miles from Sligo Harbour quayside and in about 92m water depth, it is unlikely to cause any adverse effects on seals in the area. The changes to the benthos in this region may temporarily affect prey availability to seals in the area but as it is not a known ‘hotspot’ for seal foraging, displacement resulting from impacts on available prey are unlikely. It is suggested that mitigation measures outlined in Section 6.4.8 be followed to minimise any potential impact of dumping on individual seals.
Extract from Admiralty Chart 2852 © Crown Copyright UKHO. Not for navigational use
Figure 6.50: Proposed dredging area showing main environmental designations
2 Sligo Harbour holds a number of important environmental designations including the Cummeen Strand Special Area of Conservation and the Cummeen Strand/Drumcliff Bay Special Protection Area. Nearby Drumcliff Bay is also a Special Area of Conservation
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6.4.6 Direct, Indirect and Cumulative Impacts of Proposed Dredging and Dumping of Dredged material on Cetaceans
The proposed construction activities at Sligo harbour are unlikely to cause detectable impacts on cetaceans at the population level. There is little information indicating use of the area by cetaceans and any exposure to sediment plumes or increased noise levels will be temporary and non-threatening. The noise levels from vessels or from the extraction process are unlikely to cause hearing damage to exposed cetaceans, provided they do not approach the immediate vicinity of operations and have the opportunity to leave the affected area. As the received sound pressure levels can be 140 dB re 1 ȝPa at 1 km distance from the source, a value that is detectable for most cetaceans (in particular the auditory range of harbour porpoise and minke whale, two of the most likely species of cetacean to visit the area) and as the area is of ecological importance, it is suggested that appropriate mitigation measures be put in place to minimise acoustic disturbance to cetaceans (see Section 6.4.8).
It is most likely that any effects of the proposed dredging work in Sligo harbour on cetaceans will be minimal provided correct management and communication procedures are followed.
The dumping of the dredged material of fine sand and silt will likely affect water quality and create a plume effect which will travel according to local water currents (these effects are described in more detail in Chapter 11). This may have a temporary impact on marine mammals’ visibility in the immediate vicinity of the vessel. However this effect will be temporary and as it is an open body of water 34 nautical miles from Sligo Harbour quayside and in about 92m water depth it is unlikely to cause any adverse effects on cetaceans in the area. The changes to the benthos in this region will most likely temporarily affect prey availability to cetaceans in the area, but as with seals the area is not considered (or known to be) an important cetacean foraging area and therefore displacement resulting from impacts on available prey are unlikely.
6.4.7 Assessment of impact magnitude and significance
It is considered that the proposed dredging at Sligo harbour and dumping of dredged material west of Donegal Bay will have little likelihood of impacting on marine mammals in the area at a population level. It is however recommended that vigilance should be maintained for any marine mammal approaching the area throughout operations as there will be potential effects of acoustic disturbance resulting from noise and boat activity associated with dredging and dumping. The proposed dredging will occur during high tide, there is an increased likelihood of marine mammals using the harbour at this tidal stage. As the proposed works will take place within a Special Area of Conservation it is best practise to employ a marine mammal observer to ensure impacts of coastal works (including dredging) on marine mammals are minimised (D. Lyons, NPWS pers comm). The following precautionary measures are therefore advised:
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6.4.8 Marine Mammals - Mitigation Measures
A trained and experienced Marine Mammal Observer (MMO) should be put in place during dredging and dumping operations. The MMO will scan the surrounding area to ensure no marine mammals are in a pre-determined exclusion zone in the 30 minute period prior to dredging operations. It is suggested that this exclusion zone is 500m, considering the potential risks outlined.
x Once operations have begun operations should cease temporarily if a cetacean or seal is observed swimming in the immediate (<50m) area of industrial activity and work can be resumed once the animal(s) have moved away.
x Dumping of material at sea should not take place if a cetacean or seal is within 50m of the vessel.
x Any approach by marine mammals into the immediate (<50 m) works area should be reported to the National Parks and Wildlife Service.
x The MMO will keep a record of the monitoring using an MMO form “Location and Effort (Coastal Works)” available from the National Parks & Wildlife Service (NPWS) and submit to the NPWS on completion of the works.
x If feasible, the MMO will take photographs of dorsal fins of Bottlenose dolphins encountered, for the purpose of contributing to the Irish Whale and Dolphin Group (IWDG) catalogue of images for photo-identification.
Many dredging contractors now have staff trained as MMOs within their dredging teams. If the contractor does not have suitably trained staff, the cost for a marine mammal observer is likely to be approximately €300-400 per diem (inclusive of employers PRSI & pension).
6.4.9 Marine Mammals - Residual Impacts It is unlikely that there will be negative residual impacts of the proposed works on marine mammals in the area. The changes to benthos in the dump area will most likely have short long term impacts on prey availability to marine mammals in the area but as it is not known to be a critical foraging area for marine mammals any effects will be negligible on both the population as well as the individual level. The deepening of the navigation channel will likely increase vessel activity in the area with an associated increase in underwater noise and risks of collisions for marine mammals, but it is considered that the impacts of this will not be significant on both the individual and population level for marine mammal species that frequent the area.
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7.0 FISHERIES AND AQUACULTURE
7.1 INTRODUCTION
This Chapter describes fisheries interests in the area of the proposed dredging scheme in Sligo Harbour and at the proposed dumpsite outside Donegal Bay, specifically with regard to: x Commercial fisheries x Shellfish aquaculture x Salmonid migrations x Eel & lamprey migrations x Recreational sea angling
Also included is an assessment of impacts and recommended mitigation measures.
7.2 COMMERCIAL FISHERIES Fisheries are considered in the areas of both the proposed dredging activity and the proposed dumpsite for dredged spoil materials.
Dredging Area The course of the navigation channel into Sligo port and the area proposed for dredging is shown in Figure 4.1 in Chapter 4, “Project Description”. There is little fishing activity in the proximity of area to be dredged within Sligo Harbour apart from some limited potting for lobster along the shore to the north of the channel. Outside of Sligo Harbour there is further potting for lobster and crab together with a limited degree of gill netting.
Proposed Dumpsite The material from the proposed dredging of the channel in Sligo Harbour is to be dumped at a proposed offshore location outside Donegal Bay (see Figure 4.2 in Chapter 4, “Project Description”). The dumping site is located in ICES statistical rectangle 38E0 and is approximately 17km from Malin More Head and 30km north of the nearest point on the north Mayo coast. This site is in an important area for Brown crab fishing, although the most intensive fishing activity is probably to the west of the actual dumping area.
7.2.1 Irish Brown Crab Fishery The Irish fishery for Brown crab (Cancer pagurus) has been examined in detail by Tully et al (2006) in a BIM report produced for the national Crab Management Advisory Group, a committee of the Management Framework for Shellfisheries which advises the Department of Agriculture, Food and the Marine (DAFM) on the management of shellfisheries. This assessment is based largely on the findings of the BIM report and supplemented with updated information through consultation with local BIM representatives covering the north Mayo, Sligo and Donegal region.
Landings of brown crab into Ireland in the last decade reached a peak of over 14,200 tonnes in 2004 with a value of almost €17 million, falling to 8,600 tonnes worth €12.85 million in 2010 (Table 7.1). In terms of value, from 2001 to 2005 brown crab was in the top five most
IBE00440/EAR/September ‘12 7-1 Sligo Harbour Dredging Environmental Appraisal Report Fisheries and Aquaculture important species of fish landed into Ireland; catches have since declined but remain in the top ten species landed.
Table 7.1: Total landings of brown crab into Irish ports, 2001-10 (Source: SFPA)
Year Live wt (tonnes) Value (€000s)
2001 10,312 13,109 2002 10,098 13,213 2003 10,655 10,231 2004 14,217 16,992 2005 9,527 9,571 2006 10,827 8,223 2007 9,251 na 2008 7,640 9,149 2009 6,614 na 2010 8,621 12,847
Landings increased by approximately 500 tonnes per year between 1990 and 2004 with a higher rate of increase during the latter half of this period (Figure 7.1). The Irish fleet can be divided into <12m vessels which land crab on a daily basis and a more mobile >18m vivier fleet which can carry live crab onboard and remain at sea for extended periods. The vivier fleet fishes off the northwest coast although, through modernisation, the <12m fleet has increased its seaward range and can fish outside the 12nm limit on a daily basis.
14000 National crab landings 12000 1952-2004
10000
8000
6000
4000
Tonnes of crab landed 2000
0 1952 1956 1960 1964 1968 1972 1976 1980 1984 1988 1992 1996 2000 2004
Figure 7.1: National landings of brown crab between 1952 and 2004 (from Tully et al, 2006; reproduced by permission of BIM)
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7.2.1.1 Biology of the Brown Crab The brown crab or edible crab (Plate 7.1) is a decapod crustacean and is the largest of the common crabs found in Irish waters. It is widely distributed in Irish and British waters, and throughout north-western Europe. Brown crab can live for at least 15 years - mating first takes place is in spring and summer when the females are 5-6 years old and occurs shortly after the female has moulted. Females are 'berried', carrying the eggs under the abdomen over winter for 6-9 months and releasing the larvae in late spring/early summer. Crabs have a high fecundity with each female hatching 1-4 million eggs depending on size. Post-larvae settle in inshore areas and juveniles are often found in shallow waters. Adult crabs are migratory and undertake extensive seasonal migrations, probably associated with the reproductive cycle.
Plate 7.1: Brown Crab
Tully et al (2206) consider that Irish stocks are probably regional in scale (>100km) with a variable range from the coast to offshore waters. The authors also note that crabs on the northwest coast may be regarded as a single functional unit distributed over a wide range off the northwest coast of Ireland and west of Scotland (Figure 7.2).
7.2.2 The North West Crab Fishery A significant proportion of the national crab catch is taken in the northwest fishery and is landed into Donegal and Mayo (Figure 7.3).
7.2.2.1 Fishing activity in the north Mayo area The crab grounds off the north Mayo coast form a significant part of the North West crab fishery which is the largest stock fished by Irish vessels. The area is fished predominantly by vessels of <12m from ports on the north Mayo coast but also including ports on the Sligo coast and extending round into south Donegal. These vessels may steam five to six hours offshore to the fishing grounds.
Many of the fishermen in the north Mayo area are represented by the Erris Inshore Fishermen’s’ Association (EIFA) which covers ports from Belderrig to Doohoma – the group has around 50 members. All vessels concentrate on shellfish although not all fish in the area under consideration. A second group, the Erris Lobster Conservation and Restocking Association operates more locally in the Erris area.
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Figure 7.2:Probable distribution of the northwest crab stock (from Tully et al, 2006; reproduced by permission of BIM) 9000 8000 Crab landed into Donegal and Mayo 7000 6000 5000 4000 3000 Tonnes of crab of Tonnes 2000 1000 0 1990 1991 1992 1993 1994 1995 1996 1997 1998 1999 2000 2001 2002 2003 2004
Figure 7.3: Annual landings of crab into Donegal and Mayo, 1990-2004 (from Tully et al, 2006; reproduced by permission of BIM)
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The crab fishing area overlaps with the pelagic fishery operating out of Killybegs and there is an agreement in place between EIFA and the Killybegs Fishermen’s Organisation (KFO) to avoid damage to static gear from trawling activities.
In 2004 over 1,500 tonnes of crab was taken by the Mayo <12m fleet in ICES rectangle 38E0, in which the proposed dumpsite is located (Figure 7.4). However, it is believed that more vessels are now active in this area and the annual crab catch is now in excess of 2,000 tonnes (D Nee, BIM; pers comm).
Figure 7.4: Landings of crab by statistical rectangle by the Mayo and Donegal <12m fleets in 2004 (from Tully et al, 2006; reproduced by permission of BIM)
Peak fishing activity takes place from spring to early autumn during the months May to September, with activity declining between October and December, and fewer vessels operating from February to April. However, 6-8 boats now fish year round and the fishery is developing towards a 12-month operation.
Landings per unit effort (LPUE) data for the offshore fishery has been examined by Tully et al, (2006) while LPUE data for <12m vessels from the inshore fleet at Malin Head, Co. Donegal has been compiled by Meredith & Fahy (2005). A significant decline in LPUE has been observed in both sectors although the latter dataset suggests an increase in LPUE in the inshore fishery.
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7.2.2.2 Size composition Tully et al (2006) have presented data on the size composition of landings from the inshore fishery (Figure 7.5).
1200 Female crab 1996, 1000 n=6685 800
600
400
Number of crab 200
0 130 140 150 160 170 180 190 200 210 220 Carapace length (mm)
900 800 Female crabs 700 1997,n=5788 600 500 400 300
Number ofNumber crab 200 100 0 130 140 150 160 170 180 190 200 210 220 Carapace length (mm)
45 40 Male crabs 35 1996,n=232 30 25 20 15
Number ofcrabNumber 10 5 0 130 140 150 160 170 180 190 200 210 220 Carapace length (mm)
120 Male crabs 100 1997,n=651 80
60
40
Number ofNumber crab 20
0 130 140 150 160 170 180 190 200 210 220 Carapace length (mm)
Figure 7.5: Size composition of male and female crab in the inshore landings 1996/97 (from Tully et al, 2006; reproduced by permission of BIM)
The current legal minimum landing size (MLS) of 130mm carapace width is of little significance as there is a market-driven “limit” of 140mm and the modal landing size is 155- 165mm. The size composition of crabs in both offshore and inshore fisheries remained
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Mean size at maturity is approximately 120mm carapace width and all crabs appear to be mature at about 140mm.
7.2.2.3 Changes in fishing area and effort between 1997 and 2005 Tully et al (2006) describe a shift in fishing activity between 1997 and 2005 with an increased effort in the north Mayo area. In 1997 effort by vessels <12m was concentrated to the north of Malin Head and to the west of Donegal (Figure 7.6). However, by 2005 the main area of fishing activity by these vessels had shifted to northwest Mayo and north Donegal (Figure 7.7).
Further data presented by Tully et al (2006) illustrates that the number of vessels in the northwest fishery declined significantly between 1997 and 2005 but that fishing effort in terms of the number of pots fished had increased significantly during the same period.
In 1997 there was an estimated 129 Donegal based boats fishing crab with a further 24 fishing out of north Mayo ports. By 2005 the combined number of vessels targeting the fishery from both north Mayo and Donegal had fallen to 60 including the large vivier boats fishing further offshore. There has therefore been a decline in the region of 50% in the number of vessels targeting crab during this period.
However, during this time the number of pots and the potential fishing effort has increased markedly. Data from a sample of vessels <12m in length, suggested that a total of 26,000 pots in the inshore fleet had increased by 60% to almost 42,000 by 2005. Therefore, although there was a reduction in the number of vessels in the fishery, an increase in the number of pots per vessel had resulted in an overall increase in effort.
It is understood that he density of gear deployed in the north Mayo area has increased further since 2005 (D Nee, BIM; pers comm).
7.2.3 Other Inshore Fisheries Additional fishery activity in the inshore area incorporating the proposed dumpsite includes trawling and gill-netting. The main trawling activity is associated with the pelagic fishery for mackerel, horse mackerel and herring and usually takes place between September and December.
Gill-netting for other species (e.g. turbot, rays) is a much smaller fishery. The scope of gill- netting is limited by a restriction which prohibits their deployment to the north of 54o 30’, which lies approximately 5km to the south of the proposed dumpsite.
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Figure 7.6:Distribution of fishing in the <12m and vivier crab fisheries in 1997 (from Tully et al, 2006; reproduced by permission of BIM) x Each rectangle, colour coded by Malin, Northwest Donegal and west Donegal is the approximate extent of fishing by one vessel. Mayo fishing effort is not included but was mainly distributed along the north and northwest of Mayo in 1997.
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Figure 7.7: Distribution of fishing in the <12m and vivier crab fisheries in 2004-2005 (from Tully et al, 2006; reproduced by permission of BIM) x Each rectangle, colour coded by Malin, Northwest Donegal and north Mayo is the approximate extent of fishing by one vessel
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7.3 AQUACULTURE
7.3.1 Introduction
There are three areas of shellfish production in the Sligo area – Drumcliff Bay, Sligo Harbour and Ballysadare Bay. The local industry is based on the production of bivalve molluscs and is the main area in Ireland for production of Manila clam (Tapes philippinarum or T semidecussatus); other species produced in the area are Pacific oyster (Crassostrea gigas), and Blue mussel (Mytilus edulis) (Plates 2-4). The location of areas licensed for shellfish production in the three bays and designated species are shown in Figure 7.8.
Plate 7.2: Manila clam
Plate 7.3: Blue mussel
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Plate 7.4: Pacific oyster
© Ordnance Survey Ireland. All rights reserved. Licence number 2010/20 CCMA/ Sligo County Council
Figure 7.8: Sites licensed for shellfish production in the Sligo area
7.3.2 Shellfish Production
7.3.2.1 Manila clam Manila clam is a non-native species and was introduced into Ireland in 1982 by the UCG Shellfish Research Laboratory at Carna. It is very similar to the native species, but with superior growth and survival rates. The Manila clam is also tolerant of a wide range of salinities but requires more wave-sheltered conditions for on-growing than mussel or oyster.
The introduced clam was found to be easy to produce in hatchery conditions, resistant to disease and had a high survival rate. Adult clams are conditioned in the hatchery during the
IBE00440/EAR/September ‘12 7-11 Sligo Harbour Dredging Environmental Appraisal Report Fisheries and Aquaculture winter and then induced to spawn. The resultant larvae develop into spat or seed, the first recognisable adult stage. Seed from the hatchery is placed initially in off-bottom frames until they are ready for planting into on-growing areas known as “parcs”. Half-grown clams are planted out in shore plots where they bury in the substrate. Netting is used to retain the stock within a confined area and to protect against predators - crabs and birds, notably oystercatcher, can cause serious losses if growing areas are not adequately protected. The clams feed on phytoplankton and filter their food from the water through a siphon that is pushed up through the sediment. Harvesting takes place after a growth cycle of approximately 3 years and the stock is then purified and graded in preparation for the French market.
Shellfish production is now concentrated on production of Manila clam which was first cultivated in Drumcliff Bay in the early 1980s. There are now two main companies operating in Drumcliff Bay (Armada Shellfish Co Ltd & Atlantic Clams Ireland Ltd), and a single leading company in Sligo Harbour (Coney Island Shellfish Ltd). Four on-growing companies in Sligo Harbour work collectively through Coney Island Shellfish with licensed areas in the Cummeen Strand area. Growers are supplied with juvenile clam by a locally based hatchery, Lissadell Shellfish Co Ltd, which has also been in production since the 1980s and is the largest producer of clam seed in Ireland.
7.3.2.2 Oyster Pacific oyster is also a non-native species which do not spawn naturally in local waters. The industry therefore depends on specialist hatchery producers, such as Lissadell Shellfish, for the supply of seed for on-growing in coastal areas. Pacific oysters are usually grown in plastic mesh bags secured to metal trestles in the inter-tidal zone or low-water mark. Alternatively, juveniles may be laid directly on to the seabed plots or ‘parcs’ on the inter-tidal area. The oysters feed on natural phytoplankton and reach market size of 70-100g in 2-3 years.
There are licensed areas for oyster cultivation in both Drumcliff Bay and Sligo Harbour. There has been little production in recent years but Coney Island Shellfish has taken in some stock this year in 2012.
7.3.2.3 Mussel Mussel farming is based on the bottom culture of mussels laid as seed (or spat) for growing on to harvest size. The spat is dredged from known areas around the Irish coast where it has settled in abundance - this takes place between July and November. The seed is then transferred to prepared areas where it is re-laid at lower density to promote improved growth and meat content. Harvesting of mussels is generally between November and March but can occur throughout the year.
Mussel cultivation is very much constrained by the availability of seed mussel which has been unable to fully meet the demands of the industry through a period of rapid expansion. Most of the seed mussel for the industry is dredged from the south west Irish Sea, and a Seed Mussel Allocation Committee (SMAC) comprising representatives from BIM, DCENR,
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DARD, CBAIT and the Loughs Agency considers the supply and allocation of seed throughout Ireland.
Areas of Ballysodare Bay are licensed for mussel cultivation but there does not appear to have been any production in recent years.
7.3.3 Annual Production
Shellfish have been cultivated in the Sligo Bay area since the 1980s with designated licensed areas in Drumcliff Bay, Sligo Harbour and Ballysadare Bay. Production is focussed on Manila clam and this is the main area of clam production in Ireland. Smaller quantities of Pacific oyster are also produced and areas of Ballysadare Bay are licensed for bottom grown mussel, but there appears to have been no activity with this species in recent years. Clam production is also mainly from Sligo Harbour and Drumcliff Bay.
Annual production figures for 2006 to 2011 indicate that total annual shellfish production from the area in recent years has ranged from 183 to 285 tonnes with a value of up to €1½ million.
Table 7.2: Clam and oyster production in the Sligo Bay area, 2006-11 (Source: BIM)
Clam Oyster Combined Year Volume (t) Value (€) Volume (t) Value (€) Volume (t) Value (€) 2006 244 1,374,180 34 74,800 278 1,448,980 2007 158 934,000 25 40,000 183 974,000 2008 171 922,000 114 373,000 285 1,295,000 2009 122 845,000 72 113,800 194 958,800 2010 130 825,000 68 148,400 198 973,400 2011 125 730,000 67 146,800 192 876,800
7.4 Shellfish Waters Directive The EC Shellfish Waters Directive (2006/113/EC) requires member states to designate waters that need protection in order to support shellfish life and growth. The Directive is implemented in Ireland by the European Communities (Quality of Shellfish Waters) Regulations 2006 (SI No 268 of 2006). It is designed to protect the aquatic habitat of bivalve and gastropod molluscs, and sets physical, chemical and microbiological requirements which designated waters must either comply with or endeavour to improve. Sligo Harbour and Drumcliff Bay have been designated as shellfish waters while Ballysadare Estuary/Bay has not been designated.
Article 5 of the Directive provides for the establishment of Pollution Reduction Programmes (PRPs) for designated waters. PRPs for the designated shellfish waters in County Sligo were made by the Minister of DoEHLG in December 2009. The directive will be repealed in 2013 by the EC Water Framework Directive, which will provide at least the same level of protection to shellfish waters
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7.4.1 Classification of Shellfish Production Waters Shellfish production areas are classified by the Sea Fisheries Protection Authority (SFPA) based on monthly monitoring of shellfish for bacterial contamination in accordance with the terms of EU Regulations 853 and 854 (2004). Each harvest area is assigned Class A, B or C according to their sanitary quality using E coli as an indicator of sewage contamination. Shellfish from Class A areas may be marketed for direct human consumption, while product from Class B or C areas must be relayed or subjected to purification/heat treatment prior to marketing. The most recent classifications with regard to local production sites are shown in Table 7.3. Drumcliff Bay and Ballysodare Bay have previously held Class A designation for oyster and mussel respectively.
Table 7.3: Classification of designated bivalve mollusc production areas, 2012
Production Bed Current Boundaries Species Area Name Classification Oyster B
Raghly Point to Clam B Drumcliff Bay All beds Deadman’s Point Mussel B Cockle B Deadman’s Point Oyster B Sligo Harbour All beds to Killaspug Point Clam B Killaspug Point to Ballysodare Bay All beds Mussel B Derkmore Point
Despite these controls, outbreaks of viral illness associated with shellfish consumption can occur. One of the principal agents related to such outbreaks is Norovirus (NoV) which causes gastroenteritis. Norovirus was detected in shellfish originating from Drumcliff Bay in 2010 but this has since been eradicated.
7.4.1.1 Brown Ring Disease Brown Ring Disease (BRD) is caused by Vibrio tapetis, a gram-negative, motile bacterium which can infect wild and cultivated clam species. BRD was detected in clams beds in Brittany in 1987 and has spread along the European Atlantic coast. It has recently been detected in stock from both Drumcliff Bay and Sligo Harbour but has not led to any major problems with the stock.
7.4.1.2 Biotoxin and Phytoplankton Monitoring Samples of shellfish are routinely collected from aquaculture production sites as part of the National Biotoxin Monitoring Programme. These samples are analysed for the presence of toxins belonging to the Amnesic Shellfish Poison (ASP), Diarrhetic Shellfish Poison (DSP), Paralytic Shellfish Poison (PSP) and Azaspiracid Shellfish Poison (AZP) toxin groups. Water samples from shellfish production sites are also collected for determination of the level of known toxin producing phytoplankton species and harmful/nuisance phytoplankton species.
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7.5 SALMONID MIGRATIONS
7.5.1 Life Cycle
Atlantic salmon Salmo salar and sea trout Salmo trutta (Plates 6 and 7) both have marine and freshwater phases of the life cycle. Adult fish spawn in freshwater rivers where their young develop for 1-3 years before migrating to richer feeding grounds at sea. The maturing adult fish return to freshwater to breed after 1-2 years at sea. Migrations to and from local rivers will require these fish to pass through the dredging area in Sligo Harbour.
Plate 7.5 Atlantic salmon
Plate 7.6 Sea trout
7.5.2 Salmon Conservation The Atlantic salmon is listed in Annex II of the EU Habitats Directive (92/43/EEC) as a species of European importance. EU member states are required to designate and manage sites for listed species or habitats as a part of wider measures to ensure the conservation of the habitats and species. For several years fisheries scientists have been concerned about the declining numbers of salmon returning to the Irish Coast due to a persistent phase of low marine survival. Since
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1996 a progressive series of conservation initiatives have been introduced to address this decline in stocks culminating in the closure of mixed stock coastal fisheries in 2007. Salmon stocks in Ireland are now managed on an individual river basis with the objective that each river must exceed its Conservation Limit for there to be any exploitation of fish to be permitted either by nets or rods.
The Scientific Sub-Committee of the National Salmon Commission provides annual advice on harvest options for individual rivers in order to ensure that there are sufficient spawning salmon remaining in each system to meet the required conservation limit. The leading salmon rivers in the Sligo fisheries district are currently open for salmon angling, although the Garravogue is subject to specific restrictions due to a restricted quota.
7.5.3 Local salmon/sea trout rivers There are a number of rivers discharging to Sligo Bay via Drumcliff Bay, Sligo Harbour and Ballysodare Bay, all of which support one or both of the migratory salmonids species, Atlantic salmon Salmo salar and sea trout Salmo trutta. The principal rivers in this regard are the Ballysodare, the Garravogue and the Drumcliff (Figure 7.9). Annual salmon catches in each of these river systems is shown in Figure 7.10. There is currently no commercial netting for salmon in the estuaries of these rivers.
© Ordnance Survey Ireland. All rights reserved. Licence number 2010/20 CCMA/ Sligo County Council Figure 7.9: Map of region showing principal salmonid rivers draining to Sligo Bay
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Figure 7.10: Annual salmon catch from principal local rivers, 2001-10 (Source: IFI)
7.5.3.1 Ballysodare River This is one of the leading and most productive salmon rivers in Ireland. Due to extensive conservation measures by the Ballysodare Fishing Club and IFI in recent years, there is now a substantial run of spring salmon in the river from April to mid June. This is followed by a large grilse run which peaks in June – July. There is some substantial run of sea trout into the estuary on rising tides.
7.5.3.2 Garravogue River, Lough Gill and Bonet River system The Garavogue is only just over 4 km in length from Lough Gill to the tidal reach. It is predominantly fished on the east side of Sligo town close to where it flows out of. The river gets a run of spring fish early in the year and later a larger run of grilse. There are a series of angling clubs and privately owned fisheries throughout the system.
7.5.3.3 Drumcliff River and Glencar Lake This system has a good stock of sea trout and also a modest run of salmon, both early spring fish and summer grilse.
7.5.4 RECREATIONAL SEA ANGLING
7.5.5 Shore Angling There are strong currents in the navigation channel in Sligo Harbour but there good fishing is available in the channel from the north side between Rosses Point and Deadman’s Point for sea trout, mackerel, bass, dogfish, bull huss, ray and tope. The channel can also be accessed from the south side via Coney Island. The beach on the west side of Coney Island is also noted for bass, flounder and occasional ray.
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7.5.6 Boat Angling Two charter boats based in Rosses Point and operate specifically in Sligo Bay and provide reef fishing and general inshore angling for tope, ray, spurdog, dogfish and occasional large skate. A number of boats based in Mullaghmore offer fishing in the wider Donegal Bay area. The Turbot Bank to the north west of the mouth of Ballysadare Bay is a recognised area for turbot, thornback ray and blonde ray. Another reef is ‘the Ledge’ which lies about 6.44km west of Coney Island with excellent pollack fishing. Ling, conger, tope and bull huss may also been taken in the vicinity while the area south of ‘Wheat Rock’ produces common skate to more than 150lbs (68kg).
Sligo Bay also provides good fishing opportunities locally for small boat angling and as this niche of saltwater angling increases in popularity so the fishing on Sligo Bay will be opened up to a wider public.
7.6 EEL & LAMPREY MIGRATIONS
7.6.1 Eel (Anguilla anguilla)
Eels have a catadromous life cycle - young eels (elvers) migrate from the sea into freshwater to feed and the resultant adults later return to sea to spawn. Juvenile eels are likely to be present in the local estuaries in the Sligo area during March and April. They are then believed to spend 10-15 years in freshwater systems before beginning their return migration to sea during the autumn period as silver eels. Silvers are therefore likely to be moving out through local estuaries during late autumn and early winter.
Eels have been fished commercially in the Ballysadare and Garravogue systems. However a long term and widespread decline in European eel stocks has been a matter of concern for some time leading to EC European Eel Regulation (EC) No 1100/2007 in 2007. This Regulation aims to establish measures for the recovery of the European eel stock in the form of Eel Management Plans for each eel river basin including Western River Basin District which includes all catchments draining to Sligo Bay. This will require Member States to reduce exploitation on all major eel river basins and must demonstrate that at least 40% of the biomass of adult eels are escaping to sea to spawn.
7.6.2 Lamprey
There are two migratory species of lamprey with marine phase in their life cycle, Sea lamprey (Petromyzon marinus) and River lamprey (Lampetra fluviatilis) – both are listed in Annexe 2 of the EC Habitat Directive. Adult sea lamprey enter the estuaries of rivers from April onwards, and migrate some distance upstream to spawn which usually takes place in late May or June. The juvenile larval phase is variable but averages about five years with subsequent metamorphosis to the adult form takes between July and September. The timing of the main migration downstream also varies and relatively little is known about the adults after they
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The life cycle of the River lamprey is very similar to that of the sea lamprey. Mature adults, having spent one to two years mainly in estuaries, stop feeding in the autumn and move upstream into medium to large rivers, usually migrating into fresh water from October to December.
Spawning takes place during March and April. The juveniles live and feed within silty river substrates for up to 5 or 6 years before metamorphosing into fully formed adults and then migrating downstream to estuaries or the open sea for the adult feeding cycle.
The presence of eel and lamprey including (migratory phases) in local estuaries is summarised in Table 7.4.
Month Eel Sea lamprey River Lamprey
Jan Adults present in estuary
Feb Adults present in estuary
Mar Elvers moving in Adults present in estuary through estuary
Apr Elvers moving in Adults moving Adults present in estuary through estuary upstream
May Adults moving Adults present in estuary upstream
Jun Adults present in estuary
Jul Silvers moving out Young moving Adults present in estuary through estuary downstream
Aug Silvers moving out Young moving Adults present in estuary through estuary downstream
Sep Silvers moving out Young moving Adults present in estuary through estuary downstream
Oct Adults present in estuary / Adults moving upstream
Nov Adults present in estuary / Adults moving upstream
Dec Adults present in estuary / Adults moving upstream
Table 7.4: Summary of migrations/presence of eel and lamprey in local estuaries at different times of year
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7.7 IMPACT ASSESSMENT
7.7.1 Potential Effects of Dredging and Disposal of Dredged Materials at Sea
7.7.1.1 Dredging The potential environmental impacts of marine dredging are summarised by MEMG (2003): a major effect will be the re-suspension of the bottom sediments and its effects on water turbidity and the liberation of any materials contained and sequestered within the sediments. The release of these materials into the water column will then have the potential for a biological effect. In turn, these effects have the potential to influence the fisheries and nature conservation value of the area. Specifically, in this assessment the impacts on shellfish aquaculture and salmonid migrations are considered.
The wider environmental effects of dredging have been summarised in a conceptual model (Figure 7.11). The pathway for potential impacts on shellfish aquaculture and salmonid migrations can be traced in this model.
7.7.1.2 Disposal of Dredged Materials at Sea The potential environmental impacts of disposal of dredged material are also summarised by MEMG (2003): the disposal of dredged material will have the potential to affect the water column, the bed conditions and their biota. Dumping of sediments will lead to increased turbidity in the immediate area and in the area of sediment plume dispersal. The release of any materials contained within the dredged material, may be the result of the changed chemical environment. Similarly, any organic matter in the sediment will create a water column oxygen demand. The deposited sediment will also change the nature of the bed sediment, if it is of a different particle size and it can have a smothering effect on the bed community as well as bringing new organisms to an area. Both of these features will affect the structure of the bed community and in turn the demersal and benthic fishes feeding on that bed community. This assessment is concerned primarily with near and far-field impacts on commercial fishing activities in the area of the proposed dredge disposal site.
The wider environmental effects of dredging have also been summarised in the conceptual model (Figure 7.12). The pathway for potential impacts on the commercial fishery can be traced in this model.
7.7.2 Socio-Economic and Conservation Aspects Whereas most of the above impacts of dredging and disposal of dredged materials relate to the ecological system, the resultant impacts on the uses and users of the marine environment are often of greater prominence and more public concern. These include the actual or perceived effects on socio-economic aspects such as fisheries, and aesthetic aspects including recreation and tourism.
Similarly, the perceived or actual effects on the conservation importance of an area will be of concern, especially where the habitats and species within and adjacent to the dredging and disposal areas are of importance (MEMG, 2003).
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Figure 7.11: The potential environmental impacts of marine dredging - a conceptual model (reproduced from MEMG, 2003)
Figure 7.12: The potential environmental impacts of marine dredged material disposal - a conceptual model (reproduced from MEMG, 2003)
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7.7.3 Impact Hypotheses
7.7.3.1 Dredging Area Hydrodynamic modelling was undertaken as part of the study to investigate the impact of the dredging on the hydraulic regime of Sligo Harbour and on the sedimentation in the harbour area during the dredging operations. The modelling was used to examine the effect of the dispersion and fate of material spilled during the period of the dredging operations.
Tidal flow modelling indicated that: x while the proposed dredging will lower the level of the low water spring tides in the channel at Sligo, the high spring tide level will be unaffected by the proposed dredging works. x dredging will have an insignificant effect on the current flows in the harbour area except in the area of the channel and adjoining northern section of the harbour.
