REPORT
Mitigation and Monitoring for the Stour and Orwell Estuaries SPA and Hamford Water SPA
Annual Report 2015-2016
Client: Harwich Haven Authority
Reference: I&B9Y0158R001F0.2 Status: 0.2/Final Date: 29 January 2019
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HASKONINGDHV UK LTD.
36 Park Row Leeds LS1 5JL Industry & Buildings VAT registration number: 792428892
email E royalhaskoningdhv.com W
Document title: Mitigation and Monitoring for the Stour and Orwell Estuaries SPA and Hamford Water SPA
Reference: I&B9Y0158R001F0.2 Status: 0.2/Final Date: 29 January 2019 Project name: HHA annual monitoring Project number: 9Y0158 Author(s): Matt Simpson
Drafted by: Matt Simpson
Checked by: Sian John
Date / initials: 29th January 2019 / SAJ
Approved by: Sian John
Date / initials: 29th January 2019 / SAJ
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Disclaimer No part of these specifications/printed matter may be reproduced and/or published by print, photocopy, microfilm or by any other means, without the prior written permission of HaskoningDHV UK Ltd.; nor may they be used, without such permission, for any purposes other than that for which they were produced. HaskoningDHV UK Ltd. accepts no responsibility or liability for these specifications/printed matter to any party other than the persons by whom it was commissioned and as concluded under that Appointment. The integrated QHSE management system of HaskoningDHV UK Ltd. has been certified in accordance with ISO 9001:2015, ISO 14001:2015 and OHSAS 18001:2007.
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Table of Contents
1 INTRODUCTION 1 1.1 This Report 1 1.2 Background 1 1.3 Objectives of compensation, mitigation and monitoring 2 1.4 Detailed objectives for compensation, mitigation and monitoring 4 1.4.1 Approach channel deepening 4 1.4.2 Trinity III Terminal (Phase 2) Extension 5 1.4.3 Monitoring 5
2 ONGOING ACTIVITIES 6 2.1 Introduction 6 2.2 Maintenance of Harwich Harbour: dredging and disposal 6 2.3 Approach channel deepening: habitat replacement 7 2.4 Approach channel deepening: sediment replacement 8 2.4.1 Stour estuary 8 2.4.2 Orwell estuary 9 2.4.3 Lower Harbour 10 2.5 Approach channel deepening: beneficial use schemes 10 2.6 Trinity III Terminal (Phase 2) Extension: disposal at sea 10 2.7 Trinity III Terminal (Phase 2) Extension: habitat enhancement 11 2.8 Trinity III Terminal (Phase 2) Extension: sediment replacement 11 2.9 Other activities and events 11
3 BATHYMETRIC AND TOPOGRAPHIC DATA 13 3.1 Intertidal and subtidal area and volume 13 3.1.1 Introduction 13 3.1.2 Orwell estuary 13 3.1.3 Stour estuary 14 3.2 Saltmarsh extent 14
4 BENTHIC INVERTEBRATE COMMUNITIES 17 4.1 Introduction 17 4.2 2015 annual benthic monitoring 17 4.3 Review of macrobenthic data for the monitoring period from 1997 to 2015 18 4.4 Distribution of marine invasive species in Harwich Haven 18
5 BIRD DISTRIBUTION AND ABUNDANCE 20 5.1 Background 20
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5.1.1 Introduction 20 5.1.2 High water (core) counts 20 5.1.3 Low water counts 20 5.1.4 Waterbird distribution 20 5.1.5 WeBS Alerts 20 5.2 Analysis of waterbird data 20 5.3 High water count trends 21 5.3.1 Overview of Stour and Orwell estuaries populations 21 5.3.2 Analysis of key species 22 5.3.2.1 Introduction 22 5.4 Low water count trends 29 5.4.1 Introduction 29 5.4.2 Summary of the low water count data and trends 30 5.5 Assessment of changes in the Stour and Orwell estuaries in the context of national population trends 30 5.5.1 Dark-bellied Brent goose 31 5.5.2 Shelduck 31 5.5.3 Wigeon 32 5.5.4 Pintail 32 5.5.5 Oystercatcher 33 5.5.6 Ringed plover 33 5.5.7 Grey plover 34 5.5.8 Lapwing 34 5.5.9 Knot 35 5.5.10 Dunlin 35 5.5.11 Black-tailed godwit 36 5.5.12 Curlew 36 5.5.13 Redshank 37 5.5.14 Turnstone 37 5.6 Summary of trends from all data sources 38 5.7 Waterbird distribution 40 5.7.1 Introduction 40 5.7.2 Results 40
6 STOUR AND ORWELL CONDITION ASSESSMENT 43
7 COMPLETED MONITORING STUDIES 46 7.1 Trimley Marshes managed realignment monitoring 46 7.2 Trinity III Terminal habitat enhancement monitoring 46
8 SUMMARY AND CONCLUSIONS 47 8.1 Introduction 47 8.2 Bathymetric and topographic data 47 8.3 Benthic invertebrate communities 47
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8.4 Bird distribution and abundance 48 8.5 Conclusion 48
9 References 50
Table of Tables
Table 2.1 Number of deep drafted shipping movements at Felixstowe on an annual basis 7 Table 2.2 Water column recharge in the Stour Estuary 8 Table 2.3 Water column recharge in the Orwell Estuary 10 Table 2.4 Dredge disposal returns for quantity of material deposited in the River Orwell 12 Table 3.1 Orwell estuary intertidal volume and area between 0m CD and +4m CD 13 Table 3.2 Orwell estuary subtidal volume and area below 0m CD 13 Table 3.3 Stour estuary intertidal volume and area between 0m CD and +4m CD 14 Table 3.4 Stour estuary subtidal volume and area below 0m CD 14 Table 3.5 Summary of change in saltmarsh extent between 2005, 2010 and 2015 16 Table 5.1 Trends in the mean and peak numbers of species on the Orwell, Stour and SPA (1999/2000 to 2015/2016) Colours denote an increasing (green) or decreasing (red) population and colour intensity indicates trend confidence (weak, medium or high); reproduced from Suffolk Wildlife Trust Trading Co, 2016) 30 Table 5.2 Summary of national and SPA population trends for key waterbird species 39
Table of Figures
Figure 1.1 Study area 3 Figure 2.1 Illustration of current placement strategy 9 Figure 3.1 Overview of erosion and accretion patterns between 2005 and 2015 in the Orwell and Stour estuaries 15 Figure 5.1 The features and place names of the Stour and Orwell estuaries at low tide 21 Figure 5.2 Total number of waterbirds on the Stour and Orwell estuaries (data sourced from Frost et al., 2017) 22 Figure 5.3 Numbers of dark-bellied Brent goose (2011/12 to 2015/16) 23 Figure 5.4 Numbers of shelduck (2011/12 to 2015/16) 23 Figure 5.5 Numbers of wigeon (2011/12 to 2015/16) 24 Figure 5.6 Numbers of pintail (2011/12 to 2015/16) 24 Figure 5.7 Numbers of oystercatcher (2011/12 to 2015/16) 25 Figure 5.8 Numbers of ringed plover (2011/12 to 2015/16) 25 Figure 5.9 Numbers of grey plover (2011/12 to 2015/16) 26
