North Western - Neagh Bann CFRAM Study
UoM 01 Hydrology Report
IBE0700Rp0006
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North Western – Neagh Bann CFRAM Study
UoM 01 Hydrology Report DOCUMENT CONTROL SHEET
Client OPW
Project Title North Western – Neagh Bann CFRAM Study
Document Title IBE0700Rp0006_UoM 01 Hydrology Report_F03
Document No. IBE0700Rp0006
DCS TOC Text List of Tables List of Figures No. of This Document Appendices Comprises 1 1 180 1 1 3
Rev. Status Author(s) Reviewed By Approved By Office of Origin Issue Date
B. Quigley D01 Draft U. Mandal M. Brian G. Glasgow Belfast 03/07/2013 L. Arbuckle B. Quigley F01 Draft Final U. Mandal M. Brian G. Glasgow Belfast 07/04/2014 L. Arbuckle B. Quigley F02 Draft Final U. Mandal M. Brian G. Glasgow Belfast 14/08/2015 L. Arbuckle B. Quigley F03 Final U. Mandal B. Quigley G. Glasgow Belfast 07/07/2016 L. Arbuckle
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NW-NB CFRAM Study UoM 01 Hydrology Report – FINAL
TABLE OF CONTENTS
LIST OF FIGURES ...... IV LIST OF TABLES ...... VII APPENDICES ...... IX ABBREVIATIONS ...... X 1 INTRODUCTION ...... 1 1.1 OBJECTIVE OF THIS HYDROLOGY REPORT ...... 3 1.2 SUMMARY OF THE AVAILABLE DATA ...... 4 1.2.1 Summary of Available Hydrometric Data ...... 4 1.2.2 Summary of Available Meteorological Data ...... 5 2 METHODOLOGY REVIEW ...... 7 2.1 HYDROLOGICAL ANALYSIS ...... 7 2.2 USE OF METEOROLOGICAL DATA ...... 8 2.3 DESIGN FLOW ESTIMATION ...... 8 2.3.1 Index Flood Flow Estimation ...... 9 2.3.2 Growth Curve / Factor Development ...... 10 2.3.3 Design Flow Hydrographs ...... 10 2.4 HYDROLOGY PROCESS REVIEW ...... 11 2.5 CATCHMENT BOUNDARY REVIEW ...... 13 3 HYDROMETRIC GAUGE STATION RATING REVIEWS ...... 15 3.1 METHODOLOGY ...... 15 3.2 RATING REVIEW RESULTS ...... 16 3.3 IMPACT OF RATING REVIEWS ON HYDROLOGICAL ANALYSIS ...... 19 4 INDEX FLOOD FLOW ESTIMATION ...... 21 4.1 MODEL 1 – MALIN ...... 23 4.2 MODEL 2 – CARNDONAGH ...... 25 4.3 MODEL 3 - CLONMANY ...... 27 4.4 MODEL 4 – MOVILLE ...... 29 4.5 MODEL 5 – DOWNINGS ...... 31 4.6 MODEL 6 – DUNFANAGHY ...... 33 4.7 MODEL 7 – KERRYKEEL...... 34 4.8 MODEL 8 – BUNCRANA ...... 36 4.9 MODEL 9 – RATHMULLAN ...... 39 4.10 MODEL 10 – BURNFOOT ...... 41 4.11 MODEL 11 – BRIDGE END ...... 43 4.12 MODEL 12 – RAMELTON ...... 45 4.13 MODEL 13 – NEWTOWN CUNNINGHAM ...... 47 4.14 MODEL 14 – LETTERKENNY ...... 49
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4.15 MODEL 15 – BUNBEG - DERRYBEG ...... 53 4.16 MODEL 16 – DUNGLOE...... 55 4.17 MODEL 17 – GLENTIES ...... 57 4.18 MODEL 18 – ARDARA ...... 60 4.19 MODEL 19 – BALLYBOFEY & STRANORLAR ...... 62 4.20 MODEL 20 – KILLYGORDON ...... 65 4.21 MODEL 21 – CASTLEFINN ...... 67 4.22 MODEL 22 – LIFFORD ...... 69 4.23 MODEL 23 – CONVOY ...... 71 4.24 MODEL 24 – DONEGAL TOWN ...... 73 4.25 MODEL 25 – KILLYBEGS ...... 77 4.26 INDEX FLOOD FLOW CONFIDENCE LIMITS ...... 79 5 FLOOD FREQUENCY ANALYSIS AND GROWTH CURVE DEVELOPMENT ...... 80 5.1 OBJECTIVE AND SCOPE ...... 80 5.2 METHODOLOGY ...... 80 5.2.1 Selection of Statistical Distribution ...... 80 5.2.2 Forming a Pooling Region and Groups ...... 80 5.2.3 Growth Curve Development ...... 80 5.2.4 Limitations in the FEH and FSU Studies ...... 81 5.3 DATA AND STATISTICAL PROPERTIES ...... 81 5.3.1 Flood Data ...... 81 5.3.2 Pooling Region Catchment Physiographic and Climatic Characteristic Data 84 5.3.3 Statistical Properties of the AMAX series in Pooling Region 1 ...... 86 5.4 STATISTICAL DISTRIBUTION ...... 88 5.5 GROWTH CURVE ESTIMATION POINTS ...... 90 5.6 POOLING REGION AND GROUP FOR GROWTH CURVE ESTIMATION ...... 92 5.6.1 Pooling Region ...... 92 5.6.2 Pooling Group...... 92 5.7 GROWTH CURVE ESTIMATION ...... 93 5.7.1 Choice of Growth Curve Distributions ...... 93 5.7.2 Estimation of Growth Curves ...... 94 5.7.3 Examination of Growth Curve Shape ...... 95 5.7.4 Recommended Growth Curve Distribution for the UoM 01 ...... 98 5.8 RATIONALISATION OF GROWTH CURVES ...... 100 5.8.1 Relationship of Growth Factors with Catchment Characteristics ...... 100 5.8.2 Generalised Growth Curves ...... 101 5.8.3 Results for different parent pooling regions for UoM 01 ...... 105 5.8.4 Estimated growth factors for UoM 01 ...... 107 5.8.5 Comparison of the at-site growth curves with the pooled growth curves ..... 109 5.8.6 Growth factors for all HEPs in the UoM 01 ...... 113
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5.9 COMPARISON WITH FSR GROWTH FACTORS ...... 122 5.10 GROWTH CURVE DEVELOPMENT SUMMARY ...... 123 6 DESIGN FLOWS ...... 125 6.1 DESIGN FLOW HYDROGRAPHS ...... 125 6.1.1 FSU Hydrograph Shape Generator ...... 125 6.1.2 FSSR 16 Unit Hydrograph Method...... 126 6.2 COASTAL HYDROLOGY ...... 128 6.2.1 ICPSS Levels ...... 128 6.2.2 ICWWS Levels ...... 129 6.2.3 Consideration of ICPSS and ICWWS Outputs ...... 130 6.3 JOINT PROBABILITY ...... 132 6.3.1 Fluvial – Fluvial ...... 132 6.3.2 Fluvial – Coastal ...... 132 7 FUTURE ENVIRONMENTAL AND CATCHMENT CHANGES ...... 140 7.1 CLIMATE CHANGE ...... 140 7.1.1 UOM 01 Context ...... 140 7.1.2 Sea Level Rise ...... 141 7.2 AFFORESTATION ...... 143 7.2.1 Afforestation in UoM 01 ...... 143 7.2.2 Impact on Hydrology ...... 146 7.3 LAND USE AND URBANISATION ...... 149 7.3.1 Impact of Urbanisation on Hydrology ...... 153 7.4 HYDROGEOMORPHOLOGY ...... 157 7.4.1 Soil Type ...... 157 7.4.2 Channel Typology ...... 159 7.4.3 Land Use and Morphological Pressures ...... 163 7.4.4 Arterial Drainage...... 165 7.4.5 River Continuity ...... 167 7.4.6 Localised Pressures ...... 167 7.5 FUTURE SCENARIOS FOR FLOOD RISK MANAGEMENT ...... 168 7.6 POLICY TO AID FLOOD REDUCTION ...... 169 8 SENSITIVITY AND UNCERTAINTY ...... 170 8.1 UNCERTAINTY / SENSITIVITY ASSESSMENT MODEL BY MODEL ...... 171 8.2 CONCLUSIONS OF SENSITIVITY ANALYSIS ...... 175 9 CONCLUSIONS ...... 177 9.1 SUMMARY OF THE RESULTS AND GENERAL PATTERNS ...... 177 9.2 RISKS IDENTIFIED ...... 178 9.3 OPPORTUNITIES / RECOMMENDATIONS ...... 178 10 REFERENCES: ...... 181
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LIST OF FIGURES
Figure 1.1: UoM 01 AFA Locations and Extents 2
Figure 1.2: Hydrometric Data Availability 4
Figure 1.3: Meteorological Data Availability 6
Figure 2.1: Hydrology Process Flow Chart 12
Figure 2.2: Skeoge Catchment Boundary Review 14
Figure 4.1: UoM 01 Watercourses to be Modelled 22
Figure 4.2: Model 1 HEPs and Catchment Boundaries 23
Figure 4.3: Model 2 HEPs and Catchment Boundaries 25
Figure 4.4: Model 3 HEPs and Catchment Boundaries 27
Figure 4.5: Model 4 HEPs and Catchment Boundaries 29
Figure 4.6: Model 5 HEPs and Catchment Boundaries 31
Figure 4.7: Model 7 Catchment Boundaries and HEPs 34
Figure 4.8: Model 8 Catchment Boundaries and HEPs 36
Figure 4.9: Model 9 Catchment Boundaries and HEPs 39
Figure 4.10: Model 10 Catchment Boundaries and HEPs 41
Figure 4.11: Model 11 Catchment Boundaries and HEPs 43
Figure 4.12: Model 12 Catchment Boundaries and HEPs 45
Figure 4.13: Model 13 Catchment Boundaries and HEPs 47
Figure 4.14: Model 14 Catchment Boundaries and HEPs 51
Figure 4.15: Model 15 Catchment Boundaries and HEPs 53
Figure 4.16: Model 16 Catchment Boundaries and HEPs 55
Figure 4.17: Model 17 Catchment Boundaries and HEPs 58
Figure 4.18: Model 18 Catchment Boundaries and HEPs 60
Figure 4.19: Model 19 Catchment Boundaries and HEPs 62
Figure 4.20: Model 20 Catchment Boundaries and HEPs 65
Figure 4.21: Model 21 Catchment Boundaries and HEPs 67
Figure 4.22: Model 22 Catchment Boundaries and HEPs 69
Figure 4.23: Model 23 Catchment Boundaries and HEPs 71
Figure 4.24: Model 24 Catchment Boundaries and HEPs 74
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Figure 4.25: Model 15 Catchment Boundaries and HEPs 77
Figure 5.1: Locations of 248 Gauging Stations 82
Figure 5.2: Relative frequencies of catchments sizes (AREA) within the Pooling Region 1 (31 stations) 85
Figure 5.3: Relative frequencies of the SAAR values within the Pooling Region 1 (31 stations) 85
Figure 5.4: Relative frequencies of the BFI values within the Pooling Region 1 (31 stations) 86
Figure 5.5: L-Moment Ratio Diagram (L-CV versus L-Skewness) for 31 AMAX series in the Pooling Region 1. 87
Figure 5.6: Spatial distribution of the HEPs on the modelled watercourses in UoM 01 91
Figure 5.7: L-moment ratio diagram (L-skewness versus L-kurtosis) 93
Figure 5.8: Pooled Growth Curve 109 - (a) EV1 and GEV distributions; (b) GLO distributions 96
Figure 5.9: Comparison of EV1, GEV and GLO growth curves on the EV1-y probability plot (Growth Curve No. 109) 99
Figure 5.10: Relationship of growth factors with catchment areas for 125 HEPs 100
Figure 5.11: Relationship of growth factors with SAAR for 125 HEPs 100
Figure 5.12: Relationship of growth factors with BFI for 125 HEPs 101
Figure 5.13: Relationship of growth factors with catchment areas (for 384 growth curve estimation points) 102
Figure 5.14: Comparison of growth curves for different parent pooling regions. 106
Figure 5.15: GLO growth curves for all Growth Curve Groups (7 No.) 107
Figure 5.16: Growth Curve for GC Group No. 4 with 95% confidence limits 109
Figure 5.17: The at-site and pooled frequency curves along with the 95% confidence intervals 110
Figure 5.17 (continued): The at-site and pooled frequency curves along with the 95% confidence intervals 111
Figure 6.1: Various AEP Hydrographs for Upstream HEP on Donagh River (40_1018_1) 126
Figure 6.2: Location of ICPSS Nodes in Relation to Coastal AFAs 128
Figure 6.3: Draft ICWWS potential areas of vulnerable coastline 130
Figure 6.4: Typical 1% AEP Coastal Boundary Makeup (to Staff Gauge Zero) 131
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Figure 6.5: Comparison of Extreme Water Levels at Malin Head with Swilly Fluvial Flows 135
Figure 6.6: Comparison of Extreme Water Levels at Malin Head with Crana River Fluvial Flows 136
Figure 6.7: Comparison of Extreme Water Levels at Malin Head with River Leannan Fluvial Flows 137
Figure 6.8: Comparison of Extreme Water Levels at Arranmore with Owenea Fluvial Flows 138
Figure 6.9: Comparison of Extreme Water Levels at Killybegs with Glenaddragh River Fluvial Flows 138
Figure 7.1: CORINE 2006 Forest Coverage in UoM 01 Compared to the rest of Ireland 143
Figure 7.2: Forest Coverage Changes in UoM 01 145
Figure 7.3: UOM 01 CORINE Artificial Surfaces (2000 / 2006) 151
Figure 7.4: UoM 01 Soil Types (Source: Irish Forest Soils Project, FIPS – IFS, Teagasc, 2002) 158
Figure 7.5: WFD Channel Typology UoM 01 160
Figure 7.6: Modelled Watercourses – Channel Type 161
Figure 7.7: Changes in Channel Slope UoM 01 162
Figure 7.8: UoM 01 Land Use (CORINE 2006) 164
Figure 7.9: Watercourses affected by arterial drainage in UoM 01 166
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LIST OF TABLES Table 1.1: Fluvial and Coastal Flood Risk at each AFA ...... 3
Table 2.1: Summary of Catchment Boundary Review ...... 13
Table 3.1: Existing Rating Quality Classification for Rating Review Stations in UoM 01 ...... 16
Table 3.2: AMAX Series Data Before and After Rating Review ...... 17
Table 3.3: Summary of Rating Review Effects and Mitigation ...... 20
Table 4.1: Qmed Values for Model 1 ...... 24
Table 4.2: Qmed Values for Model 2 ...... 26
Table 4.3: Qmed Values for Model 3 ...... 28
Table 4.4: Qmed Values for Model 4 ...... 30
Table 4.5: Qmed Values for Model 5 ...... 32
Table 4.6: Qmed Values for Model 7 ...... 35
Table 4.7: Qmed Values for Model 8 ...... 37
Table 4.8: Qmed Values for Model 9 ...... 40
Table 4.9: Qmed Values for Model 10 ...... 42
Table 4.10: Qmed Values for Model 11 ...... 44
Table 4.11: Qmed Values for Model 12 ...... 46
Table 4.12: Qmed Values for Model 13 ...... 48
Table 4.13: Qmed Values for Model 14 ...... 52
Table 4.14: Qmed Values for Model 15 ...... 54
Table 4.15: Qmed Values for Model 16 ...... 56
Table 4.16: Qmed Values for Model 17 ...... 59
Table 4.17: Qmed Values for Model 18 ...... 61
Table 4.19: Qmed Values for Model 20 ...... 66
Table 4.20: Qmed Values for Model 21 ...... 68
Table 4.21: Qmed Values for Model 22 ...... 70
Table 4.22: Qmed Values for Model 23 ...... 72
Table 4.23: Qmed Values for Model 24 ...... 75
Table 4.24: Qmed Values for Model 25 ...... 78
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Table 5.1: Alternative parent pooling regions ...... 82
Table 5.2: Hydrometric Station Summary for Pooling Region 1 (31 Sites) ...... 83
Table 5.3: Summary of Catchment physiographic and climatic characteristics of Pooling Region 1 (31 Sites) ...... 84
Table 5.4: Statistical properties of 31 AMAX Series in Pooling Region 1 ...... 86
Table 5.5: Summary results of probability plots assessments (EV1, LN2, GEV & GLO distributions) for all 31 AMAX series in Pooling Region 1...... 89
Table 5.6: Summary of the catchment characteristics associated with the 217 HEPs ...... 90
Table 5.7: Growth curves shape summary ...... 95
Table 5.8: Catchment descriptors for all pooled sites for growth curve No. 109 ...... 96
Table 5.9: Frequency curve shapes of the individual site’s AMAX series associated with the pooled group No. 109 ...... 97
Table 5.10: Estimated growth factors for Growth Curve No. 109 ...... 98
Table 5.11: Growth curve estimation summary ...... 103
Table 5.12: Growth Curve (GC) Groups ...... 105
Table 5.13: Growth factors for range of AEPs ...... 107
Table 5.14: Estimated percentage standard errors for growth factors (XT) for a range of AEPs ...... 108
Table 5.15: Hydrometric gauging stations located on the modelled watercourses in UoM 01 hydrometric area ...... 109
Table 5.16: Growth factors for all 217 HEPs for a range of AEPs for UoM 01 ...... 113
Table 5.17: Study growth factors compared with FSR growth factors ...... 122
Table 6.1: ICPSS Level in Close Proximity to UoM 01 AFAs ...... 129
Table 6.2: Initial Screening for Relevance of Joint Probability ...... 133
Table 7.1: Afforestation from 2000 to 2006 ...... 146
Table 7.2: Allowances for Effects of Forestation / Afforestation (100 year time horizon) ...... 148
Table 7.3: Population Growth in UoM 01 County Donegal (Source: Central Statistics Office of Ireland) ...... 149
Table 7.4: Population Growth within Urban AFAs (Source: CSO) ...... 149
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Table 7.5: Urbanisation Growth Indicators ...... 153
Table 7.6: Potential Effect of Urbanisation on Qmed Flow in HA39 ...... 154
Table 7.7: Potential Effect of Urbanisation on Qmed Flow in HA39 ...... 155
Table 7.7.8: Channel Types and Associated Descriptors ...... 159
Table 7.9: UoM 01 Allowances for Future Scenarios (100 year time horizon) ...... 168
Table 8.1: Assessment of contributing factors and cumulative effect of uncertainty / sensitivity in the hydrological analysis ...... 171
APPENDICES APPENDIX A UOM 01 Hydrometric Data Status Table 1 Pages
APPENDIX B Rating Reviews 27 Pages
APPENDIX C Design Flows for Modelling Input 47 Pages
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ABBREVIATIONS
AEP Annual Exceedance Probability
AFA Area for Further Assessment
AFF At-site Flood Frequency
AMAX Annual Maximum flood series
AREA Catchment Area
BFI Base Flow Index
CFRAM Catchment Flood Risk Assessment and Management
C4i Community Climate Change Consortium for Ireland
DTM Digital Terrain Model
EV1 Extreme Value Type 1 (distribution) (=Gumbel distribution)
EPA Environmental Protection Agency
FARL Flood Attenuation for Rivers and Lakes
FEH Flood Estimation Handbook
FRA Flood Risk Assessment
FRMP Flood Risk Management Plan
FSR Flood Studies Report
FSSR 16 Flood Studies Supplementary Report No. 16
FSU Flood Studies Update
GC Growth Curve
GDSDS Greater Dublin Strategic Drainage Study
GEV Generalised Extreme Value (distribution)
GLO General Logistic (distribution)
GSI Geological Survey of Ireland
HA Hydrometric Area
HEFS High End Future Scenario (Climate Change)
HEP Hydrological Estimation Point
HPW High Priority Watercourse
HWA Hydrograph Width Analysis
IH124 Institute of Hydrology Report No. 124
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IPCC Intergovernmental Panel on Climate Change
LA Local Authority
LN2 2 Parameter Log Normal (distribution)
L-CV Coefficient of L variation
MPW Medium Priority Watercourse
MRFS Mid Range Future Scenario (Climate Change)
NBIRDB Neagh Bann International River Basin District
NDTM National Digital Terrain Model
NWIRBD North Western International River Basin District
OD Ordnance Datum
OPW Office of Public Works
OSi Ordnance Survey Ireland
PFRA Preliminary Flood Risk Assessment
Qmed median of AMAX flood series
Qbar / QBAR mean average of AMAX flood series
RBD River Basin District
RFF Regional Flood Frequency
ROI Region of Influence
SAAR Standard Average Annual Rainfall (mm)
SuDS Sustainable Urban Drainage
UAF Urban Adjustment Factor
UoM Unit of Management
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1 INTRODUCTION
The Office of Public Works (OPW) commissioned RPS to undertake the North Western – Neagh Bann Catchment Flood Risk Assessment and Management (CFRAM) Study in March 2012. The North Western – Neagh Bann CFRAM Study was the sixth and last CFRAM Study to be commissioned in Ireland under the EC Directive on the Assessment and Management of Flood Risks, 2007 as implemented in Ireland by SI 122 of 2010 European Communities (Assessment and Management of Flood Risks) Regulations, 2010.
The North Western IRBD covers an area of 12,320 km2 with approximately 7,400 km2 of that area in the Republic of Ireland. It includes two Units of Management (UoMs), UoM 01 (Donegal) and UoM 36 (Erne). It takes in all of County Donegal as well as parts of Leitrim, Cavan, Monaghan, Longford and Sligo. There is a high level of flood risk within the North Western IRBD, with significant coastal flooding in County Donegal as well as areas of fluvial flooding throughout the district.
UoM 01 includes hydrometric areas 01, 37, 38, 39 and 40. It covers an area of 4,610 km2 and includes the majority of County Donegal. The principal river system in UoM 01 is the River Foyle (which flows northwards from the confluence of the rivers Finn and Mourne at Lifford and Strabane towns). The Foyle forms the international border between the Republic of Ireland and Northern Ireland, draining the Mourne, Finn and Deele tributaries, discharging into Lough Foyle. The Foyle River is tidal along its entire length (to Lifford) and a tidal influence has been noted in the lower reaches of the Finn as far up as Castlefinn. In addition to the Foyle River system, there are numerous rivers and streams discharging to the estuaries and coastal waters all around the Donegal coastline including the Leannan, Owenea and Owencarrow rivers.
UoM 01 is predominantly rural with the largest urban areas being Letterkenny, Donegal town, Buncrana, Ballybofey and Stranorlar. Smaller towns and villages include Lifford, Milford and Moville. The lower lying fertile soils of UoM 01 are capable of supporting intensive agriculture. However, much of UoM 01 is mountainous with coniferous forest plantations and some sheep and cattle grazing. The spectacular coastline, the surfing beaches and the remote beauty spots attract many tourists.
Within UoM 01 there are 26 Areas for Further Assessment (AFA) which were reported to the EU in March 2012. Twenty five are included under the North Western – Neagh Bann CFRAM Study as shown in Figure 1.1. These are: Buncrana; Letterkenny; Killybegs; Malin; Carndonagh; Moville; Clonmany; Rathmullan; Burnfoot; Bridge End; Newtown Cunningham; Ramelton; Kerrykeel; Downings; Dunfanaghy; Convoy; Ballybofey & Stranorlar; Killygordon; Castlefinn; Lifford; Bunbeg- Derrybeg; Glenties; Dungloe; Ardara and Donegal. As most of these areas are situated along the coastline, most experience coastal flooding. Inland AFAs experience fluvial flooding. However, some of the coastal AFAs experience both coastal and fluvial flooding.
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Figure 1.1: UoM 01 AFA Locations and Extents
Raphoe in County Donegal was also reported to the EU as an AFA but the flood risk there is being addressed by a flood study which is already underway. In accordance with the National Flood Risk Assessment and Management Programme, North West – Neagh Bann River Basin Districts Catchment-based Flood Risk Assessment and Management (CFRAM) Study, Stage II Project Brief (hereinafter referred to as the North Western – Neagh Bann CFRAM Study Brief) only those areas not afforded protection by existing or planned schemes are considered in full under the North Western – Neagh Bann CFRAM Study. For other areas within AFAs benefiting from existing flood relief schemes, assessment under the North Western – Neagh Bann CFRAM Study will be limited to development and appraisal of maintenance and management options and the consideration of any implications
IBE0700Rp00006 2 F03 NW-NB CFRAM Study UoM 01 Hydrology Report – FINAL associated with potential development as identified in relevant spatial planning documents. No such areas have been identified within the North Western – Neagh Bann study area. Areas subject to minor works are not considered as having schemes in place. The AFAs and the flood risk source to be considered within UoM 01 as part of this study are listed in Table 1.1 below. It should be noted that although Bundoran is in County Donegal, it is not in UoM 01 but instead, it is in UoM 36.
Table 1.1: Fluvial and Coastal Flood Risk at each AFA
AFA Fluvial Coastal AFA Fluvial Coastal AFA Fluvial Coastal
Ardara - Convoy - Letterkenny
Ballybofey & - Donegal Lifford - Stranorlar
Bridge End Downings Malin
Bunbeg- Dunfanaghy - Moville Derrybeg
Newtown Buncrana Dungloe Cunningham
Burnfoot Glenties - Ramelton
Individual study, Carndonagh - Kerrykeel - Raphoe largely pluvial
Castlefinn - Killybegs Rathmullan
Clonmany - Killygordon - Total = 26 24 15
1.1 OBJECTIVE OF THIS HYDROLOGY REPORT
The principal objective of this Hydrology Report is to provide detail on the outputs from the processes of hydrological analysis and design flow estimation. The details of the methodologies used and the preliminary hydrological analysis are provided in the Inception Report ‘IBE0700Rp0002_UoM 01 Inception Report_F02’ (RPS, 2012). This report provides a review and summary of the methodologies used as well as details of any amendments to the methodologies since completion of the Inception Report. The report will provide details of the results of the hydrological analysis and design flow estimation and summarise the outputs from the analysis which will be taken forward as inputs for the hydraulic modelling. Discussion will be provided within this report on the outputs in terms of the degree of confidence which can be attached to the outputs and the opportunities for providing greater certainty for future studies, including opportunities for improving the observed data used to inform the study.
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This report does not include details of the data collection process, flood history within the AFAs or methodology and results from the historic flood analysis (except where this is used to inform the design flow estimation) as this is contained within the Inception Report for UoM 01.
1.2 SUMMARY OF THE AVAILABLE DATA
1.2.1 Summary of Available Hydrometric Data
Hydrometric data is available at 33 hydrometric gauge station locations within UoM 01 as shown in Figure 1.2 below.
Figure 1.2: Hydrometric Data Availability
Only 6 stations which are located on watercourses to be modelled have data available in UoM 01 (see Table 3.1). Three of these stations were rated under FSU as having a rating classification such that there was sufficient confidence in the rating for use within FSU (A1, A2 or B). All three stations were given a rating of B indicating that there is confidence in the rating up to Qmed. This however is the
IBE0700Rp00006 4 F03 NW-NB CFRAM Study UoM 01 Hydrology Report – FINAL minimum classification for which stations were taken forward for use within FSU and indicates that there is uncertainty in the flood flows recorded for extreme flood events (above Qmed).
1.2.2 Summary of Available Meteorological Data
Observed rainfall data from a number of different sources is available within and in close proximity to UoM 01:
Met Éireann daily and hourly rainfall gauges within the North Western IRBD and beyond. The only hourly gauge for which information is available for use in UoM 01 is located at Malin Head.
National Roads Authority sub-daily precipitation sensor information has become available since the project inception phase. Data has been received for five locations within the IRBD. The information consists of varying time steps but generally at 20 minutes and 1 hour spacing. The information is of unknown accuracy as the sensor technology has been developed primarily for the identification of precipitation type rather than high accuracy rainfall recording.
The UK Met Office daily and hourly rainfall gauge information for gauges within Northern Ireland but in close proximity to the border has become available since the project inception phase. Only one hourly gauge in close proximity to the extents of UoM 01 is available at Castlederg.
Historical time series rainfall data can be used as an input to catchment scale hydrological rainfall run- off models to simulate a continuous flow record within a catchment. High resolution temporal data is required to achieve the required accuracy within the hydrological models and as such hourly time series data is required. Daily rainfall data is not considered to be of a high enough temporal resolution to be used as direct input for hydrological modelling on its own but can be used along with the hourly data to inform the spatial distribution of hourly rainfall data within the catchments. In relation to UoM 01 the only rainfall data which can be considered to be of high enough temporal resolution and accuracy such as to be of use within rainfall run-off models is that which is available from the Met Éireann hourly gauge at Malin Head (1957 – 2012) and the Met Office hourly gauge at Castlederg (1995 – 2012).
A data collection meeting held prior to commencement of the Study (between RPS, HydroLogic, OPW and Met Éireann) identified an opportunity for exploring the use and benefits of rainfall radar data in hydrological analysis. Trials undertaken within the Eastern Study area demonstrated that there were benefits to be had by using gauge adjusted radar as opposed to using rain gauge data only to drive rainfall run-off models. RPS reviewed the extents of the radar coverage in relation to the NW – NB Study area and found that the Met Éireann rainfall radars, located at Shannon and Dublin Airport, were too far away from UoM 01 to be of use within the Study. RPS also reviewed the radar coverage from the Met Office operated rainfall radar at Castor Bay, on the shore of Lough Neagh in Northern Ireland. A review of the radar coverage found that the radar images are blocked by the hilly terrain of the
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Sperrin Mountains and the interior of County Donegal. As such it was considered that processing of the Met Office Castor Bay radar would not provide sufficient benefit to rainfall run-off modelling.
In addition to the observed historical rainfall data available at the aforementioned rain gauge locations, further meteorological information is required as input to hydrological models namely observed evaporation, soil moisture deficits and potential evapotranspiration data. Historical time series data is available for these parameters at Met Éireann synoptic weather stations. The locations at which historical data is available is generally the same as for hourly rainfall data and is available at Malin Head, Ballyhaise and Clones. Figure 1.3 shows the locations of all of the rain gauges available and the availability of historic information at the hourly rainfall gauges.
Figure 1.3: Meteorological Data Availability
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2 METHODOLOGY REVIEW
The methodologies for hydrological analysis and design flow estimation were developed based on the current best practice and detailed in the UoM 01 Inception Report. In the intervening period there have been a number of developments both in best practice, and the hydrological analysis tools which are available such that it is prudent that the overall methodology is reviewed and discussed. As well as a review of the methodology this chapter seeks to discuss amendments to the catchment boundaries that have become apparent and must be considered in the hydrological analysis.
2.1 HYDROLOGICAL ANALYSIS
The main tasks of hydrological analysis of existing gauge data have been undertaken based on the best practice guidance for Irish catchments contained within the Flood Studies Update. The analysis of the data available from the hydrometric gauge stations shown in Figure 1.2 has been carried out based on the guidance contained within FSU Work Packages 2.1 ‘Hydrological Data Preparation’ and 2.2 ‘Flood Frequency Analysis’ and is detailed in Chapter 5. This analysis was undertaken prior to the receipt of survey information which would have allowed the progression of the North Western – Neagh Bann CFRAM Study gauge station rating reviews identified within the UoM 01 Inception Report. Following completion of the rating reviews at the six stations identified (Lough Eske D/S, 37003 was removed as a rating review station due to the limited benefit and the presence of freshwater pearl mussels in the upper reaches of the River Eske) there was shown to be uncertainty in the ratings at four out of the six stations. The rating reviews, the new rating relationships and the consequences of the rating reviews for hydrological analysis are discussed in detail in chapter 3 of this report. The following elements of hydrological analysis have been assessed against the potential impact of uncertainty in the rating and mitigation measures and / or re-analysis undertaken to ensure the robustness of the hydrological analysis:
Gauged Index Flood Flow (Qmed) – Where there has been shown to be uncertainty in the
rating within the range of flows up to and around Qmed, the Annual Maxima (AMAX) flow series
has been re-processed using the revised rating. The use of the gauged Qmed in design flow estimation is further discussed in 2.2.1.
Single site (historic) flood frequency analysis – As the estimated frequency of a flood event is a function of the ranking of the event within the AMAX series, and this will not change following re-processing of the AMAX series, this will have little impact on the outputs of this study.
Growth Curve Development – The inclusion of gauge years within pooled flood frequency analysis that have a high degree of uncertainty could have a skewing effect within the frequency analysis but the effect will be diluted within a group (where it is assumed other gauge years have a high degree of confidence). The cumulative effect of uncertainty in both directions at multiple gauges may also have a cancelling out effect within a pooling group and
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as such it is not necessary to re-analyse the pooling groups. However where growth curves are based on a single site analysis where it has been shown that there is uncertainty in the rating, the single site analysis has been re-analysed with the re-processed AMAX data based on the revised rating relationship.
2.2 USE OF METEOROLOGICAL DATA
Chapter 1.2.2 details how the high resolution temporal rainfall data required as input to rainfall run-off models is available at very few locations within UoM 01, namely at the top of the Inishowen Peninsula (Malin Head) and in the upper reaches of the Foyle catchment (Castlederg). Within the NW-NB CFRAM Study methodology as detailed in the UoM 01 Inception Report rainfall run-off data is used within calibrated (to hydrometric gauge data) hydrological catchment models to provide additional simulated catchment flow data to bring greater confidence to statistical design flow estimates and provide additional (simulated) historical flow data for model calibration. This supplementary aspect of the methodology is not now being taken forward within UoM 01 due to a lack of concurrent hydrometric and meteorological data within the Study catchments and as such the methodology can be considered a more standard FSU statistically based approach drawing heavily on hydrometric data from within the Study catchments in the first instance and statistical analysis of national data where catchments are ungauged.
In the case of the northern half of the Inishowen peninsula there are no modelled catchments / watercourses for which calibration data (hydrometric flow data) is available such that an accurate run- off model could be built and calibrated. The nearest gauged model is the Buncrana model (Tullyarvan G.S. 39003, OPW) and it is considered that this catchment is too far away and not sufficiently meteorologically similar to Malin Head for the observed rainfall record to be applicable. In the case of the upper reaches of the Foyle there are two catchments to be modelled which have gauged data, the River Finn and the River Deele. In the case of the River Deele the hydrometric gauge station (Sandy
Mills, 01043, OPW) is considered to have confidence at Qmed, is subject to rating review, and has a long record (1973 – 2012) and as such there would be limited additional benefit in developing a run-off model. The Finn stations (Ballybofey, 01041, OPW & Dreenan, 01042, OPW) both have very limited confidence in the rating at Qmed and as such may benefit from the development of a rainfall run-off model. However both stations are subject to rating review such that confidence at Qmed value should be achieved following the hydraulic modelling of the station and the application of the revised rating curve to the long record of water level data. In light of the limited meteorological data, limited benefit within UoM 01, and the late receipt of the data for Castlederg (May 2013) rainfall run-off modelling within UoM 01 has not been pursued further.
2.3 DESIGN FLOW ESTIMATION
The estimation of design flows is based on the best practice guidance for Irish catchments generally as outlined in the Flood Studies Update (FSU) and supplemented with other methodologies where
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these are considered more appropriate. The methodologies for estimation of the various elements which make up the design flow estimates to be used for hydraulic modelling are detailed below.
2.3.1 Index Flood Flow Estimation
Estimation of the Index Flood Flow is required for all catchments and sub-catchments to be analysed under the CFRAM Study with each sub-catchment defined by a Hydrological Estimation Point (HEP). The preferred methodologies for estimation of design flow vary depending on the size, whether or not the catchment is gauged and also based on how the run-off from the catchments impacts upon the AFA. However a comprehensive, hierarchical approach is being taken to index flood flow estimation whereby all the specified methodologies available at each HEP are employed to estimate the index flood flow and to provide robustness to the estimates. For example, in the first instance, the FSU 7- variable ungauged catchment descriptor equation (Work Package 2.3) is used to calculate an estimate of the Index Flood Flow at all HEPs and where available, gauge records, rating reviews and other applicable methodologies are used to adjust / improve the estimate as the design flow estimation is developed. The hierarchy of preferred methodologies is discussed below.
2.3.1.1 Gauged Index Flood Flow (Qmed)
HEPs have been located at all hydrometric gauging stations where flow data is available. In the case of UoM 01 there are six gauging stations located directly on modelled watercourses and all six gauging stations are subject to a review of the rating using hydraulic modelling. Following rating review
it can be considered that these gauging stations will have confidence in the rating at Qmed. Eight of the 24 designated fluvial models include watercourses which are gauged at these six stations:
Model 8 Buncrana (Tullyarvan - 39003) Model 14 Letterkenny (New Mills – 39001) Model 17 Glenties (Clonconwal Ford – 38001) Model 19 Ballybofey & Stranorlar (Dreenan – 01042, Ballybofey – 01043) Model 20 Killygordon (Dreenan – 01042, Ballybofey – 01043) Model 21 Castlefinn (Dreenan – 01042, Ballybofey – 01043) Model 22 Lifford (Dreenan – 01042, Ballybofey – 01043) Model 23 Convoy (Sandy Mills – 01041)
All of these stations, following rating review, can be considered to have a high degree of certainty in
the flow at Qmed on the main modelled watercourse. In addition to these models there are four further models which have gauging stations at which flow data is available on the main channel upstream of the modelled extents. These models are:
Model 3 Clonmany Model 12 Ramelton
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Model 15 Bunbeg - Derrybeg Model 24 Donegal Town
The quality of the data at the gauging stations upstream of these models varies in quality and as such will be considered on a case by case basis as to whether the observed AMAX series will be used to
form the basis of the Qmed value for the model. This is considered in Chapter 4.
2.3.1.2 Ungauged Index Flood Flow (Qmed)
At all catchments the ungauged catchment descriptor based method FSU WP 2.3 ‘Flood Estimation
in Ungauged Catchments’ has been used, to derive estimates of Qmed, including small ungauged catchments. This is in accordance with recently published guidance “Guidance Note 21 - CFRAM guidance note on flood estimation for ungauged catchments”. This guidance note drew on the finding that alternative methods for small catchments (Flood Studies Report, NERC, 1975; IH Report 124, Marshall and Bayliss, 1994) do not have enough empirical support in Ireland and draw on older and cruder datasets than FSU. Therefore, in the first instance, the FSU 7-variable ungauged catchment descriptor equation (Work Package 2.3) is used to calculate an estimate of the Index Flood Flow at all HEPs and where available, gauge records are used to adjust / improve the estimate as the design flow estimation is developed.
The FSU methodology outlined in WP 2.3 recommends that estimates based on the seven parameter catchment descriptor equation are adjusted based on the most hydrologically similar gauged site. The adjustment factor is applied to the regression equation estimate at the subject catchment and can be
described in simple terms as the gauged Qmed divided by the regression equation estimated Qmed at the most hydrologically similar gauged site. Hydrological analysis tools developed by OPW as part of the FSU identify 216 gauge locations which are described as ‘Pivotal Sites’ following analysis of the data available as part of FSU WP 2.1 ‘Hydrological Data Preparation’.
2.3.2 Growth Curve / Factor Development
Growth curves have been developed based on single site and pooled analysis of gauged hydrometric data based on the FSU methodology set out in Work Packages 2.1 and 2.2. Full details and discussion of the results can be found in Chapter 4.
2.3.3 Design Flow Hydrographs
The design flow hydrograph methodology for the NW-NB CFRAM Study centres around FSU Work Package 3.1 ‘Hydrograph Width Analysis’ and uses the tools developed by OPW for analysing flood hydrographs at gauged sites. Since the completion of the Inception Report the methodology for deriving design flow hydrographs has been developed further following the release of the FSU Hydrograph Shape Generator (version 5). As such the hydrograph shapes are generated based on the following methods:
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1. At HEPs representing larger catchments (generally 10km2 or larger) within UoM 01 hydrographs will be generated using the recently released Hydrograph Shape generator (version 5) developed by OPW. This tool increases the list of Pivotal Sites from which median hydrograph shape parameters can be borrowed based on the hydrological similarity of the Pivotal Site when compared to the subject site. The release of version 5 of this tool has increased the pool of Pivotal Sites to over 150. RPS trialling of this version of the FSU Hydrograph Shape Generator in CFRAMS has found that the generated hydrograph shapes provide a reasonably good fit when compared to the observed and simulated (NAM) hydrographs across the Eastern and South Eastern Study areas.
2. At HEPs representing smaller catchments (generally less than 10km2) it may not be possible to find a suitable Pivotal Site from which a comparable hydrograph shape can be borrowed, particularly for the very small sub-catchments representing tributary headwaters. In this instance hydrograph shapes have been generated using the Flood Studies Supplementary Report (FSSR) 16 Unit Hydrograph method.
Design hydrographs have been developed at all HEPs. It was originally intended that at the smallest inflow / tributary HEPs that continuous point flows could be input. However analysis of this method found that the hydrograph was critical in some of the smallest watercourses which are restricted by culverts / bridges where flood volume as opposed to flood peak flow becomes the critical characteristic of a flood. Examples of this are the watercourses emanating from the upland Windyhall and Mountain Top areas on the northern edge of Letterkenny. These streams pass through urbanised portions of Letterkenny via a number of culvert and channel structures and as such at culvert openings they may surcharge and the event flood volume may be a critical factor. Application of continuous point flows on the upstream reaches of the hydraulic models could lead to an unrealistic build up of water behind culvert structures where this is the critical flood mechanism.
2.4 HYDROLOGY PROCESS REVIEW
Following developments in best practice and guidance documents and the refinement of RPS methodology through its application on the NW-NB CFRAM Study the hydrology process has been amended slightly from that which has been presented in the UoM 01 Inception Report (summarised previously in Figure 5.2 of report IBE0700Rp0002_UoM 01 Inception Report_F02). The revised process flow chart which has been applied in carrying out the hydrological analysis and design flow estimation for UoM 01 is presented in Figure 2.1. It is worth noting that the core methodologies employed within the Study are statistically based. These approaches do not require the identification of critical storms as the method ensures that the correct frequency conditions are achieved through checking the developing modelled hydrograph moving down through the catchment and adjusting the timings and peaks on the lateral inflow and tributary point inflows where necessary. This is the process shown in boxes 13 and 14 within Figure 2.1.
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Figure 2.1: Hydrology Process Flow Chart
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2.5 CATCHMENT BOUNDARY REVIEW
In line with the CFRAM Study Stage 1 Project Brief (ref. 2149/RP/002/F, May 2010) Section 6.3 RPS have delineated the catchment boundaries at HEPs using the FSU derived ungauged and gauged catchment boundaries as a starting point. In addition to the FSU delineated catchments, sub- catchments relating to cross border catchments were also provided by Rivers Agency and where provided these tended to capture cross-border catchments more accurately and as such were used as the starting point for review. For details of the full methodology for undertaking this review see UoM 01 Inception Report Section 5.3.2. Following the completion of this process a number of the catchment boundaries were amended (less than 10% catchment area change) and in a smaller number of catchments the boundaries were amended significantly (greater than 10% catchment area change). Table 2.1 gives a summary of the changes in the catchment area at CFRAMS HEP points when compared to the equivalent FSU / Rivers Agency catchment from which they were derived. The associated final catchment boundary shapefiles have been supplied to the OPW in GIS format to inform future studies and neighbouring catchments.
Table 2.1: Summary of Catchment Boundary Review
Change in Catchment Area Number of HEPs
New Catchment Delineated 45
No change 101
0 – 10% 47
Greater than 10% 21
Total 214
Not all the catchments related to HEPs that are required to be considered within UoM 01 were previously delineated. Some of the catchments relate to small streams and land drains which were too small to be considered under FSU and as such RPS delineated these previously undelineated HEP catchments using a combination of mapping, aerial photography and the National Digital Height Model (NDHM). In addition many of the cross border catchments were not captured accurately appearing to be cut-off at either the border / boundary of UoM 01 or at the extents of the NDHM. As discussed, the Rivers Agency provided catchment boundaries for all of the cross border catchments where these eventually discharged to the sea in Northern Ireland which aided delineation of cross border catchments in particular. One example of a catchment which was required to be delineated across the border into Northern Ireland is the Skeoge river catchment emanating on the western edge of Derry and discharging to the Swilly past Bridge End. This is shown in Figure 2.2.
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Figure 2.2: Skeoge Catchment Boundary Review
The review concluded that most of the FSU ungauged catchments were already accurately delineated but 27 out of the 124 (22%) catchments previously delineated under FSU were found not to be representative of the NDHM, the mapping or draft survey information. The most common reasons for amendment were either that the FSU catchments appeared to draw boundaries between peaks, sometimes neglecting small streams reaching further up into valleys or that the position of the surveyed watercourses was not as per the EPA Blue Line Network. Seven of the catchments (6%) were found to have margins of error of over 10%. These catchments ranged from less than 1 to 66 km² in catchment area.
IBE0700Rp0006 14 F03 NW-NB CFRAM Study UoM 01 Hydrology Report - FINAL 3 HYDROMETRIC GAUGE STATION RATING REVIEWS
As a follow on from the recommendations of Work Package 2.1 of the FSU, a task was included in the North Western – Neagh Bann CFRAM Study brief to undertake further rating review of a subset of hydrometric gauging stations. Following the completion of the risk review stage and finalisation of the AFA locations seven hydrometric stations were originally specified for rating review. The Eske D/S gauging station (37003 – EPA) was subsequently dropped from the rating review specification as the station is inactive with no recent spot gaugings available which are necessary to calibrate the rating review model with confidence. Furthermore, the gauging station was located in a reach of the River Eske which is known to be a habitat for the protected freshwater pearl mussel and as such would provide great difficulty in surveying. The six stations to be taken forward for review were chosen for rating review by OPW as they had available continuous flow data, were located on (or just upstream or downstream of) watercourses to be modelled and were deemed under FSU Work Package 2.1 as currently having a rating quality classification that could be improved upon (i.e. there may be some uncertainty in the rating at extreme flood flows).
3.1 METHODOLOGY
The methodology for carrying out rating reviews entails the following general steps:
1. Gauge station reach of watercourse is surveyed in detail (site visit, cross sections and LiDAR survey). Rating review survey is prioritised ahead of survey required for hydraulic modelling.
2. A hydraulic model is constructed of the reach of the watercourse from sufficient distance upstream to a sufficient distance downstream of the gauge station.
3. Spot gauged flows are replicated within the model and the model calibrated in order to achieve the observed measured water levels at the gauge station location.
4. When calibration is achieved flows are increased from zero to above the highest design flow (>0.1% AEP event) and the corresponding modelled water levels at the gauge location are recorded.
5. The stage (water level minus gauge station staff zero level) versus discharge results are plotted to determine the modelled stage discharge (Q-h) relationship.
6. The existing Q-h relationship is reviewed in light of the modelled relationship and the existing reliable limit of the Q-h relationship is extended up to the limit of the modelled flows. In some cases where the existing Q-h relationship has been extrapolated beyond the highest gauged flow (for practical reasons) the modelled Q-h relationship may vary significantly and as such the reliability of the existing gauged flood flows is called into question.
Six hydrometric stations have been specified for this analysis within UoM 01 and are shown in Table 3.1.
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3.2 RATING REVIEW RESULTS
The current rating quality classification assigned under the FSU for each station (if available) and whether the rating review indicated that there is significant uncertainty in the existing rating, defined as a difference in Qmed of more than 10%, is stated in Table 3.1.
Table 3.1: Existing Rating Quality Classification for Rating Review Stations in UoM 01
Station Final Station Rating Quality Significant Uncertainty Station Name Number Classification Identified in current rating
01041 Sandy Mills B No
01042 Dreenan U Yes
01043 Ballybofey U Yes
38001 Clonconwal Ford B No
39001 New Mills B / U Yes
39003 Tullyarvan C Yes
A1 sites – Confirmed ratings good for flood flows well above Qmed with the highest gauged flow
greater than 1.3 x Qmed and/or with a good confidence of extrapolation up to 2 times Qmed, bank full or, using suitable survey data, including flows across the flood plain.
A2 sites – ratings confirmed to measure Qmed and up to around 1.3 times the flow above Qmed. Would have at least one gauging to confirm and have a good confidence in the extrapolation.
B sites – Flows can be determined up to Qmed with confidence. Some high flow gaugings must be
around the Qmed value. Suitable for flows up to Qmed. These were sites where the flows and
the rating was well defined up to Qmed i.e. the highest gauged flow was at least equal to or
very close to Qmed, say at least 0.95 Qmed and no significant change in channel geometry was known to occur at or about the corresponding stage.
C sites – possible for extrapolation up to Qmed. These are sites where there was a well defined rating
up to say at least 0.8 x Qmed. Not useable for the FSU.
U sites – sites where the data is totally unusable for determining high flows. These are sites that did not possess 10 years of data or more, had water level only records or sites where it is not possible to record flows and develop stage discharge relationships. Not useable for FSU.
As well as the uncertainty in the existing ratings some gauging station ratings are limited such that they do not cover the range of flood flows other than through extrapolation of the stage discharge relationship. As a result of this all of the AMAX series level data has been re-processed into AMAX flow data using the revised rating derived from the rating review models and the revised AMAX series
IBE0700Rp0006 16 F03 NW-NB CFRAM Study UoM 01 Hydrology Report - FINAL flow data presented in Table 3.2 below. Full details of the individual rating reviews can be found in Appendix B.
Table 3.2: AMAX Series Data Before and After Rating Review
01041 01042 01043 38001 39001 39003 Sandy Mills Dreenan Ballybofey Clonconwal New Mills Tullyarvan Ford
Exist RR Exist RR Exist RR Exist RR Exist RR Exist RR (m3/s) (m3/s) (m3/s) (m3/s) (m3/s) (m3/s) (m3/s) (m3/s) (m3/s) (m3/s) (m3/s) (m3/s)
1972 n.a. 62.13 1973 44.01 48.15 n.a. 71.11 37.60 53.42 1974 69.54 71.73 n.a. 64.91 43.10 54.49 1975 88.18 89.84 n.a. 70.63 53.87 52.27 1976 34.00 33.37 n.a. 68.70 33.25 47.39 1977 49.39 53.39 n.a. 60.31 46.09 71.34 1978 119.35 116.91 n.a. 61.67 50.16 52.03 1979 96.02 96.16 n.a. n.a. 74.55 55.14 77.12 1980 68.14 69.38 n.a. n.a. 63.98 43.87 70.96 1981 84.61 85.51 n.a. n.a. 49.87 N/A 114.76 1982 99.23 99.09 n.a. n.a. 71.60 38.89 51.38 1983 78.64 79.77 n.a. n.a. 74.55 40.63 49.53 1984 147.16 142.262 n.a. n.a. 72.58 61.52 92.68 1985 113.61 113.92 n.a. n.a. 61.67 51.53 90.50 1986 115.89 115.91 n.a. n.a. 73.07 47.80 55.58 1987 103.02 104.50 n.a. n.a. 80.11 51.38 206.08 1988 55.23 60.38 n.a. n.a. 70.14 38.03 50.33 46.14 1989 105.77 107.46 n.a. n.a. 80.11 55.91 79.84 67.30 1990 115.89 114.92 n.a. n.a. 83.21 60.08 89.7 90.81 75.08 1991 85.63 87.43 n.a. n.a. 241.42 113.38 44.56 60.0 85.60 70.32 1992 79.62 81.67 n.a. n.a. 272.85 68.22 30.88 33.7 110.57 89.96 1993 75.23 77.39 n.a. n.a. 239.34 64.91 28.03 30.7 86.31 69.47 1994 92.85 94.21 n.a. n.a. 296.45 58.96 43.10 43.1 65.66 55.02 1995 105.22 105.48 n.a. n.a. 308.10 73.07 57.71 64.2 86.41 69.55 1996 70.94 73.14 n.a. n.a. 252.45 70.14 44.70 44.7 54.99 47.49 1997 64.02 66.12 n.a. n.a. 236.75 77.06 78.53 33.37 33.4 55.41 47.78 1998 80.61 82.63 n.a. n.a. 258.51 72.09 75.29 38.45 41.1 90.50 72.39 1999 100.31 101.05 n.a. n.a. 291.75 83.21 82.37 41.08 43.8 69.94 58.03 2000 74.75 76.92 n.a. n.a. 235.21 77.06 78.53 33.86 36.3 57.94 49.58 2001 79.13 81.20 n.a. n.a. 289.09 51.13 59.85 45.63 48.5 94.67 75.30 2002 62.89 64.96 n.a. n.a. 207.34 72.09 75.29 31.47 33.9 78.47 64.01 2003 62.22 64.26 n.a. n.a. 263.44 53.68 61.92 31.27 33.7 62.72 52.95 2004 101.39 102.04 n.a. 277.97 60.76 67.35 48.46 51.4 65.84 55.14 2005 67.68 71.26 n.a. 239.34 48.22 57.41 28.03 30.3 92.57 73.84 2006 68.60 72.20 n.a. 281.21 63.52 69.36 32.25 34.7 68.11 56.74 2007 104.12 105.98 n.a. 257.90 60.63 67.25 44.70 47.5 67.28 56.16
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01041 01042 01043 38001 39001 39003 Sandy Mills Dreenan Ballybofey Clonconwal New Mills Tullyarvan Ford
Exist RR Exist RR Exist RR Exist RR Exist RR Exist RR (m3/s) (m3/s) (m3/s) (m3/s) (m3/s) (m3/s) (m3/s) (m3/s) (m3/s) (m3/s) (m3/s) (m3/s)
2008 85.12 88.40 n.a. 230.09 61.90 68.19 35.50 38.0 51.05 44.69 2009 90.30 93.29 n.a. 311.73 71.36 74.80 64.39 81.7 75.20 61.72 2010 280.30 n.a. 242.88 2011 385.52 n.a. 340.26 2012 232.10 n.a. 206.09 2013 270.11 n.a. 242.57
Qmed 84.61 85.51 778.01 275.20 490.51 257.90 70.14 69.36 43.48 42.1 69.94 59.87 FSU 82.61 70.63 47.80 - % +1% -65% - 47% -1% -12% -14% Diff.
Denotes data taken forward for use in FSU. Rating considered to have confidence up to Qmed
1 Note : Ratings at both these stations were deemed under FSU to be very poor. A Qmed value was extracted as part of FSU WP 2.1 (AMAX flow not provided) but with the following note: ‘Huge amount of extrapolation required to reach QMED, of limited use in terms of FSU’
Note 2: This flow value is beyond the confidence limits of the modelled rating curve and is based on extrapolation of the curve past the top of bank level. Treat with caution.
Not all of the record length of existing AMAX series data has been re-assessed given the new rating. Initially the revised ratings generally have only been applied to the period of the existing OPW / EPA rating. Where there has been a significant change in the rating during this period and the period is less than 14 years RPS have applied the rating back further such that there is statistical confidence in the revised Qmed value.
The rating review undertaken at the Sandy Mills gauging station (01043) on the Deele was limited to the portion of the rating which is within bank due to a lack of high quality floodplain level data available. However the in bank modelled rating did provide agreement with the existing rating at Qmed and as such this value can be taken forward for design flow estimation with confidence.
At the Dreenan gauging station (01042) on the Finn no rating existed for the current water level data
(since the construction of a new bridge in 2004) and the previous rating and Qmed value (pre 2003) were based on a heavy extrapolation which resulted in a Qmed value which varied massively from catchment descriptor based estimates. As such the previous Qmed value could not be taken forward for design flow estimation with any confidence. A rating has now been developed for this station from which flow data can be processed (for the period post 2004). This rating is in good agreement with the
IBE0700Rp0006 18 F03 NW-NB CFRAM Study UoM 01 Hydrology Report - FINAL upstream Ballybofey rating review (see below) and is in good agreement with the catchment descriptor based estimates of Qmed. However the new rating could be refined by the collection of further spot gaugings and adjustment of the model to improve the fit to the spot gaugings.
At the Ballybofey gauging station (01043) located 2.6km upstream of the Dreenan gauging station no satisfactory rating existed such that flow data could be produced for this gauging station and as such the previous Qmed value could not be taken forward for design flow estimation with any confidence. A rating has now been developed for this station from which flow data can be processed. This rating is well calibrated to spot gauged data, is generally in agreement with the Dreenan rating review which was derived from a separate model and also results in an observed Qmed value, based on a long term AMAX record, which is in good agreement with catchment descriptor based estimates. As a result of these two rating reviews on the River Finn an observed Qmed value can be taken forward for design flow estimation with confidence. This catchment represents one of the largest modelled catchments within the UoM and it previously could have been considered ungauged in terms of flood flow data. Furthermore these two rating reviews can be considered to have added significant confidence to flow estimates relating directly to four AFAs.
The rating review at the Clonconwal Ford (38001) on the Stracashel River did not indicate uncertainty in the existing rating at Qmed.
At the New Mills gauging station (39001) the rating review indicates some uncertainty with the difference in Qmed of 12%. However data upon which to calibrate the rating review hydraulic model is poor with the highest spot gauging for the record period less than a quarter of the Qmed value. In this case the existing FSU AMAX series is retained rather than that from the rating review due to uncertainty given the lack of high flow spot gaugings. The rating review Qmed is almost 12% lower therefore it is conservative to adopt the existing FSU Qmed value.
At the Tullyarvan gauging station (39003) the rating review Qmed value is 14% lower than the value derived from the existing rating. However at this station calibration of the rating review hydraulic model was poor owing to poor resolution survey data across the fast flowing river section which could not be safely surveyed. The existing rating is extrapolated at Qmed and as such there is significant uncertainty in the existing value also. In this case the observed Qmed at the gauging station was ultimately not used as the basis for the gauging station check point flow for model anchoring (refer to Chapter 4.8).