Dredging plume simulation modelling indicated that: x sediment is temporarily deposited along the sides of the channel and along the north shore of the harbour area during both the water injection and conventional dredging operations. x The peak deposition envelope values of 20-70mm will be of a short duration and tend to occur during the turn of the tide. Following the water injection dredging much of the displaced material will ultimately settle in the vicinity of the Bungar Bank (to depths of less than 3mm) and the remainder will settle around the training walls and Cummeen Strand, again to depths of less than 3mm (refer to Figure 11.8 in Chapter 11. Following completion of conventional dredging operations, residual deposits of sediment will be confined again to the areas around the training wall and the northern shore of Sligo Harbour (refer to Figure 11.26). x Away from these areas the amount of deposition from sediments settling out is small. x Sediment disturbed by dredging in the upper navigation channel will cause temporary increases in suspended sediment concentration in the lower 0.5m of water column at licensed aquaculture sites, but overall concentrations will remain relatively low. x During the conventional dredging operations, mean suspended sediment concentrations in the lower 0.5m of water column in the navigation channel will be within the recommended limits for salmonid waters as prescribed by the EC Freshwater Fish Directive. During the water injection dredging operations, mean suspended sediment concentrations in the lower 0.5m of water column in the navigation channel will be slightly above recommended levels, however the duration of these increases will be temporary, lasting only a few days.
7.7.3.2 Disposal Site Dispersion The impact of the dumping operation on sedimentation and suspended sediment loads in the area of the proposed dumping site outside Donegal Bay was assessed by undertaking a computational modelling exercise. Drogue measurements were also carried out to provide information on tidal currents in the surface, middle water column and bed layer during neap and spring tides – this data was used in calibration of the model.
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The key findings of this exercise are: x tidal velocities in the area the dump site are small with peak spring tidal velocities of circa 0.16 m/s. x the majority of the material will be deposited and remain within 2km of the dumping site with only a small amount of material being transported further offshore by the residual current. x finer materials will be more easily re-suspended and will be gradually transported towards the open sea due to the residual current. x suspended sediment values beyond the immediate vicinity of the dumping operation will be minimal and the material will not be transported a significant distance before current speeds reduce at slack water and the material is deposited. x sediment transport due to wave action is likely to be limited due to the water depth of 90m. x tidal currents in the area of the dump site are weak and any material driven into suspension during large swell events will not be transported far from the site due to the weak tidal currents.
7.7.4 Potential Impacts of the Scheme
7.7.4.1 Dredging Area
Shellfish Aquaculture There will be no effects on aquaculture operations in either Drumcliff or Ballysadare Bays as the respective licensed areas in each bay are sufficiently isolated from any elevations in suspended sediment or deposition of sediments due to dredging activities in Sligo Harbour. Sediment deposition at licensed aquaculture sites in Sligo Harbour during the water injection dredging is predicted to be very low (<2mm) for the short duration of these operations.
During the conventional dredging operations sedimentation is also predicted to be very low (<2 mm) during dredging of both the upper and lower channel, while on completion of the works will be lower still (0-1 mm). Manila clam under cultivation at these sites are buried naturally in the substrate and will be unaffected by these negligible levels of sediment deposition. Sediment deposition at the aquaculture sites during and following water injection maintenance dredging operations will also be barely perceptible (0-1mm).
It can be seen that when dredging operations occur during spring tides, the suspended sediment concentration at each of the four sites shown in Figures 11.11 - 11.15 and 11.36 - 11.39 in Chapter 11 rises quickly (around the period of slack water during each tide) but it also quickly returns back to the background values.
During spring tides, the suspended sediment concentrations reach relatively high peak values during each tide (when compared to the measured background in Table 11.4 in Chapter 11), however the actual duration of each “spike” is very short (as dredging only occurs for a short period each tide).
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During dredging operations the concentration peaks, or “spikes” at any given point will typically last two to three hours, but with the highest values lasting for a period of only 15-30 minutes. The period between peaks (tides), when concentrations return back to baseline, or near baseline levels, will be much longer (around 9-10 hours). Cultivated shellfish buried in the substrate at these sites will be unaffected by these short term elevations in suspended sediment.
Based on these projections there will be no impacts on shellfish aquaculture in Sligo Harbour.
Salmonid Migrations Fish migrating through estuarine environments may frequently encounter high suspended sediment loads which do not appear to impede this behavioural activity. Atlantic salmon are known to move through the Severn Estuary where sediment concentrations in suspension can reach into several thousand mg/l for periods (Gibson, 1933). Simenstad (1988) suggests that salmonids are likely to have adapted physiologically to the turbid conditions that occur naturally within estuarine and harbour areas.
It has also been shown that while the concentration of suspended sediment in the water column is important, the duration of exposure is also a key factor (Newcombe & MacDonald (1991). Salmon and other fish species will exhibit avoidance reactions to locally adverse water quality and move away from the immediate vicinity of conditions. Simenstad and Nightingale (2001) have recommended a turbidity threshold of 200 mg/l in dredging areas to avoid the higher levels of suspended materials that are known to cause physical injury.
Suspended sediment concentrations in the lower 0.5m of water column are predicted to remain relatively low throughout conventional dredging operations, however there will be significant suspended sediment levels of short duration occurring in the navigation channel during each tide for 2-3 days on the period of spring tides during and following the water injection dredging operations.
Adult salmonids are most likely to move upstream via the navigation channel where the mean concentration will be slightly higher (60mg/l) than the Fish Directive recommended limit of 25 mg/l for salmonid waters for a period of a few days during the water injection dredging. During the longer period of conventional dredging the mean suspended sediment concentrations throughout this time will be slightly higher than background, but will remain within the Fish Directive recommended limit of 25 mg/l for salmonid waters. Moreover, for all dredging activities suspended sediment concentrations are likely to be lower closer to the surface of the water column, which salmon more commonly utilise when swimming through estuarine and coastal waters.
Similarly, downstream migrant salmon and sea trout smolts will have no difficulty in dealing with the projected conditions in this respect.
Projected levels of suspended sediment are within recommended guidelines and will not have an adverse effect the upstream and downstream migration of salmonids.
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Eel & lamprey On migrating through estuarine environments these species may frequently encounter high suspended sediment loads which do not appear to impact on migrations.
Projected levels of suspended sediment are within recommended guidelines and will not have an adverse effect the upstream and downstream migrations of eels and lamprey.
Sea Angling Sediment deposition and suspended sediment concentrations are predicted to be negligible at recognised sea angling locations and outside of Sligo Harbour where all boat-based fishing activity takes place.
There will be no adverse effects on sea angling.
7.7.4.2 Dumpsite Area Based on the information generated by modelling of sedimentation and suspended sediment loads at the proposed dumping site, the impacts of dredge spoil disposal on bottom communities and fish have been discussed by Chapter 6.
North West Crab Fishery The principal conclusions with regard to crab ecology and implications for the crab fishery are: x Many sessile and some mobile species covered by the dumped material will be lost, notably where the material settles deepest after each dumping event. x This may include crab although there is evidence to show that smothering is unlikely to cause mortality in crabs, which are able to escape from under silt and migrate away from an area where dumping is taking place. x Given the relatively small footprint of the dumped material, the immediate loss of habitat to crustaceans will be negligible. x Given the relatively small area of impact relative to the surrounding habitats, there should be no significant negative impact on the bottom communities in the general Donegal Bay area. x The impacted seafloor will be re-colonised from the surrounding faunal community and will integrate as part of the overall habitat. x Re-colonisation should take place within a relatively short period of time (12-18 months).
Although there will be loss of habitat in the immediate area of dumping, the area will recolonise and recover within 12-18 months. This will not have any effect on the productivity of the north Mayo crab fishery either in the short term or in the long term.
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Other Fishery Activity It is concluded that fish may have reduced feeding opportunities in the area of the dumpsite due to short term habitat loss on the seabed and reduced productivity. However, fish in the vicinity of dredge disposal operations will avoid areas affected by the dredge plume.
There will be no impact on pelagic or demersal fisheries in the area either in the short term or in the long term.
7.8 MITIGATION MEASURES
7.8.1 Dredging Area
7.8.1.1 Water Quality Monitoring A monitoring programme is recommended to take regular measurements of dissolved oxygen (DO) and turbidity in Sligo Harbour during dredging operations. There parameters should be recorded in the immediate area of dredging and at key locations in the navigation channel and at shellfish aquaculture sites.
Turbidity is recorded in National Turbidity Units (NTU) and may be used as an indicator of the concentration of Suspended Solids (SS). A programme of calibration linking Turbidity (NTU) and SS (mg/l) should be carried out using solutions of known SS concentration made up from samples of the sediments to be excavated.
Triggers levels should be established which, if exceeded, would lead to immediate suspension of dredging until levels have recovered.
7.8.2 Dredge Disposal Site
7.8.2.1 Closure of site to fishing The dumpsite and surrounding area to a radius of 1km should be closed to commercial fishing activity during dumping operations. This will be to avoid any damage to or loss of fishing gear.
7.8.2.2 ROV monitoring of seabed ROV equipment should be deployed to verify settlement of dumped materials in the designated area.
7.8.2.3 Water Quality Monitoring A second monitoring programme is recommended for the dumpsite. This exercise would also take regular measurements of dissolved oxygen (DO) and turbidity at the site and surrounding area during dumping operations.
Triggers levels should be established for each parameter with readings to be taken along set transects emanating from the edge of the site.
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7.8.2.4 Crustacean Monitoring Programme A crustacean monitoring programme is recommended for the dumpsite to determine any impact on shellfish stocks and the recovery period – this should be based on the crab stock. It is suggested that individual fishermen should be contracted to fish at pre-determined locations in the region of the dumping site. Verification of fishing activity and catch would be required. The programme should include baseline monitoring of the site prior to dumping and resumed after dumping to examine recovery of the site.
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8.0 AIR AND CLIMATE
This chapter of the Environmental Appraisal Report describes the existing environment in terms of climate and emissions to the air, with particular reference to dust and noise. An assessment is provided of the likely impact on emissions to the air from the proposed dredging and, where possible, mitigation measures are put forward to reduce the impact of the scheme.
8.1 CLIMATE
The climate at Sligo is influenced mainly by its topography, being surrounded by relatively high ground, and coastal situation. Ireland’s climate in general is defined as a “temperate oceanic climate” and it experiences a lack of temperature extremes compared to other areas. Summers are generally warm and winters are very mild. There is a regional variation, with inland areas being cooler in winter and warmer in summer than their coastal counterparts.
8.1.1 Wind As can be seen from figure 8.1, which shows a cumulative annual average of the wind speeds and directions taken from the meteorological station at nearby Belmullet between 1957 and 2010, the prevailing winds at Sligo are from the south west. Wind blows most frequently from the south west to west sector, while winds from the north and east occur least often. In January, southerly and south-easterly winds are more prominent than in July, which has a high frequency of westerly winds. Easterly and north easterly winds occur most often between February and May and are commonly accompanied by dry weather.
Figure 8.1: Windrose for Belmullet Meteorological station 1957-2010 www.meteireann.ie (2011)
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8.1.2 Temperature The dominant influence on Ireland's climate in terms of temperature is the Atlantic Ocean. The waters around the coasts are remarkably warm, 7° to 8°C warmer than the average global sea temperature at these latitudes, thanks to the warm North Atlantic Drift, the main ocean current affecting Ireland (Met Éireann, 2011). Prevailing south westerly winds transfer the heat from the sea to the land, thus creating a lack of temperature extremes when compared to other areas of similar latitudes. Summer temperatures exceed 30°C usually only once or twice every decade (though commonly reach 29°C most summers), while severe freezes occur only occasionally in winter, with temperatures below í10°C being very uncommon, and temperatures below freezing uncommon in many coastal areas. At the Belmullet meteorological station, the coldest months are January and February, with average maximum temperatures of around 8.2°C and the warmest month is August, where average maximum temperatures are around 17°C. 30 year average sea temperatures (1961-1990), measured at Malin Head, show average sea temperatures of 6.7°C in February rising to 14.6° in August.
Figure 8.2: 30 year monthly average temperatures (Belmullet) and sea temperatures (Malin)
8.1.3 Precipitation In Ireland, the main rain-bearing winds are from the south west, therefore tending to make the western half of the country wetter. Rainfall in the west generally averages between 1,000 and 1,400 mm per year, however in mountainous districts rainfall can exceed 2,000mm per year. The eastern half of the country is generally drier, averaging between 750 and 1,000 (mm) of rainfall annually (Figure 8.3).
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The wettest months in almost all areas are December and January. April is generally the driest month generally across the country, but in some southern areas June is the driest. Hail and snow contribute relatively little to the precipitation measured.
Figure 8.3: Met Éireann 1961-1990 mean annual average rainfall
The average annual rainfall for the 5km² area in which Sligo is located, is around 1193mm per annum, with the wettest months occurring between October-January and May (Figure 8.4). On average, in Sligo the driest month is April, followed by June.
Figure 8.4: Met Éireann Average Monthly Rainfall for 5km² containing Sligo Harbour
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8.1.4 Potential Impacts on Climate There are no significant long term gaseous emissions associated with the proposed dredging which could impact air quality. The proposed dredging will therefore have no impact on the climate either locally or regionally.
8.1.5 Potential Impacts on Air Quality No disturbance of dry sediments will occur during the proposed dredging operations. Once dredged, there will be no increase to the drying areas of the foreshore. The proposed dredging will therefore have no impact on the air quality in Sligo Harbour.
8.2 NOISE
This section of the assessment will consider the potential noise impact of the proposed dredging works at Sligo Harbour. The proposed works involve the dredging of sediments from the navigation channel into Sligo Harbour and its transportation to an offshore dump site some 34 nautical miles west of the docks. No rock breaking activities will be required.
Dredging will occur along the northern shore of Sligo Harbour, within the navigation channel extending from Oyster Island to the Deepwater and Barytes jetties. There are a small number of residential units located along this length of the coast, situated at varying distances from the shore, the most proximate circa 150m from dredging activity.
Sligo Harbour is situated in an urban area; however, dredging activity will occur in close proximity to residential properties that are situated within suburban and rural areas. The dredging operations are expected to last for 4-6 months.
The location of the proposed dredging works is presented in Figure 8.5.
8.2.1 Existing Environment It is submitted that the existing noise environment in the vicinity of the proposed works is typical to that of a suburban coastal site, being shaped by the local activity and environmental conditions. Previous surveys undertaken by this consultancy at various coastal villages and harbours around Ireland indicate that background levels vary significantly depending on weather conditions. Background levels are likely range from low 30’s dB LA90 to mid to high 50’s dB LA90 under high wind and rain. Ambient levels are likely range from mid to high 30’s dB LAeq to low to mid 60’s dB LAeq, again dependant on weather.
8.2.2 Evaluation Criteria Presently, in Ireland, there are no fixed noise limits for construction noise and the control of such sources is outside the remit of the EPA. In general it is left to the discretion of the local council authority and An Bord Pleanàla to determine if fixed limits are appropriate. Such restrictions are rare, and there is little precedent. In Fingal Council Area discussions are underway with the Construction Industry Federation to agree time limits of Monday to Friday daytime, and Saturday morning, but with no restriction on noise levels. However a useful
IBE00440/EAR/September ‘12 8-4 Sligo Harbour Dredging Environmental Appraisal Report Air and Climate indication of potential impact can be gained by comparison with current practice in Northern Ireland.
The impact of the short-term works associated with the site preparation and subsequent construction will be assessed using BS5228 (2009), “Noise and Vibration Control on Construction and Open Sites”.
Figure 8.5: Location of Dredging Area
8.2.3 Assessment of Temporary Construction Noise Impact
The nearest residential properties to the proposed dredging area are at least 150m from the extents of the residential properties situated in the Ballincar area.
BS 5228 provides recommendations for temporary construction noise limits, based on an assessment of the existing ambient noise levels within the vicinity of the works. The “ABC” method, as found in BS 5228 Section E.3.2, provides an appropriate assessment method for determining temporary construction noise level targets. The level is determined by rounding the ambient noise level within the vicinity of the construction works to the nearest 5 dB. This resultant level is then compared with Category A, B and C values. When this resultant level is 5 dB less than Category A values, then noise limits should be set in line with Category A values. When the resultant level is similar to Category A values then noise limits should be set in line with Category B values. When the resultant level is similar to Category B values or
IBE00440/EAR/September ‘12 8-5 Sligo Harbour Dredging Environmental Appraisal Report Air and Climate higher, then noise limits should be set in line with Category C values. Table 8.1 below outlines values for Categories A, B and C.
Table 8.1: Example Threshold of significant impact at dwellings
Assessment Category and Threshold Value Threshold Value, in Decibels (dB) Period LAeq Category Category Category A B C Night-time (23:00-07:00) 45 50 55 Evenings and weekends 55 60 65 Daytime (07:00-09:00) and Saturdays (07:00-13:00) 65 70 75
Therefore, as it is expected that ambient levels at the most proximate residential properties to the proposed dredging activity will be up to 65 dB LAeq, it would be deemed appropriate to set construction noise target levels similar Category B.
8.2.4 Comment on Noise Associated with Dredging With reference to BS5228, noise levels of dredging works are typically 96 dB LAeq at 10m, however, manufacturers’ data suggests a sound power level of 109 dB Lw, which equates to a sound pressure level of 81 dB LAeq at 10m. Measured data of cutter suction dredging activity in Cork Harbour has resulted in an LAeq of 80 dB at 10m.
The DEFRA “Noise Database for Prediction of Noise on Construction and Open Sites” indicates that a grab hopper dredging ship produces noise levels of 82 dB LAeq at 10m. Measurement and assessment of specific “state of the art” dredging equipment (cutter suction rig type) used at Cushendall (Co. Antrim) was conducted on 9 July 1999 by this consultancy. During normal operations, dredging activity resulted in a specific activity level of 49.4 dB LAeq at 108m (typically over hard ground or water). Assuming a point source, with no soft ground absorption, this equates to 70 dB LAeq at 10m.
It can be seen that there is wide variation of noise level from dredging plant, dependant on the specific plant used. However, typical levels are circa 82 dB LAeq at 10m and this value will be used for assessment purposes.
Dredging activity will involve the removal of material from the bed of the channel, using a dredging ship. The ship collects material, through either a chain and bucket system or cutter suction system, until fully laden. The dredging ship will then steam to a location approximately 34 nautical miles from the port, outside Donegal Bay, where the material is discharged from the dredger. The dredging process within Sligo Harbour is expected to take approximately 90 minutes per tide, with the majority of the remaining time during each tide spent steaming to and from the material dumping location. Dredging activity will only occur around the high tide, as at other times the water depth is insufficient for the dredging ship to enter. Targets set with regard to BS 5228 refer to a 12 hour LAeq for daytime (07:00-19:00) and an 8 hour LAeq for night time (23:00-07:00). Therefore, it will be necessary to include a
IBE00440/EAR/September ‘12 8-6 Sligo Harbour Dredging Environmental Appraisal Report Air and Climate correction for on time, as dredging activity will only occur for a short period during daytime and night time.
Dredging activity will occur, assuming an absolute “worst case” scenario, at circa 150m from the most proximate residential properties at Ballincar. At all other times dredging activity will occur at a greater distance from residential properties. Neglecting any ground absorption or possible screening, but considering a point source, and assuming that dredging is at extent of works:
Daytime Noise Impact
Dredging Activity Level = 82 dB LAeq at 10m
Correction for “on time” = 10 log (80/720) = -10 dB
Attenuation by Distance = 20 log (150/10) = 24 dB
Impact at Property (Ballincar) = 48 dB LAeq, 12hr
It can be seen that dredging at the extent of works is within the maximum allowable daytime exposure of 70 dB LAeq, 12hr for construction noise at the nearest properties. The majority of dredging activity will occur at a greater distance, therefore it is predicted that the impact at residential properties will typically be less than calculated above.
Due to time constraints during the construction process, and the dependency on suitable weather conditions for dredging, it may be necessary for these works to continue throughout the night. In these circumstances the predicted impact at the most proximate residential property is as follows:
Night time Noise Impact
Dredging Activity Level = 82 dB LAeq at 10m
Correction for “on time” = 10 log (80/640) = -9 dB
Attenuation by Distance = 20 log (150/10) = 24 dB
Impact at Property (Ballincar) = 49 dB LAeq, 8hr
It can be seen that dredging at the extent of works is within the maximum allowable night time exposure of 50 dB LAeq, 8hr for construction noise at the nearest properties. The majority of dredging activity will occur at a greater distance, therefore it is predicted that the impact at residential properties will typically be less than calculated above. Therefore, it is possible for dredging to continue throughout the night for the majority of works, while remaining within target levels, using appropriate plant.
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8.2.5 Mitigating Measures for Temporary Construction Works
8.2.5.1 Monitoring Given the limited impact it would not be appropriate to require regular noise monitoring of the site. However, occasional measurement of noise levels generated using a Type 2 or better sound level meter should be conducted to check on the continuing impact of the works.
8.2.5.2 Responsible Person It is often recommended that the appropriate party should appoint or delegate a responsible person who will be present on site and who will be willing to answer and act upon queries from the local public.
8.2.5.3 Night Works Due to the essential nature of the works, dredging activity must occur within close proximity to residential properties. It is also likely that dredging activity will occur during night time hours. Due to the 4-6 month timescale of the works, it is recommended that local residents are duly notified of intended works in close proximity to their residences, particularly during night time hours as this will help to alleviate tensions and reduce potential for noise complaint related to the dredging activity.
8.2.6 Conclusions
The potential noise impact from the proposed works associated with the dredging of Sligo Harbour has been assessed and appropriate evaluation criteria and target noise levels have been ascertained.
It has been shown that noise from short-term construction works can be controlled to within reasonable and previously applied noise level limits at any noise sensitive locations. Some mitigating measures have been included to provide additional instruction to the contractor.
Other sources of noise effects are not likely to be significant. On completion of the project, no significant noise impact from the works will occur.
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9.0 MATERIAL ASSETS
This chapter of the Environmental Appraisal Report describes the existing infrastructure of the settlements around Sligo Harbour in terms of fresh water and waste water treatment, roads, services and communication. It provides an assessment of the impact of the proposed dredging and, where possible, puts forward mitigation measures to reduce or eliminate the impact.
9.1 INFRASTRUCTURE
9.1.1 Water Supply
Historically, there have been issues in the supply of drinking water in the Sligo region, however since the late 1990s Sligo County Council has carried out very significant investment in water infrastructure, including the implementation of the Sligo and Environs Water Supply Scheme.
The Sligo and Environs Water Supply Scheme was designed to provide for the domestic, agricultural and industrial potable water requirements for Sligo and its outlying regions and meet the highest possible standards in accordance with all national and E.U. legislation, thereby;
x providing adequate water supply for fire fighting within the Borough. x reducing leakage in the existing water supply distribution system and maximising the benefit of existing resources. x providing adequate water supply to eliminate the severe disruption to supply to consumers; and x eliminating restrictions on residential, commercial and industrial development.
The scheme provides for the domestic, agricultural and industrial water requirements of Sligo City and its outlying regions, such as Ballincar, Rosses Point, Strandhill and Ballintogher.
The majority of the drinking water supply for Sligo town and its environs is sourced from Lough Gill, supplemented by a gravity supply from Kilsellagh, located to the north of the city. Two water treatment plants are in operation treating water from Lough Gill; Cairns Hill and Foxes Den with a third plant at Kilsellagh. These three plants have been (or are in the process of being) upgraded to facilitate the improved treatment and overall quality of the water supply.
A further five regional water supply schemes supply drinking water to the wider areas of County Sligo.
However, a number of rural dwellings and small communities throughout Sligo do not have the benefit of a public mains water supply system. These dwellings rely on group schemes and individual well supplies. It is an objective of the County Council to ensure that all rural
IBE00440/EAR/September ‘12 9-1 Sligo Harbour Dredging Environmental Appraisal Report Material Assets water supplies comply with the EC (Drinking Water) (No.2) Regulations 2007 (Sligo County Council, 2005).
Many private water users rely on groundwater sources that are vulnerable to contamination. Therefore the protection of underlying aquifers is important for the environmental quality of rural water supply. As described in Chapter 10.2 of this Report, “Hydrogeology” no impacts to groundwater supplies are anticipated as a result of the dredging.
The proposed dredging will not pose any demands on or alterations to the drinking water supply for Sligo town and its environs, beyond providing potable water for the crew on board the dredging vessel. No impacts are anticipated and no mitigation is therefore required.
9.1.2 Sewerage Infrastructure
The provision of wastewater treatment infrastructure is imperative to facilitate the economic, social, and physical development of the county and to support settlement growth. In addition, the continued improvement and provision of this infrastructure is necessary to meet the requirements of the Urban Wastewater Treatment (Amendment) Regulations 2004.
The Sligo Main Drainage Scheme, commissioned in 2009, has provided Sligo City and surrounding areas with adequate treatment and drainage capacity to serve up to 50,000 PE (population equivalent), thereby allowing for future development and growth. The Waste Water Treatment Plant (WWTP) is sited on the area of reclaimed land adjacent to Sligo Port at Finisklin which was used for the previous disposal of dredged material from Sligo Harbour during maintenance dredging in the 1980s and early 1990s.
Figure 9.1: Sligo WWTP at Finisklin
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Prior to the construction of the WWTP, sewage from Sligo town was discharged untreated into Sligo Harbour.
The treatment works have a capacity to treat waste water for a combined domestic and commercial population equivalent of 50,000 and it has the capabilty to be expanded to 80,000 at a future date. The facility serves not only Sligo City, but also in the future surrounding areas including Ballincar, Cregg, Rosses Point Carrowroe and Cummeen will be connected to the scheme.
In addition to meeting the Urban Wastewater Treatment Regulations, the scheme has also significantly improved water quality within Sligo Harbour and its surrounding waters, thus also improving the water quality status in terms of the EU Water Framework Directive, the EU Bathing Waters Directive, the EU Habitats Directive, and the EU Shellfish Waters Directive.
The proposed dredging at Sligo Harbour will not generate any waste water discharge into the sewerage infrastructure, therefore it will not pose any impacts or create any additional pressure on to the provision of waste water treatment services in Sligo. The International Convention for the Prevention of Pollution from Ships (MARPOL) Annex IV “Prevention of Pollution by Sewage from Ships” contains requirements to control pollution of the sea by sewage; the discharge of sewage into the sea is prohibited, except when the ship has in operation an approved sewage treatment plant or when the ship is discharging comminuted and disinfected sewage using an approved system at a distance of more than three nautical miles from the nearest land. Sewage which is not comminuted or disinfected must be discharged at a distance of more than 12 nautical miles from the nearest land. The dredger will adhere to these regulations and will not discharge foul waste or bilge water into Sligo Harbour.
9.1.3 Surface Water
The IPCC (Intergovernmental Panel on Climate Change) predicts that due to climate change Ireland’s west coast will suffer increased rainfall intensity and more numerous and intense storms. The increase in rainfall, particularly of high intensity, is likely to result in increased river, land and associated flood plain water levels. River catchment areas that are influenced by tidal effects are likely to be impacted more frequently due to combined effects.
The Sligo and Environs Development Plan 2010 – 2016 lists a number of flood protection aims and policies which should be taken into consideration when planning new development. Surface water drainage design should reflect the likely increase in intensity and frequency of rain storms. Outfall levels should take cognisance of potentially higher receiving water levels. Future potential additional discharges into receiving water that are themselves tide- locked should be analysed and risk-assessed taking cognisance of existing predictions.
SEDP Flood prevention policies: x P-FP-1 Restrict development within 50 m of ‘soft’ shoreline. x P-FP-2 Ensure that no further reclamation of estuary land takes place. x P-FP-4 Assess all coastal defence measures for environmental impact.
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x P-FP-6 Land uses shall not give rise to increases in the run-off characteristics above those that currently exist.
The proposed dredging of the navigation channel will not pose any additional pressures on the area of Sligo town in terms of increasing flood risk.
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9.1.4 Mechanical and Electrical Services
The construction of the new waste water treatment plant at Finisklin has precipitated significant upgrades to the electricity and telecommunications infrastructure network within the docklands area (Pat Doyle, Sligo Co. Council pers.comm.). Reinforcement of the national grid to the western side of Sligo town has taken place and high speed broadband now exists at the site. It is hoped that these enhancements will assist in attracting new investment to the area, such as attracting manufacturing industries to the existing Sligo Business & Technology Park at Finisklin as a secure power supply and high speed telecommunications links are highly desirable for manufacturers. Should the former landfill site become approved for re-development in the future, this ground will also have high value for industrial or business development.
The proposed dredging of the navigation channel at Sligo Harbour will pose no significant impact to the existing mechanical and electrical services within the docklands area or the wider Sligo area. All communications and infrastructural connections beneath the channel should be buried at depths substantially below the dredging level, however the chosen contractor should have due regard to cables or pipelines beneath the channel and ensure that the position and depth of these has been correctly identified.
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9.2 TRAFFIC
This section will concentrate on the impact of the traffic generated by the dredging process on the access to the harbour and also to the adjacent National Primary Route.
9.2.1 Background The proposed dredging site is located within Sligo Harbour and as part of a recent feasibility study carried out by Sligo County Council, it has been established that the materials cannot be disposed of or re-used onshore, therefore it is proposed to dredge the material and directly transport the material to an offshore dump site, approximately 34 nautical miles from the harbour.
9.2.2 Existing Baseline Conditions
9.2.2.1 Overview of Existing Industry
The existing harbour area is a busy industrial area, which includes several large oil distributions yards, building supplier depots and various other industrial warehouses. From a traffic perspective, this generates substantial movements throughout the day, many of which are HGVs. The harbour itself is also a working port with ships importing and exporting goods of both local and national importance including mainly scrap metal, coal, timber and fish meal. Given the nature of the shallow shipping lane and the available tidal range the number of ships visiting the port is low. Table 9.1 below, reproduced from the information in Chapter 1, illustrates the docking pattern of Sligo Port over the last number of years and shows that in recent years the number of ships docking and their associated tonnages have remained fairly constant therefore causing minimal net increase in associated traffic.
Table 9.1: Docking Pattern at Sligo Harbour
Year No of Ships Tonnage 2011 21 49,000 2010 24 52,000 2009 25 53,000 2008 25 41,000 2007 26 46,000 2006 23 43,000
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9.2.2.2 Existing Access Routes The existing access to the harbour is on Deep Water Quay, which leads onto the N4 via either Ballast Quay or Finisklin Road. While both routes comprise of a carriageway approximately 8m wide and include footpaths along both sides. Ballast Quay Road is the shorter route of the two and would provide a more suitable route as Finisklin Road includes a school and a railway bridge with limited headroom. In consultation with Sligo County Council Road Design Office, it was confirmed that the Ballast Quay Road would normally be the primary route and Finisklin Road would only act as an overflow should the junction of Ballast Quay and the N4 become congested. These conditions would indicate that the Ballast Quay Road would offer the most favourable route to the National Primary Road and we will continue our assessment on this basis. Figure 9.2 below shows a drawing indicating the relationship of these junctions.
© Ordnance Survey Ireland. All rights reserved. Licence number 2010/20 CCMA/ Sligo County Council Figure 9.2 Junctions in Vicinity of Port
9.2.2.3 Existing National Primary Road and Access Junctions The junction of the Ballast Quay Road with the N4 is a signalised crossroads comprising the through bound N4 to the north and south, Ballast Quay Arm to the west, and Custom House Quay Arm to the east. The N4 Southbound Arm includes two lanes; one for left turns into Custom House Quay and ahead movements while the other is a dedicated right turning lane into Ballast Quay. The N4 Northbound Arm comprises of three lanes; the right hand lane catering for traffic turning into Custom House Quay, the middle lane for ahead movements
IBE00440/EAR/September ‘12 9-7 Sligo Harbour Dredging Environmental Appraisal Report Material Assets and the left lane for both ahead movements and for traffic turning into Ballast Quay. Custom House Quay serves several car parks and provides some limited access to the town centre and this approach has one lane for all left, right and ahead manoeuvres. The Ballast Quay Road Arm approach includes three lanes, one dedicated to each of the left, right and ahead movements. The junction is also well served by pedestrians crossings dedicated crossing points on all arms.
The access to the harbour is via a priority junction of the Ballast Quay Road and the Deepwater Quay Road. All arms of the junction are approximately 10m in width and existing radii are measured at approximately 10m and while good quality footpaths are provided no crossing points are included.
9.2.2.4 Summary of Existing Network Good provision currently exists for movements through the signalised Ballast Quay Road/N4 junction with dedicated lanes for all movements through the busiest arms and efficient pedestrian links that work with traffic flow. A high quality carriageway and footpath links this junction to the harbour access at Ballast Quay Road/Deepwater Quay Road, a priority junction with good vehicular capacity but limited pedestrian crossing points.
9.2.3 Existing Flows taken from Model A Paramics model built for Sligo Town shows 2008 traffic flows between the harbour site and the N4 national primary route via the Deepwater Quay and the Ballast Quay as per Table 9.2 below. National Traffic Forecasts published by the NRA show an average traffic increase of 5.1% between 2008 and 2010. However our assessment will be more robust if we are to assume the same traffic figures as 2008; circumstances which many would regard more likely than recent NRA forecasts.
Table 9.2: Existing Traffic Flows along Primary Route
Two Way Route Peak Period Arrivals Departures Flow AM 145 70 215 Deepwater Quay PM 54 123 177 AM 302 349 651 Ballast Quay PM 192 340 532
Deepwater Quay/Barytes Jetty experiences a two way flow of 215 in the AM Peak and 177 in the PM Peak, with Ballast Quay accommodating a two way flow of 651 in the AM Peak and 532 in the PM Peak. We will use this as a basis for our assessment of how the local infrastructure copes with the increase in traffic generated by the dredging proposals.
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9.2.4 Predicted Impacts During Dredging
As part of a feasibility report carried out previously by Sligo County Council, it was concluded that the dredged material could not be reused or disposed of in a suitable manner and so it was agreed that it should be directly shipped to an off-shore dumping site.
On the basis of the feasibility report it is assumed that the dredging operation will occur locally and that no material will be transported outside the harbour site. For this reason this assessment assumes that the only arrivals and departures generated will be the additional workers required to carry out the works.
For this dredging scheme, it currently remains undecided as to what type of dredging vessel is to be used; a trailer suction dredger, which aspirates the sediment from the bed, or a backhoe dredger which excavates the sediment from the bed. For either method, the vessel is to be deployed on a 24 hour basis with a crew of four/five working in shifts. For each tide (approx 12.4 hours) the vessel will be dredging for approx 70-80 minutes through high tide as the channel is too shallow to enter/exit during other periods of the tide. It will spend the remainder of the shift sailing to and from the dump site, 34 nautical miles offshore, outside Donegal Bay. An onshore crew of two/three crew will be required to supervise works and administer offshore operations.
9.2.4.1 Generated Traffic
As part of any Traffic and Transport Assessment, it is normal to establish the arrivals and departures of the proposed development using TRICS. This investigates arrivals and departures of sites with a similar land use and so gives trips that are representative of the proposed site. However; the trips generated by TRICS usually apply to permanent proposals and not temporary dredging practices such as this. For this reason it is necessary to apply the number of operatives required for the works and apply trip rates accordingly.
For the purposes of this assessment we have discussed the scope of the works with the marine consultants as described above and established that an additional workforce of seven will be required to crew the dredger, four/five on board the dredger and two/three on shore. It is probable that all crew would live on the dredging vessel over the course of the works and that any journeys would be taken in a communal van/mini-bus provided by their employers. This would suggest that traffic movements generated by the dredging works would be minimal; however in the next chapter we will discuss this in more detail and consider some assumptions that will ensure a robust assessment.