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Figure 5.10 Numbers of lapwing (2011/12 to 2015/16) 26 Figure 5.11 Numbers of knot (2011/12 to 2015/16) 27 Figure 5.12 Numbers of dunlin (2011/12 to 2015/16) 27 Figure 5.13 Numbers of black-tailed godwit (2011/12 to 2015/16) 28 Figure 5.14 Numbers of curlew (2011/12 to 2015/16) 28 Figure 5.15 Numbers of redshank (2011/12 to 2015/16) 29 Figure 5.16 Numbers of turnstone (2011/12 to 2015/16) 29 Figure 5.17 The mean (± SEs) (left) and peak (right) numbers of dark-bellied Brent goose on the Orwell (●), Stour (○) and whole SPA (■) in winters 1999-2000 (0) to 2015/2016 (16) (source: Suffolk Wildlife Trust Trading Co, 2016) 31 Figure 5.18 The mean (± SEs) (left) and peak (right) numbers of shelduck on the Orwell (●), Stour (○) and whole SPA (■) in winters 1999-2000 (0) to 2015/2016 (16) (source: Suffolk Wildlife Trust Trading Co, 2016) 32 Figure 5.19 The mean (± SEs) (left) and peak (right) numbers of wigeon on the Orwell (●), Stour (○) and whole SPA (■) in winters 1999-2000 (0) to 2015/2016 (16) (source: Suffolk Wildlife Trust Trading Co, 2016) 32 Figure 5.20 The mean (± SEs) (left) and peak (right) numbers of pintail on the Orwell (●), Stour (○) and whole SPA (■) in winters 1999-2000 (0) to 2015/2016 (16) (source: Suffolk Wildlife Trust Trading Co, 2016) 33 Figure 5.21 The mean (± SEs) (left) and peak (right) numbers of oystercatcher on the Orwell (●), Stour (○) and whole SPA (■) in winters 1999-2000 (0) to 2015/2016 (16) (source: Suffolk Wildlife Trust Trading Co, 2016) 33 Figure 5.22 The mean (± SEs) (left) and peak (right) numbers of ringed plover on the Orwell (●), Stour (○) and whole SPA (■) in winters 1999-2000 (0) to 2015/2016 (16) (source: Suffolk Wildlife Trust Trading Co, 2016) 34 Figure 5.23 The mean (± SEs) (left) and peak (right) numbers of grey plover on the Orwell (●), Stour (○) and whole SPA (■) in winters 1999-2000 (0) to 2015/2016 (16) (source: Suffolk Wildlife Trust Trading Co, 2016) 34 Figure 5.24 The mean (± SEs) (left) and peak (right) numbers of knot on the Orwell (●), Stour (○) and whole SPA (■) in winters 1999-2000 (0) to 2015/2016 (16) (source: Suffolk Wildlife Trust Trading Co, 2016) 35 Figure 5.25 The mean (± SEs) (left) and peak (right) numbers of dunlin on the Orwell (●), Stour (○) and whole SPA (■) in winters 1999-2000 (0) to 2015/2016 (16) (source: Suffolk Wildlife Trust Trading Co, 2016) 36 Figure 5.26 The mean (± SEs) (left) and peak (right) numbers of black-tailed godwit on the Orwell (●), Stour (○) and whole SPA (■) in winters 1999-2000 (0) to 2015/2016 (16) (source: Suffolk Wildlife Trust Trading Co, 2016) 36 Figure 5.27 The mean (± SEs) (left) and peak (right) numbers of curlew on the Orwell (●), Stour (○) and whole SPA (■) in winters 1999-2000 (0) to 2015/2016 (16) (source: Suffolk Wildlife Trust Trading Co, 2016) 37
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Figure 5.28 The mean (± SEs) (left) and peak (right) numbers of redshank on the Orwell (●), Stour (○) and whole SPA (■) in winters 1999-2000 (0) to 2015/2016 (16) (source: Suffolk Wildlife Trust Trading Co, 2016) 37 Figure 5.29 The mean (± SEs) (left) and peak (right) numbers of turnstone on the Orwell (●), Stour (○) and whole SPA (■) in winters 1999-2000 (0) to 2015/2016 (16) (source: Suffolk Wildlife Trust Trading Co, 2016) 38 Figure 5.30 Trends in winter section populations (1996-2015) (upper) and trends in section proportions of winter estuary populations (1996-2015) (lower) for dark-bellied Brent goose 41 Figure 5.31 Cumulative trends 42 Figure 6.1 Upper reaches of the Stour Estuary 43 Figure 6.2 Lower reaches of the Orwell Estuary 44 Figure 6.3 Upper reaches of the Orwell Estuary 44
Appendices
Appendix A Comparison of LiDAR and bathymetry data sets (HR Wallingford) Appendix B Monitoring of Saltmarsh in the Stour and Orwell Estuaries Appendix C Stour and Orwell Estuaries Annual Benthic Monitoring Report: 2015 survey Appendix D Stour and Orwell Estuaries benthic monitoring programme: Review of macrobenthic data from 1997 to 2015 Appendix E Distribution of Marine Invasive Species in Harwich Haven (2010-2015) Appendix F Ornithological monitoring of the Stour and Orwell Estuaries Special Protection Area: winters 1999/2000 to 2015/2016 Appendix G Changes in the distribution of birds at low water in the Stour and Orwell Estuaries SPA 1996-2015
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1 INTRODUCTION
1.1 This Report This report presents the findings of the 2015/2016 monitoring programme for the Stour and Orwell estuaries that is implemented by the Harwich Haven Authority (HHA) and has been undertaken on an annual basis since 1999. The background to, and objectives of, the monitoring programme are summarised in Sections 1.2 to 1.4.
The scope of monitoring undertaken in 2015/2016 and which is reported within this document is as follows:
• Bathymetric and topographic data (informing an understanding of intertidal and subtidal morphological change); • Benthic invertebrate communities (to 2015 only); and, • Bird distribution and abundance.
Given that the results of each years’ monitoring build on the findings of the monitoring from previous years, in addition to presenting the most recent available result of the monitoring programme (for 2015 and 2016), the findings of the monitoring for the above parameters over a longer time period are presented. This provides an understanding of changes in the estuary system over the longer term since the initiation of the monitoring programme.
As discussed in the Summary and Conclusions (Section 8), and on the basis of the evidence gathered through the monitoring programme, it is concluded that HHA has met the primary objectives of the various compensation, mitigation and monitoring agreements (as set out in sections 1.2, 1.3.1, and 1.3.2).
The relevant compensation, mitigation and monitoring plans required monitoring to be carried out for periods of no less than ten years, which have all been exceeded. Consequently the 2015/16 monitoring is the last which HHA considers it is obliged to carry out and HHA will now cease monitoring under the agreements.
However, HHA intends to continue with a range of monitoring to inform its current operations and future development plans. The bathymetric and LiDAR surveys and analysis of intertidal and subtidal areas and volume on the existing five year cycle. Water bird counts at low water will also continue on a three yearly cycle. Until a new regime of benthic monitoring is designed and put in place, HHA intends to continue the sediment and benthic analysis (as is currently undertaken) every three years.