3.3 IMPACT OF RATING REVIEWS ON HYDROLOGICAL ANALYSIS
As discussed in Chapter 2, Methodology Review much of the hydrological analysis was undertaken prior to survey information at the relevant gauging stations being available such that the rating reviews can be carried out. As such it is necessary to quantify the potential impact on the hydrological analysis and identify where re-analysis or mitigation to minimise the potential impact is required. The various elements of the hydrological analysis and design flow estimation are listed below and a summary of the potential impact and the proposed mitigation measures is detailed.
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Table 3.3: Summary of Rating Review Effects and Mitigation
Hydrological Potential Effects of Uncertainty in the Potential Mitigation Analysis Rating Impact
Most uncertainty with poor rating likely at flood flows and as such there could be Re-assess Q for FSU Gauged Q uncertainty in AMAX series. Will affect Medium med med classified sites of C or U Qmed at sites with a classification lower than B. An issue where an ungauged catchment is adjusted based on a pivotal site with Ungauged high uncertainty. As Pivotal Sites are Low None required Q med taken from A1, A2 & B classification they are unlikely to be affected.
Flood frequency is a function of the Frequency re-analysis not ranking of events within the AMAX series. required. Historic flood The position in the ranking is unlikely to frequency be affected by adjusting all the values in Medium Where event flows are analysis the series (i.e. unless adjusting a specific used for calibration historic gauge period) but the flood flow figure flows must be re- must be revised for calibration. calculated The inclusion of gauge years within pooled flood frequency analysis that have a high degree of uncertainty could skew At gauges where there has the pooled frequency analysis but the been shown to be effect will be diluted within a group (where uncertainty, re-assess Growth curve Medium / it is assumed other gauge years have a single site analysis to development Low high degree of confidence). The check that it is within 95th cumulative effect of uncertainty in both percentile confidence limits directions at multiple gauges may also of the pooled analysis. have a cancelling out effect within a pooling group. Calibration of hydraulic models is undertaken at extreme flood flows where Hydraulic highest degree of uncertainty could be Reassess calibration event model High present. Model calibration therefore flows where necessary calibration dependent on upper limits of gauge rating.
Hydrograph Uncertainty would affect values but semi- Shape dimensionless shape will not change (Q is Low None required Generation expressed factorially from 0 to 1).
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The first component in producing design flows within the majority of best practice methods widely used in the UK and Ireland is to derive the Index Flood Flow which within the FSU guidance is defined as the median value of the annual maximum flood flow series or Qmed. The methodologies being used in this study are detailed in the UoM 01 Inception Report and are reviewed in Chapter 2 of this report. As discussed the methods combine best practice statistical methods. This chapter details the Index Flood Flow estimation at each of the HEPs within UoM 01 on a model by model basis, including a discussion on the confidence and comparison of the outputs from the considered methodologies. Note that the flows contained within this Chapter represent hydrological estimates to that point in the catchment. The sum of inputs is not necessarily expected to equate exactly to the downstream flow estimate (although the sum would be expected to be at least as large) for various reasons such as hydrograph timing, catchment response, attenuation etc. Furthermore there may be instances where flow estimates along the main channel decrease even as the catchment size increases. This may occur where the catchment flattens out or where significant attenuation occurs and it is considered that these effects, reflected within the estimates, may be realistic. In some instances however where there are no obvious attenuating features such as reservoirs or lakes the decreasing Qmed values have been held at the higher values from upstream. These effects will be checked and verified through the hydraulic model to ensure that flows represented within the model are anchored to the hydrological estimates.
There are 25 models included in UoM 01 and these are shown in Figure 4.1.
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Figure 4.1: UoM 01 Watercourses to be Modelled
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4.1 MODEL 1 – MALIN
Malin Town is located at the mouth of one of the river sources of Trawbreaga Bay, a tidal estuary at the north of Inishowen in Donegal. The Ballyboe River is the main river which flows into the estuary at Malin Town but the main source of fluvial flood risk comes from two smaller watercourses which flow from the north through the village. The Ballyboe River is tidally dominant and although it is not considered here for fluvial design flow estimation, flood risk from the channel will be considered through the coastal modelling of Malin Town as discussed in Section 6.2.1. The catchment is small at less than 10km2, and is fairly steep with a fairly high proportion of peat / bog (20%). The HEPs and associated sub-catchments of the Malin model are shown in Figure 4.2.
Figure 4.2: Model 1 HEPs and Catchment Boundaries
There is one gauging station within the modelled reach (40061) operated by the Marine Institute but this is a water level recorder only and no data was provided at this station. As such the model can be considered to be totally ungauged for the purposes of flow estimation with the nearest gauging station with flow data available located near Clonmany on Lough Fad at the other side of Trawbreaga Bay. IBE0700Rp0006 23 F03 NW-NB CFRAM Study UoM 01 Hydrology Report – FINAL
The data at this station was not considered to have confidence in the flows at Qmed and was not given a rating classification under FSU. There are no FSU pivotal sites located in Hydrometric Area (HA) 40. A review of the closest geographically and the most hydrologically similar pivotal sites did not indicate a clear trend towards over or under estimation with the closest pivotal sites geographically indicating that the FSU physical catchment descriptor based equation overestimates Qmed and the most hydrologically similar sites suggesting underestimation. As there is no clear trend the FSU ungauged catchment estimates have not been adjusted based on a pivotal site. The estimated Qmed values for the various HEPs within Model 1 are shown in Table 4.1.
Table 4.1: Qmed Values for Model 1
2 3 Estimation Node ID_CFRAMS AREA (km ) Qmed (m /s) Methodology
40_958_1 2.49 1.30 FSU (unadjusted)
40_676_2 6.22 2.54 FSU (unadjusted)
40_958_2 2.71 1.38 FSU (unadjusted)
40061_RPS 9.51 3.77 FSU (unadjusted)
40_677_2 9.63 3.99 FSU (unadjusted)
Note: Flow highlighted in yellow represent total flows at that point in the model rather than input flows
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4.2 MODEL 2 – CARNDONAGH
Carndonagh is located just upstream of two of the main river sources of Trawbreaga Bay, a tidal estuary at the north of Inishowen in Donegal. The Donagh and Glennagannon Rivers are the main sources of fluvial flood risk to Carndonagh. Both catchments emanate from hilly bog land to the south of the town and are similar in size at 35km2 and 25km2 respectively. The proportion of predominantly peat soils in the Donagh and Glennagannon catchments is high at approximately 40% and 70% respectively. The HEPs and associated sub-catchments of the Carndonagh model are shown in Figure 4.3.
Figure 4.3: Model 2 HEPs and Catchment Boundaries IBE0700Rp0006 25 F03 NW-NB CFRAM Study UoM 01 Hydrology Report – FINAL
There are three gauging station sites within the modelled reaches but all are inactive, staff gauge only sites. As such the model can be considered to be totally ungauged for the purposes of flow estimation with the nearest gauging station with flow data available located near Clonmany on Lough Fad to the west of the catchment. The data at this station was not considered to have confidence in the flows at
Qmed and was not given a rating classification under FSU. There are no FSU pivotal sites located in Hydrometric Area (HA) 40. A review of the closest geographically and the most hydrologically similar pivotal sites did not indicate a clear trend towards over or under estimation and as such the FSU ungauged catchment estimates have not been adjusted based on a pivotal site. The estimated Qmed values for the various HEPs within Model 2 are shown in Table 4.3.
Table 4.2: Qmed Values for Model 2
2 3 Estimation Node ID_CFRAMS AREA (km ) Qmed (m /s) Methodology
40_982_1_RPS 24.95 17.78 FSU (unadjusted)
40003_RPS 25.87 18.20 FSU (unadjusted)
40_982_13_RPS 28.90 18.96 FSU (unadjusted)
40_1012_3 1.42 1.64 FSU (unadjusted)
40_1018_1 27.67 23.50 FSU (unadjusted)
40_1018_2 28.12 23.50 FSU (unadjusted)
40_1018_4_RPS 28.64 23.50 FSU (unadjusted)
40_1012_6_RPS 2.74 2.73 FSU (unadjusted)
40006_RPS 31.83 25.01 FSU (unadjusted)
40_1107_2_RPS 32.65 25.12 FSU (unadjusted)
40007_RPS 33.74 25.37 FSU (unadjusted)
40_1107_9_RPS 34.31 25.37* FSU (unadjusted) Note: Flow highlighted in yellow represent total flows at that point in the model rather than input * Flow at node was initially estimated to be lower than the estimate upstream. This flow has been held at the higher value from upstream as there are no obvious attenuating features. To be checked through hydraulic model.
Table 4.3: Qmed Values for Model 2
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4.3 MODEL 3 - CLONMANY
The Clonmany model represents the catchment of the Clonmany River which originates at Lough Fad in the interior of the Inishowen peninsula and flows through the village of Clonmany where it is joined by the Ballyhallan River before discharging to the sea at Tullagh Bay to the north of the village. The village itself is also affected by a small tributary of the Clonmany River flowing through the village from the north east. The catchment upstream of the AFA is approximately 35km2, and is fairly steep with a high proportion of peat / bog (40%). The HEPs and associated sub-catchments of the Clonmany model are shown in Figure 4.4.
Figure 4.4: Model 3 HEPs and Catchment Boundaries
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There is one gauging station with flow data available located to the south of Clonmany on Lough Fad. This station represents a lake outflow which contributes a small portion of the estimated flood flow.
Data from the station was not considered to have confidence in the flows at Qmed and was not given a rating classification under FSU. There are no FSU pivotal sites located in Hydrometric Area (HA) 40. A review of the closest geographically and the most hydrologically similar pivotal sites did not indicate a clear trend towards over or under estimation and as such the FSU ungauged catchment estimates have not been adjusted based on a pivotal site. The estimated Qmed values for the various HEPs within Model 3 are shown in Table 4.4.
Table 4.4: Qmed Values for Model 3
Preferred Estimation Node ID_CFRAMS AREA (km2) Q (m3/s) med Methodology
40_431_U 2.22 0.70 FSU (unadjusted)
40_565_1 33.65 23.49 FSU (unadjusted)
40_431_4 2.69 1.15 FSU (unadjusted)
40004 37.28 23.56 FSU (unadjusted)
40_293_7 8.61 6.79 FSU (unadjusted)
40_293_8 8.79 7.05 FSU (unadjusted)
40_1082_D 55.51 32.08 FSU (unadjusted)
Note: Flow highlighted in yellow represent total flows at that point in the model rather than input flows
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4.4 MODEL 4 – MOVILLE
The Moville AFA is located on the western shore of Lough Foyle on the Inishowen Peninsula. The Bredagh River is the main river which flows through the town but one of its tributaries and a stream on the eastern edge of the town have also been identified as sources of fluvial flood risk. The Bredagh catchment is less than 20km2 with the smaller catchment to the west just over 1km2. Both catchments are steep with a high proportion of peat / bog (up to 50%). The HEPs and associated sub-catchments of the Moville model are shown in Figure 4.5.
Figure 4.5: Model 4 HEPs and Catchment Boundaries
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There is one gauging station site within the town but it is a staff gauge only site and as such no data was provided at this station. As such the model can be considered to be totally ungauged for the purposes of flow estimation with the nearest gauging station with flow data available located near Clonmany on Lough Fad at the other side of Trawbreaga Bay. There are no FSU pivotal sites located in Hydrometric Area (HA) 40. A review of the closest geographically and the most hydrologically similar pivotal sites did not indicate a clear trend towards over or under estimation and as such the FSU ungauged catchment estimates have not been adjusted based on a pivotal site. The estimated
Qmed values for the various HEPs within Model 4 are shown in Table 4.5.
Table 4.5: Qmed Values for Model 4
2 3 Estimation Node ID_CFRAMS AREA (km ) Qmed (m /s) Methodology
40_460_3 1.61 1.50 FSU (unadjusted)
40_1019_2 14.44 9.18 FSU (unadjusted)
40_315_1_RPS 15.16 9.56 FSU (unadjusted)
40_315_2_RPS 15.27 9.71 FSU (unadjusted)
40_460_6_RPS 2.08 2.08 FSU (unadjusted)
40001_RPS 17.93 11.70 FSU (unadjusted)
40_516_3 18.50 12.03 FSU (unadjusted)
40_991_1 1.00 0.83 FSU (unadjusted)
40_991_3 1.32 1.16 FSU (unadjusted)
Note: Flow highlighted in yellow represent total flows at that point in the model rather than input flows
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4.5 MODEL 5 – DOWNINGS
The Downings AFA is located on the western side of the Rosguill Peninsula in Donegal. The main source of fluvial flood risk comes from a small watercourse which flows from the north through the village before discharging to the bay. The catchment is very small at 1.5km2. The HEPs and associated sub-catchments of the Downings model are shown in Figure 4.6 below.
Figure 4.6: Model 5 HEPs and Catchment Boundaries
The catchment is ungauged and there are no FSU pivotal sites which could be considered hydrologically similar given the very small size of the catchment. Furthermore the catchment was not delineated and the catchment descriptors not developed under FSU and as such these have been derived based on neighbouring catchment data, aerial photography and the national DHM. The FSU
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ungauged catchment estimates have not been adjusted based on a pivotal site. The estimated Qmed values for the various HEPs within Model 5 are shown in Table 4.6.
Table 4.6: Qmed Values for Model 5
2 3 Node ID_CFRAMS AREA (km ) Qmed (m /s) Estimation Methodology
38_1824_U 0.635 0.37 FSU (unadjusted)
38_1824_D 1.565 0.99 FSU (unadjusted) Note: Flow highlighted in yellow represent total flows at that point in the model rather than input flows
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4.6 MODEL 6 – DUNFANAGHY
The AFA of Dunfanaghy has not been identified as being at risk of fluvial flooding and as such fluvial hydrological analysis specific to Dunfanaghy has not been undertaken. For further details of the coastal data which will be input into the coastal flood models see Chapter 6.
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4.7 MODEL 7 – KERRYKEEL
Kerrykeel is located within Mulroy Bay in northern Donegal, approximately 14km within the inlet from where it meets the Atlantic. The Burnside River is the main river which flows into the bay at Kerrykeel and is the main source of fluvial flood risk along with one of its tributaries which emanates from higher ground to the north of the village. The catchment size is approximately 12km2, and is characterised by steep grazing pastures. The modelled extents and HEPs are shown in Figure 4.7 below.
Figure 4.7: Model 7 Catchment Boundaries and HEPs
The model catchment is ungauged however there are a number of gauging stations with flow data available within the neighbouring hydrometric area (39) on the Leannan catchment approximately 8km to the south. There are two stations which were deemed to have data suitable such that they were taken forward for use as pivotal sites within the FSU but both stations are on the heavily attenuated IBE0700Rp0006 34 F03 NW-NB CFRAM Study UoM 01 Hydrology Report – FINAL
Leannan system and just downstream of lakes and as such are not considered suitable for adjustment of the Qmed values estimated based on catchment descriptors. The nearest pivotal site with a fair degree of hydrological similarity is within HA39 at New Mills (39001 – OPW) on the River Swilly. However the adjustment factor at this site is 0.987 and as such suggests that the estimates based on catchment descriptors may be accurate within HA39 for a similar type catchment. As such the FSU ungauged catchment estimates have not been adjusted based on a pivotal site. The estimated Qmed values for the various HEPs within Model 7 are shown in Table 4.7.
Table 4.7: Qmed Values for Model 7
2 3 Preferred Estimation Node ID_CFRAMS AREA (km ) Qmed (m /s) Methodology
38_2247_1 9.859 7.41 FSU (unadjusted)
38_3389_1_RPS 1.011 0.92 FSU (unadjusted)
38_3389_2_RPS 1.305 1.12 FSU (unadjusted)
38_2210_D 12.270 8.82 FSU (unadjusted) Note: Flow highlighted in yellow represent total flows at that point in the model rather than input flows
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4.8 MODEL 8 – BUNCRANA
The town of Buncrana is located nearly 20km within the Lough Swilly estuary. It is affected by a number of watercourse systems. The model catchment and HEPs are shown in Figure 4.8.
Figure 4.8: Model 8 Catchment Boundaries and HEPs
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The largest watercourse affecting the AFA is the Crana River which emanates to the east of the town within the interior of the Inishowen Peninsula. This boggy catchment is quite large at approximately 100km2 and contains a dam and water abstraction reservoir in the upland portion. The Mill River catchment (44km2) is located to the south of the Crana catchment and has similar geographical characteristics with high levels of bog and significant forest coverage in the upper catchment. There are also two further minor watercourses which emanate from just outside the AFA boundary.
There is one gauging station, Tullyarvan (39003 – OPW), located within the modelled reaches on the Crana River within the AFA extents. Although a long record of flow data exists this station was not classified as being suitable for FSU although it was given a C classification suggesting the rating was 3 possible for extrapolation up to Qmed. The Qmed value from 37 years of data is 69.94 m /s which compares well to the estimate derived using the catchment descriptor based equation of 75.06 m3/s. A rating review undertaken at this station (see Section 3.2 and Appendix B) resulted in a lower Qmed value of 59.87 m3/s however there can be little confidence in this value as survey resolution was poor and good calibration to spot flow gaugings could not be achieved. In light of the degree of uncertainty in the gauged value and as it compares well but is slightly lower than the FSU catchment descriptor based estimates it is considered prudent to use the unadjusted estimates for design flow estimation.
The estimated Qmed values for the various HEPs within Model 8 are shown in Table 4.8.
Table 4.8: Qmed Values for Model 8
2 3 Preferred Estimation Node ID_CFRAMS AREA (km ) Qmed (m /s) Methodology
39_753_2 6.47 5.78 FSU (unadjusted)
39_386_2 87.36 69.72 FSU (unadjusted)
39_753_4 6.77 6.14 FSU (unadjusted)
39_571_1 97.30 74.34 FSU (unadjusted)
39003 97.87 75.06 FSU (unadjusted)
39_2542_D 98.71 75.12 FSU (unadjusted)
39_1122_U 0.05 0.07 FSU (unadjusted)
39_1122_6_RPS 3.06 2.66 FSU (unadjusted)
39_376_1_RPS 41.12 29.80 FSU (unadjusted)
39_1126_1_RPS 1.05 1.05 FSU (unadjusted)
39_1126_2_RPS 1.33 1.34 FSU (unadjusted)
39_1126_3_RPS 1.41 1.45 FSU (unadjusted)
39_2555_1_RPS 43.55 31.95 FSU (unadjusted)
39_2555_2_RPS 43.80 32.09 FSU (unadjusted)
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2 3 Preferred Estimation Node ID_CFRAMS AREA (km ) Qmed (m /s) Methodology
39002_RPS 44.18 32.32 FSU (unadjusted)
39_2556_D 44.34 33.05 FSU (unadjusted)
39_150_1_RPS 0.33 0.13 FSU (unadjusted)
39_152_2_RPS 1.52 0.58 FSU (unadjusted) Note: Flow highlighted in yellow represent total flows at that point in the model rather than input flows
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4.9 MODEL 9 – RATHMULLAN
Rathmullan village is located within the Lough Swilly estuary on the opposite side to Buncrana. Fluvial flood risk emanates from the Millbrook watercourse which flows through the southern tip of the AFA extents. This small catchment (3.4km2) is fairly steep and the watercourse channel appears to split as it approaches the Lough. The contributing catchments and HEPs are shown in Figure 4.9.
Figure 4.9: Model 9 Catchment Boundaries and HEPs
The model catchment is ungauged however there are a number of gauging stations with flow data available within the hydrometric area (39) although none can be considered to have a high degree of hydrological similarity. There are three pivotal sites located within HA39 but all represent the much larger catchments of the Swilly and the Leannan with low degrees of hydrological similarity. A review of the closest geographically and the most hydrologically similar pivotal sites did not indicate a clear trend towards over or under estimation and as such the FSU ungauged catchment estimates have not been adjusted based on a pivotal site. The estimated Qmed values for the various HEPs within Model 9 are shown in Table 4.9.
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Table 4.9: Qmed Values for Model 9
2 3 Preferred Estimation Node ID_CFRAMS AREA (km ) Qmed (m /s) Methodology
39_927_1 2.68 1.30 FSU (unadjusted)
39_927_2 3.18 1.66 FSU (unadjusted)
39_1000_D 3.27 1.78 FSU (unadjusted)
39_927_3 0.13 0.15 FSU (unadjusted) Note: Flow highlighted in yellow represent total flows at that point in the model rather than input flows
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4.10 MODEL 10 – BURNFOOT
The Burnfoot model encompasses the lower reaches of the Skeoge and Burnfoot Rivers where they pass through the village of Burnfoot. The rivers confluence downstream of the AFA extents before discharging to Lough Swilly to the rear of Inch Island. The modelled reaches are relatively flat, although there are some steep upland sections to both catchments, with the channels of both rivers canalised downstream of the AFA extents. The overall catchment is 75% pasture. The contributing catchments and HEPs are shown in Figure 4.10.
Figure 4.10: Model 10 Catchment Boundaries and HEPs
The model catchment is ungauged however there are a number of gauging stations with flow data available within the hydrometric area (39) although none can be considered to have a high degree of hydrological similarity. The most hydrologically similar pivotal site nationally is at Sandy Mills (01041 – OPW) on the Deele, a tributary of the Foyle located approximately 25km to the south (this is also the 2nd closest site geographically). As well as being hydrologically similar the Sandy Mills gauging station
IBE0700Rp0006 41 F03 NW-NB CFRAM Study UoM 01 Hydrology Report – FINAL represents a catchment which is arterially drained in its lower reaches as are the Skeoge and Burnfoot Rivers.
A review of the most hydrologically similar pivotal sites suggests the FSU equation may be underestimating the Qmed for this type of catchment. The use of the adjustment factor based on the Sandy Mills pivotal site alone would lead to a very high adjustment factor outside the confidence 68th percentile confidence limits of the equation based estimates and significantly higher than the average of the seven most hydrologically similar pivotal sites. In light of this all of the Qmed estimates have been adjusted upwards by a factor of 1.25 using a combined adjustment factor from the 2nd closest and most hydrologically similar site, Sandy Mills (01041) and moderated based on the New Mills (39001) site which is also close to the subject catchment. This adjustment factor was tested against the sub- catchments and found to be appropriate and as such was used across the model for consistency. The estimated Qmed values for the various HEPs within Model 10 are shown in Table 4.10.
Table 4.10: Qmed Values for Model 10
2 3 Preferred Estimation Node ID_CFRAMS AREA (km ) Qmed (m /s) Methodology
39016_RPS 27.20 25.32 FSU (Adjusted - 1041 & 39001)
39_480_1 19.46 14.91 FSU (Adjusted - 1041 & 39001)
39015 21.04 15.97 FSU (Adjusted - 1041 & 39001)
39_1105_6 22.60 17.21 FSU (Adjusted - 1041 & 39001)
39_1082_4 5.61 4.36 FSU (Adjusted - 1041 & 39001)
39_1162_2_RPS 65.85 40.26 FSU (Adjusted - 1041 & 39001) Note: Flow highlighted in yellow represent total flows at that point in the model rather than input flows
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4.11 MODEL 11 – BRIDGE END
The Bridge End model represents the upper reaches of the Skeoge River. The catchment emanates in Northern Ireland on the western outskirts of Derry City. Model 11 runs from the border through the village of Bridge End where it meets model number 10 (Burnfoot). The catchment is moderately steep and is largely pasture (>80%) with some urban extents and bog land. The model catchment and HEPs are shown in Figure 4.11.
Figure 4.11: Model 11 Catchment Boundaries and HEPs
The model catchment is ungauged however there are a number of gauging stations with flow data available within the hydrometric area (39) although none can be considered to have a high degree of hydrological similarity. A review of the closest pivotal sites indicates that the catchment descriptor based equation overestimates Qmed in the hydrometric areas which make up Donegal. However many of these catchments feature heavy attenuation due to reservoirs and lakes which is not reflective of the
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Skeoge catchment and when these catchments are removed the nearest pivotal sites indicate slight underestimation. A review of the most hydrologically similar pivotal sites also indicates slight underestimation. The Sandy Mills station (01041) is also one of the most hydrologically similar and also the closest pivotal site and an adjustment factor based on this station would lead to heavy upwards adjustment. The ungauged catchment descriptor based estimates have therefore been adjusted based on the hydrologically and geographically similar catchments at Sandy Mills (01041) and New Mills (39001) to achieve an upwards adjustment factor of 1.25 consistent with the most similar pivotal sites and to provide consistency with model 10. The estimated index flood flow values
(Qmed) are shown in Table 4.11.
Table 4.11: Qmed Values for Model 11
2 3 Preferred Estimation Node ID_CFRAMS AREA (km ) Qmed (m /s) Methodology
39_2174a_U 13.15 13.73 FSU (Adjusted - 1041 & 39001)
39_2088_9_RPS 4.89 2.89 FSU (Adjusted – 1041 & 39001)
39_2176_4 5.99 4.01 FSU (Adjusted - 1041 & 39001)
39_2176_6_RPS 7.29 4.79 FSU (Adjusted - 1041 & 39001)
39016_RPS 27.20 25.32 FSU (Adjusted - 1041 & 39001) Note: Flow highlighted in yellow represent total flows at that point in the model rather than input flows
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4.12 MODEL 12 – RAMELTON
The Ramelton AFA is located on the mouth of the River Leannan to the north of Letterkenny in Co. Donegal. The Leannan is a mid to large sized (262km2) catchment which stretches from the interior of Donegal in Glenveagh National Park, through Gartan Lough and Lough Fern before discharging to Lough Swilly. The catchment ranges from boggy uplands to pastures in the lower reaches and there is a fair degree of flow attenuation provided by the online lakes. The Ramelton AFA is also affected by a smaller tributary watercourse emanating from the south of the town. There is a fair amount of forested area within the greater Leannan catchment (12%) and the tributary sub-catchment (17%). The modelled watercourses are shown in Figure 4.12.
Figure 4.12: Model 12 Catchment Boundaries and HEPs
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The modelled extents are ungauged however there are two gauging stations upstream of Ramelton on the Leannan which have been deemed suitable for use as pivotal sites within FSU. The farthest upstream is Gartan Bridge (39008 – OPW) located just downstream of Lough Gartan and has an adjustment factor of 0.93. Aghawoney (39009) is the nearest upstream gauging station and is located just downstream of Lough Fern approximately 8km upstream of the modelled extents. This gauging station has an adjustment factor of 0.68. The fact that both gauging stations on the Leannan have adjustment factors less than 1 suggests that the FSU ungauged catchment descriptor model is over predicting Qmed values on the Leannan and adjustment downwards is appropriate. Aghawoney is the most directly applicable station to the model and has an adjustment factor of 0.68 and as such the adjustment factor from this site has been applied to the flows on the main channel of the River Leannan. In addition to the FSU pivotal sites is the Claragh gauging station (39006 – EPA) located approximately 2.5km upstream of the model extents. This station was not rated under FSU and no information is available from EPA relating to confidence in the rating. However spot gaugings are available up to Qmed and it would appear there is confidence in the rating at the extracted Qmed value of
44.7 m3/s for the AMAX period of 2001 – 2011. Use of this Qmed value would result in an adjustment factor of approximately 0.5. This is an even larger adjustment than would be derived from the FSU site and considering there is still some uncertainty in the rating it is not considered appropriate to apply such a large adjustment over and above the already heavy adjustment based on the Aghawoney FSU pivotal site located further upstream. Estimates of Qmed on the smaller tributary have not been adjusted as the Leannan pivotal sites are not hydrologically similar (they represent an attenuated catchment ten times in size) and a review of other hydrologically and geographically similar sites did not reveal a clear relationship in the gauged and catchment descriptor based Qmed values. The Qmed estimates for model 12 are shown in Table 4.12.
Table 4.12: Qmed Values for Model 12
2 3 Preferred Estimation Node ID_CFRAMS AREA (km ) Qmed (m /s) Methodology
39_951_3 253.76 64.64 FSU (Adjusted - 39009)
39005 255.19 65.07 FSU (Adjusted - 39009)
39_1106_2_RPS 1.74 0.99 FSU (Unadjusted)
39_1106_5_RPS 2.55 1.53 FSU (Unadjusted)
39_1591_D 262.52 66.65 FSU (Adjusted - 39009) Note: Flow highlighted in yellow represent total flows at that point in the model rather than input flows
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4.13 MODEL 13 – NEWTOWN CUNNINGHAM
The Newtown Cunningham AFA is affected by a complex drainage network made up of a number of streams and rivers collecting in a large canalised set of drains downstream of the N13 before discharging to Lough Swilly. The catchment is referred to as the Blanket Nook catchment. The main risk to the AFA of fluvial flooding has been identified as emanating from the main spine of this drainage system and from the Monfad Stream to where it crosses under the N13 along the western side of the village. The Blanket Nook catchment is fairly flat with over 90% of the catchment area made up of pasture. The lower section of the modelled watercourse has been subject to arterial drainage through the Blanket Nook Embankment Scheme. The catchment and HEPs are shown in Figure 4.13.
Figure 4.13: Model 13 Catchment Boundaries and HEPs
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The model catchment is ungauged however there are a number of gauging stations with flow data available within the hydrometric area (39) although none can be considered to have a high degree of hydrological similarity. A review of the most hydrologically similar pivotal sites nationally found there to be no clear pattern suggesting that the estimates based on ungauged catchment descriptors for catchments such as the Blanket Nook catchment were over or under estimated and as such the estimates of Qmed have not been adjusted. The Qmed values are shown in Table 4.13.
Table 4.13: Qmed Values for Model 13
2 3 Preferred Estimation Node ID_CFRAMS AREA (km ) Qmed (m /s) Methodology
39_2409_1 13.95 4.05 FSU (Unadjusted)
39013 14.56 4.12 FSU (Unadjusted)
39_2081_3 9.88 2.81 FSU (Unadjusted)
39_2252_3 31.75 8.28 FSU (Unadjusted) Note: Flow highlighted in yellow represent total flows at that point in the model rather than input flows
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Preferred Estimation Node ID_CFRAMS AREA (km2) Qmed (m3/s) Methodology
4.14 MODEL 14 – LETTERKENNY
The Letterkenny AFA is located at the top of Lough Swilly and is made up of the lower reaches of the River Swilly and a number of tributaries that flow into River / Lough Swilly through the Letterkenny AFA including the Sprack and Coravaddy Burns and the Knocknamona watercourse. The Swilly River catchment is fairly mixed in land coverage with forested land (23%), pasture (38%), peat bog (35%) and urban area (4%) due to Letterkenny. The modelled tributaries which enter the Swilly emanate from the hills surrounding Letterkenny to the north and south and some pick up a significant amount of urban drainage along the way to their discharge points into the Swilly.
The extents of model 14 have been extended such as to include the New Mills gauging station (39001 - OPW) on the River Swilly upstream of Letterkenny. This station was considered as a pivotal site under FSU and as such there is some confidence in the Qmed value extracted for the period from 1973 to 1990. A rating review undertaken at this station (see Section 3.2 and Appendix B) resulted in a lower Qmed value for the period of data since 1990 however there were no high flow spot flow gaugings upon which to calibrate the rating review model and as such confidence in the value derived from the rating review is low. As such it is appropriate that the higher FSU value is taken forward as the basis for design flow estimation at the gauging station. The gauged Qmed / estimated Qmed from physical catchment descriptors ratio is 0.924 suggesting the FSU catchment descriptor equation slightly overestimates Qmed along the main channel of the Swilly. The catchments of the tributaries which flow into the Swilly were also considered against the FSU list of sites to see if any pattern exists that suggested that geographically or hydrologically similar sites were under or overestimated using the
FSU ungauged catchment descriptor equation. No such pattern was found and as such the Qmed estimates for these watercourses are unadjusted. The modelled catchments and HEPs are shown in Figure 4.14 and the Qmed estimates shown in
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39001 50.71 47.80 Gauged Qmed
39_1398_1_RPS 75.11 60.09 FSU (Adjusted - 39001)
39_1296_1 3.35 3.28 FSU (Unadjusted)
39_2433_2 6.34 6.80 FSU (Unadjusted)
39_2433_5_RPS 7.12 7.38 FSU (Unadjusted)
39_2375_RPS 0.51 0.52 FSU (Unadjusted)
39_1406_1 1.25 1.03 FSU (Unadjusted)
39_1563_4_RPS 2.68 2.27 FSU (Unadjusted)
39_2317_U 1.08 1.07 FSU (Unadjusted)
39_2323_5 3.59 6.15 FSU (Unadjusted)
39061_RPS 96.66 71.86 FSU (Adjusted - 39001)
39_800_2 7.44 5.56 FSU (Unadjusted)
39_2152_2 3.76 3.22 FSU (Unadjusted)
39_2153_2 5.06 4.20 FSU (Unadjusted)
39_2468_3 13.81 13.75 FSU (Unadjusted)
39_304_U 0.82 1.45 FSU (Unadjusted)
39_2513_U 0.11 0.16 FSU (Unadjusted)
39_2513_1 0.65 0.75 FSU (Adjusted - 39001)
39_858_1_RPS 0.73 1.03 FSU (Unadjusted)
39_2551_2_RPS 4.59 2.90 FSU (Adjusted - 39001)
39_1507_U 0.03 0.02 FSU (Unadjusted)
39_1507_2 1.05 0.71 FSU (Unadjusted)
39_1004_D_RPS 120.83 88.58 FSU (Adjusted - 39001)
39_891_U 0.06 0.07 FSU (Unadjusted)
39_993_2 2.32 2.13 FSU (Unadjusted)
39_2505_3 8.88 6.58 FSU (Unadjusted) Table 4.14.
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Figure 4.14: Model 14 Catchment Boundaries and HEPs
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Table 4.14: Qmed Values for Model 14
2 3 Preferred Estimation Node ID_CFRAMS AREA (km ) Qmed (m /s) Methodology
39001 50.71 47.80 Gauged Qmed
39_1398_1_RPS 75.11 60.09 FSU (Adjusted - 39001)
39_1296_1 3.35 3.28 FSU (Unadjusted)
39_2433_2 6.34 6.80 FSU (Unadjusted)
39_2433_5_RPS 7.12 7.38 FSU (Unadjusted)
39_2375_RPS 0.51 0.52 FSU (Unadjusted)
39_1406_1 1.25 1.03 FSU (Unadjusted)
39_1563_4_RPS 2.68 2.27 FSU (Unadjusted)
39_2317_U 1.08 1.07 FSU (Unadjusted)
39_2323_5 3.59 6.15 FSU (Unadjusted)
39061_RPS 96.66 71.86 FSU (Adjusted - 39001)
39_800_2 7.44 5.56 FSU (Unadjusted)
39_2152_2 3.76 3.22 FSU (Unadjusted)
39_2153_2 5.06 4.20 FSU (Unadjusted)
39_2468_3 13.81 13.75 FSU (Unadjusted)
39_304_U 0.82 1.45 FSU (Unadjusted)
39_2513_U 0.11 0.16 FSU (Unadjusted)
39_2513_1 0.65 0.75 FSU (Adjusted - 39001)
39_858_1_RPS 0.73 1.03 FSU (Unadjusted)
39_2551_2_RPS 4.59 2.90 FSU (Adjusted - 39001)
39_1507_U 0.03 0.02 FSU (Unadjusted)
39_1507_2 1.05 0.71 FSU (Unadjusted)
39_1004_D_RPS 120.83 88.58 FSU (Adjusted - 39001)
39_891_U 0.06 0.07 FSU (Unadjusted)
39_993_2 2.32 2.13 FSU (Unadjusted)
39_2505_3 8.88 6.58 FSU (Unadjusted) Note: Flow highlighted in yellow represent total flows at that point in the model rather than input flows
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4.15 MODEL 15 – BUNBEG - DERRYBEG
The Bunbeg – Derrybeg model represents the watercourses affecting both villages in the Gweedore area of North West Donegal. Two watercourse systems have been identified as requiring further analysis, the Clady River with a total catchment area of 89km2 and the Catheen River representing a total catchment of 8km2. Both catchments are fairly steep and both are predominantly peat (>75%). The Clady River catchment however is heavily attenuated through Loughs Nacung (Upper and Lower) and Dunlewy with the control structure being the ESB owned and operated dam less than 2km upstream of the model extents. This dam is part of a system that diverts water to the south through a diversion channel where it then passes through a hydro-electric electricity generation station which discharges to the Gweedore River to the south of the AFA at Dore. The catchment area and HEPs are shown in Figure 4.15 below.
Figure 4.15: Model 15 Catchment Boundaries and HEPs
There are no gauging stations available within the modelled extents of the Clady or Catheen Rivers however there is some flow information available at the ESB dam control upstream of the modelled
IBE0700Rp0006 53 F03 NW-NB CFRAM Study UoM 01 Hydrology Report - FINAL extents on the Clady River (38002 – ESB). This information is presented in the form of monthly and yearly maximum, minimum and average outflows from Lough Nacung. It is not clear whether this data includes flows through the power generation facility or whether these flows are instantaneous or averaged over time. The data does not come with any quality indicators although as it is likely to be derived from measurements through hard engineered structures it is thought to be of high certainty. RPS has requested additional data from ESB such that the quality of the data can be verified. 3 Nevertheless the data indicates a Qmed outflow of 18.5 m /s from the annual maxima data. The equivalent FSU estimate based on catchment descriptors is 30 m3/s which includes a FARL (Flood Attenuation by Reservoirs and Lakes) factor of 0.753. This suggests that even with the FARL factor the FSU equation is overestimating the flow and not capturing fully the attenuating affect of the ESB dam / hydro station. Notwithstanding this, little is known about the data and as such the flow estimates are not adjusted downwards until such times as further data is made available by ESB such that this can be verified. The Catheen catchment was considered against the national list of pivotal sites but none was found to have a high degree of hydrological similarity. No pattern was observed from sites listed as the most geographically and hydrologically similar to suggest that the catchment descriptor equation was over or underestimating for the Catheen catchment. Estimates of Qmed are shown in Table 4.15.
Table 4.15: Qmed Values for Model 15
2 3 Preferred Estimation Node ID_CFRAMS AREA (km ) Qmed (m /s) Methodology
38_685_1_RPS 0.03 0.03 FSU (Unadjusted)
38_2911_U 0.40 0.56 FSU (Unadjusted)
38_2911_1 0.73 0.99 FSU (Unadjusted)
38_2585_1 2.02 2.56 FSU (Unadjusted)
38_2587_U 0.13 0.19 FSU (Unadjusted)
38_2587_1 0.16 0.25 FSU (Unadjusted)
38_4132_3 3.76 4.32 FSU (Unadjusted)
38_4130_D 7.81 5.91 FSU (Unadjusted)
38_687_1 84.93 32.31 FSU (Unadjusted)
38_3999_1 87.28 32.31* FSU (Unadjusted)
38_4124_2 88.96 32.31* FSU (Unadjusted) Note: Flow highlighted in yellow represent total flows at that point in the model rather than input * Flow at node was initially estimated to be lower than the estimate upstream. This flow has been held at the higher value from upstream as there are no obvious attenuating features. To be checked through hydraulic model.
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4.16 MODEL 16 – DUNGLOE
The Dungloe model represents the reach of the Dungloe River flowing out of Dungloe Lough and into the sea. The Dungloe River catchment is a medium sized catchment (40km2), which is characterised by a high level of attenuation with a number of on-line Loughs along the length of the river. The river channel itself is fairly flat along its length. The catchment area is over 85% peat coverage. The catchment area and HEPs are shown in Figure 4.16 below.
Figure 4.16: Model 16 Catchment Boundaries and HEPs
There are no gauging stations available within the modelled extents of the Dungloe River catchment which have continuous flow data available (the site 38006 in the centre of town is a staff gauge only site). The nearest gauging station with flow data available is at Lough Anure (38071 – EPA) to the north of the catchment. The Lough Anure site is quite hydrologically similar being similar in size and heavily attenuated but the flow data which is available was not deemed suitable for use as a pivotal site under FSU. Furthermore it is derived from a lake level to lake outflow relationship and no quality data exists regarding the rating. For these reasons it is not considered prudent to use the data for
IBE0700Rp0006 55 F03 NW-NB CFRAM Study UoM 01 Hydrology Report - FINAL pivotal site adjustment. The affect of attenuation appears to be well captured in the FSU catchment descriptors (FARL value of 0.624) and the two most hydrologically similar FSU pivotal sites suggest that the ungauged catchment descriptor equation captures the Qmed accurately with adjustment factors for sites 31002 and 39008 of 1.00 and 0.93 respectively. As such the Qmed values derived from ungauged catchment descriptor based estimates have not been adjusted and are shown in Table 4.16.
Table 4.16: Qmed Values for Model 16
2 3 Preferred Estimation Node ID_CFRAMS AREA (km ) Qmed (m /s) Methodology
38_1154_1 37.69 5.88 FSU (Unadjusted)
38006 39.30 6.22 FSU (Unadjusted)
38_1155_3 39.60 6.32 FSU (Unadjusted)
Note: Flow highlighted in yellow represent total flows at that point in the model rather than input flows
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4.17 MODEL 17 – GLENTIES
The Glenties model represents the lower reaches of the Owenea River and its tributaries where they flow through the village of Glenties in the west of Donegal. The main Owenea River passes the village to the south but the Stracashel River and the Gortnamucklagh watercourse flow through the AFA extents joining the Owenea to the south-west of the village. The Owenea flows into an estuary upstream of Loughros More Bay (Atlantic) approximately 10km to the west of Glenties. The Owenea catchment is a medium sized catchment (126km2) with a fair mix of forest (23%), pasture (15%) and peat (37%) coverage. The Stracashel catchment (49km2) has a similar land coverage mix whereas the smaller Gortnamucklagh watercourse is a mixture of pasture (46%) and peat (44%) coverage. The main river channels are fairly flat (S1085 less than 10) whereas the Gortnamucklagh watercourse is steeper (S1085 of 23.98). The HEPs and catchment boundaries are shown in Figure 4.17 overleaf.
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Figure 4.17: Model 17 Catchment Boundaries and HEPs
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The Glenties model is gauged approximately 6km downstream of the AFA extents on the Owenea River. The Clonconwal Ford gauging station (38001 – OPW) was given a B rating classification under
FSU meaning there is confidence in the flows up to around Qmed and the rating review did not indicate that there was significant uncertainty in the existing Qmed value. The adjustment factor at the gauging station, the ratio of the gauged Qmed to the Qmed from catchment descriptors, is 0.80 suggesting the catchment descriptor equation overestimates the value of Qmed in the Owenea catchment. In light of this ungauged catchment descriptor based estimates have been reduced by 20% on the Owenea and Stracashel Rivers. Ungauged catchment descriptor based estimates on the smaller Gortnamucklagh watercourse have not been adjusted. Estimates of Qmed are shown in Table 4.17.
Table 4.17: Qmed Values for Model 17
2 3 Preferred Estimation Node ID_CFRAMS AREA (km ) Qmed (m /s) Methodology
38_2761_2 41.04 33.46 FSU (Adjusted – 38001)
38010 42.33 34.54 FSU (Adjusted – 38001)
38_3860_Inter_1 42.39 34.35 FSU (Adjusted – 38001)
38_3860_Inter_2 42.51 34.44 FSU (Adjusted – 38001)
38_3822_4_RPS 49.25 39.53 FSU (Adjusted – 38001)
38_3833_1_RPS 0.11 0.17 FSU (Unadjusted)
38_23_1 1.32 1.53 FSU (Unadjusted)
38_414_4 2.46 3.08 FSU (Unadjusted)
38_442_4 102.59 69.12 FSU (Adjusted – 38001)
38001 111.25 70.14 G.S. Observed
38_2332_4 9.44 2.52 FSU (Adjusted – 38001)
38_1168_3 126.05 74.30 FSU (Adjusted – 38001)
Note: Flow highlighted in yellow represent total flows at that point in the model rather than input flows
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4.18 MODEL 18 – ARDARA
The Ardara model represents the lower reaches of the Owentocker River where it flows through the town of Ardara in west Donegal and discharges into the estuary upstream of Loughros More Bay. The Owentocker River catchment is a small to midsized catchment (43 km2) and is quite flat along the length of the main channel. There is a fairly high amount of peat land coverage in the catchment (54%) with some forest (11%) and pasture (15%) coverage also. The catchment area and HEPs are shown in Figure 4.18 below.
Figure 4.18: Model 18 Catchment Boundaries and HEPs
There are no gauging stations available within the modelled extents of the Owentocker catchment although the Clonconwal Ford gauging station (38001 – OPW) is located on the neighbouring Owenea catchment just to the north of the AFA. This site is the fifth most hydrologically similar FSU pivotal site and use of it for adjustment would mean a reduction in the Qmed values derived from the FSU ungauged catchment descriptor method by 20%. A review of the other hydrologically similar pivotal sites suggests a clear pattern of overestimation for this type of catchment with the average of the seven closest pivotal sites suggesting an adjustment downwards of 14% and the average of the
IBE0700Rp0006 60 F03 NW-NB CFRAM Study UoM 01 Hydrology Report - FINAL seven most hydrologically similar pivotal sites suggesting an adjustment downwards of 7%. The most hydrologically similar pivotal site is at New Mills on the Swilly which is also the third closest site. Use of this site would result in downwards adjustment of 8%. Both the Clonconwal Ford (38001) and New
Mills (39001) pivotal sites present a strong case for use in adjusting the Qmed value and as such a composite adjustment factor has been applied using both stations, resulting in a downwards adjustment of the FSU catchment descriptor based estimates by 14%. Estimates of Qmed are shown in Table 4.18.
Table 4.18: Qmed Values for Model 18
2 3 Preferred Estimation Node ID_CFRAMS AREA (km ) Qmed (m /s) Methodology
38_3814_1 42.05 37.30 FSU (Adjusted 38001 & 39001)
38_3037_3 43.08 37.92 FSU (Adjusted 38001 & 39001)
Note: Flow highlighted in yellow represent total flows at that point in the model rather than input flows
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4.19 MODEL 19 – BALLYBOFEY & STRANORLAR
The Ballybofey and Stranorlar AFA represents the middle reaches of the River Finn and its adjoining tributaries where they pass through the neighbouring villages of Ballybofey & Stranorlar in the east of Donegal. The River Finn is one of the major tributaries of the greater Foyle catchment (HA 01) and emanates from the Bluestack and Glendowan Mountains in the interior of Donegal. The Finn catchment to the downstream HEP of the model is a medium to large sized catchment (384km2) with a mixture of peat (43%), pasture (26%) and forest (24%) coverage. The AFA is also affected by a number of tributaries of the Finn ranging in size from 2km2 to 26km2. The largest of these is the Daurnett Burn which flows from the south west of the AFA. The Daurnett Burn represents a more upland catchment with a fair degree of peat land coverage (24%). Among the smallest tributaries considered is a watercourse at the eastern edge of the AFA which flows from north to south through the townland of Corcam and under the N15 before discharging to the Finn (01_1577_2_RA). This catchment is largely farmland (72%) and is typical of the many tributary drainage channels that drain the slopes of the Finn Valley. The catchment area and HEPs are shown in Figure 4.19 below.
Figure 4.19: Model 19 Catchment Boundaries and HEPs
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There are two gauging stations on the modelled reaches of the River Finn with data available. These stations are located in close proximity to one another approximately 2.5km apart. The upstream station is named Ballybofey (01043 – OPW) and has data available from 1992 onwards. Although a rating has been developed for this station no flow data was made available. The station was given a C rating classification under FSU indicating that there is no confidence in the rating at Qmed. The Dreenan gauging station (01042 – OPW) located downstream of Ballybofey has flow data available from 1973 – 2003. This station was also given a C rating classification under FSU. The review of the stations under FSU work package 2.1 extracted Qmed values using the available ratings of 778.0 and 490.5m3/s for the Dreenan and Ballybofey stations respectively. These values are neither in 3 agreement or close to the Qmed values derived from catchment descriptors of 270 and 256m /s respectively. Both stations were subject to rating review under the NW – NB CFRAM Study and following rating review observed Qmed values were processed from existing water level data resulting 3 3 in Qmed values of 275.2m /s for the Dreenan gauging station (01042) and 257.9m /s for the Ballybofey gauging station (01043) although there is reduced confidence in the Dreenan figure since it is only based on data collected since 2011 and as such is limited in terms of quantity and statistical confidence. These observed Qmed values are in good agreement and are very close to the values derived from physical catchment descriptors and as such can considered to have sufficient confidence for use in design flow estimation. The value from the Ballybofey station will be taken forward as a pivotal site for index flood flow adjustment for the flows along the main channel of the River Finn.
In relation to the tributary catchments examination of hydrologically and geographically similar pivotal sites did not suggest a clear pattern that the FSU equation was under or over predicting Qmed for similar catchments. Estimates of Qmed are shown in Table 4.19.
Table 4.19: Qmed Values for Model 19
2 3 Preferred Estimation Node ID_CFRAMS AREA (km ) Qmed (m /s) Methodology
01_810_2_RA 309.97 257.90 FSU (Adjusted – 01043)
01043_RA 314.12 257.90 Observed (Gauging Station)
01_186_2_RA 4.63 3.21 FSU (Unadjusted)
01_543_U 0.08 0.06 FSU (Unadjusted)
01_543_2_RA 1.16 0.82 FSU (Unadjusted)
01_542_Inter_RA 1.61 1.09 FSU (Unadjusted)
01_542_1_RA 1.96 1.25 FSU (Unadjusted)
01_551_2_RA 8.67 7.23 FSU (Unadjusted)
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2 3 Preferred Estimation Node ID_CFRAMS AREA (km ) Qmed (m /s) Methodology
01_1815_2_RA 8.93 8.01 FSU (Unadjusted)
01_223_1_RARPS 1.51 1.28 FSU (Unadjusted)
01_1825_3_RA 3.46 3.25 FSU (Unadjusted)
01_41_6_RA 3.49 0.94 FSU (Unadjusted)
01_41_9_RA 4.47 1.32 FSU (Unadjusted)
01044_RARPS 22.38 15.07 FSU (Unadjusted)
01_10000_U_RA 1.76 1.52 FSU (Unadjusted)
01_10000_RARPS 2.38 2.06 FSU (Unadjusted)
01_814_4_RA 25.55 16.08 FSU (Unadjusted)
01042_RA 350.37 273.88 FSU (Adjusted – 01043)
01_69_2_RA 4.84 2.34 FSU (Unadjusted)
01_776_3_RA 5.90 3.17 FSU (Unadjusted)
01_416_2_RA 1.23 0.88 FSU (Unadjusted)
01_1577_2_RA 2.22 1.45 FSU (Unadjusted)
01_778_7_RA 7.37 3.76 FSU (Unadjusted)
01_614_3_RA 383.52 273.88* FSU (Adjusted – 01043)
Note: Flow highlighted in yellow represent total flows at that point in the model rather than input flows
* Flow at node was initially estimated to be lower than the estimate upstream. This flow has been held at the higher value from upstream as there are no obvious attenuating features. To be checked through hydraulic model.
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4.20 MODEL 20 – KILLYGORDON
The Killygordon model represents the middle to lower reaches of the River Finn just downstream of the Ballybofey & Stranorlar model where the River Finn passes through the village of Killygordon. The Finn catchment to the downstream HEP of this model is a medium to large sized catchment (437km2) with a mixture of peat (38%), pasture (33%) and forest (23%) coverage. The AFA is also affected by a number of tributaries of the Finn ranging in size from 2km2 to 12km2. The tributaries emanate from farmland within the Finn Valley and generally represent land with a high coverage of pasture with some forested area. The catchment area and HEPs are shown in Figure 4.20 below.
Figure 4.20: Model 20 Catchment Boundaries and HEPs
As discussed in Section 4.19 there are two gauging stations upstream of the modelled reaches on the River Finn with data available. Neither of the stations (01042 & 01043) have confidence in the rating at Qmed and the values vary greatly from estimates based on catchment descriptors. Both stations
IBE0700Rp0006 65 F03 NW-NB CFRAM Study UoM 01 Hydrology Report - FINAL were subject to rating review under the NW – NB CFRAM Study and following rating review there can be considered to be confidence in the observed Qmed value at the Ballybofey station (01043) as discussed in Section 4.19. In light of this the Ballybofey station will be taken forward as a pivotal site for index flood flow adjustment for the flows along the main channel of the River Finn.
In relation to the tributary catchments examination of hydrologically and geographically similar pivotal sites did not suggest a clear pattern that the FSU equation was under or over predicting Qmed for similar catchments. Estimates of Qmed are shown in Table 4.20.
Table 4.20: Qmed Values for Model 20
2 3 Preferred Estimation Node ID_CFRAMS AREA (km ) Qmed (m /s) Methodology
01_614_3_RA 383.52 273.88* FSU (Adjusted – 01043)
01_614_Intr1_RPS 384.05 273.88* FSU (Adjusted – 01043)
01_613_1_RA 2.34 1.45 FSU (Unadjusted)
01_613_3_RA 2.79 1.54 FSU (Unadjusted)
01_615_2_RA 387.14 273.88* FSU (Adjusted – 01043)
01_1293_U 1.00 0.47 FSU (Unadjusted)
01_1293_Inter1_RA 1.64 0.65 FSU (Unadjusted)
01_1293_3_RA 1.71 0.68 FSU (Unadjusted)
01_1307_2_RA 11.28 3.88 FSU (Unadjusted)
01045_RA 11.57 4.02 FSU (Unadjusted)
01_1307_Inter1_RA 11.70 4.07 FSU (Unadjusted)
01_1307_6_RA 11.97 4.18 FSU (Unadjusted)
01_1788_8_RA 9.75 4.14 FSU (Unadjusted)
01_885_RARPS 436.80 273.88* FSU (Adjusted – 01043)
Note: Flow highlighted in yellow represent total flows at that point in the model rather than input flows
* Flow at node was initially estimated to be lower than the estimate upstream. This flow has been held at the higher value from upstream as there are no obvious attenuating features. To be checked through hydraulic model.
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4.21 MODEL 21 – CASTLEFINN
The Castlefinn model represents the lower reaches of the River Finn and also a tributary called the Castlefinn watercourse flowing through the town from the north. The Finn catchment to the downstream HEP of the model represents 494km2 and at the downstream HEP the modelled reaches are just within the tidally influenced portion of the Foyle / Mourne / Finn system. The catchment to this point is a mix of peat (35%), pasture (37%) and forest (22%) coverage. The Castlefinn watercourse represents a small catchment (4km2) which is nearly entirely pasture (97%). The catchment area and HEPs are shown in Figure 4.21 below.
Figure 4.21: Model 21 Catchment Boundaries and HEPs
As discussed in Section 4.19 there are two gauging stations upstream of the modelled reaches on the River Finn with data available. Neither of the stations (01042 & 01043) have confidence in the rating at Qmed and the values vary greatly from estimates based on catchment descriptors. Both stations were subject to rating review under the NW – NB CFRAM Study and following rating review there can be considered to be confidence in the observed Qmed value at the Ballybofey station (01043) as
IBE0700Rp0006 67 F03 NW-NB CFRAM Study UoM 01 Hydrology Report - FINAL discussed in Section 4.19. In light of this the Ballybofey station will be taken forward as a pivotal site for index flood flow adjustment for the flows along the main channel of the River Finn.
In relation to the tributary catchments examination of hydrologically and geographically similar pivotal sites did not suggest a clear pattern that the FSU equation was under or over predicting Qmed for similar catchments. Estimates of Qmed are shown in Table 4.21.
Table 4.21: Qmed Values for Model 21
2 3 Preferred Estimation Node ID_CFRAMS AREA (km ) Qmed (m /s) Methodology
01_885_RARPS 436.80 273.88* FSU (Adjusted – 01043)
01_1887_2_RA 8.49 3.82 FSU (Unadjusted)
01_633_4_RA 3.59 0.94 FSU (Unadjusted)
01_633_6_RA 3.95 1.09 FSU (Unadjusted)
01_633_7_RA 4.10 1.12 FSU (Unadjusted)
01_10001_RARPS 0.03 0.01 FSU (Unadjusted)
01_654_4_RA 12.42 4.01 FSU (Unadjusted)
01_724b_1_RA 493.75 273.88* FSU (Adjusted – 01043)
Note: Flow highlighted in yellow represent total flows at that point in the model rather than input flows
* Flow at node was initially estimated to be lower than the estimate upstream. This flow has been held at the higher value from upstream as there are no obvious attenuating features. To be checked through hydraulic model.
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4.22 MODEL 22 – LIFFORD
The Lifford model represents the lower reaches of the River Finn and the confluence point of the Rivers Finn and Mourne and the start of the River Foyle at Lifford / Strabane (the Finn and Foyle mark the border with Northern Ireland). The model represents the total Finn catchment (502km2), the inflow from the River Mourne catchment (1860km2). The total Finn catchment is a mix of peat (35%), pasture (37%) and forest (22%) coverage. The catchment area and HEPs are shown in Figure 4.22 below.
Figure 4.22: Model 22 Catchment Boundaries and HEPs
As discussed in Section 4.19 there are two gauging stations upstream of the modelled reaches on the River Finn with data available. Neither of the stations (01042 & 01043) has confidence in the rating at
Qmed and the values vary greatly from estimates based on catchment descriptors. Both stations were subject to rating review under the NW – NB CFRAM Study and following rating review there can be considered to be confidence in the observed Qmed value at the Ballybofey station (01043) as
IBE0700Rp0006 69 F03 NW-NB CFRAM Study UoM 01 Hydrology Report - FINAL discussed in Section 4.19. In light of this the Ballybofey station will be taken forward as a pivotal site for index flood flow adjustment for the flows along the main channel of the River Finn.