9.2.5 Mitigation Measures
As referred to previously in Section 9.2.4.1, there will be a limited number of additional vehicles generated by the site during dredging operations; however this does not allow us to disregard the effect that alternative travel measures will have on mitigating this traffic or our
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9.2.5.1 Walking/Cycling As mentioned earlier, the harbour can be easily accessed from the N4 through good pedestrian links already provided along both Ballast Quay Road and Deepwater Quay Road. This principle in supported by the Sligo and Environs Development Plan 2010-2016, which contains proposals to extend the pedestrian link into the town centre by providing a waterfront walkway from Hyde Bridge to Hughes Bridge (bridge at N4).
9.2.5.2 Public Transport At present there are no bus routes that serve the harbour and within the current Development Plan there are no plans to extend these services. While a railway line does exist in the harbour area it is only used for freight and not passenger traffic. Therefore public transport cannot be used as a viable option for travelling to and from the site.
9.2.5.3 Shared Transport As mentioned previously the most likely mitigation measure to be employed is shared transport. It is assumed that all of the operatives on the dredger will work for the same company and that transportation would be provided as part of their arrangement. However for the purposes of this study and to ensure a robust assessment, we will assume that each employee will use their own personal mode of transport to the site. (i.e. by car)
9.2.6 Conclusions
The normal criteria to follow when studying network and junction capacity is in line with the NRA “Traffic and Transport Assessments Guidelines”, which states that the threshold at which Transport Assessments should be carried out are 10% for normal junctions and 5% where congestion exists.
9.2.6.1 Comparing Existing and Generated Flows
Table 9.3 below shows the traffic flows received from the Sligo Town Paramics Model mentioned previously. This assessment has compared the existing arrivals and departures with associated generated trips in the relevant period.
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Table 9.3 Percentage increase during dredging operations
Deepwater Quay Ballast Quay AM PM AM PM 2008 Arrivals 145 54 302 192 2008 Departures 70 123 349 340 Proposed 2010 7 0 7 0 Arrivals Proposed 2010 0 7 0 7 Departures % INCREASE 4.8% 0% 2.3% 0% (ARRIVALS) % INCREASE 0% 5.7% 0% 2.1% (DEPARTURES)
9.2.7 Percentage Increase
As shown in Table 9.3, the percentage increase in traffic arising from the predicted trips generated by the dredging operation remain within the 10% threshold specified by the NRA. Indeed for Ballast Quay, the percentage increase does not extend beyond the more onerous 5% threshold.
9.2.7.1 Residual Impacts
On the basis of the findings above and the recommendations of the NRA “Traffic and Transport Assessment Guidelines” this assessment shows that the traffic generated by the dredging works is within the recommended thresholds. We are satisfied that the works will not have any adverse effect on the local infrastructure. Indeed the trips are likely to be further reduced due to the fact that the dredging crew are to reside within the vessel and that all travel will be via a communal van/mini-bus. This will further reduce the arrivals/departures and will probably reduce the impact on both the Deepwater Quay Road and the Ballast Quay Road below the 5% threshold.
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10.0 GEOLOGY AND SOILS
This chapter of the Environmental Appraisal Report describes the natural characteristics of the site in terms of geology, hydrogeology and the nature of the marine sediments. The geological regime has been established from the results of sediment testing and geophysical surveys, supported by a review of geological mapping records. An assessment is made of the likely impact of the proposed scheme on these natural resources and, where necessary, mitigating measures are put forward to reduce the impact of the proposed development.
10.1 SOLID GEOLOGY
The bedrock geology of County Sligo has been mapped by the Geological Survey of Ireland and is published as Sheet 7 of the 1:100,000 Solid Geology Field Series (Sligo-Leitrim).
The geology of County Sligo is complex and indirectly spans more than 1,700 million years. The geological aspect of the site relative to its regional and local setting is discussed below and illustrated in Figure 10.1.
The geology of Sligo-Leitrim can be sub-divided into five major divisions for descriptive purposes: x Metamorphic rocks of Proterozoic and partly lower Palaeozoic age (schist and gneiss), dating from about 1700 to 500 million years, exposed in the Ox Mountains, x Sedimentary rocks, often strongly folded and mildly metamorphosed (red sandstone), of lower Palaeozoic to Devonian age, from 500 to about 360 million years, x Almost unfolded sedimentary rocks of Carboniferous age (limestone, limestone/shale and sandstone), deposited during the period from 355 to 320 million years ago, x The post-Carboniferous, intrusive igneous rocks (granite) about 65 million years old; and x The Quaternary unconsolidated sediments, younger than 1.6 million years.
Site Location
Figure 10.1: Site Location
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10.1.1 Regional Geology
Sligo Harbour is within a zone where mainly Carboniferous era limestone (mainly Ballyshannon Limestone and Dartry Limestone) and shale rocks are exposed at the surface (shown in shades of blue/grey in Figure 10.2), although a small inlier of Proterozoic age rocks outcrops on Rosses Point, at the northern boundary of Sligo Harbour (shown in yellows, greens and browns on Figure 10.2). This inlier is a site of Geological Interest highlighted by the GSI in their consultation response, as it exposes the contact between the Slishwood formation (CZ on Figure 10.2) and the Dalradian (LS on Figure 10.2).
The southern shores of Sligo harbour, as well as Coney Island and Oyster Island are comprised of Glencar Limestone. The Carboniferous rocks represent a period, between around 355 and 310 million years ago, where Ireland was gradually submerged by rising sea levels (Macdermot et al, 1996). This marine transgression took millions of years to envelop Ireland, spreading northwards from Cork. On land, rivers deposited sand and silt, now represented by grey sandstones and siltstones. In the shallow nearshore waters, muddy limestones and shales were formed. Further offshore, pure limestones were formed. Low hills lay between river valleys or plains; the higher of these were never covered by river sediments, but were eventually covered by the rising sea. Where this happened, limestones rest directly on pre-Carboniferous rocks, such as at Rosses Point.
Figure 10.2: Local Geology, from GSI 100k mapping
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10.2 HYDROGEOLOGY
Groundwater in Ireland is protected under European Community Legislation (Groundwater Directive 80/68/EEC) and national legislation, namely the Local Government (Water Pollution) Acts of 1977 and 1990, which make it an offence to pollute groundwater.
Groundwater is water found below the surface of the earth, often occurring in natural reservoirs in permeable rock layers. Bedrock formations or sand and gravel deposits which yield significant quantities of water are called aquifers. The type of rock affects the volume and chemistry of the water. The limestone rock types around Sligo and Rosses Point have been identified as aquifers of both local and regional importance, as can be seen in Figure 10.3.
Figure 10.3: Bedrock Aquifers
The Water Framework Directive (WFD) is a European Union directive which commits European Union member states to achieve good qualitative and quantitative status of all water bodies by 2015. Waterbodies can relate to surface waters (these include rivers, lakes, estuaries [transitional waters], and coastal waters), or to groundwaters.
For the purposes of the WFD, Ireland has been divided into six River Basin Districts (RBDs). For each RBD, a River Basin Management Plan (RBMP) has been prepared. The RBMP contains information on the status, risks, and objectives for each water body within the RBD. For each water body, measures are proposed achieve “good status” in water bodies that are of lesser status at present and to retain good status or better where such status presently exists.
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The body responsible for monitoring groundwater quality is the Environmental Protection Agency.
10.2.1 Potential Impacts to Groundwater
A number of activities can have an impact on groundwater resources, including: x Excessive pumping e.g. from wells for water supply x Saline intrusion (risk of over-abstraction in coastal areas pulling sea water into the groundwater body x Pollution from nutrients, e.g. nitrates and phosphates x Pollution from chemicals
Figure 10.4: Groundwater Status (2010)
The groundwater bodies in proximity to the proposed dredging area are Rosses Point, Sligo and Drumcliff-Strandhill. The Sligo and Drumcliff-Strandhill groundwater bodies have achieved “good” status during their last assessment for the Water Framework Directive. The Rosses Point groundwater body failed to achieve “good”, or even “moderate” status (Figure 10.4), failing in its chemical status due to poor results in monitoring for loadings of reactive phosphates and nutrients. Nutrients can be discharged into the aquatic environment through wastewater from households and industry or by loss of nutrients from agriculture or fish farming. Agriculture is the main source of nitrogen loading and a major source of phosphorus loading, although much phosphorus also comes from point sources and sparsely built-up areas.
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All three groundwater bodies are currently assessed as being “not at risk” of saline intrusion.
10.2.2 Predicted Impacts to Groundwater.
The proposed dredging will only remove sediments from the bed of the navigation channel. No removal of bedrock is envisaged with this scheme, therefore there is no risk of creating a new pathway for saline intrusion to occur. There is no risk of increasing nutrient loadings as a result of the proposed dredging.
No mitigation measures are therefore required, in terms of groundwater.
10.3 GROUND CONDITIONS
10.3.1 Dredging Area Sediment Physical Properties
In order to gain knowledge of the physical properties of the sediments along the navigation channel and enable an appropriate side slope design, Priority Geotechnical were commissioned to carry out a marine investigation to obtain sediment cores along the shipping channel at Sligo Harbour.
Figure 10.5: Vibrocore sample stations Extract from Admiralty Chart 2852 © Crown Copyright UKHO. Not for navigational use
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The investigation comprised of vibrocore sampling to 3.0m depths at twelve locations (Figure 10.5) and took place in April 2010. Stations 1, 3 and 12 had more than one vibrocore taken.
The fieldwork was carried out in general accordance with BS 5930 (1999) “Code of Practice for Site Investigation” and Part 9 of BS 1377 (1990), “Method of Tests for Soil for Civil Engineering Purposes, in situ Tests”.
A Geo-corer 3000 was used to obtain the 100mm diameter continuous core, sediment samples (Figure 10.6).
Figure 10.6: Vibrocorer
The sediment conditions were such that there were 3 distinct sediments identified: silt, sand and coarse to fine shell.
Inside the Port of Sligo, VC01 and VC02 indicated slightly sandy silt and very clayey gravel sediments to a depth of 1.0m below the existing bed level. Location VC03 indicated slightly silty sandy shell sediment to 1.0m depth. The shell fragments accounting for 70% of the material by mass. It should be noted that these stations are outside the proposed dredging area.
Of the 8 stations inside the dredging area, locations VC04 to VC05 indicated sandy silt to 3.0m depth. At VC06 the silt containing 42% shell fragments was underlain by silty sand with 11% shell content by mass. Locations VC07 and VC08 identified slightly sandy silt with some shell fragments, 3% to 15% to 3.0m depth. The silt was of very high plasticity. At locations VC09 to VC11 slightly silty sand with up to 14% shell fragments was identified to a depth of 3.0m. VC12 was characterised by silty very sandy shell to 2.5m depth.
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The sediments are summarised in the following table, Table 10.1. The full report on the sediment properties is included in Appendix 6A.
Table 10.1: Summary of Sediment Conditions
Stratum Encountered Range of sediment thicknesses Locations VC01*, VC02*, VC07 Slightly sandy/ gravelly SILT 1.0m to 3.0m and VC11 Slightly sandy SILT with shell 1.0m to 3.0m VC06 and VC08 Sandy SILT 1.0m VC04 VC03, VC12* and Slightly silty sandy SHELL 1.0m to 2.5m VC12.1* VC04, VC05 and Very silty SAND 2.0m to 3.0m VC06 VC09 , VC10 and Slighty silty SAND 2.0m to 3.0m VC11* *Station location outside of final dredging area
10.4 OFFSHORE DISPOSAL SITE
10.4.1 INFOMAR Survey
Donegal Bay is one of the areas which has been surveyed for the INFOMAR project (The INtegrated Mapping FOr the Sustainable Development of Ireland’s MArine Resource). INFOMAR is a joint venture between the Geological Survey of Ireland and the Marine Institute. The programme is a successor to the Irish National Seabed Survey (INSS) and concentrates on creating a range of integrated mapping products of the physical, chemical and biological features of the seabed in the near-shore area. Consultation was therefore held with the Geological Survey of Ireland (GSI) regarding the proposed offshore disposal site in addition to the dredging area.
The GSI responded that the dumping site at the outer edges of Donegal Bay is located behind (west of) an important moraine (Figure 10.7), approximately running NE-SW, which, along with indentified currents, would act as a natural barrier to the re-deposition of any dredged material towards Donegal Bay and Sligo Bay. No particular forms of life (cold water corals and others) were identified in that area on the seabed during the 2008 INFOMAR survey.
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Offshore Disposal Site
Figure 10.7 GSI/Marine Institute INFOMAR Moraine Shaded Relief Image Reproduced from http://www.infomar.ie/ (2011) The moraine is a glacial deposition feature which takes the form of a large ridge running roughly north to south offshore from Rossan Point, Co. Donegal. Moraines are composed of sediments which were eroded and transported by a large ice sheet from the Northwest Ice Dome. After the Last Glacial Maximum (~14,000 years ago) there was a general trend of retreat of ice. Evidence of this is seen in the lower ridge features in the top right corner of the image above, showing the episodic retreat of the ice sheet depositing glacial sediments as it went. However, at some stage it is thought that the ice retreat was slowed/stopped or readvanced allowing large amounts of sediment to be deposited in one ridge that eventually formed this spectacular moraine feature, now lying in 60 metres of water. (GSI, 2010)
In addition to the detailed bathymetry data collected by the INFOMAR project, the GSI also were able to collect additional information on the seabed properties by analysing the strength of the acoustic signal returned from the seafloor. This is known as backscatter. Differing seafloor types, such as mud, sand, gravel and rock will have different backscatter values depending on the amount of energy they return to the receiving equipment. Rocky areas will typically have high returns, while soft sediments like mud are more likely to absorb energy and have low backscatter returns. These differing values were used to generate a grey- order image (i.e. dark for high returns, bright for low returns) of the seabed which can be used to examine the nature of the seafloor. The backscatter results are correlated with sediment grab samples also taken from the seabed during the survey, to build a more accurate picture of the physical properties of the seabed.
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Figure 10.8 GSI Backscatter Image of Dumpsite
The GSI returned backscatter and ground truthing information on the seabed in the vicinity of the proposed dump site area: x The dark part in the centre of Figure 10.8 labelled “gravel” represents the moraine; x The closest sample (blue dot) from the proposed dump site (6km) is made of coarse sand and gravel, so it is anticipated that the proposed dump site would have the same substrate; x The mixed dark and pale grey is identified as fine sand with shells (as the higher acoustic reflectivity is due to a biological component (mainly understood as shell hash accumulated by currents) and it is likely that the seabed in this area is a diverse habitat, no cold water corals though as it is not deep enough and they grow on more rocky substrates) x Any pale grey area is made of fine sand.
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10.4.2 Field Surveys
10.4.2.1 Physical properties of the dump site sediments In addition to the desktop survey of the data available from INFOMAR, two visits were made to the proposed dump site, at spring tide and neap tide, to recover sediment samples from the proposed disposal area for granulometric analysis and chemical testing as well as the collection of benthic faunal information.
Figure 10.9 Grab Sample Stations January/February 2011
Grab samples were recovered from four stations within and adjacent to the proposed dump site and were subject to analysis.
The results of the granulometric analysis carried out on the 4 sediment samples are included as Appendix 6B while Table 10.2 presents a summary of these results. In general, the sediments collected in and around the dumpsite (Stations 1-3) were typically made up of fine sand with varying amounts of coarse sand and gravel. This corresponds well with the properties of the sediment to be dredged. It can be seen on the backscatter image in Figure 10.9 that these stations fall on pale grey areas, which is consistent with the descriptions provided by the GSI.
In their survey design, the Marine Insitute requested that a sample be taken from a station located approximately 1km remote from the dump site (Station 4). The sediment collected from this station, located approximately1.5 km south west of the site, was coarser in nature with a high proportion of coarse sand. It can be seen in Figure 10.9 that this station is within
IBE00440/EAR/September ‘12 10-10 Sligo Harbour Dredging Environmental Appraisal Report Geology & Soils a darker coloured area of the backscatter image, again consistent with the GSI’s description. This station will not be within the main deposition area and is unlikely to be affected by the dumped sediments.
Table 10.2 Results of the granulometric analysis on the dump site sediments Gravel C. Sand (1 M. Sand (0.5– Fine Sand (0.063- Silt/Clay Station (>4 mm) – 4mm) 1mm) 0.5 mm) (<0.063mm)
1 0 0.4 0.7 96.0 2.8 2 0 3.1 0.6 94.9 1.4 3 0 0.2 1.8 97.0 1.0 4 9.5 70.8 16.3 3.3 0
Table 10.3 Physical properties of the dump site sediments Station Colour Smell % ID Water
Grey 1 none 21.7 brown
Grey 2 none 19.6 brown
Grey 3 none 28.6 brown
Grey 4 none 16.3 brown
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10.4.2.2 Chemical properties of the dump site sediments
In accordance with the EPA’s Dumping at Sea Licence Application Guidance (2010), samples were recovered from the proposed offshore dump site and were subjected to chemical analysis. As the proposed dumpsite is a new site, these samples provide the EPA with a baseline which will aid in considering the impacts of using the site should any future applications be made.
Sediment samples were taken at the locations outlined in Figure 10.9 by means of a 0.1 m² Day grab. It was intended to take a single grab at three stations along the southwest-north east axis of the dumpsite and a fourth approximately 1 km from the dumpsite in the direction opposite to the residual current for sediment analysis. However, bottom type dictated where it was possible to take these grabs, which returned the locations as outlined in Figure 10.9. When samples were returned from each station, notes were logged on sediment type, amount, colour, smell and any other information that was considered relevant. A sample of surface sediment was taken from the centre of the grab and placed in a suitable cleaned container. All sampling jars were marked externally with date, station number, sample number and survey reference number and placed in a cooler box.
The sampling parameters were set following consultation with members of the Marine Licensing Vetting Committee (MLVC). Although the MLVC no longer directly assess dumping at sea licence applications, a number of its members are on the EPA advisory committee. The results of the sediment chemical testing are presented below.
Table 10.4 Proposed Dumpsite Baseline Sediment Testing Results St1 St2 St3 St4 CRM Carbon, Organic (%) 0.94 0.570 0.47 3.57 0.524 Mercury (mg/kg) 0.007 0.005 0.003 0.001 0.0866 Aluminium (mg/kg) 28300 28200 24700 19800 65800 Arsenic (mg/kg) 4.15 5.10 5.64 64.8 21.1 Cadmium (mg/kg) 0.145 0.158 0.209 0.088 0.216 Chromium (mg/kg) 272 304 693 21.4 89.0 Copper (mg/kg) 555 628 669 2.72 36.7 Lead (mg/kg) 11.7 11.0 11.4 15.5 21.7 Lithium (mg/kg) 13.8 12.7 8.48 11.6 70.7 Nickel (mg/kg) 184 223 447 7.54 42.4 Zinc (mg/kg) 99.7 109 112 22.5 156 Dibutyl Tin (ȝg/kg) 9.00 <3 656 Tributyl Tin (ȝg/kg) <3 <3 478 CaCO3 (mg/kg) 3.60 3.78 3.03 3.42 0.013 Aldrin (ȝg/kg) <1 - - <1 17.8 DDE-pp (ȝg/kg) <2 - - <2 21.3 DDT-op (ȝg/kg) <1 - - <1 19.0
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DDT-pp (ȝg/kg) <2 - - <2 19.2 Dieldrin (ȝg/kg) <3 - - <3 21.6 Endrin (ȝg/kg) <2 - - <2 24.3 HCH-alpha (ȝg/kg) <1 - - <1 22.4 HCH-beta (ȝg/kg) <1 - - <1 23.3 HCH-delta (ȝg/kg) <1 - - <1 21.1 HCH-gamma (ȝg/kg) <1 - - <1 22.3 Hexachlorobenzene <1 - - <1 24.4 (ȝg/kg) Hexachlorobutadiene <1 <1 24.0 (ȝg/kg) Isodrin (ȝg/kg) <2 - - <2 18.0 TDE-pp (ȝg/kg) <1 - - <1 23.3 PCB28 (ȝg/kg) <0.1 - - <0.1 4.48 PCB52 (ȝg/kg) <0.1 - - <0.1 5.56 PCB101 (ȝg/kg) <0.1 - - <0.1 5.16 PCB118 (ȝg/kg) <0.1 - - <0.1 4.28 PCB138 (ȝg/kg) <0.1 - - <0.1 3.60 PCB153 (ȝg/kg) <0.1 - - <0.1 5.52 PCB180 (ȝg/kg) <0.1 - - <0.1 3.31 Hydrocarbons, total 4.95 - - 0.08 1.43 (mg/kg)
10.4.3 Dumpsite Sediments Properties Conclusions
The sediments at the proposed dumpsite are typically made up of fine sand with varying amounts of coarse sand and gravel. The sediments are brown or grey/brown in colour with no particular smell. Contaminant analysis of sediments was undertaken at four stations within and adjacent to the dump site to provide a baseline record of sediment chemistry.
Disposal of the dredged material at the proposed dump site will pose no significant impact to the physical or chemical properties of the bottom sediments at this site.
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11.0 HYDRODYNAMIC MODELLING Hydrodynamic modelling was undertaken to investigate the impact of the dredging operations on Sligo Harbour. The modelling examines the effect of the dispersion and fate of material put into suspension during the period of the dredging operations.
11.1 COMPUTATIONAL MODEL OF WATER INJECTION DREDGING OPERATIONS (5,500m³)
Hydrodynamic modelling was undertaken to investigate the impact of the dredging operations on Sligo Harbour. The modelling examines the effect of the dispersion and fate of material put into suspension during the period of the dredging operations.
11.1.1 Modelling Software
The computational models used in this study were based on the MIKE 21 coastal process software which has been developed by the Danish Hydraulics Institute. The modules of this coastal process modelling system used in this study comprised: x 2D hydrodynamic flow models
x Particle tracking models
11.1.2 Hydrodynamic Flow Model
The main hydrodynamic flow model used in the study was a 2D MIKE21 nested HD flow model consisting of a 30m grid outer model and a finer 10m grid inner model. The extent of the nested flow model is shown in Error! Reference source not found. below.
11.1.2.1 Dredged Spoil Dispersal Model
The dredged spoil disposal modelling was undertaken using the MIKE 321npa model. This is a particle tracking model that uses the hydraulic flow regime from the MIKE21 nHD model to simulate the transport and fate of material discharged to the water column. The model can include variable graded material and takes effect of re-erosion of deposited sediment so it is particularly suitable for the simulation of the disposal of dredged spoil.
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Figure 11.1: Extent of 30 and 10 metre grid nested flow model
11.1.3 Bathymetry
The bathymetry for the model studies was taken from very detailed LiDAR and multi-beam hydrographic surveys of the entire model area undertaken by the Geological Survey of Ireland in 2008 under the INFOMAR project. These surveys comprised some 46 Gigabytes of xyz data. A narrow beam hydrographic survey was undertaken of c.850m of the navigation channel leading to the Deepwater Jetty in October 2011 (Figure 11.2) to provide accurate data on the quantity of material to be dredged.
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Figure 11.2: Extent of LiDAR Bathymetry and 2011 Bathymetric Survey
11.1.4 Model Calibration
The models were calibrated against flow measurements undertaken in December 2009 using two ADCP current meters, one deployed to the west of Deadman's Point and the other in the channel to Drumcliff Bay. The model and current meter velocities were compared for tidal conditions with the same tidal range and the model results were found to be consistent with the field measurements.
11.1.5 Model Simulations
11.1.5.1 Tidal Flow Modelling
Model Tidal Flow Regime The tidal flow modelling was undertaken for a whole month of tides based on a typical period 31 January 2003 to 2 March 2003. The fresh water flow into Sligo harbour was set at 14.7 cumecs which was derived from the annual average flow for the catchments feeding into the Garavogue River. The tidal curve at Oyster Island for the model period is shown in Figure 11.3.
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Figure 11.3: Tidal curve for 1 month simulation period.
The tidal modelling was undertaken for the existing bathymetry and for the bathymetry with the proposed dredged channel completed. Typical flow patterns are shown in Figure 11.4 and Figure 11.5; which illustrate mid flood and mid ebb tides respectively around Sligo harbour for a spring tide.
Figure 11.4: Typical flow patterns in Sligo harbour - flood tide
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Figure 11.5: Typical flow patterns in Sligo harbour - ebb tide
11.1.6 Dredging Plume Simulation Modelling
11.1.6.1 Dredging Programme
The dredged plume modelling simulations were undertaken to provide information on the dispersion and fate of dredged material discharged to the water column during the water injection dredging of some 5,500 cubic metres of material required to clear the approach channel to the Deepwater jetty and remove pockets of sediment from the berths at both the Deepwater and the Barytes jetties.
The dredging will focus on 5 target sites within the dredging area outlined, as shown in Figure 11.6, where the channel depth has become dangerously shallow.
A conservative approach has been taken to calculate the dredging impacts, using the “worst case” impacts.
General information on the water injection dredging process has been obtained from dredging contractors Van Oord, who have substantial experience in this field.
It is proposed that dredging will take place over a period of spring tides. The water depth and current velocities in the channel are such that the dredger will only be able to work for approximately 4.5 hours of every tidal cycle. Dredging operations will only occur on the ebbing tide in order to assist with the travel of the mobilised sediment away from the port area.
The quantities involved (5,500m³) are relatively small. It is thought that the dredger will be able to remove around 1,000m³ of sediment per tide, therefore it will take only around 5 or 6
IBE00440/EAR/September ‘12 11-5 Sligo Harbour Dredging Environmental Appraisal Report Coastal Processes tides to complete the operations. In order to take account of the length of time it may take for particles put in to re-suspension during subsequent tides to settle out, the model has been run for 28 days to present a complete picture of final dispersion and settlement patterns.
11.1.6.2 Flow Model Data
The dredging plume modelling was undertaken using the M321 npa particle tracking model which simulates the transport and deposition of material discharged into the water column. The model uses the data from the tidal model simulation as the basic hydrodynamic input to the simulations. 11.1.6.3 Sediment Composition
As part of the sampling regime for the larger capital and maintenance dredge project proposed within Sligo Harbour, 12 No. samples from the bottom sediments along the entire 5.2km length of the navigation channel were collected for physical, chemical and radiological testing. The full results of this testing are presented in Attachment C.1 and C.2.
The location of the sampling stations in relation to the dredging area is shown in Drawing 4 It can be seen that Station Dr-5 is within the proposed Water Injection Maintenance Dredging Area, whilst Stations Dr-4 and Dr-6 are approximately 150m upstream and downstream of the Dredging Area respectively.
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Figure 11.6: Target areas (A-E) for maintenance dredging by Water Injection Dredging
Table 11.1: Dredging Area Sediment Samples – Descriptions Station Location Colour Smell % ID Water Dr-4 Channel Grey/brown none 66.6 c. 200m south Mud east of dredging area boundary
WGS84 54° 16' 52.79" N 8° 29' 21.3" W
ITM 568140, 837059
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Dr-5 Inside Grey/brown none 54.4 dredging area Muddy sand
WGS84 54° 17' 1.93" N 8° 29' 32.86" W
ITM 567932, 837343 Dr-6 Channel Grey/brown none 64.3 c. 200m north Muddy/sand west of dredging area boundary
WGS84 54° 17' 9.89" N 8° 29' 41.78" W
ITM 567773, 837590
Table 11.2: Dredging Area Sediment Samples – Granulometry Results
Gravel C. Sand M. Sand Fine Sand Silt/Clay Station (>4 mm) (1 – 4mm) (0.5– 1mm) (0.063-0.5 mm) (<0.063mm) Dr-4 0 2.1 5.4 52.8 39.6 Dr-5 0 1.0 2.5 83.4 13.1 Dr-6 0.5 0.4 0.3 85.4 13.4
The information from the three samples shows that the material to be dredged is predominantly a fine grey silty sand.
Water Injection Dredging puts the seabed layer into suspension by injecting water into the subsoil, thus fluidising it. This fluidised bottom layer, the thickness of which (typically between 1m and 3m) is highly sensitive to both the soil parameters and the distance between the injector pipe and the seabed ("stand-off distance"), then behaves as a density current.
The low injector pressure (approx.1 bar) and keeping a small stand-off distance are key factors in minimising turbidity. The optimum stand-off distance, which depends upon the settled sediments’ particle size distribution and permeability, is often determined through
IBE00440/EAR/September ‘12 11-8 Sligo Harbour Dredging Environmental Appraisal Report Coastal Processes practical experience. The properties of the induced fluid mud layer depend on a large number of factors, but of prime importance are the particle size and viscosity of the sediment.
The fate of the material being put into suspension by the dredger has been assessed using the Mike 321 npa model. The model simulates the fate of the material from the dredger by releasing particles into the water column at a source 0.5m above the bed and tracking each particle throughout the simulation process. A range of grain sizes have been used in the model, in order to cater for the sediment grading of the dredged material. The grading used for the main source was based on the grading in the PSA results from the bed material samples. This source had the distribution of grain size shown below.
Grain Dia mm % Occurrence 0.375 6 0.187 62 0.090 20 0.050 7 0.030 5
11.1.6.4 Dredging Simulations
The dredging programme and tidal conditions were as noted in the above sections. Dredging operations were assumed to be undertaken over 5 consecutive tides.
The simulations for the dredging were run for the full 28 day tidal sequence to give the overall pattern of dispersion and deposition including the effects of particle re-suspension from the whole of the dredging operation.
11.1.7 Results of the Dredging Simulations
11.1.7.1 Sediment Deposition The results of the water injection dredging simulations are shown graphically by a series of model output diagrams. The figures show the sediment deposition depths during dredging and at the completion of the dredging, as well as the peak and average envelope values for the suspended sediment concentrations throughout the dredging.
The maximum deposition envelope diagram (Figure 11.7) represents the maximum value that occurred at each grid point in the model at any time during the simulation period, even if the period of the peak value is very short.
The maximum peak sediment deposition depth in mm can be roughly calculated by dividing the kg/m² by a figure of 1.65. This shows that in the areas of the harbour coloured green, the maximum peak deposition depth is c.4mm – 6mm. However, in some areas around the training walls, peak deposition could reach c.24mm to 48mm.
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However, it should be noted that these peak values are typically of a very short duration and tend to occur as current speeds drop during slack tide. The material may then be raised into suspension again and moved further from the dredging area as the tidal currents pick up during the next tide.
This re-suspension will cause the final settlement pattern to be more defined (Figure 11.8), with the dredged material settling around the training wall, in sheltered areas on the northern shore of Cartron Marsh and some of being swept out of the harbour to settle on the Bungar Bank and offshore from Rosses Point.
The pattern of residual sediment deposition following the completion of the dredging is shown in Figure 11.8.
In general, deposition depths in these areas will be beneath 3.0mm with only very limited areas receiving more than 10mm of deposition. Overall the amount of sediment deposition in the harbour area on completion of water injection maintenance dredging operations is considered to be a localised temporary impact of moderate negative magnitude1.
1 When using the NRA EcIA criteria for assessing impact magnitude
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Figure 11.7: Peak sediment deposition depths in Sligo Harbour during water injection dredging operations (also showing sensitive areas/monitoring stations – See 1.1.9)
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Figure 11.8: Final sediment deposition depths on completion of water injection dredging operations (also showing sensitive areas/monitoring stations – see 1.1.9)
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11.1.8 Suspended Sediments, pH and Dissolved Oxygen
Dredging also has the potential to cause temporary increases to the amount of suspended sediments held in the water column.
The hydrodynamic model was also used to predict the duration and extent of the changes to suspended sediments within the sensitive environment of Sligo Harbour.
In accordance with the monitoring requirements of Council Directive 79/923/EEC, on the quality required of shellfish waters, and Council Directive 91/492/EEC, which sets down the health conditions for the production and placing on the market of live bivalve molluscs, the Marine Institute collect water and shellfish samples from major shellfish growing areas at regular intervals and analyses them for physicochemical parameters, trace metal levels and chlorinated hydrocarbon concentrations. Sampling results were obtained from the Marine Institute for the shellfish beds within Sligo Harbour for use as a baseline indicator of suspended sediments.
Table 11.3 below shows suspended sediment concentration values measured in 2009 -2011 at this water quality sampling location. The station is also shown as Station Mon-3 in Figure 11.10.
Table 11.3: Measured suspended sediment in Sligo Harbour by Probe By Lab Date Actual Actual Sample D pH PSAL TEMP TURB CPHL SUSP COLOR Lat Long Depth OXY (sc) (PSU) (degC) (%) (ȝg/l) (mg/l) (sc) (m) (%) 03/12/09 54.2893 -8.5238 0.5 99 8 16.19 8.2 25.6 18.6 16/12/09 54.2893 -8.5238 0.5 96.3 8.11 26.5 7.79 20/01/10 54.2893 -8.5238 0.5 109 8.23 13.03 7.05 16/02/10 54.2893 -8.5238 0.5 108 8.45 23.7 7.57 12 13.6 23/03/10 54.2893 -8.5238 0.5 103 8.32 31.69 9.7 14/04/10 54.2893 -8.5238 0.5 135 8.48 16.65 13.1 17/05/10 54.2893 -8.5238 0.5 124 8.31 31.85 13.7 <2 6.6 23/06/10 54.2892 -8.5287 0.5 140 8.68 28.12 18.1 13/07/10 54.2892 -8.5242 0.5 130 8.42 32.22 17.7 23/08/10 54.2898 -8.5252 0.5 102 8.34 28.46 17 72 7.9 20/09/10 54.2883 -8.5263 0.5 143 8.8 25.32 16.4 21/10/10 54.2893 -8.5232 0.5 114 8.11 30.11 13.2 13/06/11 54.2895 -8.5240 0.5 110 8.27 28.74 18.9 8 <4 11/07/11 54.2895 -8.5242 0.5 131 8.15 24.5 18.8 <2 30.2 14/12/11 54.2893 -8.5238 0.16 108 7.97 25.58 5.3 22.9 136 (Source: Marine Institute data request)
It can be seen that measured values vary widely depending on the date when the measurements were taken (from <2 to 72 mg/l). The sediments disturbed by the dredging process in the navigation channel will cause temporary increases in suspended sediment concentration within Sligo Harbour during dredging operations.
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As stated above, actual dredging operations will only occur for around 4.5 hours per tide (12.4 hours) and dredging should be substantially completed over a period of 5 tides. The dredging should be timed to occur only during the early part of the ebbing tide, in order to give the mobilised particles the greatest opportunity of being transported a sufficient distance downstream.
The influence of the dredging may continue for several more days, as the sediments removed from the site are brought into re-suspension during subsequent tides, therefore the simulations were run for a total of 28 days.
The average value envelope for the suspended sediment concentrations throughout the dredging is presented below in Figure 11.9.
On this figure the green areas show mean suspended sediment concentrations of 80- 100mg/l, rising to 200-300mg/l in the yellow areas immediately surrounding the dredging area during the water injection maintenance dredging campaign.
In practice however, dredging does not cause a continuous increase above background for the duration of operations but rather causes the suspended sediment concentration to rise rapidly shortly after active dredging begins during each tide, achieving a peak around the period of slack water, before returning back to background or near-background values before the next dredging session begins on the next tide. Following completion of dredging, the displaced material lying on the seabed will be swept up into suspension during subsequent tides as current speeds increase, settling out temporarily as speeds drop again during slack water before being picked up again and moved on during the next tide.