1.2 Background In October 1998, works to deepen the approach channel to the Haven Ports commenced; the works were completed in April 2000. The HHA’s Mitigation and Monitoring Package (MMP) for the scheme (PDE and HR Wallingford, 1998) was incorporated by the Department for Transport (DfT) (formerly the DTLR) into the consent for the works under the Coast Protection Act, 1949. The Department for Environment, Food and Rural Affairs (Defra) (formerly MAFF) also issued consents to the HHA for the various sediment placement schemes associated with the package under the Food and Environment Protection Act (FEPA) 1985.
In 2002, consent was granted for the Trinity III Terminal (Phase 2) Extension at the Port of Felixstowe; this scheme was completed in September 2004. A Compensation, Mitigation and Monitoring Agreement (CMMA) for the terminal extension was produced. FEPA consents were issued for habitat enhancement schemes that were implemented in connection with the project and the disposal of capital silts at sea; these
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consents included monitoring conditions. The HHA undertook to implement the actions set out in the CMMA as an agent to the Port of Felixstowe in respect of the compensation requirement arising from the terminal extension.
The MMP and CMMA require that the results of the monitoring programme are reported in order to assess the progress of the mitigation and compensation packages against their objectives. To this end an Annual Report is produced presenting the information collated on the various habitat and sediment replacement schemes and monitoring activities during the preceding year. This report is provided to Natural England and Cefas (acting on behalf of Defra). Annual meetings are required to be held between the HHA, Natural England, Cefas and the Environment Agency to ensure the monitoring results are understood by the statutory parties responsible under the Habitats Directive (Council Directive 92/43/EEC on the conservation of natural habitats and of wild fauna and flora).
The area of study can be seen in Figure 1.1.
Since completion of the approach channel deepening works in April 2000, annual meetings have been held with key statutory bodies as required. In 2001 the Stour and Orwell Estuary Research Group ceased to exist and since that time attendance at the annual meetings has expanded to include the local wildlife charities, local government and other government bodies.
At the meeting held in March 2013, HHA agreed that future annual reports would summarise the findings of the previous reporting for those areas of the programme where no additional work had been undertaken in the past calendar year (in this case during 2015). The exception to this is cases where a particular element of the monitoring programme has ceased.
1.3 Objectives of compensation, mitigation and monitoring The primary objectives of the compensation and mitigation for both schemes (i.e. the approach channel deepening and the Trinity III Terminal (Phase 2) Extension are:
1. To avoid any impacts as a result of the works on the favourable conservation status of both habitats, as defined under Article 1(e) of the Habitats Directive, and species, as defined under the Article 1(i); and, 2. To remove any adverse effects arising from the works in order to maintain site integrity in so far as this will be affected by the schemes.
Where ‘favourable conservation status’ is defined as:
Intertidal habitats (i.e. saltmarsh, soft muddy and granular habitats) that, in combination, maintain the geomorphological form and functioning of the estuaries, so that they are capable of sustaining the populations of internationally and nationally important overwintering birds for which the site qualifies.
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Figure 1.1 Study area
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When the MMP and CMMA were produced, the qualification of the Stour and Orwell Estuaries Special Protection Area (SPA) was as follows:
Populations of internationally / nationally important overwintering birds, based on:
• Notable numbers of golden plover (under Article 4.1); and, • Important populations of dunlin; shelduck; dark-bellied geese; redshank; grey plover; black-tailed godwit; turnstone; ringed plover; wigeon; knot; curlew; pintail; mute swans; goldeneye and scaup (under Article 4.2).
Since qualification in 2003, the boundaries of the constituent Sites of Special Scientific Interest (SSSIs) have been extended and, in May 2005, the SPA boundary was extended to include an additional 360 hectares. The SPA boundary extensions coincide with areas incorporated within enlarged boundaries of the Orwell Estuary SSSI and Stour Estuary SSSI, as well as the whole of Cattawade Marshes SSSI.
Following the renotification of SSSIs in 2003 and the SPA in 2005, the site now qualifies under Article 4.1 of the Wild Birds Directive (79/409/EEC) by supporting 1% or more of the Great Britain population of avocet Recurvirostra avosetta. Over the period 1996 to 2000 the SPA supported 21 breeding pairs. It also qualifies under Article 4.2 of the Directive as it is used regularly by 1% or more of the biogeographical populations of a number of migratory species.
The site further qualifies under Article 4.2 as it is used regularly by over 20,000 waterbirds in any season. In the non-breeding season, the site regularly supports around 63,000 individual waterbirds (based on the 5 year peak mean recorded between 1993/94 and 1997/98).
1.4 Detailed objectives for compensation, mitigation and monitoring
1.4.1 Approach channel deepening Detailed objectives for compensation and mitigation of the effects in the Stour and Orwell estuaries associated with the 1998/2000 approach channel deepening have also been defined in order to ensure the achievement of the primary objectives (set out above). They can be summarised as follows:
1. To create 4 hectares of intertidal habitat (compensation) to replace predicted habitat loss due to the change in tidal range. 2. To prevent the predicted loss of up to 5 hectares per annum of intertidal habitat due to increased rates of erosion, through sediment replacement (mitigation). 3. To create 12.5 hectares of intertidal habitat (compensation) to replace habitat which might be lost before the mitigation becomes fully effective.
Further research was required by the CMMA into the likelihood of the deepening having an impact on Hamford Water. The objectives for this can be summarised as:
4. To define existing sand transport pathways offshore. 5. To define existing fine sediment transport pathways in and out of Hamford Water.
In the event that an impact was demonstrated, appropriate compensation and/or mitigation was to be implemented.
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1.4.2 Trinity III Terminal (Phase 2) Extension Detailed objectives of the compensation and mitigation for the Trinity III Terminal (Phase 2) Extension are as follows:
6. To provide an enhanced level of protection to the seawalls along the Shotley and Trimley frontages by raising the intertidal area. 7. By creating additional protection for the seawalls, to enhance the ecological value of some 23ha of the intertidal habitat (of which approximately 20ha will be intertidal mud and 3ha saltmarsh), replacing the feeding habitat lost due to the immediate effect of the quay extension and dredge over the short to medium term. 8. To raise the level of the intertidal mud, thereby increasing its exposure and providing a feeding habitat for waterfowl for a longer period in the tidal cycle (i.e. increasing the number of bird feeding hours), mitigating the effect of a reduced tidal range. 9. To offset the predicted increase in the rate of erosion of the intertidal in the Stour and Orwell estuaries by increasing the existing sediment replacement programme by 5%.
Objectives 6 to 8 were achieved through the establishment of the habitat enhancement schemes on the Shotley and Trimley foreshores (see Section 2.7).
The habitat enhancement schemes proposed in conjunction with the Trinity III Terminal (Phase 2) Extension also have the following objectives:
10. To increase the stability of the lower Orwell flood defences and provide the opportunity for the development of a long term strategy for the sustainable management of the estuary. 11. To compensate for any adverse effect on the integrity associated with the works, while not constraining future options for the sustainable management of flood defences and habitats in the estuarine system.
It was accepted in the CMMA that the habitat enhancement schemes would erode over time and were intended to provide a medium term solution to a long term problem, whilst the key regulators developed a long term sustainable solution.
1.4.3 Monitoring Detailed objectives for monitoring have also been defined in order to determine whether or not any impacts on the favourable conservation status of the European site(s) arise as a result of the dredging, quay extension and their associated mitigation schemes. They can be summarised as:
12. To increase understanding of the processes operating in the Stour and Orwell estuaries and Hamford Water and to define those aspects that relate to the projects. 13. To validate and refine the mitigation actions. 14. To fully monitor the effect and thereby success of mitigation.