Estimates of the Qmed value from the Mourne catchment have been derived using the Flood Estimation Handbook (FEH). The Mourne catchment descriptors were identified from the Flood
Estimation Handbook CD-ROM 3 and Qmed estimated based on the four variable FEH equation. The flows for the Mourne catchment have been adjusted based on the latest observed Qmed value at the Drumnabuoy House (01010 – Rivers Agency NI) gauging station located just upstream of Strabane. This site is considered to have high confidence in the rating at Qmed and has been designated as a UK Hi-Flows site. AMAX series data is available from 1981 to 2011 and the Qmed value at the station 3 is 598.3 m /s. Estimates of Qmed are shown in Table 4.22.
Table 4.22: Qmed Values for Model 22
2 3 Preferred Estimation Node ID_CFRAMS AREA (km ) Qmed (m /s) Methodology
01_724b_1_RA 493.75 273.88* FSU (Adjusted – 01043)
01_724b_2_RARPS 502.42 273.88* FSU (Adjusted – 01043)
Flood Estimation Handbook 01_1883c_1_RARPS 1861.05 603.72 (FEH)
To be considered though the application of a tidal boundary 01_1883d_D_RA 2363.33 n.a. (tidal) in the hydraulic model.
Note: Flow highlighted in yellow represent total flows at that point in the model rather than input flows
* Flow at node was initially estimated to be lower than the estimate upstream. This flow has been held at the higher value from upstream as there are no obvious attenuating features. To be checked through hydraulic model.
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4.23 MODEL 23 – CONVOY
The Convoy model represents the River Deele catchment, a tributary of the Foyle. The catchment is a medium sized catchment (134km2) originating in the hilly area to the west of the village of Convoy. The catchment is largely agricultural land (68% pastures) with some peat (22%) and forest (14%) land coverage also. The modelled reaches of the Deele are fairly flat (S1085 ranging from 5 to 10). The Tullydonnell Upper watercourse also flows through the AFA extents representing a catchment area of less than 5km2. This catchment is also largely agricultural land (87%) but is fairly steep. The catchment area and HEPs are shown in Figure 4.23 below.
Figure 4.23: Model 23 Catchment Boundaries and HEPs
The Sandy Mills gauging station (01041 – OPW) is located along the modelled reaches of the Deele approximately 10km downstream of the AFA. This station was given a B rating classification under
FSU indicating there is confidence in the rating at Qmed and the rating review did not indicate that there was significant uncertainty in the existing Qmed value. This station was taken forward as a pivotal
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site under FSU and indicates the observed Qmed (derived from the AMAX series) is higher than the
Qmed which is derived from catchment descriptors by a factor of 1.58 at the gauging station.
Considering the confidence in the rating at Qmed and the long period of record (1973 – 2009) it is considered prudent that all of the Qmed values derived from catchment descriptors on this model are adjusted upwards in line with the adjustment factor at the gauging station. Estimates of Qmed are shown in Table 4.23.
Table 4.23: Qmed Values for Model 23
2 3 Preferred Estimation Node ID_CFRAMS AREA (km ) Qmed (m /s) Methodology
01_801_3_RA 81.87 78.86 FSU (Adjusted – 01041)
01_801_Int_1_RPS 82.20 78.86 FSU (Adjusted – 01041)
01_801_Int_2_RPS 83.10 78.92 FSU (Adjusted – 01041)
01046_RA 83.17 78.92 FSU (Adjusted – 01041)
01_1518_1_RA 2.72 1.75 FSU (Adjusted – 01041)
01_1518_4_RA 4.72 2.81 FSU (Adjusted – 01041)
01_1557_3_RA 102.65 81.15 FSU (Adjusted – 01041)
01041_RA 114.29 84.61 G.S. Observed
01048_RA 123.71 86.41 FSU (Adjusted – 01041)
01_1913_2_RA 134.00 88.72 FSU (Adjusted – 01041)
Note: Flow highlighted in yellow represent total flows at that point in the model rather than input flows
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4.24 MODEL 24 – DONEGAL TOWN
The Donegal Town model represents a number of watercourses flowing the through the Donegal Town AFA extents including the River Eske and the Drummenny River. All of the modelled watercourses discharge into Donegal Bay at the western side of the town. The Eske catchment is the largest (116km2) and emanates from the interior of County Donegal in the Bluestack Mountains. The catchment has a mix of land coverage of pasture (33%), peat (32%) and forest (13%). The catchment is heavily attenuated by Lough Eske which lies to the north east of Donegal Town. The other watercourses to be modelled represent catchments ranging in size from 1km2 to 10km2 and are mostly agricultural land (pasture n> 60%). The catchment area and HEPs are shown in Figure 4.24 below.
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Figure 4.24: Model 24 Catchment Boundaries and HEPs
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There are no gauging stations directly on the modelled watercourses with flow data available however there are two gauging station locations upstream of the modelled watercourses on the Eske system. The Eske D/S (37003 – EPA) station is located just downstream of Lough Eske but has been inactive since 1988 and no AMAX series flow data is available. The Lough Eske (37071 – EPA) station is located on Lough Eske towards the downstream end. The station uses a Lough level / outlet flow relationship to provide estimates of flow at the outfall point. Although not a typical rating relationship the rating is reasonably well developed. Spot gaugings and the rating curve suggest there is confidence in the rating up to approximately 2/3 Qmed. The observed Qmed value from the available AMAX series (1976 – 2002) is 30.4 m3/s which is just under 10% lower than the estimate based on 3 catchment descriptors of 33.3 m /s suggesting the Qmed equation may overestimate Qmed just downstream of Lough Eske. Some confidence is gained from the reasonable agreement between the two figures however given that there is still some uncertainty in the Lough Eske gauging station at
Qmed it is prudent that the higher catchment descriptor based estimate is retained for design flow estimation. The catchments representing the two small streams to the south of the AFA are both geographically and hydrologically similar to the FSU pivotal site Mourne Beg Weir (01055 – EPA) which has an adjustment factor of 0.72 based on nine years of data suggesting the FSU equation may be overestimating for this type of catchment. The estimates based on the FSU ungauged catchment descriptors have been retained in line with a precautionary approach. These may be reduced downwards in line with the pivotal site 01055 for the two minor watercourses to the south of the AFA if it is found during calibration that the flows appear overestimated. Estimates of Qmed are shown in Table 4.24.
Table 4.24: Qmed Values for Model 24
2 3 Preferred Estimation Node ID_CFRAMS AREA (km ) Qmed (m /s) Methodology
37_2565_2 3.45 4.32 FSU (Unadjusted)
37_2673_1 2.16 2.12 FSU (Unadjusted)
37_2673_3 2.84 2.57 FSU (Unadjusted)
37_3644_2_RPS 9.62 8.04 FSU (Unadjusted)
37_2262_6 91.10 35.45 FSU (Unadjusted)
37_1301_1 1.72 1.05 FSU (Unadjusted)
37_1302_2 3.09 1.77 FSU (Unadjusted)
37_3590_1 14.70 16.47 FSU (Unadjusted)
37_3590_Int_1 15.01 16.59 FSU (Unadjusted)
37_3590_3 15.10 16.81 FSU (Unadjusted)
37_1727_U 0.44 0.35 FSU (Unadjusted)
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2 3 Preferred Estimation Node ID_CFRAMS AREA (km ) Qmed (m /s) Methodology
37_1727_1_RPS 0.94 0.71 FSU (Unadjusted)
37_3589_2_RPS 16.90 18.45 FSU (Unadjusted)
37_2587_Inter 111.59 38.54 FSU (Unadjusted)
37_2408_2 1.31 0.72 FSU (Unadjusted)
37_2589_2 2.90 1.82 FSU (Unadjusted)
37_2588_2_RPS 115.62 40.04 FSU (Unadjusted)
37_1462_1 2.76 1.35 FSU (Unadjusted)
37_1500_3 4.68 2.56 FSU (Unadjusted)
37_1832_1_RPS 0.02 0.02 FSU (Unadjusted)
37_1832_2 1.31 0.98 FSU (Unadjusted)
Note: Flow highlighted in yellow represent total flows at that point in the model rather than input flows
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4.25 MODEL 25 – KILLYBEGS
The Killybegs model represents the lower reaches of the Cashelcummin River as it passes through the town and discharges into Killybegs Harbour. The River drains a small catchment of 2km2 which is mainly made up of agricultural land (80% pastures) to the north of the town. The main channel of the watercourse is moderately steep. The catchment area and HEPs are shown in Figure 4.25 below.
Figure 4.25: Model 15 Catchment Boundaries and HEPs
There are no gauging stations within the Cashelcummin catchment and the nearest FSU pivotal site is located in hydrometric area 38 approximately 16km to the north of Killybegs. A review of the most similar pivotal sites both geographically and hydrologically did not indicate a pattern of over or
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underestimation of Qmed using the FSU catchment descriptor based method and as such the estimates have not been adjusted. Estimates of Qmed are shown in Table 4.25.
Table 4.25: Qmed Values for Model 25
2 3 Preferred Estimation Node ID_CFRAMS AREA (km ) Qmed (m /s) Methodology
37_2465_1_RPS 1.35 1.79 FSU (Unadjusted)
37_1289_2_RPS 1.98 2.88 FSU (Unadjusted)
Note: Flow highlighted in yellow represent total flows at that point in the model rather than input flows
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4.26 INDEX FLOOD FLOW CONFIDENCE LIMITS
As has been shown previously the catchments within UoM 01 are sparsely gauged. Less than half of the watercourse models have data either on, upstream or downstream of the modelled extents and of these much of the flow data available contains a moderately high degree of uncertainty. Only four models have gauging stations on, upstream or downstream which have data deemed to be of a high enough quality such as to be taken forward as pivotal sites within FSU (confidence in the rating at
Qmed). Following the rating reviews at the Ballybofey and Dreenan gauging stations on the River Finn this number is improved to eight models having gauging stations on, upstream or downstream which have confidence in the rating at Qmed. These rating reviews were particularly beneficial in terms of adding confidence to the design flow estimates. Despite the long term collection of water level data the ratings at these stations were so poor as to be unusable for flood estimation (they were heavily extrapolated at Qmed). The rating reviews were undertaken using separate models despite being only
2.6km apart. The Qmed values derived from the rating reviews were found to be in good agreement with each other and furthermore were found to be in good agreement with the FSU physical catchment descriptor based estimates. As a result the River Finn which was previously effectively ungauged for the purposes of flood flow now has an observed Qmed estimate for which there is high confidence.
The FSU method for Flood Estimation in Ungauged Catchments (WP 2.3) is the preferred methodology for the estimation of the index flood flow in ungauged catchments. In the first instance the index flood flow has been estimated using this method at all HEPs. The estimates are then adjusted where possible based on observed flow data with confidence at the index flood flow (Qmed). Data is applied from sites, in order of preference, on the modelled watercourse, just upstream or downstream of the modelled extents or from remote sites which have a gauging station representing a catchment that is deemed to be hydrologically or geographically similar to the subject site. For UoM 01 the transfer of data from gauged sites is deemed applicable (subject to rating review at some sites) for 10 out of the 25 fluvial models. The factorial standard error (FSE) associated with Qmed ungauged catchment descriptor equation (FSU WP 2.3) is 1.37. Applying data from gauged sites will help to improve the confidence in Qmed to varying degrees depending on the applicability of the gauged data and therefore within UoM 01 we can consider that the FSE is reduced in 10 of the fluvial models below 1.37.
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5 FLOOD FREQUENCY ANALYSIS AND GROWTH CURVE DEVELOPMENT
5.1 OBJECTIVE AND SCOPE
This chapter deals with the estimation of flood growth curves for the 01-Donegal Unit of Management (UoM 01; Hydrometric Areas – HA01 (part of), HA37, HA38, HA39 and HA40) of the North Western – Neagh Bann CFRAM study areas. The estimated growth curves will be used in determining the peak design flood flows for all Hydrological Estimation Points (HEP) located on the modelled tributary and main river channels within the UoM 01 study area.
The scope of this chapter includes:
(i) Selection of a statistical distribution suitable for regional flood frequency analysis, (ii) Selection of pooling region and groups, and (iii) Growth curve estimation.
5.2 METHODOLOGY
5.2.1 Selection of Statistical Distribution
The suitable distributions for the Annual Maximum (AMAX) series for all hydrometric gauging sites located within UoM 01 were determined based on the statistical distribution fitting technique described in the Flood Studies Update (FSU) Programme Work Package 2.2 “Frequency Analysis” (OPW, 2009), UK Flood Estimation Handbook (FEH) (Institute of Hydrology, 1999) and 1975 Flood Studies Report (NERC, 1975).
5.2.2 Forming a Pooling Region and Groups
The pooling group associated with each of the growth curves was formed based on the Region-of- Influence (ROI) approach (Burn, 1990) recommended in FSU (2009). The region from which the AMAX series were pooled to form a pooling group for each of the growth curves was selected based on the similarity in catchment characteristics (both in terms of climatic and physiographic) in the neighbouring geographical region.
5.2.3 Growth Curve Development
Growth curves for each of the HEP locations were developed / estimated in accordance with the methodologies set out in the FSU, FSR and FEH studies. The Hosking and Wallis (1997) proposed L-Moment theories were used in estimating the parameters of the statistical distributions. The growth curve estimation process was automated through development of a FORTRAN 90 language based computational program.
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5.2.4 Limitations in the FEH and FSU Studies
There is no explicit guidance provided in FEH or FSU for dealing with the issues surrounding the production of a large number of growth factors within a river system and the associated problems with consistency and transition from growth curve to growth curve. For UoM 01, a catchment characteristic based generalised growth curve estimation method, as discussed later in Sections 5.7.4 and 5.8, was used to deal with this real world problem.
5.3 DATA AND STATISTICAL PROPERTIES
5.3.1 Flood Data
The AMAX series for all hydrometric gauging sites located within the UoM 01 area (HA01, HA37, HA38, HA39 and HA40) and also in the neighbouring rivers catchments (HA03) were obtained from the OPW, EPA and the Rivers Agency of Northern Ireland. In addition to these, the AMAX data series used in FSU research (216 AMAX series for the entire country) were also obtained from OPW to form a pooling region for growth curve analysis. There were only five stations classified under FSU within the Unit of Management and only one of these, Gartan Bridge on the Leannan, was given an A1 / A2 classification. Stations which were not classified under FSU WP 2.1 were included within the pooling group as it was considered beneficial to include these stations such that gauge data from throughout the Unit of Management was represented. Despite the uncertainty in the ratings it is considered that skewness within the data owing to uncertainty in the ratings, would be evened out within a pooling group and that the potential benefits (of having relevant catchment data) outweighed the potential inaccuracies. Figure 5.1 illustrates spatial distribution of the gauging sites for which AMAX records were collected (total 248 gauging sites except Northern Ireland). The record lengths in these gauging stations vary from 7 to 65 years (up to year 2011) with a total of 7,750 station-years of AMAX values. The UoM 01 study area has 611 station-years of AMAX values from 21 hydrometric gauging sites.
There are climatic differences between the North-West and other parts of the country and restricting the choice of pooling stations to the North West region should ensure an additional degree of homogeneity. However, in light of the small number of AMAX values (971 station-years) available in the North-West HAs, the pooling region outside this region could prove to be useful. Four alternative extended parent pooling regions, as outlined in Table 5.1, have been considered for estimating the growth curves for UoM 01. The parent pooling region which provides the highest growth curve, i.e. the most conservative flood estimate, will be adopted as the basis for the design floods. This has been explained further in Section 5.8.3.
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Table 5.1: Alternative parent pooling regions Pooling No. of Records Region Hydrometric Areas Stations (Station-years) No. 1 HA01, HA02, HA37, HA38, HA39 & HA40 31 971 HA01, HA02, HA37, HA38, HA39, HA40 & 2 38 1169 HA03 HA01, HA02, HA37, HA38, HA39, HA40, 3 74 2415 HA03, HA36, HA06 & HA35 4 FSU data , HA03 & HA01 248 7750
Figure 5.1: Locations of 248 Gauging Stations
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Table 5.2 presents the locations details, record lengths and some of the catchment characteristics of the hydrometric stations located in the Pooling Region 1 (North-West of Ireland). In this region 971 station-years of AMAX values are available from 31 gauging sites. The record lengths range from 11 to 56 years.
Table 5.2: Hydrometric Station Summary for Pooling Region 1 (31 Sites) Record Gauge Rating Area SAAR Stations Waterbody Location Length BFI FARL Classification (Km2) (Mm) (Years)
1002 FAIRYWATER DUDGEON BRIDGE 36 158.22 1285.00 0.419 0.992
1005 CAMOWEN CAMOWEN TCE 39 276.57 1144.00 0.514 0.989
1006 DRUMARAGH CAMPSIE BRIDGE 39 319.94 1163.00 0.441 0.998
1007 BURNDENNET BURNDENNET 38 147.14 1186.00 0.455 0.994
1008 DERG CASTLEDERG 37 335.39 1558.00 0.504 0.914
1009 OWENKILLEW CROSH 33 440.50 1367.00 0.355 0.997
DRUMNABOUY
1010 MOURNE HOUSE 31 1844.19 1288.00 0.448 0.977
1041 DEELE SANDY MILLS 37 116.18 1329.37 0.379 1.00 B
1042 FINN [Donegal] DREENAN 29 349.39 1936.43 0.298 0.965
1043 FINN [Donegal] BALLYBOFEY 32 313.30 1989.00 0.300 0.964
CROAGHNAGOWNA
1054 BUNADAOWEN FRST. 14 4.93 1911.00 0.284 0.934
1055 MOURNE BEG MOURNE BEG WEIR 14 9.70 1975.76 0.508 0737 B
1071 MOURNE LOUGH MOURNE 11 8.50 1993.00 0.283 1.000
2001 ROE ARDNARGLE 38 365.69 1250.00 0.403 0.993
2002 FAUGHAN DRUMAHOE 37 273.03 1219.00 0.426 1.000
37003 ESKE ESKE D/S 29 80.80 2176.00 0.529 0.727
37020 GLENADDRAGH VALLEY BR 34 14.08 1916.31 0.285 0.994
37070 L. ADEERY ADEERY 13 7.73 1762.52 0.357 0.819
37071 L. ESKE L. ESKE 34 80.10 2175.00 0.529 0.726
38001 OWENEA CLONCONWAL FORD 38 111.20 1753.74 0.285 0.922 B
38004 LACKAGH CREESLOUGH 56 124.44 1646.57 0.447 0.781
38071 L. ANURE L. ANURE 33 36.80 1769.66 0.447 0.747
39001 SWILLY NEW MILLS 36 50.70 1764.16 0.298 0.987 B
39003 CRANA TULLYARVAN 37 97.90 1525.39 0.285 0.993
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Record Gauge Rating Area SAAR Stations Waterbody Location Length BFI FARL Classification (Km2) (Mm) (Years)
39006 LEANNAN CLARAGH 34 245.10 1525.15 0.329 0.841
39008 LEANNAN GARTAN BR. 38 77.40 1796.33 0.441 0.781 A2
39010 CRANA ILLIES 32 36.50 1667.46 0.283 1.000
39020 GLASKEELAN INSAGH 29 8.70 1725.46 0.451 0.749
39070 L. GARTAN L. GARTAN 21 9.93 1549.07 0.554 0.776
39072 L. FERN L. FERN 22 206.60 1570.47 0.405 0.815
40070 L. FAD(W) MEENDORAN 20 3.00 1320.00 0.291 1.000
The various calculation steps associated with the growth curve estimations for UoM 01 have been presented only for the Pooling Region 1. The results for all pooling regions have been compared in Section 5.8.3.
5.3.2 Pooling Region Catchment Physiographic and Climatic Characteristic Data
In addition to the AMAX series, some catchment physiographic and climatic characteristics information including the catchment sizes (AREA), Standard Average Annual Rainfall (SAAR) and catchment Base Flow Index (BFI) for all 248 stations were also obtained from OPW.
Table 5.3 presents a summary of the catchment characteristics for all gauging sites in the Pooling Region 1 (North-West region of Ireland). Catchment sizes range from 3 to 1,844 km2 with a median value of 111 km2, SAAR values range from 1,144 to 2,176 mm with a median value of 1,647 mm, while the BFI values vary from 0.283 to 0.544.
Table 5.3: Summary of Catchment physiographic and climatic characteristics of Pooling Region 1 (31 Sites)
Characteristics Minimum Maximum Average Median
AREA (km2) 3.00 1844.19 198.50 111.20
SAAR (mm) 1144.00 2176.00 1620.58 1646.57
BFI 0.283 0.554 0.395 0.405
Furthermore the relative frequencies of the AREA, SAAR and BFI values within the 31 stations are also presented in Figure 5.2, Figure 5.3 and Figure 5.4 respectively. It can be seen from Figure 5.2 that the majority of the catchment areas in the selected sites fall in the range of 3 to 300 km2. Figure 5.3 shows that the SAAR values in the majority of the stations range from 1100 to 1800 mm. Similarly, Figure 5.4 shows the relative frequency of the BFI values within the 31 catchments. It can be seen
IBE0700Rp0006 84 F03 NW-NB CFRAM Study UoM 01 Hydrology Report - FINAL from this figure that the BFI values in the majority of the 31 catchments range from 0.25 to 0.55. Within this range the vast majority of the BFI values fall into three distinct categories ranges, 0.25 – 0.30, 0.40 – 0.45 and -0.50 – 0.55.
Figure 5.2: Relative frequencies of catchments sizes (AREA) within the Pooling Region 1 (31 stations)
Figure 5.3: Relative frequencies of the SAAR values within the Pooling Region 1 (31 stations)
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Figure 5.4: Relative frequencies of the BFI values within the Pooling Region 1 (31 stations)
5.3.3 Statistical Properties of the AMAX series in Pooling Region 1
Table 5.4: Statistical properties of 31 AMAX Series in Pooling Region 1 Table 5.4 provides a summary of the statistical properties of the AMAX series for all 31 gauging sites 3 in the Pooling Region 1. The median annual maximum flows (Qmed) range from 0.45 to 760.42 m /s with an average value of 109.15 m3/s. The L-CV values range from 0.071 to 0.351 with an average value of 0.162, while the L-Skewness values range from -0.108 to 0.645 with an average value of 0.183 which is greater than the theoretical L-Skewness of the EV1 distribution. Figure 5.5 shows the L-CV versus L-Skewness diagram for the 31 AMAX series in the Pooling Region 1.
Table 5.4: Statistical properties of 31 AMAX Series in Pooling Region 1
Parameters Minimum Maximum Average Median
Record Lengths (years) 11 56 31 34
Mean Flow (m3/s) 0.46 742.96 113.66 52.07
Median Flow (m3/s) 0.45 760.42 109.15 47.31
L-CV 0.071 0.351 0.162 0.152
L-Skewness -0.108 0.645 0.183 0.143
L-Kurtosis -0.008 0.509 0.179 0.149
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Figure 5.5: L-Moment Ratio Diagram (L-CV versus L-Skewness) for 31 AMAX series in the Pooling Region 1.
It can be seen from Figure 5.75 that there are two large outliers at -0.1 (L-Skewness) and 0.64 (L- Skewness). Investigation of these outliers shows that they relate to stations with short records and / or unclassified ratings and as such are more likely to have more extreme shape parameters. Such stations were included within the analysis to maximise the range of types of catchments within the pooling group despite there being some uncertainty with the data.
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5.4 STATISTICAL DISTRIBUTION
The individual gauging site’s AMAX series were fitted to four flood like distributions, namely EV1, GEV, GLO and LN2 distributions. The EV1 and LN2 distributions are two-parameter distributions while the GLO and GEV distributions each have three-parameters.
The choice of distributions used for this study was guided by the findings in the FSU Report (September, 2009). In the case of 2-parameter distributions, the FSU Work Package 2.2 report states (Section 4.2, page 40) “It can be deduced from the linear patterns that Irish flood data are more likely to be distributed as EV1 or LN2 rather than Logistic distribution (LO) among 2-parameter distributions”. Therefore the elimination of LO as a 2-parameter distribution is robustly based on a study of all relevant Irish data. Also, FSU concentrated on GEV and GLO from among the available 3- parameter distributions. The lack of emphasis on LN3 by FSU was possibly based on the L-kurtosis vs. L-skewness moment ratio diagram (FSU WP 2.2 Report, Figure 3.10, page 30) and that one could be used as a surrogate for the other. Then, because of the overwhelmingly central role, traditionally playing by GEV in flood frequency analysis, the FSU decided to base its analysis using the GEV rather than LN3. The same reasoning was adopted for the present study.
Based on the visual inspections of the probability plots of all 31 AMAX series in Pooling Region 1, it was found that the three-parameter distributions provide better fits to the majority of the 31 AMAX series. Between the GEV and GLO distributions, the GLO distribution was found to be the better. For the GLO distribution, out of 31 frequency curves, 28 showed concave upward shape, one convex upward and 2 straight line. For the GEV distribution, 13 showed concave upward shape, 13 showed convex upward and 5 are of straight line type. Table 5.5 presents the summary results of the visual assessments of the probability plots for all 31 AMAX series in Pooling Region 1. It should be noted here that one reason for the change of concave / convex upwards shapes seen in GEV and GLO is due to the difference in abscissa used in the probability plots i.e. EV1y = -ln{-ln(1-1/T)} for GEV distribution and GLOy = -ln{1/(T-1)} for GLO distribution.
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Table 5.5: Summary results of probability plots assessments (EV1, LN2, GEV & GLO distributions) for all 31 AMAX series in Pooling Region 1.
No. distribution in each quality ranks (1, 2 & 3) Distrib Fitted line type ution Rank 1 Rank 2 Rank 3 (very good) (good) (fair)
EV1 9 12 10 All straight line
LN2 8 7 16 All concave upward (At Log n scale)
5 – straight line (GEV type I) GEV 11 19 1 13 – concave upward (GEV Type II) 13 – convex upward (GEV Type III)
2 – straight line, GLO 17 12 2 28 – concave upward & 1 – convex upward
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5.5 GROWTH CURVE ESTIMATION POINTS
In order to estimate the peak design flows for each of the 217 HEPs located on the modelled watercourses in UoM 01 using the ‘index-flood’ method (FEH, 1999; FSU, 2009), growth curves for each of the HEPs are required. The selection of the HEPs was based on the hydraulic model conceptualisation of the modelled watercourses within each of the Areas for Further Assessment (AFA) in UoM 01. For the integration of hydrological input to the hydraulic model and also for the calibration and verification of the hydraulic models the HEPs were identified at the following locations on the modelled watercourses:
- HEPs at the upstream limit of model, - HEPs where tributaries enter the modelled channels, - HEPs at gauged stations on modelled channels, - HEPs at intermediate points on the modelled channels, and - HEPs at downstream limit of model.
The details of the selection process for the HEPs are discussed in the UoM 01 Inception Report (Section 5.3). Table 5.6 presents a summary of the catchment characteristics associated with the 217 HEPs in UoM 01. The catchment areas vary from close to 0 (at the top of modelled tributaries) to 2363 km2. The SAAR values range from 983 to 2177 mm, while the BFI values vary from 0.282 to 0.686.
Table 5.6: Summary of the catchment characteristics associated with the 217 HEPs
Catchment Maximu Minimum Average Median descriptors m
AREA (KM2) 0.02 2363.33 59.72 8.79
SAAR (MM) 983 2177 1400 1354
BFI 0.282 0.686 0.387 0.344
Based on the similarity of the catchment characteristics of these HEPs with the selected gauging sites located within the Pooling Region 1, growth curves for all HEPs with areas greater than 5 km2 were estimated. Almost 95% of the selected gauging sites in the Pooling Region 1 have catchment areas more than 5 km2. Therefore, the pooling groups for the HEPs with catchment areas less than 5 km2 would not be the homogeneous groups and therefore the errors in the estimated growth curves would be larger. All HEPs with catchment areas less than 10 km2 are considered to have the same growth curve. Based on these considerations, 125 HEPs (out of 217) were initially selected as points for the estimation of growth curves within UoM 01 but as will be discussed in Section 5.8.2 this was extended with the addition of a further 259 Growth Curve Estimation Points (GC_EPs) in order to aid
IBE0700Rp0006 90 F03 NW-NB CFRAM Study UoM 01 Hydrology Report - FINAL rationalisation of the growth factors. Figure 5.6 shows the spatial distribution of these HEPs on the modelled watercourses in UoM 01. Figure 5.6 also identifies the location of the subject site for growth curve no. 109 which is considered as an example in Section 5.7.3 to demonstrate sample growth curve distributions when applied to a typical UoM 01 HEP.
Figure 5.6: Spatial distribution of the HEPs on the modelled watercourses in UoM 01
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5.6 POOLING REGION AND GROUP FOR GROWTH CURVE ESTIMATION
5.6.1 Pooling Region
Based on the similarity of climatic characteristics, it has been initially decided that the AMAX series from the North West region of Ireland i.e. from the UoM 01 study area and also from the neighbouring hydrometric area 03 (HA03 – Bann) will be pooled to form a pooling group for growth curve estimation for UoM 01. However, in light of the small number of AMAX values (971 station-years) available in the North-West HAs, the pooling region outside this region could prove to be useful. Based on this, three additional alternative extended parent pooling regions have also been considered for estimating the growth curves for UoM 01. The details of these pooling regions were outlined in Table 5.1. The parent pooling region which provides the highest growth curve, i.e. the most conservative flood estimate, will be adopted as the basis for the design floods. This has been explained further in Section 5.8.3.
The values of AREA, SAAR and BFI encountered in the 217 HEPs are summarised by their minimum, maximum, average and median values in Table 5.6. Comparison of these with the selected stations’ corresponding catchment characteristics show a good overlap, which indicates that the selected stations provide good coverage for the range of catchments encountered in the HEPs in UoM 01.
5.6.2 Pooling Group
Pooling groups can be formed on the basis of geographical proximity to the subject site. However in the UK FEH study (1999) it was found that such pooling groups were less homogeneous than those formed by ROI approach of the type proposed by Burn (1990). The ROI approach selects stations, which are nearest to the subject site in catchment descriptor space, to form the pooling group for that subject site. In the FSU studies a distance measure in terms of three catchment descriptors of AREA, SAAR and BFI was used in forming a pooling group. The recommended distance measure in the FSU studies is:
2 2 2 ln AREA ln AREA ln SAAR ln SAAR BFIBFI i j i j i j d ij 7.1 2.0 ln AREA ln SAAR BFI (5.1)
Where i is the subject site and j=1,2,….M are the donor sites.
In this study, the pooling group was formed based on the above distance measure. The size of the pooling groups was determined based on the FEH recommended 5T rules (i.e. the total number of station-years of data to be included when estimating the T-year flood should be at least 5T). The donor sites associated with this pooling group size are selected based on the lowest distance measures among the available gauging sites in the pooling region.
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5.7 GROWTH CURVE ESTIMATION
5.7.1 Choice of Growth Curve Distributions
In the ‘index-flood’ method one of the major assumptions is that the frequency distributions at different sites in the pooled group are identical apart from a scale factor, which is the median flow (Qmed).
As discussed in Section 5.4, the three-parameter GEV and GLO distributions were found to be the better suited distribution for most of the 31 AMAX series than the two-parameter distributions. Furthermore, it can be seen from the L-moment ratio diagram for these 31 AMAX series as shown in Figure 5.7 that the GEV distribution is providing better fits than the GLO distribution, since the theoretical values of the GEV distribution’s L-Skewness and L-Kurtosis pass centrally through the observed L-moments ratios of the 31 AMAX series.
UoM01 Pooling Region (31 Stns): L-moment ratio diagram
0.700
0.600
0.500
0.400
0.300 Observed GEV
L-kurtosis 0.200 GLO 0.100 EV1 0.000
-0.100 -0.300 -0.100 0.100 0.300 0.500 0.700 0.900 L-skewness
Figure 5.7: L-moment ratio diagram (L-skewness versus L-kurtosis)
Based on the above, the GEV distribution can be adopted as the best candidate distribution for the regional growth curve for the UoM 01. However, since the probability plots show that the GLO distribution is also suitable, this distribution is also considered as a candidate distribution for the regional growth curve estimation. Although the two-parameter distributions exhibit more bias in the regional flood frequency estimates as compared to the three-parameter distributions, the two- parameter EV1 distribution is also used in the growth curve estimation process for comparison purposes and to replace the GEV or GLO growth curve when the shape displayed by either of these two distributions is convex upward in order to avoid potential underestimation of extreme event growth factors.
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5.7.2 Estimation of Growth Curves
The algebraic equations of the EV1, GEV and GLO growth curves and associated parameters are given below:
EV1 distribution:
Growth Curve: xT /11lnln2lnln1 T (5.2)
t Parameter: 2 (5.3) t2 2lnln2ln
where, t2 is the L-coefficient of variation (L-CV) and is Euler’s constant = 0.5772.
GEV distribution:
k k T Growth Curve: x ln2ln1 , k 0 (5.4) T k T 1
The parameters kand are estimated from sample t2=L-CV and sample t3=L-skewness as follows: [Hosking & Wallis (1997, p.196)]
2 2ln k 9554.28590.7 cc 2 where c (5.5) 3 t3 3ln
kt 3 (5.6) k k 2 kt k 2112ln1
GLO distribution:
k Growth Curve: xT T 111 , k 0 (5.7) k
The parameters kand are estimated from sample t2=L-CV and sample t3=L-skewness as follows [Hosking & Wallis (1997, p.197)]:
2 sinkkt tk 3 and (5.8) 22 sin kttkk
The pooled regional values of the t2 (L-CV) and t3 (L-skewness) have been estimated as the weighted average values of corresponding at-site sample values weighted by the at-site record lengths. These values were equated to the expressions for these quantities written in terms of the
IBE0700Rp0006 94 F03 NW-NB CFRAM Study UoM 01 Hydrology Report - FINAL distribution’s unknown parameters as given above and the resulting equations are solved for the unknown parameters.
5.7.3 Examination of Growth Curve Shape
Growth curves for all of the selected 125 HEPs for a range of Annual Exceedance Probabilities (AEPs) were estimated in accordance with the above methodologies. An examination of the derived shapes of the growth curves showed that, because of the fixed shape distribution, the EV1 growth curves are of straight-line type for all 125 HEPs, while in the GEV and GLO distribution cases growth curves take either the concave upwards (upward bend) or convex upwards (downward bend) shapes based on the skewness of the pooled group. In the GEV distribution case, out of 125 curves, 23 showed convex upward shape, 87 showed concave upward shape and 15 showed almost a straight line; while in the GLO distribution case, all 125 curves showed the concave upward shape (see Table 5.7).
Table 5.7: Growth curves shape summary
Distribution Growth Curve Shape
EV1 All straight lines 23 - convex upward
GEV 87 – concave upward
15 – straight line
GLO All concave upward
An assessment of the suitability of the above three growth curve distributions was carried out by examining the suitability of these distributions in fitting the AMAX series in the pooling groups associated with all 125 HEPs. In other words, for a particular HEP, the pooled growth curves, based on EV1, GEV and GLO, were superimposed on the standardised probability plots of the AMAX series which form the pooling group (typically 10 to 12 such series). A visual comparison of the suitability of the growth curves was made and recorded. An example of this is shown in Figure 5.8 (Figure 5.6 shows the location of this HEP), where the HEP No. 109 (River Swilly at Farsetmore) was selected for the growth curve analysis in UoM1. The HEP No. 109 was selected to illustrate the composition of one pooling group. Figure 5.8 shows the estimated EV1, GEV and GLO growth curves for the growth curve No. 109. The GEV growth curve is a convex upward shaped curve while the GLO one is a concave upward shaped curve.
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Figure 5.8: Pooled Growth Curve 109 - (a) EV1 and GEV distributions; (b) GLO distributions
In estimating the pooled growth curve for HEP No.109, 530 station-years of records from 15 sites were pooled. Table 5.8 shows the catchment characteristics, statistical properties and estimated distance measures for each of the sites from the subject HEP.
Table 5.8: Catchment descriptors for all pooled sites for growth curve No. 109
Record Specific Hydrometric AREA SAAR Qbar L- length BFI Qbar L-CV L-kur dij stations (km2) (m3/s) 2 skew (years) (mm) (m3/s/km )
39003 37 97.90 1525.39 0.285 75.13 0.767 0.179 0.307 0.202 0.283
38001 38 111.20 1753.74 0.285 68.85 0.619 0.087 0.076 0.234 0.593
39006 34 245.10 1525.15 0.329 52.07 0.212 0.141 0.135 0.203 0.609
39072 22 206.60 1570.47 0.405 46.42 0.225 0.106 0.067 0.182 0.614
38004 56 124.44 1646.57 0.447 53.65 0.431 0.234 0.336 0.261 0.677
01041 37 116.18 1329.37 0.379 84.78 0.730 0.157 0.025 0.133 0.900
39001 36 50.70 1764.16 0.298 43.51 0.858 0.131 0.076 0.065 0.941
39008 38 77.40 1796.33 0.441 28.24 0.365 0.145 0.098 0.123 0.985
39010 32 36.50 1667.46 0.283 35.12 0.962 0.173 0.270 0.092 1.056
01002 36 158.22 1285.00 0.419 64.93 0.410 0.112 0.140 0.056 1.157
01008 37 335.39 1558.00 0.504 193.84 0.578 0.071 0.039 0.102 1.246
01009 33 440.50 1367.00 0.355 276.78 0.628 0.097 0.182 0.187 1.299
38071 33 36.80 1769.66 0.447 11.19 0.304 0.192 0.250 0.110 1.322
01042 29 349.39 1936.43 0.297 742.96 2.126 0.196 -0.108 0.166 1.391
01043 32 313.30 1989.00 0.300 400.43 1.278 0.251 0.346 0.094 1.447
Subject site (Growth Curve - 120.83 1570 0.320 - - 0.154* 0.158* - - EP- 109)
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*Pooled regional values
It can be seen from the above table that the subject site’s catchment characteristics are well placed within the pooled sites’ catchment descriptor space. The subject site has an upstream catchment area of 120.83 km2, SAAR and BFI values of 1570 mm and 0.320 respectively which are located approximately at the median locations of the pooled sites’ corresponding values.
The estimated pooled average L-CV and L-Skewness are 0.154 and 0.158 respectively. This suggests that the pooled growth curve would follow a distribution which has L-Skewness slightly less than that of the EV1 distribution (0.167).
An assessment of the at-site GEV and GLO growth curves were carried out through a visual inspection of their individual probability plots. A summary of this assessment is provided in Table 5.9.
Table 5.9: Frequency curve shapes of the individual site’s AMAX series associated with the pooled group No. 109
Individual at-site growth curves Hydrometric stations GEV (EV1y Plot) GLO (Loy Plot) Comparison of performances (visual)
39003 Mild concave upward Moderate concave upward GLO fits slightly better
38001 Mild convex upward Mild concave upward Both fit equally well to the observed records
39006 Mild convex upward Mild concave upward GLO fits slightly better
39072 Mild convex upward Mild concave upward GLO fits slightly better
38004 Moderate concave upward Moderate concave upward Both fit equally well to the observed records
01041 Moderate convex upward Mild concave upward GLO fits slightly better
39001 Mild convex upward Mild concave upward GEV fits slightly better
39008 Mild convex upward Mild concave upward GEV fits slightly better
39010 Mild concave upward Moderate concave upward GEV fits slightly better
01002 Straight line Mild concave upward Both fits equally well to the observed records
01008 Mild convex upward Straight line Both fits equally well to the observed records
01009 Straight line Mild concave upward GLO fits slightly better
38071 Mild concave upward Moderate concave upward GLO fits slightly better
01042 Moderate convex upward Mild convex upward GLO fits slightly better
01043 Moderate concave upward Moderate concave upward Both fit equally well to the observed records
The above assessment shows that both the GEV and GLO distributions fit the observed at-site records quite well at all fifteen sites with a slightly better performance by the GLO distribution. In the case of GEV distribution eight sites showed convex upward shaped curves (mild to moderate), five concave upward and two sites showed straight lines. While in the GLO distribution case, thirteen
IBE0700Rp0006 97 F03 NW-NB CFRAM Study UoM 01 Hydrology Report - FINAL showed concave upward curves, one showed convex upward shape curve and the remaining one site is of straight line type. This suggests that, the shape of the pooled growth curves in the case of GEV distribution can be expected as convex upward while for the GLO distribution case it would be concave upward.
Table 5.10: Estimated growth factors for Growth Curve No. 109
AEP (%) EV1 GEV GLO
50 1.000 1.000 1.000 20 1.264 1.264 1.239 10 1.440 1.435 1.405 5 1.608 1.597 1.578 2 1.825 1.804 1.828 1 1.988 1.957 2.040 0.5 2.150 2.107 2.276 0.1 2.526 2.448 2.930
Table 5.10 shows the estimated growth factors for a range of AEPs for Growth Curve No. 109. The estimated 1% AEP growth factors for the EV1, GEV and GLO distributions are 1.988, 1.957 and 2.040 respectively.
5.7.4 Recommended Growth Curve Distribution for the UoM 01
The following factors were considered to select an appropriate growth curve distribution for the UoM 01 area:
(i) Suitability of a distribution in fitting the individual at-site records, (ii) No. of distribution parameters, and (iii) Shape of the pooled growth curve
A visual examination of the at-site frequency curves for all 31 gauging sites showed that the AMAX series for most of these sites can be described slightly better by the GLO distribution than by the EV1 and GEV distributions.
The number of distribution parameters also plays an important role in deriving an appropriate growth curve. The fixed skewness two-parameter distributions generally suffer from large biases, particularly at the upper tail of the distribution. The three-parameter distributions, in contrast, suffer from larger standard error though they are less biased. However this standard error is generally reduced by the pooled estimation process. The use of two-parameter distributions such as the Gumbel distribution is not therefore recommended in regional frequency analysis (Hosking and Wallis, 1996). The use of a two-parameter distribution is beneficial only if the investigator has complete confidence that the at site distribution’s L-Skewness and L-Kurtosis are close to those of the frequency distributions. As
IBE0700Rp0006 98 F03 NW-NB CFRAM Study UoM 01 Hydrology Report - FINAL discussed in Section 5.7.1, the L-CV and L-Skewness of most of the sites in the Pooling Region differ from those of the theoretical values of the EV1 distribution. This suggests that a three-parameter distribution would be more appropriate to describe the growth curves for the UoM 01.
The shape of the growth curve also plays an important role in the design and operation of the flood management scheme for a river catchment. It is generally not considered appropriate to have a growth curve with the convex downward shape. A significant number of the GEV growth curves showed convex upward shape (23 out 125). In contrast, all 125 GLO growth curves are of concave upward shape.
The estimated 1%-AEP GLO growth factor is slightly greater than the GEV growth factor, for almost all 125 growth curves by an amount of 0.1 to 5% (see Table 5.10 for growth curve No.109). This is largely due to the concavity noted above. Figure 5.9 shows a comparison of the GEV, GLO and EV1 growth curves for growth curve No.109, all plotted in the EV1 probability plot.
Figure 5.9: Comparison of EV1, GEV and GLO growth curves on the EV1-y probability plot (Growth Curve No. 109)
Based on the above, it is recommended to adopt the GLO distribution derived concave upward shape growth curve for UoM 01.
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5.8 RATIONALISATION OF GROWTH CURVES
5.8.1 Relationship of Growth Factors with Catchment Characteristics
In order to reduce the number of growth curves to a practicable number, the relationship between the estimated growth factors for a range of AEPs and the relevant catchment descriptors were examined. The catchment descriptors used were the AREA, SAAR and BFI. Figures 5.10, 5.11 and 5.12 show the variations of growth factors with AREA, SAAR and BFI respectively for all 125 HEPs.
Figure 5.10: Relationship of growth factors with catchment areas for 125 HEPs
Figure 5.11: Relationship of growth factors with SAAR for 125 HEPs
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Figure 5.12: Relationship of growth factors with BFI for 125 HEPs
It can be seen from the above figures that the growth factors generally increase with a decrease in catchment sizes for the catchment areas less than 150 km2 and also for the larger AEP growth factors. This can be attributed to the smaller upland catchment areas where catchment response time is shorter and where no flow attenuation is available. For the larger catchments flow attenuation is generally provided by lakes and wider downstream channels. For catchment areas larger than 500 km2 the growth factors do not change noticeably with the further increase in catchment area. No particular patterns in the relationships of the growth factors with the SAAR and BFI values were found.
5.8.2 Generalised Growth Curves
Based on the findings as discussed in Section 5.8.1, growth curves for UoM 01 were further generalised based on catchment size. To examine further the relationship of the catchment size with the growth factors and also to generalise the growth factor estimates, an additional 259 growth curve estimation points with various catchment sizes were selected on the modelled watercourses. Figure 5.6 shows the spatial distribution of these points. The catchment physiographic and climatic characteristics data associated with these additional growth curve estimation points were obtained from OPW.
Figure 5.13 shows the variation of the estimated growth factors for a range of AEPs and catchment sizes for all 384 HEPs (125 HEPs plus 259 additional points). Similar catchment size-growth factor relationships were found in this case as were found in the 125 HEPs case. It can be seen from this figure that the growth factors for catchment areas greater that 500 km2 do not change appreciably with the increase in catchment sizes. However, the variations in growth factors for the smaller catchment sizes are significant.
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Figure 5.13: Relationship of growth factors with catchment areas (for 384 growth curve estimation points)
As a result of the above growth curves are generalised based on ranges of catchment size as shown below:
1. AREA < 10 km2 2. 10 < AREA <= 25 km2 3. 25 < AREA < = 50 km2 4. 50 < AREA < = 100 km2 5. 100 < AREA < = 150 km2 6. 150 < AREA < = 200 km2 7. 200 < AREA < = 300 km2 8. 300 < AREA < = 400 km2 9. 400 < AREA < = 600 km2 10. 600 < AREA < = 800 km2 11. 800 < AREA < = 1200 km2 12. AREA > 1200 km2
Table 5.11 shows the estimated average and median growth factors for the above 12 categories of growth curves along with their associated group standard deviations for a range of AEPs. The number of HEPs used for the standard deviation calculation in each of the catchment size categories is presented in column 2 of Table 5.11. It can be seen from this that the standard deviations in the 1% AEP growth factors in these catchment size categories range from 0% to 8.6%. The highest variations were found in the catchment size categories of 2, 3, 4 and 5 (there were no catchments within category 6). Hence, it is considered that the growth factors for all HEPs with catchment sizes falling in these catchment area categories (i.e. from 10 to 200 km2) be estimated from the separate growth curve estimation process. In other words, separate growth curves should be estimated for all HEPs with the catchment areas falling in the range of 10 to 200 km2. Furthermore, because of the small
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number of growth curve estimation points or HEPs (only 2) available in the catchment size category 12 (AREA>1200km2), separate growth curves are recommended to be used for these two HEPs. All HEPs with catchment areas less than 10 km2 are considered to have the same growth curve. For the remaining categories the median growth curves will be used.
Table 5.11: Growth curve estimation summary
Growth factors No of HEPs AEP (%) 50% 20% 10% 5% 4% 2% 1% 0.50% 0.20% 0.10% Catchment size range in size range Return Period 2 5 10 20 25 50 100 200 500 1000 (years)
Average 1.000 1.261 1.448 1.648 1.717 1.946 2.205 2.498 2.949 3.345 1. AREA < 10 km2 52 Median 1.000 1.256 1.438 1.632 1.698 1.918 2.164 2.442 2.866 3.236
St. dev 0.000 0.006 0.013 0.021 0.024 0.036 0.051 0.071 0.105 0.139
Average 1.000 1.262 1.452 1.654 1.724 1.958 2.221 2.522 2.985 3.393 2. 10 < AREA <= 25 2 km 63 Median 1.000 1.262 1.452 1.657 1.728 1.965 2.234 2.541 3.017 3.438
St. dev 0.000 0.006 0.013 0.021 0.024 0.036 0.052 0.073 0.109 0.146
Average 1.000 1.253 1.432 1.623 1.688 1.904 2.146 2.418 2.834 3.196 3. 25 < AREA <= 50 2 km 75 Median 1.000 1.251 1.430 1.618 1.682 1.896 2.135 2.403 2.811 3.166
St. dev 0.000 0.007 0.015 0.025 0.029 0.044 0.063 0.087 0.129 0.171
Average 1.000 1.243 1.413 1.592 1.652 1.852 2.073 2.320 2.692 3.013 4. 50 < AREA <= 100 2 km 60 Median 1.000 1.240 1.409 1.586 1.646 1.844 2.062 2.305 2.669 2.983
St. dev 0.000 0.013 0.025 0.039 0.044 0.063 0.086 0.114 0.160 0.204
Average 1.000 1.235 1.400 1.573 1.631 1.825 2.040 2.280 2.640 2.951 5. 100 < AREA < = 150 2 km 71 Median 1.000 1.224 1.380 1.544 1.600 1.784 1.987 2.214 2.555 2.849
St. dev 0.000 0.015 0.026 0.039 0.042 0.057 0.073 0.092 0.122 0.148
Average N/A N/A N/A N/A N/A N/A N/A N/A N/A N/A 6. 150 < AREA < = 200 2 km N/A Median N/A N/A N/A N/A N/A N/A N/A N/A N/A N/A
St. dev N/A N/A N/A N/A N/A N/A N/A N/A N/A N/A
Average 1.000 1.228 1.382 1.539 1.592 1.764 1.950 2.152 2.450 2.701 7. 200 < AREA < = 300 2 km 6 Median 1.000 1.228 1.382 1.539 1.592 1.764 1.950 2.152 2.450 2.701
St. dev 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000
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Growth factors No of HEPs AEP (%) 50% 20% 10% 5% 4% 2% 1% 0.50% 0.20% 0.10% Catchment size range in size range Return Period 2 5 10 20 25 50 100 200 500 1000 (years)
Average 1.000 1.251 1.429 1.617 1.681 1.893 2.131 2.398 2.804 3.158
8. 300 < AREA< = 400 2 25 Median 1.000 1.252 1.432 1.623 1.688 1.904 2.147 2.420 2.837 3.201 km
St. dev 0.000 0.002 0.005 0.010 0.011 0.017 0.026 0.036 0.054 0.071
Average 1.000 1.226 1.379 1.537 1.590 1.762 1.950 2.155 2.458 2.714 9. 400 < AREA < = 600 2 km 30 Median 1.000 1.222 1.372 1.525 1.577 1.743 1.924 2.121 2.410 2.653
St. dev 0.000 0.006 0.011 0.018 0.020 0.029 0.040 0.053 0.076 0.097
Average N/A N/A N/A N/A N/A N/A N/A N/A N/A N/A 10. 600 < AREA < = 800 2 km N/A Median N/A N/A N/A N/A N/A N/A N/A N/A N/A N/A
St. dev N/A N/A N/A N/A N/A N/A N/A N/A N/A N/A
Average N/A N/A N/A N/A N/A N/A N/A N/A N/A N/A 11. 800 < AREA < = 1200 2 km N/A Median N/A N/A N/A N/A N/A N/A N/A N/A N/A N/A
St. dev N/A N/A N/A N/A N/A N/A N/A N/A N/A N/A
Average 1.000 1.229 1.388 1.554 1.609 1.793 1.995 2.219 2.555 2.842 12. AREA> 1200 km2 2 Median 1.000 1.229 1.388 1.554 1.609 1.793 1.995 2.219 2.555 2.842
St. dev 0.000 0.001 0.006 0.012 0.014 0.025 0.040 0.058 0.091 0.123
Thus for the UoM 01 the above mentioned 12 categories of catchment size have been reduced to 7 categories (hereafter called Growth Curve Groups) as presented in Table 5.12. The estimated growth curve types in each category are also presented in Table 5.12.
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Table 5.12: Growth Curve (GC) Groups
Growth Growth curves type / Curve Catchment size range estimation process Group No.
GC01 AREA < 10 km2 Use median growth curve
GC02 10 < AREA <= 200 km2 Use individual growth curve
GC03 200 < AREA < = 300 km2 Use median growth curve
GC04 300 < AREA < = 400 km2 Use median growth curve
GC05 400 < AREA < = 600 km2 Use median growth curve
GC06 AREA = 1,860 km2 Use individual growth curve
GC07 AREA = 2,363 km2 Use individual growth curve
5.8.3 Results for different parent pooling regions for UoM 01
Similar to Pooling Region 1, the generalised growth curve groups have also been estimated for all of the remaining parent pooling regions (regions 2, 3 and 4). Figure 5.14 shows the comparisons of these growth curve groups for all parent pooling regions. It can be seen from this figure that no one particular pooling region gives the largest growth curve/factor estimates for all growth curve groups. The Pooling Region 1 (31 Sites) gives steeper growth curves for the growth curve groups of GC04, GC06 and GC07, Pooling Region 2 (38 Sites) gives the steeper curves for the growth curve groups of GC02 and GC03, while the Pooling Region 4 (248 Sites - entire country) gives the steeper growth curves for the growth curve groups of GC01 and GC05. The Pooling Region 3 gives the smallest estimates for all growth curve groups. The differences in the Pooling Regions 2 and 4 estimates are in the range of 1 to 2%, i.e. the Pooling Region 2 estimates are only 1 to 2% larger than that of the Pooling Region 4 estimates.
Based on the above, it is considered prudent to adopt the parent pooling region which provides the highest growth curve, i.e. the most conservative flood estimate. Given the small differences in the growth curves for the Pooling Regions 2 and 4, the Pooling Region 4 estimates have been used / adopted as the basis for the design flood estimates for the growth curve groups of GC02 and GC03.
In summary, the design growth curves for the growth curve groups of GC04, GC06 and GC07 have been estimated from the Pooling Region 1 (31 Sites), while for the remaining four growth curve groups (GC01, GC02, GC03 and GC05), the Pooling Region 4 derived estimates have been used. These design growth factors for a range of AEPs are presented in Table 5.13 in Section 5.8.4.
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GC01:AREA<=10km2 GC02 (Median): 10 < AREA <= 200 km2 4.0 4.0 PR-1PR-1(31Sties) (31 Sites) PR-1(31Sties)PR-1 (31 Sites) AEPAEP(%) (%) AEP(%)AEP (%) 3.0 PR-4PR-4(FSU (FSU Sties) Sites) 3.0 PR-4(FSUPR-4 (FSU Sties) Sites) PR-2PR-2(38 (38 Sties) Sites) PR-2(38PR-2 (38 Sties) Sites) PR-3PR-3(74Sties) (74 Sites) PR-3(74Sties)PR-3 (74 Sites) 2.0 2.0
1.0 Growth factors Growth Growth factors 1.0 20% 10% 5% 4% 2% 1% 0.5% 0.2% 0.1% 20% 10% 5% 4% 2% 1% 0.5% 0.2% 0.1%
0.0 0.0 0.01.53.04.56.0 0.0 1.5 3.0 4.5 6.0 LogisticLogistic reduced vatiate variate LogisticLogistic reducedreduced vatiatevariate
GC03: 200 < AREA < = 300 km2 GC04: 300 < AREA < = 400 km2 4.0 4.0 PR-1PR-1(31Sties) (31 Sites) PR-1PR-1(31Sties) (31 Sites) AEPAEP(%) (%) AEPAEP(%) (%) 3.0 PR-4PR-4(FSU (FSU Sties) Sites) 3.0 PR-4PR-4(FSU (FSU Sties) Sites) PR-2(38 Sties) PR-2PR-2(38 (38 Sties) Sites) PR-2 (38 Sites) PR-3(74Sties) PR-3PR-3(74Sties) (74 Sites) PR-3 (74 Sites) 2.0 2.0
1.0 Growth factors 1.0 Growth factors Growth 20% 10% 5% 4% 2% 1% 0.5% 0.2% 0.1% 20% 10% 5% 4% 2% 1% 0.5% 0.2% 0.1%
0.0 0.0 0.01.53.04.56.0 0.0 1.5 3.0 4.5 6.0 LogisticLogistic reduced reduced variatevatiate LogisticLogistic reduced reduced variatevatiate
GC05: 400 < AREA < = 600 km2 GC06: AREA = 1860 km2 4.0 4.0 PR-1PR-1(31Sties) (31 Sites) PR-1PR-1(31Sties) (31 Sites) AEPAEP(%) (%) AEPAEP(%) (%) PR-4PR-4(FSU (FSU Sties) Sites) PR-4PR-4(FSU (FSU Sties) Sites) 3.0 3.0 PR-2 (38 Sites) PR-2(38 Sties) PR-2(38 Sties) PR-2 (38 Sites) PR-3PR-3(74Sties) (74 Sites) PR-3PR-3(74Sties) (74 Sites) 2.0 2.0
Growth factors 1.0 1.0 Growth factors 20% 10% 5% 4% 2% 1% 0.5% 0.2% 0.1% 20% 10% 5% 4% 2% 1% 0.5% 0.2% 0.1%
0.0 0.0 0.0 1.5 3.0 4.5 6.0 0.0 1.5 3.0 4.5 6.0 LogisticLogistic reduced variatevatiate LogisticLogistic reduced reduced variate vatiate
GC06: AREA = 2363 km2 4.0 PR-1PR-1(31Sties) (31 Sites) AEPAEP(%) (%) PR-4 (FSU Sites) 3.0 PR-4(FSU Sties) PR-2PR-2(38 (38 Sties) Sites) PR-3PR-3(74Sties) (74 Sites)
2.0
1.0 Growth factors 20% 10% 5% 4% 2% 1% 0.5% 0.2% 0.1%
0.0 0.0 1.5 3.0 4.5 6.0 Logistic reduced variate Logistic reduced vatiate Figure 5.14: Comparison of growth curves for different parent pooling regions.