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Figure 11.9: Mean suspended sediment concentrations during water injection dredging operations (for bottom 0.5m of water column) (also showing sensitive areas/monitoring stations – see 1.1.9)
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11.1.9 Sensitive Areas During the ecological baseline studies (see Appendix D.1(viii)), four areas which have the potential to be vulnerable to adverse impacts of the dredging activities were identified. These areas are indicated on Figure 11.10.
Figure 11.10: Location of Identified Sensitive Areas and Timeseries Locations Google aerial photo dated 2006 © Google/Digitalglobe/NASA
Area 1: The area surrounding Cartron Marsh and Standalone Point, where dredging activity has the potential to cause impacts on important bird feeding areas by affecting forage or prey species.
Area 2: an environmentally important habitat of seagrass (Zostera) which may be vulnerable to smothering caused by the dredging.
Area 3: encompassing the main area of commercial and natural shellfish beds, including the large mussel bank in the centre of the harbour.
Area 4: a commercial clam production area
In order to portray in a more appropriate manner the magnitude and duration of the changes to the suspended sediment concentrations within the harbour, a time series showing the peak concentration of suspended sediments in the bottom 0.5m of the water column during and after dredging as well as sedimentation depths has been produced for 4 points: Point Mon-1 (Cartron Marsh) Point Mon-2 (Southern Cummeen Strand) Point Mon-3 (Commercial mussel bed and Marine Institute baseline monitoring station) Point Mon-4 (Commercial clam bed)
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The results are presented only for the bottom 0.5m as it is changes to this part of the water column that will have greatest impacts on the shellfish and intertidal/subtidal bird prey and forage species which are present within the harbour.
Figure 11.11 to Figure 11.14 shows the time series of peak suspended sediments and peak sedimentation for the duration of the proposed water injection dredging campaign at each of the four stations within Sligo Harbour.
Figure 11.11: Time series showing peak Suspended Sediment Concentration in bottom 0.5m and Sedimentation for Carton Marsh Area during dredging campaign (Point Mon- 1)
It can be seen in Figure 11.11 that the area most affected, with the highest peak values of all of the time series recorded is in Cartron Marsh, due to it being the closest station to the dredging area. The red lines show the predicted peak suspended sediment concentrations in the bottom 0.5m of the water column while the blue lines show the peak depth of sediment settling out (depths in mm being approximately equivalent to the kg/m² divided by 1.65). It can be seen that during dredging operations, which will occur for 3 days over the first spring tide period in the model, the peak suspended sediment levels increase rapidly with increasing current speed during each tide. The highest peaks, occurring on 3 of the spring tides, reach levels of around 4-5g/l, but more typical peak values are below 1.5g/l.
The temporary rises in suspended sediment concentration typically last up to 3 hours, but with the peak values (seen as “spikes” on Figure 11) lasting for a much shorter period of only
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15-30 minutes. The period between peaks (tides), when concentrations return back to baseline, or near baseline, levels will be much longer (around 9 hours). The short duration of the peak concentrations is confirmed when we revisit the mean suspended sediment concentration values for the time series (Figure 9) which shows a mean concentration of 60mg/l throughout the duration of the timeseries at Point Mon-1.
It can be seen from the blue lines in the Carton Marsh time series that when the current speeds drop, the material settles out with the greatest peak sedimentation depth of around 13mm occurring during the tide immediately following the completion of the dredging operations. After 5 days, the depth of sediment being settled out during the slack tide is in the order of 2.5mm. It can be seen that during the neap tides the current speeds are not sufficiently strong to pick up the deposited material during each tide and it remains in place for several days, however during the next spring tide the stronger current speeds pick up more sediment, causing a brief rise in both suspended sediments and subsequent settlement, before the material is finally flushed out of the area at the end of the spring tide, around 20 days after dredging operations began.
The effects of the water injection dredging at Cartron Marsh can therefore be predicted to be moderate negative in magnitude but temporary in duration.
Figure 11.12: Time series showing peak Suspended Sediment Concentration in bottom 0.5m and Sedimentation for Southern part of Cummeen Strand during dredging campaign (Point Mon-2)
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At Point 2, on the southern shore of Cummeen Strand, it can be seen in Figure 11.12 that it takes until the next spring tide before the sediment mobilised by the dredging reaches the site. Peak suspended sediments at this site are modelled to reach around 600mg/l on the highest spring tide following the dredging, with more typical peak values below 100mg/l. The average suspended concentration at this point across the modelling period is less than 20mg/l. In between tides, sedimentation will be barely perceptible with levels of around 0.4mm occurring during slack tide. The impact arising from this small increase in suspended sediment and sedimentation is predicted to be neutral and temporary.
Figure 11.13: Time series showing peak Suspended Sediment Concentration in bottom 0.5m and Sedimentation near commercial shellfish farm during dredging campaign (Point Mon-3)
At Point 3, which is located at the Marine Institute monitoring station close to the commercial shellfish farm on Cummeen Strand, small peaks in suspended sediment (red lines) can be seen during the spring tides (Figure 11.13). These peak increases will be in the order of 50- 250mg/l with a small number of tides where material in suspension will settle out temporarily in this site. Average suspended sediment concentrations throughout the modelled period at this site are below 20mg/l. The depths of sedimentation are not predicted to be significant, with temporary sedimentation depths in the order of 0.4 to 0.8mm (blue line) predicted. The impact arising from this small increase in suspended sediment and sedimentation at Point 3 is predicted to be neutral and temporary.
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Figure 11.14: Time Series showing peak Suspended Sediment Concentration in bottom 0.5m and Sedimentation for commercial clam farm during dredging campaign (Point Mon-4)
At Point 4, the commercial clam farm to the west of Cummeen Strand, the effects of the dredging will be barely perceptible (Figure 11.14). During the spring tide following the dredging, very small peak suspended sediment concentrations of less than 60mg/ will be experienced at this site. The predicted impact at this site is anticipated to be neutral and temporary.
11.1.10 Conclusion
It can be seen from the modelling results that significant elevations in suspended sediment within Sligo Harbour caused by the dredging only occur in the immediate vicinity of where the dredger is working, and within the confines of the navigation channel.
The areas in which sensitive habitats have been identified, at Cartron Marsh, southern Cummeen Strand and at the nearby aquaculture sites will experience very short term increases in suspended sediment concentrations in the lowest 0.5m of the water column and small amounts of temporary sedimentation, particularly during the water injection dredging phase. However, the majority of the dredged material will eventually settle out around the training walls or will be transported out of the harbour during the following spring tide where the material will settle out on the sand banks at the entrance to Sligo Harbour and the residual effects will not be significant.
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The chemical analysis of the proposed material to be dredged has shown that it has a relatively low organic content. The risk of the dredging causing significant impacts to dissolved oxygen levels in the harbour is therefore considered to be low. Mitigation measures including real time monitoring of suspended sediment levels and dissolved oxygen levels are described in Chapter 7, Fisheries and Aquaculture.
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11.2 COMPUTATIONAL MODEL OF CONVENTIONAL DREDGING OPERATIONS (250,000M³)
11.2.1 Introduction Hydrodynamic modelling was undertaken as part of the study to investigate the impact of the dredging on the hydraulic regime of Sligo Harbour and on the sedimentation in the harbour area during the dredging operations. The modelling was used to examine the effect of:
1. The change in channel bathymetry on the tidal flows and water levels, and 2. The dispersion and fate of material spilled during the period of the dredging operations.
11.2.2 Computational Models
11.2.2.1 Modelling Software
The computational models used in this study were based on the MIKE 21 coastal process software which has been developed by the Danish Hydraulics Institute. The modules of this coastal process modelling system used in this study comprised: x 2D hydrodynamic flow models x Particle tracking models
11.2.2.1.1 Hydrodynamic Flow Model The main hydrodynamic flow model used in the study was a 2D MIKE21 nested HD flow model consisting of a 30m grid outer model and a finer 10m grid inner model. The extent of the nested flow model is shown above in Figure 11.1 in Section 11.1.3.
Figure 11.15: Extent of 30 and 10 metre grid nested flow model
11.2.2.1.2 Dredged Spoil Disposal Models The dredged spoil disposal modelling was undertaken using the MIKE 321npa model. This is a particle tracking model that uses the hydraulic flow regime from the MIKE21 nHD model to simulate the transport and fate of material discharged to the water column. The model can include variable graded material and takes effect of re-erosion of deposited sediment so it is particularly suitable for the simulation of the disposal of dredged spoil.
11.2.2.2 Bathymetry
The bathymetry for the model studies was taken from very detailed LiDAR and multi-beam hydrographic surveys of the entire model area undertaken by the Geological Survey of Ireland in 2008 under the INFOMAR project. These surveys comprised some 46 Gigabytes of xyz data.
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11.2.2.3 Model Calibration
The models were calibrated against flow measurements undertaken in December 2009 using two ADCP current meters, one deployed to the west of Deadman's Point and the other in the channel to Drumcliff Bay. The model and current meter velocities were compared for tidal conditions with the same tidal range and the model results were found to be consistent with the field measurements.
11.2.3 Model simulations
11.2.3.1 Tidal Flow Modelling
11.2.3.1.1 Model Tidal Flow Regime The tidal flow modelling was undertaken for a whole month of tides based on a typical period 31 January 2003 to 2 March 2003. The fresh water flow into Sligo harbour was set at 14.7 cumecs which was derived from the annual average flow for the catchments feeding into the Garavogue River. The tidal curve at Oyster Island for the model period is shown in Figure 11.3 above in 11.1.4.
The tidal modelling was undertaken for the existing bathymetry and for the bathymetry with the proposed dredged channel completed. Typical flow patterns are shown in Section 11.1.5 in Figure 11.4 and Figure 11.5; which illustrate mid flood and mid ebb tides respectively around Sligo harbour for a spring tide.
11.2.3.1.2 Impact of Dredging on Tidal Flow Regime The impact of the proposed dredging of the channel to the deepwater quay was assessed in terms of changes to overall tidal levels and tidal flow velocities.
Figure 11.16 – Figure 11.18 show a comparison of the tidal curves at Sligo town for the existing situation (blue) and with the post-dredging channel in place (red). It can be seen in Figure 11.16 that during a neap tidal cycle there is an imperceptible difference in water levels between the existing and post-dredging channels.
The overall average tidal curve shows a minor reduction in water level during low tide, but no increase in water level at high tide. During an extreme spring tide, there is a slightly greater reduction in the water level during low tide. The proposed dredging will not result in any increase in water level at high tide, therefore the proposed dredging of the channel will not cause any increase in the risk of flooding in Sligo from high spring tides.
The reduction in water level during an extreme low spring tide is caused by the removal of the bar within the shipping channel by the proposed dredging. At present, this bar slows down the passage of water exiting the channel at low tide, causing some water be retained or pooled behind it. If the bar is dredged, the water will be able to drain more freely at low tide, thus causing lower water levels and possible drying out of the channel upstream of the
IBE00440/EAR/September ‘12 11-23 Sligo Harbour Dredging Environmental Appraisal Report Coastal Processes bar at extreme low spring tides. As can be seen on Figure 11.18 this drying will last for a maximum of 2 hours.
Figure 11.16: Comparison of existing and dredged channel tidal curves at Sligo (neap tide)
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Figure 11.17: Comparison of existing and dredged channel tidal curves at Sligo (overall average)
Figure 11.18: Comparison of existing and dredged channel tidal curves at Sligo (extreme spring tide)
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The impact of the proposed dredging on the flow regime in Sligo Harbour has been assessed by comparing the mean and peak flow velocities for both flood and ebb tides. Different plots have been used to highlight the magnitude and location of changes in the tidal current velocities which are predicted to occur due to the proposed dredging of the channel into Sligo's deep water quay. The analysis has been shown only for spring tides, as the differences will be more pronounced during spring tides compared to the effect at neap tides.
Figure 11.19 and Figure 11.20 show the difference in the mean tidal velocity for both flood and ebb spring tides. In these diagrams, the difference in the tidal velocity is calculated by comparing the average tidal velocity over the flood or ebb period for the model with the dredged channel in place and subtracting the equivalent flows for the model with the existing bathymetry. It will be seen from these diagrams that the difference in the mean velocities is generally very small (less than 0.1 m/s) and the changes are restricted to the area around the channel and the northern section of the harbour area.
Figure 11.19: Difference in mean spring flood tide velocity - proposed minus existing
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Figure 11.20: Difference in mean spring ebb tide velocity - proposed minus existing
Figure 11.21 and Figure 11.22 show the difference in the peak tidal velocity for both flood and ebb spring tides. The diagrams show the difference in the maximum tidal velocity that occurs at any time during the period at every grid cell within the model area. It should be noted that these peak velocities will not necessarily occur at the same time in each part of the harbour area. In these diagrams the difference in the tidal velocity is calculated by taking the peak tidal velocity during the flood or ebb period for the model with the dredged channel in place and subtracting the equivalent flows for the model with the existing bathymetry.
Figure 11.21: Difference in peak spring flood tide velocity - proposed minus existing
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Figure 11.22: Difference in peak spring ebb tide velocity - proposed minus existing
As with the mean tidal flow difference plots, it can be seen that the impact of the dredging on the peak tidal flow speeds is generally insignificant, except in the area of the channel itself where increases of up to 0.4m/s may be experienced in localised areas. Peak speeds in the area north of the navigation channel may be slightly decreased by around 0.1m/s.
In summary, the tidal flow modelling indicates that while the proposed dredging will lower the level of the low water spring tides in the channel at Sligo, the high spring tide level will be unaffected by the proposed dredging works. The dredging will have an insignificant effect on the current flows in the harbour area except in the area of the channel and adjoining northern section of the harbour. The secondary main harbour drainage channel, to the south of middle bank, experiences a drop in peak current speeds of up to 0.2 m/s whilst parts of the navigation channel have increased speeds of up to +0.4 m/s in very localised areas with more typical peak speed changes in the order of -0.05 to +0.05m/s.
11.2.3.2 Dredging Plume Simulation Modelling
11.2.3.2.1 Dredging Programme The dredged plume modelling simulations were undertaken to provide information on the dispersion and fate of dredged material discharged to the water column during the dredging of some 250,000 cubic metres of material required to deepen the approach channel.
The precise methodology for dredging will not be known until a dredging contractor has been appointed, therefore a conservative approach has been taken to calculate the dredging impacts, using the “worst case” impacts. The water depths in the existing channel are such that it is likely that the dredger will have to dig its way upstream and that it will only be able to dredge during the upper half of the tidal cycle. Thus for the modelling simulations it has been assumed that the dredging programme will be organised to dredge during periods when the water levels are above mid tide level and sail to and from the disposal area during the lower
IBE00440/EAR/September ‘12 11-28 Sligo Harbour Dredging Environmental Appraisal Report Coastal Processes half of the tidal cycle. For the purposes of the simulation it was assumed that it will take four months to undertake the dredging work. This gives an average dredging quantity of about 2,100 m³ per day and an excavation rate of about 175 m³ per hour while the dredger is working in the channel. These figures represent a “worst case” scenario using a stationary dredger and more than one transportation barge to transport the dredged material to the proposed dump site. In the event of the dredging operations using a mobile dredger or single barge, the dredging will take place over a longer period of time with lesser quantities of suspended sediments being released and the impacts on the environment will be reduced.
11.2.3.2.2 Flow Model Data The dredging plume modelling was undertaken using the M321 npa particle tracking model which simulates the transport and deposition of material discharged into the water column. The model uses the data from the tidal model simulation as the basic hydrodynamic input to the simulations.
The tidal models for both the existing channel and with the proposed dredged channel in place were used for the dredging simulation modelling. The hydrodynamics with the existing channel were used for the dredging of lower section of the channel, i.e. seaward of the end of the rebuilt training wall, while the hydrodynamics with the proposed deepened channel in place were used for the simulations of the dredging of the upper channel section up to the deep water quay. The 30 day tidal curve used in the simulations is shown in Figure 11.23.
Figure 11.23: Tidal curve for hydrodynamic regime used in the dredging simulations
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11.2.3.2.3 Bed sediments and dredging losses As noted in Chapter 10 “Geology and Soils”, a number of bed samples were analysed as part of the study. The information from the various samples shows consistently that the material to be dredged is predominantly a fine grey silty sand. Even though there is an increase in the shell and gravel fraction further downstream in the channel, only the finer fractions are put into suspension in the water column during dredging, with the heavier fractions settling out within a few metres of the dredger.
The losses from the dredger have been assessed using on on-site measurements made during the construction of the Denmark – Sweden fixed link tunnel and bridge and by reference to data contained in “Scoping the Assessment of Sediment Plumes from Dredging” CIRIA 547. As the exact type of dredger which will undertake the work is unknown at this stage, a conservative approach to the losses of material to the water column was taken. Thus the total losses to the water column were assumed to be 3% of the dredged volume represented by a 2% source at 2.5 metre below the surface and a 1% source at the surface.
The Mike 321 npa model simulates the fate of the loss of material from the dredgers by releasing particles into the water column and tracking each particle throughout the simulation process. A range of grain sizes have been used in the model, in order to cater for the sediment grading of the dredged material. The grading used for the main source located at 2.5 metres below the surface was based on the grading in the PSA results from the bed material samples. This source had the distribution of grain size shown below.
Grain Dia mm % Occurrence 0.375 6 0.187 62 0.090 20 0.050 7 0.030 5
The source at the surface had a finer grading, as the losses at the surface come from overspill or washout of finer fractions of the dredged material. The grading of the source at the surface used in the study was as follows:
Grain Dia mm % Occurrence 0.090 45 0.050 30 0.030 25
11.2.3.2.4 Dredging Simulations The dredging programme and tidal conditions were as noted in Sections 11.2.3.2.1 and 11.2.3.1.1 above. The dredging of the channel was considered in two halves, i.e. a lower section comprising the channel up to the commencement of the rebuilt training wall on the western side of the channel and an upper section consisting of the section of the channel
IBE00440/EAR/September ‘12 11-30 Sligo Harbour Dredging Environmental Appraisal Report Coastal Processes beside the rebuilt training wall, up to the deep water berth. Each section of the channel was assumed to take 2 months to dredge giving a total of 4 months dredging. This is the worst case scenario, assuming the dredging would be done as quickly as possible. In reality the dredging could take longer in which case the scale of the impact on the harbour will be reduced.
In the simulations the dredger was assumed to work its way up the channel from seaward dredging half the channel width at a time. The sources in the model were moved to keep track of the dredger with breaks in the sequence while the dredger was travelling to and from the dump site.
The simulations for the lower and upper channel sections were each run for the 30 day tidal sequence and then results for each area multiplied up by two to match the appropriate dredging period. Finally, the results of the dredging of the two channel sections were combined to give the overall deposition from the whole of the dredging operation.
11.2.3.2.5 Results of the Dredging Simulations The results of the dredging simulations are shown graphically by a series of model output diagrams. The figures show the sediment deposition depths at the completion of the dredging as well as the average value envelopes for the suspended sediment concentrations throughout the dredging of each of the channel sections. The maximum sediment deposition depth envelopes are also shown for the deposition of sediment during the dredging of each of the channel sections.
The maximum deposition envelope diagrams represent the maximum value that occurred at each grid point in the model at any time during the simulation period, even if the period of the peak value is very short. The average concentration envelope is the average value at each grid cell in the model throughout the period when the cell is wet. In these diagrams the period when the cell dries out (e.g. at low tide) is ignored when calculating the average.
Figure 11.24 - Figure 11.26 show the peak sedimentation depth during the dredging of the lower and upper channel sections and on final completion of dredging operations. It will be seen from these diagrams that sediment is temporarily deposited in a small number of sheltered areas, mainly along the sides of the channel and along the north shore of the harbour area, during dredging. Away from these sites the deposition depth is low. It should be noted that these peak values are typically of a short duration and tend to occur during the turn of the tide. The material may then be re-suspended as the tidal currents pick up during the next tidal cycle. If unacceptable localised deposits remain at the end of the dredging process, these may be cleaned up and reinstated after dredging operations are completed.
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Figure 11.24 Peak sediment deposition depths during dredging of lower channel
Figure 11.25 Peak sediment deposition depths during dredging of upper channel
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The pattern of residual sediment deposition following the completion of the dredging is shown in Figure 11.26. It will be seen that significant deposition only occurs in a small number of sheltered areas along the coastline, particularly in the lee of the training wall and along small parts of the north shoreline.
Figure 11.26 Sediment deposition depths on completion of all dredging operations
The maximum peak sedimentation during dredging in the affected areas is between 20 and 70mm (Figure 11.24 and Figure 11.25). As described above, much of this deposition is temporary; occurring only for a very short period of time during slack tide and much of the material will be re-suspended when current speeds pick up during the following tide.
This resuspension will significantly decrease the final residual amount of deposited sediment (Figure 11.26), which is therefore lower than the “during dredging” peak values within these localised areas.
The maximum deposition depth of dredged sediments in Sligo Harbour on completion of dredging is less than 1mm in the majority of the harbour area. The deposition exceeds 25mm only in a small number of very localised sites, which are mainly around the training wall and northern shore of the harbour. Outside of this area, two very small sites (less than 300m²) will experience final sediment deposition depths in excess of 25mm adjacent to Coney Island and at the southern shore of Cummeen Strand.
The combined area of the intertidal sites where deposition depths in excess of 25mm will occur is 3.5ha. This represents 0.07% of the overall SAC area (c.4854ha).
Overall the amount of sediment deposition in the harbour area on completion of dredging is considered to be insignificant.
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11.2.4 Impacts of Dredging on Sensitive Habitats
During the intertidal/subtidal and birds baseline studies, three areas which have the potential to be vulnerable to adverse impacts of the dredging activities were identified.
These areas are outlined on Figure 11.27, which also shows the mean suspended sediment concentration in lower 0.5m of water column during dredging of the lower section of the channel.
Area 1: The area surrounding Cartron Marsh and Standalone Point, where dredging activity has the potential to cause impacts on important bird feeding areas. The mean suspended sediment concentration at this location arising from the dredging operations in the lower part of the channel is shown in more detail on Figure 11.28 and the upper part of the channel inFigure 11.32.
Area 2: an environmentally important habitat of seagrass (Zostera) which may be vulnerable to smothering caused by the dredging. The mean suspended sediment concentration at this location arising from the dredging operations in the lower part of the channel for this area are shown in detail on Figure 11.29 and for operations in the upper channel in Figure 11.33.
Area 3: encompassing the main area of commercial and natural shellfish beds, including the large mussel bank in the centre of the harbour. The mean suspended sediment concentration at this location arising from the dredging operations in the lower part of the channel is shown in more detail in Figure 11.30 and for operations in the upper channel in Figure 11.34.
In all cases the suspended sediment concentration within the bottom 0.5m of the water column has been plotted as it is changes to this part of the water column that will have greatest impacts on the shellfish and intertidal/subtidal bird prey and foraging species which are present within the harbour.
Figure 11.27: Location of potentially vulnerable areas
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Mean suspended sediment concentration in lower 0.5m of water column during dredging of the lower section of the channel
Figure 11.28: Lower channel dredging - mean suspended sediment concentration in Area 1 – Cartron/Standalone Point
Figure 11.29: Lower channel mean suspended sediment concentration in Area 2 – seagrass habitat in southern part of Cummeen Strand
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Figure 11.30: Lower channel mean suspended sediment concentration in Area 3 – commercial shellfish farm
The average level of suspended sediment in the bottom 0.5m of the water column during the dredging operations of the upper section of the channel is shown in Figure 11.31 and in more detail on Figure 11.32 - Figure 11.34.
Figure 11.31: Mean suspended sediment concentration in lower 0.5m of water column during dredging of the upper section of the channel
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Figure 11.32: Upper channel dredging - mean suspended sediment concentration in Area 1 –Cartron Marsh/Standalone Point
Figure 11.33: Upper channel dredging - mean suspended sediment concentration in Area 2 – Seagrass habitat in southern part of Cummeen Strand
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Figure 11.34: Upper channel mean suspended sediment concentration in Area 3 – commercial and natural shellfish beds
The concentrations shown in Figure 11.27 - Figure 11.34 are above background values and are the average over the time when the particular part of the area is wet during the period of time that particular section of the channel is being dredged.
Overall the impact of the dredging is expected to be relatively small, as both the deposition depths and the increase in the level of the suspended sediment concentrations in the greater part of the harbour area are not particularly significant.
In accordance with the monitoring requirements of Council Directive 79/923/EEC, on the quality required of shellfish waters, and Council Directive 91/492/EEC, which sets down the health conditions for the production and placing on the market of live bivalve molluscs, the Marine Institute collect water and shellfish samples from major shellfish growing areas at regular intervals and analyses them for physicochemical parameters, trace metal levels and chlorinated hydrocarbon concentrations. Sampling results were obtained from the Marine Institute for the shellfish beds within Sligo Harbour for use as a baseline indicator of suspended sediments.
Table 11.4 below shows suspended sediment concentration values measured in 2009 and 2010 at the same sample location.
IBE00440/EAR/September ‘12 11-38 Table 11.4: Water Quality Measurements in Sligo Harbour
by Probe Lab Analysis Date Fixed Sample DOXY PSAL TEMP TURB CPHL AG AS CD CR CU NI PB ZN SUSP COLOR (yymmdd) Fixed Lat Long Depth (m) (%) PH (sc) (PSU) (degC) (%) (ug/l) (ug/l) (ug/l) (ug/l) (ug/l) (ug/l) (ug/l) (ug/l) (ug/l) (mg/l) (sc) 091203 54.2893 -8.5238 0.5 99 8 16.19 8.2 Ͳ Ͳ Ͳ Ͳ Ͳ Ͳ Ͳ Ͳ Ͳ Ͳ 25.6 18.6 091216 54.2893 -8.5238 0.5 96.3 8.11 26.5 7.79 Ͳ Ͳ Ͳ Ͳ Ͳ Ͳ Ͳ Ͳ Ͳ Ͳ Ͳ Ͳ 100120 54.2893 -8.5238 0.5 109 8.23 13.03 7.05 Ͳ Ͳ Ͳ Ͳ Ͳ Ͳ Ͳ Ͳ Ͳ Ͳ Ͳ Ͳ 100216 54.2893 -8.5238 0.5 108 8.45 23.7 7.57 Ͳ Ͳ Ͳ Ͳ Ͳ Ͳ Ͳ Ͳ Ͳ Ͳ 12 13.6 100323 54.2893 -8.5238 0.5 103 8.32 31.69 9.7 Ͳ Ͳ Ͳ Ͳ Ͳ Ͳ Ͳ Ͳ Ͳ Ͳ Ͳ Ͳ 100414 54.2893 -8.5238 0.5 135 8.48 16.65 13.1 Ͳ Ͳ Ͳ Ͳ Ͳ Ͳ Ͳ Ͳ Ͳ Ͳ Ͳ Ͳ 100517 54.2893 -8.5238 0.5 124 8.31 31.85 13.7 Ͳ Ͳ Ͳ Ͳ Ͳ Ͳ Ͳ Ͳ Ͳ Ͳ <2 6.6 100623 54.2893 -8.5238 0.5 140 8.68 28.12 18.1 Ͳ Ͳ Ͳ Ͳ Ͳ Ͳ Ͳ Ͳ Ͳ Ͳ Ͳ Ͳ 100713 54.2893 -8.5238 0.5 130 8.42 32.22 17.7 Ͳ Ͳ Ͳ Ͳ Ͳ Ͳ Ͳ Ͳ Ͳ Ͳ Ͳ Ͳ 100823 54.2893 -8.5238 0.5 102 8.34 28.46 17 Ͳ Ͳ Ͳ Ͳ Ͳ Ͳ Ͳ Ͳ Ͳ Ͳ 72 7.9 100920 54.2893 -8.5238 0.5 143 8.8 25.32 16.4 Ͳ Ͳ Ͳ Ͳ Ͳ Ͳ Ͳ Ͳ Ͳ Ͳ Ͳ Ͳ 101021 54.2893 -8.5238 0.5 114 8.11 30.11 13.2 Ͳ Ͳ Ͳ Ͳ Ͳ Ͳ Ͳ Ͳ Ͳ Ͳ Ͳ Ͳ 110613 54.2893 -8.5238 0.5 110 8.27 28.74 18.9 Ͳ Ͳ Ͳ Ͳ Ͳ Ͳ Ͳ Ͳ Ͳ Ͳ 8 <4 110711 54.2893 -8.5238 0.5 131 8.15 24.5 18.8 Ͳ Ͳ Ͳ Ͳ Ͳ Ͳ Ͳ Ͳ Ͳ Ͳ <2 30.2 111214 54.2893 -8.5238 0.16 108 7.97 25.58 5.3 22.9 136 Ͳ Ͳ Ͳ Ͳ Ͳ Ͳ Ͳ Ͳ Ͳ Ͳ 111214 54.2893 -8.5238 0.5 ------<1 <1 <0.04 <0.5 0.7 0.47 0.19 2.88 - -
120423 54.2893 -8.5238 0.5 ------<5 11.8
120423 54.2893 -8.5238 1.72 105 7.99 30.17 11.2 - 0.49 ------
120521 54.2893 -8.5238 1.35 122 8.22 30.76 16.74 9.7 5.83 ------
Source: Marine Institute Data Request Sligo Harbour Dredging Environmental Appraisal Report Coastal Processes
Figure 11.35 shows the locations of 4 model points which have been chosen as they represent potentially vulnerable areas. These stations are also replicated as suggested monitoring points Mon-1 to Mon-4. Month-long time series of the suspended sediment concentration at these stations have been extracted from the model and are presented in in Figure 11.36 - Figure 11.39. Point 3 (Mon-3) marked on this figure represents the location of the measured baseline values shown in Table 11.4.
Figure 11.35: Mean suspended sediment concentration in bottom 0.5m at location of 4 points in potential vulnerable areas
It can be seen that measured values vary widely depending on the date when the measurements were taken (from <2 to 72 mg/l). The sediments disturbed by the dredging process in the navigation channel will cause temporary increases in suspended sediment concentration within Sligo Harbour during dredging. Figure 11.36 to Figure 11.39 shows a time series of the modelled peak suspended sediment concentrations spanning a typical month at each of the four “vulnerable area” points.
Figure 11.36: Time series showing Suspended Sediment Concentration in Cartron Marsh Area during dredging (Point 1)
IBE00440/EAR/September ‘12 11-40 Sligo Harbour Dredging Environmental Appraisal Report Coastal Processes
Figure 11.37: Time series showing Suspended Sediment Concentration in Southern part of Cummeen Strand during dredging (Point 2)
Figure 11.38: Time series showing Suspended Sediment Concentration near commercial shellfish farm during dredging (Point 3)
Figure 11.39: Time Series showing Suspended Sediment Concentration near commercial clam farm during dredging (Point 4)
It can be seen that when dredging operations occur during spring tides, the suspended sediment concentration at each of the four sites shown in Figure 11.36 to Figure 11.39 rises quickly (around the period of slack water during each tide) but it also quickly returns back to the background values.
During the spring tide period, the suspended sediment concentrations reach relatively high peak values during each tide (when compared to the measured background in Table 11.4);
IBE00440/EAR/September ‘12 11-41 Sligo Harbour Dredging Environmental Appraisal Report Coastal Processes however the actual duration of each “spike” is very short (as dredging only occurs for a short period each tide). The concentration peaks, or “spikes” at any given point will typically last up to two hours, but with the highest values lasting for a period of only 15-30 minutes. The period between peaks (tides), when concentrations return back to near baseline levels, will be much longer (around 10 hours).
As can be seen on Figure 11.36 to Figure 11.39, during the neap tides suspended sediment concentration levels at each of the four sites remain at background levels during dredging operations.
In summary, the modelling shows that significant elevations in suspended sediment within Sligo Harbour caused by the dredging only occur in the immediate vicinity of where the dredger is working, within the confines of the navigation channel during periods of spring tides..
The areas in which sensitive habitats have been identified, at Cartron Marsh, southern Cummeen Strand and at the various aquaculture sites will experience very short term increases in suspended sediment concentrations in the lowest 0.5m of the water column, mainly during slack water at spring tides. As described in Section 6.2.4 of Chapter 6, “Intertidal and Subtidal Flora and Fauna and Marine Mammals,” as these increases are of short term duration and are well within the tolerance levels of the sensitive flora and fauna within the harbour, they are not considered to be significant.
IBE00440/EAR/September ‘12 11-42 Sligo Harbour Dredging Environmental Appraisal Report Coastal Processes
11.3 DUMPSITE PLUME MODELLING
11.3.1 Disposal Site Dispersion
Material from the planned channel dredging in Sligo Harbour is to be dumped at a proposed location offshore of Donegal Bay. The impact of the dumping operation on sedimentation and suspended sediment loads in the area was assessed by undertaking a computational modelling exercise using the MIKE321 NPA particle tracking model.
The dispersion characteristics of the proposed disposal site were assessed by simulating the disposal of circa 49,300m3 of saturated silty sand over a one month period. With an approximate specific gravity of 1.41t/m3 for 25% saturated silty sand, this equated to circa 69,600 tonnes of dredge material for disposal at the dumping site. The grading of the disposal material used in the dumping simulations was in accordance with those used in dredge modelling and are presented in Table 11.1.
The location of the proposed dumping site is shown in Figure 11.40 as a red square, with the surrounding blue square indicating the extent of the detailed area used in the sediment modelling.
Extract from Admiralty Chart 2725 & 2767 © Crown Copyright UKHO. Not for navigational use
Figure 11.40: Extents of sediment dumping hydrodynamic model (blue square) and proposed dump site location (red square)
Given the distance from the dredging site to the disposal site (approx. 50km) and the time restriction due to the movement of tides in the area, it was calculated that the dredging would take 5-6 months. In order to understand the effects of the dumping process one month of dumping was necessary to be modelled, with the assumption that the disposal will occur during every low tide, with an average dredging rate of 850m3 per dump cycle. This value is
IBE00440/EAR/September ‘12 11-43 Sligo Harbour Dredging Environmental Appraisal Report Coastal Processes dependant upon barge capacity which was assumed at 1200 tonnes per barge. The speed of the barge during the dumping was assumed to be 4mph with 10 minutes being required for the dumping process. It was assumed that no washout from the barges will occur, and that the disposal source will be located at the water surface.
11.3.2 Modelling System
For the sediment dispersion simulations RPS used the MIKE321 NPA model which describes the transport and fate of solutes or suspended matter and uses data from the corresponding hydrodynamic model to provide information on the general movement of the water body. Within MIKE 321 NPA the sediment is considered as a series of discrete particles being advected with the surrounding water body and dispersed as a result of random processes in a 2-Dimensional or 3-Dimensional regime using the Lagrangian approach. Hence, the resolution of the sediment plume is not restricted by the grid size of the current field.
The model can be used to determine the fate of suspended or dissolved matter that is discharged or accidentally spilled in lakes, estuaries, coastal areas or the open sea. The model can simulate the effects of wind driven currents, including a mechanism for dealing with the overturning currents at the shoreline. The loss of active material from the water column through either settling or decay can also be included within the model simulations.
The model can use data from 2-Dimensional depth averaged hydrodynamic flow models; in such cases the MIKE321 NPA model applies a logarithmic vertical velocity profile to the tidal current component to provide a more accurate assessment of the displacement of particles located at different depths in the water column. This facility provides a more realistic representation of the situation at full scale.