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2 ONGOING ACTIVITIES
2.1 Introduction This section provides summary information on accretion, dredging volumes, shipping activity and the sediment replacement activities within the estuary system. Information presented here covers the period 2007-2016, and focuses on 2015/2016 data.
2.2 Maintenance of Harwich Harbour: dredging and disposal Objective: To maintain the harbour and access to the Haven Ports.
Based on HHA dredger records a total of about 1,095,000 dry tonnes of maintenance dredged material from Harwich Harbour was deposited at the Inner Gabbard between 1 January 2015 and 31 December 2015. A further 44,000 dry tonnes was distributed within the estuarine system as part of the sediment replacement programme. The total amount of dredging, based on dredger records, was thus 1.14M dry tonnes.
Based on bathymetric records for the maintained area of the Harbour it is estimated that for the period 1 January 2015 to 31 December 2015 the average rate of observed siltation in the Harbour was equivalent to about 4,100m3/day. This equates to an annual siltation rate of about 1.51Mm3. Over the year, the backlog of material in the Harbour reduced by about 520,000m3. Thus, based on the bathymetric surveys, about 2.03Mm3 of material was removed through maintenance dredging. At an in-situ dry density of 530 kg/m3 a volume of 2.03Mm3 is estimated to be equivalent to about 1.08M dry tonnes of material. It should be noted that the observed siltation rate (of 4,100m3/day) is based on comparison of pre- and post-dredge surveys and, due to the effect of the dredging on the characteristics of the surface of the seabed, the two surveys are measuring a surface with different physical properties (in terms of consolidation), which means the siltation rate quoted above must be viewed as an approximation.
From the dredger records described above it is apparent that, during the 2015 calendar year, the total mass dredged from the Harbour and berths, measured in the dredgers, was more than the total mass removed when assessed by survey.
Using a similar approach for the 2016 calendar year, the total amount of dredging, based on dredger records, was 958,000 dry tonnes. The mass removed, based on bathymetric records and allowing for an increased backlog of sediment over the year, was 690,000 dry tonnes. From these records, the total mass dredged from the Harbour and berths was significantly more than the total mass removed when assessed by survey. However, as has been stated before, these two methods of assessing mass of material removed have differing degrees of accuracy for the reason described above.
The number of deep drafted vessel movements (greater than 13.5m draft) in Harwich Harbour is summarised in Table 2.1 which shows the vessel movements and measured accumulation rate data calculated on an annual basis between 2007 and 2016. The average annual observed rate of accumulation in the Harbour during this period has been about 5,900m3/day.
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Table 2.1 Number of deep drafted shipping movements at Felixstowe on an annual basis Number of vessel Observed average Number of vessel Period movements (15m or accumulation rate of silt movements (>13.5m) * greater) (m3/day)
Jan 1 2007 to Dec 31 2007 140 1 5,000
Jan 1 2008 to Dec 31 2008 177 0 4,900
Jan 1 2009 to Dec 31 2009 197 0 4,100
Jan 1 2010 to Dec 31 2010 142 0 8,500
Jan 1 2011 to Dec 31 2011 182 25 8,100
Jan 1 2012 to Dec 31 2012 327 29 6,700
Jan 1 2013 to Dec 31 2013 281 15 9,300
Jan 1 2014 to Dec 31 2014 323 27 4,300
Jan 1 2015 to Dec 31 2015 306 52 4,100
Jan 1 2016 to Dec 31 2016 343 75 4,050
Average for period - - 5,900 * Draft of 'greater than 13.5m' does not include 13.5m
As shown in Table 2.1 the observed average daily accumulation rate of silt in 2015 and 2016 were slightly less than that observed during 2014 and less than that observed in any year since 2007 (except 2009, when a similar rate of siltation was observed). The vessel movement data shows that during 2015 and 2016, whilst there were a similar number of vessels over 13.5m draft to 2014, there were more vessel movements of greater than 15m draft. It has previously been surmised that there could be a relationship between the number of vessel movements within the Harbour during the year and the average daily accumulation rate. The recent data would tend to support this idea, though it should be noted that accumulation rates do vary widely over short term periods, with little correlation to the number of deeper vessels.
This indicates that any relationship between vessel movements and accumulation rate is not straightforward and, as suggested in the 2014 annual report (Royal HaskoningDHV, 2015a), may be more closely related to the times (the stage of the tidal cycle) that vessels are manoeuvring within the Harbour and natural variability in the rate of accumulation, rather than the number of the largest vessels themselves.
2.3 Approach channel deepening: habitat replacement Objective: To create 4 hectares (ha) of intertidal habitat to replace the habitat lost due to the immediate effect of the change on tidal range and to create 12.5ha of intertidal habitat to mitigate losses that could occur before sediment replacement measures can be expected to be fully effective.
The managed realignment site at Trimley Marshes was completed in February 2001, with the sea wall breached in November 2000. Since the sea wall was breached, ecological surveys have been carried out to monitor the rate at which the site has been colonised by fauna and flora, as well as use by birds and the particle size of sediments. Section 7.1 describes the monitoring undertaken at the Trimley Marshes managed realignment site.
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2.4 Approach channel deepening: sediment replacement Objective: To prevent, through the immediate reintroduction of sediment into the system for as long as the channel is maintained, the annual loss of 1.7ha of intertidal (mean springs) (plus 1.1ha from the 1994 dredge) and 3.3ha of intertidal (mean neaps) (plus 2.2ha from the 1994 dredge) due to increased rates of erosion. The sediment replacement works as set out in the original CMMA were modified in 2007 following a review of the works in previous years. HHA now place 50,000 dry tonnes of material back into the estuaries on an annual basis - this is generally achieved through three dredging campaigns per autumn / winter season. This is undertaken by pumped discharge whilst the dredger is underway (35,000 dry tonnes into the Stour and 15,000 dry tonnes into the Orwell) at a minimum of 4 knots discharging over an agreed track. This revised sediment replacement strategy commenced in the autumn of 2008.
In addition, subtidal placement at North Shelf was to be reduced to 50,000 dry tonnes per year. However, no material has been placed in the subtidal at the North Shelf since early April 2009 when the capital dredging works associated with the FSR (i.e. widening the north side of the channel in the vicinity of North Shelf) commenced. These placements could be reinstated should monitoring demonstrate that placement at the North Shelf is required as mitigation for any observed erosion in the estuaries. This location is not included in the current disposal licence.
The modified approach to placing material along tracks in the Stour and Orwell estuaries is illustrated in Figure 2.1.
2.4.1 Stour estuary The water column placements shown in Table 2.2 were made in the middle and lower Stour up to the end of December 2016.
Table 2.2 Water column recharge in the Stour Estuary Timing Sediment replacement (dry tonnes)
Mid January 2013 10,000
Late March 2013 10,100
Late November 2013 9,200
Early February 2014 14,500
Early April 2014 10,100
Mid November 2014 9,800
Mid February 2015 9,700
Early April 2015 10,000
Mid November 2015 11,300
Mid January 2016 10,700
Late April 2016 10,700
Early November 2016 12,700
Total 128,800
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Figure 2.1 Illustration of current placement strategy
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2.4.2 Orwell estuary The water column placements shown in Table 2.3 were made in the Orwell estuary up to the end of December 2016.