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5.8.4 Estimated growth factors for UoM 01
Table 5.13 presents the estimated design growth factors for a range of AEPs for each of the growth curve groups. Figure 5.15 shows the estimated growth curves (GLO) for all growth curve groups.
Table 5.13: Growth factors for range of AEPs
GLO - Growth factors GC Catchment size Group range No. AEP AEP AEP AEP AEP AEP AEP AEP AEP AEP 50% 20% 10% 5% 4% 2% 1% 0.5% 0.2% 0.1%
GC01 AREA<=10km2 1.000 1.297 1.518 1.761 1.846 2.135 2.468 2.856 3.468 4.022
GC02 1.190 1.312 1.432 1.472 1.596 1.726 1.863 2.055 2.211 10 < AREA <= 2 1.000 to to to to to to to to to 200 km 1.369 1.640 1.939 2.044 2.398 2.807 3.287 4.028 4.073
GC03 200 < AREA < = 300 km2 1.000 1.225 1.379 1.539 1.592 1.768 1.961 2.172 2.487 2.754
GC04 300 < AREA < = 400 km2 1.000 1.252 1.432 1.623 1.688 1.904 2.147 2.420 2.837 3.201
GC05 400 < AREA < = 600 km2 1.000 1.264 1.445 1.632 1.696 1.902 2.129 2.378 2.749 3.064
GC06 AREA = 1,860 km2 1.000 1.228 1.384 1.545 1.599 1.775 1.967 2.178 2.491 2.755
GC07 AREA = 2,363 km2 1.000 1.230 1.392 1.562 1.619 1.810 2.023 2.260 2.619 2.929
4.5 GC01: AREA<=10km2 4.0 GC02: 10 < AREA <= 200 km2 (Median) GC03: 200 < AREA < = 300 km2 3.5 GC04: 300 < AREA < = 400 km2 GC05: 400 < AREA < = 600 km2 3.0 GC06: AREA = 1860 km2 AEP(%) 2.5 GC07:AREA = 2363 km2
2.0
Growth factors Growth 1.5
1.0 20% 10% 5% 4% 2% 1% 0.5% 0.2% 0.1% 0.5
0.0 0.0 1.0 2.0 3.0 4.0 5.0 6.0 7.0 ` LoLogisticgistic Reduced reduced Variate vatiate
Figure 5.15: GLO growth curves for all Growth Curve Groups (7 No.)
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The uncertainties associated with the above growth curve estimates are expressed in terms of 95% confidence interval of these estimates and were calculated using the following relationship:
T T XseXileX T )(96.1)%95( (5.8)
The standard error (se) of the growth curves is estimated in accordance with the FSU recommended methodology.
Table 5.14 presents the estimated standard errors in terms of percentage of the estimated growth factor for a range of AEPs. The upper and lower limits of the confidence interval were estimated using the above mentioned Eq. 5.8. For example, for the GC Group No. 4, the estimated 1%-AEP growth factor is 2.147 and the associated 95% upper and lower confidence limits are 2.357 and 1.937 respectively. Figure 5.16 shows the estimated growth curve along with the 95% upper and lower confidence limits for GC Group No. 4.
Table 5.14: Estimated percentage standard errors for growth factors (XT) for a range of AEPs
(source FSU Work- Package 2.2 “Frequency Analysis” Final Report – Section 13.3)
Return Annual periods Exceedance Se (XT) % (years) probabilities (%)
2 50% 0.60 5 20% 1.00 10 10% 1.80 20 5% 2.77 25 4% 3.00 50 2% 3.90 100 1% 5.00 200 0.5% 5.94 500 0.2% 7.30 1000 0.1% 8.30
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4.0 GC04: 300 < AREA < = 400 km2 3.5 AEP(%) 3.0 95%ile CI 2.5
2.0
1.5
Growth factors Growth 1.0 20% 10% 5% 4% 2% 1% 0.5% 0.2% 0.1% 0.5
0.0 0.01.02.03.04.05.06.07.0
Logistic reduced variate `
Figure 5.16: Growth Curve for GC Group No. 4 with 95% confidence limits
5.8.5 Comparison of the at-site growth curves with the pooled growth curves
The FSU programme recommended that “in the event that the at-site estimate of Q-T relation is steeper than the pooled one then consideration will have to be given to using a combination of the at-site estimate and the pooled estimate for design flow estimation”. In light of this, the at-site frequency curves (Q-T) for each of the gauging sites located on the modelled watercourses (7 No. gauging sites) in UoM 01 were examined and compared with the relevant pooled frequency curves. In the case where the pooled frequency curve is flatter than the at-site curve, the design growth curves/factors should be estimated from the at-site records. If the pooled growth curve is convex upwards then a two parameter distribution should be fitted to the pooled growth curve so as to avoid the upper bound.
Further the FSU study recommended that “If a very large flood is observed during the period of records the question arises as to whether it should over-ride any more modest estimate of QT obtained by a pooling group approach or whether a weighted combination of the pooling group estimate and the at-site estimate should be adopted. If a combination is used, the weights to be given to the two components of the combination cannot be specified by any rule based on scientific evidence.” Table 5.15 shows the hydrometric gauges (7 gauging sites) located on the UoM 01 modelled watercourses. The estimated pooled growth curve group numbers associated with these gauges are also included therein.
Table 5.15: Hydrometric gauging stations located on the modelled watercourses in UoM 01 hydrometric area
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Catchment Area Growth Curve Stations WATERBODY LOCATION (km2) Group No.
01041 Deele Sandy Mills 114 GC02
01042 Finn (Donegal) Dreenan 350 GC04
37003 Eske Eske d/s 81 GC02
37071 L. Eske L. Eske 80 GC02
39001 Swilly New Mills 51 GC02
39003 Crana Tullyarvan 98 GC02
39006 Leannan Claragh 245 GC03
Figure 5.17 shows the comparisons of the At-site (fitted to the observed flow data) and Regional Flood Frequency (AFF and RFF) curves for the above mentioned hydrometric gauging sites. The EV1 distribution was used for these comparisons. In addition to the frequency curves, the 95%ile confidence intervals associated with the regional estimates were also included in these plots. The EV1 straight line was used as an indicative descriptor of the at-site distribution, rather than a GEV or GLO curve, because the latter when fitted at-site, is liable to be misleading due to the large standard error involved in the shape parameter in particular. This was used for those stations where the individual AMAX series standardised growth curves were considerably different, in some cases, from the pooling growth curve. In such cases, EV1 regional growth curves were used instead of GLO curves; because the nature of the adjustment implies that an appropriate curved shape could not be determined with more accuracy than that of a straight line i.e. persevering with a curved growth curve in such cases would be an “illusion of accuracy”.
Figure 5.17: The at-site and pooled frequency curves along with the 95% confidence intervals
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Figure 5.17 (continued): The at-site and pooled frequency curves along with the 95% confidence intervals
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Despite the at site flood frequency relationship being a direct representation of the subject catchments frequency behaviour it is not considered appropriate to base design flow estimates solely on these frequency relationships for a number of reasons:
1. The short record periods available in single at site record periods limits the annual exceedance probability / return period for which the relationship can predict extreme events with statistical confidence. The FSR adopted a limit of N > 0.5T where N is the desired return period and T is the at site record length. The records available within UoM 01 are generally no longer than 40 years and based on this rule would only be appropriate for estimations of flood events up to the 80 year return period (1.25% AEP).
2. At site records typically have a degree of uncertainty within the more extreme flood events due to uncertainty in the ratings. This could lead to a degree of skew within the upper end of a single site frequency relationship. This effect is likely to be balanced out within a pooled growth curve. This may be a source of increased scatter within the plots shown in Figure 5.17.
3. The use of growth curves based solely on a single site analysis at gauging station locations and based on a pooled analysis at ungauged sites could lead to inconsistency within the design flow estimation moving up and down the catchment.
Nevertheless it is appropriate that some consideration is given to the at site flood frequency within the design flow estimation, albeit balanced by pooled data to provide additional statistical confidence.
It can be seen from the frequency curves in Figure 5.17 that at 4 sites (out of 7), the AFF curves are slightly steeper than the RFF curves, suggesting that the regional curves slightly underestimate when compared with a number of observed floods at these stations. At one site, Tullyarvan (39003) there is a significant outlier in the observed flood flows. There is little confidence in the rating of flood flows at this site and as such there can be little confidence in the magnitude of this outlier. At the Eske D/S site (37003) the AFF curve is close to the upper 95%ile confidence limit but there is significant uncertainty in this rating (unclassified under FSU) and as such little confidence can be attached to the AFF curve. All of the at-site growth curves fall within the 95%ile confidence limits of the estimated associated regional growth curves despite the uncertainty attached to some of the AFF curves and therefore it is considered appropriate that the regional curves are used.
If an AFF curve lies below the confidence limits of the RFF curve then we consider it prudent to adopt the RFF curve as the design curve, on the basis that the observed flood record has, by chance, fallen below the regional average and that there is a chance or possibility that the record of the next 20 or 30 years will revert to resembling the RFF curve rather than reproduce a re-occurrence of the recent past. It has to be acknowledged that this type of decision may lead to a degree of over-design but it is recommended that this be knowingly accepted.
On the other hand if an AFF curve lies above the RFF curve, then we consider it prudent to take account of both when deciding on the design curve/flood. This could be done by calculating a weighted average of the two curves. The relative weights should be decided, on a case by case basis, following examination of the degree of difference between the two curves, including consideration of
IBE0700Rp0006 112 F03 NW-NB CFRAM Study UoM 01 Hydrology Report - FINAL the confidence limits of the RFF curve, shape of the at-site probability plot and the number of observed large outliers in the data series.
Based on the above, the design growth curves for all HEPs located in close proximity to the above stations have been estimated from their relevant regional growth curves.
5.8.6 Growth factors for all HEPs in the UoM 01
Based on the catchment sizes associated with each of the 217 HEPs, the relevant estimated growth factors for a range of AEPs are presented in Table 5.16 below.
Table 5.16: Growth factors for all 217 HEPs for a range of AEPs for UoM 01
Node Growth factors (XT) No. AREA 1% AEP 0.2% AEP 0.1% AEP Node ID_CFRAMS 2 (km ) Lower Upper Lower Upper Lower Upper X X X 95%ile T 95%ile 95%ile T 95%ile 95%ile T 95%ile
1 40_676_2 6.22 2.226 2.468 2.710 2.972 3.468 3.964 3.368 4.022 4.676
2 40_958_1 2.49 2.226 2.468 2.710 2.972 3.468 3.964 3.368 4.022 4.676
3 40_958_2 2.71 2.226 2.468 2.710 2.972 3.468 3.964 3.368 4.022 4.676
4 40_677_2 9.63 2.226 2.468 2.710 2.972 3.468 3.964 3.368 4.022 4.676
5 40_1018_1 27.67 1.772 1.964 2.156 2.162 2.523 2.884 2.356 2.814 3.272
6 40_1018_2 28.12 1.772 1.964 2.156 2.162 2.523 2.884 2.356 2.814 3.272
7 40_1012_6_RPS 2.74 2.226 2.468 2.710 2.972 3.468 3.964 3.368 4.022 4.676
8 40_1012_3 1.42 2.226 2.468 2.710 2.972 3.468 3.964 3.368 4.022 4.676
9 40_1107_2_RPS 32.65 1.799 1.995 2.191 2.198 2.565 2.932 2.394 2.859 3.324
10 40_1107_9_RPS 34.31 1.799 1.995 2.191 2.198 2.565 2.932 2.394 2.859 3.324
11 40_982_13_RPS 28.90 1.791 1.986 2.181 2.196 2.563 2.930 2.397 2.863 3.329
12 40_982_1_RPS 24.95 1.861 2.063 2.265 2.315 2.702 3.089 2.544 3.038 3.532
13 40_991_1 1.00 2.226 2.468 2.710 2.972 3.468 3.964 3.368 4.022 4.676
14 40_991_3 1.32 2.226 2.468 2.710 2.972 3.468 3.964 3.368 4.022 4.676
15 40_460_3 1.61 2.226 2.468 2.710 2.972 3.468 3.964 3.368 4.022 4.676
16 40_1019_2 14.44 2.215 2.456 2.697 2.940 3.431 3.922 3.322 3.968 4.614
17 40_516_3 18.50 2.104 2.333 2.562 2.715 3.168 3.621 3.028 3.616 4.204
18 40_315_1_RPS 15.16 2.187 2.425 2.663 2.887 3.369 3.851 3.254 3.886 4.518
19 40_315_2_RPS 15.27 2.187 2.425 2.663 2.887 3.369 3.851 3.254 3.886 4.518
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Node Growth factors (XT) No. AREA 1% AEP 0.2% AEP 0.1% AEP Node ID_CFRAMS 2 (km ) Lower Upper Lower Upper Lower Upper X X X 95%ile T 95%ile 95%ile T 95%ile 95%ile T 95%ile
20 40_460_6_RPS 2.08 2.226 2.468 2.710 2.972 3.468 3.964 3.368 4.022 4.676
21 40_565_1 33.65 1.731 1.919 2.107 2.088 2.437 2.786 2.263 2.703 3.143
22 40_431_4 2.69 2.226 2.468 2.710 2.972 3.468 3.964 3.368 4.022 4.676
23 40_431_U 2.22 2.226 2.468 2.710 2.972 3.468 3.964 3.368 4.022 4.676
24 40_293_7 8.61 2.226 2.468 2.710 2.972 3.468 3.964 3.368 4.022 4.676
25 40_293_8 8.79 2.226 2.468 2.710 2.972 3.468 3.964 3.368 4.022 4.676
26 40_1082_D 55.51 1.696 1.880 2.064 2.017 2.354 2.691 2.172 2.594 3.016
27 39_386_2 87.36 1.914 2.122 2.330 2.386 2.784 3.182 2.622 3.131 3.640
28 39_753_2 6.47 2.226 2.468 2.710 2.972 3.468 3.964 3.368 4.022 4.676
29 39_753_4 6.77 2.226 2.468 2.710 2.972 3.468 3.964 3.368 4.022 4.676
30 39_571_1 97.30 1.894 2.100 2.306 2.345 2.736 3.127 2.567 3.066 3.565
31 39_1122_U 1.11 2.226 2.468 2.710 2.972 3.468 3.964 3.368 4.022 4.676
32 39_1122_6_RPS 3.06 2.226 2.468 2.710 2.972 3.468 3.964 3.368 4.022 4.676
33 39_2542_D 98.71 1.848 2.049 2.250 2.272 2.651 3.030 2.482 2.964 3.446
34 39_376_1_RPS 41.12 1.790 1.985 2.180 2.180 2.544 2.908 2.371 2.832 3.293
35 39_1126_1_RPS 1.05 2.226 2.468 2.710 2.972 3.468 3.964 3.368 4.022 4.676
36 39_1126_2_RPS 1.33 2.226 2.468 2.710 2.972 3.468 3.964 3.368 4.022 4.676
37 39_1126_3_RPS 1.41 2.226 2.468 2.710 2.972 3.468 3.964 3.368 4.022 4.676
38 39_2555_1_RPS 43.55 1.790 1.985 2.180 2.180 2.544 2.908 2.371 2.832 3.293
39 39_2555_2_RPS 43.80 1.790 1.985 2.180 2.180 2.544 2.908 2.371 2.832 3.293
40 39_2556_D 44.34 1.738 1.927 2.116 2.077 2.424 2.771 2.240 2.675 3.110
41 39_150_1_RPS 0.33 2.226 2.468 2.710 2.972 3.468 3.964 3.368 4.022 4.676
42 39_152_2_RPS 1.52 2.226 2.468 2.710 2.972 3.468 3.964 3.368 4.022 4.676
43 39_2176_4 5.99 2.226 2.468 2.710 2.972 3.468 3.964 3.368 4.022 4.676
44 39_2174a_U 13.15 2.368 2.625 2.882 3.207 3.743 4.279 3.655 4.365 5.075
45 39_1105_6 22.60 1.865 2.068 2.271 2.309 2.695 3.081 2.531 3.023 3.515
46 39_480_1 19.46 2.057 2.281 2.505 2.707 3.159 3.611 3.054 3.647 4.240
47 39_1082_4 5.61 2.226 2.468 2.710 2.972 3.468 3.964 3.368 4.022 4.676
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Node Growth factors (XT) No. AREA 1% AEP 0.2% AEP 0.1% AEP Node ID_CFRAMS 2 (km ) Lower Upper Lower Upper Lower Upper X X X 95%ile T 95%ile 95%ile T 95%ile 95%ile T 95%ile
48 39_1162_2_RPS 65.85 1.721 1.908 2.095 2.025 2.363 2.701 2.166 2.587 3.008
49 39_2409_1 13.95 2.532 2.807 3.082 3.452 4.028 4.604 3.938 4.703 5.468
50 39_2081_3 9.88 2.226 2.468 2.710 2.972 3.468 3.964 3.368 4.022 4.676
51 39_2252_3 31.75 2.081 2.307 2.533 2.690 3.139 3.588 3.003 3.587 4.171
52 39_927_1 2.68 2.226 2.468 2.710 2.972 3.468 3.964 3.368 4.022 4.676
53 39_927_3 3.31 2.226 2.468 2.710 2.972 3.468 3.964 3.368 4.022 4.676
54 39_1000_D 0.09 2.226 2.468 2.710 2.972 3.468 3.964 3.368 4.022 4.676
55 39_951_3 253.76 1.769 1.961 2.153 2.131 2.487 2.843 2.306 2.754 3.202
56 39_1106_2_RPS 1.74 2.226 2.468 2.710 2.972 3.468 3.964 3.368 4.022 4.676
57 39_1106_5_RPS 2.55 2.226 2.468 2.710 2.972 3.468 3.964 3.368 4.022 4.676
58 39_1591_D 262.52 1.769 1.961 2.153 2.131 2.487 2.843 2.306 2.754 3.202
59 39_891_U 0.06 2.226 2.468 2.710 2.972 3.468 3.964 3.368 4.022 4.676
60 39_2505_3 8.88 2.226 2.468 2.710 2.972 3.468 3.964 3.368 4.022 4.676
61 39_2513_U 0.11 2.226 2.468 2.710 2.972 3.468 3.964 3.368 4.022 4.676
62 39_304_U 0.41 2.226 2.468 2.710 2.972 3.468 3.964 3.368 4.022 4.676
63 39_2513_1 0.65 2.226 2.468 2.710 2.972 3.468 3.964 3.368 4.022 4.676
64 39_2551_2_RPS 4.59 2.226 2.468 2.710 2.972 3.468 3.964 3.368 4.022 4.676
65 39_1507_U 0.03 2.226 2.468 2.710 2.972 3.468 3.964 3.368 4.022 4.676
66 39_1507_2 1.05 2.226 2.468 2.710 2.972 3.468 3.964 3.368 4.022 4.676
67 39_2152_2 3.76 2.226 2.468 2.710 2.972 3.468 3.964 3.368 4.022 4.676
68 39_800_2 7.44 2.226 2.468 2.710 2.972 3.468 3.964 3.368 4.022 4.676
69 39_2153_2 5.06 2.226 2.468 2.710 2.972 3.468 3.964 3.368 4.022 4.676
70 39_2468_3 13.81 2.164 2.399 2.634 2.826 3.298 3.770 3.169 3.785 4.401
71 39_1406_1 1.25 2.226 2.468 2.710 2.972 3.468 3.964 3.368 4.022 4.676
72 39_1563_4_RPS 2.68 2.226 2.468 2.710 2.972 3.468 3.964 3.368 4.022 4.676
73 39_1398_1_RPS 75.11 1.914 2.122 2.330 2.380 2.777 3.174 2.612 3.119 3.626
74 39_2433_5_RPS 7.12 2.226 2.468 2.710 2.972 3.468 3.964 3.368 4.022 4.676
75 39_2433_2 6.34 2.226 2.468 2.710 2.972 3.468 3.964 3.368 4.022 4.676
IBE0700Rp0006 115 F03 NW-NB CFRAM Study UoM 01 Hydrology Report - FINAL
Node Growth factors (XT) No. AREA 1% AEP 0.2% AEP 0.1% AEP Node ID_CFRAMS 2 (km ) Lower Upper Lower Upper Lower Upper X X X 95%ile T 95%ile 95%ile T 95%ile 95%ile T 95%ile
76 39_1296_1 3.35 2.226 2.468 2.710 2.972 3.468 3.964 3.368 4.022 4.676
77 39_2375_RPS 0.51 2.226 2.468 2.710 2.972 3.468 3.964 3.368 4.022 4.676
78 39_2317_U 1.08 2.226 2.468 2.710 2.972 3.468 3.964 3.368 4.022 4.676
79 39_2323_5 3.59 2.226 2.468 2.710 2.972 3.468 3.964 3.368 4.022 4.676
80 39_1004_D_RPS 120.83 1.872 2.075 2.278 2.288 2.670 3.052 2.489 2.973 3.457
81 01_810_2_RA 309.97 1.937 2.147 2.357 2.431 2.837 3.243 2.680 3.201 3.722
82 01_186_2_RA 4.63 2.226 2.468 2.710 2.972 3.468 3.964 3.368 4.022 4.676
83 01_543_U 0.08 2.226 2.468 2.710 2.972 3.468 3.964 3.368 4.022 4.676
84 01_543_2_RA 1.16 2.226 2.468 2.710 2.972 3.468 3.964 3.368 4.022 4.676
85 01_542_Inter_RA 1.61 2.226 2.468 2.710 2.972 3.468 3.964 3.368 4.022 4.676
86 01_542_1_RA 1.96 2.226 2.468 2.710 2.972 3.468 3.964 3.368 4.022 4.676
87 01_551_2_RA 8.67 2.226 2.468 2.710 2.972 3.468 3.964 3.368 4.022 4.676
88 01_1815_2_RA 8.93 2.226 2.468 2.710 2.972 3.468 3.964 3.368 4.022 4.676
89 01_1825_3_RA 3.46 2.226 2.468 2.710 2.972 3.468 3.964 3.368 4.022 4.676
90 01_223_1_RARPS 1.51 2.226 2.468 2.710 2.972 3.468 3.964 3.368 4.022 4.676
91 01_41_6_RA 3.49 2.226 2.468 2.710 2.972 3.468 3.964 3.368 4.022 4.676
92 01_41_9_RA 4.47 2.226 2.468 2.710 2.972 3.468 3.964 3.368 4.022 4.676
93 01_10000_U_RA 1.76 2.226 2.468 2.710 2.972 3.468 3.964 3.368 4.022 4.676
94 01_10000_RARPS 2.38 2.226 2.468 2.710 2.972 3.468 3.964 3.368 4.022 4.676
95 01_814_4_RA 25.55 2.019 2.238 2.457 2.655 3.098 3.541 2.996 3.578 4.160
96 01_69_2_RA 4.84 2.226 2.468 2.710 2.972 3.468 3.964 3.368 4.022 4.676
97 01_776_3_RA 5.90 2.226 2.468 2.710 2.972 3.468 3.964 3.368 4.022 4.676
98 01_416_2_RA 1.23 2.226 2.468 2.710 2.972 3.468 3.964 3.368 4.022 4.676
99 01_1577_2_RA 2.22 2.226 2.468 2.710 2.972 3.468 3.964 3.368 4.022 4.676
100 01_778_7_RA 7.37 2.226 2.468 2.710 2.972 3.468 3.964 3.368 4.022 4.676
101 01_613_1_RA 2.34 2.226 2.468 2.710 2.972 3.468 3.964 3.368 4.022 4.676
102 01_613_3_RA 2.79 2.226 2.468 2.710 2.972 3.468 3.964 3.368 4.022 4.676
103 01_615_2_RA 387.14 1.937 2.147 2.357 2.431 2.837 3.243 2.680 3.201 3.722
IBE0700Rp0006 116 F03 NW-NB CFRAM Study UoM 01 Hydrology Report - FINAL
Node Growth factors (XT) No. AREA 1% AEP 0.2% AEP 0.1% AEP Node ID_CFRAMS 2 (km ) Lower Upper Lower Upper Lower Upper X X X 95%ile T 95%ile 95%ile T 95%ile 95%ile T 95%ile
104 01_614_3_RA 383.52 1.937 2.147 2.357 2.431 2.837 3.243 2.680 3.201 3.722
105 01_1293_U 1.00 2.226 2.468 2.710 2.972 3.468 3.964 3.368 4.022 4.676
106 01_1307_2_RA 11.28 2.210 2.450 2.690 2.858 3.335 3.812 3.186 3.805 4.424
107 01_1307_6_RA 11.97 2.210 2.450 2.690 2.858 3.335 3.812 3.186 3.805 4.424
108 01_1293_3_RA 1.71 2.226 2.468 2.710 2.972 3.468 3.964 3.368 4.022 4.676
109 01_1307_Inter1_RA 11.70 2.210 2.450 2.690 2.858 3.335 3.812 3.186 3.805 4.424
110 01_1293_Inter1_RA 1.64 2.226 2.468 2.710 2.972 3.468 3.964 3.368 4.022 4.676
111 01_1788_8_RA 9.75 2.226 2.468 2.710 2.972 3.468 3.964 3.368 4.022 4.676
112 01_633_6_RA 3.95 2.226 2.468 2.710 2.972 3.468 3.964 3.368 4.022 4.676
113 01_10001_RARPS 0.03 2.226 2.468 2.710 2.972 3.468 3.964 3.368 4.022 4.676
114 01_633_7_RA 4.10 2.226 2.468 2.710 2.972 3.468 3.964 3.368 4.022 4.676
115 01_1887_2_RA 8.49 2.226 2.468 2.710 2.972 3.468 3.964 3.368 4.022 4.676
116 01_633_4_RA 3.59 2.226 2.468 2.710 2.972 3.468 3.964 3.368 4.022 4.676
117 01_654_4_RA 12.42 2.379 2.637 2.895 3.183 3.714 4.245 3.602 4.302 5.002
118 01_801_3_RA 81.87 1.873 2.077 2.281 2.313 2.699 3.085 2.530 3.021 3.512
119 01_1518_4_RA 4.72 2.226 2.468 2.710 2.972 3.468 3.964 3.368 4.022 4.676
120 01_1518_1_RA 2.72 2.226 2.468 2.710 2.972 3.468 3.964 3.368 4.022 4.676
121 01_1913_2_RA 134.00 1.557 1.726 1.895 1.761 2.055 2.349 1.851 2.211 2.571
122 37_1832_1_RPS 0.02 2.226 2.468 2.710 2.972 3.468 3.964 3.368 4.022 4.676
123 37_1832_2 1.31 2.226 2.468 2.710 2.972 3.468 3.964 3.368 4.022 4.676
124 37_1462_1 2.76 2.226 2.468 2.710 2.972 3.468 3.964 3.368 4.022 4.676
125 37_1500_3 4.68 2.226 2.468 2.710 2.972 3.468 3.964 3.368 4.022 4.676
126 37_3590_1 14.70 2.118 2.348 2.578 2.820 3.291 3.762 3.198 3.819 4.440
127 37_1727_1_RPS 0.94 2.226 2.468 2.710 2.972 3.468 3.964 3.368 4.022 4.676
128 37_1727_U 0.44 2.226 2.468 2.710 2.972 3.468 3.964 3.368 4.022 4.676
129 37_1301_1 1.72 2.226 2.468 2.710 2.972 3.468 3.964 3.368 4.022 4.676
130 37_3437_1 80.12 2.048 2.271 2.494 2.655 3.098 3.541 2.971 3.548 4.125
131 37_2105_1 80.45 2.048 2.271 2.494 2.655 3.098 3.541 2.971 3.548 4.125
IBE0700Rp0006 117 F03 NW-NB CFRAM Study UoM 01 Hydrology Report - FINAL
Node Growth factors (XT) No. AREA 1% AEP 0.2% AEP 0.1% AEP Node ID_CFRAMS 2 (km ) Lower Upper Lower Upper Lower Upper X X X 95%ile T 95%ile 95%ile T 95%ile 95%ile T 95%ile
132 37_2262_6 91.10 2.021 2.241 2.461 2.602 3.037 3.472 2.904 3.468 4.032
133 37_1302_2 3.09 2.226 2.468 2.710 2.972 3.468 3.964 3.368 4.022 4.676
134 37_3589_2_RPS 16.90 2.132 2.364 2.596 2.849 3.325 3.801 3.237 3.866 4.495
135 37_2587_Inter 111.59 2.161 2.396 2.631 2.866 3.344 3.822 3.239 3.868 4.497
136 37_2408_2 1.31 2.226 2.468 2.710 2.972 3.468 3.964 3.368 4.022 4.676
137 37_2589_2 2.90 2.226 2.468 2.710 2.972 3.468 3.964 3.368 4.022 4.676
138 37_2588_2_RPS 115.62 2.161 2.396 2.631 2.866 3.344 3.822 3.239 3.868 4.497
139 37_2565_2 3.45 2.226 2.468 2.710 2.972 3.468 3.964 3.368 4.022 4.676
140 37_2673_1 2.16 2.226 2.468 2.710 2.972 3.468 3.964 3.368 4.022 4.676
141 37_2673_3 2.84 2.226 2.468 2.710 2.972 3.468 3.964 3.368 4.022 4.676
142 37_3644_2_RPS 9.62 2.226 2.468 2.710 2.972 3.468 3.964 3.368 4.022 4.676
143 37_2465_1_RPS 1.35 2.226 2.468 2.710 2.972 3.468 3.964 3.368 4.022 4.676
144 37_1289_2_RPS 1.98 2.226 2.468 2.710 2.972 3.468 3.964 3.368 4.022 4.676
145 38_2761_2 41.04 1.993 2.209 2.425 2.573 3.003 3.433 2.878 3.437 3.996
146 38_23_1 1.32 2.226 2.468 2.710 2.972 3.468 3.964 3.368 4.022 4.676
147 38_414_4 2.46 2.226 2.468 2.710 2.972 3.468 3.964 3.368 4.022 4.676
148 38_2332_4 9.44 2.226 2.468 2.710 2.972 3.468 3.964 3.368 4.022 4.676
149 38_1168_3 126.05 1.937 2.147 2.357 2.404 2.805 3.206 2.634 3.146 3.658
150 38_3814_1 42.05 1.994 2.211 2.428 2.572 3.001 3.430 2.874 3.432 3.990
151 38_3037_3 43.08 1.994 2.211 2.428 2.572 3.001 3.430 2.874 3.432 3.990
152 38_1154_1 37.69 1.992 2.208 2.424 2.565 2.993 3.421 2.864 3.420 3.976
153 38_1155_3 39.60 1.992 2.208 2.424 2.565 2.993 3.421 2.864 3.420 3.976
154 38_687_1 84.93 2.078 2.304 2.530 2.657 3.101 3.545 2.951 3.524 4.097
155 38_4124_2 88.96 2.078 2.304 2.530 2.657 3.101 3.545 2.951 3.524 4.097
156 38_685_1_RPS 0.03 2.226 2.468 2.710 2.972 3.468 3.964 3.368 4.022 4.676
157 38_2585_1 2.02 2.226 2.468 2.710 2.972 3.468 3.964 3.368 4.022 4.676
158 38_4132_3 3.76 2.226 2.468 2.710 2.972 3.468 3.964 3.368 4.022 4.676
159 38_4130_D 7.81 2.226 2.468 2.710 2.972 3.468 3.964 3.368 4.022 4.676
IBE0700Rp0006 118 F03 NW-NB CFRAM Study UoM 01 Hydrology Report - FINAL
Node Growth factors (XT) No. AREA 1% AEP 0.2% AEP 0.1% AEP Node ID_CFRAMS 2 (km ) Lower Upper Lower Upper Lower Upper X X X 95%ile T 95%ile 95%ile T 95%ile 95%ile T 95%ile
160 38_1824_U 0.05 2.226 2.468 2.710 2.972 3.468 3.964 3.368 4.022 4.676
161 38_1824_D 1.57 2.226 2.468 2.710 2.972 3.468 3.964 3.368 4.022 4.676
162 38_3389_1_RPS 1.01 2.226 2.468 2.710 2.972 3.468 3.964 3.368 4.022 4.676
163 38_2247_1 9.86 2.226 2.468 2.710 2.972 3.468 3.964 3.368 4.022 4.676
164 38_3389_2_RPS 1.31 2.226 2.468 2.710 2.972 3.468 3.964 3.368 4.022 4.676
165 38_2210_D 12.27 2.215 2.456 2.697 2.940 3.431 3.922 3.322 3.968 4.614
166 01042_RA 350.37 1.937 2.147 2.357 2.431 2.837 3.243 2.680 3.201 3.722
167 01043_RA 314.12 1.937 2.147 2.357 2.431 2.837 3.243 2.680 3.201 3.722
168 37003 80.80 2.048 2.271 2.494 2.655 3.098 3.541 2.971 3.548 4.125
169 39003 97.87 1.848 2.049 2.250 2.272 2.651 3.030 2.482 2.964 3.446
170 01044_RARPS 22.38 2.013 2.232 2.451 2.636 3.076 3.516 2.967 3.544 4.121
171 01045_RA 11.57 2.210 2.450 2.690 2.858 3.335 3.812 3.186 3.805 4.424
172 01046_RA 83.17 1.873 2.077 2.281 2.313 2.699 3.085 2.530 3.021 3.512
173 01048_RA 123.71 1.608 1.783 1.958 1.838 2.145 2.452 1.941 2.318 2.695
174 37002_RPS 111.56 2.161 2.396 2.631 2.866 3.344 3.822 3.239 3.868 4.497
175 38006 39.30 1.992 2.208 2.424 2.565 2.993 3.421 2.864 3.420 3.976
176 38010 42.33 1.965 2.179 2.393 2.507 2.926 3.345 2.787 3.328 3.869
177 39002_RPS 44.18 1.738 1.927 2.116 2.077 2.424 2.771 2.240 2.675 3.110
178 39005 255.19 1.769 1.961 2.153 2.131 2.487 2.843 2.306 2.754 3.202
179 39013 14.56 2.468 2.736 3.004 3.295 3.845 4.395 3.722 4.445 5.168
180 39015 21.04 1.891 2.097 2.303 2.375 2.772 3.169 2.622 3.131 3.640
181 39016_RPS 27.20 1.983 2.199 2.415 2.481 2.895 3.309 2.726 3.256 3.786
182 39061_RPS 96.66 1.894 2.100 2.306 2.345 2.736 3.127 2.567 3.066 3.565
183 40001_RPS 17.93 2.189 2.427 2.665 2.855 3.332 3.809 3.199 3.820 4.441
184 40002_RPS 9.51 2.226 2.468 2.710 2.972 3.468 3.964 3.368 4.022 4.676
185 40003_RPS 25.87 1.760 1.951 2.142 2.148 2.507 2.866 2.341 2.796 3.251
186 40004 37.28 1.688 1.871 2.054 2.021 2.358 2.695 2.183 2.607 3.031
187 40006_RPS 31.83 1.799 1.995 2.191 2.198 2.565 2.932 2.394 2.859 3.324
IBE0700Rp0006 119 F03 NW-NB CFRAM Study UoM 01 Hydrology Report - FINAL
Node Growth factors (XT) No. AREA 1% AEP 0.2% AEP 0.1% AEP Node ID_CFRAMS 2 (km ) Lower Upper Lower Upper Lower Upper X X X 95%ile T 95%ile 95%ile T 95%ile 95%ile T 95%ile
188 40007_RPS 33.74 1.799 1.995 2.191 2.198 2.565 2.932 2.394 2.859 3.324
189 40061_RPS 9.51 2.226 2.468 2.710 2.972 3.468 3.964 3.368 4.022 4.676
190 01041_RA 114.29 1.697 1.881 2.065 1.985 2.317 2.649 2.118 2.529 2.940
191 38001 111.25 1.978 2.193 2.408 2.492 2.908 3.324 2.751 3.285 3.819
192 39_993_2 2.32 2.226 2.468 2.710 2.972 3.468 3.964 3.368 4.022 4.676
193 38_3999_1 87.28 2.078 2.304 2.530 2.657 3.101 3.545 2.951 3.524 4.097
194 38_442_4 102.59 1.991 2.207 2.423 2.511 2.930 3.349 2.772 3.310 3.848
195 01_724b_1_RA 493.75 1.920 2.129 2.338 2.356 2.749 3.142 2.566 3.064 3.562
196 01_1883d_D_RA 2363.33 1.825 2.023 2.221 2.244 2.619 2.994 2.453 2.929 3.405
197 01_1557_3_RA 102.65 1.769 1.961 2.153 2.112 2.465 2.818 2.275 2.717 3.159
198 40_1018_4_RPS 28.64 1.772 1.965 2.158 2.164 2.525 2.886 2.359 2.817 3.275
199 39_927_2 3.18 2.226 2.468 2.710 2.972 3.468 3.964 3.368 4.022 4.676
200 38_3833_1_RPS 0.11 2.226 2.468 2.710 2.972 3.468 3.964 3.368 4.022 4.676
201 38_3860_Inter_2 42.51 1.965 2.179 2.393 2.507 2.926 3.345 2.787 3.328 3.869
202 38_3860_Inter_1 42.39 1.965 2.179 2.393 2.507 2.926 3.345 2.787 3.328 3.869
203 38_3822_3 49.23 2.024 2.244 2.464 2.613 3.049 3.485 2.920 3.487 4.054
204 38_3822_4_RPS 49.25 2.024 2.244 2.464 2.613 3.049 3.485 2.920 3.487 4.054
205 37_3437_Inter 80.17 2.048 2.271 2.494 2.655 3.098 3.541 2.971 3.548 4.125
206 37_3590_Int_1 15.01 2.118 2.348 2.578 2.820 3.291 3.762 3.198 3.819 4.440
207 37_3590_3 15.10 2.118 2.348 2.578 2.820 3.291 3.762 3.198 3.819 4.440
208 01_614_Intr1_RPS 384.05 1.937 2.147 2.357 2.431 2.837 3.243 2.680 3.201 3.722
209 01_801_Int_2_RPS 83.10 1.873 2.077 2.281 2.313 2.699 3.085 2.530 3.021 3.512
210 01_801_Int_1_RPS 82.20 1.873 2.077 2.281 2.313 2.699 3.085 2.530 3.021 3.512
211 38_2587_U 0.13 2.226 2.468 2.710 2.972 3.468 3.964 3.368 4.022 4.676
212 38_2911_U 0.40 2.226 2.468 2.710 2.972 3.468 3.964 3.368 4.022 4.676
213 38_2587_1 0.16 2.226 2.468 2.710 2.972 3.468 3.964 3.368 4.022 4.676
214 38_2911_1 0.73 2.226 2.468 2.710 2.972 3.468 3.964 3.368 4.022 4.676
215 39_2176_6_RPS 7.29 2.226 2.468 2.710 2.972 3.468 3.964 3.368 4.022 4.676
IBE0700Rp0006 120 F03 NW-NB CFRAM Study UoM 01 Hydrology Report - FINAL
Node Growth factors (XT) No. AREA 1% AEP 0.2% AEP 0.1% AEP Node ID_CFRAMS 2 (km ) Lower Upper Lower Upper Lower Upper X X X 95%ile T 95%ile 95%ile T 95%ile 95%ile T 95%ile
216 01_1883c_1_RARPS 1859.97 1.774 1.967 2.160 2.135 2.491 2.847 2.307 2.755 3.203
217 01_724b_2_RARPS 502.42 1.920 2.129 2.338 2.356 2.749 3.142 2.566 3.064 3.562
The design flood flows for any required AEP will be calculated by multiplying the Index Flood, Qmed of each HEP by the above estimated relevant growth factors. The Qmed at gauged sites will be estimated from the observed AMAX series and at ungauged sites based on the methodology outlined in FSU Work Package 2.3 ‘Flood Estimation in Ungauged Catchments’.
It should be noted here that any uncertainties in the design flood estimates obtained from the index- flood method generally result from the uncertainties associated with both the index-flood (Qmed) and growth factor estimates. The uncertainties in the growth factor estimates can result both from the sampling variability and misspecification of the growth curve distribution. The sampling error is considered to be small due to the larger record lengths (pooled records) used in the estimation process.
Furthermore, it should also be noted here that, any allowances for future climate change in the design flood flow estimate should be applied to the median flow estimates. Any effects of the climate change on the growth curves are expected to be minimal.
IBE0700Rp0006 121 F03 NW-NB CFRAM Study UoM 01 Hydrology Report - FINAL
5.9 COMPARISON WITH FSR GROWTH FACTORS
A comparison of the estimated growth factors for the UoM 01 was carried out with the FSR growth factors for a range of AEPs as can be seen in Table 5.17. All growth curves were indexed to the median annual maximum flows (Qmed).
Table 5.17: Study growth factors compared with FSR growth factors
AEP (%) 50% 20% 10% 4% 2% 1% 0.5% 0.2% 0.1%
1.190 1.312 1.472 1.596 1.726 1.863 2.055 2.211 UoM 01 1.000 to to to to to to to to 1.367 1.640 2.044 2.398 2.807 3.281 4.028 4.703
Average of UoM 01 1.000 1.278 1.482 1.780 2.040 2.336 2.677 3.210 3.687
FSR 1.000 1.260 1.450 1.630 1.870 2.060 2.250 2.620 2.750
It can be noticed from Table 5.17 that the study area growth factors (average values) are slightly higher than the FSR growth factors. These differences in growth factors for the UoM 01 watercourses can be attributed to the Region of Influence Approach to pooling and the development of growth curves for individual catchments including a high number representing small upland and tributary catchments affecting the AFAs. It is worth noting that the growth curves developed for the largest catchments GC06 & GC07 compare well to the FSR growth factors for the more extreme AEP events. This is due to the FSR growth factors having been derived from data pooled predominantly from larger catchment gauging station records. The approach taken in developing individual growth curves to capture differing frequency conditions across the Unit of Management can be considered to be a more refined approach to growth curve development than the application of one growth curve across the study as per FSR.
IBE0700Rp0006 122 F03 NW-NB CFRAM Study UoM 01 Hydrology Report - FINAL
5.10 GROWTH CURVE DEVELOPMENT SUMMARY
Growth curves for all HEPs were estimated from the regional flood frequency analysis technique as recommended in the FEH, FSU and FSR studies (Region of Influence Approach).
The AMAX series for all hydrometric gauging sites located within the UoM 01 area (HA01, HA37, HA38, HA39 and HA40) and also in the neighbouring rivers catchments (HA03) were obtained from the OPW, EPA and the Rivers Agency of Northern Ireland. In addition to these, the AMAX data series used in FSU research (216 AMAX series for the entire country except Northern Ireland) were also obtained from OPW to form a pooling region for growth curve analysis. The selection of the pooling region for UoM 01 was based on the similarity of catchment characteristics both in terms of climatic and physiographic characteristics. In light of the small number of AMAX values (971 station-years) available in the North-West HAs, three additional alternative extended parent pooling regions (including the entire country) were considered for estimating the growth curves for UoM 01. The parent pooling region which provided the highest growth curve, i.e. the most conservative flood estimate, was adopted as the basis for the design floods. The size of a pooling group associated with each of the HEPs was determined based on the FEH recommended 5T rule (with a minimum of 500 station-years AMAX series for each pooled growth curve). The pooling process was based on the FSU recommended catchment characteristics based (AREA, SAAR and BFI) distance measures between the subject and donor sites.
The statistical distribution suitable for a pooled growth curve was determined based on a number of factors such as - the suitability of this distribution for fitting the contributory stations’ at-site AMAX series, the number of distribution parameters and shape of the growth curves (concave upward or convex upward). Four flood like distributions namely, the EV1, LN2, GEV and GLO distributions were considered. The three-parameter GLO distribution was found to be the best suited distribution in all respects and therefore was chosen as the growth curve distribution for all HEPs in UoM 01.
Initially, growth curves for each of the 217 HEPs in UoM 01 were estimated separately. Subsequently, the number of growth curves was reduced based on their relationship with the catchment areas. It was found that the growth factors generally increase with the decrease in catchment sizes. This increase in rate is larger for the catchment areas less than 400 km2 and also for the larger AEP growth factors. For any catchment areas larger than 500 km2 the growth factors remained unchanged with the further increase in catchment areas. Based on this the following 7 generalised growth curve groups were recommended for the UoM 01:
1. GC group No. 1: AREA < 10 km2
2. GC group No. 2: 10 < AREA <= 200 km2
3. GC group No. 3: 200 < AREA < = 300 km2
4. GC group No. 4: 300 < AREA < = 400 km2
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5. GC group No. 5: 400 < AREA < = 600 km2
6. GC group No. 6: AREA = 1860 km2
7. GC group No. 6: AREA = 2,363 km2
It was decided that the growth factors for all HEPs with catchment sizes ranging from 10 to 200 km2 (Growth Curve Group No. 2) and also for HEPs with catchment areas greater than 1200 km2 be estimated from the separate growth curve estimation process. For the remaining growth curve groups the median growth curves will be used.
The design growth curves for the growth curve groups of GC04, GC06 & GC07 were estimated from the Pooling Region 1 (31 Sites), while for the remaining four growth curve groups (GC01, GC02, GC03 and GC05) the Pooling Region 4 derived estimates were used.
The estimated 1% AEP growth factors for the UoM 01 vary from 1.726 to 2.807 depending on the catchment sizes. Growth factors for the smaller catchments are generally larger than those of the larger catchments.
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6 DESIGN FLOWS
6.1 DESIGN FLOW HYDROGRAPHS
Following estimation of the Index Flood Flow (Qmed) and growth factors for each HEP it is possible to estimate the peak design flows for a range of Annual Exceedance Probabilities (AEPs). In addition to the total design flows estimated for each HEP, lateral inflows must be generated to represent the flow from the lateral catchment between HEPs. Catchment descriptors do not exist for the lateral inflow catchments within FSU and these have not been derived as part of this Study. The RPS methodology involves using the catchment descriptors of the total catchment at the downstream HEP with the area replaced by the difference in area between the upstream and downstream nodes / HEPs to derive an estimate of the lateral inflow Qmed based on FSU WP 2.3. In some instances where it is obvious that the catchment descriptors of the total catchment are not representative of the lateral / top-up catchment (particularly URBEXT and FARL) these have been adjusted based on orthophotography / Corine datasets. These will be reviewed as required during the hydraulic analysis stage as part of a hierarchical approach to ensuring the correct frequency conditions are achieved (i.e. the total flow in the model at each intermediate / gauging station / downstream limit HEP is correct) as we move down through the models.
All of the design flows which will be used for hydraulic modelling input are detailed in Appendix C. The final component of estimating the fluvial design flows is to ascertain the profile of the design flow hydrograph for each HEP, i.e. the profile of the flow over time as a flood event rises from its base flow to achieve the peak design flow (rising limb) and then as the flood flow rate decreases and the watercourse returns to more normal flows (recession limb). As discussed in Chapter 2 of this report the methodology for this study has been developed further since production of the Inception Report and as such two methodologies have been used UoM 01 to derive the design flow hydrograph shapes (widths) such that these can be applied to a range of design events:
1. FSU Hydrograph Shape generation tool (developed from FSU WP 3.1) for all HEPs representing catchments more than 10 km2
2. FSSR 16 Unit Hydrograph method for catchments less than 10 km2 where no suitable pivotal site is available
6.1.1 FSU Hydrograph Shape Generator
For all of the HEPs which represent catchments larger than 10 km2 the Hydrograph Shape Generator tool developed as an output from FSU WP 3.1 is used to derive the design hydrograph. The Hydrograph Shape Generator Tool is an excel spreadsheet containing a library of parametric, semi- dimensionless hydrograph shapes derived from gauge records of pivotal sites using the HWA software previously discussed. Based on hydrological similarity, a pivotal site hydrograph is ‘borrowed’ and applied at the subject site (in this case the CFRAMS HEP) based on catchment
IBE0700Rp0006 125 F03 NW-NB CFRAM Study UoM 01 Hydrology Report - FINAL descriptors. One potential issue with the use of the Hydrograph Shape Generator tool is the lack of small catchments from which suitably short hydrographs are available. This, along with overly long receding limbs on hydrographs, was particularly noticeable in earlier versions of the software but is much improved with the addition of further pivotal sites to bring the number within the library up to 145.
An example is shown in Figure 6.1 for the HEP 40_1018_1 upstream of Carndonagh on the Donagh River and representing a catchment of 27.7 km2. The hydrograph shape parameters have been adjusted based on the two most hydrologically similar pivotal sites, New Mills on the Swilly (39001) representing a catchment area of 50.7 km2 and Kiltybardan on the Yellow River / Erne system (36021) representing a catchment area of 23.4 km2.
Figure 6.1: Various AEP Hydrographs for Upstream HEP on Donagh River (40_1018_1)
6.1.2 FSSR 16 Unit Hydrograph Method
Early testing of the FSU Hydrograph Shape Generator tool found that for smaller catchments the shape that was derived appeared to be unrealistically long for some of the smaller catchments when compared to the available observed / simulated flow data for small sites. It is thought that this is as a result of a lack of pivotal sites within the library representing small catchments with only two pivotal sites representing a catchment area of less than 10km2 included (with shape parameters identified). Based on this experience it was found that below 10 km2 it was difficult to obtain a suitable pivotal site such that the duration of the hydrograph was not significantly overestimated and therefore for catchments less than 10km2 (but not limited to) an alternative but tried and tested methodology is used to derive the hydrograph. The FSSR 16 Unit Hydrograph method was used for these
IBE0700Rp0006 126 F03 NW-NB CFRAM Study UoM 01 Hydrology Report - FINAL catchments whereby semi dimensionless hydrographs were derived with the same timestep as used for the other hydrographs within the model using the ISIS FSSR 16 UH tool. The methodology followed to derive the FSSR 16 semi dimensionless hydrograph for a subject catchment is summarised below:
1. Time to Peak of the 1 hour unit hydrograph estimated from FSU PCDs (area, MSL, S1085, SAAR & URBEXT) and adjusted for time step
2. The design storm duration is estimated as a function of SAAR and the estimated time to peak
3. An areal reduction factor is calculated as a function of design storm duration and catchment area.
4. Catchment Wetness Index is calculated as a function of SAAR.
5. A soil index is calculated using on FSR Winter Rain Acceptance Potential soil mapping
6. The Standard Percentage Runoff (SPR) is calculated as a function of the soil types within the subject catchment
7. Rainfall characteristics for the subject catchment are derived from FSU DDF gridded outputs (M5-2D & M5-25D) and FSR maps (Jenkinson’s Ratio r)
8. The outputs from steps 2 to 7 are input to the ISIS FSSR 16 boundary unit module to produce a semi dimensionless hydrograph (fitted to a peak of 1) based on Unit Hydrograph principles which can then be scaled to the various design peak flows
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6.2 COASTAL HYDROLOGY
Analysis of the hydrological elements which contribute to coastal flood risk has been undertaken at a national level through the Irish Coastal Protection Strategy Study (ICPSS) and the Irish Coastal Wave and Water level Study (ICWWS). This study does not seek to re-analyse these elements of coastal flood risk but rather seeks to combine them, along with the fluvial elements where applicable, such that the total combined fluvial and coastal flood risk is assessed on an AFA by AFA basis. In the case of the Dunfanaghy AFA the coastal elements (wave, tide and storm surge) only are being considered.
6.2.1 ICPSS Levels
Outputs from the Irish Coastal Protection Strategy Study have resulted in extreme tidal and storm surge water levels being made available around the Irish Coast for a range of Annual Exceedance Probabilities (AEPs). The location of ICPSS nodes are shown in Figure 6.2.
Figure 6.2: Location of ICPSS Nodes in Relation to Coastal AFAs
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Levels for a range of AEPs have been extracted from the ICPSS and are shown in Table 6.1.
Table 6.1: ICPSS Level in Close Proximity to UoM 01 AFAs
Annual Exceedance Probability (AEP) %
2 5 10 20 50 100 200 1000 ICPSS Node AFA Highest Tidal Water Level to OD Malin (m)
NW13 Donegal 2.60 2.75 2.86 2.97 3.11 3.22 3.32 3.57
NW15 Killybegs 2.54 2.68 2.79 2.88 3.01 3.11 3.20 3.43
NW24 Dungloe 2.50 2.64 2.73 2.83 2.95 3.04 3.13 3.35
NW28 Bunbeg - Derrybeg 2.49 2.62 2.71 2.80 2.92 3.01 3.09 3.30
NW35 Dunfanaghy 2.53 2.66 2.76 2.85 2.97 3.06 3.15 3.36
NW36 Downings 2.65 2.79 2.88 2.97 3.09 3.18 3.27 3.48
Bridge End Burnfoot Letterkenny NW42 Newtown Cunningham 2.93 3.06 3.15 3.23 3.35 3.43 3.52 3.71 Ramelton Rathmullan Buncrana
NW46 Malin Town 2.70 2.85 2.95 3.06 3.19 3.29 3.39 3.63
NW52 Moville 1.83 1.97 2.07 2.16 2.28 2.37 2.47 2.68 (Extract from: Irish Coastal Protection Strategy Study, Phase 5 – North West Coast, Work Packages 2, 3 & 4A)
6.2.2 ICWWS Levels
The Irish Coastal Wave and Water level Study (ICWWS) is being progressed by OPW in order to consider the potential risk associated with wave overtopping at exposed coastal locations. The study is currently ongoing but preliminary analysis has been made available for the North Western – Neagh Bann CFRAM Study to identify the areas within UoM 01 which have been identified as potentially vulnerable to this flood mechanism. The length of vulnerable coastline and the affected AFAs are shown in Figure 6.3.
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Figure 6.3: Draft ICWWS potential areas of vulnerable coastline
As shown in Figure 6.3 seven AFAs are potentially vulnerable to flooding due to wave overtopping. These are Buncrana, Downings, Dunfanaghy, Killybegs, Letterkenny, Moville and Rathmullan. The study outputs will be in the form of a range of combinations of water level and wave characteristics (wave height, period, frequency and the joint probability assessed extreme water level) for each annual exceedance probability (AEP %).
6.2.3 Consideration of ICPSS and ICWWS Outputs
It is important to note that the outputs from both the ICPSS and the ICWWS are to be considered separately. The Dunfanaghy AFA which has been identified as only to be analysed for coastal flooding will be assessed through 2D modelling only while the remaining AFA will consist of both 1D and 2D modelled portions. Tidal boundaries will be applied within the 2D models at a scale and distance necessary to capture the complete effects of a dynamic tide and the propagation effects within the relevant bay / inlet areas and at the mouths of watercourse channels to be modelled which have a coastal outfall. At AFAs where fluvial flooding is a consideration within the model the ICPSS levels will be applied considering a range of joint probability scenarios (as detailed in 6.3.2) in order to determine the most onerous flood outline for any AEP. The levels which have been derived from the
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ICPSS will be applied within the 2D portion of the hydraulic (hydrodynamic) models. All ICPSS levels will be applied as the maximum level on the oscillating average tidal cycle observed at the nearest tidal gauge. A typical 1% AEP surge on tidal cycle to staff gauge zero is shown in Figure 6.4 below. Bathymetric and cross sectional survey has been undertaken within the tidal reaches of coastal models in order to accurately capture the effects of tidal propagation within the estuaries and into the tidal reaches of the watercourses where relevant. Details on the model specific application of the ICPSS levels at the coastal boundaries will be contained within the subsequent Hydraulic Modelling report.
Figure 6.4: Typical 1% AEP Coastal Boundary Makeup (to Staff Gauge Zero)
It is important to note that the outputs from the ICWWS are not directly applicable through the standard 2D hydraulic modelling packages used for coastal flood modelling. The assessment of the volume of flood water from wave overtopping is a function of the outputs from the ICWWS (wave height, period, frequency and the joint probability assessed extreme water level), the duration of the event and the dimensions and hydraulic performance of the sea defence and foreshore. At each of the seven AFAs that have been identified as vulnerable to wave overtopping, preliminary analysis will identify the location and length of sea defence / frontage which is vulnerable to wave overtopping. This section will then be assessed against the range of wave / extreme water level combinations for each annual exceedance probability (AEP %) to determine the most onerous scenario. The total overtopping volume from the most onerous scenario for each AEP will then be assessed against the digital terrain model (LiDAR based) to ascertain the mapped flood extents, depth and hazard behind the sea defence / frontage within the AFA. Further details of the methodology for assessment and modelling of the wave overtopping flood risk will be contained within the Hydraulic Modelling report.
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6.3 JOINT PROBABILITY
Joint probability is a consideration within UoM 01 in relation to the occurrence of fluvial – fluvial events, where extreme flood events on tributaries and the main channel of rivers coincide. This is the same for the downstream tidal reaches of UoM 01 models where tidal – fluvial events become a consideration in the 14 models identified for analysis of fluvial and coastal flooding.
6.3.1 Fluvial – Fluvial
There are modelled watercourse confluence points on most of the models within UoM 01. At these confluence points consideration must be given to the probability of coincidence of flood flows within the model. The vast majority of the models in UoM 01 however represent relatively small catchments and as such the critical storm in these small catchments is likely to be similar. Where fluvial to fluvial joint probability is likely to be a significant consideration is at confluence points where two catchments with remote catchment centroids meet or where it is apparent that two catchments may have very different response times. Where a small tributary enters a much larger river system such that the increase in flow is small the consideration of joint probability is unlikely to be significant. The models identified where fluvial to fluvial joint probability is likely to be a significant consideration are at Letterkenny, Ramelton, Ballybofey and Stranorlar and at Lifford.