In order to run the Mike 321 NPA model, it was necessary to determine the hydrodynamic conditions across the model domain by means of a series of Mike 21 flexible mesh and rectangular mesh models. A one month hydrodynamic model with fluxes was used to construct the 45m grid model used in the dispersion modelling. Tidal level boundaries for the model which formed the basis of the hydrodynamic data were extracted from RPS’s flexible mesh Irish Seas Tidal and Surge model (ISTSM) which provides hydrodynamic information offshore in the water bodies surrounding Ireland. The extent of this base model covered much of Ireland’s west coast centred on Donegal Bay and the Atlantic Ocean as shown in Figure 11.41.
IBE00440/EAR/September ‘12 11-44 Sligo Harbour Dredging Environmental Appraisal Report Coastal Processes
Figure 11.41: Flexible mesh model base model
The sediment modelling was undertaken on a 45m grid rectangular mesh, the domain of which is shown in Figure 11.42 as a red square on the zoomed extent of the flexible mesh base model. Figure 11.43 shows the extent of the 45m grid model and its bathymetry. The extent of the deposition area was given as 1km2 and is depicted by a yellow square. Analysis of the tidal excursion and residual current was used to determine the necessary extent of the sediment transport model. Due to the low current velocities at the site, the extent of the 45m grid NPA model was a 11.25 km square area with the dumping site located in its centre. The model size was sufficient for the analysis as no material exited the model domain during the course of the simulations, as can be seen in the result plots in Section 11.3.4.
IBE00440/EAR/September ‘12 11-45 Sligo Harbour Dredging Environmental Appraisal Report Coastal Processes
Figure 11.42: Flexible mesh model – zoomed extents
Figure 11.43: Extent of 45m grid with deposition area marked by yellow square
11.3.3 Ambient Tidal and flow Conditions In order to determine the influence of the proposed disposal, the plume extent and sedimentation was established over a simulation period of 1 month from mid September till mid October 2009 and incorporated both spring and neap tidal ranges. A time series of tidal elevation over the modelling period is shown for the dump site in Figure 11.44.
IBE00440/EAR/September ‘12 11-46 Sligo Harbour Dredging Environmental Appraisal Report Coastal Processes
Figure 11.44: Tidal elevations at the dump site over simulation period
The peak spring flood and ebb tide flow patterns are shown in Figure 11.45 and Figure 11.46 respectively. The tidal velocities in the extent of the model including the dump site are small with peak spring tidal velocities of circa 0.16 m/s.
Figure 11.45: Tidal flow around deposition site - Mid flood spring tide
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Figure 11.46: Tidal flow around deposition site - Mid ebb spring tide
Dredged spoil deposited on the sea bed at the proposed disposal site may also be subjected to wave action during gales and storms; this is examined in Section 11.3.5.
11.3.4 Modelling Results
11.3.4.1 Model calibration data
The NPA model was verified using field data collected specifically for this study. Drogue measurements were carried out to provide information on tidal currents in the surface, middle water column and bed layer during neap (27 Jan 2011) and spring (17 Feb. 2011) tides. In addition to the release of drogues, current speed and direction was measured at the site of each drogue drop location. The series of figures below show current speed and current direction recorded at these locations in the mid water column depth and current speed and direction from the model results (shown as a solid line).
It should be noted that the model simulation period was not the same as the monitoring period and therefore data was compared in terms of tidal range. In order to match the data from when the measurements were collected with the modelled tides the tidal elevation for Jan 2011 and Feb 2011 was predicted using harmonic data published by the UK Hydrographic Office. The predicted tidal ranges were aligned with those in the model results on 6 Oct 2009 for the spring tide (Figure 11.47 and Figure 11.48) and for the neap tide on 11 Oct 2009 (Figure 11.49 and Figure 11.50).
IBE00440/EAR/September ‘12 11-48 Sligo Harbour Dredging Environmental Appraisal Report Coastal Processes
Figure 11.47: Measured and modelled current speed – site of drogue release 1 spring Tide
Figure 11.48: Measured and modelled current direction – site of drogue release 2 spring tide
Values for current direction measured during the spring tide are slightly higher than those modelled but current direction correlates well with the measured values. Current speed measured during neap tide (Figure 11.49) show widely scattered values. As it is very unlikely that the current speed changed its magnitude so rapidly between successive readings and that the current changed direction every 10 minutes with such a magnitude, it has to be concluded that due to low tidal range during neap tide there is significant amount of noise in the measurement data.
IBE00440/EAR/September ‘12 11-49 Sligo Harbour Dredging Environmental Appraisal Report Coastal Processes
Figure 11.49: Measured and modelled current speed – site of drogue release 1 neap tide
Figure 11.50: Measured and modelled current speed – site of drogue release 2 neap tide
The following figures present in detail a sample of the particle tracks for different tidal conditions and drogue measurements. In each case, the particle tracking facility within the MIKE modelling software was used to describe the route of a particle when released at an equivalent location and tidal state as each drogue released in the field measurements. The hydrodynamic model data was used to determine the course of the particle under advection for the same duration as the drogue release.
Figure 11.51 shows a drogue drop during neap tide at high water. Figure 11.52 shows a drogue drop during spring tide at low water and Figure 11.53 shows a mid flood drogue drop along with Figure 11.54 a mid ebb drop. The white line on the figures indicates the modelled track of a single particle in the middle of the water column whereas the coloured points indicate the measured drogue position at a particular time in approximately 5 minute intervals.
IBE00440/EAR/September ‘12 11-50 Sligo Harbour Dredging Environmental Appraisal Report Coastal Processes
Figure 11.51: Drogue track at neap tide in mid layer (drop at high water) and particle track from the model
Figure 11.52: Drogue track at Spring tide - mid layer (drop at low water) and particle track from the model .
IBE00440/EAR/September ‘12 11-51 Sligo Harbour Dredging Environmental Appraisal Report Coastal Processes
Figure 11.53: Drogue track at mid layer (mid flood drogue drop) and particle track from the model
Figure 11.54: Drogue track at mid layer (mid ebb drogue drop) and particle track from the model
As can be seen on these figures, the modelling results largely correspond to the measured data in terms of direction and the distance the particles will travel. It should be noted that the
IBE00440/EAR/September ‘12 11-52 Sligo Harbour Dredging Environmental Appraisal Report Coastal Processes modelled data is driven by tidal currents alone and will not replicate meteorological conditions which may have been present at the time of the field studies.
11.3.4.2 Sedimentation and concentration modelling
Sediment sampling at the proposed dredging site has indicated that the sediment comprises sand and silt. Table 11.11.5 shows grain distribution used in the modelling. This is in accordance with the modelling of the dredging process in Sligo Harbour channel.
Table 11.11.5: Grain diameter occurrence used in modelling
Grain Diameter [mm] % Occurrence
0.375 6 0.187 62
0.090 20
0.050 7 0.030 5
Deposition of the dredged spoil at the disposal site was simulated by modelling the dispersion of the spoil as the dredger carried out the dumping process at the site. The dredger was assumed to traverse over the disposal site as it released each load over a 10 minute period. This occurred once in every circa 12 hours at a distance of 1m below the sea surface. Due to operational constraints the dumping took place during low tide and the simulations were run for a full month. Figure 11.55 below shows a plot of the course of a particle released in the centre of disposal area over the modelled 1 month period. This would represent the path of the finer material which is more easily re-suspended and it can be seen that the material will be gradually transported towards the open sea due to the residual current.
IBE00440/EAR/September ‘12 11-53 Sligo Harbour Dredging Environmental Appraisal Report Coastal Processes
Figure 11.55: Track of suspended sediment over a month of tides
The maximum plume concentration in the water column during the modelled period is shown in Figure 11.56. These values are the maximum that occur at any time during the dredging operation even if it is only for a very short period of time and would therefore not necessarily occur concurrently. The mean value of the suspended sediment concentration in the water column over the one month period is shown in Figure 11.57. It can be seen from these diagrams that the suspended sediment values beyond the immediate vicinity of the dumping operation are minimal. Figure 11.58 illustrates total sedimentation depth (in mm) after deposition of 250,000m3 dredged material, and was calculated by scaling the deposition observed during the 1 month simulation period. It indicates that the majority of the material will be deposited and remain within 2km on the dumping site with only a small amount of material being transported further offshore by the residual current.
IBE00440/EAR/September ‘12 11-54 Sligo Harbour Dredging Environmental Appraisal Report Coastal Processes
Figure 11.56: Maximum suspended sediment concentration in the water column
Figure 11.57: Mean suspended sediment concentration in the water column
IBE00440/EAR/September ‘12 11-55 Sligo Harbour Dredging Environmental Appraisal Report Coastal Processes
Figure 11.58: Final Deposition of sediment at the end of dredging operations
11.3.5 Wave induced Sediment Transport
In addition to the sediment transport induced by tidal currents, wave induced sediment transport was also investigated. The sediment which is proposed for deposition at the site is mainly fine sand and silt; it is therefore relatively easily re-suspended. However the water depth at the site is of the order of 90m which will reduce the impact of waves. Analysis of the nature of the material suggests that in order for significant re-suspension to occur current speeds in excess of 0.05m/s would be required, although the very fine silt fraction would require lower velocities.
Using the horizontal velocity equation it was determined that longer period swell waves would be required in order to penetrate to the deposited material on the bed; in excess of 10 seconds mean period and with a significant wave-height greater than 3m. The wave climate within Donegal Bay, for a location close to the proposed dumping site, was examined using a 9 year dataset supplied by the European Centre for Medium-range Weather Forecasting. Statistical analysis showed that the conditions required to mobilised material at the seabed occurred for less than 15% of the time. Figure 11.59 shows the wave rose for this period while Figure 11.60 shows the corresponding plot for the mean wave period.
IBE00440/EAR/September ‘12 11-56 Sligo Harbour Dredging Environmental Appraisal Report Coastal Processes
Figure 11.59: Significant wave height Donegal Bay
Figure 11.60: Mean wave period Donegal Bay
During these events the material at the bed may be re-suspended however any subsequent transport will take place by advection on tidal currents. In the area of the dump site the tidal currents are weak and the material would not be transported significant distance before the current speeds reduce at slack water and the material is deposited, or if it remains in suspension it will be carried back to the site on the returning tide. This has already been demonstrated in Figure 11.55.
11.3.6 Dumping at Sea Impacts Summary & Conclusions
The final settlement model (Figure 11.58) shows that most of the dumped sediment will settle on the seabed close to the dump site. Some of the material will migrate towards the east under the influence of tidal action, but all particles will settle within 5.5km of the dump site.
IBE00440/EAR/September ‘12 11-57 Sligo Harbour Dredging Environmental Appraisal Report Coastal Processes
An area extending across approximately 2km to the east and south of the dumpsite will experience deposition in excess of 20mm. Within this, an area measuring approximately 0.5km² will experience deposition depths in excess of 130mm.
It can be seen from the suspended sediment and deposition diagrams that the proposed dredging will not have a significant impact on bed sediments or water quality in a waters beyond the immediate vicinity of the dumping site. No mitigation is possible to reduce the extent of the affected areas, however Section 6.3.4.1 of Chapter 6, “Intertidal and Subtidal Flora and Fauna and Marine Mammals” describes the significance of this impact, and concludes that as the impacts are temporary in nature with recolonisation occurring within a year, there is no significant impact arising from the deposition of the dumped sediments.
Sediment transport due to wave action is likely to be limited at the site due to the 90m water depth. Any material which is driven into suspension during large swell events will not be transported far from the site due to the weak tidal currents.
IBE00440/EAR/September ‘12 11-58 Sligo Harbour Dredging Environmental Appraisal Report Cultural Heritage
12.0 CULTURAL HERITAGE
12.1 Introduction The Archaeological Diving Company Ltd (ADCO) was appointed by RPS Consulting Engineers on behalf of Sligo County Council to undertake an archaeological and architectural heritage assessment in advance of dredging works proposed within Sligo Harbour and its approach channel.
The dredging will occur along the existing approach channel from the quays in Sligo Port to Oyster Island (Figure 12.1). The dredged material will be disposed of at an approved marine disposal area located some 52 km (28 nautical miles) northwest of Bungar Bank, west of Donegal Bay and southwest of Malin More Head, Co. Donegal and north of Downpatrick Head, Co. Mayo (Figure 12.2).
The study area comprises the works areas, while the architectural heritage assessment is required to include the immediate vicinity of Sligo Harbour and the wider locality where there might be any significant impact. The dredge areas are located within a Natural Heritage Area (NHA), a Special Area of Conservation (SAC) and a Special Protection Area (SPA).
The archaeological and architectural assessment is based on a desktop review of existing archival and published information. The architectural heritage assessment included a site inspection of the Sligo Port area and immediate vicinity and is reported as Appendix 7C of the Report. A marine geophysical survey of the dredge areas and the disposal area was carried out under licence from the Department of the Environment, Heritage and Local Government (DoEHLG)1, licence 11D010, and is reported in Appendix 7D of the Environmental Report. The primary geophysical survey data was reviewed and interpreted by a maritime archaeologist and is absorbed within the present report.
The following Chapter addresses the known and potential archaeological and architectural heritage environment; assesses the actual and proposed impacts on that environment from the works programme; and makes recommendations to resolve any further archaeological requirements prior to the works programme commencing and during dredging operations.
A full description of the dredging works is presented in Chapter 4, “Project Description”
12.2 ASSESSMENT METHODOLOGY
A desk study of cartographic and archival information was conducted as a preliminary stage of archaeological assessment for the project. x Topographical files in the National Museum of Ireland; x Register of Monuments and Places in the Department of Arts, Heritage and the Gaeltacht (DoA,H&G);
1 Heritage functions were transferred from the Department of Environment, Heritage and Local Government (which has since been re-named to the Department of Environment, Community and Local Government) to the Department of Arts, Heritage and the Gaeltacht with effect from 1 May 2011
IBE00440/EAR/September ‘12 12-1 Sligo Harbour Dredging Environmental Appraisal Report Cultural Heritage
x National Inventory of Architectural Heritage; x Ordnance Survey mapping for the area since the First Edition six-inch series in 1838; x Admiralty Charts; x Other historic mapping; x Inventory of Historic Shipwrecks and the Ports and Harbours record at the DoA,H&G x the record of licensed archaeological work; x relevant published sources were reviewed.
The following legislation, standards and guidelines were considered and consulted for the purposes of this evaluation: x Advice Notes on Current Practice (in preparation of Environmental Impact Statements), 2003, EPA; x Architectural Heritage (National Inventory) and Historic Monuments (Miscellaneous Provisions) Act, 2000 and the Local Government (Planning and Development) Act 2000; x Frameworks and Principles for the Protection of the Archaeological Heritage, 1999, (formerly) Department of Arts, Heritage, Gaeltacht and Islands; x Guidelines for the Assessment of Archaeological Heritage Impacts of National Road Schemes, NRA; x Guidelines on the information to be contained in Environmental Impact Statements, 2002, EPA; x Heritage Act, 1995; x National Monuments Acts, 1930-2004; x Planning and Development (Strategic Infrastructure) Bill, 2006; x Strategic Environmental Assessment (SEA) Pack, 2010 EPA; x In the absence of a specific Code of Practice between the Marine Industry and the Minister of the Environment, Heritage and Local Government, the following Codes of Practice that exist between industry and the Minister were consulted: Bord Gáis Éireann (2002); .Coillte (no date); EirGrid (2009); ESB Networks (2009), Irish Concrete Federation (2009), National Roads Authority (no date), Railway Procurement Agency (2007). x The following county and local development plans were considered and consulted for the purposes of this evaluation: x County Sligo Heritage Plan 2007-2011. x County Donegal Development Plan 2006-2012.
On-site marine geophysical survey and architectural fieldwork has been carried out as part of the present report.
12.2.1 Limitations No limitations were encountered during the desk study.
12.2.2 Classification of Impacts/Effects Impact/effect categories will typically have regard to those set out in the ‘Guidelines on the information to be contained in Environmental Impact Statements’, 2002, EPA; ‘Advice notes on Current Practice (in preparation of Environmental Impact Statements), 2003, EPA;
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‘Strategic Environmental Assessment (SEA), 2010’; and ‘Guidelines for the Assessment of Archaeological Heritage Impacts of National Road Schemes’, no date, National Roads Authority. Impacts/effects are generally categorised as either being a direct impact, an indirect impact or as having no predicted impact.
12.3 THE RECEIVING ENVIRONMENT
The specific details of individual observations are set out in Appendix 7A. A general overview of what the sum of these observations implies is presented below, and this is followed with individual presentations of the relevant source material.
12.3.1 Overview
The presence of Maeve’s Cairn southwest of Sligo town bears witness to the importance of Sligo Harbour as a natural inlet and landing place since early prehistoric times. The cairn which sits on top of Knocknarea acts as a sentinel overlooking the harbour and the landscape around and about. It would also have served as a beacon, to draw early settlers safely in from the Atlantic to the haven of the harbour. The development area for the present project occurs beyond the limits of what was subsequently to become the town of Sligo, and there is a small collection of artefacts and small field monuments, such as burials known as barrows, which reveal the extent of the prehistoric footprint on the headlands around the harbour. Shell middens are found in some numbers along the shoreline and these sites serve as the real testimony to active marine exploitation. Although none of the midden sites have been subject to scientific dating, it is clear from their partially buried nature that these most reasonably belong to the preshistoric period. Oysters, winkles and periwinkles were caught and processed on the shore, the users then throwing the shells into large heaps or middens, where they were discarded.
Later settlement sites of enclosures and ringforts are positioned at a slight remove from the shoreline. They reveal the imprint of settlement in the period after saints Palladius and Patrick worked in Ireland in the fifth century to bring Christianity and to usher in a social transformation that was in keeping with change across Europe. Society in the early medieval period remained rural, and would have focused on crop husbandry and livestock, while the proximity to the sea that we see around the harbour would have dictated a continued relationship with fishing and coastal trade.
It is in the later medieval period that Sligo town emerges. A bridge existed in 1188 across the Garvogue river, establishing the importance attached to the settlement’s location on the main road north from Galway to Donegal. The word Sligo, Irish Sligeach meaing ‘shelly place’, tempts one to see the continued connection with shell-fishing. A description of the island at the mouth of the Garavogue or Sligo River in the year 1599 mentions that, ‘at every tide they may gather great store of oysters, cockles and mussels, all of which will be a great help with
IBE00440/EAR/September ‘12 12-3 Sligo Harbour Dredging Environmental Appraisal Report Cultural Heritage her Majesty's stores’.2 Certainly from the seventeenth century, the town relied heavily on fishing and oyster in particular.
Sligo is also linked intrinsically to the O’Conors during the later middle ages, and the settlement’s strategic importance, both as a safe haven from the Atlantic and as a communications hub was endorsed by the construction of a fortification, the arrival of the Domincans in1253, and also town defences. Sligo was pivotal to powers seeking to control Ulster. It presented the first significant harbour on the northwest coast south of Donegal, while routeways through the hills inland gave access across the Curlews to Boyle in north Roscommon, after which there were ample connections south and east to Roscommon town, Athlone and ultimately Dublin. These routes on land and sea were to be of critical importance to the Tudor administration in their attempts to ‘plant’ Connacht and subdue Ulster in the late 1500s, and conversely Sligo was a prize to be kept by the Irish. The presence of Ballincar castle on the north shore of the harbour reveals something of the later medieval ownership. The star-shaped fort on Coney Island at the mouth of the harbour is a more telling statement of the manner in which the town and its settlement were protected in the seventeenth century.
With relative peace and prosperity in the period after Cromwell, Sligo was able to realize its trading potential in terms of Atlantic traffic and also fishing, particularly with oysters and mussels. Navigation into the harbour required the construction of various markers and buoys. The early nineteenth-century construction on Perch Rock, the Metal Man (1822), is an example of Victorian prosperity and confidence, with this popular figure pointing out the direction of safe passage across the straits into the harbour. The presence of private weirs and mills were increasingly seen as problematic to the growth of the town’s trade. A series of reports focus on such issues and ultimately reveal the frustration that the compact medieval town experienced as it tried to grow beyond its boundaries. The town remained focused and congested to the south of the current works area. By 1884, however, deep water berths had been constructed, while a railway established in 1898 connected Sligo to Ireland more generally. Further work in the 1930s looked at the old timber jetties in the deep water quay area, and replaced them with a 245-feet long concrete wharf. Additional growth occurred in 1936. As will be seen below, the geophysical survey conducted for the present project reveals crisp images of the navigation aid perches that line the approach channel. Built on mounds of stone, the perches are particularly apparent across the north side of the Middle Bank sand mass, where they and the training wall that was built after the perches, serve to constrain the bank from reforming. The dredging project that is currently proposed is the most recent in Sligo’s long history of port development, balancing the natural dynamic of a tidal haven with the need to maintain access from the sea.
2 Quoted from A. J. Went, ‘Historical notes on the oyster fisheries of Ireland’, Proceedings of the Royal Irish Academy 62 (1961-63): 195-223, p. 213.
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12.3.2 Placenames
Archaeological information is generally identified and located with reference to townland names, and consequently the townland is the principal basis for registration in both the archives of the National Museum of Ireland and in the Department of Arts, Heritage and the Gaeltacht. It is the case that sometimes more local names are cited as well, particularly with reference to maritime information, which can derive from location at sea, removed from actual townlands on the shore. The townlands and placenames/topographic features considered for the present study are indicated in Table 12.1.
Table 12.1 Townlands and placenames identified within the Sligo study area. Maps Townland Other placename Ordnance Survey Ballincar Cartron Marsh 6-inch series, Sligo Cartron Cummeen Strand Sheet 14 Cartron (Honoria Duff) Doonanpatrick Cummeen Dorrines Strand Finiskilin Garavogue River Inishmulclohy or Coneyisland Inner Harbour Knappagh More Middle Bank Rathedmond Oyster bed Rathquarter Seal Bank Rinn Srunamoyle Shannon Eighter Standalone Point Sligo Tully OS 6-inch series, Ballyweelin Bomore Race Course Sligo Sheet 8 Rosses Lower Deadman’s Point Rosses Upper Drumcliff Bay Rosses Point The Metal man OS 6-inch series, Ardtermon Ardtermon Strand Sligo Sheet 7 Cloghcor Bird’s Rock Raghly Black rock Sea Charts Ardboline Altconeen Ballysadare Bay Black Rock Blind Rock Bomore Strand/Point Bungar Bank Cartron Marsh Cluckhorn Drumcliff Bar Drumcliff Spit Pool Doy Raghly Ledge
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Maps Townland Other placename Sligo Bay Sligo Harbour 12.3.3 Topographic files, National Museum of Ireland
The National Museum of Ireland’s Topographical Files is the national archive of all known objects reported to the National Museum. These files relate primarily to artefacts but also include references to monuments and contain a unique archive of records of previous archaeological excavations. The Museum's files present an accurate catalogue of objects reported to that institution from 1928. There is a computerised database of finds from the 1980s onwards. The find-spots of artefacts can be an important indication of the archaeological potential of the related or surrounding area.
There are seven series of entries noted in the records of the National Museum of Ireland and these are listed in Appendix 7A. An old find provenanced as being ‘from Sligo’ represents an exotic figurine whose origins are not clear but may ultimately suggest an Iron Age piece from Iberia. A small amount of artefacts have been deposited in the Museum from the study area more recently, including two copper axes from Sligo (1959:65, 92), a chert flake (1934:4267) and three stones flakes (1936:1577-79) from Rosses Lower. These do not amount to observations of great significance but they do attest to evidence for prehistoric activity in the wider area. Small collections of material from Raghly suggest the presence of more substantial archaeological material, ranging from prehistoric times into the early medieval period (1905:5-9, 1934:4182-4225). There are no apparent records in the Museum for artefacts or features observed from within the proposed dredging or disposal areas.
12.3.4 Record of Monuments and Places3
The Record of Monuments & Places (RMP) is a list of archaeological sites known to the National Monuments Service with accompanying RMP Maps, based on OS 6-inch Sheets, which indicate the location of each recorded site. The RMP list is based on the Sites and Monuments Record (SMR) files housed in the National Monuments Services offices. The SMR comprises lists with accompanying maps and files of all known or possible archaeological sites and monuments, predominately pre-1700 AD in date, for all counties. These lists were, in many cases, initially based on cartographic, documentary and aerial photographic sources. The SMR (as revised in the light of available fieldwork) forms the basis of the statutory RMP. The record is updated on a constant basis and focuses on monuments that predate 1700 AD. Buildings belonging to the seventeenth-century and later are not well represented in the archive, although they are considered as archaeological sites today.
A large number of archaeological sites exist in the landscape around Sligo, ranging in date from early prehistory to more recent times (Figure 12.3). For the purposes of the present
3 The RMP is maintained by the National Monument Section, Department of Arts, Heritage and the Gaeltacht.
IBE00440/EAR/September ‘12 12-6 Sligo Harbour Dredging Environmental Appraisal Report Cultural Heritage study, those monuments that lie within c. 500m of the proposed dredging operations were considered as they are most likely to reflect the immediate maritime/foreshore context. In addition, sites on Oyster Island and Coney Island were included for the same reason, although they are at a further remove from the development areas. The selection presents a total of twenty-one known monuments, as listed and described in Appendix 7A. None of the sites occur within the areas proposed for dredging operations.
Sligo is known for its attention to the fishing industry during the nineteenth and early twentieth centuries, where particular emphasis was given to oyster fishing. The tradition continues into the present day with aquaculture. It is therefore of little surprise that there are five known shell midden sites observed on the foreshore around the harbour area (SL008- 099 and -101, and SL014-13, -56, -63). They are found widely distributed on Coney Island, Oyster Island, Ballincar, Finisklin and Cartron respectively, as shallow exposures of concentrated heaps of shells that have become buried over time by the natural accumulation of soils and sands. These sites do not refer to the recent exploitation of shell fish but rather to a much older exploitation that may extend back into prehistory, and reveal the presence of fishing-related activities along the foreshore, where presumably the early fishermen processed their harvest of shells from netting activity and possibly from work on boats and small craft. An intertidal survey of the harbour area conducted in 2010 identified a further midden site southwest of the present study area, on Doonan Patrick Island. The work also identified a probable fishtrap on the marshy ground in Cartron townland.4
Of the remaining known archaeological sites, the most numerous is a set of three enclosures and four ringforts, which are located overlooking the northern shoreline of the study area. Enclosures refer to circular earthworks whose remains are quite denuded but may originally have been more clearly defined as ringforts. These sites served as the household residences for the freemen of society in the early medieval period, and the more elaborate types, which are encircled by more than one bank and ditch, are believed to have been associated with those of higher status. They are a common site type across Ireland and reveal the presence of a well settled and populated rural landscape in the period c. 500-1000 AD, which exploited the marine environment just as it cultivated the soil and raised livestock. There are no early church sites within the immediate study area, but the well known island site of Inishmurray lies some kilometres to the north.
The only vestiges within the study area of the bustling activity associated with the late sixteenth century is a small star-shaped earthen fort on Coney Island (SL014-002), and a slightly later fortified house and associated wider settlement at Ballincar (SL014-005). The location of both sites close to the navigation channel reflect the obvious interest in using the resources that come in from the sea and in controlling them. The location of the star-shaped fort on Coney Island is positioned on its NE extremity, looking into the harbour rather than defending its external approaches. A slipway has been identified that may have been
4 Auriel Robinson, ‘Discovering the maritime archaeological heritage of Sligo Harbour and environs’, unpublished report submitted to the Heritage Council in 2010, grant reference R00697, pp 245, 38. Further reference is made in Appendix 1 of the present report.
IBE00440/EAR/September ‘12 12-7 Sligo Harbour Dredging Environmental Appraisal Report Cultural Heritage associated with the fort.5 This would have permitted the occupants to have quick access to the deep water of Srunamoyle. Without doubt the fort would have served as part of the larger defences of the town in the seventeenth century, where most attention was given to the Green Fort, positioned to the north of the town on high ground overlooking the bridge.6
12.3.5 Intertidal Survey
An intertidal archaeological study of Sligo Harbour and its environs was completed in 2010, and the results of that useful work have been made available and absorbed in the present study (Table A7.3 in Appendix 7A).7 As noted above, Robinson has added a series of observations that provide additional sites, including a prehistoric midden on Doonan Patrick Island, a probable fish-trap in Cartron, and the early slipway on Coney Island. The study has also presented a large number of mainly nineteenth-century and early twentieth-century features that comprise of a series of formal bathing places, small jetties, and a number of abandoned boats and trawlers (Figure 12.4). None of the sites or features occur within the areas proposed for dredging operations.
12.3.6 National Inventory of Architectural Heritage
The National Inventory of Architectural Heritage (NIAH) is a county by county database that identifies, records and evaluates the post-1700 architectural heritage of Ireland, uniformly and consistently as an aid to the protection and conservation of the nation’s built heritage. The NIAH surveys provide the basis for the recommendations of the Minister for the Environment, Heritage and Local Government to the planning authorities for the inclusion of particular structures in their Record of Protected Structures (RPS).
The series of structures recorded for the present project are listed in Table A7.4 in Appendix 7 and are also summarised in Figure 12.4. It amounts to a small number of largely nineteenth- and early twentieth-century structures, most of which are domestic residences, but one is a warehouse site on the Sligo quays (Batchelors/Davitt’s warehouse), and all are at a remove from the development areas. The baseline information serves to further inform the more recent history and development of Sligo town and the extension of settlement along the coast, but none of this material will be impacted in any way by the proposed dredging works.
5 Robinson, ‘Discovering the maritime archaeological heritage of Sligo Harbour’, p. 31. 6 The Coney Island fort does not appear to have received scholarly attention, but the Green Fort is mentioned in Paul Kerrigan, Castles and fortifications in Ireland 1485-1945 (Collins Press, Cork 1975), pp 98, 102, 122-3. 7 Robinson, ‘Discovering the maritime archaeological heritage of Sligo Harbour’.
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12.3.7 Cartographic Sources
12.3.7.1 Sligo Sea charts and Admiralty charts showing Sligo Harbour and the wider area of the Bay reveal useful information concerning the depths and presence of navigation hazards, as well as naming places and locations of topographic interest, but they show little that is of archaeological interest. A series of charts was examined, including Chart 2767 Sligo and Killalla Bays, 1852-4, reprinted 1957, and Chart 2852 Approaches to Sligo and Sligo Harbour, 1998. One chart of Sligo and Ballysadare Harbours dated 1852 and corrected in 1859 does show the location of the wreck Lord Drogheda’s yacht, which was lost in 1859 while navigating into Sligo. The yacht ran aground on shallows to the west of Coney Island. The shallows had been marked by a buoy but that had fallen into disrepair and had not been in place for two years, to the detriment of the luckless yacht (Figure 12.5).
The Ordnance Survey First edition 6-inch series made in 1838 in turn reveals little information about the active water bodies within the harbour but does record a series of elements along the foreshore that reveal the landscape prior to the development of the quay walls in the 1840s (Figure 12.6). A series of marker buoys and posts define the natural course of the Garavogue river as it makes its way seawards, meandering through the mud flats of the inner harbour. This is in contrast to the defined linear navigation channel which is maintained today and is the subject of the present study, running northwest before enhancing the relatively straight channel alongside Ballincar and Ballyweelin townlands. The new dredging works will maintain the approach channel that has been in use for some considerable time, stopping short of Oyster Island to its East. The 1838 maps record the foreshore in considerable detail. Apart from the navigation aids there is an absence of obvious features such as fish traps and quays/jetties that attest to the active use of this area. Yet, as Robinson’s intertidal survey suggests below, there are features of archaeological interest that predate the 1800s and were not noted on the early maps. These include a fish- trap and/or fording point across tidal mudflats in Shannon Eighter townland, some 350m from the navigation channel, and a series of shell middens that complement the existing evidence of middens recorded in the SMR, attesting to the widespread use of the Bay over time to exploit oysters as well as periwinkle and other such shellfish.
12.3.7.2 Marine disposal area Sea charts examined for the marine disposal area included Chart 3471, Irlande Côte Nord- Ouest 1956, and US Chart 4722, Downpatrick Head to Horn Head, 3rd edition 1948. In no instance were any features observed that indicate the presence of shipwreck material within the disposal area.
12.3.8 Shipwreck Inventory
The Shipwreck Inventory in the Department of Arts, Heritage and the Gaeltacht’s archive is a list of recorded instances of wrecking since 1750. The details provided describe the type of vessel, the journey it foundered on, and information on the ultimate plight of the vessel and its crew, where possible. In describing the wrecking event, the records will locate the incident
IBE00440/EAR/September ‘12 12-9 Sligo Harbour Dredging Environmental Appraisal Report Cultural Heritage in relation to the nearest headland or other topographic marker where known. This is not however a record of where the wreckage lies, since the historic records generally only deal with the vessel before it sank. Such finer details emerge from other sources, such as fishermens’ records of snag points and diver records of sites located underwater. These are included in the Inventory wherever possible but it is true to say that most entries lack this final level of data. Finally, it should be pointed out that while the Inventory provides a record of wrecking incidents since 1750, it does not claim to be a comprehensive record for earlier events, and therefore the medieval and prehistoric periods are not represented in the archive.
12.3.8.1 Sligo Thirty-five shipwreck incidents are listed in Table A7.6 of Appendix 7A for the Sligo Harbour and Bay area. A further twenty-four events are noted in the Historic Shipwreck Inventory but the information pertaining to their location is quite vague, registered broadly to ‘Sligo’, and nine more wrecking events are registered to Sligo Bay. Overall, the number of wrecking events is not significantly large when compared with other coastal stretches around Ireland, even allowing for the relatively short amount of coastline in the county.8 The known shipwreck location of the 1588 Spanish Armada vessels to the north of the study area on Streedagh Strand are without doubt the most discussed of the county’s wrecks. Leaving these aside, the wrecking events considered for the Sligo Harbour area retain a similar chronological spread to those recorded elsewhere. Nine relate to the eighteenth century. The earliest recorded wrecking took place in 1757, when the Sarah was sailing to the Virgin Islands from Liverpool and was driven ashore in Sligo Bay during foul weather and was damaged considerably. The ship Brothers had almost made port, sailing from New York in 1788 when she struck on Sligo Bar and was lost. Wreckage because of underwater obstructions led inevitably to the formalization of safe navigation channels, and the figurative navigation beacon on Perch Rock, known as the Metal Man and cast in 1819, has his hand pointing to the safe passage for shipping as they enter and leave the harbour. The largest number of wrecking events belongs however to the nineteenth century, where a total of forty- two events are recorded. To encounter foul weather and storms at sea continued to prove very hazardous, but the large numbers also attest to the growth in maritime traffic associated with the burgeoning economies of the industrial age. This in turn presented the opportunities to invest in shore-based infrastructures, and it is in the 1830s and ‘40s that we see the development of the quayside at Sligo and their extension seawards, and also the improvement to the pier at Raghly.
There are two known instances of wrecking on the Bungar Bank, and both date to 1859. An Austrian brig, the Naslieduk was carrying a cargo of maize when she wrecked, while Lord Drogheda’s yacht, the Fancy, ran aground on shallows just off Coney Island where a navigation buoy had fallen into disrepair. The site of the Fancy is plotted on an 1859 chart but it is not plotted on current charts. The specific location of the Naslieduk is not known. In this, the Austrian brig shares much in common with the majority of the recorded
8 The East coast area has considerable numbers of wrecks clustered around the principal coastal towns; see Karl Brady, Shipwreck inventory of Ireland. Louth, Meath, Dublin and Wicklow (Dublin, Stationary Office, no date).