Table 2.3 Water column recharge in the Orwell Estuary Timing Sediment replacement (dry tonnes)
Mid January 2013 3,600
Late March 2013 4,300
Late November 2013 4,300
Early February 2014 5,000
Early April 2014 5,000
Mid November 2014 3,300
Mid February 2015 4,400
Early April 2015 3,900
Mid November 2015 4,900
Mid January 2016 5,100
Late April 2016 4,400
Early November 2016 5,400
Total 53,600
2.4.3 Lower Harbour Subtidal placements at the North Shelf ceased in early April 2009.
2.5 Approach channel deepening: beneficial use schemes
Objective: To meet the FEPA requirement to seek beneficial uses, as far as possible, for the material arising from the channel deepening. Details of the beneficial use schemes that have been implemented by the HHA were provided in the 2001 Annual Report (PDE and HR Wallingford, 2001) and recorded in the 2003 Compliance Report.
2.6 Trinity III Terminal (Phase 2) Extension: disposal at sea Objective: To allow the construction of the Trinity III (Phase 2) Extension. Dredging and disposal for this scheme was completed on 28 March 2003. Approximately 500,000m3 was deposited at the Inner Gabbard, with 28,000m3 used to feed an Environment Agency beneficial use scheme at Horsey Island. Bathymetric and benthic invertebrate surveys of the Inner Gabbard were carried out, the findings of which were reported in the 2004 Annual Report.
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2.7 Trinity III Terminal (Phase 2) Extension: habitat enhancement Objective: To provide an improved level of protection to the seawalls along the Shotley and Trimley frontages through the placement of dredged materials (clay/gravel bunds and silts) and enhance the ecological value of the associated intertidal habitat. The habitat enhancement schemes for the Trinity III (Phase 2) Extension were completed in October 2003. The schemes utilised about 107,000 dry tonnes of maintenance dredged silts which would otherwise have been placed offshore at the Inner Gabbard disposal site. The schemes comprised the placement of clay and gravel bunds on the Trimley and Shotley foreshores which were backfilled with silt and sandy gravel.
The habitat enhancement schemes have been monitored by Royal HaskoningDHV on behalf of the HHA as part of the Trinity III (Phase 2) Extension CMMA and LiDAR data is also available. Further details on the construction of the bunds can be found in the 2004 Annual Report.
The current status of the monitoring of the habitat enhancements is described in Section 7.2.
In addition to the HHA monitoring, a Defra research project undertaken by HR Wallingford and Cefas looked at the correlation between benthic recovery and physical processes on parts of the site on the Shotley side of the Orwell Estuary through intensive benthic and physical process monitoring for 3 years following construction. Monitoring of the site under this scheme ceased in September 2005. The technical reports arising from this project were produced in December 2006.
2.8 Trinity III Terminal (Phase 2) Extension: sediment replacement Objective: To offset the predicted increase in the rate of erosion of the intertidal in the Stour and Orwell Estuaries. The CMMA for Trinity III Terminal (Phase 2) Extension specified that the sediment replacement volumes should be increased by 5% to mitigate the effect of the extension on intertidal erosion. However, in light of the modelling undertaken for FSR which was updated from earlier modelling studies and took into account more recent data, there was no requirement to increase the volume of sediment replacement.
2.9 Other activities and events In 2010 the Port of Ipswich modified its maintenance dredging strategy resulting in greater volumes of material being deposited subtidally in the deeper sections of the main navigational channel in the Orwell Estuary (disposal site TH034).
Table 2.4 summarises the quantity of material deposited in the Orwell Estuary in 2015 and 2016 (figures are wet tonnes).
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Table 2.4 Dredge disposal returns for quantity of material deposited in the River Orwell Date Quantity deposited (wet tonnes)
October 2014 – April 2015 Nil May 2015 44,398
June 2015 – March 2016 Nil April 2016 68,005
May 2016 – December 2016 Nil Total deposited in period 112,403
During 2015 and 2016, HHA dredged material from the edges and areas in the outer channel offshore. During 2015, 72,000 dry tonnes of material was deposited at the Inner Gabbard dispersive site and 360,000 dry tonnes was deposited at the Inner Gabbard East non-dispersive site. During 2016, 50,000 dry tonnes of material was deposited at the Inner Gabbard dispersive site and 86,000 dry tonnes was deposited at the Inner Gabbard East non-dispersive site.
During 2016, about 409,000 dry tonnes of the material from the Harbour was disposed of at the new Harwich Haven disposal site in a trial authorised by the MMO. This monitored trial was part of the consenting process for the new disposal site, intended to lead towards the approval of the new site for ongoing disposal operations. As at the end of September 2017, the MMO had not approved the use of the new disposal site.
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3 BATHYMETRIC AND TOPOGRAPHIC DATA
3.1 Intertidal and subtidal area and volume
3.1.1 Introduction A comparison of bathymetry and LiDAR data sets for the Stour and Orwell estuaries (measured in 2005/2006, 2010/2011 and 2015/2016) has been undertaken by HR Wallingford. Based on the results of this comparison, calculations of intertidal and subtidal levels, surface areas and volume differences have been derived.
Appendix A contains the full methodology and results of the analysis undertaken by HR Wallingford. It describes the approach taken to the analysis of the bathymetry and LiDAR data sets and the combination of the two data sets for use in the analysis of intertidal and subtidal changes over the period 2005/2006 to 2015/2016.
3.1.2 Orwell estuary Analysis of intertidal and subtidal planar area and volume changes in the Orwell estuary between 2005 and 2015 has been carried out based on the combined bathymetry and LiDAR data surfaces. The results of this analysis are provided in Table 3.1 and Table 3.2.
The figures for intertidal volume are a measure of sediment volume above a datum, so a negative number represents the erosion of sediment. The figures for subtidal volume are a measure of subtidal water volume, so a negative number represents accretion of sediment.
Table 3.1 Orwell estuary intertidal volume and area between 0m CD and +4m CD Volume change Area change Volume change Year Area (m2) Volume (m3) 2005 to 2015 (m2) (m3) (m3)
2005 6,386,627 - 10,527,475 - -
2010 6,473,583 86,956 gain 10,336,007 -191,468 erosion -
2015 6,596,099 122,516 gain 10,665,451 329,444 accretion 137,976 accretion
Table 3.2 Orwell estuary subtidal volume and area below 0m CD Volume change Area change Volume change Year Area (m2) Volume (m3) 2005 to 2015 (m2) (m3) (m3)
2005 4,189,873 - 16,617,406 - -
2010 4,102,917 -86,956 loss 16,088,471 -528,935 accretion -
2015 3,980,401 -122,516 loss 16,460,622 372,152 erosion -156,784 accretion
Between 2005 and 2015, the trend for both the intertidal and subtidal zones is one of accretion at an average annual rate of about 13,800m3 in the intertidal zone and 15,700m3 in the subtidal zone.
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3.1.3 Stour estuary Analysis of intertidal and subtidal planar area and volume changes in the Stour estuary between 2005 and 2015 has been carried out based on the combined bathymetry and LiDAR data surfaces. The results of this analysis are provided in Table 3.3 and Table 3.4.