RPS has specified a high number of HEPs such that as we move down the model, i.e. past confluence points, the hydraulic modeller has to hand the design flows downstream of the confluence point such that they can check that the sum of the inflows within the tributary and the main channel are creating the correct frequency conditions downstream of the confluence point. Where these conditions are not being achieved the modeller will adjust the flows depending on the relationship between catchment descriptors of the main channel and tributary such that the joint probability relationship can be determined to create the correct frequency conditions downstream of the confluence point. This is a modelling consideration and may require an iterative approach. These adjustments will be carried out in line with the guidance provided in FSU WP 3.4 ‘Guidance for River Basin Modelling’ and detailed in the Hydraulic Modelling report.
6.3.2 Fluvial – Coastal
In terms of the CFRAM Study and UoM 01 this category of joint probability may be relevant in the 14 models identified as being at risk of coastal and fluvial flooding. The RPS methodology for assessing joint probability for coastal and fluvial flooding is outlined in the CFRAM Study technical note ‘NTCG GN20 Joint Probability Guidance (RPS, June 2013)’. It advocates a stepped approach to the consideration of fluvial coastal joint probability whereby the relevance is assessed to ascertain at which sites dependence may exist and further analysis is needed:
The first stage in any Joint Probability analysis should be to ascertain whether the flooding mechanisms in any particular area, either AFA or MPW, actually warrant the consideration of the joint probability of occurrence. This screening stage should involve a review of all existing information on
IBE0700Rp0006 132 F03 NW-NB CFRAM Study UoM 01 Hydrology Report - FINAL flooding within the area of interest, such as records of historic events or previous studies including the output from the CFRAM PFRA and the complementary ICPSS data. Where this review identifies either a significant overlap in the areas of fluvial and tidal flood risk or a proven history of significant flooding from both sources, joint probability should be considered. Where the flooding mechanism is heavily dominated by one particular source it is questionable whether joint probability analysis is justified.
An initial screening process has been undertaken on the 14 AFAs within UoM 01 which have been identified as potentially at risk from fluvial and coastal flooding. The results of this screening are shown in Table 6.2 below:
Table 6.2: Initial Screening for Relevance of Joint Probability
Evidence / Model Further JP AFA Name History of Joint Comments No. Analysis Occurrence
1 Malin Town No Small steep catchment, no overlap of No fluvial and coastal flood outlines within the AFA extents
4 Moville No Small steep catchment, small overlap of Check for fluvial and coastal flood outlines at mouth dependence of Bredagh
5 Downings No Coastal flooding liable to enter Downings Check for via the watercourse. Fluvial and coastal dependence could contribute to same flood volume
8 Buncrana No Some overlap of fluvial and coastal and Check for property may be affected. dependence
9 Rathmullan No Small steep catchment, no overlap of No fluvial and coastal flood outlines within the AFA extents
10 Burnfoot Yes Big overlap of flood extents. Low lying Check for area. dependence
11 Bridge End As per above, Some overlap of flood extents. Low lying Check for less relevant area. dependence
12 Ramelton No Some overlap of flood extents. Large Check for flows on Leannan combined with high dependence tides could exacerbate flooding
13 Newtown Yes Big overlap of flood extents. Low lying Check for Cunningham area. dependence
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14 Letterkenny Yes Low lying area of AFA susceptible to Check for coastal and fluvial flooding. dependence
15 Bunbeg – Yes AFA extents generally at higher level Check for Derrybeg above coast. Small overlap of flood dependence outlines
16 Dungloe No Small overlap of fluvial and coastal flood No outlines within the AFA extents
24 Donegal Yes Tidal flood outline reaches far into River Check for Town Eske. dependence
25 Killybegs Yes Small steep catchment, no overlap of Check for fluvial and coastal flood outlines within the dependence AFA extents. ESB report states:‘
A combination of heavy rain and high tides causes flooding every year. The road is liable to flood and properties are affected.
Following initial screening three of the AFAs were removed from the consideration of joint probability of fluvial and coastal flood events. This was generally as a result of there being little potential additional impact of both events occurring simultaneously (e.g. little or no overlap of the extreme fluvial and coastal flood outlines) and there being no evidence of the joint occurrence of both events. In the case of Killybegs there is evidence of the joint occurrence of flood events but a review of the PFRA fluvial flood extents and the ICPSS coastal flood extents showed little overlap of flood extents with the Cashelcummin River which drops steeply through the town before discharging to Killybegs Harbour. There is sufficient uncertainty though to merit further consideration of dependence at the Killybegs AFA.
11 AFAs have therefore been identified as requiring consideration of the joint probability of fluvial and coastal flood events. These are Bridge End, Buncrana, Burnfoot, Letterkenny, Newtown Cunningham and Ramelton within Lough Swilly, Moville within Lough Foyle and separately around the coast Downings, Bunbeg – Derrybeg, Killybegs and Donegal Town. The next stage in assessing the joint probability is to review the available data to ascertain if there is a dependence relationship between extreme coastal and fluvial events. Tidal data is available at four locations which are relevant: Malin Head, Lisahally (Lough Foyle), Arranmore and at Killybegs. Only Malin Head has a long enough record such that it could be used with confidence to ascertain a dependence relationship but the shorter records have been considered where necessary remote from Malin Head. Peak water levels have been extracted from the coastal gauge records for comparison with fluvial flow records. Peak
IBE0700Rp0006 134 F03 NW-NB CFRAM Study UoM 01 Hydrology Report - FINAL water levels representing potential coastal events were identified by setting a threshold value of 0.5m above mean high water neap tides and extracting the peak water level and date & time at the top of the tidal cycle. These were then cross referenced against fluvial flow values where available (water level if little or no flow data was available) from hydrometric river gauges.
Lough Swilly
Fluvial hydrometric data exists for the Swilly River at New Mills (39001 – OPW), the Crana River at Tullyarvan (39003 – OPW) and the River Leannan upstream of Ramelton at Claragh (39006 – EPA). At New Mills continuous flow data is only available from 2004 to 2008 and as such the much longer water level record from 1973 to 2008 was considered. A scatter plot of water levels at Malin Head against the simultaneous water levels from the New Mills gauge is shown below in Figure 6.5.
Figure 6.5: Comparison of Extreme Water Levels at Malin Head with Swilly Fluvial Flows
A visual inspection of the data in Figure 6.5 does not identify a definite correlation between extreme water levels and high flows between the Malin Head coastal gauge and the New Mills fluvial gauge, located approximately 8km upstream of the tidally influenced reaches of the Swilly. The most extreme fluvial water level shown in the scatter plot, approximately 1.8m on the staff gauge, represents a flow of approximately Qmed. The recorded tidal level of approximately 1.65m (chart datum) represents a coastal water level of approximately 0.4m above a mean high water spring tide indicating that there is at least one instance of coincidence between extreme water levels (with a surge element present) and flood flows.
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At Tullyarvan located on the Crana River within the Buncrana AFA extents a long record of continuous flow data is available which can be cross referenced against the coastal gauge record at Malin Head. A scatter plot of water levels at Malin Head against the simultaneous flow data at the Tullyarvan gauge is shown below in Figure 6.6.
Figure 6.6: Comparison of Extreme Water Levels at Malin Head with Crana River Fluvial Flows
From a visual inspection of the data in Figure 6.6 there does not appear to be any correlation between extreme coastal water levels and fluvial flows. There are two instances of fluvial flows above the Qmed value of 75 m3/s within the scatter plot but only one of these is at a water level significantly above a mean high water spring tidal level.
At Claragh located on the River Leannan upstream of the Ramelton AFA extents a long record of continuous flow data is available which can be cross referenced against the coastal gauge record at Malin Head. A scatter plot of water levels at Malin Head against the simultaneous flow data at the Claragh gauge is shown below in Figure 6.7.
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Figure 6.7: Comparison of Extreme Water Levels at Malin Head with River Leannan Fluvial Flows
From a visual inspection of the data in Figure 6.7 there does not appear to be any significant correlation between extreme coastal water levels and fluvial flows. There are four instances of fluvial 3 flows above the Qmed value of approximately 75 m /s within the scatter plot but only one of these is at a water level significantly above a mean high water spring tidal level.
Other Locations
The only other locations in close proximity to AFAs where both fluvial and coastal data is available is at Arranmore (tidal gauge) and on the Owenea River (38001 – OPW) off the west coast of Donegal and at Killybegs Harbour (tidal gauge) and on the Glenaddragh River (37020 – EPA) representing Donegal Bay. Neither tidal record is sufficiently long such that confidence could be gained in any relationship but the consideration of the data available may give some clues as to the presence of dependency.
Only two years of data is available at the Arranmore Tidal gauge the peak water levels of which have been plotted against the simultaneous flows at the Clonconwal Ford gauging station near Glenties (38001 – OPW). No correlation is evident within the simultaneous records although one data point is available which represents the fifth highest coastal water level recorded within the two year period occurring at the same time as a fluvial flood flow. This represents a flow above Qmed (between a 50% and 20% AEP event) occurring simultaneously with a water level approaching a 50% AEP. A scatter plot of the simultaneous water level and flow data is shown in Figure 6.8.
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Figure 6.8: Comparison of Extreme Water Levels at Arranmore with Owenea Fluvial Flows
Twelve years of data is available at the Killybegs Tidal gauge although there are significant gaps in the record. The peak water levels at the gauge have been plotted against the simultaneous flows at the Valley Bridge gauging station (37020 – EPA) on the Glenaddragh River approximately 5km to the west of Killybegs. No correlation is evident within the simultaneous records and no significant coinciding events are evident. A scatter plot of the simultaneous water level and flow data is shown in Figure 6.9.
Figure 6.9: Comparison of Extreme Water Levels at Killybegs with Glenaddragh River Fluvial Flows
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No obvious significant correlations were observed at any of the river flow hydrometric gauging stations when compared to the nearest tidal gauge. However there are some instances of events whereby a fluvial flood flow, albeit with a frequent return period, has occurred at the same time as a water level which is significantly above a mean high water spring tide indicating that some element of extreme water level over and above the effect of the astronomical tide is present at the same time as a potential flood flow.
If we consider the climatic / meteorological conditions which drive both fluvial flood events and extreme water levels it is conceivable that there could be some dependency in the north west of Ireland. The low pressure systems which drive extreme water levels in the Atlantic are also likely to create the conditions for heavy rainfall and hence high fluvial flows when these fronts make landfall. There is however likely to be a delay between storms driving high coastal water levels, when travelling from the prevailing south westerly wind direction, and catchment run-off along the south and west coasts of Donegal. These delays are likely to be smallest for small coastal catchments which have a quick response time to rainfall. This is a consideration for the Cashelcummin River affecting the Killybegs AFA and the Catheen River catchment in the Bunbeg – Derrybeg AFA but not the Clady River catchment as this is highly controlled and attenuated by the ESB Dam on Lough Nacung. The Donegal Town AFA modelled catchments are likely to see significant delay between fluvial flood flows and extreme coastal water levels due to the prevailing direction of travel of weather fronts and due to the highly attenuated nature of the Eske catchment. As such the Donegal Town AFA can be considered to have low dependency and can be ruled out for further analysis.
If we consider Lough Swilly and northern Donegal (eight out of 11 AFAs) there is likely to be some dependency due to weather fronts travelling from the south west (prevailing wind direction) and then creating the conditions for extreme water levels in Lough Swilly, Lough Foyle and off the coast.
In light of the consideration of the available data and climatic / meteorological conditions it is likely that there is dependency in ten of the 14 AFAs where coastal and fluvial flooding is a consideration. The joint probability relationship is likely to be varying but data scarcity will mean that it will not be possible to derive joint probability curves at each of the ten AFAs identified. Therefore it is considered that one joint probability curve is developed for these AFAs based on the best available data and supplemented where relevant with data from similar UK coastal areas based on the methodology outlined in the DEFRA guidance ‘Use of Joint Probability Methods in Flood Management (R&D Technical Report FD2308/TR2)’. This joint probability relationship will be developed in conjunction with the hydraulic modelling and detailed in the Hydraulic Modelling and Mapping Report for UoM 01.
Where further analysis concludes that correlation between total water levels and fluvial flood flow at an AFA can be considered to be negligible it is proposed to follow a simplified conservative approach whereby the 50% AEP design event is maintained for one mechanism while the whole range of design AEP events for the other mechanism are tested and vice versa. This may be subject to sensitivity testing where necessary to ensure the approach does not yield results which could lead to unrealistic flood extents or over design of measures.
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7 FUTURE ENVIRONMENTAL AND CATCHMENT CHANGES
There are a number of future potential changes which may affect the outputs of this study and as such it is prudent that they are identified and their potential impact quantified such that the outputs can accommodate as much as practically possible these changes. This chapter outlines potential environmental changes such as climate change and changes to the catchment such as afforestation and changing land uses. UoM 01 represents catchments which are mostly entirely rural but it has been shown (Chapter 4) that many of them feature high degrees of forest coverage which is known to have affected catchment run-off. Despite the rural nature of the catchments there are some highly urbanised catchments such as the Sprack Burn flowing through Letterkenny and the effect of further urbanisation on the watercourses flowing through AFAs must be considered. These issues, along with potential management and policy changes are considered in this chapter.
7.1 CLIMATE CHANGE
According to the United Nations Intergovernmental Panel on Climate Change (2007) there is “unequivocal” evidence of climate change and furthermore:
"most of the observed increase in global average temperatures since the mid-20th century is very likely due to the observed increase in anthropogenic greenhouse gas concentrations."
(Climate Change 2007, IPCC, Fourth Assessment Report AR4)
The effects of climate change on flood risk management are obvious but in terms of fluvial flooding they are not straightforward to quantify. Changes in sea level have direct impact on coastal flooding and a range of predictions on projected rises are available. A number of meteorological projections are also available for changes in rainfall but these have a wide degree of variance particularly from season to season and are difficult to translate into river flow.
7.1.1 UOM 01 Context
Research into climate change in Ireland is coordinated by Met Éireann through the Community Climate Change Consortium for Ireland (www.c4i.ie). Research summarised in the report ‘Ireland in a Warmer World – Scientific Predictions of the Irish Climate in the 21st Century’ (Mc Grath et al, 2008) seeks to quantify the impact of climate change on Irish hydrology and considers the impacts of nine Irish catchments all of which were outside UoM1 with the nearest being the Moy catchment in Mayo / Sligo. The ensemble scenario modelling from the regional climate change model predicts that between the two periods of 1961 – 2000 and 2021 – 2060 that Ireland is likely to experience more precipitation in autumn and winter (5 – 10%) and less precipitation in summer (5 – 10%). Between the periods of 1961 – 2000 and 2060 – 2099 this trend is likely to continue with increases of 15 – 20% generally, but up to 25% in the northern half of the country in autumn and drier summers of up to 10 – 18%.
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The report seeks to further quantify the impact on hydrology in Ireland through the use of a HBV-Light conceptual rainfall run-off model (provided by Prof. Jan Seibert of Stockholm University) to simulate the effects of climate change on stream flow within the nine Irish catchments. The HBV-Light conceptual rainfall run-off model of the Moy catchment (HA34) was calibrated using historical meteorological data against the hydrometric gauge record at the Rahans gauging station (34001). The Moy model was found to be the best calibrated of the nine catchment run-off models when considered in terms of the R2 error measurement. Validation of the model against observed data at the gauging station found that the Moy model was moderately well calibrated when it came to simulating the annual maximum daily mean flow but that the model appeared to be underestimating mean winter flow. Following simulation of the meteorological climate change ensembles within the run-off models the following observations were made in the Moy and other catchments for the changes between the periods (1961 – 2000) and (2021 – 2060):
Reductions in mean daily summer flow of up to 60% and increases in mean winter flow of up to 20% are the general pattern across all nine study catchments. In the Moy catchment this increase in mean winter flow was found to occur in February and March as opposed to January which was typical in the other catchments.
Mixed results were obtained in terms of increased risk of extremely high winter flows in the Moy catchment although some other catchments such as the Feale and Suir showed risk doubling. It is thought that increased risk is more likely on catchments with a quicker response time.
No change in annual maximum daily mean flow is apparent in the Moy catchment for all return periods but a moderate increase in risk is apparent on two of the other eight.
7.1.2 Sea Level Rise
Research from c4i summarised in the aforementioned report states that sea levels around Ireland have been rising at an annual rate of 3.5mm per year for the period 1993 – 2003 which is higher than the longer term rate of 1.8mm per year for the period 1963 – 2003. This trend is likely to be more modest in the Irish Sea with a ‘net trend’ (allowing for isostatic adjustment of the earth’s crust) of 2.3 – 2.7mm per year. On top of this the report notes that storm surges are likely to increase in frequency.
The latest UK Climate Projections are covered in UKCP09 and put the central estimate of relative sea level rise at Belfast (to the east of UoM 01), based on a medium emissions scenario for the year 2095 at 31.6cm. The central estimate of a high emissions scenario for 2095 is 40.3cm but the predictions range from approximately 10cm to 70cm. The relative sea level rise detailed in UKCP09 allows for vertical land movement (isostatic adjustment) based on estimates taken from Bradley et al (2009). Storm surge models using the operational Storm Tide Forecasting Service (STFS) also show some increase in extreme storm surge although these rises are much less than was predicted in UKCIP02. It is not projected that the surge which could be expected to be exceeded for the 2, 10, 20 or 50 year
IBE0700Rp0006 141 F03 NW-NB CFRAM Study UoM 01 Hydrology Report - FINAL return periods will increase by any more than 9cm by 2100 anywhere along the UK coast. It is noted however that other international climate models predict the rises to be much greater and these cannot be completely ruled out. In particular one high end surge scenario H++ combined with sea level rise infers increases in the 50 year return period extreme water level of as much as 3m by 2100 in some places around the UK.
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7.2 AFFORESTATION
7.2.1 Afforestation in UoM 01
There is much legislation governing forestry practices in Ireland but it is implemented through the document ‘Growing for the Future – A Strategic Plan for the Development of the Forestry Sector in Ireland’ (Department for Agriculture, Food & Forestry, 1996). The plan points out that over the period from 1986 to 1996 afforestation saw quite a dramatic growth in Ireland from a level of approximately 70 km2 annually to almost 240 km2 annually in 1996 largely driven by a growth in private forestry activities. Within UoM 01 the current forest coverage as recorded in the 2006 CORINE land maps for the hydrometric area / UoM is shown in Figure 7.1.
Figure 7.1: CORINE 2006 Forest Coverage in UoM 01 Compared to the rest of Ireland
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The total forested area, including transitional woodland scrub, within UoM 01 is 547km² which is approximately 12% of the total area. The average for the country is approximately 10%. Forest cover spans across most of the UoM with the densest coverage in the south of the Donegal, in particular the south east, on the foothills of the Bluestack Mountains and surrounding Lough Derg. When we compare the CORINE 2006 database to the 2000 database there appears to have been some increase in the forested area as shown in Figure 7.2.
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Figure 7.2: Forest Coverage Changes in UoM 01
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As can be seen from Figure 7.2 there appears to be an increase in the amount of forested area overall but the increase has mostly been in transitional woodland scrub as opposed to actual forest. The areas of forest from the two periods of the CORINE 2006 database are broken down further in Table 7.1.
Table 7.1: Afforestation from 2000 to 2006
CORINE CORINE Annualised Change 2000 2006 Change
Area % of Area % of Area % of Area % of (km²) catch. (km²) catch. (km²) catch. (km²) catch.
Forest 181 3.9 183 4 +2.0 +0.04 +0.3 +0.006
Transitional 283 6.1 364 7.9 +81.0 +1.8 +13.5 +0.29 Woodland Scrub
Total 464 10 547 11.9 +83.0 +1.84 +13.8 +0.35
Total Countrywide 6,631 9.4 7,087 10.1 456 + 0.65 76 +0.11
From Table 7.1 it can be shown that total forest / woodland scrub has increased in UoM 01 between 2000 and 2006 but the actual forest coverage has only slightly increased. When considered together the total area of forest / woodland scrub as a proportion of the catchment is slightly higher than the national average of approximately 10%. Also the rate of increase between 2000 and 2006 is considerably higher than the national average of + 0.11% per year. If the annualised increase in afforestation were to continue for the next 100 years it would more than treble the forest coverage in UoM 01 from 547 km² (11.9%) to 1927 km² (41.8%).
The strategic plan sets out a target for the increase of forest area to 11,890 km² by 2035 in order to achieve a critical mass for a successful high-value added pulp and paper processing industry and this is the main driver behind the increases in forested area. If this value is to be realised nationally the rates of forestation will need to double in comparison to the change observed between 2000 and 2006.
7.2.2 Impact on Hydrology
A number of studies have been carried out on a range of catchments in an attempt to capture the effects of afforestation on run-off rates and water yields. The DEFRA (UK) report ‘Review of impacts of rural land use management on flood generation’ (2004) considers a number of case studies where the effects of afforestation on the catchment run-off were considered. The report concluded that the
IBE0700Rp0006 146 F03 NW-NB CFRAM Study UoM 01 Hydrology Report - FINAL effects of afforestation are complex and change over time. A summary of the main findings in relation to afforestation are given below in relation to the River Irthing catchment in the north of England:
Water yield tends to be less from forest than pasture;
In the Coalburn sub-catchment (1.5 km²) study peak flows were found to increase by 20% in the first 5 years and times to peak decreased, with the effect reducing over time (to 5% after 20 years). The time to peak was also reduced;
In the overall River Irthing catchment (335 km²) the same effect was observed but to a much smaller degree.
The Coalburn catchment provides lessons which may be relevant to parts of UoM 01. The overall impact of afforestation is likely to be negligible in the larger river catchments considering the small proportion of recently forested area against the larger catchment area. However the models receiving waters from upland areas that are likely to see afforestation may be susceptible to the potential effects of afforestation and as such some sensitivity analysis of the effects of afforestation would be prudent. As such it is recommended that sensitivity analysis to quantify the effects of potential afforestation is analysed at:
Model 8 – Buncrana
Model 9 – Rathmullan
Model 10 - Burnfoot
Model 14 – Letterkenny
Model 17 - Glenties
Model 18 - Ardara
Model 19 – Ballybofey & Stranorlar
Model 20 – Killygordon
Model 24 – Donegal Town
In each of these models the effects of afforestation will be modelled using the recommended adjustments to the input parameters shown in Table 7.2.
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Table 7.2: Allowances for Effects of Forestation / Afforestation (100 year time horizon)
Mid Range Future Scenario High End Future Scenario (MRFS) (HEFS)
- 1/3 Tp¹ - 1/6 Tp¹ + 10% SPR² Note 1: Reduce the time to peak (Tp) by one sixth / one third: This allows for potential accelerated run-off that may arise as a result of drainage of afforested land
Note 2: Add 10% to the Standard Percentage Run-off (SPR) rate: This allows for increased run-off rates that may arise following felling of forestry
(Extracted from ‘Assessment of Potential Future Scenarios for Flood Risk Management’ OPW, 2009)
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7.3 LAND USE AND URBANISATION
The proportion of people living in urban areas (classified as towns with a population of 1,500 or more) has increased dramatically in recent years with a nationwide increase of over 10% in the total urban population recorded between the 2006 census and the 2011 census. The total population within County Donegal (UoM 01 lies totally within County Donegal) has increased by varying degrees since 1991 as demonstrated by Table 7.3.
Table 7.3: Population Growth in UoM 01 County Donegal (Source: Central Statistics Office of Ireland)
1991 1996 2002 2006 2011
Donegal Population (Number) 128,117 129,994 137,575 147,264 161,137
Actual Change Since -1,086 1,877 7,581 9,689 13,873 Previous Census (Number) Population Change Since -2.1 1.5 5.8 7.0 9.4 Previous Census (%)
As indicated by Table 7.3, County Donegal has seen significant population rise since 1991. It is evident that the percentage of population change in the county has been steadily increasing with an average annual growth rate of 1.2% since the 1991 census. The county did not show an increase in the share of the rural population since 2006 and as such the data would suggest that the population growth within UoM 01 has been almost entirely within the urban centres.
confirms that urban population growth within the urban AFAs (population > 1500) for the period 2006 – 2011 has been significant ranging from 0.8% in Killybegs up to 31.8% in Carndonagh over the five year census period.
Table 7.4: Population Growth within Urban AFAs (Source: CSO)
Urban Area Population 2011 Increase Since 2006 (%)
Buncrana 6,839 15.7 Letterkenny 19,588 11.4 Donegal 3,982 6.1 Killybegs 2,343 0.8 Carndonagh 2,534 31.8 Moville 2,338 7.5 Convoy 2,376 8.6 Stranorlar 4,529 9.2 Glenties 1,507 1.8
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The total percentage population growth in these AFAs however is 10.3% for the period 2006 – 2011 which equates to an average annual growth rate of approximately 1.6%. To determine if these changes translate into equivalent increases in urbanised areas we must examine the CORINE database within UoM 01 and the changes from 2000 to 2006. A simple comparison of the datasets within UoM 01 appears to show that there has been quite a considerable increase in artificial surfaces within UoM 01 from 45 km² in 2000 to 58 km² in 2006 which represents an increase of just over 28.9% in six years (see Figure 7.3).
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Figure 7.3: UOM 01 CORINE Artificial Surfaces (2000 / 2006)
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Closer inspection of the CORINE datasets shows that a notable proportion of this growth in artificial surfaces is due to changes directly outside the AFAs. There are 3 km² of additional sports and leisure facilities within UoM 01 which accounts for 23.8% of the additional artificial surfaces. A large proportion of which are golf courses, particularly in close proximity to the Downings and Dunfanaghy AFAs, which are generally permeable surfaces and although from first glance at the dataset may appear to be areas of hardstanding will not contribute to surface runoff increase, thus having little impact on the AFAs in terms of the effect of increasing urbanisation on hydrological processes. The AFAs with an increase in the extent of artificial surfaces are:
Buncrana 49.3% increase (6.9% annually) Letterkenny 39.6% increase (5.7% annually) Carndonagh 69.7% increase (9.2% annually) Moville 20% increase (3.1% annually) Clonmany 63% increase (8.5% annually) Newtown Cunningham 5.6% increase (0.9% annually) Ramelton 50% increase (7.0% annually) Downings 110% increase (13.3% annually) Dunfanaghy 27.8% increase (4.2% annually) Convoy 16.7% increase (2.6% annually) Bunbeg & Derrybeg 172.4% increase (18.2% annually) Dungloe 100% increase (12.2% annually) Ardara 21.1% increase (3.2% annually) Donegal 9.1% increase (1.5% annually)
Killygordon, Castlefinn, Lifford and Glenties are the only AFAs where no change in terms of artificial surface land cover was experienced between 2000 and 2006 and Killybegs and Ballybofey/Stranorlar are the only cases which saw decreases in artificial surfaces in the same period.
Killybegs 5.6% decrease (-0.9% annually)
Ballybofey & Stranorlar 8.5% decrease (-1.4% annually)
The Corine dataset used to obtain the above information was not of a high enough resolution to provide data for some smaller AFAs, including; Malin, Burnfoot and Bridge End for both study periods and Rathmullan and Kerrykeel for the 2000 study period. Therefore it was not possible to compare datasets to calculate artificial land cover increase in these areas. Therefore the calculation for annual growth rate below is based on figures for the 20 AFAs with sufficient comparable data.
The average annual growth rate in the artificial surfaces within all UoM 01 AFA extents is just under 5%.
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The CSO has also produced Regional Population Predictions for the period of 2011 - 2026 based on a number of scenarios considering birth rates and emigration. Under all the modelled scenarios considered by the CSO the Border region is set to experience strong population growth.
Under the M0F1 Traditional model, which tends to reflect longer term growth trends, the projected rise for the region in the 15 year period equals 6.3% equating to an average annual growth rate of 0.4%. Under the M2F1 Recent model, which tends to reflect more recent growth rates, the projected rise in population is 25% equating to an annual average growth rate of 1.5%. Any estimation of the rate of urbanisation should consider the three measures of recent growth which have been examined along with the projected population increases from CSO for the region. These are summarised in Table 7.5 below:
Table 7.5: Urbanisation Growth Indicators
Population in Population in Artificial Surfaces CSO M0F1 CSO M2F1 Donegal UoM 01 Urban (CORINE) within Population Population AFAs UoM 01 AFA Projection Projection 1991 - 2011 Extent 2006 - 2011 2011 - 2016 2011 - 2016 2000 - 2006
Average Annual 1.2% 1.6% 4.7% 0.4% 1.5% Growth Rate (%)
7.3.1 Impact of Urbanisation on Hydrology
The effect of urbanisation on run-off is well documented. The transformation from natural surfaces to artificial surfaces, which in almost all cases are less permeable, increases surface run-off such that it is generally faster and more intense. If for example we consider the FSU ‘URBEXT’ catchment descriptor at the most downstream FSU node in the Swilly catchment (at Letterkenny) currently at 4.2% (approximately 4km2) the URBEXT could potentially rise to between 6.3% (approximately 6km2) urbanised (based on growth of 0.4% per annum) and full urbanisation (based on growth of 4% per annum) in the 100 year span which must be considered under the future scenarios. Based on the
FSU equation (WP 2.3) for index flow estimation (Qmed) based on catchment descriptors, the Urban Adjustment Factor (UAF) for the Swilly catchment would vary as shown in Table 7.6 if we consider growth of 1% and 2.5% respectively for the 100 year mid range (MRFS) and high end (HEFS) future scenarios.
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Table 7.6: Potential Effect of Urbanisation on Qmed Flow in HA39 Total Catchment Growth Rate URBEXT1 UAFS2 Qmed Flow m3/s Present Day n.a. 4.2 1.063 72.82
100 Year MRFS 1% p.a. 11.36 1.173 80.36
100 Year HEFS 2.5% p.a. 49.62 1.817 124.47
Note 1: URBEXT is the percentage of urbanisation in the catchment Note 2: Urban Adjustment Factor (UAF) = (1 + URBEXT/100)1.482
Table 7.6 represents one of the more urbanised catchments within UoM 01 and as such can be considered a more onerous example of the potential effect of urbanisation within UoM 01. At the less onerous end catchments with no existing urbanisation could remain totally rural. There are also examples of catchments representing small watercourses on the edges of AFAs which are currently totally rural but which could become totally urbanised in 100 years time if the spatial growth of the urban fabric of the AFA occurs in the direction of that small catchment. In this scenario the application of growth rates to a URBEXT value of zero will have no effect and as such the effect could be missed using a methodology that applies factors to the URBEXT values. It must also be considered that any attempts to predict the spatial growth of AFAs on a 100 year time frame would be highly uncertain as growth rates and growth direction are dictated by complex social, economic and cultural factors which cannot be predicted far into the future.
In light of these large uncertainties it is not considered prudent to attempt to predict the varying effects of urbanisation on a HEP by HEP basis and as such it is considered prudent to apply a factor based on the average URBEXT values within the Unit of Management and the growth rates considered above of 1% and 2.5% respectively for the medium and high end future scenarios. It is still considered prudent though that small urban watercourses with catchments that emanate around the periphery of AFA extents are considered to become much more urbanised and as such will be considered as having URBEXTs of 50% for the mid range and 85% for the high end future scenarios (85% is considered the urban saturation level as some green spaces will always remain).
We must also consider the effect of recent developments in sustainable drainage policy and guidance. The move away from conventional drainage systems is likely to gather pace with the aim of these policies and systems to provide drainage for urban areas which recreates the run-off behaviour of the rural catchment in an attempt to mitigate flood risk. Sustainable drainage policy is already being implemented in Dublin through the Greater Dublin Strategic Drainage Strategy (GDSDS) but is largely in its infancy outside the capital although it would be expected to develop greatly throughout time span of the future scenarios. Therefore the current effect of urbanisation on catchment run-off could be expected to reduce over time as sustainable drainage policy and systems develop.
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There is no directly applicable data / research into the likely effectiveness of SuDS policies at reducing the impact of future urbanisation on catchment run-off in an Irish context. The paper titled ‘Performance and Design Detail of SUDS’ (Macdonald & Jefferies, 2003) outlines research undertaken in Scotland on the effectiveness of a range of different systems implemented and found that the effectiveness is dependent on the type of system implemented (source control or site / regional) but that all systems considered delivered at least a 50% reduction in peak run-off rate rising to over 80% for source control systems.
Given the development of SuDS policies in recent years it is appropriate that some allowance is made for the effectiveness of SuDS at mitigating the impact of urbanisation on peak run-off rates. It is therefore assumed that SuDS policies and systems will mitigate the impact of future urbanisation by half (50% effective) within the tributary watercourses affecting the AFAs where SuDS implementation is most likely to be focussed.
The urban adjustment factors which will therefore be applied to the design flow estimates for the mid range and high end future scenarios for a typical UoM 01 catchment (shown here as a catchment average HEP) and for a small tributary catchment which may be susceptible to full urbanisation are shown below:
Table 7.7: Potential Effect of Urbanisation on Qmed Flow in HA39
UAF Growth Rate URBEXT1 UAF2 (adjusted for SuDS)
HEP Average 1.33 1.020 n.a.
100 Year MRFS 1% p.a. 3.60 1.054 n.a.
100 Year HEFS 2.5% p.a. 15.71 1.241 n.a.
Tributary Catchments susceptible varies varies varies to full urbanisation
100 Year MRFS n.a. 50 1.824 1.412
100 Year HEFS 85 2.488 1.744
Note 1: URBEXT is the percentage of urbanisation in the catchment Note 2: Urban Adjustment Factor (UAF) = (1 + URBEXT/100)1.482
The allowances for urbanisation are based on a robust analysis of population growth, recent increases in artificial surfaces and population projections from CSO. However this is based on extrapolation of current growth rates which are dependent on complex social, economic and environmental factors. Furthermore the estimation of the Urban Adjustment Factor under FSU is based on data from existing urban catchments and therefore does not reflect the impact of recent policy changes and changes to drainage design guidelines where the emphasis is on developments
IBE0700Rp0006 155 F03 NW-NB CFRAM Study UoM 01 Hydrology Report – FINAL replicating the existing ‘greenfield’ flow regime through attenuation and sustainable urban drainage systems. An approach has been developed that considers an average adjustment factor for the majority of HEPs across UoM 01. These adjustment factors will translate into increases in flow of approximately 3% and 22% for the mid range and high end future scenarios respectively. Small catchments emanating from just outside AFAs which would be susceptible to full urbanisation are to be considered separately and will see their flows increase by up to 41% and 74% for the mid range and high end future scenarios respectively.
There is high uncertainty in all of these allowances as discussed above and it is recommended that they are reviewed at each cycle of the CFRAM Studies.
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7.4 HYDROGEOMORPHOLOGY
Hydrogeomorphology refers to the interacting hydrological, geological and surface processes which occur within a watercourse and its floodplain. Erosion and deposition of sediment are natural river processes that can be exacerbated by anthropogenic pressures such as land use practices and arterial drainage.
7.4.1 Soil Type
Figure 7.4 overleaf illustrates the soil types that characterise UoM 01. The predominantly mountainous landscape is reflected by the predominance of peats, and peaty podzols, transitioning to deep gleys as the topography begins to gradually flatten out moving towards the east or to the northern and southern coastlines. The flatter landscape within the Finn and Foyle catchments around Convoy, Castlefinn, Lifford, Ballybofey and Stranorlar and Killygordon are generally characterised by deep well drained mineral podzols, with alluvium soils in the vicinity of the Finn and Foyle. Deep gleys are also predominant along the southern coastline of UoM 01 in the vicinity of Killybegs and Donegal, and along the shores of Lough Foyle at Moville; and Lough Swilly at Bridge End, Burnfoot, Letterkenny, Ramelton, Newtown Cunningham, Rathmullan and Buncrana. Deep gleys indicate a relatively high potential for surface water run-off.
There is currently ongoing research in Ireland and the UK involving modelling the risk of diffuse pollution in river catchments, including sediment transport. Recent research has focussed attention on assessing risk based on erodibility and hydrological connectivity to the river network, with land use/land cover the most common measure of erodibility. While soil type clearly has an influence on erodibility, Reaney et al. (2011) argue that an emphasis upon land cover is warranted as land cover is typically correlated with soil type (refer to Section 7.4.3).
The well drained mineral soils to the east are conducive to its agricultural land uses; pasture and arable (refer to Section 7.4.3). The predominance of peaty soils in the uplands across UoM 01 would indicate relatively high susceptibility to soil erosion and can be considered a source of sediment which if accelerated due to anthropogenic pressures and given the right pathway (channel typology) can make its way to the watercourse networks that drain towards low lying AFAs at the downstream end of these mountainous catchments. In the case of UoM 01 this really applies to all AFAs given the predominance of low lying and/or coastal locations with mountainous areas an upstream feature of all catchments.
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Figure 7.4: UoM 01 Soil Types (Source: Irish Forest Soils Project, FIPS – IFS, Teagasc, 2002)
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7.4.2 Channel Typology
As part of national Water Framework Directive studies on hydromorphology through River Basin District projects a national channel typology dataset was defined for Irish rivers1. It classified river channels into channel type at 100m node points along each reach based on four key descriptors. Table 7.7.8 below outlines the four main channel types and how these relate to valley confinement, sinuosity, channel slope and geology.
Table 7.7.8: Channel Types and Associated Descriptors Channel Type Confinement Sinuosity Slope Geology
Step Pool / Cascade High Low High Solid
Bedrock High Low Variable Solid
Riffle & Pool Low - Moderate Moderate Moderate Drift / Alluvium
Lowland Meander Low High Low Drift / Alluvium
Typical undisturbed channel behaviour in terms of flow is described as follows for each of the channel types shown.
Bedrock: Boulders and cobbles often exposed, but few isolated pools Overbank flows uncommon. Morphology only changes in very large floods.
Cascade and step-pool: At low flows, many of the largest particles (boulders, cobbles) may be exposed, but there should be continuous flow with few isolated pools
Pool-riffle: Gravel bars may be exposed in low water conditions, but gravels and cobbles in riffles as well as logs and snags are mainly submerged.
Lowland Meandering: In low flow conditions some bars or islands may be exposed, but water fills the majority of the channel.
In the national context, UoM 01 is a relatively high slope, high energy system due to the mountainous landscape particularly resulting from small steep coastal catchments. There are also larger river systems further inland, consistent with the lowland meandering type such as the River Finn.
1 (http://www.wfdireland.ie/docs/20_FreshwaterMorphology/CompassInformatics_MorphologyReport)
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There is a predominance of step-pool-cascade and bedrock channels in the mountainous areas to the west of County Donegal with lower lying areas to the east characterised by pool riffle and lowland meandering channels as indicated by Figure 7.5.
Figure 7.5: WFD Channel Typology UoM 01
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Figure 7.6: Modelled Watercourses – Channel Type
Figure 7.6 indicates channel type of the modelled watercourses affecting each AFA which are largely affected by higher energy step-pool cascade river channels and pool-riffle type rivers in the upland areas to the west and south west: However Ballybofey and Stranorlar, Killygordon, Castlefinn and Lifford are part of the Finn/Foyle System which is predominantly low energy lowland meandering at these locations. Similarly the Letterkenny AFA is affected by the lowland meandering Swilly River; Ramelton is affected by the lowland meandering downstream reaches of the River Leannan; Burnfoot and Bridgend are affected by the lowland meandering River Skeoge; and Donegal Town is affected by the River Eske as it meanders towards Donegal Bay. The Owenea River downstream of Glenties AFA is also lowland meandering as it enters Loughros Bay, but the Stracashel and Straboy rivers that flow through Glenties are higher energy pool riffle channels.
These channel types also represent the change in channel slope from relatively steep in upland areas to relatively shallow moving downstream. Figure 7.7 indicates the change in channel steepness across the catchment.
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Figure 7.7: Changes in Channel Slope UoM 01
The steepest channels are located at the mountainous areas of the county including the Slieve League peninsula, Bluestack and Derryveagh Mountains; and Slieve Snaght and its foothills in Inishowen ranging from 0.122 to a maximum of 0.54 (in other words from 1 in 8 to almost 1 in 2). The lower slope channels are predominantly in the east of the county, and to the far west where coastal AFAs (that are also subject to fluvial flood risk) including Dungloe and Bunbeg/Derrybeg are located. These channels generally range from less than 0.033 in lower reaches to 0.07 further upstream (in other words less than 1 in 30 to 1 in 14).
These channel types are typical of Irish catchments. Sediment transport, erosion and deposition are natural morphological processes. In larger catchments it is expected that the upper reaches will be more dynamic with erosion taking place and as the river moves to the lower lands, sediment is accumulated and transported. Sediment deposition is expected where the channel meanders and loses energy. Based on the aforementioned figures, the AFAs that could be affected by sediment deposition are:
Ballybofey and Stranorlar Killygordon Castlefinn Lifford
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Letterkenny
This only becomes an issue if too much sediment is transported from the upper reaches and deposited causing channel capacity issues or localised damage to flood defence structures from scour. Lifford in particular could be affected by sediment build up as it is located at the confluence of The River Mourne and River Finn which meet and become the River Foyle. Here, energy loss from the river system causes sediment deposition which can affect channel capacity and the integrity of the flood walls and embankments located there. Similarly sediment build up at Letterkenny could also be significant. Both situations may be exacerbated by the degree of channelisation and embankments protecting the towns at present.
7.4.3 Land Use and Morphological Pressures
As discussed in Section 7.4.1 land use/land cover is becoming the most common measure of soil erodibility in national research. Figure 7.8 illustrates the land use types within UoM 01. It is essentially rural dominated by peat bogs (37% of catchment area) with pockets of forest (12%) in western upland areas and pasture (22%) to the east. There are several pockets of agricultural areas with significant natural vegetation (10%) across the county. Drainage of bog lands and peat extraction activities potentially lead to large quantities of peat silt being discharged to the receiving waters. The predominance of peat bogs and associated drainage of the land suggests that in general, the level of exposed soil is significant within the catchment and therefore sediment loss to the modelled watercourses is a consideration, particularly within AFAs to the north and west – Bunbeg/Derrybeg, Dungloe, Glenties, Ardara, Carndonagh and Malin.
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Figure 7.8: UoM 01 Land Use (CORINE 2006)
Overgrazing of soils in areas of commonage is also a source of exposed soils washing into headwaters, increasing flashiness through more rapid run-off and erosion increased sediment load to rivers resulting in increased deposition downstream. In Donegal, commonage land accounts for 17.5% of the total area, focussed in the north, west and south west extremities of the county. Under the Water Framework Directive this pressure was identified as a potential risk to river morphological status in the national context. However the Commonage Areas Dataset published by National Parks and Wildlife Service2 in February 2013 designates 70% of the commonage areas in Donegal as undamaged, suggesting that overgrazing is not an issue, certainly not from a flood risk management perspective.
The impact of hydro-geomorphological changes on UoM 01 ultimately applies to the performance of flood risk management options. The impact of sediment transport and deposition within the AFAs highlighted here will be considered further under the hydraulic modelling of options stage of the CFRAM Study.
The transportation of sediment and subsequent deposition within the following AFAs is identified for further consideration under hydraulic modelling.
2 http://www.npws.ie/mapsanddata/habitatspeciesdata/ IBE0700Rp0006 164 F03 NW-NB CFRAM Study UoM 01 Hydrology Report – FINAL
Ballybofey and Stranorlar Killygordon Castlefinn Lifford Letterkenny Bunbeg/Derrybeg Dungloe Glenties Ardara Carndonagh Malin
7.4.4 Arterial Drainage
A further consideration in UoM 01 is the potential effect of arterial drainage on watercourse channel and floodplain geomorphology. The original Arterial Drainage Act, 1945 was a result of the Browne Commission which examined the issue of flooding and the improvement of land through drainage works and was mainly focussed on the agricultural context. Following flood events in the mid to late 80s the emphasis on flood management shifted to the protection of urban areas and as such the Arterial Drainage Amendment Act was passed in 1995. This widened the scope of the act to cover the provision of localised flood relief schemes. The OPW have used the Arterial Drainage Acts to implement various catchment wide drainage and flood relief schemes. Arterial drainage scheme works may consist of dredging of the existing watercourse channels, installation of field drains / drainage ditches and the construction of earthen embankments using dredged material to protect agricultural land.
The extent of the modelled watercourses affected by arterial drainage within UoM 01 is conveyed by the Arterial Drainage Scheme and Drainage District GIS shapefiles provided by OPW. The modelled watercourses which have been subject to arterial drainage schemes and subsequent channel maintenance are shown in Figure 7.9.
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Figure 7.9: Watercourses affected by arterial drainage in UoM 01
As indicated, the modelled reaches affected are those of Letterkenny, Burnfoot and Bridgend AFAs. The Deele and Swillyburn Arterial Drainage Scheme took place downstream of Convoy AFA and flows far enough north of Lifford AFA such that it does not affect either AFA. Similarly the Blanket Nook scheme relates to the watercourses downstream of the Newtown Cunningham AFA extents.
7.4.4.1 The Impact of Arterial Drainage Scheme on UoM 01 Hydrology
The effect of arterial drainage within UoM 01 relates to the River Swilly in Letterkenny and the River Skeoge in Burnfoot/Bridgend. Both schemes involved river widening and deepening and construction of flood embankments. The long term effect of the scheme is land improvement, with some secondary increases in channel conveyance for lower AEP event flows
The effect of arterial drainage schemes across Ireland was considered in FSU WP 2.3 Flood Estimation in Ungauged Catchments through the analysis of gauging station records where there was a pre and post arterial drainage scheme record. Analysis of the gauge station record showed a wide degree of variance in the pre and post arterial drainage index flood flow (Qmed) values but the average change was to increase the Qmed value by approximately 50%. This is in line with previous research carried out on Irish catchments which suggested that arterial drainage schemes can lead to significant changes in peak discharge of up to 60% (Bailey and Bree 1981).
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In the case of Letterkenny and Burnfoot/Bridgend, hydrometric data is not available to compare pre and post drainage Qmed values. The only gauging station located on previously drained rivers is Station 1041 Sandy Mills which is located on the previously drained Swillyburn. This station only has data since 1973 while the drainage scheme was completed in the1960s and as such no records are available for pre and post drainage comparison.
The hydrological analysis and design flow estimation undertaken as part of this study seek to represent as accurately as possible the present day scenario. The ARTDRAIN2 FSU catchment descriptor is included in the ungauged index flow estimation equation where applicable. All of the catchment rainfall run-off models have been generated using the CORINE 2006 database and GSI datasets and have been calibrated against post scheme continuous flow data where available. As such the hydrological inputs derived so far for modelling are considered to accurately reflect the effect of arterial drainage and should represent the best estimates of the present day scenario.
7.4.5 River Continuity
River continuity is primarily an environmental concept relating to the linear nature of the river ecosystem and its disruption due to manmade structures such as weirs and dams which alter river flow and can impede fish migration. It is a morphological pressure which has been given consideration under the Water Framework Directive. Any collated data is of use from a flood risk management perspective as it provides information on such structures and as such can be accounted for in terms of flow regulation in hydraulic modelling.
The risk of impassability may also be an indication of significant hydraulic control and as such is useful in hydraulic modelling. The channel and structure survey undertaken specifically for the North-West Neagh-Bann CFRAM Study includes full geometric survey of these structures and as such ensures their inclusion in the hydraulic modelling phase.
7.4.6 Localised Pressures
As well as the catchment based pressures discussed in this report, localised morphological changes can have an impact on channel capacity and the structural integrity of flood defences due to the effects of scour from high sediment loads within rivers. For example known areas of bank erosion within AFAs can undermine existing channel structures. At this stage of the study, data relating to such localised effects within AFAs has not been received for inclusion in this analysis. Localised areas of bank erosion caused by e.g. cattle poaching were recorded and photographed within AFAs during CFRAM Study team site audits. These are documented and will be fed into the option development process so that such localised risks in terms of channel capacity issues or adverse affects on channel structures can be mitigated. It is also recommended that Progress Group members confirm if such data is available within their organisations that could be of use in the options development process.
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7.5 FUTURE SCENARIOS FOR FLOOD RISK MANAGEMENT
OPW does not have a specific policy for the design of flood relief schemes but has produced a draft guidance note ‘Assessment of Potential Future Scenarios for Flood Risk Management’ (OPW, 2009). The document gives guidance on the allowances for future scenarios based on climate change (including allowing for the isostatic movement of the earth’s crust), urbanisation and afforestation. Table 1 from the guidance has been adapted for the purposes of this study to take into account catchment specific effects and is presented here as the basis for the design flow adjustment for the mid range (MRFS) and high end (HEFS) future scenarios.
Table 7.9: UoM 01 Allowances for Future Scenarios (100 year time horizon)
MRFS HEFS
Extreme Rainfall Depths + 20% + 30%
Flood Flows + 20% + 30%
Mean Sea Level Rise + 500mm + 1000mm
Urbanisation URBEXT multiplied by 2.73 URBEXT multiplied by 11.83 Susceptible sub-catchments Susceptible sub-catchments URBEXT = 50%4 URBEXT = 85%4
Afforestation - 1/3 Tp¹ - 1/6 Tp¹ + 10% SPR² Note 1: Reduce the time to peak (Tp) by one sixth / one third: This allows for potential accelerated run-off that may arise as a result of drainage of afforested land
Note 2: Add 10% to the Standard Percentage Run-off (SPR) rate: This allows for increased run-off rates that may arise following felling of forestry
Note 3: Reflects growth rates of 1% and 2.5% p.a. for mid range and high end future scenarios. To be applied to FSU URBEXT Physical Catchment Descriptor (PCD) up to a maximum of 85%.
Note 4: Applied to areas of sub-catchment or tributary catchment within the AFA which are susceptible to rapid urbanisation but which at present are predominantly undeveloped (i.e. growth rates applied to existing low FSU URBEXT PCD would result in an unrealistically low future scenario URBEXT).
The peak flows for each of the future scenario design events for every HEP can be found in Appendix C.
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7.6 POLICY TO AID FLOOD REDUCTION
Considering the projected growth in population predicted within UoM 01 the main future change which could increase flood risk is urbanisation of the catchment. If not managed correctly rapid urbanisation could lead to large swathes of some catchments becoming hard paved and drained through conventional drainage systems which are designed to remove water from the urban area quickly and efficiently. This could have potentially significant implications for fluvial flooding as the flood flows in the watercourses and rivers would intensify. Some of the smaller watercourses in particular could become prone to flash flooding if they become urbanised.
Sustainable Urban Drainage (SuDS) policy has been about for over a decade now in the UK and Ireland. It is a key concept in OPW’s “The Planning System and Flood Risk Management Guidelines for Planning Authorities” as published in November 2009. The term covers a range of practices and design options that aim to replicate the pre-development surface water run-off characteristics of the undeveloped catchment following development both in terms of water quality but more importantly, from the perspective of flood risk management, in terms of run-off peak flow, intensity and volume. Typical measures include soft engineered solutions such as filter strips, swales, ponds and wetlands and hard engineered solutions such as permeable paving, ‘grey water’ recycling underground storage and flow control devices. The implementation of successful SuDS requires a joined up policy that covers planning, design, construction and maintenance. One of the biggest issues surrounding SuDS implementation is long term ownership and maintenance although the long term benefits of SuDS can be shown to outweigh the costs associated with these issues.
If a comprehensive SuDS policy is implemented covering planning, implementation and maintenance, then the impacts of urbanisation on flood flows can be substantially mitigated.
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8 SENSITIVITY AND UNCERTAINTY
Hydrological analysis and design flow estimation are probabilistic assessments which originate from observed data. The long term conditions which affect the observations, whether they are climatic or catchment, have been shown to varying degrees to be changing over time. Further to this the degree of uncertainty within the sub-catchments analysed under the North Western – Neagh Bann CFRAM Study varies greatly due to the quality and availability of observed data. The following factors which may affect the quality of both the analysed historic events and the estimation of the future design events are listed below:
Hydrometric data record length and gaps Hydrometric data quality (classified in terms of the rating confidence under FSU WP 2.1) High quality meteorological data availability Calibration quality of hydrological models (generally a result of all of the above) Standard error of flow estimation (catchment descriptor based) techniques Future catchment changes, urbanisation, afforestation etc. Climate change
The above list is not exhaustive but seeks to identify the main potential sources of uncertainty in the hydrological analysis. Further to these the list of factors which could potentially affect the uncertainty and sensitivity of the assessment of flood risk under the North Western – Neagh Bann CFRAM Study is subject to further uncertainties and sensitivities related to the hydraulic modelling and mapping stages. Examples of some of the modelling considerations which will further affect the sensitivity / uncertainty of the CFRAM Study outputs going forward from the hydrological analysis are past and future culvert blockage and survey error (amongst others). These considerations will be considered through the hydraulic modelling and mapping report along with the hydrological considerations listed here to build a complete picture of uncertainty / sensitivity of Study outputs.
It is not possible to make a quantitative assessment of all of the uncertainties as some of the factors are extremely complex. Nevertheless it is important that an assessment is made such that the results can be taken forward and built upon through the subsequent phases of the study. It is also important that the potential sources of uncertainty in the hydrological analysis and design flow estimation are flagged such that the integrated process of refining the hydrological inputs and achieving model calibration can be achieved more efficiently through a targeted approach. A qualitative assessment has therefore been undertaken to assess the potential for uncertainty / sensitivity for each of the models and is provided in this chapter. The assessed risk of uncertainty is to be built upon as the study progresses through the hydraulic modelling and mapping stages. Following completion of the present day and future scenario models the assessed cumulative uncertainties can be rationalised into a sensitivity / uncertainty factor for each scenario such that a series of hydraulic model runs can be performed which will inform the potential error on the flood extent maps.
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8.1 UNCERTAINTY / SENSITIVITY ASSESSMENT MODEL BY MODEL
Table 8.1: Assessment of contributing factors and cumulative effect of uncertainty / sensitivity in the hydrological analysis
Model Model Uncertainty / Sensitivity – Present Uncertainty / Sensitivity – Future Notes No. Name Day Scenario Scenarios
Observed Catchment Ungauged Forest- Urban- Climate Sedimen- Flow Data2 Flow ation4 isation5 Change6 tation7 Data1 Estimates3
1 Malin n.a. Low High / Low Low Medium Medium Estimates dependent on FSU equation on small catchment Medium with no applicable pivotal sites. Catchment delineated to high degree of certainty and little scope for urbanisation or afforestation. Exposed soils in upper catchment but little scope for deposition in steep modelled reaches. However effect of sediment deposition at discharge points to estuary (within coastal model) must be considered further. 2 Carndonagh n.a. Low Medium Low Low Medium Medium / Estimates dependent on FSU equation with no applicable pivotal sites. Catchment delineated to high degree of Low certainty and little scope for urbanisation or afforestation. Exposed soils in upper catchment but likely to deposited in flatter reaches below the AFA. 3 Clonmany n.a. Low Medium Low Low Medium Low Estimates dependent on FSU equation with no applicable pivotal sites. Catchment delineated to high degree of certainty and little scope for urbanisation or afforestation. 4 Moville n.a. Low Medium Low Low Medium Low Estimates dependent on FSU equation with no applicable pivotal sites. Catchment delineated to high degree of certainty and little scope for urbanisation or afforestation 5 Downings n.a. High / High Low Medium Medium Low Estimates dependent on FSU equation with no applicable Medium pivotal sites. Catchment not delineated under FSU so catchment descriptors calculated or donated from nearby sites. Some uncertainty in urbanised (present & future) extents due to growth of caravan parks. 6 Dunfanaghy n.a. n.a. n.a. n.a. n.a. Medium / n.a. Coastal flood risk only. Climate change uncertainty in sea Low level rise considered lower than catchment hydrology uncertainty. 7 Kerrykeel n.a. Low Medium Low Low Medium Low Estimates dependent on FSU equation with no applicable pivotal sites. Catchment delineated to high degree of certainty and little scope for urbanisation or afforestation
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Model Model Uncertainty / Sensitivity – Present Uncertainty / Sensitivity – Future Notes No. Name Day Scenario Scenarios
Observed Catchment Ungauged Forest- Urban- Climate Sedimen- Flow Data2 Flow ation4 isation5 Change6 tation7 Data1 Estimates3
8 Buncrana Medium Medium / Medium / Medium Medium Medium Low Gauge station on modelled watercourse although Low Low uncertainty in rating. Dam constructed in catchment approximately 20 years ago. Potential for urbanisation in smaller catchments around AFA extents and forestation in upland catchments of Crana and Mill Rivers. 9 Rathmullan n.a. Medium High / Medium Low Medium Low Estimates dependent on FSU equation on small catchment Medium with no applicable pivotal sites. Uncertainty in catchment flow path at AFA extents. Potential for forestation. 10 Burnfoot n.a. Medium / Medium Medium Low Medium Low No gauged data although some suitable pivotal site data Low informs adjustment factor. Some uncertainty in the Skeoge catchment as it crosses the border. Potential for forestation. 11 Bridge End n.a. Medium Medium Low Low Medium Low No gauged data although some suitable pivotal site data informs adjustment factor. Uncertainty in the Skeoge catchment as it crosses the border. Potential for some urbanisation of minor trib. 12 Ramelton Medium / Low Low Low Low Medium Low Leannan catchment well gauged with FSU pivotal sites Low upstream. Small trib ungauged. Potential for forestation in Leannan catchment but impact would be very diluted within large catchment area. 13 Newton n.a. Medium / Medium Low Low Medium Low Flat catchment subject in the past to arterial drainage. No Cunningham Low gauge data applicable for adjustment. No significant potential urbanisation or forestation. 14 Letterkenny Medium / Medium Medium Medium High / Medium Medium FSU pivotal site just upstream of AFA extents. Potentially Low Medium some uncertainty in the catchment descriptors due to the rapid urbanisation in last ten years. Low uncertainty in main Low channel of Swilly River but high in tribs running of Letterkenny hills. Potential for further urbanisation and some forestation in catchment. Swilly is low lying / meandering through the AFA so susceptible to sediment deposition. 15 Bunbeg - High / Low Medium Low Low Medium Medium / High uncertainty in ESB data for Clady River. Catheen River Derrybeg Medium Low catchment not hydrologically similar. Little or no scope for future urbanisation or forestation. Exposed soils in upper catchment of Clady River but dam upstream and modelled reach generally steep.