IBE00440/EAR/September ‘12 12-10 Sligo Harbour Dredging Environmental Appraisal Report Cultural Heritage shipwrecking, but eight (including the Fancy) have been accurately positioned (Figure 12.4). They include the ruined remnants of the two lighters Gartnasheerie and Molbec, which were in service in the early twentieth century but are now pulled ashore onto the mudflats. The majority of such known shipwreck site locations refer to twentieth-century wrecks, and none of shipwrecks are observed within the works area.
12.3.8.2 Marine disposal area There are no known shipwreck sites located within the marine disposal area, but three wrecksites are recorded some distance away, the nearest being the wreck of the Ashcrest located some 575m SW of the disposal area (Figure 12.7). The Ashcrest was torpedoed in 1940, as was the Hans Broge in 1917 (Figure 12.8), wrecking some 12km away from the disposal area. The third vessel is that of a modern trawler, the Lady Christine, which was lost in 2003 and lies c. 3.8km from the disposal area.
12.3.9 Licensed archaeological work
The Excavations Bulletin publishes annual summary accounts of licensed archaeological excavations undertaken throughout Ireland, which is currently published up to and including 2007.9 Summaries may also be submitted for inter-tidal survey, underwater assessments, and the archaeological monitoring of marine dredging works (although the former two categories are not required to be submitted for publication in the Bulletin). The entries relating to the townlands surrounding Sligo Harbour are presented in Table A7.7 of Appendix 7A and Figure 12.4. There have been thirty-two events recorded. Fourteen of these projects revealed nothing of archaeological significance. Of the remaining licenses, three were granted for work within or on the site of known archaeological monuments. Many of the rest revealed small-scale features such a burned spreads or ditch features, and do not contribute additional relevant information to the current study. A small series of work has taken place in Sligo town along the river bank and quaysides area, revealing a range of pre-existing riverside features. Only three projects are reported in relation to marine activity, excluding work on the Garvogue river itself. One was for a monitoring project associated with the redevelopment of Raghly pier (Licence 07E0969). Another was for monitoring work associated with the laying of a cable on Coney Island (no license number reported). The third relates to the installation of a new timber jetty within Sligo Port, which required dredging to a depth of 2.5m. A former timber pile was observed (08D079).
12.3.10 Conclusion
Maritime activity within Sligo Harbour is documented from early prehistoric times. The study of the wider area indicates a range of sites and features that highlight an active awareness of the importance of navigation into and out of the town, as a principal port on Ireland’s northwest coast. The presence of prehistoric midden sites reveals foreshore activity.
9 Isabel Bennett (ed.) Excavations Bulletin: summary accounts of archaeological excavations in Ireland, (Bray, Wordwell).
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Reference to known shipwrecking events highlights the Bungar Bank as a location where wreckage debris can be expected to be observed, while the attention paid to establishing safe access through the shallows of the inner harbour suggests an awareness of hazardous access into Sligo. So too does the presence of twentieth-century wrecks on the mudflats. While no archaeological material has occurred within the locations of proposed dredging, there is an inherent potential for new archaeology to be revealed during capital dredging projects along the approach channel to the port and on Bungar Bank. The potential was confirmed within Sligo Port with the observation of a timber pile associated with the work to insert a timber jetty in 2008. In such instances, there is a need for archaeological resolution strategies, to mitigate the possibility for new discoveries.
The presence of three known wreck sites in proximity to the marine disposal area highlights the need to assess the disposal area more fully for the presence of previously unrecorded wreckage.
12.4 ARCHITECTURAL SITE ASSESSMENT
A desktop review of existing maps and historic photographs was supported by a series of site visits in May 2011 (Appendix 7C) in the area around the harbour and around the shore at Rosses Point near both Coney Island and Oyster Island, to see if any structures there could be affected by the proposed dredging works.10 There are no protected structures in the area of proposed development, and no structures of architectural heritage merit were observed in the vicinity of the site where excavation work and dredging would take place. It can only be concluded that work should be allowed to continue without any further investigation in relation to architectural heritage or conservation proposals.
12.5 MARINE GEOPHYSICAL SURVEY
A marine geophysical survey was commissioned to contribute a further level of insight prior to the commencement of the dredging and marine disposal operations. Such surveys operate on the basis of emitting sonic pulses through the water column to detect material and features on and under the seabed. It is usual to deploy a series of devices because each one is designed to detect particular materials. The present project used two standard devices for archaeological work: side-scan sonar and magnetometer, and was in compliance with the requirements set by the DoEHLG for marine geophysical survey for archaeological purposes. The survey was conducted along the approach channel, on Bungar Bank, and at the marine disposal area. The work was conducted by Irish Hydrodata Ltd in April 2011, under licence 11R010. The primary data and associated mapping were examined by ADCO and the results are presented below. Irish Hydrodata’s own report is included as Appendix 7D of this Report.
Side-scan sonar captures data to construct an image of the seabed surface over the area it operates. It is an excellent device for mapping the seabed and for detecting hard anomalies, such as those of stone and metal, and also of hard wood. It cannot detect material that is
10 A comprehensive statement of the architectural heritage assessment is presented as Appendix 7c of the Report.
IBE00440/EAR/September ‘12 12-12 Sligo Harbour Dredging Environmental Appraisal Report Cultural Heritage buried, and it is difficult to observe soft woods because the sonic pulse passes through such material without registering a difference with the ambient water. Magnetometers are used to detect ferrous metal. In this they can complement the sonar by clarifying whether a sonar contact contains significant metal – and is therefore manmade. Magnetometers also detect anomalies below the seabed surface, and therefore can detect buried material. However, unlike the sonar devices, magnetometers gather their information by emitting pulses directly underneath; they cannot sweep the seabed from one side to the other as sonar does, and consequently are limited to a vertical and near-vertical range of detection. The magnetometer needs to pass more or less directly overhead of an anomaly to detect it.
12.5.1 Nature of record The record is comprehensive. Side-scan sonar and magnetometer survey was conducted over the survey areas. The following equipment was used: x L³-Klein System 3000 simultaneous dual frequency digital side-scan sonar system. x Geometrics G882 marine magnetometer (caesium)
12.5.2 Harbour
12.5.2.1 Survey Grid The narrowness of the survey area resulted in two survey lines of data being acquired, extending from the quays in Sligo Port to a point off the north side of Oyster Island (Figure 12.9). The lines were acquired in opposite directions to each other. Towards the western extent of the survey area where the channel broadens sufficiently, the lines were spaced 90m apart, but were generally much closer to each other because of the confined nature of the approach channel, and in places overlapped. Each line was set at a range of 75m. The survey has provided ample overlap and the ability to view the same areas of seabed from opposed directions.
12.5.2.2 Side-scan Sonar Survey The data is generally very well defined. The bed area varies in consistency along the surveyed route (Figure 12.10). There is a confused pattern of folded siltation at the quays area, which gives way to a compacted hard bottom to the north as the approach channel passes by Cartron and Ballincar townlands. The bed then retains greater amounts of siltation as one proceeds through the harbour westwards, with patches of regular sand ripples evident south of Rosses Upper.
The primary observations relate to the series of navigation aids, perches and markers that define either side of the approach channel (a detailed list of side-scan sonar [ss] anomalies is presented in Appendix 7D; see also Figure 12.13 - Figure 12.16). Those on the West and South side of the channel survive as well-constructed circular mounds of foundation stones, often measuring 10-12m in diameter and rising c. 3m in height (Figure 12.11). Lengths of cable or chain are sometime apparent down one side. A training wall has been constructed to link the perches on the south side of the approach channel as it crosses Middle Bank. The sonar data clearly shows that building of the perches predates the training wall, and that the wall is fractured in places. Anomaly ss5 represents the perch that defines the terminus of the
IBE00440/EAR/September ‘12 12-13 Sligo Harbour Dredging Environmental Appraisal Report Cultural Heritage training wall. A noticeable scour pocket has developed on the western or seaward side of the perch, indicative of the exposed nature of the harbour area in this location. The navigation aids on the North and East side of the channel are not as well defined but are nevertheless clearly visible.
There are few indications of anomalies that cannot be explained in terms of the channel markers. A series of anomalies were observed in this regard (Appendix 7D). All but one occur as small-scale linear or irregularly-shaped features that are observed on the bed of the approach channel, and may result from casual discard and are probably best described as debris. In one instance however (ss25) the anomaly may be indicative of a more significant feature. It survives as a c. 16m long negative anomaly that is long and narrow, almost boat- shaped in form with a defined bow section and a stern section (Figure 12.12). It is 3.1m wide at its centre. The anomaly is located at a point where the Cartron marsh enters the river. A spread of stonework is evident on one side, while the anomaly itself is situated in silt. This suggests the possible presence of a small quay area that is now inundated. The stonework may also retain the base of a former navigation marker. It is some 70m from the recorded location of the Gartsheerie that is pulled ashore. The magnetometer survey detected elevated readings adjacent to the sonar anomaly, indicating the presence of a substantive metal feature. The location is positioned adjacent to the proposed dredging area, and should be assessed further for its archaeological potential.
Table 12.2 Side-scan sonar anomalies identified within the harbour area*
Reference Description Archaeological Potential ss25 Boat-shaped negative anomaly Unclear, possibly high measuring 16m long by 3.1m wide in the middle, this feature has what appears to be a defined bow and stern, and rests in an area of silt directly against a stone area that appears to be set, measuring 8m by 7m in size. Corresponds to mg9. However the data presents it as a negative image with no internal features that one can expect of actual wreck sites. It remains unclear what this image is. *Anomalies listed cannot be explained as modern features associated with the Port or as most likely casual debris (for further information see detailed description, Appendix 7D).
12.5.2.3 Magnetometer Survey The magnetometer survey was conducted in tandem with the side-scan sonar survey. Overall, the survey has highlighted little evidence of natural background variation so that any fluctuations observed most probably derive from human activity (a detailed list of magnetometer [mg] anomalies is presented in Appendix 7D; see also Figure 12.13 - Figure 12.16). As can be expected, the survey conducted within the active port area produced
IBE00440/EAR/September ‘12 12-14 Sligo Harbour Dredging Environmental Appraisal Report Cultural Heritage excessively high levels of magnetic readings, reflecting the presence of working boats and other devices. Elsewhere, the survey revealed a complementary sequence of localised anomalies that correspond to the locations of the navigations aids. In a small number of instances there was also a localised variation where no buoys or other navigation aids can be identified. In those instances, the magnetic anomaly must derive from another metallic source. Some of these locations correspond with sonar anomalies, indicating that the anomaly lies exposed on the channel bed. In those instances where the magnetic anomaly does not correspond with sonar data, it suggests that the magnetic feature is either very small in scale and/or is buried. The results are presented in Table 12.3.
Table 12.3 Magnetometer anomalies identified within the harbour area*
Reference Description Archaeological Potential mg9 Extended intense fluctuation in magnetic Unknown, possibly high field over 28m-long area (recorded reference point refers to the centre of the highest readings). This anomaly is within 20m of the centrepoint of ss25 and logically refers to the same feature. * Anomalies listed cannot be explained as modern features associated with the Port (for further information see detailed description, Appendix 7D).
12.5.3 Marine Disposal Area
12.5.3.1 Survey Grid A 1km² grid was surveyed by running lines E-W in opposite directions, achieving a standard zig-zag pattern of data acquisition. Lines spacing was set at 45m with range at 75m, ensuring ample overlap. Because of the depth of the seabed in this location (approx. 90m), particular set-up was required to ensure that the sonar towfish would be sufficiently weighted. As indicated on Figure 12.17, the survey lines had to take account of sea-swell, but the close spacing of the tracklines ensured that the full survey area was covered adequately.
12.5.3.2 Side-scan Sonar Survey The underwater sea state intruded into the survey data, but the level of overlap in the survey tracklines accounted for the intrusion. The seabed has a sandy/silty surface, with some sand ripples noticeable (Figure 12.18).
Only a small number of anomalies were identified (a detailed list of side-scan sonar [ss] anomalies is presented in Appendix 7D; see also Figure 12.19). The majority are probably natural features and are considered as such. Two anomalies may represent manmade remains. Anomaly ss307 is a well-defined isolated short linear object occurring in a sandy area; it appears to be a piece of debris. Anomaly ss300 is poorly defined at the very north end of the survey area, c. 100m north of and outside the defined disposal area. It is possible to discern a boat-shaped profile, measuring 24.9m long x 5.9m wide. The anomaly is not clearly visible, and it was not detected on the other survey lines, but it represents the only
IBE00440/EAR/September ‘12 12-15 Sligo Harbour Dredging Environmental Appraisal Report Cultural Heritage anomaly detected in the marine disposal area data that suggests the possible presence of in situ wreckage debris. The magnetometer data does not indicate an anomaly, but it passed to the south and may not have been able to detect the feature at that distance. Anomaly ss300 lies outside the defined limits of the disposal area and will therefore not be impacted on.
Table 12.4 Side-scan sonar anomalies identified on marine disposal area survey*
Reference Description Archaeological Potential ss300 A boat-shaped anomaly measuring Unclear, possibly high 24.9m long x 5.9m wide, located c. 100m north of disposal area. The data trace shows a principal area of anomaly on one side, with a less-clearly defined tapering shape on the other.
*Anomalies listed cannot be explained as modern features or as most likely casual debris (for further information see detailed description, Appendix 7D).
12.5.3.3 Magnetometer Survey The magnetometer survey was conducted in tandem with the side-scan sonar survey. It indicates a natural variation within the seabed deposits but few localized fluctuations suggestive of manmade remains. Three anomalies in total were observed, each representing very small-scale and localized fluctuations.
12.5.4 Conclusion The area surveyed included the development areas and the channel to the north of the jetties. Side-scan sonar and magnetometer surveys were conducted within the specifications for marine geophysical surveys as defined by the DoA,H&G. The survey revealed the navigation aids that line the approach channel to the Port. A single possible feature of archaeological interest was observed within the harbour area, close to Cartron marsh, which may represent the presence of a submerged iron wreck (anomaly ss25/mg9). However the details are not entirely clear. A series of other anomalies were highlighted throughout the areas surveyed. Correspondences of sonar contacts with magnetometer contacts indicates metallic remains on the surface, while magnetometer targets in isolation indicate that there is material buried beneath the covering sands. A single target identified adjacent to and outside the marine disposal area may indicate the presence of a previously unrecorded feature (ss300), but the nature is the data is not entirely clear. As it lies c. 100m outside the disposal area, it will not be impacted upon.
The assessment and surveys conducted for the present report are very comprehensive, and have not identified material of archaeological significance within any of the project impact areas. There is no archaeological reason why the dredging works proposed should not proceed.
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12.6 PREDICTED IMPACTS11 To achieve the required dredging design, the alignment of the proposed dredge channel will follow very closely the alignment of the existing channel. The proposed channel depth will be to -3.0m CD. The proposed channel bottom width with be 50m with channel side slopes of 1 in 7. Of the 250,000m³ of material that it is proposed to dredge, 55% lies in the easterly 1500m of the channel nearest the town quays, while the bulk of the remaining 45% lies in the westerly length of channel, which is approximately 2,200m long, from No 14 buoy to Ballyweelin Point. The specific type of dredger to be used will not be known until a contractor is appointed, but it is envisaged that either a suction dredger or a backhoe dredger will be employed for the work. It is anticipated that dredging will proceed in an upstream direction, and that dredging will be limited to the upper half of the tidal cycle.
The dredged material will be transported to the disposal area, where it is proposed to release between 500m³ and 1,050m³ per dredging cycle. Modelling of the dispersion of the sediment at the disposal area indicates that most of the deposited material will remain close to the disposal site, with a small amount material migrating towards the east under the influence of tidal action. The impact of the dumped sediments settling on the sea bed around the dump site is not considered to be significant.
The dredging represents a direct impact on the seabed, and archaeological monitoring of the dredging operation is recommended, to ensure the recovery of archaeological material that may be recovered during the excavation works.
12.7 RECOMMENDATIONS
12.7.1 Pre-construction Measures The need for further architectural heritage assessment for the dredging project is not necessary as there will be no impact on features of architectural interest.
12.7.2 Construction Phase Measures Dredging works will be take place as the primary activity of the present development. Archaeological monitoring, licensed to the DoA,H&G is recommended during all works where foreshore or seabed deposits will undergo removal. A suitably qualified competent maritime archaeologist with experience in riverine/marine dredging environments should undertake the archaeological monitoring. The archaeological monitoring should be undertaken with the proviso for full excavation of any archaeologically significant material uncovered as part of the operation. Licence processing takes a minimum of three working weeks to be processed by the Department, and archaeologists cannot present on site before the licence is granted.
12.7.3 Archaeological/Cultural Heritage Management x Retaining an Archaeologist: a competent maritime archaeologist should be retained for the duration of the relevant works. The time scale for the construction phase should be
11 Based on information from Chapter 4, “Project Description “and Chapter 11 “Coastal Processes” of the Report.
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made available to the archaeologist, with information on where and when ground disturbances and dredging will take place. x Sufficient notice: It is essential for the developer to give sufficient notice to the archaeologist/s in advance of the construction works commencing. This will allow for prompt arrival on site to monitor the ground disturbances. As often happens, intervals may occur during the construction phase. In this case, it is also necessary to inform the archaeologist/s as to when ground disturbance works will recommence. x Discovery of Archaeological Material: In the event of archaeological features or material being uncovered during the construction phase, it is crucial that any machine work cease in the immediate area to allow the archaeologist/s to inspect any such material. x Archaeological Material: If the presence of archaeologically significant material is established, full archaeological recording of such material is recommended. If it is not possible for the construction works to avoid the material, full excavation would be recommended. The extent and duration of excavation would be a matter for discussion between the client and the licensing authorities. x Archaeological Team: It is recommended that the core of a suitable archaeological team be on standby to deal with any such rescue excavation. This would be complemented in the event of a full excavation. x Archaeological Dive Team: It is recommended that an archaeological dive team be on standby to deal with any underwater rescue excavation. This team will carry the necessary commercial dive insurance, be fully certified to HSE/ HSA requirements, and will conduct its work according to Safety in Industry (Diving Operations) Regulations 1981, SI 422, and 2010 SI (Draft), HSA Diving Standards 2010. x Secure wet storage facilities should be provided for the storage of archaeological material derived from the marine environment within the project works compound. x Secure site offices and facilities should be provided on or near those sites where excavation is required. x Fencing/buoying of any such areas would be necessary once discovered and during excavation. x Adequate funds to cover excavation, post-excavation analysis, and any testing or conservation work required should be made available. x Spoil should not be dumped on any of the selected sites or their environs.
Recommendations are subject to the approval of The Department of Arts, Heritage and the Gaeltacht.
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12.8 FIGURES
Extract from Admiralty Chart 2852 © Crown Copyright UKHO. Not for navigational use
Figure 12.1: Admiralty Chart showing Harbour area and proposed dredging works
Figure 12.2: Admiralty Chart showing proposed marine disposal site.
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Figure 12.3: Distribution of RMP sites in Harbour area. © Ordnance Survey Ireland. All rights reserved. Licence number 2010/20 CCMA/ Sligo County Council
Figure 12.4: Distribution of NIAH sites in Harbour area.
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Figure 12.5: Extract from 1859 sea chart showing the location of the Fancy. Source: DoEHLG. Note: the wrecksite location is marked by a simple cross NW of Altconeen.
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Figure 12.6: Extracts from OS First Edition 1838 Sheet 14 and Third Edition - the contrasting topographies of the inner harbour at Finisklin
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Figure 12.7: Map of known wrecksites in the vicinity of the marine disposal site.
Figure 12.8: The Hans Broge, before she wrecked, c. 1907. Source: www.wrecksite.eu
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Figure 12.9: Marine geophysical survey tracklines within the Harbour area.
Outer harbour, S of Rosses Approach channel, S Approach channel at of Ballincar deepwater berths, indicating a timber pile jetty Figure 12.10: Seabed images from the sonar data, Harbour area.
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Figure 12.11: Sonar trace showing the terminal perch, ss5. Note the scour pocket that is developing at the seaward end of the perch. It is also possible to observe that the training wall is constructed on top of the pre-existing perch foundation.
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Figure 12.12: Sonar trace showing anomaly ss25 within its local context. North is to the bottom of the image. The anomaly occurs as a tapering linear black feature that lies against a stony shoreline. The stones appear to be constructed intentionally to create a right-angled plan, and there is the suggestion of some mounding of stone to the left. This complex of features may represent a former landing area on the east bank of the river, close to Cartron marsh.
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Figure 12.13: Distribution of marine geophysical anomalies observed within the Harbour area.
Figure 12.14: Distribution of marine geophysical anomalies observed within the Harbour area, East side.
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Figure 12.15: Distribution of marine geophysical anomalies observed within the Harbour area, central zone.
Figure 12.16: Distribution of marine geophysical anomalies observed within the Harbour area, West side.
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Figure 12.17: Marine geophysical survey tracklines at the marine disposal site.
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Figure 12.18: Sonar trace showing nature of seabed imaged at the marine disposal site. The sandy seabed with minor fluctuations is shown on the left side of the image. The dark mottled space in the right side of the image refers to the water column through which the sonar device is being towed, and the linear yellow line on the far right side is the sonar trackline.
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Figure 12.19: Distribution of marine geophysical anomalies observed at the marine disposal site.
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13.0 HUMAN BEINGS
13.1 INTRODUCTION
Several aspects of the well-being of the local community and the wider community within the vicinity of Sligo Harbour have already been addressed within this Environmental Appraisal Report:
x Impact on commercial fishing activities – Chapter 7 x Impact on air quality and noise – Chapter 8 x Impact on material assets including traffic – Chapter 9
The potential impacts of the proposed dredging of the navigation channel are described in detail within these chapters and, where appropriate, mitigation measures are presented.
This chapter of the Environmental Report details the human ‘environment’ of the hinterland of the subject site in terms of population profile and trends, employment and community aspects. It then discusses the impact of the proposed dredging on the overall amenity of the area and puts forward a series of mitigation measures to offset any potential negative impacts. This chapter of the Report describes how the proposed development will impact on human beings in the surrounding area, in terms of tourism potential and socio-economic profile.
13.2 SOCIO-ECONOMIC PROFILE
According to preliminary results from the 2011 Census enumeration (CSO, 2011) the population of Ireland in 2011 was 4,581,269 persons, compared with 4,239,848 persons in April 2006. This represents an increase of 341,421 persons since 2006, or 8.1 per cent. In terms of annual average increase, this translates to an annual increase of 68,284 people, or 1.6 per cent.
Over the previous four-year inter-censal period between 2002 and 2006, the population increased by 322,645 persons or 2 per cent per annum, which equates to an annual average total of 80,661; the highest on record. This compares with 1.3 per cent for the preceding inter-censal period 1996-2002 and the previous high of 1.5 per cent which occurred between 1971 and 1979. The 2011 population was last exceeded in the census of 1861 when the recorded population was 4.4 million (CSO, 2007).
The very high births in the late 1970s and early 1980s, which reached a peak in 1980 with 74,000 births (today’s 31 and 32 year olds) is a strong distinguishing feature of the State’s population pyramid (Figure 13.1), as is the sharp fall in births over the subsequent 15 year period reaching a low point in 1994 (today’s 17 and 18 year olds). The recent recovery in births, particularly in the last four years, is also clearly evident. The pyramid shape from age 30 and over reflects the effects of mortality as the population grows older (CSO, 2012).
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Within County Sligo, the population has risen by 4,376 persons in the five years 2006-2011 and now stands at 65,393. In percentage terms the increase (7.2 per cent) is marginally below the State average of 8.1 per cent, but is significantly higher than neighbouring county Mayo where the population rise is a more modest 5.4 per cent. The average for the entire western region is 6.1 per cent (Western People, 2011).
A breakdown of the figures shows that the rise in Sligo’s population is fairly evenly spread across the sexes with 2,263 females and 2,119 males making up the total of 4,376.
The population of Co Sligo now stands at its highest since World War II. After plummeting to an all-time low of 50,275 in 1971 it has rebounded significantly in recent decades and one has to go back to the census of 1936 to find a higher population for Co Sligo (67,447).
The population of the three electoral districts (Sligo East, North and West) comprising Sligo city centre in the 2011 census (CSO 2012) was 17,568 (27% of the overall population of the county). However, a further 18,145 people live in the wider Sligo city area, outside these electoral boundaries but within 10 kilometres of the city centre, making a total of 35,713 people, or almost 55% of the county’s population living within 10km of the city centre including the docks area.
More detailed population breakdown figures for Sligo are not yet available on the 2011 census, however the preliminary report on age breakdown across the County (CSO, 2012) presents a population pyramid (Figure 13.1) showing that Sligo has very little fluctuation across all age groups up to the elderly ages. The typical bend in the graph seen for the State overall and centred around those aged 17 is compensated for by the presence of a higher number of young people in the student years, no doubt due to the presence of third level institutions.
State Sligo County Figure 13.1 Population pyramids (2011 census) for State and Sligo County
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13.3 ECONOMIC PROFILE
13.3.1 Labour Force
Sligo serves as an administrative, employment, commercial, healthcare and education centre for the North-West, which accounts for many of the professional services and administration jobs in the area. The services sector is the primary employer in the City. Sligo also acts as a distribution centre in the North-West and continues to retain a number of manufacturing jobs. The IDA has two business parks in Sligo, one at Finisklin, next to the port, and another at Cleveragh, which accommodate mainly knowledge-based industries and small engineering companies. The pharmaceutical industry is significant, with several companies producing goods for this sector (Sligo Co. Co., 2009).
Within broad occupational groups, professional, technical and healthcare workers are a sizeable percentage of the labour force in Sligo at 18%, with clerical, managerial and government workers forming 15.9% of the workforce.
This illustrates the importance of (decentralised) government agencies, local authorities and the regional hospital as a source of employment.
Outside Sligo city, agriculture remains an important part of the local economy, though its share of economic output and employment is declining. Other related industries such as forestry, tourism and other rural-based economic activities are emerging and helping to support the smaller towns and villages of the County.
Figure 13.2 Composition of Working Labour Force in Co. Sligo and State (2006)
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The Financial Crisis of 2008 affected the Irish economy severely, compounding domestic economic problems related to the collapse of the Irish property bubble. Unemployment within the State has risen sharply since 2008 (Figure 13.3) from levels of around 4.5% to over 14%. Many of these job losses have occurred within the construction, property and financial sectors. The economic climate has also led to increased emigration.
Figure 13.3 State Unemployment Rate
Figure 13.2 shows the composition of the working labour force, as presented in the 2006 census in County Sligo (2011 figures were not yet available at the time of writing). It can be seen that although the majority of the labour force in Sligo at that time worked in service industries, a significant proportion worked in Manufacturing (13.3%), Construction (11.5%) and Wholesale and Retail Trade (12.6%). These occupations (which comprised more than 37% of the workforce in Sligo in 2006 but realistically are expected to be significantly less in 2011) could benefit from development of the port and increased economic activity resulting from the proposed dredging. The ability to export directly by sea from Sligo could also assist in attracting new manufacturing businesses to the area.
13.3.2 Fisheries and Aquaculture
There are several licenced aquaculture sites operating within the boundaries of the Harbour, (although not all are currently actively farmed) with further aquaculture sites within Drumcliff Bay and Ballysadare Bay (refer to Chapter 7 “Fisheries and Aquaculture”). The local employment in fisheries and shellfish will remain unaffected, as impacts are not anticipated to extend beyond the dredging area (also see Chapter 11, “Hydrodynamic Modelling”).
Fishing, as well as potting for lobster and crab also take place within Donegal Bay, including the area of the proposed offshore dump site. The predicted impacts on fisheries are also discussed in more detail in Chapter 7, “Fisheries and Aquaculture” and are not expected to be significant.
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13.3.3 Sligo Port
The economic inputs of Sligo Port are discussed in more detail in Chapter 1.2 “Project Justification”. Whilst the number of vessels berthing at the port each year has remained fairly constant, the tonnages transported by these vessels has been increasing steadily. However, the channel depth is posing a constraint on the future viability of these transport routes as without dredging these vessels will have to reduce their cargo load to allow adequate clearance, which may threaten their economic viability. As described in Chapter 1.2, more than 180 jobs are directly dependent on the Port and the indirect benefits extend to an much wider range of industries. Should the existing cargo vessels be forced to berth at other ports, it is estimated that €2 million of disposable income would be lost to Sligo Town and its environs. This would have a major negative impact on local retailers, restaurants and other services.
13.4 TOURISM
Sligo is part of the north west tourism region, which also encompasses the counties of Cavan, Donegal, Leitrim and Monaghan. The most recent available regional tourism figures are from 2009, during which there were 1.4 million tourist visits, generating €319 million in revenue. Approximately half of the visitors (754,000) were domestic trips made by Irish residents, earning the region €115 million in revenue. Another significant proportion of visitors came from Northern Ireland, whose residents made 254,000 visits to the north west, spending €64 million.
Overseas visitors make a significant contribution to the economy of the north west, having a much higher per capita spend during their visits. Figure 13.4, from Failte Ireland, shows annual overseas visitor figures to the north west region between 1999 and 2009. Overseas visitor numbers dropped substantially in 2001-2002, a pattern reflected in tourist figures throughout Ireland and not just the north west. The reduction in numbers of overseas visitors during this period was attributed principally to the outbreak of Foot & Mouth Disease in Britain in February 2001 and the terrorist attacks on the United States in late 2001. These events brought to an end the growth trend that had developed across the whole of Ireland over the previous nine years. From 2002 visitor numbers gradually rose again, however it can be seen in Figure 13.4 that the global financial crisis in 2008 has had a significant impact on overseas visitor numbers with a substantial drop in numbers in 2009.
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Figure 13.4 North West Region Overseas Visitor Numbers 1999-2009 Failte Ireland, 2010 Sligo is the second most visited county in the north west region after Donegal (Table 13.1)
Table 13.1 Visitor numbers/revenue north west region 2009
Visitors ‘000s Revenue € million Cavan 72 30 Donegal 161 43 Leitrim 27 14 Monaghan 32 12 Sligo 142 42
Figures provided by Failte Ireland (2010) state that angling tourism brought 132,000 overseas visitors to Ireland in 2009 (2% of all visitor numbers) and generated an estimated spend of €105 million. Golf tourism attracted a further 146,000 overseas visitors (2.2% of all visitor numbers) generating an estimated spend of €110 million. These activities form a much greater proportion of the tourism in the north west region, but the Failte Ireland figures do not include figures from domestic or Northern Ireland tourists, many of whom would travel to the north west to engage in these activities while on short trips.
Economically tourism is very important to Co. Sligo and provides much needed revenue and employment, especially in remote rural areas. Golf and fishing therefore form an extremely important sector of the economy within this region, with other outdoors activities such as surfing, horse riding and hiking making smaller but nonetheless significant contributions to the tourism revenue.
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The government sees tourism as a key sector in rebuilding the Irish economy. Whilst the main aims are to re-attract the lost numbers of tourists from Britain and overseas, there are significant opportunities to expand within the domestic market and Northern Ireland as reduced incomes in these areas may prompt families to choose a domestic destination for their holidays in favour of travelling overseas. This has been helped by cuts in the VAT rate for restaurants, hotels and tourist attractions from 13.5% to 9% from 2011-2013.
One of the target areas for Tourism Ireland is sea angling, where a group of anglers would hire a boat and the focus is on catching big fish offshore. The focus is on anticipation of how big the fish will be rather than the effort/techniques and the main potential market is the domestic/UK market. In this respect these groups require experienced skippers and usually have an all-in deal with hotel accommodation (Failte Ireland, 2005).
The potential impact of the proposed dredging on fish and fisheries within the Garavogue Estuary and the wider Sligo Harbour/Donegal Bay area has been examined in detail in Chapter 7 – Fisheries and Aquaculture. There will be some limited disturbance during the dredging activities but these will be temporary in nature and will not pose any significant impact to recreational or commercial game fishing within the Garavogue River, Lough Gill or the wider Sligo harbour area.
A recent report commissioned by businesses in Sligo (O’Rourke, 2012) criticises the failure of Sligo to capitalise on its natural resources as a tourism attraction. Whilst the city itself has less potential as a tourist attraction, its wealth of quality hotels, bars and restaurants mean that it is more than equipped to serve as a focal point and base for a successful tourism industry, linked to the county’s resources of landscape and archaeology.
The O’Rourke report also describes the impact of the Economic Collapse on the retail sector in Ireland as being “profound”. CSO figures indicate that the total value of retail sales fell by 24% between 2007 and 2011. The fall in sales has not been uniform over the different sectors of retailing with families concentrating on buying “basics” and cutting down on all luxury or discretionary expenditure. Sales in Pubs fell by 28% over the period 2007 to 2011 with the fall in sales in some sectors even bigger with a 33% decline in sales in Books and Newspaper Stores and a 52% decline in sales in Furniture Stores. Tourism is one of the few industries which has real potential for rapid growth in business activity and employment in Sligo over the next five years. An increase in tourism will boost employment directly, but will also support the retail sector which has suffered such a rapid decline in Sligo.
The O’Rourke report makes recommendations for inexpensive improvements to increase access to the county’s natural resources, such as improving access to sites such as Benbulben, creating a cycle path network linking the attractions within Strandhill peninsula and Rosses Point and improving signage to visitor attractions throughout the county. The report does not make specific recommendations towards maritime tourism, however the enhancement in accessibility of the navigation channel coupled with the establishment of the pontoons at the Timber Jetty could create a more rounded tourism experience, where perhaps visitors could take a boat ride to Rosses Point and subsequently return to the city by bicycle. In addition, added opportunities for sea angling could be created, as skippers will be
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13.4.1 Bathing Waters
Rosses Point beach, just north of the entrance to Sligo Harbour, is a designated bathing water and also holds Blue Flag and Green Coast awards. The EPA monitors designated bathing waters in Ireland against standards in the Bathing Water Quality Regulations 2008 (as amended 2011) which are derived from the EC Bathing Water Directive (76/160/EEC). Further information on water quality in the context of the EC Bathing Water Directive is presented in Chapter 14, “Sediment and Water Quality”.
The commissioning of the new waste water treatment works in Sligo has had a significant positive effect on water quality within the harbour. There are not anticipated to be any negative impacts associated with the dredging activities within the harbour at Rosses Point beach; the dredging activities will not contribute to any increase in bacteriological activity and the influence of other parameters such as turbidity will not extend outside the confines of the harbour.
13.4.2 Sailing
Sligo has a vibrant marine recreation and leisure culture. Activities such as sailing, windsurfing, angling, motor boating and rowing are available in Sligo Harbour. Sligo Yacht Club is located at Rosses Point and hosts competitions in three classes: x Cruisers x GP 14s x Mirrors with two further classes, Optimist and Laser being promoted (Sligo Yacht Club, 2012). Sailing takes place 5 days a week between April and October with sailing activities concentrated outside the harbour in Sligo Bay.
The World Championships for the Mirror class were held at Rosses Point in 1987 and it also hosted the European Championships more recently in 2010. Rosses Point is one of the locations competing to again host the Mirror class World Championships in August 2013. In June 2011 over 100 boats competed in a fortnight long International and World Championship event for the Fireball class, which was held at Sligo Yacht Club.