Table 3.3 Stour estuary intertidal volume and area between 0m CD and +4m CD Volume change Area change Volume change Year Area (m2) Volume (m3) 2005 to 2015 (m2) (m3) (m3)
2005 16,828,224 - 27,709,810 - -
2010 16,916,194 87,970 gain 27,673,606 -36,203 erosion -
2015 17,061,070 144,876 gain 27,965,316 291,710 accretion 255,507 accretion
Table 3.4 Stour estuary subtidal volume and area below 0m CD Volume change Area change Volume change Year Area (m2) Volume (m3) 2005 to 2015 (m2) (m3) (m3)
2005 10,087,276 - 42,320,455 - -
2010 9,999,306 -87,970 loss 41,565,792 -754,663 accretion -
2015 9,854,430 -144,876 loss 41,628,497 62,705 erosion -691,958 accretion
Between 2005 and 2015, the trend for both the intertidal and subtidal zones is one of accretion at an average annual rate of about 25,500m3 in the intertidal zone and 69,000m3 in the subtidal zone.
3.1.4 Overview of erosion and accretion patterns Figure 3.1 presents an overview of the erosion and accretion patterns for the Orwell and Stour estuaries for the period 2005 to 2015 (i.e. a visual representation of the combination of changes reported in Tables 3.1 to 3.4).
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Figure 3.1 Overview of erosion and accretion patterns between 2005 and 2015 in the Orwell and Stour estuaries
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3.2 Saltmarsh extent The extent of saltmarsh within the Stour and Orwell estuarine system was calculated using high resolution photographs gained from an aerial survey undertaken in 2015. The methodology used for the analysis of the aerial photographs was the same as that used to calculate saltmarsh extent based on aerial surveys undertaken in 2005 and 2010 (reported in Royal HaskoningDHV, 2013). The results of the 2015 saltmarsh extent assessment are reported in Royal HaskoningDHV (2015b) (Appendix B) and summarised below.
The results of the analysis of the 2015 aerial photographs are presented in Table 3.5 for each zone of the estuarine system; the results of the 2005 and 2010 surveys are included for comparison of difference in saltmarsh extent over the course of the monitoring.
Table 3.5 Summary of change in saltmarsh extent between 2005, 2010 and 2015 2005 2010 2015 Difference Difference Percentage Percentage Location saltmarsh saltmarsh saltmarsh 2005-2010 2010-2015 difference difference area (ha) area (ha) area (ha) (ha) (ha) 2005-2010 2010-2015
Harbour 2.04 3.97 4.03 1.93 0.06 94.87 1.51
Lower Orwell 26.31 29.68 30.34 3.37 0.66 12.82 2.22
Lower Stour 52.61 55.82 57.22 3.21 1.40 6.11 2.51
Mid Stour 19.06 22.31 22.24 3.25 -0.07 17.05 -0.31
Upper Orwell 10.50 11.43 11.44 0.93 0.01 8.89 0.09
Upper Stour 28.09 31.50 29.15 3.41 -2.35 12.15 -7.46
Total 138.59 154.70 154.42 16.11 -0.28 11.63 -0.18
Comparison of the saltmarsh extent within the estuary system based on the 2015 survey with the results of the 2005 and 2010 surveys shows an increase in extent within the system of 15.8ha over the monitoring period, equating to approximately 1.6ha/year on average. Over the last 5 years (between 2010 and 2015), a very minor decrease in extent has been recorded. The magnitude of this change is considered to be within the margin of error of the analysis.
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4 BENTHIC INVERTEBRATE COMMUNITIES
4.1 Introduction This section summarises the results of the following studies:
1) 2015 annual benthic monitoring (Thomson Unicomarine, 2016a) (full report included in Appendix C). 2) Review of macrobenthic data for the monitoring period from 1997 to 2015 (Thomson Unicomarine, 2016b) (full report included in Appendix D). 3) A report on the distribution of marine invasive species in Harwich Haven (2010-2015) (Thomson Unicomarine, 2016c) (full report included in Appendix E). It should be noted that HHA does not have any commitment to study or report on the distribution of marine invasive species and this is reported for information only.
4.2 2015 annual benthic monitoring As with previous monitoring surveys, samples were collected from 44 stations belonging to 11 sample groups (four sample groups for the Orwell (OrA-D) and seven for the Stour (StA-G)). The full report of the 2015 benthic monitoring (Thomson Unicomarine, 2016a) is included in Appendix C, with a summary of the key findings provided below:
• Two littoral sediment biotopes (LS.LMu.MEst.HedMac1 and LS.LMx.Mx.CirCer2) and one subtidal biotope (SS.SMx.SMxVS.CreMed3) were identified. • The species assemblages in the Stour and Orwell Estuaries are equally similar to each other (and this result is statistically significant). • The SS.SMx.SMxVS.CreMed subtidal biotope increased in extent between 2014 and 2015. • LS.LMu.MEst.HedMac remains the most dominant intertidal biotope. • In 2015 the LS.LMx.Mx.CirCer biotope is present, suggesting that the intertidal sediments have become more mixed, moving away from fine sediments in 2014. • 21 of the 44 sampling stations have the same biotope as in 2014. • The upper reaches of the Stour estuary were the most stable areas. The Orwell estuary appears to have more variation in biotopes than the Stour estuary.
Thomson Unicomarine (2016a) concludes that the Stour and Orwell estuaries support relatively abundant and diverse macrobenthic communities, which are typical of coastal and estuarine waters in south-east England. The biotopes identified are also typical of estuarine habitats.
The communities are dominated by detritivore, mainly deposit-feeder species, such as the mud snail Peringia ulvae, polychaetes of the genera Streblospio and Tharyx, oligochaetes and nematodes.
1 Hediste diversicolor and Macoma balthica in littoral sandy mud
2 Cirratulids and Cerastoderma edule in littoral mixed sediment
3 Crepidula fornicata and Mediomastus fragilis in variable salinity infralittoral mixed sediment
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4.3 Review of macrobenthic data for the monitoring period from 1997 to 2015 Thomson Unicomarine undertook a review of macrobenthic data for the period 1997 to 2015 (Thomson Unicomarine, 2016b).
The review concludes that there has been stability in macrobenthic abundance, diversity and biomass over the monitoring period. An increase in abundance has been observed in the Stour estuary between 1997 and 2015 at subtidal sites, with abundance being stable at intertidal sites. In the Orwell estuary, an increase in abundance has been observed at intertidal sites, while it remained relatively stable in subtidal sites (Thomson Unicomarine, 2016b).
Intertidal and subtidal community diversity has remained stable in the Orwell estuary, while it has increased in all intertidal and subtidal sites in the Stour estuary (Thomson Unicomarine, 2016b).
Biomass has remained relatively constant over the monitoring period, though there were significant differences in the total biomass recorded in 2013 and 2015, with values largely exceeding those of 2014 and the other years (Thomson Unicomarine, 2016b).
The biotopes that have been assigned to the sampling stations have been observed to shift between years; only nine sampling stations were assigned to the same biotope in 2015 as in 2003. This does not, however, mean that overall biotope extent within the estuaries has changed over the course of the monitoring. It is noted that there are often small-scale spatial variations, even within two replicate samples from the same sampling station.