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Model Model Uncertainty / Sensitivity – Present Uncertainty / Sensitivity – Future Notes No. Name Day Scenario Scenarios
Observed Catchment Ungauged Forest- Urban- Climate Sedimen- Flow Data2 Flow ation4 isation5 Change6 tation7 Data1 Estimates3
16 Dungloe n.a. Low Medium / Low Low Medium Medium / No gauge data but a lot of applicable pivotal sites. Little or Low Low no scope for future urbanisation or forestation. Exposed soils in upper catchment however Loughs upstream likely to intercept most sediments. 17 Glenties Medium / Low Low Medium Low Medium Medium / FSU pivotal site downstream of AFA. Potential for future Low Low forestation of the catchment. Exposed soils in upper catchment but modelled reaches within AFA generally steep. 18 Ardara n.a. Low Medium Medium Low Medium Medium Estimates dependent on FSU equation with no applicable / Low pivotal sites. Catchment delineated to high degree of certainty and little scope for urbanisation but some scope for forestation. Exposed soils in upper catchment and potential for deposition within AFA must be considered further. 19 Ballybofey & Medium / Low Medium Medium Low Medium Medium Flow data available on main channel of River Finn with good Stranorlar Low degree of confidence following rating review. Potential for future forestation of some of the tributary sub-catchments. Meandering reaches of River Finn to be considered further for potential sediment deposition. 20 Killygordon Medium / Low Medium Medium Low Medium Medium Flow data available on main channel of River Finn with good Low degree of confidence following rating review. Potential for future forestation of some of the tributary sub-catchments. Meandering reaches of River Finn to be considered further for potential sediment deposition. 21 Castlefinn Medium / Low Medium Low Low Medium Medium / Flow data available on main channel of River Finn with good Low degree of confidence following rating review. Meandering Low reaches of River Finn to be considered further for potential sediment deposition although River Finn does not flow through AFA extents 22 Lifford Medium / Low Low Low Low Medium High Flow data available on main channel of River Finn with good Low degree of confidence following rating review and good gauged data on River Mourne just upstream of AFA. Large catchment so unlikely to be greatly affected by urbanisation or forestation. Downstream limit of River Finn where it confluences with the Mourne adjacent to AFA. Potential river energy losses at this location may mean high susceptibility to sediment deposition.
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Model Model Uncertainty / Sensitivity – Present Uncertainty / Sensitivity – Future Notes No. Name Day Scenario Scenarios
Observed Catchment Ungauged Forest- Urban- Climate Sedimen- Flow Data2 Flow ation4 isation5 Change6 tation7 Data1 Estimates3
23 Convoy Medium / Low Low Low Low Medium Low FSU pivotal site downstream of AFA. Little scope for future Low urbanisation or forestation. 24 Donegal Medium Low Medium / Medium Medium Medium Low Gauging stations located upstream of AFA on Eske but a fair Town Low degree of uncertainty. All catchments could be subject to future urbanisation and smaller catchments susceptible to urbanisation. 25 Killybegs n.a. Low High / Low Medium Medium Low Estimates dependent on FSU equation on small catchment Medium with no applicable pivotal sites. Some scope for urbanisation of small catchment emanating from edge of AFA extents.
1 Observed flow data marked n.a. where there is no gauged data within the modelled catchment to inform the flood flow estimation for the model. Low to high reflects uncertainty in the gauged data at Qmed if available. 2 Catchment data refers to delineated catchment extents or catchment descriptors. Low to high reflects uncertainty in physical catchment descriptors or catchment delineation. 3 Ungauged flow estimates based on FSU WP 2.3. Dependent on 1 & 2. Where high quality gauge data is available along modelled reach upon which adjustment can be performed then uncertainty is considered low. Where no gauge data is available within catchment then certainty is considered medium to high. Uncertainty greater in smaller, urbanised catchments where ungauged estimation methodologies are considered to be more sensitive. 4 See Section 7.2 Considered to be low risk of uncertainty to hydrological analysis in most of UoM 01. High risk where there is significant risk of forestation of small catchment just upstream of AFA which is the dominant source of flood risk to the catchment. 5 See Section 7.3 Considered generally to be a medium to high risk of uncertainty to hydrological analysis in urban areas where potential significant, dense urbanisation is possible which would make up a significant proportion of the catchment. High risk where small catchments largely contained within the AFA extents and potentially subject to high risk of urbanisation. 6 See Section 7.1 Considered a medium risk of uncertainty to hydrological analysis in all cases due to the range of projections. 7 Sedimentation of channels causing capacity issues or localised impacts on channel structures are to be considered in options development phase of CFRAM Study where relevant. Degree of uncertainty indicated here is based on qualitative assessment of accelerated soil erosion risk due to land use pressures and pathways to watercourses. Considered under future scenarios only as present day sediment conditions are reflected by recently captured channel survey data.
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8.2 CONCLUSIONS OF SENSITIVITY ANALYSIS
The assessment of uncertainty and sensitivity in each category is relative within UoM 01. The assessment of uncertainty as being medium or high does not suggest that the analysis is poor but rather in the context of the design flow estimation techniques being employed in the North Western – Neagh Bann CFRAM Study that uncertainty in that category is towards the higher end of the range. For example the modelled watercourse which affects the Ardara AFA is fairly small, ungauged and mainly rural but is well defined in terms of catchment data. However the flow estimation methods used are based on catchment descriptors only. Other sites which are either nearby or hydrologically similar have been considered for the transfer of data but no site could be considered definitively for the transfer of data and consideration of multiple sites did not indicate a clear pattern such that adjustment of the Qmed value could be done with confidence. In light of this the estimates are based solely on the FSU catchment descriptor equation. The ungauged estimates have therefore been labelled as having a medium to high degree of uncertainty yet the procedure for estimating and adjusting is in line with best practice and would be consistent with the recommended estimation methodology for a typical ungauged rural Irish catchment. This is common within UoM 01 due to the lack of high quality gauge data and the disparate nature and small scale of the catchments.
In UoM 01 the largest degree of uncertainty for the present day scenarios is attributed to Downings. The unavailability of gauge data for the catchment, its small size and lack of FSU catchment data all results in a high degree of uncertainty in the ungauged catchment estimates.
In the future scenarios climate change has been defined as a potential source of significant uncertainty due to the inherent uncertainties surrounding climate change science and how these will translate into changes in fluvial flood flows in Ireland. Within UoM 01 it is considered that urbanisation is not generally a source of high uncertainty in the prediction of future flood flows with the exception of Buncrana, Donegal Town, Downings, Killybegs and Letterkenny. These AFAs are generally of a size and growing such that large swathes of dense development drained through conventional drainage systems could in the future make up a large proportion of the catchment or sub-catchments. The factors which affect urbanisation are difficult to predict for a 100 year time horizon due to the complex social, cultural and economic factors which affect it. At the upper limit of the predictions large swathes of the smaller catchments on the periphery of towns could become fully urbanised which could more than double some of the index flood flows. There is also the affect of sustainable drainage to consider which adds a further degree of uncertainty depending on the extent to which it is successfully implemented.
Afforestation has been identified as a potential source of future uncertainty for nine of the AFAs / models. In the majority of catchments / sub-catchments in these models the proportion of recently forested land coverage is likely to be low but for AFAs which have an area directly upstream which could be newly forested over a short time frame (such as sub-catchments which are on the edge of forested area) this could be significant. The impact of hydro-geomorphological changes has been
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9 CONCLUSIONS
Limited hydrometric data exists within UoM 01 which is of sufficient quality such as to be of use for design flow estimation and as such there is generally a high degree of uncertainty in design flow estimates, although there is no evidence to suggest that the FSU Qmed equation (WP 2.3) performs poorly within the unit of management. Meteorological data is also sparse within the catchment with the high temporal resolution data needed for driving rainfall run-off models being available in only a few locations. These locations are lacking any hydrometric data that would allow some calibration of rainfall run-off models and as such it has not been possible to apply this approach within UoM 01.
Design flow estimates have been compared to those for similar catchments where high quality gauge data is available to arrive at improved adjusted estimates of flood flow. The calibration of the hydraulic models to historic flood data and observed evidence will further help to screen out design flow estimates which are not reflective of the actual behaviour of these sub-catchments.
There are many potential future changes to the catchment, margins of error and uncertainties which must be considered within the study. However the cumulative application of worst case scenarios, one on top of the other could lead to erroneous flood extents which do not take into account the diminishing cumulative joint probability of these factors. For this reason this report has separated future UoM 01 changes that have a high degree of certainty in the projections from those changes which are less certain. Future changes which have a high degree of uncertainty, along with margins of error and other uncertainties have been risk assessed individually. This risk assessment is to be taken forward and built upon through the hydraulic modelling phase with the ultimate goal of providing a single error margin for the flood extent maps on an AFA by AFA basis. This rationalised single error margin is designed to inform end users in a practical way as to the varying degree of caution to which mapped flood extents are to be treated.
9.1 SUMMARY OF THE RESULTS AND GENERAL PATTERNS
The catchment can be characterised hydrologically as follows:
The catchment has a wide range of climatic and physiographic characteristics. The drier, lowland areas in the Foyle floodplain have SAAR values as low as 1000mm while catchments in the upland areas of the Bluestack and Derryveagh Mountains have SAAR values in excess of 2000mm.
Hydrometric data is of poor quality and availability.
Meteorological data is of low availability in the catchment.
Flood behaviour when defined in terms of the growth curve, i.e. in orders of magnitude greater than the median event, is relatively more extreme in the upper catchment than would have
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been thought based on older methodologies (FSR). This is in line with other more recent, catchment specific studies.
The 1% AEP flood event ranges from approximately 1.7 to 2.8 times larger than the median flood flow. This compares to approximately 2 under FSR.
Design flow estimation is the primary output of this study and has been developed based on the analysis contained in this report. This analysis is based on quality assessed observed data and the latest Irish catchment flood hydrology techniques. This analysis will require further validation through the calibration of the hydraulic models. As modelling progresses there may be some elements of the hydrological analysis that might need to be questioned and interrogated further. This is reflective of best practice in hydrology / hydraulic modelling for flood risk assessment. RPS believe that through the use of best practice statistical methods that the design flow estimation has as high a degree of certainty as is possible prior to calibration / validation and that this will save time and increase accuracy as UoM 01 moves into the hydraulic modelling phase of the CFRAM Study process. Nevertheless the modelling may necessitate the adjustment of some of the design flows and as such any adjustments made will be summarised within the Hydraulic Modelling Report.
9.2 RISKS IDENTIFIED
The main potential source of uncertainty in the analysis is due to the lack of hydrometric gauge data in the majority of catchments and to a lesser extent the lack of high resolution rainfall data which can be used to simulate catchment run-off.
Following this cycle of the North Western – Neagh Bann CFRAM Study the main potential adverse impact on the hydrological performance of the catchments is the effect of future changes and in particular the scope for rapid urbanisation of towns, particularly Letterkenny. Further rapid urbanisation of the tributary catchments around Letterkenny could significantly increase flood risk if this leads to development which is unsustainable from a drainage perspective.
9.3 OPPORTUNITIES / RECOMMENDATIONS
The lack of available hydrometric and meteorological data for use in the study highlights potential opportunities to improve the hydrological analysis further in the next cycle of the North Western – Neagh Bann CFRAM Study:
1. There are only six stations with flow data available located on the modelled reaches within UoM 01 and of these stations only three were classified as having a good enough rating such that they were taken forward for use within the Flood Studies Update. If all the stations with flow data are considered which are on or directly upstream or downstream of the rivers to be modelled there are still 15 AFAs which can be considered ungauged. Any of these ungauged AFAs would obviously benefit from the addition of a hydrometric gauge.
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Recommending that new gauging stations are installed on the ungauged watercourses affecting the AFAs is unrealistic within the timeframe of this or even the next CFRAM Study cycle. Multiplied up nationally this would lead to a long list of gauging stations which would likely remain unrealised at a time when many organisations are rationalising their existing networks and may even obscure the case for those gauging stations which are more acutely needed. A more focussed exercise to identify the most acutely needed gauging stations would be more effectively undertaken following hydraulic modelling and consultation such that the AFAs which are at greatest risk, are most affected by uncertainty in the design flow estimates and which would significantly benefit from additional calibration data are identified as priorities. As such it is recommended that this exercise is undertaken following the hydraulic modelling stage.
In the interim improvements to the existing hydrometric gauge network should focus on improving the ratings through the collection of additional spot flow gaugings at flood flows at the existing stations on, directly upstream or downstream of AFAs:
01041 Sandy Mills (OPW) 01042 Dreenan (OPW) 01043 Ballybofey (OPW) 37071 L. Eske (EPA) 38001 Clonconwal Ford (OPW) 38002 Gweedore (ESB) 39001 New Mills (OPW) 39003 Tullyarvan (OPW) 39006 Claragh (EPA) 39009 Aghawoney (OPW)
Furthermore there is a shortage nationally of very small and / or heavily urbanised catchment gauge data and as such new gauging stations on this type of catchment, ideally within a CFRAM Study AFA, could be progressed immediately.
2. The availability of high temporal resolution rainfall data may be used to supplement hydrometric data. Efforts should be made prior to the next cycle of the North Western – Neagh Bann CFRAM Study to improve the availability of high resolution rainfall data within UoM 01. This may take the form of additional hourly rainfall gauges or may involve the improvement of data collected at alternative sources such as the Castor Bay radar at Lough Neagh.
3. There are 10 coastal AFAs for which the consideration of the joint occurrence of high river flows and extreme coastal water levels is necessary. The only long term tidal gauge data within UoM 01 of sufficient length for extreme value analysis is at Malin Head which is so remote from any long term fluvial gauge locations that the applicability of the data for joint
IBE0700Rp0006 179 F03 NW-NB CFRAM Study UoM 01 Hydrology Report - FINAL
probability analysis is poor. In order to develop an improved understanding of the dependence between river flows and extreme coastal water levels in around the Donegal / UoM 01 coastline it is recommend that extended records are collected and made available for the next cycle of the CFRAM Study at the existing tidal gauges at Arranmore, Killybegs, Malin Head and Lisahally (NI).
4. There is high uncertainty in the projections for future scenarios and it is recommended that these are reviewed in future cycles of the CFRAM Studies.
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10 REFERENCES:
1. EC Directive on the Assessment and Management of Flood Risks (2007/60/EC)
2. S. Ahilan, J.J. O’Sullivan and M. Bruen (2012): Influences on flood frequency distributions in Irish river catchments. Hydrological Science Journal, Vol. 16, 1137-1150, 2012.
3. J.R.M. Hosking and J.R.W. Wallis (1997): Regional Frequency Analysis – An approach based on L-Moments. Cambridge University Press.
4. Flood Studies Update Programme – Work Package 2.1 – Review of Flood Flow Ratings for Flood Studies Update – Prepared by Hydrologic Ltd. for Office of Public Works (March 2006)
5. Flood Studies Update Programme – Work Package 2.2 – “Frequency Analysis” – Final Report – Prepared by the Department of Engineering Hydrology of National University of Ireland, Galway for Office of Public Works (September 2009).
6. Flood Studies Update Programme – Work Package 2.3 – Flood Estimation in Ungauged Catchments – Final Report – Prepared by Irish Climate Analysis and Research Units, Department of Geography, NUI Maynooth (June 2009)
7. Flood Studies Update Programme – Work Package 3.1 – Hydrograph Width Analysis – Final Report – Prepared by Department of Engineering Hydrology of National University of Ireland, Galway for Office of Public Works (September 2009)
8. Flood Studies Update Programme – Work Package 5.3 – Preparation of Digital Catchment Descriptors – Pre-Final Draft Report – Prepared by Compass Infomatics for Office of Public Works (January 2009)
9. Michael Bruen and Fasil Gebre (2005). An investigation of Flood Studies Report – Ungauged catchment method for Mid-Eastern Ireland and Dublin. Centre for Water Resources Research, University College Dublin.
10. North Western - Neagh Bann CFRAM Study – UoM 01 Inception Report. Office of Public Works, 2012.
11. Flood Estimation Handbook- Statistical Procedures for Flood Frequency Estimation, Vol. 3. Institute of Hydrology, UK (1999).
12. NERC, 1975. Flood Studies Report. Natural Environment Research Council.
13. Institute of Hydrology Report No. 124 – Flood Estimation for Small Catchments (D.C.W. Marshall and A.C. Bayliss, June 1994)
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14. Ireland in a Warmer World, Scientific Predictions of the Irish Climate in the Twenty First Century Prepared by Met Éireann and UCD (R. McGrath & P. Lynch, June 2008)
15. Growing for the Future – A Strategic Plan for the Development of the Forestry Sector in Ireland (Department for Agriculture, Food and Forestry, 1996)
16. Review of Impacts of rural land use management on flood generation (DEFRA, 2004)
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APPENDIX A
UOM 01 HYDROMETRIC DATA STATUS TABLE
A1
APPENDIX B
RATING REVIEWS
SANDY MILLS (01041)
The Sandy Mills gauging station 01041 is located in County Donegal on the River Deele. The river reach represents the model connection between modelled reaches of the River Deele for the Convoy (upstream) and Lifford (downstream) AFA models.
The gauge is located approximately 15m upstream of the road bridge over the River Deele, on the Raphoe to Cloughfin road, which is approximately 3.5km upstream of the R264 bridge over the River Deele at Ballindrait. The gauge is in a cross section approximately 20m wide with a minimum bed level of 3.315m OD Malin and bank levels of 6.888m OD Malin (left bank) and 7.054 m OD Malin (right bank). The current ordnance datum level of the gauge zero was surveyed as 4.019m OD Malin which is 379mm above the previous stated OPW staff gauge zero level of 6.340m OD Poolbeg. It is not known why there is such a large discrepancy between the two staff gauge zero levels but the OPW staff gauge zero level was used to complete the rating review as the spot gauge and water level data produced by OPW relates to their zero level and any discrepancy is thought to be relative.
Figure 1: Modelled Reaches and Gauging Station Location
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The gauging station is managed by the OPW and is currently active. Continuous water level records have been provided from 1973 - 2011. Spot flow gaugings for the station have been provided with the highest flow gauging recorded at 34.67m3/s relative to a stage height of 1.58m on the gauge board. The rating was given a classification of B under the national review undertaken for FSU Work Package
2.1. This indicates there is confidence in the rating up to Qmed which equates to a stage height of
The rating review modelled reach extends approximately 450m in the upstream direction and 3.5km downstream of the gauge. There is one bridge along this reach of the River Deele located just downstream of the gauge. The upstream and downstream approaches to the gauge have slight bends as the river gently meanders in the vicinity of the gauge. The one dimensional hydraulic model uses information from 32 original cross sections, including the bridge structure.
9.0
8.0
7.0
6.0
5.0 Elevation (m AD) (m Elevation
4.0
3.0 0 50 100 150 200 Offset (m)
Figure 2: Model Cross-Section at Gauge Location (Top); Photo of gauge location (Bottom)
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The downstream boundary condition applied to the model was calculated as the normal flow Q-h relationship with the upstream boundary consisting of a hydrograph with a peak flow of 203 m3/s representing an estimated 0.1% AEP flood event. This section of the River Deele is not represented by LiDAR and as such it was only possible to model the reaches in a 1D model. Due to the nature of the floodplain which is generally flat and at many locations having a level below the top of bank level it was considered that its inclusion within a 1D model would lead to flow within the floodplain at stage levels which are unrealistic and therefore only the flows that were contained within or near the banks were considered in the model calibration and rating curve creation. The model was calibrated by applying at the upstream boundary, lower flow gauged data, using spot gauge and the most up to date rating curve information for the Sandy Mills gauge. Adjustments were made to the Manning’s n values for channel and bank roughness to reflect vegetation growth and channel roughness in order to develop a realistic model of the channel and flow conditions that is calibrated to the spot gaugings. The results of the rating review are shown below in Figure 3 and Table 1. The graph demonstrates the derived RPS rating curve and shows the comparison between the OPW rating curve (which consists of 1 equation) and spot gaugings.
Figure 3: Comparison of Existing OPW Rating Curve and RPS Rating Curve for all flows
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Min Stage Max Stage Section C a b (m) (m)
1 0.13 0.68 10.524 0.029 2.079 2 0.68 1.75 4.973 0.337 2.793 3 1.75 2.21 0.005 3.874 5.234 4 2.21 3.56 37.654 -0.737 1.148
Where: Q = C(h+a)b and h = stage readings (metres)
Table 1: Rating Equations for Gauge 01041
Figure 3 shows that the model fairly represents the OPW rating curve based on the flow gaugings up to the limit of the OPW rating at 110 m3/s. Calibration at lower flows was found to be poor although the model provides a good fit to the highest spot flow gaugings. The best fit rating curve was achieved with a Manning’s n value of 0.035. Analysis of the results show that floodwaters remain in bank at the gauged section until river flow exceeds 124 m3/s or 7.2m (OD Malin). As the model was unable to represent out of bank flows accurately it has not been possible to extend the rating curve into the out of bank range with confidence. The modelled rating curve does not suggest uncertainty in the rating at the median flood flow.
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DREENAN (01042)
The Dreenan gauging station 01042 is located in the AFA of Ballybofey & Stranorlar in County Donegal on the River Finn. The river reach represents the reaches of the River Finn just downstream of the centre of the Ballybofey & Stranorlar AFA and is also located upstream of the Killygordon, Castlefinn and Lifford AFAs.
The gauging station is located approximately 40m upstream of the Millbrae Bridge, which is approximately 1km downstream of the Main Street (N15) Bridge, over the River Finn. The gauge is located on the right bank of a cross section approximately 50m wide with a minimum bed level of 11.044m OD Malin and bank levels of 14.711m OD Malin (left bank) and 15.979m OD Malin (right bank). The current ordnance datum level of the gauge zero was surveyed as 11.604m OD Malin which is 51mm above the previous stated OPW staff gauge zero level of 14.290m OD Poolbeg. The surveyed staff gauge zero level was used to complete the rating review.
Figure 1: Modelled Reaches and Gauging Station Location
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The gauging station is managed by the OPW and is currently active. Continuous water level records have been provided from 1972 - 2011. The gauge was however temporarily removed in 2004 due to the construction of the road bridge at Millbrae just downstream of the gauge. Spot flow gaugings and flow data are available for the period of 1972 – 2004 but OPW have indicated that the reliable limit of the rating for this period is very low (stage height of 0.8m) and there can be no confidence in the rating at flood flows. For this reason OPW have not produced an AMAX series for this station. No spot gaugings were initially provided for the period since 2004 when the new bridge was constructed and as such it is not possible to calibrate the modelled rating curve to observed data.
The study reach extends approximately 400m in the upstream direction and 2.2km downstream of the gauge. There is one bridge structure (Millbrae Bridge) along this reach of the River Finn located approximately 40m downstream of the gauge location. The upstream and downstream approaches to the gauge are relatively straight. The one dimensional hydraulic model uses information from 60 original cross sections, including the bridge structure. The downstream boundary condition applied to the model was calculated as the normal flow Q-h relationship with the upstream boundary consisting of a hydrograph with a peak flow of 880 m3/s representing an estimated 0.1% AEP flood flow in the River Finn.
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18.0
16.0
14.0 Elevation (m AD) (m Elevation 12.0
10.0 0 50 100 150 Offset (m)
Figure 2: Model Cross-Section at Gauge Location (Top); Photo of gauge location (Bottom)
As discussed no observed flow data for the period since the new Millbrae Road bridge was constructed was available and flow data from before this period could not be considered representative of the current flow – water level relationship. As such calibration of the rating curve was focussed on the estimating the roughness co-efficients based on site photographs and the Manning’s ‘n’ values which were used to achieve calibration of the Ballybofey (01043) rating review model located approximately 2.6km upstream on the River Finn. However, following completion of the rating review model spot gaugings taken since late 2011, representing the period since the Millbrae Road Bridge was built, were made available which have been used to validate the modelled rating curve.
The results of the rating review are shown below in Figure 3 and Table 1. The graph demonstrates the derived RPS rating curve and shows the comparison with the spot gaugings received post rating review.
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Figure 3: Modelled Rating Curve and Spot Gaugings for Validation
Min Stage Max Stage Section C a b (m) (m) 1 -0.158 0.02 39.004 0.432 4.6119 2 0.02 0.86 32.297 0.180 2.2641 3 0.86 2.08 50.341 -0.111 1.1976 4 2.08 3.47 0.007 5.782 4.7188 5 3.47 3.83 0.009 4.198 5.0171 6 3.83 4.3 2.469 0.027 3.5791 7 4.3 4.91 243.854 -2.727 1.4438 8 4.91 5.13 939.004 -4.890 0.0540
Where: Q = C(h+a)b and h = stage readings (metres)
Note: Sections 1 & 2 are existing OPW rating curve segments
Table 1: Rating Equations for Gauge 01042
Figure 3 shows that the spot gaugings received after calibration of the rating review model are a good fit and provide validation of the model up to approximately 100m3/s. The discrepancy between the spot
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gauged flows and modelled rating is approximately 10 – 15% with the modelled rating overestimating the flows. The modelled rating curve was achieved with a Manning’s ‘n’ value of 0.04. The validation spot gaugings suggest that the rating may be improved by increasing the roughness in the rating review model.
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BALLYBOFEY (01043)
The Ballybofey gauging station 01043 is located in the AFA of Ballybofey & Stranorlar in County Donegal on the River Finn. The river reach represents the upstream extents of the modelled reaches of the River Finn within the Ballybofey & Stranorlar model and is also located upstream of the Killygordon, Castlefinn and Lifford AFAs.
The gauge is located on the downstream face of the centre pier of a footbridge which is approximately 1km upstream of the Main Street (N15) Bridge over the River Finn. The gauge is in a cross section approximately 40m wide with a minimum bed level of 13.049m OD Malin and bank levels of 17.235m OD Malin (left bank) and 19.060m OD Malin (right bank). The current ordnance datum level of the gauge zero was surveyed as 13.239m OD Malin which is 56mm above the previous stated OPW staff gauge zero level of 15.930m OD Poolbeg. The surveyed staff gauge zero level was used to complete the rating review as any discrepancy is thought to be relative.
Figure 1: Modelled Reaches and Gauging Station Location
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The gauging station is managed by the OPW and is currently active. Continuous water level records have been provided from 1972 - 2011. Spot flow gaugings for the station have been provided with the highest flow gauging recorded at 157.44m3/s relative to a stage height of 3.11m on the gauge board. OPW have also provided a rating for the gauging station that suggests confidence in the rating up to a stage height of 3.4m although no derived flow information was provided. No information was provided on the confidence in the rating and under the review of national gauged data as part of FSU the rating was given a classification of U suggesting that either no rating was available or was totally unusable for determining flood flows.
The rating review modelled reaches extend approximately 400m in the upstream direction and 2.2km downstream of the gauge. In addition to the footbridge at which the gauge is located there is one bridge along this reach of the River Finn located approximately 1km downstream. The upstream approach to the gauge has a slight bend in the river and downstream of the gauge (Figure 2) is relatively straight. The one dimensional hydraulic model uses information from 58 original cross sections, including the bridge structure.
25.0
20.0
15.0 Elevation (m AD)
10.0 0 16 32 48 64 80 Offset (m)
Figure 2: Model Cross-Section at Gauge Location (Top); Photo of gauge location (Bottom)
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The downstream boundary condition applied to the model was calculated as the normal flow Q-h relationship with the upstream boundary consisting of a hydrograph with a peak flow of 850m m3/s representing an estimated 0.1% AEP flood event. The model was calibrated by applying at the upstream boundary, lower flow gauged data, using spot gauge and the most up to date rating curve information for the Ballybofey gauge. Adjustments were made to the Manning’s n values for channel and over bank roughness to reflect vegetation growth and channel roughness in order to develop a realistic model of the channel and flow conditions that is calibrated to the spot gaugings.
The results of the rating review are shown below in Figure 3 and Table 1. The graph demonstrates the derived RPS rating curve and shows the comparison between the OPW rating curve (which consists of 3 equations) and spot gaugings.
Figure 3: Comparison of Existing OPW Rating Curve and RPS Rating Curve for all flows
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Min Stage Max Stage Section C a b (m) (m)
1 0.008 0.581 15.708 -0.008 1.726 2 0.581 3.4 32.848 -0.25 1.537 3 3.4 4.01 7.9486 1.004 2.1359 4 4.01 5.03 0.1195 3.791 3.7221 5 5.03 6.3 0.0024 5.573 5.0868 6 6.3 6.74 3.6066 -0.026 2.8672 7 6.74 6.8 1.9062 -1.350 3.6198
Where: Q = C(h+a)b and h = stage readings (metres)
Note: Sections 1 & 2 are existing OPW rating curve segments
Table 1: Rating Equations for Gauge 01043
Figure 3 shows that the model accurately represents the OPW rating curve based on the flow gaugings up to the limit of the OPW rating at 189 m3/s. There is a slight divergence in the existing and modelled rating at the two highest spot gaugings of up to 50mm but the modelled rating curve is closer to the highest spot gauged flow recorded at a stage height of 3.11m on the staff gauge. The best fit rating curve was achieved with a Manning’s n value of 0.04. Analysis of the results show that floodwaters remain in bank at the gauged section until river flow exceeds 320 m3/s or 17.8m (OD Malin).
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NEW MILLS (39001)
Gauge 39001 is located to the East of Letterkenny on the River Swilly, approximately 5700m upstream of its confluence with the Ballymacool tributary. The gauge is located off the R250, approximately 250m upstream of a skewed weir and 780m upstream of a road bridge. The gauge is located in an open channel section approximately 14m wide with a minimum bed level of 17.33m OD Malin and bank levels of 20.25m OD Malin (left bank) and 19.70m OD Malin (right bank). The current ordnance level of the gauge zero is 20.635m OD Poolbeg (as stated by OPW).
Figure 1: Gauging Station Location
The gauge is operated by OPW, with continuous water level and derived flow records available from 1973 to 2008. The study reach extends approximately 2310m in the upstream direction and 1270m downstream of the gauge. There are three bridge structures and one weir along this reach of the River Swilly. The gauge is located on a meander. The two dimensional hydraulic model uses information from 50 original cross sections. The downstream boundary condition applied to the model was
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calculated as the critical flow Q-h relationship with the upstream boundary consisting of a hydrograph with a peak flow of 149.0 m3/s, equivalent to an estimated 0.1% AEP event.
Figure 2: Model Cross-Section at Gauge Location (Top); Photo of gauge location (Bottom)
From analysing the spot gauging data received from OPW it can be seen that the river or catchment characteristics have changed pre and post 1995. The is no record of a staff datum change around this time, but there is a defined difference in the ratings pre and post 1995, and this is reflected in OPWs rating curve history.
OPW state their most recent rating for New Mills (post 1995) is of "fair quality" up to a gauge level of 1.635m. Beyond this level the rating is based on an extrapolated curve and the reliability is "unknown".
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The National Review under FSU Work Package 2.1 assigned data recorded from the gauge a quality classification of B (i.e. flows can be determined up to Qmed with confidence), but this classification 3 refers to data pre-1990. Under FSU, a value of 47.8m /s is estimated for Qmed. Post 1995 there are limited spot gaugings available (highest flow is 6m3/s), but the available gaugings show a steady 3 relationship. The spot gauging period post 1995 gives an estimate of 41.1m /s for Qmed. The upper limit of the "fair quality" rating curve is at a stage of 1.635m which equates to a flow of less than Qmed (approximately 40.4m3/s, based on the OPW rating curve). Therefore, for the purposes of the NWNB CFRAM study, it is proposed to use the existing OPW rating curve to calibrate the model rating up to the limits of the "fair quality" curve.
The model was calibrated for low flows by applying a low flow to the start of the hydrograph at the upstream boundary and comparing model outputs with spot gauge data and existing rating curve information. Adjustments were made to the Manning’s n values for channel and over bank roughness to reflect vegetation growth and channel roughness in order to develop a realistic model of the channel and flow conditions.
The results of the rating review, including a comparison with the spot gauges since 1995 and the existing rating equation, are shown in Figure 3 and Table 1. Note that the first two rating equation values are taken from the existing OPW rating curve.
Figure 3: Comparison of Existing OPW Rating Curve and RPS Rating Curve for all flows
Table 1: Rating equation values for gauge 39001
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Min Stage Max Stage Section C a b (m) (m)
1 0 0.41 19.4 0.09 2.3
2 0.41 1.75 14.5 0.09 1.88
3 1.75 1.85 33.1459 -0.5525 1.7574
4 1.85 2.26 26.4975 -0.4708 2.1002
5 2.26 2.729 39.1330 -0.6558 1.7556
Where: Q = C(h+a)b and h = stage readings (metres)
Note: Sections 1 & 2 are existing OPW rating curve segments which have been retained
Figure 3 shows that the model accurately represents the OPW rating curve based on the lower flow gaugings up to approximately 6 m3/s. The best fit rating curve was achieved with a Manning's n value of 0.05. This describes a channel which is clean, winding but with weeds and a lot of stones. This is considered the upper limit of a suitable value to describe of the Swilly channel but is justified in its use as the best calibration with the observed data was achieved with this value. Analysis of the results show that floodwaters remain in bank at the gauged section until river flow exceeds 45 m3/s.
Flow will start to spill out-of-bank at a gauge level of approximately 1.75. The model rating curve for out-of-bank flow was found to be considerably different from the existing extrapolated curve. A Manning's n value of 0.1 was used for the floodplain.
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CLONCONWAL FORD (38001)
Gauging station 38001 Clonconwal Ford is located in the west of County Donegal on the Owenea River. The main river passes to the south of Glenties town, where it merges with the Stracashel River. To the south-west of Glenties town the Gorthnamucklagh watercourse merges with the main Oweanea River. The Owenea then flows into an estuary upstream of Loughros More Bay (Atlantic) approximately 10km to the west of Glenties Town. The Clonconwal Ford gauging station is located approximately 4km upstream from the estuary referred to as Ranny Point South and 5km west of Glenties Town, it is located at cross-section 0112M00387 (Irish Grid 176545 392706). The area is rural and surrounded by flat agricultural fields and forestry. The river cross-section measures approximately 23.9m wide with the lowest bed level of 22.85m OD Malin and bank levels of 26.28m OD Malin for the left bank and 26.07m OD Malin for the right bank. The surveyed gauge zero ordnance level is currently 23.517m OD Malin. This gauge is managed by OPW and is currently active. The current OPW staff gauge zero level is listed as 26.225m OD Poolbeg which is in good agreement with the surveyed level. As such the OPW staff gauge zero level is used as the basis for this review such that the model rating curve is considered relative to the OPW spot gaugings and rating curve. Continuous water level and derived flow records have been provided from October 1972 to October 2011. This gauging station is a HEP for the Glenties model (UoM 01_Model 17). The location of the gauge and modelled watercourse are shown in Figure 1 below:
Figure 1: Modelled Watercourse and Gauge Station Location
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Figure 2: Model Cross-Section at Gauge Location (A); Photo of gauge location (B)
A.
B.
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The HPW section of the study reach, measures approx 1.2 km in length. Along this particular section, there is a foot-bridge structure (0112M00380D) located 35.6m downstream of the gauge and beyond that there is a set of stepping stones. This feature was incorporated into the model as a weir (0112M00380D). The immediate approach to the Clonconwal Ford gauge is relatively straight flowing towards the west. Close to the gauge, the river changes direction to flow in a west north west direction. The bed is mainly composed of gravels and pebbles. This section of the model was represented in one dimension only, since Lidar information was unavailable for this location. A Q-h relationship was applied to the downstream boundary of the Glenties model. This condition was calculated as the critical flow Q-h relationship with the upstream boundary consisting of a hydrograph with a peak flow of 230.19 m3/s, equivalent to an estimated 0.1% AEP event.
A review of the spot gaugings has revealed that the highest spot gauging had a measured flow of 30.33m3/s and a level of 1.52 mOD (01/12/1975). The range of spot gaugings equates to 30.2 m3/s. It was noted on the OPW AMAX series ranging from 1972 to 2009 that the reliable rating limit equates to 30m3/s. Flows derived using the rating above this level have been extrapolated, and therefore treated 3 with caution. Considering that the observed Qmed is 70.17m /s it would suggest that there is no confidence in the rating at Qmed however the rating was given a B classification under FSU Work
Package 2.1 suggesting the rating could be extrapolated up to Qmed with some confidence. The estimated Qmed derived from catchment descriptors is 25% larger than the existing value.
The model was calibrated for low flows by comparing the modelled Q-h relationship at low flows with spot gauge data and the existing rating curve information. Adjustments were made to the Manning’s n values for channel and over bank roughness to reflect vegetation growth and channel roughness in order to develop a realistic model of the channel and flow conditions. The head loss factor relating to the weir located at cross-section 0112M00377W was adjusted; where the positive flow, 'Inflow' was increased from its default value of 0.5 to 0.6 and the 'Free Overflow' was increased from its default value of 1 to 1.2.
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Figure 3: Comparison of Existing OPW Rating Curve and RPS Rating Curve for all flows
Min Stage Max Stage Section (m) (m) C a b
1 0 0.517 18.19 -0.05 2.86
2 0.517 1.023 13.43 -0.05 2.475
3 1.023 1.24 13.17 -0.05 1.772
4 1.24 1.407 0.736 0.525 5.619
5 1.407 3.058 46.807 -0.835 0.79
6 3.058 3.505 88.311 -2.057 0.98
7 3.505 5.128 132.34 -2.565 0.679
Where: Q = C(h+a)b and h = stage readings (metres)
Note: Sections 1, 2 & 3 are existing OPW rating curve segments
Table 1: Rating equation values for gauge 38001
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The results of the rating review, including a comparison with the spot gaugings are shown in Figure 3 and Table 1. Note that the first three rating equation values are retained from the existing OPW rating curve as they are considered to have a high degree of certainty. The other existing segments ranged from fair to poor to extrapolated.
Figure 3 shows the existing OPW rating to its reliable limit, the spot gaugings and the modelled extension to the existing rating curve from the reliable limit. Calibration at lower flows (≤ 1m Above SG0) was initially found to be poor although the model provided a reasonable fit with the higher spot flow gaugings. An explanation of poor correlation of spot levels and model results can be explained by the lack of survey detail associated with the weir (0112M00377W). This series of stepping stones that expands across the width of the river (chainage 9129.67), was surveyed as a weir and initially incorporated into the model as such. Consequently, measurements regarding the spacing between the rocks were omitted. It is recommended that this rating review is revised, following the re-surveying of cross-section 0112M00377W. It has been shown that the best fit rating curve was achieved with a Mannings n value of 0.055 and using an edited cross-section, that has estimated the spacing between the stepping stones, based upon the existing survey and photographs. This Manning's value describes a main channel with clean, winding reaches with some weeds and a lot of stones which although towards the upper end is a fair description of this reach of the Stracashel River. Figure 4 Illustrates the edited cross-section A, the original cross-section B and a photo of the stepping stones looking downstream from the gauging station C, respectively.
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Figure 4 Cross-Section Weir 0112M00377W (A) Edited, (B) Unedited and Photograph (C).
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TULLYARVAN (39003)
The Gauging Station at Tullyarvan (39003) is located on the Crana River approx 1km north of Buncrana, County Donegal approximately 2.7km downstream of its confluence with the Umrycam River. The staff gauge and recorder house is located on the right hand bank of an open channel section upstream of a weir (Section ID 0141M00179). The channel is approximately 21m wide with a minimum bed level of 15.523m OD Malin and bank levels of 19.318 mOD Malin (Left bank) and 18.680 m OD Malin (Right bank). The current ordnance level of the gauge zero is 19.25m OD Poolbeg (as stated by OPW) which is approximately 80mm lower than the surveyed level of 16.632m OD Malin. For the purposes of tying into the existing rating and spot gaugings the SG0 as stated by OPW has been used as the basis for this review. The location of the gauge and modelled watercourse are shown in Figure 1 below:
Figure 1: Modelled Watercourse and Gauge Station Location
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The gauge is operated by OPW, with continuous water level and derived flow records available from November 1972 to November 2011.
Figure 2: Model cross-section closest to gauge location (Top); Photo of gauge location (Bottom)
The study reach extends approximately 2.76km upstream and 1.85km downstream of the gauge. There are four bridge structures and eleven weirs (with an additional three weirs added in for stability) along this reach of the Crana River. The confluence point of Crana Tributary 1 is 21.47m upstream of the gauging station. Along the Crana the immediate upstream and downstream approaches to the
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gauge meander. There are 125 cross sections included in the 1D hydraulic model for the Crana reach. The upstream boundary input was set with a hydrograph with a peak flow of 217.74 m3/s equivalent to an estimated 0.1% AEP event.
From a review of the spot gaugings and the rating equation history it was noted that there was a significant shift in the staff gauge zero level between 1987 and 1988. The highest spot gauging and 3 also the limit of reliable rating for this period is 38m /s. The Qmed for this period based on the AMAX data and the OPW rating is 73m3/s. Although a long record of flow data exists at this station it was not classified as being suitable for FSU although it was given a C classification suggesting the rating was possible for extrapolation up to Qmed
The model was calibrated for low flows by applying a hydrograph with base flow removed (i.e. starting from 0m3/s) at the upstream boundary and comparing model outputs with spot gauge data and existing rating curve information. Adjustments were made to the Manning’s n values for channel and over bank roughness to reflect vegetation growth and channel roughness in order to develop a realistic model of the channel and flow conditions.
The results of the rating review, including a comparison with the spot gauges since 1993 and the existing rating equation, are shown in Figure 3 and Table 1.
Figure 3: Comparison of Existing OPW Rating Curve and RPS Rating Curve for all flows
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Min Stage Max Stage Section C a b (m) (m)
1 0 0.751 23 0.124 3.544
2 0.751 1.000 42.8 -0.216 1.75
3 1 1.883 22.422 0.126 1.863
4 1.883 2.916 12.119 0.2365 2.555
Where: Q = C(h+a)b and h = stage readings (metres)
Note: Section 1&2 are existing OPW rating curve segments
Table 1: Rating equation values for gauge 06003
The best model calibration with the spot gaugings was achieved using roughness values of Manning's n of 0.035 for the channel and 0.045 for the floodplain along the gauging station reach. These describe a clean winding channel with stones and a floodplain which is characterised by brush and urban fabric. These are considered accurate descriptions of the gauged reach. However calibration to the low flow spot gaugings is poor with the zero flow stage and spot gaugings up to 10 m3/s found to be generally 150-200mm higher than the model. The low flow is controlled by the weir approximately 50m downstream of the gauging station. The survey resolution is poor at the weir with certain portions of the surveyed section marked 'no access - rocks, dangerous fast flow'. To achieve the best calibration at low flows and good calibration to the two higher flow spot gaugings required adjustment of the weir overflow and inflow parameters from their default values.
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APPENDIX C
DESIGN FLOWS FOR MODELLING INPUT
Model 1 - Malin Town Flows for AEP AREA Model Node ID_CFRAMS 2 Qmed 0.5% 0.1% (km ) 50% (2) 20% (5) 10% (10) 5% (20) 2% (50) 1% (100) number (200) (1000) 40_958_1 2.486 1.30 1.30 1.69 1.98 2.30 2.78 3.22 3.72 5.24 Model 1 40_676_2 6.217 2.54 2.54 3.29 3.85 4.47 5.42 6.26 7.25 10.21 Model 1 40_958_2 2.708 1.38 1.38 1.78 2.09 2.42 2.94 3.40 3.93 5.53 Model 1 Top-up flow between 0.222 0.13 0.13 0.17 0.20 0.23 0.28 0.33 0.38 0.53 Model 1 40_958_1 & 40_958_2 40061_RPS 9.506 3.77 3.77 4.88 5.72 6.63 8.04 9.29 10.75 15.14 Model 1 Top-up flow between 0.581 0.27 0.27 0.36 0.42 0.48 0.59 0.68 0.78 1.10 Model 1 40_676_2 & 40061 40_677_2 9.634 3.99 3.99 5.17 6.05 7.02 8.51 9.84 11.38 16.03 Model 1 Top-up flow between 0.128 0.07 0.07 0.09 0.11 0.12 0.15 0.17 0.20 0.28 Model 1 40_677_2 & 40061
MRFS Flows for AEP HEFS Flows for AEP AREA Model Node ID_CFRAMS 2 50% 10% 5% 2% 1% 0.5% 0.1% 10% 0.1% (km ) 20% (5) 1% (100) number (2) (10) (20) (50) (100) (200) (1000) (10) (1000) 40_958_1 2.49 1.63 2.11 2.47 2.87 3.47 4.02 4.65 6.54 3.03 4.93 8.04 Model 1 40_676_2 6.22 3.17 4.11 4.81 5.58 6.77 7.82 9.05 12.75 5.91 9.61 15.66 Model 1 40_958_2 2.71 1.72 2.23 2.61 3.02 3.67 4.24 4.90 6.91 3.20 5.21 8.49 Model 1 Top-up flow between 0.22 0.16 0.21 0.25 0.29 0.35 0.41 0.47 0.66 0.31 0.50 0.81 Model 1 40_958_1 & 40_958_2 40061_RPS 9.51 4.70 6.10 7.14 8.28 10.04 11.60 13.42 18.91 8.77 14.25 23.23 Model 1 Top-up flow between 0.58 0.60 0.78 0.91 1.06 1.28 1.48 1.72 2.42 1.35 2.19 3.57 Model 1 40_676_2 & 40061 40_677_2 9.63 4.98 6.45 7.55 8.76 10.62 12.28 14.21 20.01 9.28 15.09 24.59 Model 1 Top-up flow between 0.13 0.15 0.20 0.23 0.27 0.32 0.38 0.43 0.61 0.34 0.56 0.90 Model 1 40_677_2 & 40061
Input flows Top-up flows. These flows should be entered laterally Check flows. Modellers should check to make sure these flows are being reached at each HEP Some of these flows may be put in at the US point due to a small difference between US & DS flows.
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Model 2 - Carndonagh Flows for AEP AREA Model Node ID_CFRAMS Qmed (km2) 50% 20% 10% 5% 2% 1% 0.5% 0.1% number (2) (5) (10) (20) (50) (100) (200) (1000) 40_982_1_RPS 24.952 17.78 17.78 21.71 24.48 27.40 31.67 35.31 39.38 50.91 Model 2 40003_RPS 25.866 18.20 18.20 22.22 25.06 28.05 32.42 36.15 40.32 52.11 Model 2 Top-up flow between 40_982_1 and 0.914 0.85 0.85 1.04 1.17 1.31 1.51 1.69 1.88 2.43 Model 2 40003 40_982_13_RPS 28.896 18.96 18.96 23.14 26.10 29.21 33.76 37.65 41.99 54.27 Model 2 Top-up flow between 40003 & 3.03 2.29 2.29 2.80 3.15 3.53 4.08 4.55 5.07 6.56 Model 2 40_982_13 40_1018_1 27.668 23.50 23.50 28.60 32.20 35.96 41.48 46.16 51.40 66.14 Model 2 40_1018_2 28.118 23.50 23.50 28.60 32.20 35.96 41.48 46.15 51.39 66.13 Model 2 Top-up flow between 40_1018_1 & 0.45 0.47 0.47 0.57 0.65 0.72 0.83 0.93 1.03 1.33 Model 2 40_1018_2 40_1018_4_RPS 28.642 23.50 23.50 28.60 32.20 35.96 41.48 46.15 51.39 66.13 Model 2 Top-up flow between 40_1018_2 & 0.524 0.46 0.46 0.56 0.63 0.71 0.82 0.91 1.01 1.30 Model 2 40_1018_4_RPS 40_1012_3 1.416 1.64 1.64 2.13 2.49 2.89 3.50 4.05 4.69 6.60 Model 2 40_1012_6_RPS 2.737 2.73 2.73 3.54 4.14 4.80 5.82 6.73 7.79 10.97 Model 2 Top-up flow between 40_1012_3 & 1.321 1.38 1.38 1.79 2.09 2.43 2.94 3.40 3.94 5.54 Model 2 40_1012_6_RPS 40006_RPS 31.831 25.01 25.01 30.66 34.61 38.77 44.77 49.90 55.60 71.51 Model 2 Top-up flow between 40_1018_4_RPS 0.452 0.46 0.46 0.57 0.64 0.72 0.83 0.93 1.03 1.33 Model 2 & 40006_RPS 40_1107_2_RPS 32.654 25.12 25.12 30.80 34.77 40.34 44.96 50.11 55.84 71.82 Model 2 Top-up flow between 40006_RPS & 0.823 0.80 0.80 0.98 1.10 1.28 1.43 1.59 1.77 2.28 Model 2 40_1107_2_RPS 40007_RPS 33.735 25.37 25.37 31.10 35.11 39.32 45.41 50.62 56.40 72.54 Model 2 Top-up flow between 40_1107_2_RPS 1.081 1.01 1.01 1.24 1.40 1.57 1.81 2.01 2.24 2.89 Model 2 & 40007_RPS 40_1107_9_RPS 34.31 25.37 25.37 31.10 35.11 39.32 45.41 50.61 56.40 72.53 Model 2
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MRFS Flows for AEP HEFS Flows for AEP AREA Model Node ID_CFRAMS (km2) 50% 20% 10% 5% 2% 1% 0.5% 0.1% 10% 1% 0.1% number (2) (5) (10) (20) (50) (100) (200) (1000) (10) (100) (1000) 40_982_1_RPS 24.952 22.20 27.10 30.56 34.20 39.53 44.08 49.16 63.55 37.55 54.16 78.07 Model 2 40003_RPS 25.866 22.72 27.74 31.29 35.02 40.47 45.13 50.33 65.05 38.44 55.44 79.92 Model 2 Top-up flow between 0.914 1.86 2.27 2.56 2.87 3.31 3.69 4.12 5.32 3.78 5.46 7.87 Model 2 40_982_1 and 40003 40_982_13_RPS 28.896 23.32 28.47 32.11 35.93 41.53 46.31 51.65 66.75 39.45 56.89 82.01 Model 2 Top-up flow between 3.03 4.94 6.03 6.80 7.61 8.80 9.81 10.94 14.15 10.06 14.50 20.91 Model 2 40003 & 40_982_13 40_1018_1 27.668 28.20 34.32 38.64 43.15 49.78 55.39 61.68 79.37 41.86 60.01 85.98 Model 2 40_1018_2 28.118 28.20 34.32 38.63 43.15 49.77 55.38 61.67 79.35 41.85 60.00 85.97 Model 2 Top-up flow between 40_1018_1 & 0.45 0.59 0.72 0.81 0.90 1.04 1.16 1.29 1.66 0.99 1.42 2.03 Model 2 40_1018_2 40_1018_4_RPS 28.642 28.20 34.32 38.63 43.15 49.77 55.38 61.67 79.35 41.85 60.00 85.97 Model 2 Top-up flow between 40_1018_2 & 0.524 1.00 1.22 1.37 1.53 1.77 1.97 2.19 2.82 2.03 2.91 4.17 Model 2 40_1018_4_RPS 40_1012_3 1.416 2.05 2.66 3.11 3.61 4.37 5.05 5.85 8.24 3.82 6.21 10.12 Model 2 40_1012_6_RPS 2.737 3.58 4.65 5.44 6.31 7.65 8.84 10.23 14.41 8.86 14.40 23.47 Model 2 Top-up flow between 40_1012_3 & 1.321 2.85 3.70 4.33 5.02 6.09 7.04 8.15 11.47 6.40 10.41 16.96 Model 2 40_1012_6_RPS 40006_RPS 31.831 30.94 37.93 42.82 47.95 55.38 61.72 68.77 88.45 54.02 77.86 111.59 Model 2 Top-up flow between 40_1018_4_RPS & 0.452 1.00 1.22 1.38 1.55 1.79 1.99 2.22 2.85 2.04 2.94 4.22 Model 2 40006_RPS 40_1107_2_RPS 32.654 31.98 39.21 44.27 51.37 57.25 63.81 71.10 91.44 63.60 91.68 131.38 Model 2 Top-up flow between 40006_RPS & 0.823 1.69 2.07 2.33 2.71 3.02 3.36 3.75 4.82 3.45 4.97 7.12 Model 2 40_1107_2_RPS
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MRFS Flows for AEP HEFS Flows for AEP AREA Model Node ID_CFRAMS (km2) 50% 20% 10% 5% 2% 1% 0.5% 0.1% 10% 1% 0.1% number (2) (5) (10) (20) (50) (100) (200) (1000) (10) (100) (1000) 40007_RPS 33.735 32.44 39.77 44.90 50.28 58.07 64.72 72.11 92.74 65.65 94.63 135.61 Model 2 Top-up flow between 40_1107_2_RPS & 1.081 1.29 1.58 1.79 2.00 2.31 2.58 2.87 3.69 2.61 3.77 5.40 Model 2 40007_RPS 40_1107_9_RPS 34.31 30.44 37.32 42.13 47.19 54.49 60.74 67.68 87.04 45.65 65.80 94.29 Model 2
Input flows Top-up flows. These flows should be entered laterally Check flows. Modellers should check to make sure these flows are being reached at each HEP Some of these flows may be put in at the US point due to a small difference between US & DS flows.
Model 3 - Clonmany Flows for AEP AREA Model Node ID_CFRAMS Qmed (km2) 50% 20% 10% 5% 2% 1% 0.5% 0.1% number (2) (5) (10) (20) (50) (100) (200) (1000)
40_431_U 2.218 0.70 0.70 0.90 1.06 1.22 1.48 1.72 1.99 2.80 Model 3 40_565_1 33.645 23.49 23.49 28.45 31.90 35.48 40.69 45.09 49.95 63.50 Model 3 40_431_4 2.687 1.15 1.15 1.49 1.75 2.03 2.46 2.84 3.29 4.63 Model 3 Top-up flow between 40_431_U & 0.469 0.22 0.22 0.29 0.34 0.39 0.48 0.55 0.64 0.90 Model 3 40_431_4 40004 37.278 23.56 23.56 28.30 31.60 35.02 39.94 44.09 48.71 61.43 Model 3 Top-up flow between 40_565_1 & 0.946 0.83 0.83 0.99 1.11 1.23 1.40 1.55 1.71 2.16 Model 3 40004 40_293_7 8.613 6.79 6.79 8.80 10.30 11.95 14.49 16.75 19.39 27.30 Model 3 40_293_8 8.785 7.05 7.05 9.14 10.69 12.41 15.04 17.39 20.12 28.34 Model 3 Top-up flow between 40_293_7 & 0.172 0.25 0.25 0.32 0.38 0.44 0.53 0.61 0.71 1.00 Model 3 40_293_8 40_1082_D 55.511 32.08 32.08 38.76 43.31 48.00 54.70 60.32 66.44 83.22 Model 3
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Model 3 - Clonmany Flows for AEP AREA Model Node ID_CFRAMS Qmed (km2) 50% 20% 10% 5% 2% 1% 0.5% 0.1% number (2) (5) (10) (20) (50) (100) (200) (1000)
Top-up flow between 40_293_7 & 9.448 6.10 6.10 7.37 8.24 9.13 10.41 11.48 12.64 15.84 Model 3 40_1082_D
MRFS Flows for AEP HEFS Flows for AEP AREA Node ID_CFRAMS 2 Model number (km ) 50% 20% 10% 5% 2% 1% 0.5% 0.1% 10% 1% 0.1% (2) (5) (10) (20) (50) (100) (200) (1000) (10) (100) (1000) 40_431_U 2.218 0.89 1.16 1.35 1.57 1.90 2.20 2.54 3.58 1.99 3.24 5.28 Model 3 40_565_1 33.645 29.33 35.52 39.83 44.29 50.80 56.28 62.35 79.27 48.93 69.15 97.40 Model 3 40_431_4 2.687 1.38 1.79 2.10 2.43 2.95 3.41 3.94 5.55 2.67 4.33 7.06 Model 3 Top-up flow between 0.469 0.47 0.60 0.71 0.82 0.99 1.15 1.33 1.87 1.05 1.70 2.77 Model 3 40_431_U & 40_431_4 40004 37.278 29.42 35.33 39.45 43.71 49.86 55.04 60.80 76.69 48.46 67.62 94.21 Model 3 Top-up flow between 0.946 1.81 2.17 2.43 2.69 3.07 3.39 3.74 4.72 3.59 5.01 6.98 Model 3 40_565_1 & 40004 40_293_7 8.613 8.47 10.99 12.86 14.92 18.09 20.91 24.20 34.08 15.80 25.69 41.87 Model 3 40_293_8 8.785 8.73 11.32 13.25 15.37 18.63 21.54 24.92 35.10 16.28 26.46 43.12 Model 3 Top-up flow between 0.172 0.38 0.50 0.58 0.68 0.82 0.95 1.10 1.54 0.86 1.40 2.28 Model 3 40_293_7 & 40_293_8 40_1082_D 55.511 39.64 47.88 53.51 59.30 67.58 74.52 82.09 102.82 65.74 91.55 126.32 Model 3 Top-up flow between 9.448 7.54 9.11 10.18 11.28 12.86 14.18 15.62 19.57 12.51 17.42 24.04 Model 3 40_293_7 & 40_1082_D
Input flows Top-up flows. These flows should be entered laterally Check flows. Modellers should check to make sure these flows are being reached at each HEP. Some of these flows may be put in at the US point due to a small difference between US & DS flows.