These sailing events provide a significant boost to the local economy with sailing teams, their families, support staff and sponsors staying in local accommodation. The Fireball championships also coincided with a series of fringe events such as a Sea Shanty and Seafearing festival (Sligo Champion, 2011), which attracted significant numbers of local visitors who would not normally attend sporting events.
As the dredging is to take place within Sligo Harbour, outside the main sailing area, it is expected that there will be limited impacts to recreational sailing. During dredging, there will
IBE00440/EAR/September ‘12 13-8 Sligo Harbour Dredging Environmental Appraisal Report Human Beings be an exclusion zone set up around the dredger for safety reasons. This will cause a temporary restriction to leisure craft using the area of the harbour within the immediate vicinity of the dredger.
It is recommended that Sligo County Council sets up a liaison with Sligo Sailing Club and any other clubs with significant numbers of leisure craft users in the harbour to facilitate a safe co-existence between the dredger and leisure craft. Timetables showing the programmed dredging activity should be published locally giving adequate advance notice of the areas that will be affected.
13.5 CONCLUSIONS
13.5.1 Predicted Impacts
The proposed dredging at Sligo harbour will have no negative impacts on the existing tourism and retail industries in Sligo and should have a positive impact on both sectors upon completion of the works. During the dredging operations, there may be some temporary minor disruption to using leisure craft within the harbour, depending on the time of year the dredging takes place.
13.5.2 Mitigation Measures
Sligo County Council will establish a mechanism for liaison with the local sailing clubs and recreational users of the harbour. Harbour users will be informed of the programme of works anticipated over the dredging period, e.g. by newspaper notices and information boards at slipways and launching sites.
Of particular importance will be the requirement to coordinate with local sailing organisations to ensure that dredging activities do not pose a conflict with any scheduled major sailing events.
13.5.3 Residual Impacts
Around 180 jobs directly linked to the port’s commercial activity will be safeguarded by the proposed dredging works. There is potential for increasing employment both directly and indirectly as it is hoped that the scheme will become a catalyst to boost tourism and commercial activity within Sligo city and the wider Sligo Harbour area.
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14.0 WATER QUALITY AND SEDIMENT
This chapter describes the potential impacts of the proposed dredging in relation to the marine sediments and water quality. The study area for this assessment is Sligo Harbour, the Garavogue Estuary1 and the eastern section of Sligo Bay.
14.1 Overview of Existing Legislation
Water Quality data within the study area is monitored by the Environmental Protection Agency (EPA), the Local Authority and the Marine Institute in response to the following legislation:
x EC Bathing Waters Directive (76/160EEC) x EC Shellfish Waters Directive (2006/113/EC) x EC Water Framework Directive
Monitoring data are then compared against environmental quality standards (EQS) which are designed to protect the environment and human health. Monitoring is also carried out for compliance with the EC Urban Waste Water Treatment Directive (91/271/EEC).
14.1.1 Bathing Waters The nearest designated bathing water to Sligo Harbour is Rosses Point, which is approximately 2km from the westernmost limit of the dredging area (Figure 14.1). Rosses Point is also a Blue Flag beach, although it temporarily lost its blue flag between 2008 and 2010 due to failing to meet the guideline (higher) standards for faecal coliforms in a small minority of samples taken in 2007 and 2008. County Sligo has two further designated bathing waters at Enniscrone and Mullaghmore, both of which are more than 5km from the proposed dredging area and are therefore outside the study area for this Environmental Report. © Ordnance Survey Ireland. All rights reserved. Licence number 2010/20 CCMA/ Sligo County Council
Figure 14.1: Designated Bathing Water
1 Garavogue is intentionally spelled a number of different ways in this section, dependent on the spelling used in the source documentation. E.g. the WFD waterbodies are named “Garavoge Estuary” and “Gill, tributary of Garavogue” in the Local Authority’s River Basin Management Plan.
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14.1.2 Shellfish Waters In 2009, the Department of the Environment, Heritage and Local Government designated Sligo Bay and Drumcliff Bay (Figure 14.2) as shellfish areas in accordance with the Shellfish Waters Directive 2006/113/EC and the European Communities (Quality of Shellfish Waters) Regulations 2006 (as amended 2009).
Sligo Bay has been listed as a Class B (oysters and clams) bivalve mollusc production area in the Sea Fisheries Protection Authorities (SFPA) publication “Classified Bivalve Mollusc Production Areas in Ireland” (2009)”. Drumcliff Bay has also been assigned Class B status as a production area for mussels, oysters, clams and cockles.
© Ordnance Survey Ireland. All rights reserved. Licence number 2010/20 CCMA/ Sligo County Council Figure 14.2: Sligo Bay and Drumcliff Bay EC Designated Shellfish Waters
Class B areas are areas from which live bivalve molluscs may be collected, but placed on the market for human consumption only after treatment in an approved purification centre, or after relaying relaying in an approved relaying area, or after an EC approved heat treatment process.
The Sligo Bay designated shellfish water covers an area of 8.6km². The dredging area ranges from approximately 130 metres at its closest point to 500 metres from the designated area. Drumcliff Bay shellfish water is more than 3km at its closest point from the dredging area. The Marine Institute undertake water quality sampling at a station in the eastern portion of the shellfish area, within one of the licensed clam areas (Figure 14.2).
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Compliance with the Directive is measured against achievement of shellfish water quality parameter values outlined in Annex I of the Shellfish Waters Directive (2006/113/EC) which was transposed into Irish law under the European Communities (Quality of Shellfish Waters) Regulations 2006 - Schedules 2 and 4. Schedule 2 Mandatory values must be fully achieved, while it must be endeavoured to achieve Guideline values (Schedule 4).
The Regulations in Schedule 4 include a Guide value for faecal coliforms in the shellfish flesh, but there is no standard or guide value for faecal coliforms in ambient water.
The DOEHLG has published Pollution Reduction Programmes for both Sligo Bay and Drumcliff Bay which must be implemented by Sligo County Council.
14.1.2.1 Sligo Bay Pollution Reduction Programme (PRP) The DoEHLG’s Sligo Bay Pollution Reduction Programme (PRP) for this designated shellfish area was signed into effect by the Minister in December 2009. Under this programme the Marine Institute is required to carry out a monitoring programme to monitor the condition of waters in the shellfish growing area and to verify compliance, or otherwise with the water quality standards outlined in Schedules 2 and 4 of the Quality of Shellfish Waters Regulations (S.I. No. 268 of 2006) The Marine Institute submits a report on water quality in respect of the designated area to the Minister each year, and brings to the attention of the Department any non-compliance with a water quality standard.
UV treatment to protect the shellfish waters has been in place on the primary discharge since the commissioning of the new WWTP in January 2009.
14.1.3 The Water Framework Directive Directive 2000/60/EC, establishing a framework for Community action in the field of water policy (the Water Framework Directive), was adopted by the European Parliament and Council in 2000. It was transposed into Irish law via the European Communities (Water Policy) Regulations, 2003 (S.I. No. 722 of 2003), as amended by the European Communities (Water Policy) (Amendment) Regulations, 2005.
The Water Framework Directive (WFD) creates a legal framework for the protection, improvement and sustainable management of rivers, lakes, transitional waters (estuaries), coastal waters and groundwater. It is an over-arching piece of legislation, superseding and updating existing legislation, and will be the most significant piece of legislation governing the water environment for the foreseeable future.
The aim of the WFD is to prevent deterioration of the existing status of waters and to ensure that all waters are classified as at least ‘good’ status (by 2015 in most cases, with all waters achieving good status by 2027 at the latest). A water body must achieve both good ‘ecological status’ and good ‘chemical status’ before it can be considered to be at good overall status.
The proposed dredging area extends across two water bodies (Figure 14.3):
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x Garavoge Estuary transitional water body (water body code: IE_WE_470-0100) x Sligo Harbour coastal water body (water body code: IE_WE_470-0000).
Two further water body boundaries are within close proximity to the proposed dredging area and may also be influenced by the proposed project. These are: x Sligo Bay coastal water body (code: IE_WE_450-0000) x Gill, tributary of Garavogue (code: IE_WE_35_4183)
© Ordnance Survey Ireland. All rights reserved. Licence number 2010/20 CCMA/ Sligo County Council
Figure 14.3: Water Framework Directive Water Body Boundaries and Overall Status
Sligo Harbour also holds SAC, SPA and EC shellfish water designations. The water quality requirements for these areas relating to the Habitats, Birds and Shellfish Water Directives are discussed separately in Chapter 6, Intertidal & Marine Flora and Fauna, Chapter 5, Birds and Chapter 7, Fisheries and Aquaculture respectively.
This section presents surface water quality information for the waters in the vicinity of Sligo Harbour where the dredging works are proposed. The sources of the water quality information summarised in this chapter are: x Water body status information arising from the Water Framework Directive monitoring programme and outlined in the Western River Basin Management Plan (2009-2015) (WRBD, 2010). x Water quality information outlined in the EPA’s most recent water quality report, “Water Quality in Ireland 2007-2009” (EPA, 2011).
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14.1.3.1 WFD Status Classifications
Environmental Quality Standards (EQSs) for classifying surface water status are established in the European Communities Environmental Objectives (Surface Waters) Regulations, 2009 (S.I. 272 of 2009). These regulations set standards for biological quality elements, physicochemical conditions supporting biological elements (including general conditions and specific pollutants), priority substances and priority hazardous substances.
The ‘ecological status’ of a water body is established according to compliance with the EQS for biological quality elements, physico-chemical conditions supporting biological elements and relevant pollutants.
The ‘chemical status’ of a water body is established according to compliance with the EQS for priority substances and priority hazardous substances.
As well as achieving good ecological and chemical status, a water body must achieve compliance with standards and objectives specified for protected areas, which include areas designated by the Bathing Water, Urban Waste Water Treatment, Shellfish Waters, Habitats and Birds Directives. Waters bodies that are compliant with WFD standards, but that contain protected areas that are non-compliant with protected area standards, are downgraded to ‘less than good’ status.
In order to establish the WFD status of water bodies, the EPA developed a new, WFD compliant monitoring programme which began in 2006. It builds on previous monitoring programmes and provides a comprehensive assessment of water quality and quantity. WFD status classifications apply at the water body scale and are based on several samples/surveys targeting the variety of parameters, including biological, physico-chemical, chemical and hydromorphological elements, required to establish WFD status. The current status classification is based on monitoring information collected between 2007 and 2009 (EPA, 2011). The final status classifications, based on the results of this complete monitoring cycle, i.e. 2007 to 2009, were reported in 2011 (EPA, 2011).
The status classification of transitional and coastal water bodies is primarily based on information and data collected by the EPA, Marine Institute and Central Fisheries Board (now Inland Fisheries Ireland) between 2007 and 2009. In addition, assessments of the conservation status of protected areas carried out by NPWS are also taken into account.
14.2 EXISTING WATER QUALITY
14.2.1 Bathing Waters
Pre 2011, bathing water compliance assessment was based on five microbiological and physicochemical parameters as required under the 1992 “Quality of Bathing Waters Regulations”. From 2011 onwards, bathing water compliance is assessed under the requirements of the 2008 “Bathing Water Quality Regulations” which only monitors two
IBE00440/EAR/September ‘12 14-5 Sligo Harbour Dredging Environmental Appraisal Report Water Quality and Sediment microbiological parameters; Intestinal enterococci and Escherichia coli. For the 2011 bathing season, Rosses Point Beach achieved good water quality status and complied with both the EU guideline and mandatory values (Figure 14.4 - EPA, 2012). Rosses Point Beach also achieved good water quality status in the periods 2009 to 2010 and 2003 to 2006 but only had “sufficient” water quality status in the period 2007 to 2008.
Source: Splash! www.bathingwater.ie Figure 14.4: Bathing Water Quality Status
The loss of the Blue Flag in 2008 was in part due to adverse weather conditions, but also the lack of adequate foul waste treatment for Sligo city up to that year. Since the commissioning of the Sligo waste water treatment plant in 2009, the water quality has risen significantly, allowing the Blue Flag to be reinstated in 2010 after the beach had achieved the guideline standard for two consecutive years. With the treatment plant operational, Rosses Point has comfortably exceeded both the mandatory and guideline water quality targets since 2009.
14.2.2 Shellfish waters
Monitoring of seawater from the designated areas is carried out by the Marine Institute, who provided RPS with water quality measurement data acquired between 2007 and 2012. During this time, the water quality in the shellfish waters was generally very good and comfortably exceeded the guideline values for shellfish waters. The EPA “Water Quality in Ireland 2007-2009”, Chapter 5 “Quality of Estuarine and Coastal Waters” also confirms that levels of trace metals in shelfish tissue were also well within EU limits for this period. Monitoring for microbiological criteria such as levels of E. coli in shellfish waters as well as phytoplankton and marine biotoxins takes place on a more frequent weekly or monthly basis and no issues with microbiological tests have been reported in the 6 months to June 2012 (Marine Institute, 2012).
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14.2.3 The Water Framework Directive The EPA Water Water Framework Status Update based on Monitoring Results 2007-2009 was published in 2011 and presents a review of Irish ambient water quality for the years 2007 to 2009.
The water quality information in relation to transitional and coastal waters outlined in the report was generated by the EPA as well as other organisations including:
x Central and Regional Fisheries Boards (now Inland Fisheries Ireland); x Marine Institute; x Sea Fisheries Protection Authority (SFPA); x National Parks and Wildlife Service (NPWS); x Waterways Ireland; and x Irish Coast Guard.
A water body must achieve both good ‘ecological status’ and good ‘chemical status’ before it can be considered to be at good overall status. It must also be compliant with standards for protected areas in the vicinity. The extents of each of the water bodies have been shown above in Figure 14.3 (on page 14-4).
14.2.3.1 Garavoge Estuary As shown in Table 14.1, the Garavoge Estuary water body achieved “high” status in relation to many of the physico-chemical and biological parameters and is compliant with the standards established in the Habitats and Birds Directives. However, the Garavoge Estuary failed to achieve overall ‘high’ status due to below high status threshold values measured for Dissolved Oxygen and therefore was only classified overall as having achieved “good” status. The water body has been rated as being “1b - probably at risk” of failing to achieve “good” or “high” status by the end of the WFD cycle in 2015 and its overall objective in the RBMP is therefore to “protect” the existing status (or improve upon it).
14.2.3.2 Sligo Harbour Sligo Harbour water body is incorrectly reported in the wfdireland water maps tool as having achieved “high” status. The tool may not yet have been fully updated following last year’s publication of the 2007-2009 results. Although the waterbody achieved high status for almost all the criteria (Table 14.1) and is compliant with the standards established in the Birds and Habitats Directives, it only achieved “good” status for its morphology due to its phytoplankton measurements. This status reduces the overall classification to “good” as the WFD operates on a One Out – All Out (OOAO) basis The water body has been rated as being “1a - at risk” of failing to achieve “good” or “high” status by the end of the WFD cycle in 2015 and its overall objective in the RBMP is therefore to “protect” the existing status (or improve upon it).
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Table 14.1: Site Area Transitional and Coastal Waterbody Status Garavoge Estuary Sligo Harbour Sligo Bay Status Element Description Result Result Result Status Information Dissolved Inorganic Nitrogen status High High High Molybdate Reactive Phosphorus status High High High Dissolved oxygen as per cent saturation status Good High High Biochemical Oxygen Demand (5-days) status High High High Macroalgae - phytobiomass status High High High Macroalgae - opportunistic algae status N/A N/A N/A Macroalgae - reduced species list status N/A N/A High Angiosperms - Seagrass and Saltmarsh status High N/A N/A Benthic Invertebrates status N/A N/A N/A Fish status Good N/A N/A Hydrology status N/A N/A N/A Morphology status Good Good High Specific Pollutant Status Pass N/A N/A Overall protected area status At least good At least good At least good Ecological Status Good High High Chemical Status Pass N/A N/A Surface Water Status N/A N/A N/A Extrapolated status N/A N/A N/A Donor water bodies N/A N/A N/A OVERALL STATUS GOOD GOOD HIGH N/A = not assessed Source: wfdireland.com& EPA (2011)
Table 14.2: Site Area River water body status Gill, Tributary of Garvogue Status Element Description Result Status information Macroinvertebrate status High General physico-chemical status Good Freshwater Pearl Mussel / Macroinvertebrate status N/A Diatoms status N/A Hydromorphology status Good Fish status N/A Specific Pollutants status (SP) N/A Overall ecological status Good Overall chemical status (PAS) n/a Extrapolated status N/A Monitored water body YES Donor water bodies N/A OVERALL STATUS GOOD
N/A = not assessed Source: wfdireland.com& EPA (2011)
14.2.3.3 Sligo Bay As shown in Table 14.1, Sligo Bay water body achieved “high” status in relation to all of the physico-chemical and biological parameters and is compliant with the standards established in the Habitats and Birds Directives. The water body therefore was awarded “high” status overall. The water body has been rated as being “1a - at risk” of failing to achieve “good” or “high” status by the end of the WFD cycle in 2015 and its overall objective in the RBMP is therefore to “protect” the existing status.
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14.2.3.4 Gill, Tributary of Garvogue As shown in Table 14.2, the Gill, Tributary of Garvogue water body achieved “good” status in relation to all but one of the physico-chemical and biological parameters. The water body therefore was awarded “good” status overall. The water body has been rated as being “2b – not at risk” of failing to achieve “good” or “high” status by the end of the WFD cycle in 2015 and its overall objective in the RBMP is therefore to “protect” (or improve) the existing status.
14.2.3.5 Trophic Status The trophic status of transitional and coastal water bodies is assessed using the EPA’s Trophic Status Assessment Scheme (TSAS). This assessment is required for the Urban Waste Water Treatment Directive and Nitrates Directive. The scheme compares the compliance of individual parameters against a set of criteria indicative of trophic state (DIN, MRP, chlorophyll, macroalgae, dissolved oxygen). These criteria fall into three different categories which broadly capture the cause-effect relationship of the eutrophication process, namely nutrient enrichment, accelerated plant growth, and disturbance to the level of dissolved oxygen normally present;
x Eutrophic water bodies are those in which criteria in each of the categories are breached, i.e. where elevated nutrient concentrations, accelerated growth of plants and undesirable water quality disturbance occur simultaneously; x Potentially Eutrophic water bodies are those in which criteria in two of the categories are breached and the third falls within 15 per cent of the relevant threshold value; x Intermediate status water bodies are those which breach one or two of the criteria; x Unpolluted water bodies are those which do not breach any of the criteria in any category.
“Water Quality in Ireland 2007-2009” (EPA, 2010) has published the most recent trophic status for the transitional and coastal waterbodies around Ireland. Since the previous report in 2005, five water bodies have improved from intermediate to unpolluted status and these include the Garavogue Estuary, Sligo Harbour in addition to Kinsale Harbour, McSwyne’s Bay and the Lower Liffey estuary. This marked improvement in status is directly attributable to the commissioning of the Sligo WWTP.
14.2.3.6 Dissolved Oxygen Levels Low levels of Dissolved Oxygen (DO) can have adverse effects on aquatic organisms including slower growth rates, impaired immune response and, in severe cases, mortality. DO levels are classified as follows: x Anoxic (0 - 0.5 mg l-1) x Hypoxic (0.5 – 2.0 mg l-1) x Deficient (2.0 – 6.0 mg l-1) x Sufficient (6.0 – 10.0 mg l-1)
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Sligo Harbour water body has been measured as having “sufficient” Dissolved Oxygen levels during sampling. The Garavogue Estuary has had some “deficient” results which lowered its WFD DO status to “good”.
14.3 Sediment Quality
14.3.1 Dredging Area – Sediment Chemical Properties
As the approximately 250,000 cubic metres of dredged material is to be disposed of at sea, sediment contamination testing was undertaken for fourteen marine sediment samples taken within and adjacent to the dredging area, to ensure that disturbance of these sediments would not pose a threat of releasing contaminants.
Consultation was held with the Marine Institute, Galway, to determine location stations, parameters and detection limits for contamination testing, in accordance with the Guidelines for the Assessment of Dredge Material for Disposal in Irish Waters” (2006).
The sampling programme was undertaken by Aqua-Fact International Services in September 2009. Surface samples were taken by means of a 0.025m² VanVeen grab for subsequent contaminant analysis, organic carbon content and granulometric analysis. When samples were recovered on board from each station, notes were logged on sediment type, amount, colour and smell (Table 14.3).
Granulometric analysis was undertaken by Aqua-Fact in their laboratory.
Sub-samples were sent to the UK Environment Agency’s National Laboratory Service Facility at Leeds for chemical contaminant analysis of the sand-mud fraction (Ø<2mm). Appropriate marine Certified Reference Material (CRM) was analysed alongside the samples to ensure calibration.
Additional samples were also taken from 5 stations (St1, 4, 7, 10 & 12) and were sent to the Radiological Protection Institute of Ireland for radiological analysis.
14.3.1.1 Sampling Station Locations
The sample locations were specified by the Marine Institute as presented in Figure 14.5.
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Extract from Admiralty Chart 2852 © Crown Copyright UKHO. Not for navigational use Figure 14.5: Sligo Sediment Chemical Sampling Stations
Table 14.3: Dredging Area Sediment Samples - Descriptions
Station Colour Smell % ID Water 1* black/grey Mud Weak 72.9 H2S
2* black/grey Mud Weak 61.0 H2S
3* black/grey Mud Weak 70.2 H2S
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4* Grey/brown none 66.6 Mud
5 Grey/brown none 54.4 Muddy sand
6 Grey/brown none 64.3 Muddy/sand
7 Brown/grey none 30.1 Sand
8 brown/grey none 24.9 Sand
9 Grey none 56.4 Muddy sand
10 Brown/grey none 21.6 sand
11 Brown/grey none 25.6 sand
12* Brown/grey none 16.4 sand
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* Asterisked Stations are located outside the final dredging area (Stations 1-4 and Station 12)
14.3.1.2 Sediment Quality Results
The results of the granulometric analysis showed that the surface sediments in the inner harbour area (Stations 1 – 4) were typically made up of fine mud with varying amounts of fine sand. Consistent with the vibrocore results, the sediment samples collected in the outer harbour had increasingly higher grain size content (Stns 5 – 12).
The results of the contamination analysis showed compliance with the guideline limits proposed by the Marine Institute and DCMNR in the publication “Guidelines for the assessment of dredge material for disposal in Irish Waters” (2006) with the exception of Stn 1, which had elevated Polycyclic Aromatic Hydrocarbons (PAH) levels.
PAHs are one of the most widespread organic pollutants occurring in oil, coal and tar deposits and are produced as a by-product of fuel burning. In addition to their presence in fossil fuels they are also formed by incomplete combustion of carbon-containing fuels such as wood, coal, diesel, fat, tobacco so they can come from many sources. PAHs in the environment are found primarily in soil sediment, but can also be found in water.
The results of the sediment quality sampling and analysis programme were sent to the Marine Institute for their review and comment. The Marine Institute reverted with a requirement to undertake additional PAH analysis. The results of the additional analysis are also presented in Appendix 8. These additional results were sent to the Marine Institute for further review and comment.
The most likely source of the elevated PAH levels was a ship which caught fire in the upstream portion of the port. Although the ship has been removed, residual contamination may remain in the upper part of the channel. The sampling results confirm that this contamination is localised only to the immediate area of the channel surrounding the former location of the vessel.
As the upper part of the channel, above the Barytes and Deepwater jetties is only in use by recreational vessels which have a much smaller draft than the commercial vessels, there are no immediate requirements to dredge this part of the channel. Therefore, in consultation with the Marine Institute it was agreed that dredging would only take place alongside and downstream of the commercial jetties, thus avoiding disturbance of any of the sediments in the upper part of the channel (thereby excluding the channel from dredging between Stations 1-4).
During the course of consultations with local fishermen, concerns were raised regarding contamination of the sediments by the former operation of the untreated sewage outfall at Finisklin, prior to the commissioning of the new waste water treatment works. The analysis of the sediments shows that the organic content within all the samples, including those within the port, is low. Consultation has been held with the Marine Institute who have confirmed
IBE00440/EAR/September ‘12 14-13 Sligo Harbour Dredging Environmental Appraisal Report Water Quality and Sediment that the history of the site has been taken into consideration in setting the parameters for testing. The results of these tests show that the suspension of sediments in the navigation channel during the dredging process pose no chemical risk to the sensitive habitats within the harbour nor the habitats at the proposed dump site. The physical impacts of the sediments (e.g. smothering, increased turbidity) are considered in more detail in Chapter 6.
The results of the radiological analysis undertaken by the Radiological Protection Institute of Ireland have confirmed that the sediments to be dredged pose no radiological risk.
The Marine Institute have confirmed that the sediment quality of the material to be dredged is clean and suitable for disposal in Irish Waters (pers comm. Margot Cronin, Marine Institute 15 February 2010) and a separate dumping at sea licence will be applied for in parallel to the planning/foreshore consents.
14.3.2 Dredged Sediments Properties Conclusions
Physical, chemical and radiological testing of the sediments within the navigation channel at Sligo Harbour have been undertaken to determine whether these sediments are suitable for dredging and dumping at sea. The results of the tests have shown that the sediments within the dredging area are clean and free from contamination and will not pose any significant impact on the sensitive habitats and species within both the dredging area and the proposed offshore dump site.
Mitigation measures to reduce the amount of sediment placed into suspension during dredging activities and thus limit the physical impact of the dredging activity within Sligo Harbour are described in Chapter 4.0 Project Description and Chapter 11 Coastal Processes.
14.4 Potential Impacts during Dredging
14.4.1 Short term increase in Suspended Sediment and Turbidity The scale and extent of increases to suspended sediment during dredging operations are described in detail in section 11.1.4 of Chapter 11 “Coastal Processes”. The modelled results show that during dredging, the suspended sediment concentration rapidly increases during slack water as the tide turns, but quickly returns back to the background values once current speeds pick up again. Although the concentration reaches relatively high values, the periods during which this occurs are very short in duration. The period during which suspended sediment concentrations are elevated within any of the sensitive areas within the harbour will last on average up to two hours, with the highest peak values lasting 15-30 minutes. The period between peaks, where concentrations return to baseline levels, will be much longer, around 10 hours per tide.
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The areas which experience the greatest peaks in suspended sediments are along the northern shore of the harbour, the eastern shore of Coney Island and the area south of the training wall.
Environmental Quality Standards (EQS) for certain pollutants in surface waters in Ireland are outlined in the European Communities Environmental Objectives (Surface Waters) Regulations, 2009 (S.I. No. 272 of 2009). The purpose of the EQS is to limit the quantity of certain pollutants in surface waters in order to achieve the environmental objectives established for waters by Directive 2000/60/EC, the Water Framework Directive (WFD).
However, an EQS is not established in these Regulations for suspended sediments. Article 5 of the Shellfish Directive (2006/113/EC) and section 6 of the Quality of Shellfish Waters Regulations, 2006 (S.I. No. 268 of 2006) require the development of Pollution Reduction Plans (PRPs) for designated shellfish areas in order to improve water quality in designated shellfish areas and to achieve compliance with water quality parameter values outlined in Annex I of the Directive and Schedules 2 and 4 of the Regulations. Imperative (I) values must be fully achieved while it must be endeavoured to achieve guideline values (G).
There are no guideline values for suspended solids established in the Regulations, however the mandatory value states:
“A discharge affecting shellfish waters must not cause the suspended solid content of the waters to exceed the content in unaffected waters by more than 30%”
This measure can be considered conservative as it is designed to protect shellfish life and growth and shellfish are sensitive to suspended solids as shellfish species are generally bottom dwellers and/or filter feeders.
In order to be compliant with the shellfish mandatory value for suspended solids, suspended solid concentrations much not be raised more than 30% above background concentration. This standard is expressed as a 75-percentile, i.e. the value below which 75 percent of the observations may be found.
Available suspended solid monitoring results from the Marine Institute water quality monitoring station in Sligo Harbour (listed in Table 11.1 in Chapter 11) demonstrate that the background levels measured at the monitoring station in Sligo Harbour have varied between <2mg/l and 72mg/l between 2009 and 2011.
If we eliminate the highest 25% of readings, the 75th percentile level for suspended sediments is between 12.0-25.6mg/l. Although there will be some very short term peaks in suspended sediments, the modelling in Chapter 11 shows that concentrations will return to background levels within a short period of time. The predicted average increase in suspended sediments at the Marine Institute water quality sampling point is 10mg/l, therefore proposed dredging works will not cause water quality issues in this area to an extent that would constitute a non-compliance with the Shellfish Regulations.
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The localised nature of the impact and the short duration of dredging activity mean that the impact to water quality within Sligo Harbour is anticipated to be of minor adverse impact over a short term period.
14.4.1.1 Mitigation and Residual Impact Solids will be monitored during the dredging. If it is deemed that these concentrations are rising above predicted concentrations, then a decision can be made to slow the dredging rate in order to reduce the level of solids escapement.
The short term temporary suspension of solids during dredging will not have any significant impact on the receiving area in terms of meeting the requirements of the EC Bathing Waters Directive , the EC Shellfish Waters Directive or the EC Water Framework Directive.
14.4.2 Potential for the Spread of Contaminated Dredged Material As described above in 14.3.1.2 “Sediment Quality Results”, the material to be dredged has been extensively tested for levels of contamination by a certified laboratory under the supervision of the Marine Institute. All of the sediment samples within the area to be dredged have contaminant levels beneath the lower level2.
There are therefore no significant impacts to water quality arising from contaminated dredged material anticipated for this scheme. No mitigation is therefore necessary.
14.4.3 Potential for impacts to Dissolved Oxygen and Nutrients Dissolved oxygen concentrations may decrease in the vicinity of the dredge during the dredging operation due to increased levels of suspended sediment. Levels of organic material within the sediment to be dredged have been measured as low, which lowers the risk of DO reduction. There may also be low levels of nutrients within the silty surface layer of sediment which may be resuspended and therefore may enter the water column. Again these events will be short-lived and mostly confined to the dredge area. Any changes outside of the dredge area will be minimal and transient, returning to background levels following completion of the dredge. The impact to water quality in terms of dissolved oxygen levels and nutrient levels is anticipated to be of minor adverse impact over a short term period.
The dredging will not have any significant impact on the receiving area in terms of meeting the requirements of the EC Bathing Waters Directive, the EC Shellfish Waters Directive or the EC Water Framework Directive.
14.4.4 Potential for impact on Water Quality in the wider Sligo Bay area As described in Chapter 11 “Coastal Processes” there will be temporary short term increases in suspended sediment within the harbour during the dredging period. Due to the enclosed nature of Sligo Harbour, which only drains into Sligo Bay through the channels to the north
2 The lower level (Level 1) defines a concentration (i.e. guidance value) of a contaminant in sediment below which biological effects would not be anticipated (Cronin et al, 2006).
IBE00440/EAR/September ‘12 14-16 Sligo Harbour Dredging Environmental Appraisal Report Water Quality and Sediment and south of Coney Island, these increases will be almost entirely confined to the harbour area. Some areas, near the drainage channels will experience very slight increases in suspended sediment of less than 5mg/l during the dredging. The potential impact on water quality in the wider Sligo Bay area is therefore regarded to be insignificant and there will be no impact on the designated bathing waters at Rosses Point due to the dredging project.
14.4.5 Accidental Spillages during Dredging Operations During dredging, there is the potential for accidental spillages from the dredger itself, such as fuel oil. However, it will be a requirement of the contract documents that operational safeguards in regards to best environmental practice will be in place by the dredging operator who must also demonstrate specific experience in working in environmentally sensitive areas. With all necessary safeguards in place, the anticipated potential impact will be of minor adverse significance.
14.4.5.1 Accidental Spillages - Mitigation Measures and Residual Impact The port of Sligo will already have an oil spill contingency plan in place as required by the Sea Pollution Act 1999. The Irish Coast Guard is the lead authority designated by the Minister of Transport to approve plans and levels of response and resources required to comply with the requirements of this Act. The appointed dredging contractor will be required to prepare and submit an Environmental Management Plan (EMP) which will be implemented to reduce or eliminate, where possible, the likelihood of any impact to the marine environment during construction. The EMP must include the procedures which will be put in place to deal with any accidental spillages. With these measures in place, the residual impact of accidental spillages is anticipated as of negligible significance.
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15.0 SUMMARY OF IMPACTS AND MITIGATION MEASURES
15.1 INTRODUCTION
Chapters 5.0 to 14.0 of this Environmental Appraisal Report assess the likely significant impacts arising from the proposed coastal protection scheme. This section summarises the impacts identified and the suggested mitigation, where necessary, to reduce or eliminate the negative impacts.
Table 15.1 provides a summary of the potential impacts identified within the Environmental Report and identifies the mitigation measures outlined to reduce or eliminate these impacts. The timescale during which the mitigation is appropriate is also outlined, as well as who will be responsible for implementing the mitigation.
15.2 TECHNICAL DIFFICULTIES
The studies involved in assessing the environmental impact of the project have been undertaken throughout a period spanning more than two years, during which extensive baseline surveying was carried out, during the appropriate season. As a result, there were no technical difficulties encountered during the preparation of this Environmental Appraisal Report.
IBE0440/EAR/September ‘12 15-1 Sligo Harbour Dredging Environmental Appraisal Report Summary of Impacts and Mitigation Measures Not Not Not significant significant significant significant Significant Significant Residual Impact will be will the contractor implemented by implemented by These measures Who will be responsible for implementation n/a n/a n/a n/a n/a n/a Dredging relative to mitigation project, of Time scale, Design & During implementation Proposed Mitigation Measure Bird species in the harbour are alreadyin the subject to disturbance fromBird species recreation, transport (shipping movements in the harbour and low aircraft inflying the area of Sligo Airport) and other activities and appear to be habituated to current levels of disturbance. Disturbance to specieswaterbird result of the proposed as a alonedredging activities (either existing combination with or in is an imperceptible impact. It in result will disturbance levels) toextremely have a unlikely on significant negative effect waterbirds within Harbour/Cummeen Sligo Strand, even in the short term therefore no mitigation is necessary. aside loss, are possible in terms of habitat No mitigation measures from ensuring that dredging is kept to minimum required footprint. The proposed dredging leave adequate distance from thewill are so that the training not disturbed. walls walls No mitigation necessary. Areas being dredged are demonstrated as not in Appraisal Report being the principal areas feeding for cSAC/SPA feature bird species Potential Impact Removal of sediments from the estuary along the shipping channel. the on and has benthic environment directly the impact This will acts impact on the infaunal macrobenthos potential to negatively which as important food source for waterbird species in the estuary. Removal of sediments from the estuary along the shipping channel. result in the loss of some sub-tidal and intertidal habitat and This will along of the training has the potentialwalls to impact on the stability the shipping channel, which are an important roost site for waterbirds. Physical DisturbancePhysical has crew the by act of dredging vessel and its dredging The physical temporary disturbance to waterbird some the potential to cause populations in Sligo Harbour. BIRDS Table 15.1 Summary of Measures Mitigation and Proposed Potential Impacts Summary Table 15.1
15-2 Sligo Harbour Dredging Environmental Appraisal Report Summary of Impacts and Mitigation Measures Not Not Not significant significant significant significant significant Residual Impact will be will the contractor implemented by implemented by These measures Who will be responsible for implementation
n/a n/a n/a n/a n/a n/a relative to mitigation project, of Time scale, During Dredging implementation Proposed Mitigation Measure No mitigation measures are possible, aside from ensuring that dredging is kept to minimum required footprint. No mitigation measures are possible. be monitored dredging during may to confirm Sensitive habitats that sedimentation is not exceeding predicted levels. No mitigation necessary. No mitigation necessary. Areas being dredged demonstrated are in Appraisal Report as not being the principal feeding areas for cSAC/SPA feature bird species. Potential Impact Deposition of sediments on mudflats and sandflats During and after is the proposed operations, sediment dredging deposited along the sides of the navigation channel and along the north shore of the harbour area. Some of the deposition is temporary be and resuspendedwill and transported away in subsequent tidal remain will sedimentation of residual however a small amount cycles, completion of dredging operations.following The removalThe of estuarinesediments There be a habitat loss of benthic will along the navigational channel as a result of sediment removal. where dredging Along the channel associated fauna will occurs, removal of all surface sediment and short timeoccur over a relatively (The dredging frame. extend will across an area of up to 271,910m²,SAC is 0.56% of the areawhich (48,541,373m²). INTERTIDAL FLORA (DREDGING FAUNA AND AREA) Deposition of sediments on mudflats and sandflats The dispersion and settlement sediment of released during the on the directly impacts has the potential to cause dredging works (habitats andintertidal environment fauna) Sligo Harbour within and have associated species within also may on waterbird indirect impacts the SPA.