The most abundant biotope in all survey years is the LS.LMu.MEst.HedMac biotope; this is the only biotope recorded in 2003 that is still present in the sampling locations (Thomson Unicomarine, 2016b).
Intertidal sediments are dominated by fine and muddy sediments and Thomson Unicomarine (2016b) notes that the change in biotopes observed are a result of slight changes in the species composition rather than notable changes in sediment composition. The sediment composition of the subtidal samples has changed from mixed sediment and fine sand and mud dominated by polychaete worms to a more mixed, coarse sediment environment which supports communities of Crepidula fornicata as well as polychaete worms.
4.4 Distribution of marine invasive species in Harwich Haven Thomson Unicomarine (2016c) undertook a review of the current abundance and distribution of invasive non-native species (INNS) through the analysis of macrobenthic samples (collected on behalf of several organisations, including the HHA) over the period 2010 to 2014.
In total the following marine invasive species were recorded in the Stour and Orwell estuaries from the surveys:
• Ammothea hilgendorfi (sea spider); • Crepidula fornicata (slipper limpet); • Austrominius modestus (Australasian barnacle); • Ensis americanus (American jack knife clam); • Eusarsiella zostericola (American ostracod); • Mya arenaria (soft-shelled clam); • Petricola pholadiformis (American piddock);
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• Sargassum muticum (wireweed); and, • Styela clava (leathery sea squirt).
Thomson Unicomarine (2016c) report that there has been a slight increase in the total number of invasive individuals recorded over the 5 year period since 2010, but the pattern is not consistent across all species, with some species reducing in abundance and others increasing over the period.
All species are present throughout the Stour and Orwell Estuaries apart from A. hilgendorfi (sea spider), which was only recorded in the Stour Estuary. The majority of species are also found at the confluence of the estuaries and at the mouth with the North Sea, offshore from Landguard Point.
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5 BIRD DISTRIBUTION AND ABUNDANCE
5.1 Background
5.1.1 Introduction The Stour and Orwell estuaries are comprised of a range of habitats, including extensive mudflats, low cliffs, saltmarsh and small areas of vegetated shingle, making them a wetland of major international importance. The estuaries provide overwintering habitat for a number of wildfowl and wader species. The estuaries are designated as an SPA and Ramsar site due to the presence of these wintering waterfowl populations. When first designated, the SPA was known to regularly support over 20,000 waterfowl and populations of a number of species which were considered to be of national or international importance4.
Sections 5.1.2 to 5.1.4 describe the waterbird studies that are undertaken for the estuary system.
5.1.2 High water (core) counts High water counts are undertaken as part of the Wetland Bird Survey (WeBS)5. WeBS provide a long- running data set, with the most recent information available for the Stour and Orwell estuaries deriving from surveys undertaken in 2015/16 (Frost et al., 2017).
5.1.3 Low water counts Coordinated low water count surveys of the overwintering bird populations on the Stour and Orwell estuaries are undertaken as part of the HHA’s monitoring programme. The results are analysed and reported each year by the Suffolk Wildlife Trust.
5.1.4 Waterbird distribution During 2015, HHA and Natural England carried out a study assessing changes in the distribution of SPA bird species within the estuaries.
5.1.5 WeBS Alerts
WeBS Alerts are normally reviewed as part of the BTO’s reporting process every three years. The last evaluation period for the Stour and Orwell Estuaries SPA was for the winter of 2010/2011 and the BTO has confirmed that the Alerts will not be reviewed again until 2017 at the earliest (Neil Calbrade, BTO, pers. comm.), but have not been reviewed at the time of writing. The outputs from the WeBS Alerts were reported in the 2014 annual monitoring report and, as they have not been updated, are not reported again herein.
5.2 Analysis of waterbird data The results of the high water and low tide counts provide a good basis for describing the waterbird populations of the Stour and Orwell estuaries. The following sub-sections discuss the bird data for the estuaries available from reports and studies referred to above and include the WeBS high water counts up to and including the winter of 2015/16 (Frost et al., 2017) and low water counts to 2015/2016 (Suffolk Wildlife Trust Trading Co, 2015).
4 To be classified as being of national or international importance, over 1% of the Great Britain and East Atlantic populations respectively, must be present, 5 WeBS is a scheme run by the British Trust for Ornithology (BTO), the Wildfowl & Wetlands Trust, the Royal Society for the Protection of Birds and the Joint Nature Conservation Committee
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Figure 5.1 shows a location plan of the Stour and Orwell estuaries with place names referred to in this section and its associated appendices.
Figure 5.1 The features and place names of the Stour and Orwell estuaries at low tide
5.3 High water count trends
5.3.1 Overview of Stour and Orwell estuaries populations High water data from WeBS (Frost et al., 2017) is available up to and including the winter of 2015/16. The numbers of waterfowl over the winter periods for the most recent 5 years for which data is available (2011/12 to 2015/16) are presented for the Stour and Orwell estuaries in Figure 5.2 below.
Since 2012/13, the number of birds recorded on the Stour estuary has been increasing. A less notable increasing trend is seen in the Orwell estuary since 2011/12, although a decline is observed between 2014/15 and 2015/16.
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60,000
50,000
40,000
30,000 Stour Estuary Orwell Estuary 20,000
10,000
0 2011/12 2012/13 2013/14 2014/15 2015/16 Stour Estuary 50,276 44,520 48,566 52,699 54,283 Orwell Estuary 21,377 22,155 25,283 26,121 22,249
Figure 5.2 Total number of waterbirds on the Stour and Orwell estuaries (data sourced from Frost et al., 2017)
5.3.2 Analysis of key species
5.3.2.1 Introduction An analysis of population changes for key species in the Stour and Orwell estuaries using WeBS data for the period 2011/12 to 2015/16 has been undertaken. The analysis considered the same species that are included in the reporting of the low water counts undertaken by the Suffolk Wildlife Trust, which defines ‘key species’ as those included in the citation for the SPA (i.e. those occurring in nationally or internationally important numbers), plus other species that have either held this status previously or are prominent in the communities of the estuaries.
Figures 5.3 to 5.16 present the population size of each key species over the period 2011/2012 to 2015/2016.