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Model 4 - Moville Flows for AEP AREA Model Node ID_CFRAMS Qmed (km2) 50% 20% 10% 5% 2% 1% 0.5% 0.1% number (2) (5) (10) (20) (50) (100) (200) (1000) 40_460_3 1.61 1.50 1.50 1.95 2.28 2.64 3.20 3.70 4.29 6.03 Model 4 40_1019_2 14.442 9.18 9.18 11.90 13.93 16.14 19.53 22.54 26.01 36.41 Model 4 40_315_1_RPS 15.158 9.56 9.56 12.37 14.44 16.70 20.14 23.18 26.70 37.14 Model 4 Top-up flow between 40_1019_2 & 0.716 0.57 0.57 0.74 0.86 1.00 1.20 1.39 1.60 2.22 Model 4 40_315_1_RPS 40_315_2_RPS 15.265 9.71 9.71 12.56 14.67 16.96 20.46 23.54 27.12 37.73 Model 4 Top-up flow between 40_315_1_RPS & 0.107 0.15 0.15 0.19 0.22 0.26 0.31 0.36 0.41 0.57 Model 4 40_315_2_RPS 40_460_6_RPS 2.076 2.08 2.08 2.70 3.16 3.67 4.45 5.14 5.95 8.38 Model 4 Top-up between 40_460_3 & 0.466 0.57 0.57 0.74 0.87 1.00 1.22 1.41 1.63 2.30 Model 4 40_460_6_RPS 40001_RPS 17.932 11.70 11.70 15.25 17.82 20.59 24.75 28.40 32.55 44.70 Model 4 Top-up flow between 40_315_2_RPS & 0.591 0.74 0.74 0.96 1.13 1.30 1.56 1.79 2.06 2.82 Model 4 40001_RPS 40_516_3 18.501 12.03 12.03 15.47 17.95 20.62 24.60 28.06 32.02 43.49 Model 4 Top-up flow between 40001_RPS & 0.569 0.46 0.46 0.59 0.69 0.79 0.94 1.07 1.23 1.67 Model 4 40_516_3 40_991_1 1.003 0.83 0.83 1.08 1.27 1.47 1.78 2.06 2.38 3.35 Model 4 40_991_3 1.315 1.16 1.16 1.50 1.76 2.04 2.47 2.85 3.30 4.65 Model 4 Top-up flow between 40_991_1 & 0.312 0.31 0.31 0.40 0.47 0.55 0.66 0.77 0.89 1.25 Model 4 40_991_3
MRFS Flows for AEP HEFS Flows for AEP AREA Model Node ID_CFRAMS 2 (km ) 50% 20% 10% 5% 2% 1% 0.5% 0.1% 10% 1% 0.1% number (2) (5) (10) (20) (50) (100) (200) (1000) (10) (100) (1000) 40_460_3 1.61 1.87 2.43 2.84 3.30 4.00 4.62 5.35 7.53 3.49 5.68 9.26 Model 4 40_1019_2 14.442 11.45 14.86 17.39 20.15 24.37 28.13 32.47 45.45 21.36 34.56 55.84 Model 4 40_315_1_RPS 15.158 11.93 15.44 18.03 20.84 25.14 28.93 33.32 46.37 22.15 35.55 56.96 Model 4 Top-up flow between 40_1019_2 & 0.716 0.74 0.95 1.11 1.29 1.55 1.79 2.06 2.86 1.68 2.70 4.33 Model 4 40_315_1_RPS
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MRFS Flows for AEP HEFS Flows for AEP AREA Model Node ID_CFRAMS (km2) 50% 20% 10% 5% 2% 1% 0.5% 0.1% 10% 1% 0.1% number (2) (5) (10) (20) (50) (100) (200) (1000) (10) (100) (1000) 40_315_2_RPS 15.265 12.07 15.61 18.23 21.08 25.42 29.26 33.70 46.89 22.40 35.95 57.61 Model 4 Top-up flow between 40_315_1_RPS & 0.107 0.28 0.36 0.42 0.48 0.58 0.67 0.77 1.07 0.45 0.73 1.16 Model 4 40_315_2_RPS 40_460_6_RPS 2.076 2.77 3.59 4.20 4.88 5.91 6.83 7.91 11.14 7.15 11.62 18.94 Model 4 Top-up between 40_460_3 & 0.466 0.88 1.14 1.33 1.55 1.87 2.17 2.51 3.53 2.37 3.85 6.28 Model 4 40_460_6_RPS 40001_RPS 17.932 14.77 19.25 22.50 26.00 31.24 35.85 41.09 56.43 24.37 38.84 61.13 Model 4 Top-up flow between 40_315_2_RPS & 0.591 1.38 1.80 2.11 2.44 2.93 3.36 3.85 5.29 2.28 3.64 5.73 Model 4 40001_RPS 40_516_3 18.501 15.34 19.73 22.89 26.29 31.37 35.79 40.84 55.47 33.11 51.77 80.24 Model 4 Top-up flow between 40001_RPS & 0.569 0.59 0.76 0.88 1.01 1.20 1.37 1.56 2.12 1.27 1.98 3.07 Model 4 40_516_3 40_991_1 1.003 1.04 1.35 1.58 1.83 2.22 2.57 2.97 4.19 1.94 3.16 5.14 Model 4 40_991_3 1.315 1.43 1.85 2.17 2.51 3.05 3.52 4.08 5.74 2.66 4.33 7.05 Model 4 Top-up flow between 0.312 0.40 0.52 0.61 0.71 0.86 0.99 1.15 1.62 0.94 1.53 2.50 Model 4 40_991_1 & 40_991_3
Input flows Top-up flows. These flows should be entered laterally Check flows. Modellers should check to make sure these flows are being reached at each HEP Some of these flows may be put in at the US point due to a small difference between US & DS flows.
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Model 5 - Downings Flows for AEP AREA Model Node ID_CFRAMS Qmed (km2) 50% 20% 10% 5% 2% 1% 0.5% 0.1% number (2) (5) (10) (20) (50) (100) (200) (1000) 38_1824_U 0.64 0.37 0.37 0.48 0.56 0.65 0.79 0.91 1.05 1.48 Model 5 38_1824_D 1.57 0.99 0.99 1.29 1.51 1.75 2.12 2.45 2.84 4.00 Model 5
Top-up flow between 38_1824_U & 0.93 0.61 0.61 0.79 0.93 1.08 1.30 1.51 1.74 2.46 Model 5 38_1824_D
MRFS Flows for AEP HEFS Flows for AEP AREA Model Node ID_CFRAMS (km2) 50% 20% 10% 5% 2% 1% 0.5% 0.1% 10% 1% 0.1% number (2) (5) (10) (20) (50) (100) (200) (1000) (10) (100) (1000) 38_1824_U 0.64 0.69 0.89 1.05 1.21 1.47 1.70 1.97 2.77 1.58 2.56 4.18 Model 5 38_1824_D 1.57 1.67 2.17 2.54 2.95 3.58 4.13 4.78 6.73 3.83 6.23 10.15 Model 5 Top-up flow between 38_1824_U & 0.93 1.03 1.33 1.56 1.81 2.20 2.54 2.94 4.14 2.35 3.82 6.23 Model 5 38_1824_D
Input flows Top-up flows. These flows should be entered laterally Check flows. Modellers should check to make sure these flows are being reached at each HEP Some of these flows may be put in at the US point due to a small difference between US & DS flows.
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Model 7 - Kerrykeel Flows for AEP AREA Model Node ID_CFRAMS Qmed (km2) 50% 20% 10% 5% 2% 1% 0.5% 0.1% number (2) (5) (10) (20) (50) (100) (200) (1000) 38_2247_1 9.859 7.41 7.41 9.61 11.24 13.04 15.81 18.28 21.15 29.79 Model 7 38_3389_1_RPS 1.011 0.92 0.92 1.19 1.39 1.62 1.96 2.27 2.62 3.70 Model 7 38_3389_2_RPS 1.305 1.12 1.12 1.45 1.70 1.97 2.39 2.77 3.20 4.51 Model 7 Top-up between 38_3389_1_RPS & 0.294 0.28 0.28 0.36 0.42 0.49 0.59 0.68 0.79 1.12 Model 7 38_3389_2_RPS 38_2210_D 12.27 8.82 8.82 11.43 13.38 15.51 18.76 21.65 24.99 34.98 Model 7 Top-up between 38_2247_1 & 1.106 1.03 1.03 1.33 1.56 1.81 2.19 2.54 2.94 4.13 Model 7 38_2210_D
MRFS Flows for AEP HEFS Flows for AEP AREA Model Node ID_CFRAMS (km2) 50% 20% 10% 5% 2% 1% 0.5% 0.1% 10% 1% 0.1% number (2) (5) (10) (20) (50) (100) (200) (1000) (10) (100) (1000) 38_2247_1 9.859 9.25 11.99 14.03 16.28 19.74 22.82 26.41 37.19 17.24 28.03 45.69 Model 7 38_3389_1_RPS 1.011 1.15 1.49 1.74 2.02 2.45 2.83 3.28 4.61 2.14 3.48 5.67 Model 7 38_3389_2_RPS 1.305 1.40 1.82 2.12 2.46 2.99 3.45 4.00 5.63 2.61 4.24 6.92 Model 7 Top-up between 38_3389_1_RPS & 0.294 0.35 0.45 0.53 0.61 0.74 0.85 0.99 1.39 0.65 1.05 1.71 Model 7 38_3389_2_RPS 38_2210_D 12.27 11.01 14.27 16.71 19.36 23.42 27.03 31.20 43.67 20.52 33.21 53.65 Model 7 Top-up between 38_2247_1 1.106 1.45 1.89 2.21 2.56 3.10 3.59 4.15 5.85 4.54 7.38 12.03 Model 7 & 38_2210_D
Input flows Top-up flows. These flows should be entered laterally Check flows. Modellers should check to make sure these flows are being reached at each HEP Some of these flows may be put in at the US point due to a small difference between US & DS flows.
C9
Model 8 - Buncrana Flows for AEP AREA Model Node ID_CFRAMS Qmed (km2) 50% 20% 10% 5% 2% 1% 0.5% 0.1% number (2) (5) (10) (20) (50) (100) (200) (1000) 39_753_2 6.467 5.78 5.78 7.49 8.77 10.18 12.34 14.26 16.50 23.24 Model 8 39_386_2 87.356 69.72 69.72 87.15 99.42 112.46 131.56 147.95 166.28 218.29 Model 8 39_753_4 6.767 6.14 6.14 7.97 9.32 10.82 13.11 15.16 17.54 24.71 Model 8 Top-up flow between 39_753_2 & 0.3 0.33 0.33 0.43 0.50 0.58 0.70 0.81 0.94 1.32 Model 8 39_753_4 39_571_1 97.297 74.34 74.34 92.78 105.79 119.32 139.17 156.12 174.93 227.94 Model 8 Top-up flow between 39_386_2 & 3.174 3.01 3.01 3.76 4.28 4.83 5.63 6.32 7.08 9.23 Model 8 39_571_1 39003 97.866 75.06 75.06 92.92 105.79 119.32 139.17 156.12 174.93 227.94 Model 8 Top-up flow between 39_571_1 & 0.569 0.60 0.60 0.75 0.85 0.95 1.11 1.24 1.38 1.79 Model 8 39003 39_2542_D 98.71 75.12 75.12 93.00 105.79 119.32 139.17 156.12 174.93 227.94 Model 8 Top-up flow between 39003 & 0.844 0.87 0.87 1.07 1.22 1.37 1.59 1.78 1.98 2.57 Model 8 39_2542_D 39_1122_U 0.05 0.07 0.07 0.09 0.10 0.12 0.14 0.16 0.19 0.27 Model 8 39_1122_6_RPS 3.064 2.66 2.66 3.45 4.03 4.68 5.67 6.56 7.59 10.69 Model 8 Top-up flow between 39_1122_U & 3.014 2.62 2.62 3.39 3.97 4.61 5.59 6.46 7.47 10.52 Model 8 39_1122_6_RPS 39_376_1_RPS 41.115 29.80 29.80 36.50 41.18 46.07 53.16 59.15 65.83 84.39 Model 8 39_1126_1_RPS 1.052 1.05 1.05 1.36 1.59 1.85 2.24 2.59 3.00 4.22 Model 8 39_1126_2_RPS 1.328 1.34 1.34 1.74 2.04 2.36 2.87 3.31 3.83 5.40 Model 8 Top-up flow between 39_1126_1_RPS 0.276 0.31 0.31 0.40 0.47 0.54 0.66 0.76 0.88 1.24 Model 8 & 39_1126_2_RPS 39_1126_3_RPS 1.41 1.45 1.45 1.89 2.21 2.56 3.10 3.59 4.15 5.85 Model 8 Top-up flow between 39_1126_2 & 0.082 0.10 0.10 0.13 0.15 0.18 0.22 0.25 0.29 0.41 Model 8 39_1126_3_RPS 39_2555_1_RPS 43.549 31.95 31.95 39.14 44.15 49.39 57.00 63.42 70.57 90.48 Model 8 Top-up flow between 39_761_1_RPS 1.024 0.95 0.95 1.17 1.31 1.47 1.70 1.89 2.10 2.69 Model 8 & 39_2555_1_RPS 39_2555_2_RPS 43.801 32.09 32.09 39.31 44.35 49.62 57.25 63.70 70.89 90.89 Model 8
C10
Flows for AEP AREA Model Node ID_CFRAMS Qmed (km2) 50% 20% 10% 5% 2% 1% 0.5% 0.1% number (2) (5) (10) (20) (50) (100) (200) (1000) Top-up flow between 39_2555_1 & 0.252 0.26 0.26 0.31 0.35 0.40 0.46 0.51 0.56 0.72 Model 8 39_2555_2 39002_RPS 44.18 32.32 32.32 39.44 44.35 49.62 57.25 63.70 70.89 90.89 Model 8 Top-up flow between 39_2555_2 & 0.379 0.37 0.37 0.46 0.51 0.57 0.65 0.72 0.80 1.00 Model 8 39002_RPS 39_2556_D 44.336 33.05 33.05 40.32 45.28 50.37 57.64 63.70 70.89 90.89 Model 8 Top-up flow between 39002_RPS & 0.156 0.17 0.17 0.20 0.23 0.25 0.29 0.32 0.35 0.44 Model 8 39_2556_D 39_150_1_RPS 0.327 0.13 0.13 0.17 0.20 0.24 0.29 0.33 0.38 0.54 Model 8 39_152_2_RPS 1.521 0.58 0.58 0.75 0.87 1.01 1.23 1.42 1.64 2.32 Model 8 Top-up flow between 39_150_1_RPS 1.194 0.48 0.48 0.62 0.73 0.85 1.03 1.19 1.37 1.93 Model 8 & 39_152_2_RPS
MRFS Flows for AEP HEFS Flows for AEP AREA Model Node ID_CFRAMS (km2) 50% 20% 10% 5% 2% 1% 0.5% 0.1% 10% 1% 0.1% number (2) (5) (10) (20) (50) (100) (200) (1000) (10) (100) (1000) 39_753_2 6.467 7.21 9.36 10.95 12.70 15.40 17.80 20.60 29.01 13.45 21.87 35.64 Model 8 39_386_2 87.356 87.03 108.79 124.11 140.38 164.23 184.68 207.57 272.50 152.48 226.90 334.79 Model 8 39_753_4 6.767 7.60 9.86 11.54 13.39 16.23 18.76 21.71 30.57 14.18 23.05 37.56 Model 8 Top-up flow between 0.3 0.41 0.53 0.62 0.72 0.88 1.01 1.17 1.65 0.76 1.24 2.03 Model 8 39_753_2 & 39_753_4 39_571_1 97.297 91.95 114.75 130.84 147.57 172.12 193.09 216.35 281.91 160.75 237.22 346.34 Model 8 Top-up flow between 3.174 3.72 4.64 5.30 5.97 6.97 7.81 8.76 11.41 6.51 9.60 14.02 Model 8 39_386_2 & 39_571_1 39003 97.866 92.42 114.42 130.26 146.92 171.36 192.24 215.40 280.66 160.04 236.18 344.82 Model 8 Top-up flow between 0.569 0.74 0.92 1.04 1.17 1.36 1.52 1.70 2.20 1.28 1.87 2.71 Model 8 39_571_1 & 39003 39_2542_D 98.71 92.72 114.79 130.57 147.27 171.77 192.69 215.91 281.33 163.07 240.65 351.35 Model 8
C11
MRFS Flows for AEP HEFS Flows for AEP AREA Model Node ID_CFRAMS (km2) 50% 20% 10% 5% 2% 1% 0.5% 0.1% 10% 1% 0.1% number (2) (5) (10) (20) (50) (100) (200) (1000) (10) (100) (1000) Top-up flow between 0.844 1.07 1.32 1.50 1.69 1.96 2.19 2.45 3.17 1.88 2.74 3.96 Model 8 39003 & 39_2542_D 39_1122_U 0.05 0.08 0.11 0.13 0.15 0.18 0.21 0.24 0.34 0.16 0.25 0.41 Model 8 39_1122_6_RPS 3.064 3.66 4.75 5.55 6.44 7.81 9.03 10.45 14.72 10.70 17.39 28.35 Model 8 Top-up flow between 39_1122_U & 3.014 3.60 4.67 5.47 6.35 7.69 8.89 10.29 14.49 10.57 17.18 28.00 Model 8 39_1122_6_RPS 39_376_1_RPS 41.115 37.20 45.57 51.41 57.51 66.36 73.84 82.17 105.35 63.16 90.72 129.43 Model 8 39_1126_1_RPS 1.052 1.31 1.70 1.99 2.31 2.80 3.24 3.74 5.27 2.45 3.98 6.48 Model 8 39_1126_2_RPS 1.328 1.78 2.31 2.71 3.14 3.81 4.40 5.10 7.18 4.61 7.50 12.22 Model 8 Top-up flow between 39_1126_1_RPS & 0.276 0.64 0.82 0.97 1.12 1.36 1.57 1.82 2.56 1.42 2.31 3.76 Model 8 39_1126_2_RPS 39_1126_3_RPS 1.41 1.74 2.26 2.65 3.07 3.73 4.31 4.98 7.02 3.66 5.94 9.69 Model 8 Top-up flow between 39_1126_2 & 0.082 0.20 0.26 0.31 0.36 0.44 0.50 0.58 0.82 0.46 0.75 1.21 Model 8 39_1126_3_RPS 39_2555_1_RPS 43.549 39.63 48.55 54.77 61.27 70.70 78.67 87.54 112.23 67.29 96.65 137.89 Model 8 Top-up flow between 39_761_1_RPS & 1.024 2.07 2.53 2.86 3.20 3.69 4.11 4.57 5.86 4.23 6.07 8.66 Model 8 39_2555_1_RPS 39_2555_2_RPS 43.801 39.58 48.49 54.70 61.19 70.61 78.57 87.43 112.09 67.20 96.53 137.72 Model 8
Top-up flow between 0.252 0.55 0.68 0.76 0.85 0.99 1.10 1.22 1.56 1.13 1.62 2.31 Model 8 39_2555_1 & 39_2555_2
39002_RPS 44.18 39.85 48.62 54.68 61.16 70.58 78.53 87.40 112.04 67.17 96.48 137.65 Model 8
Top-up flow between 0.379 0.81 0.99 1.11 1.23 1.41 1.56 1.72 2.16 1.64 2.30 3.20 Model 8 39_2555_2 & 39002_RPS
39_2556_D 44.336 41.57 50.71 56.95 63.35 72.50 80.12 89.16 114.31 67.51 94.97 135.50 Model 8
C12
MRFS Flows for AEP HEFS Flows for AEP AREA Model Node ID_CFRAMS (km2) 50% 20% 10% 5% 2% 1% 0.5% 0.1% 10% 1% 0.1% number (2) (5) (10) (20) (50) (100) (200) (1000) (10) (100) (1000) Top-up flow between 39002_RPS & 0.156 0.35 0.43 0.48 0.54 0.62 0.68 0.75 0.94 0.72 1.01 1.40 Model 8 39_2556_D 39_150_1_RPS 0.327 0.17 0.22 0.26 0.30 0.37 0.42 0.49 0.69 0.38 0.61 1.00 Model 8 39_152_2_RPS 1.521 0.90 1.17 1.37 1.59 1.92 2.22 2.57 3.62 2.17 3.53 5.76 Model 8 Top-up flow between 39_150_1_RPS & 1.194 0.80 1.03 1.21 1.40 1.70 1.96 2.27 3.20 1.88 3.06 4.98 Model 8 39_152_2_RPS
Input flows Top-up flows. These flows should be entered laterally Check flows. Modellers should check to make sure these flows are being reached at each HEP Some of these flows may be put in at the US point due to a small difference between US & DS flows.
C13
Model 9 - Rathmullan Flows for AEP AREA Model Node ID_CFRAMS Qmed (km2) 50% 20% 10% 5% 2% 1% 0.5% 0.1% number (2) (5) (10) (20) (50) (100) (200) (1000) 39_927_1 2.683 1.30 1.30 1.68 1.97 2.29 2.77 3.20 3.71 5.22 Model 9 39_927_2 3.181 1.66 1.66 2.15 2.52 2.92 3.54 4.09 4.74 6.67 Model 9 Top-up flow between 39_927_1 & 0.498 0.37 0.37 0.48 0.56 0.65 0.79 0.92 1.06 1.49 Model 9 39_927_2 39_1000_D 3.27 1.78 1.78 2.31 2.70 3.14 3.80 4.40 5.09 7.17 Model 9 Top-up flow between 39_927_2 & 0.089 0.12 0.12 0.15 0.18 0.20 0.25 0.29 0.33 0.47 Model 9 39_1000_D 39_927_3 0.13 0.15 0.15 0.19 0.22 0.26 0.31 0.36 0.41 0.58 Model 9
MRFS Flows for AEP HEFS Flows for AEP AREA Model Node ID_CFRAMS (km2) 50% 20% 10% 5% 2% 1% 0.5% 0.1% 10% 1% 0.1% number (2) (5) (10) (20) (50) (100) (200) (1000) (10) (100) (1000) 39_927_1 2.683 1.62 2.10 2.46 2.85 3.46 4.00 4.63 6.52 3.02 4.91 8.01 Model 9 39_927_2 3.181 2.07 2.69 3.14 3.65 4.42 5.11 5.91 8.33 3.86 6.28 10.23 Model 9 Top-up flow between 39_927_1 & 39_927_2 0.498 0.46 0.60 0.70 0.82 0.99 1.14 1.32 1.86 0.86 1.41 2.29 Model 9 39_1000_D 3.27 2.20 2.85 3.33 3.87 4.69 5.42 6.27 8.83 4.09 6.66 10.85 Model 9 Top-up flow between 39_927_2 & 39_1000_D 0.089 0.17 0.22 0.25 0.29 0.35 0.41 0.47 0.67 0.37 0.61 0.99 Model 9 39_927_3 0.13 0.30 0.38 0.45 0.52 0.63 0.73 0.84 1.19 0.66 1.08 1.76 Model 9
Input flows Top-up flows. These flows should be entered laterally Check flows. Modellers should check to make sure these flows are being reached at each HEP Some of these flows may be put in at the US point due to a small difference between US & DS flows.
C14
Models 10 & 11 - Burnfoot & Bridge End Flows for AEP AREA Model Node ID_CFRAMS Qmed (km2) 50% 20% 10% 5% 2% 1% 0.5% 0.1% number (2) (5) (10) (20) (50) (100) (200) (1000) 39_2174a_U 13.148 13.73 13.73 18.20 21.55 25.24 30.94 36.03 41.96 59.91 Model 11 39_2088_9_RPS 4.887 2.89 2.89 3.75 4.38 5.09 6.17 7.13 8.25 11.62 Model 11 39_2176_4 5.991 4.01 4.01 5.21 6.09 7.07 8.57 9.91 11.46 16.14 Model 11 39_2176_6_RPS 7.287 4.79 4.79 6.21 7.27 8.43 10.22 11.82 13.68 19.26 Model 11 Top-up flow between 39_2176_4 & 1.296 0.95 0.95 1.26 1.49 1.75 2.14 2.49 2.90 4.14 Model 11 39_2176_6_RPS 39016_RPS 27.202 25.32 25.32 32.15 36.96 42.00 49.37 55.67 62.69 82.43 Model 11 Top-up flow between 39_2174a_U & 1.88 2.07 2.07 2.75 3.25 3.81 4.67 5.44 6.33 9.04 Model 11 39016_RPS 39_480_1 19.455 14.91 14.91 18.45 20.99 23.71 27.75 31.26 35.22 46.67 Model 10 39015 21.04 15.97 15.97 19.77 22.49 25.41 29.74 33.49 37.74 50.00 Model 10 Top-up flow between 39_480_1 & 1.585 1.42 1.42 1.75 1.99 2.25 2.64 2.97 3.35 4.43 Model 10 39015 39_1105_6 22.599 17.21 17.21 21.30 24.23 27.38 32.04 36.09 40.66 53.88 Model 10 Top-up flow between 39015 & 1.559 1.40 1.40 1.74 1.98 2.24 2.62 2.95 3.32 4.40 Model 10 39_1105_6 39_1082_4 5.612 4.36 4.36 5.66 6.62 7.68 9.31 10.77 12.46 17.54 Model 10 39_1162_2_RPS 65.847 40.26 40.26 49.27 55.31 61.35 69.84 76.81 84.30 104.14 Model 10 Top-up flow between 39016_RPS & 10.434 7.16 7.16 8.77 9.84 10.92 12.43 13.67 15.00 18.53 Model 10 39_1162_2
MRFS Flows for AEP HEFS Flows for AEP AREA Model Node ID_CFRAMS 2 50% 10% 5% 2% 1% 0.5% 0.1% 10% 1% 0.1% (km ) 20% (5) number (2) (10) (20) (50) (100) (200) (1000) (10) (100) (1000) 39_2174a_U 13.148 20.37 27.01 31.98 37.46 45.92 53.48 62.28 88.92 60.51 101.18 168.25 Model 11 39_2088_9_RPS 4.887 3.60 4.67 5.47 6.34 7.69 8.89 10.29 14.49 6.72 10.93 17.82 Model 11 39_2176_4 5.991 5.02 6.50 7.61 8.83 10.71 12.38 14.32 20.17 9.36 15.22 24.81 Model 11 39_2176_6_RPS 7.287 5.98 7.75 9.07 10.52 12.76 14.75 17.07 24.04 11.15 18.12 29.53 Model 11
C15
MRFS Flows for AEP HEFS Flows for AEP AREA Model Node ID_CFRAMS 2 50% 10% 5% 2% 1% 0.5% 0.1% 10% 1% 0.1% (km ) 20% (5) number (2) (10) (20) (50) (100) (200) (1000) (10) (100) (1000) Top-up flow between 1.296 1.18 1.57 1.86 2.18 2.67 3.11 3.62 5.17 2.28 3.82 6.35 Model 11 39_2176_4 & 39_2176_6_RPS 39016_RPS 27.202 34.09 43.30 49.78 56.56 66.48 74.97 84.42 111.01 88.88 133.86 198.20 Model 11 Top-up flow between 1.88 2.79 3.70 4.38 5.13 6.29 7.32 8.53 12.18 7.82 13.07 21.74 Model 11 39_2174a_U & 39016_RPS 39_480_1 19.455 18.61 23.04 26.20 29.60 34.65 39.02 43.97 58.26 32.19 47.94 71.57 Model 10 39015 21.04 19.94 24.68 28.07 31.72 37.12 41.80 47.11 62.42 34.49 51.36 76.69 Model 10 Top-up flow between 39_480_1 1.585 1.77 2.19 2.49 2.81 3.29 3.71 4.18 5.53 3.06 4.55 6.80 Model 10 & 39015 39_1105_6 22.599 21.40 26.49 30.13 34.04 39.84 44.87 50.56 66.99 37.01 55.12 82.30 Model 10 Top-up flow between 39015 & 1.559 1.75 2.16 2.46 2.78 3.25 3.66 4.13 5.47 3.02 4.50 6.72 Model 10 39_1105_6 39_1082_4 5.612 5.80 7.52 8.81 10.22 12.38 14.32 16.57 23.33 15.03 24.43 39.81 Model 10 39_1162_2_RPS 65.847 49.82 60.98 68.45 75.92 86.43 95.05 104.3 128.87 84.09 116.78 158.33 Model 10 Top-up flow between 10.434 8.87 10.85 12.18 13.51 15.38 16.91 18.56 22.93 14.97 20.78 28.18 Model 10 39016_RPS & 39_1162_2
Input flows Top-up flows. These flows should be entered laterally Check flows. Modellers should check to make sure these flows are being reached at each HEP Some of these flows may be put in at the US point due to a small difference between US & DS flows.
C16
Model 12 - Ramelton Flows for AEP AREA Model Node ID_CFRAMS Qmed (km2) 50% 20% 10% 5% 2% 1% 0.5% 0.1% number (2) (5) (10) (20) (50) (100) (200) (1000) 39_951_3 253.756 64.64 64.64 79.19 89.14 99.48 114.29 126.76 140.40 178.02 Model 12 39005 255.192 65.07 65.07 79.71 89.73 100.14 115.04 127.60 141.33 179.20 Model 12 Top-up flow between 39_951_3 & 1.436 0.51 0.51 0.62 0.70 0.78 0.90 1.00 1.10 1.40 Model 12 39005 39_1106_2_RPS 1.744 0.99 0.99 1.28 1.50 1.74 2.11 2.44 2.82 3.97 Model 12 39_1106_5_RPS 2.55 1.53 1.53 1.99 2.32 2.70 3.27 3.78 4.37 6.16 Model 12 Top-up flow between 0.806 0.58 0.58 0.76 0.88 1.03 1.24 1.44 1.66 2.34 Model 12 39_1106_2_RPS & 39_1106_5_RPS 39_1591_D 262.523 66.65 66.65 81.65 91.91 102.57 117.84 130.70 144.76 183.55 Model 12 Top-up flow between 39005 & 4.781 1.56 1.56 1.91 2.15 2.40 2.76 3.06 3.39 4.30 Model 12 39_1591_D
MRFS Flows for AEP HEFS Flows for AEP AREA Model Node ID_CFRAMS (km2) 50% 20% 10% 5% 2% 1% 0.5% 0.1% 10% 1% 0.1% number (2) (5) (10) (20) (50) (100) (200) (1000) (10) (100) (1000) 39_951_3 253.756 80.02 98.02 110.34 123.15 141.47 156.91 173.80 220.37 135.57 192.78 270.74 Model 12 39005 255.192 80.55 98.67 111.07 123.96 142.41 157.95 174.95 221.82 136.46 194.06 272.53 Model 12 Top-up flow between 1.436 0.63 0.77 0.87 0.97 1.11 1.23 1.36 1.73 1.06 1.51 2.13 Model 12 39_951_3 & 39005 39_1106_2_RPS 1.744 1.23 1.60 1.87 2.17 2.63 3.04 3.52 4.96 2.30 3.74 6.09 Model 12 39_1106_5_RPS 2.55 2.21 2.87 3.36 3.89 4.72 5.46 6.32 8.89 4.46 7.24 11.80 Model 12 Top-up flow between 39_1106_2_RPS & 0.806 1.08 1.40 1.64 1.90 2.30 2.66 3.08 4.33 2.42 3.93 6.40 Model 12 39_1106_5_RPS 39_1591_D 262.523 82.41 100.95 113.64 126.82 145.69 161.60 178.98 226.94 139.61 198.54 278.82 Model 12 Top-up flow between 4.781 3.39 4.15 4.67 5.21 5.99 6.64 7.36 9.33 6.90 9.82 13.79 Model 12 39005 & 39_1591_D
C17
MRFS Flows for AEP HEFS Flows for AEP AREA Model Node ID_CFRAMS (km2) 50% 20% 10% 5% 2% 1% 0.5% 0.1% 10% 1% 0.1% number (2) (5) (10) (20) (50) (100) (200) (1000) (10) (100) (1000) 39_951_3 253.756 80.02 98.02 110.34 123.15 141.47 156.91 173.80 220.37 135.57 192.78 270.74 Model 12 39005 255.192 80.55 98.67 111.07 123.96 142.41 157.95 174.95 221.82 136.46 194.06 272.53 Model 12 Top-up flow between 1.436 0.63 0.77 0.87 0.97 1.11 1.23 1.36 1.73 1.06 1.51 2.13 Model 12 39_951_3 & 39005 39_1106_2_RPS 1.744 1.23 1.60 1.87 2.17 2.63 3.04 3.52 4.96 2.30 3.74 6.09 Model 12 39_1106_5_RPS 2.55 2.21 2.87 3.36 3.89 4.72 5.46 6.32 8.89 4.46 7.24 11.80 Model 12 Top-up flow between 39_1106_2_RPS & 0.806 1.08 1.40 1.64 1.90 2.30 2.66 3.08 4.33 2.42 3.93 6.40 Model 12 39_1106_5_RPS 39_1591_D 262.523 82.41 100.95 113.64 126.82 145.69 161.60 178.98 226.94 139.61 198.54 278.82 Model 12 Top-up flow between 4.781 3.39 4.15 4.67 5.21 5.99 6.64 7.36 9.33 6.90 9.82 13.79 Model 12 39005 & 39_1591_D
Input flows Top-up flows. These flows should be entered laterally Check flows. Modellers should check to make sure these flows are being reached at each HEP Some of these flows may be put in at the US point due to a small difference between US & DS flows.
C18
Model 13 - Newtown Cunningham Flows for AEP AREA Model Node ID_CFRAMS Qmed (km2) 50% 20% 10% 5% 2% 1% 0.5% 0.1% number (2) (5) (10) (20) (50) (100) (200) (1000) 39_2409_1 13.952 4.05 4.05 5.54 6.64 7.85 9.71 11.37 13.29 19.05 Model 13 39013 14.564 4.12 4.12 5.63 6.72 7.91 9.70 11.26 13.05 18.29 Model 13 Top-up flow between 39_2409_1 & 39013 0.612 0.21 0.21 0.29 0.35 0.41 0.50 0.58 0.67 0.94 Model 13 39_2081_3 9.877 2.81 2.81 3.65 4.27 4.96 6.01 6.95 8.04 11.32 Model 13 39_2252_3 31.754 8.28 8.28 10.57 12.24 14.04 16.73 19.10 21.80 29.70 Model 13 Top-up flow between 39013 & 39_2081_3 7.313 2.09 2.09 2.67 3.09 3.55 4.23 4.83 5.51 7.50 Model 13
MRFS Flows for AEP HEFS Flows for AEP AREA Model Node ID_CFRAMS 2 50% 20% 10% 1% 0.5% 0.1% 10% 1% 0.1% (km ) 5% (20) 2% (50) number (2) (5) (10) (100) (200) (1000) (10) (100) (1000) 39_2409_1 13.952 5.06 6.91 8.29 9.80 12.13 14.19 16.59 23.78 10.19 17.44 29.22 Model 13 39013 14.564 5.13 7.02 8.39 9.87 12.10 14.05 16.28 22.82 10.31 17.26 28.04 Model 13 Top-up flow between 39_2409_1 & 39013 0.612 0.46 0.63 0.75 0.89 1.09 1.26 1.46 2.05 1.12 1.87 3.03 Model 13 39_2081_3 9.877 3.51 4.56 5.33 6.19 7.50 8.67 10.03 14.13 6.55 10.65 17.36 Model 13 39_2252_3 31.754 10.23 13.06 15.12 17.34 20.67 23.60 26.94 36.69 18.97 29.61 46.04 Model 13 Top-up flow between 39013 & 39_2081_3 7.313 2.58 3.30 3.82 4.38 5.22 5.96 6.80 9.27 4.79 7.48 11.63 Model 13
Input flows Top-up flows. These flows should be entered laterally Check flows. Modellers should check to make sure these flows are being reached at each HEP Some of these flows may be put in at the US point due to a small difference between US & DS flows.
C19
Model 14 - Letterkenny Flows for AEP AREA Model Node ID_CFRAMS Qmed (km2) 50% 20% 10% 5% 2% 1% 0.5% 0.1% number (2) (5) (10) (20) (50) (100) (200) (1000) 39001 50.71 47.80 47.80 59.85 68.31 77.25 90.30 101.44 113.91 149.10 Model 14 39_1398_1_RPS 75.11 60.09 60.09 75.23 85.87 97.11 113.51 127.51 143.19 187.42 Model 14 Top-up flow between 39001 & 24.40 24.09 24.09 30.16 34.42 38.93 45.50 51.11 57.40 75.13 Model 14 39_1398_1_RPS 39_1296_1 3.35 3.28 3.28 4.26 4.99 5.78 7.01 8.11 9.38 13.21 Model 14 39_2433_2 6.34 6.80 6.80 8.82 10.33 11.98 14.53 16.79 19.43 27.36 Model 14 Top-up flow between 39_1296_1 & 2.99 3.36 3.36 4.36 5.10 5.92 7.17 8.29 9.60 13.51 Model 14 39_2433_2 39_2433_5_RPS 7.12 7.38 7.38 9.58 11.21 13.00 15.77 18.23 21.09 29.70 Model 14 Top-up flow between 39_2433_2 & 0.78 0.92 0.92 1.20 1.40 1.63 1.97 2.28 2.64 3.72 Model 14 39_2433_5 39_2375_RPS 0.51 0.52 0.52 0.68 0.79 0.92 1.11 1.29 1.49 2.10 Model 14 Top-up flow between 39_2433_2 & 0.51 0.52 0.52 0.68 0.79 0.92 1.11 1.29 1.49 2.10 Model 14 39_2375_RPS 39_1406_1 1.25 1.03 1.03 1.34 1.56 1.81 2.20 2.54 2.94 4.14 Model 14 39_1563_4_RPS 2.68 2.27 2.27 2.95 3.45 4.00 4.85 5.61 6.49 9.14 Model 14 Top-up flow between 39_1406_1 & 1.43 1.26 1.26 1.64 1.92 2.23 2.70 3.12 3.61 5.09 Model 14 39_1563_4_RPS 39_2317_U 1.08 1.07 1.07 1.38 1.62 1.88 2.27 2.63 3.04 4.28 Model 14 39_2323_5 3.59 6.15 6.15 7.98 9.34 10.83 13.14 15.18 17.57 24.75 Model 14 Top-up flow between 39_2317_U & 2.51 5.05 5.05 6.55 7.67 8.89 10.78 12.46 14.42 20.31 Model 14 39_2323_5 39061_RPS 96.66 71.86 71.86 89.69 102.26 115.34 134.53 150.92 169.10 220.34 Model 14 Top-up flow between 39_1398_1 & 7.66 6.55 6.55 8.18 9.33 10.52 12.27 13.76 15.42 20.09 Model 14 39061_RPS 39_800_2 7.44 5.56 5.56 7.21 8.44 9.79 11.87 13.72 15.87 22.35 Model 14 39_2152_2 3.76 3.22 3.22 4.18 4.89 5.67 6.88 7.95 9.20 12.96 Model 14 39_2153_2 5.06 4.20 4.20 5.45 6.38 7.40 8.97 10.37 12.00 16.90 Model 14 Top-up flow between 39_2152_2 & 1.29 1.17 1.17 1.52 1.78 2.06 2.50 2.89 3.35 4.71 Model 14 39_2153_2
C20
Flows for AEP AREA Model Node ID_CFRAMS Qmed (km2) 50% 20% 10% 5% 2% 1% 0.5% 0.1% number (2) (5) (10) (20) (50) (100) (200) (1000) 39_2468_3 13.81 13.75 13.75 17.79 20.74 23.95 28.76 32.98 37.82 52.03 Model 14 Top-up flow between 39_800_2 & 1.31 1.52 1.52 1.96 2.29 2.64 3.17 3.64 4.17 5.74 Model 14 39_2468_3 39_304_U 0.82 1.45 1.45 1.88 2.20 2.56 3.10 3.58 4.15 5.84 Model 14 39_2513_U 0.11 0.16 0.16 0.21 0.25 0.28 0.34 0.40 0.46 0.65 Model 14 39_2513_1 0.65 0.75 0.75 0.97 1.14 1.32 1.60 1.85 2.14 3.01 Model 14 Top-up flow between 39_2513_U & 0.54 0.63 0.63 0.82 0.96 1.11 1.35 1.56 1.80 2.54 Model 14 39_2513_1 39_858_1_RPS 0.73 1.03 1.03 1.34 1.57 1.82 2.20 2.54 2.94 4.15 Model 14 39_2551_2_RPS 4.59 2.90 2.90 3.77 4.41 5.12 6.20 7.17 8.30 11.68 Model 14 Top-up flow between 39_304_U & 2.40 1.58 1.58 2.05 2.40 2.78 3.38 3.90 4.52 6.36 Model 14 39_2551_2 RPS 39_1507_U 0.03 0.02 0.02 0.03 0.03 0.04 0.04 0.05 0.06 0.08 Model 14 39_1507_2 1.05 0.71 0.71 0.92 1.07 1.24 1.51 1.74 2.02 2.84 Model 14 Top-up between 39_1507_U & 1.02 0.69 0.69 0.89 1.05 1.21 1.47 1.70 1.97 2.77 Model 14 39_1507_2 39_1004_D_RPS 120.83 88.58 88.58 110.72 126.04 141.81 164.66 183.79 204.96 263.33 Model 14 Top-up between 39061_RPS & 4.72 4.24 4.24 5.30 6.04 6.79 7.89 8.80 9.82 12.61 Model 14 39_1004_D_RPS 39_891_U 0.06 0.07 0.07 0.09 0.11 0.12 0.15 0.17 0.20 0.28 Model 14 39_993_2 2.32 2.13 2.13 2.77 3.24 3.76 4.55 5.26 6.09 8.58 Model 14 Top-up flow between 39_891_U & 2.27 2.08 2.08 2.70 3.16 3.67 4.45 5.14 5.95 8.38 Model 14 39_993_2 39_2505_3 8.88 6.58 6.58 8.54 10.00 11.60 14.06 16.25 18.81 26.48 Model 14 Top-up flow between 39_993_2 & 6.56 4.96 4.96 6.43 7.52 8.73 10.58 12.23 14.15 19.93 Model 14 39_2505_3
C21
MRFS Flows for AEP HEFS Flows for AEP AREA Model Node ID_CFRAMS (km2) 50% 20% 10% 5% 2% 1% 0.5% 0.1% 10% 1% 0.1% number (2) (5) (10) (20) (50) (100) (200) (1000) (10) (100) (1000) 39001 50.71 59.40 74.37 84.88 95.99 112.21 126.05 141.55 185.27 104.96 155.86 229.09 Model 14 39_1398_1_RPS 75.11 75.01 93.91 107.19 121.22 141.70 159.18 178.75 233.96 131.69 195.56 287.44 Model 14 Top-up flow between 39001 & 39_1398_1_RPS 24.40 30.07 37.65 42.97 48.59 56.80 63.81 71.66 93.79 52.79 78.39 115.23 Model 14 39_1296_1 3.35 4.10 5.32 6.22 7.22 8.75 10.12 11.71 16.49 7.65 12.43 20.26 Model 14 39_2433_2 6.34 9.79 12.70 14.87 17.25 20.91 24.17 27.97 39.39 29.68 48.25 78.64 Model 14 Top-up flow between 39_1296_1 & 39_2433_2 2.99 6.53 8.47 9.92 11.50 13.95 16.12 18.66 26.27 14.66 23.83 38.84 Model 14 39_2433_5_RPS 7.12 10.40 13.49 15.79 18.32 22.21 25.68 29.71 41.84 32.71 53.18 86.67 Model 14 Top-up flow between 39_2433_2 & 39_2433_5 0.78 1.83 2.37 2.77 3.22 3.90 4.51 5.21 7.34 4.10 6.66 10.86 Model 14 39_2375_RPS 0.51 0.65 0.85 0.99 1.15 1.39 1.61 1.86 2.62 1.22 1.98 3.22 Model 14 Top-up flow between 39_2433_2 & 39_2375_RPS 0.51 1.14 1.48 1.73 2.01 2.44 2.82 3.26 4.59 2.56 4.17 6.79 Model 14 39_1406_1 1.25 1.29 1.67 1.95 2.26 2.74 3.17 3.67 5.17 2.40 3.90 6.35 Model 14 39_1563_4_RPS 2.68 2.84 3.68 4.30 4.99 6.05 7.00 8.10 11.41 5.29 8.60 14.01 Model 14 Top-up flow between 39_1406_1 & 39_1563_4_RPS 1.43 2.77 3.59 4.20 4.87 5.91 6.83 7.90 11.13 6.21 10.10 16.45 Model 14 39_2317_U 1.08 1.33 1.72 2.02 2.34 2.84 3.28 3.80 5.35 2.48 4.03 6.57 Model 14 39_2323_5 3.59 9.78 12.69 14.85 17.23 20.89 24.15 27.94 39.35 16.09 26.16 42.63 Model 14 Top-up flow between 39_2317_U & 39_2323_5 2.51 6.99 9.07 10.61 12.31 14.92 17.25 19.96 28.11 11.50 18.69 30.46 Model 14 39061_RPS 96.66 95.18 118.78 135.44 152.76 178.17 199.88 223.96 291.82 227.59 335.86 490.36 Model 14 Top-up flow between 39_1398_1 & 39061_RPS 7.66 13.49 16.84 19.20 21.65 25.26 28.33 31.75 41.36 28.38 41.88 61.15 Model 14 39_800_2 7.44 6.94 9.00 10.53 12.22 14.81 17.12 19.81 27.90 14.23 23.14 37.71 Model 14 39_2152_2 3.76 4.02 5.22 6.11 7.08 8.59 9.93 11.49 16.18 17.40 28.30 46.11 Model 14 39_2153_2 5.06 5.20 6.74 7.89 9.15 11.09 12.82 14.84 20.90 20.27 32.95 53.70 Model 14 Top-up flow between 1.29 2.52 3.27 3.82 4.44 5.38 6.22 7.19 10.13 5.65 9.19 14.97 Model 14
C22
MRFS Flows for AEP HEFS Flows for AEP AREA Model Node ID_CFRAMS (km2) 50% 20% 10% 5% 2% 1% 0.5% 0.1% 10% 1% 0.1% number (2) (5) (10) (20) (50) (100) (200) (1000) (10) (100) (1000) 39_2152_2 & 39_2153_2 39_2468_3 13.81 19.37 25.06 29.22 33.74 40.52 46.46 53.28 73.30 60.53 96.23 151.83 Model 14 Top-up flow between 39_800_2 & 39_2468_3 1.31 2.99 3.87 4.52 5.21 6.26 7.18 8.23 11.33 6.67 10.61 16.74 Model 14 39_304_U 0.82 2.46 3.20 3.74 4.34 5.26 6.08 7.04 9.91 4.05 6.59 10.73 Model 14 39_2513_U 0.11 0.28 0.37 0.43 0.50 0.61 0.70 0.81 1.14 0.60 0.97 1.59 Model 14 39_2513_1 0.65 0.99 1.28 1.50 1.74 2.11 2.44 2.83 3.98 2.53 4.11 6.69 Model 14 Top-up flow between 39_2513_U & 39_2513_1 0.54 1.30 1.69 1.97 2.29 2.77 3.21 3.71 5.23 2.92 4.74 7.72 Model 14 39_858_1_RPS 0.73 1.61 2.09 2.44 2.83 3.44 3.97 4.60 6.47 3.61 5.87 9.57 Model 14 39_2551_2_RPS 4.59 4.07 5.28 6.19 7.18 8.70 10.06 11.64 16.39 9.14 14.87 24.23 Model 14 Top-up flow between 39_304_U & 39_2551_2 RPS 2.40 3.03 3.92 4.59 5.33 6.46 7.47 8.64 12.17 4.98 8.09 13.19 Model 14 39_1507_U 0.03 0.03 0.04 0.05 0.05 0.07 0.08 0.09 0.12 0.09 0.15 0.24 Model 14 39_1507_2 1.05 1.66 2.15 2.51 2.92 3.54 4.09 4.73 6.66 3.01 4.89 7.97 Model 14 Top-up between 39_1507_U & 39_1507_2 1.02 1.31 1.70 1.99 2.31 2.80 3.23 3.74 5.27 2.94 4.78 7.79 Model 14 39_1004_D_RPS 120.83 148.67 185.83 211.55 238.01 276.37 308.48 344.01 441.98 280.51 409.04 586.05 Model 14 Top-up between 39061_RPS & 39_1004_D_RPS 4.72 8.73 10.91 12.43 13.98 16.23 18.12 20.20 25.96 18.37 26.78 38.37 Model 14 39_891_U 0.06 0.09 0.11 0.13 0.15 0.19 0.22 0.25 0.35 0.16 0.27 0.43 Model 14 39_993_2 2.32 2.66 3.45 4.04 4.69 5.68 6.57 7.60 10.71 4.97 8.07 13.16 Model 14 Top-up flow between 39_891_U & 39_993_2 2.27 4.56 5.92 6.93 8.03 9.74 11.26 13.03 18.35 10.24 16.64 27.12 Model 14 39_2505_3 8.88 8.22 10.66 12.48 14.47 17.55 20.29 23.48 33.06 15.33 24.92 40.62 Model 14 Top-up flow between 39_993_2 & 39_2505_3 6.56 10.85 14.07 16.46 19.10 23.15 26.77 30.97 43.62 24.34 39.57 64.48 Model 14 Input flows Top-up flows. These flows should be entered laterally Check flows. Modellers should check to make sure these flows are being reached at each HEP Some of these flows may be put in at the US point due to a small difference between US & DS flows.
C23
Model 15 - Bunbeg / Derrybeg Flows for AEP AREA Model Node ID_CFRAMS Qmed (km2) 50% 20% 10% 5% 2% 1% 0.5% 0.1% number (2) (5) (10) (20) (50) (100) (200) (1000) 38_685_1_RPS 0.03 0.03 0.03 0.04 0.04 0.05 0.06 0.07 0.08 0.11 Model 15 38_2911_U 0.40 0.56 0.56 0.73 0.86 0.99 1.20 1.39 1.61 2.27 Model 15 38_2911_1 0.73 0.99 0.99 1.28 1.50 1.74 2.11 2.44 2.83 3.98 Model 15 Top-up flow between 38_2911_U & 38_2911_1 0.33 0.47 0.47 0.61 0.71 0.83 1.00 1.16 1.34 1.89 Model 15 38_2585_1 2.02 2.56 2.56 3.32 3.88 4.50 5.46 6.31 7.31 10.29 Model 15 38_2587_U 0.13 0.19 0.19 0.25 0.29 0.33 0.41 0.47 0.54 0.76 Model 15 38_2587_1 0.16 0.25 0.25 0.32 0.37 0.43 0.52 0.60 0.70 0.99 Model 15 Top-up flow between 38_2587_U & 38_2587_1 0.04 0.06 0.06 0.08 0.10 0.11 0.14 0.16 0.18 0.26 Model 15 38_4132_3 3.76 4.32 4.32 5.60 6.55 7.60 9.22 10.65 12.33 17.36 Model 15 Top-up flow between 38_2585_1_RPS & 38_4132_3 1.58 1.92 1.92 2.49 2.91 3.37 4.09 4.73 5.47 7.71 Model 15 38_4130_D 7.81 5.91 5.91 7.67 8.98 10.41 12.63 14.59 16.89 23.78 Model 15 Top-up flow between 38_685_1_RPS & 38_4130_D 4.02 3.17 3.17 4.11 4.81 5.59 6.77 7.83 9.06 12.76 Model 15 38_687_1 84.93 32.31 32.31 41.48 48.04 55.05 65.45 74.43 84.61 113.84 Model 15 38_3999_1 87.28 31.60 31.60 40.58 46.99 53.85 64.03 72.81 82.77 111.37 Model 15 Top-up flow between 38_687_1 & 38_3999_1 2.36 1.07 1.07 1.38 1.59 1.83 2.17 2.47 2.81 3.78 Model 15 38_4124_2 88.96 32.03 32.03 41.13 47.63 54.58 64.90 73.80 83.89 112.88 Model 15 Top-up flow between 38_3999_1 & 38_4124_2 1.67 0.77 0.77 0.99 1.15 1.32 1.57 1.78 2.03 2.73 Model 15
MRFS Flows for AEP HEFS Flows for AEP AREA Model Node ID_CFRAMS (km2) 50% 20% 10% 5% 2% 1% 0.5% 0.1% 10% 1% 0.1% number (2) (5) (10) (20) (50) (100) (200) (1000) (10) (100) (1000) 38_685_1_RPS 0.03 0.04 0.05 0.05 0.06 0.08 0.09 0.10 0.14 0.07 0.11 0.17 Model 15 38_2911_U 0.40 0.70 0.91 1.07 1.24 1.50 1.74 2.01 2.83 1.31 2.13 3.48 Model 15 38_2911_1 0.73 1.24 1.60 1.88 2.18 2.64 3.05 3.53 4.97 2.31 3.75 6.11 Model 15 Top-up flow between 0.33 0.59 0.76 0.89 1.03 1.25 1.45 1.68 2.36 1.10 1.78 2.90 Model 15 38_2911_U & 38_2911_1 38_2585_1 2.02 3.19 4.14 4.85 5.62 6.82 7.88 9.12 12.84 5.96 9.68 15.78 Model 15
C24
MRFS Flows for AEP HEFS Flows for AEP AREA Model Node ID_CFRAMS (km2) 50% 20% 10% 5% 2% 1% 0.5% 0.1% 10% 1% 0.1% number (2) (5) (10) (20) (50) (100) (200) (1000) (10) (100) (1000) 38_2587_U 0.13 0.24 0.31 0.36 0.42 0.51 0.59 0.68 0.95 0.44 0.72 1.17 Model 15 38_2587_1 0.16 0.31 0.40 0.46 0.54 0.65 0.76 0.87 1.23 0.57 0.93 1.51 Model 15 Top-up flow between 0.04 0.08 0.10 0.12 0.14 0.17 0.20 0.23 0.32 0.15 0.24 0.39 Model 15 38_2587_U & 38_2587_1 38_4132_3 3.76 5.39 6.99 8.18 9.49 11.51 13.30 15.39 21.68 10.05 16.34 26.63 Model 15 Top-up flow between 38_2585_1_RPS & 1.58 4.19 5.44 6.37 7.38 8.95 10.35 11.98 16.87 9.41 15.30 24.93 Model 15 38_4132_3 38_4130_D 7.81 7.38 9.57 11.21 13.00 15.76 18.22 21.08 29.69 13.77 22.38 36.48 Model 15 Top-up flow between 38_685_1_RPS & 4.02 6.94 9.00 10.54 12.22 14.82 17.13 19.82 27.92 15.58 25.32 41.27 Model 15 38_4130_D 38_687_1 84.93 40.33 51.78 59.97 68.72 81.70 92.91 105.62 142.11 73.67 114.15 174.60 Model 15 38_3999_1 87.28 40.33 51.78 59.97 68.72 81.70 92.91 105.62 142.11 73.67 114.15 174.60 Model 15 Top-up flow between 2.36 2.35 3.01 3.49 4.00 4.75 5.40 6.14 8.27 5.16 7.99 12.22 Model 15 38_687_1 & 38_3999_1 38_4124_2 88.96 40.33 51.78 59.97 68.72 81.70 92.91 105.62 142.11 73.67 114.15 174.60 Model 15 Top-up flow between 1.67 1.69 2.17 2.52 2.88 3.43 3.90 4.43 5.96 3.72 5.76 8.82 Model 15 38_3999_1 & 38_4124_2
Input flows Top-up flows. These flows should be entered laterally Check flows. Modellers should check to make sure these flows are being reached at each HEP Some of these flows may be put in at the US point due to a small difference between US & DS flows.
C25
Model 16 - Dungloe Flows for AEP AREA Model Node ID_CFRAMS 2 Qmed 10% 0.5% 0.1% (km ) 50% (2) 20% (5) 5% (20) 2% (50) 1% (100) number (10) (200) (1000) 38_1154_1 37.69 5.88 5.88 7.36 8.45 9.63 11.41 12.98 14.78 20.11 Model 16 38006 39.30 6.22 6.22 7.79 8.94 10.18 12.06 13.73 15.63 21.27 Model 16 Top-up flow between 1.61 0.31 0.31 0.39 0.45 0.51 0.60 0.69 0.78 1.07 Model 16 38_1154_1 & 38006 38_1155_3 39.60 6.32 6.32 7.91 9.08 10.34 12.25 13.95 15.88 21.60 Model 16 Top-up flow between 0.30 0.13 0.13 0.16 0.19 0.21 0.25 0.29 0.32 0.44 Model 16 38006 & 38_1155_3
MRFS Flows for AEP HEFS Flows for AEP AREA Model Node ID_CFRAMS 2 (km ) 50% 20% 10% 5% 2% 1% 0.5% 0.1% 10% 1% 0.1% number (2) (5) (10) (20) (50) (100) (200) (1000) (10) (100) (1000) 38_1154_1 37.69 7.06 8.83 10.14 11.55 13.69 15.58 17.74 24.13 14.25 21.90 33.92 Model 16 38006 39.30 7.49 9.38 10.77 12.26 14.53 16.54 18.84 25.62 13.67 21.01 32.54 Model 16 Top-up flow between 38_1154_1 1.61 0.53 0.67 0.76 0.87 1.03 1.17 1.34 1.82 1.44 2.22 3.44 Model 16 & 38006 38_1155_3 39.60 7.72 9.66 11.09 12.63 14.96 17.03 19.39 26.37 13.77 21.16 32.76 Model 16 Top-up flow between 38006 & 0.30 0.19 0.24 0.28 0.31 0.37 0.42 0.48 0.66 0.30 0.46 0.71 Model 16 38_1155_3 Input flows Top-up flows. These flows should be entered laterally Check flows. Modellers should check to make sure these flows are being reached at each HEP Some of these flows may be put in at the US point due to a small difference between US & DS flows.