15-3 Sligo Harbour Dredging Environmental Appraisal Report Summary of Impacts and Mitigation Measures Not Not Not Not significant significant significant significant Significant Significant Residual Impact will be will will be will be will the contractor the contractor the contractor implemented by implemented by implemented by implemented by implemented by These measures These measures These measures Who will be responsible for implementation n/a n/a relative to mitigation project, of Time scale, During Dredging During Dredging During Dredging implementation Proposed Mitigation Measure No mitigation measures are however a monitoring necessary, programme to is recommended ensure that modelled levels are not exceeded (see fisheries and aquaculture section below) No mitigation measures are possible,No mitigation measures that aside from ensuring required footprint.dredging is kept to minimum as suspended during sediment levels No mitigation is necessary dredging have been modelled as being well within the tolerances thesupported by harbour. Suspendedin the sediment species be monitored duringlevels at vulnerable locations will dredging to ensure that they are the modelledwithin parameters. No mitigation measures are possible. Post-dumping monitoring is recommended (see fisheries and aquaculture section below) Potential Impact Elevation of suspended sediment levels in the water column be temporarilySuspended solids in the dumpsite area increasedwill during the dumping phase. have However, mobile the species will from the to move plume. dredge opportunity areas affected by away settle through as they rapidly dilute and disperse The sediments will above background. columnthe to insignificant levels water The settling of dumped sediments on the sea bed be deposited and will ofThe majority the dumped sediments will area this remain dumpsite. Benthic species within 2km of the within are unable through to burrow which the dumpedbe sediment may the of impact relative to smothered. Given the relatively small area surrounding habitats, negative impact on there should be no significant the bottom communities from Donegal Bay Elevation of suspended sediment levels in the water column column can be in the water Large quantities of suspended sediment detrimental to fish, bivalves and other aquatic organisms due to of proper and excretoryrespiratory clogging of the gills and impairment functioning and feeding activities. SITE) DUMP (PROPOSED FAUNA FLORA AND SUBTIDAL The removalThe of benthic habitat be aThere habitat along the loss of benthic will channel asnavigation a result of sediment removal. Along the channel dredgingwhere will surface sediment and associated fauna occurs, removal of all short timeoccur over a relatively frame. (The dredging extend will to 271,910m²,across an area of up is 0.56% of the SAC areawhich (48,541,373m²). SUBTIDAL FLORA AND FAUNA (DREDGING AREA) (DREDGING FAUNA FLORA AND SUBTIDAL
15-4 Sligo Harbour Dredging Environmental Appraisal Report Summary of Impacts and Mitigation Measures Not Significant Significant Residual Impact will be will the contractor implemented by implemented by These measures Who will be responsible for implementation relative to mitigation project, of Operations Time scale, and Dumping During Dredging implementation Proposed Mitigation Measure A trained and experienced Marine (MMO) Mammal Observer during should be put in place dredging and dumping operations. The MMO scan the surrounding will area to ensure no marine mammals are in a pre-determined zone in the 30 minute exclusion period prior to dredging commencing operations. Once operations operations have begun temporarily should cease in the immediate observed swimming if a cetacean or seal is and(<50m) area of industrialcan be activity resumed once work the animal(s) have moved away. Dumping of material at sea should not take place if a cetacean or 50m of the vessel. seal is within approachAny by marine mammals into the immediate (<50 m) area shouldworks be reported to the National Parks and Wildlife Service. The MMO keep a record of thewill monitoring using an MMO form “Location and Effort (Coastal Works)” National available from the to theParks & Wildlife Service (NPWS) and submit NPWS on completion of the works. photographs take If feasible, the MMO of dorsalwill fins of Bottlenose dolphins encountered, for the purpose of contributing to the Irish Whale and Dolphin Group (IWDG) catalogue of images for photo-identification. Potential Impact Collision Risk or causing injury that collision impacts There is a small possibility death may be suffered or by harbour individual grey seals entering the zone works Risk of hearing or disturbance/displacement as a result of noise Underwater works can generate noise at levels harmful to cetaceans and pinnipeds. MARINE MAMMALS MARINE
15-5 Sligo Harbour Dredging Environmental Appraisal Report Summary of Impacts and Mitigation Measures Not Not significant significant Significant Significant Residual Impact will be will be will the contractor the contractor implemented by implemented by implemented by These measures These measures Who will be responsible for implementation relative to mitigation project, of Operations Time scale, and Dumping During Dredging During Dredging implementation Proposed Mitigation Measure Water Quality Water Quality Monitoring A monitoring programme is recommended to take regular (DO) and in Sligo measurements turbidity of dissolved oxygen Harbour during dredging operations. There parameters should be locations in recorded in the immediate area of dredging and at key the navigation channel and at shellfish aquaculture sites. Units is recorded in National Turbidity (NTU) and beTurbidity may used as an indicator of the concentration of Suspended Solids (SS). A programme (NTU) linking Turbidity of calibration andSS (mg/l) should be carried out SSusing solutions of known concentration made up from samples of the sediments to be excavated. if exceeded, wouldTriggers levels should be established which, have untillead to immediate suspension of dredging levels recovered. Water Quality MonitoringQuality Water section(See fisheries and aquaculture below) Potential Impact Impacts of increased suspended sediment on salmonids Suspended sediment concentrations in the lower 0.5m of water lowcolumn are predicted throughout to remain relatively dredging the to move upstream via operations. Adult are most likely salmonids the meannavigation channel where higher concentration be slightly remain within the Fish Directive recommended limit of 25 mg/l but will Moreover, for salmonid waters. concentrations suspended sediment are likely to be lower in the upper layers of the columnwater which salmon more commonly utilise when swimming through estuarine and coastal waters. Impacts of increasedsuspended sediment and deposition of suspended sediments on aquaculture aquaculture sites in Sligo Harbour is Sediment deposition at licensed (<2 mm) low predicted to be during dredging of both the uppervery channel,and lower while completion of the be lower still (0-1 will works at these sites and pacific oysters under cultivation mm). Manila clam are buried in the naturally substrate and be unaffected by will these of sediment deposition. negligible levels FISHERIES AND AQUACULTURE FISHERIES AND Elevation of suspended sediment levels in thewater column at Dredging Site and Dumping Site disturbance to presentlevel of habitat a small Sediment plumes may be may temporarily reduced. the area. Visibility local seals foraging in the dredging and dumping be influenced by will The areas which plumes are not as important feedingknown areas for pinnipeds or cetaceans.
15-6 Sligo Harbour Dredging Environmental Appraisal Report Summary of Impacts and Mitigation Measures Not Not significant significant Significant Significant Residual Impact will be will will be will authority the licensing the contractor implemented by implemented by implemented by implemented by These measures These measures Who will be responsible for implementation relative to mitigation project, of Time scale, During Dumping During Dumping implementation Proposed Mitigation Measure Closure of sitefishingClosure of to The dumpsite and surrounding area to a radius of 1km should be during dumpingclosed to commercial fishing activity operations. be to avoid damage gear.This will any to of fishing or loss Water Quality Water Quality Monitoring A second monitoring programme is recommended for the alsodumpsite. This exercise would take regular measurements of (DO)dissolved oxygen and turbidity at the site surroundingand area during dumping operations. parameter with be established for each should Triggers levels readings to be taken along set transects emanating from the edge of the site. Potential Impact Impact of offshore disposal on crab fishery the dumped by some mobile species covered and sessile Many material settles deepest after the be lost, notably where material will include crab although thereeach dumping event. This may is to cause mortality in that smothering is unlikely evidence to show from away migrate under silt and to escape from are able crabs, which an area where place. dumping is taking be re-colonised from the surrounding faunalThe impacted seafloor will Re- habitat. integrate as part of the overall andcommunity will short period of take place within a relatively timecolonisation should (12-18 months). Impact of offshore disposal on other fishery activity haveFish may feeding reduced opportunities in the area of the dumpsite due to short term habitat loss on the seabed and reduced Impact of dredging on sea angling sediment concentrations are and suspended Sediment deposition predicted to be negligible at recognised sea angling and locations outside of Sligo Harbour where all takesboat-based fishing activity place Impacts of increased suspended sediment on eel and lamprey Eel and lamprey migrating through estuarine environments may encounter higher than suspended background loads. sediment are within recommendedsediment Projected levels of suspended upstream and adverse effect the not have an will guidelines and lamprey migrations of eels and downstream
15-7 Sligo Harbour Dredging Environmental Appraisal Report Summary of Impacts and Mitigation Measures Not Not Significant Significant Significant Residual Impact will be will be will authority authority licensing licensing under the under the the relevant the relevant the applicant the applicant supervision of supervision of implemented by implemented by implemented by These measures These measures Who will be responsible for implementation relative to mitigation project, of of Dumping of Dumping Time scale, During Dumping During Dredging implementation and on completion and on completion Proposed Mitigation Measure Monitoring Occasional measurement of noise levels generated using a Type 2 to check on the or better sound level meter should be conducted continuing impact of the works. Responsible Person It is recommended that the applicant and contractor should appoint or delegate a responsible be present person who on site and will to answer and be who act upon querieswilling will local from the public. notified of intendedIt is recommended that local residents are duly during toproximity their residences, particularly in close works to alleviate tensions and reduce help night time hours as this will potential for noise complaint related to the dredging activity. ROV monitoring of seabed ROV equipment should be deployed following completion of operations to verify settlement of dumped in thematerials designated area. Crustacean Monitoring Programme programme is recommended for theA crustacean monitoring dumpsite to determine any impact on shellfish stocks and the It is based on the crab stock. period – this should be recovery to fish at fishermen should be contracted suggested that individual pre-determined of the dumping site. in the region locations and catch beVerification of fishing activity would required. The programme should include baseline monitoring of the site prior to dumping and resumed after dumping of the to examine recovery site. Potential Impact AIR AND CLIMATE AND AIR Dredginglocal noise impacton residents occur along the northernDredging shorewill of Sligo Harbour, within the navigation channel extending Island to the Deepwaterfrom Oyster and Barytes jetties. There are a small number of residential units distances at varying located along this length of the coast, situated from the shore, the most proximate circa 150m from dredging activity occur on at Ballincar. Dredging operations24 houra will basis, but for a shortonly period (1-2 hours) 12 every hours. productivity. However, fish in the vicinity of dredge disposal operationsHowever, fish in the vicinity productivity. avoid areas affected the by dredge plume. will
15-8 Sligo Harbour Dredging Environmental Appraisal Report Summary of Impacts and Mitigation Measures Not Not Not Not Significant Significant Significant Significant Significant Residual Impact Who will be responsible for implementation relative to mitigation project, of Time scale, implementation Proposed Mitigation Measure No mitigation measures are possible n/a n/a No mitigation measures are necessaryNo mitigation measures No mitigation measures are necessary n/a No mitigation measures are necessary n/a n/a n/a n/a n/a Potential Impact HYDRODYNAMIC MODELLING Levels Water on Dredging of Impact level increase in water at in any not result The proposed dredging will high tide, therefore the proposed not dredging of the channel will increasecause any in the of flooding in Sligo fromrisk high spring larger drying be a slightly tides there will spring tides. At extreme low area for a maximum of 2 hours. Potential Impact to seabed at dumpsite due to physical or chemical properties of dredged spoil and chemical testing has been undertaken for Both physical the The the dump site. dredged sediment and the receiving sediments at propertiesphysical at the dump site are similar to the of the sediments dredged material, and the dredged material is free from contamination. Potential impacts to Groundwater Resource The proposed only dredging remove sedimentswill from the bed of the navigation channel. No removal with of bedrock is envisaged this scheme, therefore there is no risk of creating a new pathway for saline intrusion to occur. There is no risk of increasing nutrient loadings as a result of the proposed dredging. Impact of Traffic portDredging traffic to the has the potential to create additional works area. However, the port the increase in vehicle numbers travelling to is not significant. GEOLOGY MATERIAL ASSETS ASSETS MATERIAL
15-9 Sligo Harbour Dredging Environmental Appraisal Report Summary of Impacts and Mitigation Measures Not Not Not significant significant Significant Significant Significant Residual Impact will be will the contractor implemented by implemented by These measures Who will be responsible for implementation relative to mitigation project, of Operations Time scale, During Dredging implementation Proposed Mitigation Measure No mitigation measures are necessary MonitoringQuality Water n/a (See fisheries and aquaculture section above) n/a No mitigation measures are possible No mitigation measures n/a n/a Potential Impact Impact of Dredging on suspended sediment levels in Sligo Harbour in suspended sedimentelevations Modelling shows that significant the occur in the by Sligo Harbour caused dredgingwithin only of the dredger the confineswhere is within working, immediate vicinity of the navigation channel. The areas in which sensitive habitats have been identified, at Cartron Marsh, southern Cummeen Strand and at the various aquaculture suspended sediment short term increases in very experience sites will concentrations in the lowest 0.5m of the column,water mainly during at springslack water tides. However, these increases are of short the sensitive of within the tolerance levels term duration and are well flora and fauna within the harbour. Impact of Dredging on sedimentation in Sligo Harbour During dredging, small areas of the harbour temporarily may experience sedimentation of up for to 70mm short periods. The maximum final deposition depth of dredged Sligo sediments in Harbour on completion of dredging is less than 1mm in the majority of the harbour area. The deposition 25mm exceeds in a small only around the and training number of very mainly wall localised sites, northern shore of the harbour. small areas (less than 300m²) Two very experience sediment deposition final will depths in excess of 25mm. Impact of Dredging on Tidal Current Speeds The difference in the mean tidal current velocities is generally very are restricted to the area 0.1 m/s) and the changes small (less than around the channel of the harbour and the northern section area. increases of up to 0.4m/s may be experiencedPeak velocity in localised areas north of the navigation channel.
15-10 Sligo Harbour Dredging Environmental Appraisal Report Summary of Impacts and Mitigation Measures Not Not Not significant significant Significant Significant Significant Significant Residual Impact will be will will be will will be will authority authority licensing licensing under the under the the relevant the relevant the applicant the applicant the contractor supervision of supervision of implemented by implemented by implemented by implemented by implemented by implemented by These measures These measures These measures Who will be responsible for implementation Dumping relative to mitigation project, of Operations Time scale, During Dumping During Dredging implementation On completion of Proposed Mitigation Measure ROV monitoring of seabed ROV equipmentshould be deployed following of completion operations to verify settlement of dumped materials in the designated area. Water Quality MonitoringQuality Water section(See fisheries and aquaculture above) Archaeological Monitoring A competent maritimefor the archaeologist should be retained duration of the relevant In the works. event of archaeological features or material being uncovered during dredging,crucial it is that any the immediate cease in machine thearea to allow work archaeologist/s to inspect such any material. If the presence significant material is of archaeologically ofestablished, full archaeological recording such material is recommended. Potential Impact . CULTURAL HERITAGE Physical impact of dredgingwithin the navigation channel unrecorded previously Excavation has the potential to disturb archaeological artefacts Impact of dumping by depositing sediments on sea bed at Offshore Dump Site that the dumped sediment will model shows The final settlement accumulate on the seabed close to the dump site. An area extending approximately 2km to the east and south of the dumpsite will experiencedeposition in excess of 20mm. Within this, an area measuring approximately 0.5km² experiencewill deposition depths in excess of 130mm. No mitigation is possible to reduce the extent of the area experiencing and the dumped sediments, recolonisation however final settlement of should a occur within year.recovery Impact of dumping on suspended sediment at levels Offshore Dump Site during Modelling shows that be there dumping operations will the water sediment levels within increasestemporary in suspended materials settle out. column as the dumped the in The increases are shown models to be temporary in nature and thatrecommended quality water it is however not significant during monitoring is undertaken dumping operations to confirm that the modelling predictions are accurate.
15-11 Sligo Harbour Dredging Environmental Appraisal Report Summary of Impacts and Mitigation Measures Not Not significant significant Significant Significant Residual Impact will be will with thewith Contractor the applicant implemented by implemented by These measures assistance of the Who will be responsible for implementation relative to mitigation project, of Time scale, During Dredging implementation ed of the programme of works Proposed Mitigation Measure anticipated over the dredging period, newspaper by e.g. notices and information and launching sites. boards at slipways Of particular be the requirement importance will to coordinate with local sailing organisations to ensure that dredging do not activities scheduled any sailing events major pose a conflict with Communicationwith stakeholder groups with liaison for a mechanism establish CouncilSligo County will clubs and recreationalthe local sailing users of the harbour. be inform Harbour users will No mitigation measures necessary No mitigation measures n/a n/a Potential Impact . Impact of dredging operations on recreation activitiesin the harbour During the dredging there operations, may be some temporary minor the harbour,disruption to using leisure craft within depending on the the time of dredging takes place. year HUMAN BEINGS HUMAN Physical impactPhysical of dumping on the sea bed unrecorded potential to disturb previously Dumping has the archaeological artefacts
15-12 Sligo Harbour Dredging Environmental Appraisal Report Summary of Impacts and Mitigation Measures Not significant significant Residual Impact will be will the contractor implemented by implemented by These measures Who will be responsible for implementation relative to mitigation project, of Operations Time scale, During Dredging implementation Proposed Mitigation Measure Water Quality MonitoringQuality Water (See fisheries and aquaculture section above) Potential Impact EU Bathing watersEU Bathing directive EU Shellfishwaters directive EU Water Framework Directive x x x Temporary increases in Suspended Sediment and Turbidity within Sligo Harbour in the context of: SEDIMENT AND WATER QUALITY QUALITY WATER SEDIMENT AND During dredging operations, the suspended sediment concentrationDuring dredging the suspended sediment operations, as the tidewater increasesturns, but quickly rapidly during slack current speeds pick up once background values returns back to the the high values, relatively again. Although the concentration reaches periods during which this occurs are very short in duration. The changes tosediment suspended and turbidity have been assessed to not have any significant impact to the sensitive species and habitats monitoring. be verified by within the harbour area, this will Potential for impacts to Dissolved Oxygen and Nutrients of the decrease in the vicinity concentrations may Dissolved oxygen dredge during the dredging operation levels of due to increased the sediment organic material within suspended sediment. Levels of the risk of lowers to be dredged havewhich been measured as low, DO reduction. There may levels of nutrients the also be within silty low be of may surface layer resuspendedsediment andwhich therefore be short-lived the enter these events will water column. Again may confined to the dredgeand mostly changes area. Any outside of the transient, returning to background be minimal and dredge area will completion of the dredge. levels following
15-13 Sligo Harbour Dredging Environmental Appraisal Report Summary of Impacts and Mitigation Measures Not Not Not significant significant significant significant Residual Impact will be will the contractor implemented by implemented by These measures Who will be responsible for implementation relative to mitigation project, of Operations Time scale, During Dredging implementation Proposed Mitigation Measure No mitigation measures necessary The appointed dredging contractorbe required to prepare andwill submit an Environmental Management Plan (EMP) be will which implemented to reduce or eliminate, possible, the likelihood where impact to theof any marine environment during construction. in place tobe put The EMP must include the procedures will which in place, With these measures any accidental spillages. deal with the residual impact of accidental as of anticipated spillages is n/a negligible significance. n/a No mitigation measures necessary No mitigation measures n/a n/a Potential Impact Impact of Accidental Spillages during Dredging Operations Accidental pollution from dredging plant has the potential to degrade habitats and bird feeding resources in the harbour. Potential for impact on Waterwider in Quality the Sligo Bay area nature of Due to the enclosed drains only Sligo Harbour, which into throughSligo Bay to the north the channels and south of Coney be almostIsland, these increases will entirely to the confined harbour area. Some areas, near the drainage experience channels verywill slight increases in suspended sediment of less than 5mg/l during the dredging. The potential impact on water quality in the Sligo Baywider area is therefore regarded to be be insignificant and there nowill at Rossesimpact on the designated bathing waters Point due to the dredging project. Potential for the Spread of Contaminated Dredged Material During dredging if the material to be dredged contains operations, The be spread contaminants, these can across the receiving area. sediments to be dredged at Sligo harbour have been tested chemically and have been found to be free from contamination therefore there is occurring in this project. no risk of this impact
15-14 Sligo Harbour Dredging Environmental Impact Statement Summary of Impacts and Mitigation Measures
Table 15.2 Interactions (see text below for brief description of the interactions) Underwater Flora Cultural Heritage Material Assets Human Beings Hydrogeology Air & Climate Intertidal and Processes Geology & & Fauna Coastal Birds
Birds
Intertidal and Subtidal Flora A & Fauna
Air & Climate B None
Material None None None Assets
Coastal C E None None Processes
Geology None None None None None
Cultural None None None None None None Heritage
Human Beings None None G H I None None
Sediment and D F None None J K None L Water Quality
A Birds and intertidal/subtidal flora and fauna Reductions in species abundance and diversity within the intertidal and subtidal habitats within the harbour has the potential to impact Bird as there may be an associated reduction in availability of prey or foraging areas. No significant impacts are predicted to intertidal and subtidal flora and fauna. Mitigation in the form of monitoring during dredging operations has been recommended in Table 15.1 to verify that predicted suspended sediment concentrations are achieved. If agreed trigger levels are exceeded, the dredging methodology can be altered to ensure that harmful levels are not encountered.
IBE0440/EAR/September ‘12 15-15 Sligo Harbour Dredging Environmental Impact Statement Summary of Impacts and Mitigation Measures
B Birds and air and climate Birds have the potential to be disturbed by dredging noise. However the birds within the harbour are already subject to disturbance by recreation and commercial vessel movement within the harbour and are unlikely to be significantly impacted.
C Birds and coastal processes The dredging will allow water to drain out of the navigation channel more quickly during the ebb tide. This will result in a lower low water level during extreme spring tides, creating a larger drying area than before the channel was dredged for a period of approximately two hours per affected tide (a few times per year). This impact cannot be mitigated against but is not considered to be significant.
D Birds and sediment and water quality Increased levels of suspended sediments and turbidity have the potential to impact bird feeding. Mitigation measures in the form of monitoring of suspended sediments to ensure they are in accordance with the levels predicted in the model (which are not significant) and do not exceed agreed trigger levels during dredging are recommended in Table 15.1
E Intertidal and underwater flora and fauna and coastal processes Physical alterations to the channel as a result of dredging will have localised minor adverse impacts on intertidal and subtidal flora and fauna due to alterations in current speeds. No mitigation is possible, however the estuary is a dynamic environment and the affected species are adapted to changes in current speeds.
F Intertidal and Underwater Flora & Fauna and Sediment and Water Quality Increased levels of suspended sediments and turbidity have the potential to impact intertidal and subtidal species. Mitigation measures in the form of monitoring of suspended sediments to ensure they are in accordance with the levels predicted in the model (which are not significant) and do not exceed agreed trigger levels during dredging are recommended in Table 15.1. Settlement of suspended sediments has the potential to impact intertidal and subtidal habitats. Sensitive habitats may be monitored during dredging to confirm that sedimentation is not exceeding predicted levels.
G Air and Climate and Human Beings Noise from dredging operations has the potential to cause nuisance to residents of nearby dwellings. Mitigation measures are recommended in Table 15.1.
H Material Assets and and Human Beings Increases in traffic generation associated with dredging have the potential to cause nuisance to commuters. The traffic associated with the proposed scheme has been assessed and found to be not significant.
I Coastal Processes and Human Beings Dredging activities have the potential to cause temporary disruption to recreational use of the navigation channel. Mitigation measures are recommended in Table 15.1.
IBE0440/EAR/September ‘12 15-16 Sligo Harbour Dredging Environmental Impact Statement Summary of Impacts and Mitigation Measures
J Coastal Processes and Sediment and Water Quality Alterations to the coastal processes in a beach environment harbour have the potential to alter the distribution of sediments within the harbour, such as causing accelerated erosion or accumulation of sediments. The changes to current speeds around the navigation channel associated with the dredging will have no impact on the coastal processes within Sligo Harbour.
K Geology and Sediment and Water Quality Dumping the dredged sediments at an offshore dump site has the potential to significantly alter the composition of the bed sediments, both in terms of physical properties or if the sediment is chemically contaminated. The dredged sediments have been tested and have a similar granulometry profile to the bed sediments at the dump site. The sediments have also been chemically tested and have been found to be free of contamination therefore no significant impacts are anticipated and recolonisation and restoration of habitats on the seabed at the dump site will be able to occur relatively quickly.
L Human Beings and Sediment and Water Quality Excessive levels of suspended sediments or contaminants caused by the dredged sediments being brought into suspension during dredging operations have the potential to impact recreation activities such as bathing, or commercial activities such as aquaculture if safe thresholds are exceeded. Mitigation measures in the form of monitoring confirm that suspended sediments are not exceeding predicted levels is recommended in Table 15.1.
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15.3 Conclusions
The Environmental Appraisal and Appropriate Assessment have examined in detail the potential impacts of the proposed dredging scheme at Sligo Harbour on the sensitive habitats within the receiving area.
Where possible, every effort has been made to eliminate adverse impacts at source, through the dredging methodology or by site selection. Where the risk of adverse impact remains, mitigation has been outlined to reduce the significance of the impact to a level which is considered to be not significant.
The impact of the generation of suspended sediments and subsequent settlement of these sediments out of suspension as a by-product of the dredging has been extensively modelled and assessed. The location of the offshore dump site has been carefully chosen to reduce the impact of its use by placing at a distance from shore which allows the impacts of the sediments being dumped to be confined to a small footprint. Detailed hydrodynamic models have been prepared for both the dredge area and dump site which have been calibrated against field data collected specifically for this purpose.
Upon completion of dredging and dumping operations, no significant residual negative impacts have been identified. Some areas within the dredging area and dump site will be temporarily affected by settling out of suspended sediments but these areas will recover rapidly.
Monitoring of suspended sediment levels at sensitive areas during dredging has been recommended as a mitigation measure to protect local aquaculture interests in addition to the sensitive SAC and SPA habitats and species.
Impacts on commercial fishing for crustaceans at the dump site through damage to stocks either by mortality or, more likely, by evacuation of the area are expected to be confined to the immediate locality; probably no more than 0.5km from the dump site. At the proposed dump site a ROV survey to monitor seabed impact has been proposed.
Throughout the dredging programme it will be important to involve stakeholders, in particular commercial fishermen, commercial shellfish producers sailing clubs and local residents.
It is recommended that ongoing communication occurs with representatives of the local crab fishing industry to ensure that fishermen are kept adequately informed with regard to project progress and information from monitoring as it becomes available.
Sligo County Council, having overall responsibility for Sligo Port, is confident that the proposed dredging will generate major positive benefits to Sligo city and the wider North West region by securing its viability as a working commercial port, safeguarding existing jobs and potentially creating new jobs by attracting businesses requiring cargo transport, and avoiding the need for future investment in road transportation infrastructure.
IBE0440/EAR/September ‘12 15-18 Sligo County Council – Sligo Harbour Dredging Environmental Appraisal Report Bibliography and References
BIBLIOGRAPHY AND REFERENCES
CHAPTER 1 INTRODUCTION
CIRIA (2010) “The Beach Management Manual (Second Edition)” Environment Agency
Cronin, M., McGovern, E., McMahon, T., Boelens, R. (2006) “Guidelines for the Assessment of Dredge Material for Disposal in Irish Waters”.
Central Statistics Office (2012) Census 2011
Department of Transport (2005) Irish National Ports Policy Statement
Department of Transport (2010) “Ports Policy Review Consultation Document”
Department of Transport (2009) Smarter Travel – A Sustainable Future; A New Transport Policy for Ireland 2009 – 2020
Department of the Environment, Heritage and Local Government (2008) “Statement of Strategy 2008-2010”
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CHAPTER 2 CONSULTATIONS
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CHAPTER 3 SITE DESCRIPTION
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CHAPTER 4 PROJECT DESCRIPTION
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CHAPTER 5 BIRDS
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CHAPTER 7 – FISHERIES AND AQUACULTURE
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CHAPTER 8 AIR AND CLIMATE
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CHAPTER 9 MATERIAL ASSETS
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CHAPTER 10 GEOLOGY AND SOILS
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CHAPTER 12 CULTURAL HERITAGE
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Kerrigan, Paul, (1975) Castles and fortifications in Ireland 1485-1945 (Collins Press, Cork). Robinson, Auriel, (2010) ‘Discovering the maritime archaeological heritage of Sligo Harbour and environs’, unpublished report submitted to the Heritage Council in 2010, grant reference R00697.
Went, A. J., (1963) ‘Historical notes on the oyster fisheries of Ireland’, Proceedings of the Royal Irish Academy 62 (1961-63): 195-223
CHAPTER 13 HUMAN BEINGS
CSO Ireland (2011) “Census Of Population 2011 Preliminary Results” http://www.cso.ie/census/2011_preliminaryreport.htm accessed 05/08/11
CSO Ireland (2007) “Census 2006” Central Statistics Office, Ireland
CSO Ireland (2007) “Census 2006, Volume 7 - Principal Economic Status and Industries” Central Statistics Office, Ireland.
CSO Ireland (2007) “Census 2006, Theme 13 - 1 : Persons at work or unemployed by sex and occupation, 2006” Central Statistics Office, Ireland
CSO Ireland (2007) “Census 2006, SAPS - Small Area Population Statistics” Central Statistics Office, Ireland
CSO Ireland (2007) “Census 2006 Volume 8, Occupations” Central Statistics Office, Ireland.
CSO Ireland (2012) Census 2011, Profile 2: Older & Younger Stationery Office, Dublin
EPA (2011) “Splash – Annual Water Quality Results” http://www.bathingwater.ie/epa/home.htm
Failte Ireland (2010) “Tourism Facts 2009-Angling” http://www.failteireland.ie/FailteCorp/media/FailteIreland/documents/Research%20and%20S tatistics/Tourism%20Facts/2009/Tourism_Facts_Angling_2009.pdf accessed 11/08/11
IBE0440/EAR/September ‘12 B-13 Sligo County Council – Sligo Harbour Dredging Environmental Appraisal Report Bibliography and References
Failte Ireland (2010) “Tourism in the North West, 2009” http://www.failteireland.ie/FailteCorp/media/FailteIreland/documents/Research%20and%20S tatistics/Tourism%20Facts/2009/rerevised-North-West-2009.pdf accessed 11/08/11
Failte Ireland (2005) “A New Strategy for Irish Angling Tourism”
Government of Ireland (2008) “Bathing Water Quality Regulations 2008”
Irish Tourist Industry Confederation (2011) “Tourism Opportunity – Driving Economic Renewal”
O’Rourke, F. (2012) “Report on the Tourism Industry in the environs of Sligo City”
Pobal (2007) “Area Profile - Sligo county report” Trutz Haase Social & Economic Consultants
Sligo County Council (2009) Sligo and Environs Development Plan 2010-2016
Sligo Champion (2011) World Sailing event for Sligo http://www.sligochampion.ie/sport/other-sports/world-sailing-event-for-sligo-2574735.html accessed 18/07/2012
Sligo Yacht Club (2012) “About Us” http://www.sligoyachtclub.ie/index.php?id=2 accessed 25.06.2012
Western People (2011) “Sligo population rises by over 7%” http://www.westernpeople.ie/news/eysnqlgbgb/ accessed 08/08/2011
CHAPTER 13 SEDIMENT AND WATER QUALITY
Appleby, J.A., and Scarratt, D.J. (1989) Physical effects of suspended solids on marine and estuarine fish and shellfish with special reference to ocean dumping: a literature review. Can. Tech. Rep. Fish. Aquat. Sci. No. 1681.
Cronin, M, McGovern. E, McMahon,T. & Boelens, R. (2006) Guidelines for the Assessment of Dredge Material for Disposal In Irish Waters
Water Framework Directive (2012) Full Report for Sligo Harbour Waterbody (www.wfdireland.ie accessed 04/05/2012)
Water Framework Directive (2012) Full Report for Garavoge Estuary Waterbody (www.wfdireland.ie accessed 04/05/2012)
Water Framework Directive (2012) Full Report for Sligo Bay Waterbody (www.wfdireland.ie accessed 04/05/2012)
Water Framework Directive (2012) Full Report for Sligo Harbour Waterbody (www.wfdireland.ie accessed 04/05/2012)
IBE0440/EAR/September ‘12 B-14 Sligo County Council – Sligo Harbour Dredging Environmental Appraisal Report Bibliography and References
Water Framework Directive (2012) Full Report for Gill, Tributary of Garvogue Waterbody (www.wfdireland.ie accessed 04/05/2012)
Western River Basin District (2010) Western River Basin Management Plan (2009-2015)
EPA (2010) Water Quality in Ireland 2007-2009
EPA (2011) Water Framework Status Update - based on Monitoring Results 2007-2009
Sea Fisheries Protection Authority (2009) “Classified Bivalve Mollusc Production Areas in Ireland” (2009)”.
EPA (2012) Rosses Point Beach Bathing Water Quality Status www.bathingwater.ie/epa/ accessed 06/06/2012
IBE0440/EAR/September ‘12 B-15 Sligo County Council – Sligo Harbour Dredging Environmental Appraisal Report Bibliography and References
This Environmental Appraisal Report was prepared by:
RPS Consulting Engineers Elmwood House 74 Boucher Road Belfast BT12 6RZ Northern Ireland
Telephone +44 (0)28 90 667 914 Facsimile +44 (0)28 90 668 286 email [email protected] web www.rpsgroup.com/ireland
On behalf of:
Sligo County Council Market Yard Buildings Market Yard Sligo Co. Sligo Ireland
Telephone 071 9111960 Facsimile 071 9111990 email [email protected] web sligococo.ie
The following sub-consultants carried out specialist studies
Aqua-fact International Limited Intertidal and Underwater Ecology Natura Environmental Consultants Birds Michelle Cronin, BSc. MSc. PhD . Marine Mammals Paul Johnston Fisheries F.R. Mark and Associates Noise and Vibration Impact ADCO Intertidal and Underwater Archaeological Impact Raymond Burke Consulting Economic Appraisal
IBE0440/EAR/September ‘12 B-16