C26
Model 17 - Glenties Flows for AEP AREA Model Node ID_CFRAMS Qmed (km2) 50% 20% 10% 5% 2% 1% 0.5% 0.1% number (2) (5) (10) (20) (50) (100) (200) (1000) 38_2761_2 41.04 33.46 33.46 41.83 48.02 54.75 64.92 73.92 84.29 115.01 Model 17 38010 42.33 34.54 34.54 43.17 49.45 56.22 66.38 75.25 85.37 114.93 Model 17 Top-up flow between 38_2761_2 & 1.29 1.31 1.31 1.64 1.88 2.14 2.52 2.86 3.24 4.36 Model 17 38010 38_3860_Inter_1 42.39 34.35 34.35 42.94 49.19 55.93 66.03 74.85 84.92 114.33 Model 17 Top-up flow between 38010 & 0.07 0.08 0.08 0.10 0.12 0.13 0.15 0.18 0.20 0.27 Model 17 38_3860_Inter_1 38_3860_Inter_2 42.51 34.44 34.44 43.05 49.32 56.07 66.20 75.05 85.14 114.62 Model 17 Top-up flow between 38_3860_Inter_1 0.12 0.14 0.14 0.17 0.20 0.23 0.27 0.30 0.34 0.46 Model 17 & 38_3860_Inter_2 38_3822_4_RPS 49.25 39.53 39.53 49.81 57.36 65.51 77.84 88.71 101.16 137.85 Model 17 38_3833_1_RPS 0.11 0.17 0.17 0.21 0.25 0.29 0.35 0.41 0.47 0.66 Model 17 38_23_1 1.32 1.53 1.53 1.99 2.33 2.70 3.27 3.78 4.38 6.16 Model 17 38_414_4 2.46 3.08 3.08 4.00 4.68 5.43 6.58 7.61 8.81 12.40 Model 17 Top-up flow between 38_23_1 & 1.14 1.61 1.61 2.09 2.45 2.84 3.45 3.99 4.61 6.49 Model 17 38_414_4 38_442_4 102.59 69.12 69.12 87.51 100.64 114.47 135.00 152.55 172.39 228.79 Model 17 Top-up flow between 38_3860_Inter_2 8.27 6.53 6.53 8.26 9.50 10.81 12.75 14.40 16.28 21.60 Model 17 & 38_442_4 38001 111.25 70.14 70.14 88.59 101.70 115.59 136.14 153.82 173.67 230.41 Model 17 Top-up flow between 38_442_4 & 8.65 6.41 6.41 8.09 9.29 10.56 12.44 14.05 15.86 21.05 Model 17 38001 38_2332_4 9.44 2.52 2.52 3.26 3.82 4.43 5.37 6.21 7.18 10.12 Model 17 38_1168_3 126.05 74.30 74.30 93.62 107.14 121.34 141.99 159.53 179.07 233.75 Model 17 Top-up flow between 38001 & 5.36 3.86 3.86 4.86 5.56 6.30 7.37 8.28 9.29 12.13 Model 17 38_1168_3
C27
MRFS Flows for AEP HEFS Flows for AEP AREA Model Node ID_CFRAMS (km2) 50% 20% 10% 5% 2% 1% 0.5% 0.1% 10% 1% 0.1% number (2) (5) (10) (20) (50) (100) (200) (1000) (10) (100) (1000) 38_2761_2 41.04 40.67 50.84 58.36 66.53 78.90 89.84 102.44 139.78 72.13 111.03 172.76 Model 17 38010 42.33 41.96 52.46 60.09 68.32 80.65 91.44 103.74 139.66 74.27 113.02 172.61 Model 17 Top-up flow between 1.29 2.15 2.69 3.08 3.50 4.13 4.68 5.31 7.15 4.39 6.69 10.21 Model 17 38_2761_2 & 38010 38_3860_Inter_1 42.39 41.74 52.17 59.77 67.95 80.22 90.94 103.17 138.90 73.88 112.42 171.71 Model 17 Top-up flow between 38010 & 0.07 0.13 0.17 0.19 0.21 0.25 0.29 0.33 0.44 0.26 0.40 0.61 Model 17 38_3860_Inter_1 38_3860_Inter_2 42.51 41.84 52.31 59.92 68.12 80.42 91.18 103.44 139.26 74.07 112.70 172.13 Model 17 Top-up flow between 38_3860_Inter_1 & 0.12 0.23 0.29 0.33 0.37 0.44 0.50 0.56 0.76 0.47 0.71 1.08 Model 17 38_3860_Inter_2 38_3822_4_RPS 49.25 48.04 60.53 69.70 79.60 94.58 107.79 122.92 167.50 78.32 121.12 188.21 Model 17 38_3833_1_RPS 0.11 0.20 0.26 0.31 0.36 0.44 0.50 0.58 0.82 0.37 0.61 0.99 Model 17 38_23_1 1.32 1.91 2.47 2.90 3.36 4.07 4.71 5.45 7.67 3.91 6.35 10.35 Model 17 38_414_4 2.46 4.10 5.32 6.23 7.23 8.76 10.13 11.72 16.51 10.72 17.42 28.39 Model 17 Top-up flow between 38_23_1 1.14 3.07 3.98 4.66 5.41 6.56 7.58 8.77 12.36 6.89 11.20 18.25 Model 17 & 38_414_4 38_442_4 102.59 84.00 106.34 122.30 139.10 164.05 185.39 209.50 278.04 137.42 208.30 312.40 Model 17 Top-up flow between 8.27 7.93 10.04 11.55 13.14 15.49 17.51 19.78 26.25 12.97 19.65 29.48 Model 17 38_3860_Inter_2 & 38_442_4 38001 111.25 85.24 107.65 123.59 140.47 165.44 186.92 211.04 280.00 138.87 210.03 314.61 Model 17 Top-up flow between 8.65 7.79 9.84 11.29 12.83 15.12 17.08 19.28 25.58 12.69 19.19 28.74 Model 17 38_442_4 & 38001 38_2332_4 9.44 3.06 3.97 4.65 5.39 6.53 7.55 8.74 12.31 5.21 8.47 13.80 Model 17 38_1168_3 126.05 90.30 113.78 130.21 147.46 172.56 193.87 217.62 284.08 146.31 217.85 319.21 Model 17 Top-up flow between 38001 & 5.36 4.68 5.90 6.75 7.64 8.94 10.05 11.28 14.72 7.59 11.30 16.56 Model 17 38_1168_3
Input flows Top-up flows. These flows should be entered laterally Check flows. Modellers should check to make sure these flows are being reached at each HEP Some of these flows may be put in at the US point due to a small difference between US & DS flows.
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Model 18 - Ardara Flows for AEP AREA Model Node ID_CFRAMS Qmed (km2) 50% 20% 10% 5% 2% 1% 0.5% 0.1% number (2) (5) (10) (20) (50) (100) (200) (1000) 38_3814_1 42.05 37.30 37.30 46.69 53.59 61.09 72.43 82.46 93.95 128.00 Model 18 38_3037_3 43.08 37.92 37.92 47.48 54.49 62.11 73.64 83.84 95.52 130.14 Model 18 Top-up flow between 38_3814_1 & 38_3037_3 1.03 1.15 1.15 1.44 1.65 1.88 2.23 2.54 2.90 3.95 Model 18
MRFS Flows for AEP HEFS Flows for AEP AREA Model Node ID_CFRAMS 2 10% 1% 0.5% 0.1% 10% 1% 0.1% (km ) 50% (2) 20% (5) 5% (20) 2% (50) number (10) (100) (200) (1000) (10) (100) (1000) 38_3814_1 42.05 46.56 58.29 66.91 76.27 90.42 102.94 117.28 159.79 82.20 126.47 196.31 Model 18 38_3037_3 43.08 47.03 58.88 67.58 77.03 91.33 103.98 118.46 161.40 83.02 127.73 198.27 Model 18 Top-up flow between 38_3814_1 & 1.03 2.50 3.12 3.59 4.09 4.85 5.52 6.29 8.57 5.31 8.17 12.69 Model 18 38_3037_3
Input flows Top-up flows. These flows should be entered laterally Check flows. Modellers should check to make sure these flows are being reached at each HEP Some of these flows may be put in at the US point due to a small difference between US & DS flows.
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Ballybofey & Stranorlar – Model 19 Flows for AEP AREA Model Node ID_CFRAMS Qmed (km2) 50% 20% 10% 5% 2% 1% 0.5% 0.1% number (2) (5) (10) (20) (50) (100) (200) (1000) 01_810_2_RA 309.97 257.90 257.90 322.89 369.31 418.57 491.04 553.71 624.12 825.54 Model 19 01043_RA 314.12 257.90 257.90 322.89 369.31 418.57 491.04 553.71 624.12 825.54 Model 19 01_186_2_RA 4.63 3.21 3.21 4.16 4.87 5.65 6.86 7.93 9.17 12.92 Model 19 01_543_U 0.08 0.06 0.06 0.07 0.09 0.10 0.12 0.14 0.16 0.23 Model 19 01_543_2_RA 1.16 0.82 0.82 1.07 1.25 1.45 1.76 2.03 2.35 3.31 Model 19 Top-up flow between 01_543_U & 1.08 0.77 0.77 1.00 1.17 1.36 1.65 1.91 2.21 3.11 01_543_2_RA Model 19 01_542_Inter_RA 1.61 1.09 1.09 1.41 1.65 1.92 2.33 2.69 3.11 4.38 Model 19 Top-up flow between 01_543_2_RA & 0.46 0.20 0.20 0.26 0.31 0.36 0.43 0.50 0.58 0.82 01_542_Inter_RA Model 19 01_542_1_RA 1.96 1.25 1.25 1.62 1.90 2.20 2.67 3.09 3.57 5.03 Model 19 Top-up flow between 0.35 0.16 0.16 0.20 0.24 0.28 0.34 0.39 0.45 0.64 01_542_Inter_RA & 01_542_1_RA Model 19 01_551_2_RA 8.67 7.23 7.23 9.38 10.97 12.73 15.44 17.84 20.65 29.08 Model 19 Top-up flow between 01_186_2_RA & 2.08 1.90 1.90 2.46 2.88 3.34 4.05 4.69 5.42 7.64 01_551_2_RA Model 19 01_1815_2_RA 8.93 8.01 8.01 10.39 12.16 14.11 17.10 19.77 22.88 32.22 Model 19 01_223_1_RARPS 1.51 1.28 1.28 1.66 1.94 2.25 2.73 3.16 3.66 5.15 Model 19 01_1825_3_RA 3.46 3.25 3.25 4.21 4.93 5.72 6.93 8.01 9.27 13.06 Model 19 Top-up flow between 1.95 1.90 1.90 2.46 2.88 3.34 4.05 4.69 5.42 7.64 01_223_1_RARPS & 01_1825_3_RA Model 19 01_41_6_RA 3.49 0.94 0.94 1.22 1.43 1.66 2.01 2.32 2.68 3.78 Model 19 01_41_9_RA 4.47 1.32 1.32 1.72 2.01 2.33 2.82 3.26 3.78 5.32 Model 19 Top-up flow between 01_41_6_RA & 0.99 0.41 0.41 0.54 0.63 0.73 0.88 1.02 1.18 1.67 01_41_9_RA Model 19 01044_RARPS 22.38 15.07 15.07 18.81 21.61 24.69 29.42 33.64 38.57 53.42 Model 19 Top-up flow between 01_1815_2_RA 5.52 5.77 5.77 7.20 8.28 9.46 11.27 12.88 14.77 20.46 & 01044_RARPS Model 19 01_10000_U_RA 1.76 1.52 1.52 1.97 2.30 2.67 3.24 3.75 4.33 6.10 Model 19 01_10000_RARPS 2.38 2.06 2.06 2.68 3.13 3.64 4.41 5.10 5.90 8.30 Model 19
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Flows for AEP AREA Model Node ID_CFRAMS Qmed (km2) 50% 20% 10% 5% 2% 1% 0.5% 0.1% number (2) (5) (10) (20) (50) (100) (200) (1000) Top-up flow between 01_10000_U_RA & 0.62 0.58 0.58 0.73 0.83 0.94 1.11 1.25 1.41 1.86 01_10000_RARPS Model 19 01_814_4_RA 25.55 16.08 16.08 20.03 23.03 26.32 31.40 35.99 41.32 57.53 Model 19 Top-up flow between 01044_RARPS 0.79 0.62 0.62 0.77 0.89 1.02 1.21 1.39 1.59 2.22 & 01_814_4_RA Model 19 01042_RA 350.37 273.88 273.88 342.90 392.20 444.51 521.48 588.03 662.80 876.70 Model 19 Top-up flow between 01043_RA & 2.02 2.18 2.18 2.73 3.12 3.54 4.15 4.68 5.27 6.97 01042_RA Model 19 01_69_2_RA 4.84 2.34 2.34 3.04 3.55 4.12 5.00 5.78 6.68 9.41 Model 19 01_776_3_RA 5.90 3.17 3.17 4.11 4.81 5.58 6.77 7.82 9.05 12.75 Model 19 Top-up flow between 01_692_2_RA & 1.06 0.64 0.64 0.82 0.96 1.12 1.36 1.57 1.82 2.56 01_776_3_RA Model 19 01_416_2_RA 1.23 0.88 0.88 1.14 1.33 1.55 1.88 2.17 2.51 3.54 Model 19 01_1577_2_RA 2.22 1.45 1.45 1.88 2.20 2.55 3.09 3.58 4.14 5.83 Model 19 Top-up flow between 01_416_2_RA & 0.99 0.68 0.68 0.88 1.03 1.20 1.45 1.68 1.94 2.73 01_1577_2_RA Model 19 01_778_7_RA 7.37 3.76 3.76 4.88 5.71 6.63 8.03 9.29 10.74 15.13 Model 19 01_614_3_RA 383.52 273.88 273.88 342.90 392.20 444.51 521.47 588.02 662.79 876.69 Model 19 Top-up flow between 01042_RA & 17.66 14.54 14.54 18.20 20.82 23.60 27.68 31.22 35.19 46.54 01_614_3_RA Model 19
MRFS Flows for AEP HEFS Flows for AEP AREA Model Node ID_CFRAMS (km2) 50% 20% 10% 5% 2% 1% 0.5% 0.1% 10% 1% 0.1% number (2) (5) (10) (20) (50) (100) (200) (1000) (10) (100) (1000) 01_810_2_RA 309.97 309.48 387.47 443.18 502.29 589.25 664.45 748.94 990.65 518.51 777.41 1159.05 Model 19 01043_RA 314.12 321.96 403.09 461.04 522.54 613.01 691.24 779.14 1030.59 564.80 846.81 1262.52 Model 19 01_186_2_RA 4.63 4.44 5.76 6.74 7.82 9.48 10.95 12.67 17.85 7.80 12.67 20.65 Model 19 01_543_U 0.08 0.09 0.12 0.14 0.16 0.19 0.22 0.26 0.36 0.15 0.24 0.39 Model 19 01_543_2_RA 1.16 1.38 1.78 2.09 2.42 2.94 3.40 3.93 5.53 2.26 3.68 6.00 Model 19
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MRFS Flows for AEP HEFS Flows for AEP AREA Model Node ID_CFRAMS (km2) 50% 20% 10% 5% 2% 1% 0.5% 0.1% 10% 1% 0.1% number (2) (5) (10) (20) (50) (100) (200) (1000) (10) (100) (1000) Top-up flow between 01_543_U & 1.08 1.69 2.20 2.57 2.98 3.61 4.18 4.83 6.81 3.80 6.18 10.07 01_543_2_RA Model 19 01_542_Inter_RA 1.61 1.36 1.76 2.06 2.40 2.90 3.36 3.89 5.47 2.49 4.04 6.59 Model 19 Top-up flow between 01_543_2_RA & 0.46 0.25 0.33 0.38 0.45 0.54 0.62 0.72 1.02 0.47 0.77 1.25 01_542_Inter_RA Model 19 01_542_1_RA 1.96 1.56 2.02 2.37 2.75 3.33 3.85 4.46 6.27 2.86 4.65 7.58 Model 19 Top-up flow between 01_542_Inter_RA & 0.35 0.20 0.26 0.30 0.35 0.42 0.49 0.56 0.79 0.37 0.60 0.97 01_542_1_RA Model 19 01_551_2_RA 8.67 10.70 13.88 16.24 18.84 22.84 26.41 30.56 43.03 30.90 50.24 81.88 Model 19 Top-up flow between 01_186_2_RA & 2.08 2.81 3.64 4.26 4.95 6.00 6.93 8.02 11.30 8.11 13.19 21.50 01_551_2_RA Model 19 01_1815_2_RA 8.93 10.00 12.97 15.18 17.61 21.35 24.68 28.56 40.22 20.52 33.35 54.36 Model 19 01_223_1_RARPS 1.51 1.60 2.07 2.43 2.81 3.41 3.94 4.56 6.43 3.30 5.36 8.74 Model 19 01_1825_3_RA 3.46 4.05 5.26 6.15 7.14 8.66 10.01 11.58 16.30 7.64 12.42 20.24 Model 19 Top-up flow between 01_223_1_RARPS & 1.95 2.37 3.07 3.60 4.17 5.06 5.85 6.77 9.54 4.47 7.26 11.84 01_1825_3_RA Model 19 01_41_6_RA 3.49 1.17 1.52 1.78 2.07 2.51 2.90 3.35 4.72 2.19 3.56 5.80 Model 19 01_41_9_RA 4.47 1.65 2.14 2.51 2.91 3.53 4.08 4.72 6.64 3.08 5.01 8.16 Model 19 Top-up flow between 01_41_6_RA & 0.99 0.91 1.18 1.38 1.60 1.93 2.24 2.59 3.65 0.96 1.57 2.55 01_41_9_RA Model 19 01044_RARPS 22.38 20.30 25.33 29.11 33.25 39.62 45.31 51.95 71.94 33.15 51.59 81.92 Model 19 Top-up flow between 01_1815_2_RA & 5.52 7.77 9.70 11.15 12.74 15.18 17.35 19.90 27.55 26.78 41.68 66.19 01044_RARPS Model 19 01_10000_U_RA 1.76 1.89 2.46 2.88 3.34 4.04 4.68 5.41 7.62 3.53 5.74 9.36 Model 19 01_10000_RARPS 2.38 2.58 3.34 3.91 4.54 5.50 6.36 7.36 10.37 4.81 7.81 12.73 Model 19
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MRFS Flows for AEP HEFS Flows for AEP AREA Model Node ID_CFRAMS (km2) 50% 20% 10% 5% 2% 1% 0.5% 0.1% 10% 1% 0.1% number (2) (5) (10) (20) (50) (100) (200) (1000) (10) (100) (1000) Top-up flow between 01_10000_U_RA & 0.62 0.73 0.91 1.04 1.18 1.38 1.56 1.76 2.32 2.69 4.04 6.02 01_10000_RARPS Model 19 01_814_4_RA 25.55 19.80 24.67 28.35 32.41 38.66 44.30 50.87 70.83 34.83 54.43 87.02 Model 19 Top-up flow between 01044_RARPS & 0.79 0.76 0.95 1.09 1.25 1.49 1.71 1.96 2.73 2.83 4.43 7.08 01_814_4_RA Model 19 01042_RA 350.37 339.02 424.45 485.48 550.23 645.50 727.88 820.43 1085.21 601.04 901.13 1343.52 Model 19 Top-up flow between 2.02 2.70 3.38 3.86 4.38 5.13 5.79 6.52 8.63 4.78 7.17 10.68 01043_RA & 01042_RA Model 19 01_69_2_RA 4.84 2.92 3.79 4.43 5.14 6.24 7.21 8.34 11.75 5.99 9.74 15.87 Model 19 01_776_3_RA 5.90 3.96 5.13 6.01 6.97 8.45 9.77 11.30 15.92 7.38 12.00 19.55 Model 19 Top-up flow between 01_692_2_RA & 1.06 1.39 1.80 2.11 2.45 2.97 3.43 3.97 5.59 3.12 5.08 8.27 01_776_3_RA Model 19 01_416_2_RA 1.23 1.10 1.42 1.67 1.93 2.34 2.71 3.13 4.41 2.05 3.33 5.42 Model 19 01_1577_2_RA 2.22 1.82 2.37 2.77 3.21 3.89 4.50 5.21 7.34 3.37 5.48 8.94 Model 19 Top-up flow between 01_416_2_RA & 0.99 1.49 1.93 2.26 2.62 3.18 3.67 4.25 5.99 3.34 5.43 8.85 01_1577_2_RA Model 19 01_778_7_RA 7.37 4.70 6.09 7.13 8.27 10.03 11.59 13.41 18.89 8.76 14.24 23.21 Model 19 01_614_3_RA 383.52 339.02 424.45 485.48 550.23 645.50 727.88 820.43 1085.21 601.04 901.13 1343.52 Model 19 Top-up flow between 01042_RA & 17.66 17.99 22.52 25.76 29.20 34.25 38.63 43.54 57.59 66.77 100.10 149.25 01_614_3_RA Model 19
Input flows Top-up flows. These flows should be entered laterally Check flows. Modellers should check to make sure these flows are being reached at each HEP Some of these flows may be put in at the US point due to a small difference between US & DS flows.
C33
Model 20 - Killygordon Flows for AEP AREA Model Node ID_CFRAMS 2 Qmed 50% 20% 10% 5% 2% 1% 0.5% 0.1% (km ) number (2) (5) (10) (20) (50) (100) (200) (1000) 01_614_3_RA 383.52 273.88 273.88 342.90 392.20 444.51 521.47 588.02 662.79 876.69 Model 20 01_614_Intr1_RPS 384.05 273.88 273.88 342.90 392.20 444.51 521.47 588.02 662.79 876.69 Model 20 Top-up flow between 01_614_3_RA & 01_614_Intr1_RPS 0.53 0.54 0.54 0.68 0.78 0.88 1.03 1.16 1.31 1.74 Model 20 01_613_1_RA 2.34 1.45 1.45 1.88 2.20 2.55 3.09 3.57 4.14 5.83 Model 20 01_613_3_RA 2.79 1.54 1.54 2.00 2.34 2.71 3.29 3.80 4.40 6.20 Model 20 Top-up flow between 01_613_1_RA & 01_613_3_RA 0.45 0.28 0.28 0.36 0.42 0.49 0.59 0.68 0.79 1.12 Model 20 01_615_2_RA 387.14 273.88 273.88 342.90 392.20 444.51 521.47 588.02 662.79 876.69 Model 20 Top-up flow between 01_614_Intr1_RPS & 01_615_2_RA 0.30 0.31 0.31 0.39 0.45 0.51 0.60 0.67 0.76 1.00 Model 20 01_1293_U 1.00 0.47 0.47 0.60 0.71 0.82 0.99 1.15 1.33 1.87 Model 20 01_1293_Inter1_RA 1.64 0.65 0.65 0.84 0.99 1.14 1.39 1.60 1.85 2.61 Model 20 Top-up flow between 01_1293_U & 01_1293_Inter1_RA 0.65 0.27 0.27 0.35 0.41 0.48 0.58 0.67 0.77 1.09 Model 20 01_1293_3_RA 1.71 0.68 0.68 0.89 1.04 1.20 1.46 1.69 1.95 2.75 Model 20 Top-up flow between 01_1293_Inter1_RA & 01_1293_3_RA 0.06 0.03 0.03 0.04 0.05 0.05 0.06 0.07 0.09 0.12 Model 20 01_1307_2_RA 11.28 3.88 3.88 5.11 5.99 6.92 8.31 9.51 10.87 14.77 Model 20 01045_RA 11.57 4.02 4.02 5.29 6.20 7.17 8.61 9.85 11.26 15.30 Model 20 Top-up flow between 01_1307_2_RA & 01045_RA 0.29 0.16 0.16 0.22 0.25 0.29 0.35 0.40 0.46 0.63 Model 20 01_1307_Inter1_RA 11.70 4.07 4.07 5.36 6.28 7.26 8.72 9.98 11.41 15.50 Model 20 Top-up flow between 01045_RA & 01_1307_1_RA 0.13 0.06 0.06 0.08 0.10 0.11 0.14 0.16 0.18 0.24 Model 20 01_1307_6_RA 11.97 4.18 4.18 5.51 6.45 7.46 8.96 10.25 11.72 15.92 Model 20 Top-up flow between 01_1307_Inter1_RA & 01_1307_6_RA 0.28 0.12 0.12 0.16 0.19 0.22 0.26 0.30 0.34 0.47 Model 20 01_1788_8_RA 9.75 4.14 4.14 5.37 6.29 7.29 8.84 10.22 11.83 16.66 Model 20 01_885_RARPS 436.80 273.88 273.88 342.90 392.20 444.51 521.47 588.02 662.79 876.69 Model 20 Top-up flow between 01_615_2_RA & 01_885_2_RARPS 26.24 10.58 10.58 13.37 15.29 17.26 20.12 22.52 25.16 32.41 Model 20
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MRFS Flows for AEP HEFS Flows for AEP AREA Model Node ID_CFRAMS (km2) 50% 20% 10% 5% 2% 1% 0.5% 0.1% 10% 1% 0.1% number (2) (5) (10) (20) (50) (100) (200) (1000) (10) (100) (1000) 01_614_3_RA 383.52 339.02 424.45 485.48 550.23 645.50 727.88 820.43 1085.21 601.04 901.15 1343.53 Model 20 01_614_Intr1_RPS 384.05 339.02 424.45 485.48 550.23 645.50 727.88 820.43 1085.21 601.04 901.15 1343.53 Model 20 Top-up flow between 01_614_3_RA & 01_614_Intr1_RPS 0.53 0.67 0.84 0.96 1.09 1.28 1.44 1.62 2.15 1.18 1.77 2.64 Model 20 01_613_1_RA 2.34 1.81 2.35 2.74 3.18 3.86 4.46 5.16 7.27 3.37 5.48 8.93 Model 20 01_613_3_RA 2.79 1.92 2.49 2.92 3.39 4.11 4.75 5.49 7.74 3.56 5.78 9.43 Model 20 Top-up flow between 01_613_1_RA & 01_613_3_RA 0.45 0.60 0.78 0.91 1.06 1.29 1.49 1.72 2.42 1.34 2.18 3.56 Model 20 01_615_2_RA 387.14 339.02 424.45 485.48 550.23 645.50 727.88 820.43 1085.21 601.04 901.15 1343.53 Model 20 Top-up flow between 01_614_Intr1_RPS & 01_615_2_RA 0.30 0.61 0.77 0.88 0.99 1.17 1.31 1.48 1.96 0.68 1.02 1.52 Model 20 01_1293_U 1.00 0.61 0.78 0.92 1.07 1.29 1.49 1.73 2.43 1.43 2.33 3.80 Model 20 01_1293_Inter1_RA 1.64 0.87 1.12 1.31 1.53 1.85 2.14 2.47 3.48 2.27 3.68 6.00 Model 20 Top-up flow between 01_1293_U & 01_1293_Inter1_RA 0.65 0.36 0.47 0.55 0.63 0.77 0.89 1.03 1.45 0.94 1.53 2.50 Model 20 01_1293_3_RA 1.71 0.91 1.18 1.38 1.60 1.94 2.24 2.59 3.65 2.35 3.82 6.22 Model 20 Top-up flow between 01_1293_Inter1_RA & 01_1293_3_RA 0.06 0.04 0.05 0.06 0.07 0.09 0.10 0.11 0.16 0.11 0.17 0.28 Model 20 01_1307_2_RA 11.28 4.85 6.38 7.47 8.64 10.37 11.87 13.57 18.44 9.18 14.58 22.65 Model 20 01045_RA 11.57 4.97 6.54 7.67 8.86 10.64 12.18 13.92 18.92 9.64 15.32 23.79 Model 20 Top-up flow between 01_1307_2_RA & 01045_RA 0.29 0.29 0.38 0.44 0.51 0.61 0.70 0.80 1.09 0.63 0.99 1.54 Model 20 01_1307_Inter1_RA 11.70 5.05 6.64 7.78 9.00 10.80 12.37 14.13 19.21 9.90 15.73 24.43 Model 20
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MRFS Flows for AEP HEFS Flows for AEP AREA Model Node ID_CFRAMS (km2) 50% 20% 10% 5% 2% 1% 0.5% 0.1% 10% 1% 0.1% number (2) (5) (10) (20) (50) (100) (200) (1000) (10) (100) (1000) Top-up flow between 01045_RA & 01_1307_1_RA 0.13 0.09 0.11 0.13 0.15 0.18 0.21 0.24 0.33 0.24 0.38 0.59 Model 20 01_1307_6_RA 11.97 5.19 6.82 8.00 9.25 11.10 12.70 14.52 19.73 10.17 16.16 25.09 Model 20 Top-up flow between 01_1307_Inter1_RA & 01_1307_6_RA 0.28 0.15 0.20 0.23 0.27 0.32 0.37 0.42 0.58 0.30 0.47 0.73 Model 20 01_1788_8_RA 9.75 5.17 6.71 7.85 9.10 11.04 12.76 14.77 20.79 9.64 15.68 25.55 Model 20 01_885_RARPS 436.80 339.02 424.45 485.48 550.23 645.50 727.88 820.43 1085.21 601.04 901.15 1343.53 Model 20 Top-up flow between 01_615_2_RA & 01_885_2_RARPS 26.24 13.08 16.53 18.90 21.34 24.87 27.84 31.10 40.07 23.22 34.21 49.23 Model 20
Input flows Top-up flows. These flows should be entered laterally Check flows. Modellers should check to make sure these flows are being reached at each HEP Some of these flows may be put in at the US point due to a small difference between US & DS flows.
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Model 21 - Castlefinn Flows for AEP AREA Model Node ID_CFRAMS 2 Qmed 10% 0.5% 0.1% (km ) 50% (2) 20% (5) 5% (20) 2% (50) 1% (100) number (10) (200) (1000) 01_885_RARPS 436.80 273.88 273.88 342.90 392.20 444.51 521.47 588.02 662.79 876.69 Model 21 01_1887_2_RA 8.49 3.82 3.82 4.95 5.80 6.72 8.15 9.42 10.91 15.36 Model 21 01_633_4_RA 3.59 0.94 0.94 1.22 1.42 1.65 2.00 2.32 2.68 3.77 Model 21 01_633_6_RA 3.95 1.09 1.09 1.41 1.65 1.92 2.33 2.69 3.11 4.38 Model 21 Top-up flow between 01_633_4_RA & 0.36 0.14 0.14 0.18 0.21 0.24 0.29 0.34 0.39 0.55 Model 21 01_633_6_RA 01_10001_RARPS 4.10 1.12 1.12 1.45 1.70 1.98 2.39 2.77 3.20 4.51 Model 21 Top-up flow between 01_633_6_RA & 0.16 0.06 0.06 0.08 0.09 0.11 0.13 0.15 0.17 0.24 Model 21 01_10001_RARPS 01_633_7_RA 0.03 0.01 0.01 0.01 0.01 0.02 0.02 0.02 0.03 0.04 Model 21 01_654_4_RA 12.42 4.01 4.01 5.36 6.37 7.45 9.11 10.56 12.25 17.23 Model 21 01_724b_1_RA 493.75 273.88 273.88 342.90 392.20 444.51 521.47 588.02 662.79 876.69 Model 21 Top-up flow between 01_885_2_RARPS & 31.92 20.08 20.08 25.14 28.75 32.59 38.23 43.11 48.59 64.27 Model 21 01_724b_1_RA
MRFS Flows for AEP HEFS Flows for AEP AREA Model Node ID_CFRAMS (km2) 50% 20% 10% 5% 2% 1% 0.5% 0.1% 10% 1% 0.1% number (2) (5) (10) (20) (50) (100) (200) (1000) (10) (100) (1000) 01_885_RARPS 436.80 339.02 424.46 485.48 550.24 645.50 727.88 820.44 1085.22 601.04 901.13 1343.52 Model 21 01_1887_2_RA 8.49 4.76 6.18 7.23 8.39 10.17 11.76 13.61 19.16 8.88 14.44 23.53 Model 21 01_633_4_RA 3.59 1.18 1.53 1.79 2.07 2.51 2.90 3.36 4.73 2.19 3.56 5.80 Model 21 01_633_6_RA 3.95 1.39 1.81 2.11 2.45 2.97 3.44 3.98 5.60 3.02 4.91 8.00 Model 21 Top-up flow between 01_633_4_RA & 01_633_6_RA 0.36 0.24 0.31 0.36 0.42 0.51 0.59 0.69 0.97 0.39 0.64 1.05 Model 21 01_10001_RARPS 4.10 1.45 1.88 2.20 2.56 3.10 3.58 4.15 5.84 3.39 5.52 8.99 Model 21 Top-up flow between 01_633_6_RA & 01_10001_RARPS 0.16 0.11 0.14 0.16 0.19 0.23 0.27 0.31 0.43 0.18 0.29 0.47 Model 21
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MRFS Flows for AEP HEFS Flows for AEP AREA Model Node ID_CFRAMS (km2) 50% 20% 10% 5% 2% 1% 0.5% 0.1% 10% 1% 0.1% number (2) (5) (10) (20) (50) (100) (200) (1000) (10) (100) (1000) 01_633_7_RA 0.03 0.01 0.02 0.02 0.02 0.03 0.03 0.03 0.05 0.02 0.03 0.05 Model 21 01_654_4_RA 12.42 5.00 6.70 7.95 9.31 11.37 13.20 15.30 21.53 9.77 16.21 26.45 Model 21 01_724b_1_RA 493.75 339.02 424.46 485.48 550.24 645.50 727.88 820.44 1085.22 601.04 901.13 1343.52 Model 21 Top-up flow between 01_885_2_RARPS & 01_724b_1_RA 31.92 25.07 31.39 35.90 40.69 47.73 53.82 60.66 80.24 44.10 66.12 98.58 Model 21
Input flows Top-up flows. These flows should be entered laterally Check flows. Modellers should check to make sure these flows are being reached at each HEP Some of these flows may be put in at the US point due to a small difference between US & DS flows.
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Model 22 - Lifford Flows for AEP AREA Model Node ID_CFRAMS 2 Qmed 0.5% 0.1% (km ) 50% (2) 20% (5) 10% (10) 5% (20) 2% (50) 1% (100) number (200) (1000) 01_724b_1_RA 493.75 273.88 273.88 346.18 395.76 446.97 520.92 583.09 651.29 839.17 22 01_724b_2_RARPS 502.42 273.88 273.88 346.18 395.76 446.97 520.92 583.09 651.29 839.17 22 Top-up flow between 01_724b_1_RA & 8.67 7.46 7.46 9.43 10.78 12.17 14.19 15.88 17.74 22.86 22 01_724b_2_RARPS 01_1883c_1_RARPS 1,861.05 603.72 603.72 741.37 835.55 932.75 1071.60 1187.52 1314.90 1663.25 22 01_1883d_D_RA 2,363.33 Within tidal reaches 22
MRFS Flows for AEP HEFS Flows for AEP AREA Model Node ID_CFRAMS (km2) 50% 20% 10% 5% 2% 1% 0.5% 0.1% 10% 1% 0.1% number (2) (5) (10) (20) (50) (100) (200) (1000) (10) (100) (1000) 01_724b_1_RA 493.75 346.40 437.85 500.55 565.33 658.86 737.49 823.75 1061.38 638.48 940.71 1,353.85 Model 22 01_724b_2_RARPS 502.42 346.40 437.85 500.55 565.33 658.86 737.49 823.75 1061.38 638.48 940.71 1,353.85 Model 22 Top-up flow between 01_724b_1_RA & 8.67 9.44 11.93 13.63 15.40 17.95 20.09 22.44 28.91 17.39 25.63 36.88 Model 22 01_724b_2_RARPS 01_1883c_1_RARPS 1,861.05 763.59 937.68 1056.8 1179.8 1355.4 1502.0 1663.1 2103.7 1348.0 1,915.8 2,683.3 Model 22 01_1883d_D_RA 2,363.33 Within tidal reaches Model 22
Input flows Top-up flows. These flows should be entered laterally Check flows. Modellers should check to make sure these flows are being reached at each HEP Some of these flows may be put in at the US point due to a small difference between US & DS flows.
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Model 23 - Convoy Flows for AEP Model Node ID_CFRAMS AREA (km2) Qmed 10% 1% 0.5% 0.1% 50% (2) 20% (5) 5% (20) 2% (50) number (10) (100) (200) (1000) 01_801_3_RA 81.87 78.86 78.86 96.21 107.65 119.24 135.33 148.34 162.46 199.45 Model 23 01_801_Int_1_RPS 82.20 78.86 78.86 96.21 107.64 119.24 135.32 148.33 162.45 199.43 Model 23 Top-up flow between 01_801_3_RA & 0.33 0.27 0.27 0.34 0.38 0.43 0.50 0.56 0.63 0.81 Model 23 01_801_Int_1_RPS 01_801_Int_2_RPS 83.10 78.92 78.92 96.29 107.73 119.33 135.43 148.45 162.58 199.60 Model 23 Top-up flow between 01_801_Int_1_RPS & 0.90 0.69 0.69 0.86 0.98 1.10 1.28 1.43 1.61 2.09 Model 23 01_801_Int_2_RPS 01046_RA 83.17 78.92 78.92 96.29 107.73 119.33 135.43 148.45 162.58 199.60 Model 23 Top-up flow between 01_801_Int_2_RPS & 0.07 0.06 0.06 0.08 0.09 0.10 0.12 0.13 0.15 0.19 Model 23 01046_RA 01_1518_1_RA 2.72 1.75 1.75 2.26 2.65 3.07 3.73 4.31 4.99 7.02 Model 23 01_1518_4_RA 4.72 2.81 2.81 3.65 4.27 4.95 6.00 6.94 8.03 11.30 Model 23 Top-up flow between 01_1518_1_RA and 2.00 1.26 1.26 1.51 1.68 1.84 2.06 2.24 2.43 2.91 Model 23 01_1518_4_RA 01_1557_3_RA 102.65 81.15 81.15 99.00 110.76 122.69 139.25 152.63 167.16 205.22 Model 23 Top-up flow between 01046_RA & 14.76 8.00 8.00 9.85 11.09 12.37 14.18 15.69 17.32 21.73 Model 23 01_1557_3_RPS 01041_RA 114.29 84.61 84.61 103.22 115.49 127.93 145.19 159.15 174.30 213.98 Model 23 Top-up flow between 01_1557_3_RPS & 11.65 6.04 6.04 7.37 8.25 9.13 10.37 11.36 12.44 15.28 Model 23 01041_RA 01048_RA 123.71 86.41 86.41 105.42 117.95 130.65 148.27 162.53 178.00 218.52 Model 23 Top-up flow between 9.41 4.69 4.69 5.65 6.26 6.87 7.70 8.37 9.07 10.88 Model 23 01041_RA & 01048_RA 01_1913_2_RA 134.00 88.72 88.72 108.24 121.10 134.14 152.24 166.88 182.76 224.37 Model 23 Top-up flow between 01048_RA - 10.29 4.86 4.86 5.78 6.38 6.96 7.76 8.39 9.05 10.74 Model 23 01_1913_2_RA
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MRFS Flows for AEP HEFS Flows for AEP AREA Model Node ID_CFRAMS 2 20% 10% 5% 2% 1% 0.5% 0.1% 10% 1% 0.1% (km ) 50% (2) number (5) (10) (20) (50) (100) (200) (1000) (10) (100) (1000) 01_801_3_RA 81.87 97.42 118.86 132.98 147.31 167.18 183.26 200.69 246.39 163.38 225.15 302.71 Model 23 01_801_Int_1_RPS 82.20 97.42 118.86 132.98 147.31 167.18 183.26 200.69 246.39 164.28 226.39 304.38 Model 23 Top-up flow between 01_801_3_RA & 0.33 0.33 0.41 0.47 0.53 0.62 0.69 0.78 1.01 0.58 0.85 1.24 Model 23 01_801_Int_1_RPS 01_801_Int_2_RPS 83.10 97.42 118.86 132.98 147.31 167.18 183.26 200.69 246.39 165.28 227.76 306.23 Model 23 Top-up flow between 01_801_Int_1_RPS & 0.90 1.50 1.86 2.12 2.39 2.78 3.11 3.48 4.52 1.48 2.18 3.17 Model 23 01_801_Int_2_RPS 01046_RA 83.17 97.80 119.32 133.50 147.88 167.83 183.97 201.48 247.35 165.53 228.11 306.69 Model 23 Top-up flow between 01_801_Int_2_RPS & 0.07 0.14 0.17 0.19 0.22 0.25 0.28 0.31 0.41 0.28 0.41 0.60 Model 23 01046_RA 01_1518_1_RA 2.72 2.17 2.81 3.29 3.82 4.63 5.35 6.19 8.72 4.04 6.58 10.72 Model 23 01_1518_4_RA 4.72 3.73 4.84 5.66 6.57 7.96 9.21 10.65 15.00 9.76 15.87 25.86 Model 23 Top-up flow between 01_1518_1_RA and 2.00 2.56 3.08 3.42 3.75 4.20 4.57 4.95 5.94 5.05 6.75 8.78 Model 23 01_1518_4_RA 01_1557_3_RA 102.65 99.39 121.26 135.67 150.28 170.55 186.95 204.74 251.36 166.68 229.69 308.81 Model 23 Top-up flow between 01046_RA & 14.76 9.84 12.12 13.65 15.23 17.45 19.30 21.31 26.75 16.78 23.72 32.86 Model 23 01_1557_3_RPS 01041_RA 114.29 104.11 127.02 142.11 157.42 178.66 195.84 214.47 263.30 174.60 240.60 323.49 Model 23 Top-up flow between 01_1557_3_RPS & 11.65 7.45 9.08 10.16 11.26 12.78 14.01 15.34 18.83 12.49 17.21 23.13 Model 23 01041_RA 01048_RA 123.71 106.08 129.42 144.80 160.40 182.04 199.54 218.53 268.29 177.90 245.16 329.61 Model 23 Top-up flow between 9.41 5.79 6.97 7.72 8.48 9.50 10.32 11.19 13.42 9.49 12.68 16.49 Model 23 01041_RA & 01048_RA 01_1913_2_RA 134.00 108.84 132.79 148.57 164.57 186.77 204.73 224.21 275.26 182.53 251.53 338.18 Model 23
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MRFS Flows for AEP HEFS Flows for AEP AREA Model Node ID_CFRAMS 2 20% 10% 5% 2% 1% 0.5% 0.1% 10% 1% 0.1% (km ) 50% (2) number (5) (10) (20) (50) (100) (200) (1000) (10) (100) (1000) Top-up flow between 01048_RA - 10.29 5.99 7.13 7.86 8.58 9.56 10.34 11.16 13.25 9.66 12.70 16.27 Model 23 01_1913_2_RA
Input flows Top-up flows. These flows should be entered laterally Check flows. Modellers should check to make sure these flows are being reached at each HEP Some of these flows may be put in at the US point due to a small difference between US & DS flows.
Model 24 - Donegal Town Flows for AEP AREA Model Node ID_CFRAMS 2 Qmed 10% 1% 0.5% 0.1% (km ) 50% (2) 20% (5) 5% (20) 2% (50) number (10) (100) (200) (1000)
37_2565_2 3.45 4.32 4.32 5.61 6.56 7.61 9.23 10.67 12.34 17.38 Model 24 37_2673_1 2.16 2.12 2.12 2.76 3.22 3.74 4.54 5.24 6.07 8.54 Model 24 37_2673_3 2.84 2.57 2.57 3.33 3.90 4.52 5.48 6.34 7.34 10.33 Model 24 Top-up flow between 01_2673_1 Model 24 & 01_2673_3 0.68 0.67 0.67 0.86 1.00 1.16 1.40 1.61 1.85 2.60 37_3644_2_RPS 9.62 8.04 8.04 10.43 12.21 14.16 17.17 19.85 22.97 32.35 Model 24 Top-up flow between 01_2565_2 Model 24 & 01_3644_2_RPS 3.34 2.98 2.98 3.87 4.53 5.25 6.37 7.36 8.52 11.99 37_2262_6 91.10 35.45 35.45 44.71 51.48 58.78 69.77 79.45 90.51 122.95 Model 24 37_1301_1 1.72 1.05 1.05 1.36 1.59 1.84 2.23 2.58 2.99 4.21 Model 24 37_1302_2 3.09 1.77 1.77 2.29 2.68 3.11 3.77 4.36 5.04 7.10 Model 24 Top-up flow between 37_1301_1 Model 24 & 37_1302_2 1.38 0.83 0.83 1.07 1.26 1.46 1.77 2.04 2.36 3.33 37_3590_1 14.70 16.47 16.47 20.86 24.19 27.86 33.54 38.66 44.64 62.88 Model 24
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Model 24 - Donegal Town Flows for AEP AREA Model Node ID_CFRAMS 2 Qmed 10% 1% 0.5% 0.1% (km ) 50% (2) 20% (5) 5% (20) 2% (50) number (10) (100) (200) (1000)
37_3590_Int_1 15.01 16.59 16.59 21.02 24.37 28.07 33.80 38.96 44.98 63.37 Model 24 Top-up flow between 37_3590_ & Model 24 37_3590_Int_1 0.32 0.45 0.45 0.57 0.66 0.76 0.91 1.05 1.21 1.71 37_3590_3 15.10 16.81 16.81 21.29 24.69 28.44 34.24 39.46 45.56 64.18 Model 24 Top-up flow between Model 24 37_3590_Int_1 & 37_3590_3 0.09 0.14 0.14 0.18 0.20 0.23 0.28 0.32 0.37 0.53 37_1727_U 0.44 0.35 0.35 0.45 0.53 0.62 0.75 0.86 1.00 1.41 Model 24 37_1727_1_RPS 0.94 0.71 0.71 0.93 1.08 1.26 1.52 1.76 2.04 2.87 Model 24 Top-up flow between 37_1727_U Model 24 & 37_1727_1_RPS 0.50 0.24 0.24 0.32 0.37 0.43 0.52 0.60 0.69 0.98 37_3589_2_RPS 16.90 18.45 18.45 23.41 27.16 31.33 37.79 43.62 50.45 71.33 Model 24 Top-up flow between 37_3590_3 Model 24 & 37_3589_2_RPS 0.86 1.13 1.13 1.44 1.67 1.92 2.32 2.67 3.09 4.37 37_2587_Inter 111.59 38.54 38.54 49.45 57.59 66.49 80.17 92.35 106.54 149.09 Model 24 Top-up flow between 37002_RPS Model 24 & 37_2587_Inter 0.03 0.02 0.02 0.02 0.03 0.03 0.04 0.04 0.05 0.07 37_2408_2 1.31 0.72 0.72 0.93 1.09 1.26 1.53 1.77 2.05 2.89 Model 24 37_2589_2 2.90 1.82 1.82 2.36 2.76 3.20 3.88 4.49 5.19 7.31 Model 24 Top-up flow between 37_2408_2 Model 24 & 37_2589_2 1.59 1.13 1.13 1.47 1.72 2.00 2.42 2.80 3.24 4.56 37_2588_2_RPS 115.62 40.04 40.04 51.37 59.82 69.07 83.28 95.94 110.67 154.88 Model 24 Top-up flow between 37_2587_Int Model 24 & 37_2588_2_RPS 1.14 0.53 0.53 0.67 0.79 0.91 1.09 1.26 1.45 2.03 37_1462_1 2.76 1.35 1.35 1.76 2.06 2.38 2.89 3.34 3.87 5.45 Model 24 37_1500_3 4.68 2.56 2.56 3.32 3.89 4.51 5.47 6.32 7.31 10.30 Model 24
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Model 24 - Donegal Town Flows for AEP AREA Model Node ID_CFRAMS 2 Qmed 10% 1% 0.5% 0.1% (km ) 50% (2) 20% (5) 5% (20) 2% (50) number (10) (100) (200) (1000)
Top-up flow between 37_1462_1 Model 24 & 37_1500_3 1.92 1.27 1.27 1.64 1.92 2.23 2.70 3.12 3.61 5.09 37_1832_1_RPS 0.02 0.02 0.02 0.03 0.03 0.04 0.05 0.06 0.06 0.09 Model 24 37_1832_2 1.31 0.98 0.98 1.27 1.48 1.72 2.09 2.41 2.79 3.93 Model 24 Top-up flow between Model 24 37_1832_1_RPS & 37_1832_2 1.28 0.96 0.96 1.25 1.46 1.69 2.05 2.37 2.75 3.87
Input flows Top-up flows. These flows should be entered laterally Check flows. Modellers should check to make sure these flows are being reached at each HEP Some of these flows may be put in at the US point due to a small difference between US & DS flows.
Model 24 - Donegal Town MRFS Flows for AEP HEFS Flows for AEP AREA Model Node ID_CFRAMS (km2) 50% 20% 10% 5% 2% 1% 0.5% 0.1% 10% 1% 0.1% number (2) (5) (10) (20) (50) (100) (200) (1000) (10) (100) (1000) 37_2565_2 3.45 5.40 7.00 8.19 9.50 11.52 13.32 15.41 21.70 11.07 18.00 29.33 Model 24 37_2673_1 2.16 2.65 3.44 4.03 4.67 5.66 6.54 7.57 10.67 5.44 8.84 14.41 Model 24 37_2673_3 2.84 3.21 4.16 4.87 5.65 6.85 7.91 9.16 12.90 6.58 10.69 17.43 Model 24 Top-up flow between 01_2673_1 & 01_2673_3 0.68 1.47 1.88 2.19 2.53 3.05 3.52 4.06 5.68 3.24 5.20 8.40 Model 24 37_3644_2_RPS 9.62 10.43 13.53 15.83 18.37 22.27 25.74 29.79 41.95 24.52 39.86 64.96 Model 24 Top-up flow between 01_2565_2 & 01_3644_2_RPS 3.34 6.22 8.07 9.45 10.96 13.28 15.36 17.77 25.03 13.96 22.70 36.99 Model 24 37_2262_6 91.10 44.38 55.97 64.45 73.59 87.35 99.46 113.31 153.92 78.96 121.86 188.59 Model 24
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Model 24 - Donegal Town MRFS Flows for AEP HEFS Flows for AEP AREA Model Node ID_CFRAMS (km2) 50% 20% 10% 5% 2% 1% 0.5% 0.1% 10% 1% 0.1% number (2) (5) (10) (20) (50) (100) (200) (1000) (10) (100) (1000) Top-up flow between 37003 & 37_2262_6 10.30 1.07 1.35 1.56 1.78 2.11 2.40 2.74 3.72 1.91 2.95 4.56 Model 24 37_1301_1 1.72 1.32 1.71 2.00 2.32 2.82 3.25 3.77 5.30 2.43 3.96 6.45 Model 24 37_1302_2 3.09 2.43 3.15 3.69 4.28 5.19 6.00 6.94 9.77 7.08 11.51 18.76 Model 24 Top-up flow between 37_1301_1 & 37_1302_2 1.38 1.66 2.15 2.52 2.92 3.55 4.10 4.74 6.68 3.73 6.06 9.87 Model 24 37_3590_1 14.70 20.55 26.04 30.19 34.78 41.87 48.26 55.72 78.50 37.10 59.29 96.44 Model 24 37_3590_Int_1 15.01 20.71 26.24 30.43 35.05 42.19 48.63 56.15 79.10 37.38 59.75 97.18 Model 24 Top-up flow between 37_3590_ & 37_3590_Int_1 0.32 0.56 0.71 0.82 0.95 1.14 1.32 1.52 2.14 1.01 1.61 2.62 Model 24 37_3590_3 15.10 20.82 26.38 30.58 35.23 42.41 48.88 56.44 79.51 37.57 60.06 97.68 Model 24 Top-up flow between 37_3590_Int_1 & 37_3590_3 0.09 0.17 0.22 0.25 0.29 0.35 0.40 0.46 0.65 0.31 0.49 0.80 Model 24 37_1727_U 0.44 0.57 0.74 0.86 1.00 1.21 1.40 1.62 2.29 1.39 2.26 3.69 Model 24 37_1727_1_RPS 0.94 1.16 1.50 1.76 2.04 2.47 2.86 3.31 4.66 2.84 4.61 7.52 Model 24 Top-up flow between 37_1727_U & 37_1727_1_RPS 0.50 0.53 0.68 0.80 0.93 1.13 1.30 1.51 2.12 1.18 1.93 3.14 Model 24 37_3589_2_RPS 16.90 23.18 29.42 34.13 39.37 47.48 54.81 63.39 89.63 46.28 74.33 121.55 Model 24 Top-up flow between 37_3590_3 & 37_3589_2_RPS 0.86 1.42 1.80 2.09 2.41 2.91 3.36 3.89 5.50 2.84 4.56 7.45 Model 24 37_2587_Inter 111.59 47.72 61.22 71.29 82.32 99.26 114.34 131.90 184.58 87.59 140.47 226.77 Model 24 Top-up flow between 37002_RPS & 37_2587_Inter 0.03 0.02 0.03 0.03 0.04 0.05 0.05 0.06 0.09 0.09 0.14 0.22 Model 24 37_2408_2 1.31 0.90 1.16 1.36 1.58 1.91 2.21 2.56 3.60 1.67 2.72 4.43 Model 24 37_2589_2 2.90 2.63 3.41 3.99 4.63 5.61 6.49 7.51 10.58 7.91 12.86 20.95 Model 24
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Model 24 - Donegal Town MRFS Flows for AEP HEFS Flows for AEP AREA Model Node ID_CFRAMS (km2) 50% 20% 10% 5% 2% 1% 0.5% 0.1% 10% 1% 0.1% number (2) (5) (10) (20) (50) (100) (200) (1000) (10) (100) (1000) Top-up flow between 37_2408_2 & 37_2589_2 1.59 2.00 2.60 3.04 3.53 4.27 4.94 5.72 8.05 4.49 7.30 11.90 Model 24 37_2588_2_RPS 115.62 49.32 63.28 73.69 85.08 102.59 118.18 136.33 190.79 90.54 145.20 234.40 Model 24 Top-up flow between 37_2587_Int & 37_2588_2_RPS 1.14 0.65 0.83 0.97 1.12 1.35 1.55 1.79 2.51 2.51 4.02 6.49 Model 24 37_1462_1 2.76 1.69 2.19 2.57 2.98 3.61 4.17 4.83 6.80 3.47 5.64 9.19 Model 24 37_1500_3 4.68 3.38 4.38 5.13 5.95 7.21 8.34 9.65 13.59 8.51 13.83 22.54 Model 24 Top-up flow between 37_1462_1 & 37_1500_3 1.92 2.30 2.98 3.48 4.04 4.90 5.66 6.56 9.23 5.15 8.37 13.65 Model 24 37_1832_1_RPS 0.02 0.04 0.05 0.06 0.07 0.08 0.09 0.11 0.15 0.07 0.12 0.19 Model 24 37_1832_2 1.31 1.54 2.00 2.34 2.71 3.29 3.80 4.40 6.20 2.72 4.42 7.20 Model 24 Top-up flow between 37_1832_1_RPS & 37_1832_2 1.28 1.74 2.26 2.65 3.07 3.72 4.30 4.98 7.01 3.91 6.36 10.37 Model 24
Input flows Top-up flows. These flows should be entered laterally Check flows. Modellers should check to make sure these flows are being reached at each HEP Some of these flows may be put in at the US point due to a small difference between US & DS flows.
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Model 25 - Killybegs Flows for AEP AREA Model Node ID_CFRAMS 2 Qmed 0.5% 0.1% (km ) 50% (2) 20% (5) 10% (10) 5% (20) 2% (50) 1% (100) number (200) (1000) 37_2465_1_RPS 1.35 1.79 1.79 2.32 2.72 3.16 3.83 4.42 5.12 7.21 Model 25 37_1289_2_RPS 1.98 2.88 2.88 3.73 4.37 5.07 6.15 7.11 8.22 11.58 Model 25 Top-up flow between 37_2465_1_RPS & 0.627 1.33 1.33 1.72 2.02 2.34 2.84 3.28 3.80 5.34 Model 25 37_1289_2_RPS
MRFS Flows for AEP HEFS Flows for AEP AREA Model Node ID_CFRAMS (km2) 50% 20% 10% 5% 2% 1% 0.5% 0.1% 10% 1% 0.1% number (2) (5) (10) (20) (50) (100) (200) (1000) (10) (100) (1000) 37_2465_1_RPS 1.35 2.31 3.00 3.51 4.07 4.93 5.70 6.60 9.29 4.45 7.24 11.79 Model 25 37_1289_2_RPS 1.98 4.41 5.73 6.70 7.77 9.43 10.90 12.61 17.76 7.81 12.70 20.69 Model 25 Top-up flow between 37_2465_1_RPS & 0.627 2.48 3.22 3.77 4.37 5.30 6.13 7.09 9.99 4.08 6.64 10.82 Model 25 37_1289_2_RPS
Input flows Top-up flows. These flows should be entered laterally Check flows. Modellers should check to make sure these flows are being reached at each HEP Some of these flows may be put in at the US point due to a small difference between US & DS flows.
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