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Dark-bellied Brent goose 5,000 4,500 4,000 3,500 3,000 2,500 2,000 1,500 1,000 500 0 2011/12 2012/13 2013/14 2014/15 2015/16
Stour Orwell Stour and Orwell
Figure 5.3 Numbers of dark-bellied Brent goose (2011/12 to 2015/16)
Shelduck 3,500 3,000 2,500 2,000 1,500 1,000 500 0 2011/12 2012/13 2013/14 2014/15 2015/16
Stour Orwell Stour and Orwell
Figure 5.4 Numbers of shelduck (2011/12 to 2015/16)
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Wigeon 4,500 4,000 3,500 3,000 2,500 2,000 1,500 1,000 500 0 2011/12 2012/13 2013/14 2014/15 2015/16
Stour Orwell Stour and Orwell
Figure 5.5 Numbers of wigeon (2011/12 to 2015/16)
Pintail 800 700 600 500 400 300 200 100 0 2011/12 2012/13 2013/14 2014/15 2015/16
Stour Orwell Stour and Orwell
Figure 5.6 Numbers of pintail (2011/12 to 2015/16)
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Oystercatcher 2500
2000
1500
1000
500
0 2011/12 2012/13 2013/14 2014/15 2015/16
Stour Orwell Stour and Orwell
Figure 5.7 Numbers of oystercatcher (2011/12 to 2015/16)
Ringed plover 700 600 500 400 300 200 100 0 2011/12 2012/13 2013/14 2014/15 2015/16
Stour Orwell Stour and Orwell
Figure 5.8 Numbers of ringed plover (2011/12 to 2015/16)
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Grey plover 3,500 3,000 2,500 2,000 1,500 1,000 500 0 2011/12 2012/13 2013/14 2014/15 2015/16
Stour Orwell Stour and Orwell
Figure 5.9 Numbers of grey plover (2011/12 to 2015/16)
Lapwing 7,000 6,000 5,000 4,000 3,000 2,000 1,000 0 2011/12 2012/13 2013/14 2014/15 2015/16
Stour Orwell Stour and Orwell
Figure 5.10 Numbers of lapwing (2011/12 to 2015/16)
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Knot 14,000 12,000 10,000 8,000 6,000 4,000 2,000 0 2011/12 2012/13 2013/14 2014/15 2015/16
Stour Orwell Stour and Orwell
Figure 5.11 Numbers of knot (2011/12 to 2015/16)
Dunlin 12,000
10,000
8,000
6,000
4,000
2,000
0 2011/12 2012/13 2013/14 2014/15 2015/16
Stour Orwell Stour and Orwell
Figure 5.12 Numbers of dunlin (2011/12 to 2015/16)
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Black-tailed godwit 4,000 3,500 3,000 2,500 2,000 1,500 1,000 500 0 2011/12 2012/13 2013/14 2014/15 2015/16
Stour Orwell Stour and Orwell
Figure 5.13 Numbers of black-tailed godwit (2011/12 to 2015/16)
Curlew 3,000
2,500
2,000
1,500
1,000
500
0 2011/12 2012/13 2013/14 2014/15 2015/16
Stour Orwell Stour and Orwell
Figure 5.14 Numbers of curlew (2011/12 to 2015/16)
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Redshank 3,000
2,500
2,000
1,500
1,000
500
0 2011/12 2012/13 2013/14 2014/15 2015/16
Stour Orwell Stour and Orwell
Figure 5.15 Numbers of redshank (2011/12 to 2015/16)
Turnstone 800 700 600 500 400 300 200 100 0 2011/12 2012/13 2013/14 2014/15 2015/16
Stour Orwell Stour and Orwell
Figure 5.16 Numbers of turnstone (2011/12 to 2015/16)
5.4 Low water count trends
5.4.1 Introduction Coordinated counts of waterbirds at low tide have been undertaken throughout the Stour and Orwell estuaries each winter since 1999/2000. Counts are undertaken in November, December, January and February. The objective of the low water counts is to assess the low water wintering population of waterbirds within the Stour and Orwell Estuaries SPA.
The report produced in July 2016 (Suffolk Wildlife Trust Trading Co, 2016) is included as Appendix F. The report presents the results of the monitoring programme from 1999/2000 to 2015/2016.
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It is noteworthy that the aftermath of the surge tide of December 2013 reduced access to some mid-estuary sections on both the Stour and Orwell estuaries and compromised the efficiency of subsequent counts in the winter of 2013/2014, particularly the January 2014 count.
5.4.2 Summary of the low water count data and trends Table 5.1 summarises the increases and decreases in the mean and peak numbers of waterbird species on the Orwell, Stour and for the whole SPA for the period 1999/2000 to 2015/2016. Detailed species accounts are provided in Appendix F.
Table 5.1 Trends in the mean and peak numbers of species on the Orwell, Stour and SPA (1999/2000 to 2015/2016) Colours denote an increasing (green) or decreasing (red) population and colour intensity indicates trend confidence (weak, medium or high); reproduced from Suffolk Wildlife Trust Trading Co, 2016) Mean numbers Peak numbers Orwell Stour SPA Orwell Stour SPA Dark-bellied brent goose Shelduck Wigeon Pintail Oystercatcher Ringed plover Grey plover Knot Dunlin Black-tailed godwit Curlew Redshank Turnstone
The mean winter populations of six species show significant declines (Table 5.1). Suffolk Wildlife Trust Trading Co (2016) notes that, at low water, five of these species (pintail, ringed plover, grey plover, curlew and redshank) have shown consistent and strengthening trends after each of the last five winters.
The mean low water winter populations of ringed plover and redshank are declining on both estuaries, and those of curlew and grey plover are restricted to the Orwell and Stour respectively.
Oystercatcher shows a decline on the Stour and turnstone shows a decline on the Orwell at low water. Shelduck, dunlin and black-tailed godwit do not show any trend in mean numbers. Brent goose and knot show an increasing and strengthening trend in 2015/2016, largely due to increases on the Stour.
Trends in peak numbers largely reflect changes in the mean populations of most species and, after 2015/2016, six of the 13 species show a declining trend in the peak number recorded in the SPA.
5.5 Assessment of changes in the Stour and Orwell estuaries in the context of national population trends A review of the annual WeBS report (Frost et al., 2017) has been undertaken to describe the national population trends of the key waterbird species of the Stour and Orwell estuaries. The national trend in the population of a particular species is an important contextual consideration when describing and analysing changes in the waterbird populations in the Stour and Orwell estuaries.
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5.5.1 Dark-bellied Brent goose Frost et al. (2017) report an increasing national population trend for this species, with an increase in the 10- year population (2004/05 to 2014/15) of 42% (with a 17% increase over the 25-year period 1989/90 to 2014/15). This direction of change appears consistent with the trend observed in the population of this species from the low water counts (mean numbers) in the SPA, and notably on the Stour (Table 5.1).
There is no obvious trend in the WeBS core count data for the Stour and Orwell estuaries over the period 2011/12 to 2015/16. Numbers on the Orwell appears stable, with more variability in the Stour population over this period (see Figure 5.3).
The low water data show a statistically significant increase in mean and peak numbers in the Stour estuary and an increase in mean numbers in the SPA. No trend is apparent on the Orwell estuary (Table 5.1 and Figure 5.17).
4000 5000
4000 3000
3000 2000 2000
1000 1000
0 0 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16
Figure 5.17 The mean (± SEs) (left) and peak (right) numbers of dark-bellied Brent goose on the Orwell (●), Stour (○) and whole SPA (■) in winters 1999-2000 (0) to 2015/2016 (16) (source: Suffolk Wildlife Trust Trading Co, 2016)
5.5.2 Shelduck According to Frost et al. (2017) the UK overwintering population of shelduck has been declining. The 10- year trend for this species (2004/05 to 2014/15) shows a decrease of 27% in the UK (with a 32% decrease over the 25-year period 1989/90 to 2014/15).
Figure 5.4 shows variability in shelduck numbers for the Stour and Orwell estuarine system as a whole over the period to 2014/15, with no clear trend. The changes in the estuarine system appear to be largely driven by changes in the population on the Stour. A fall in the population is seen from 2014/15 to 2015/16 on the Stour.
No trend (i.e. no statistically significant increase or decrease) in the population of this species in the Stour and Orwell estuaries is evident from the low water data (Table 5.1 and Figure 5.18), and the high water data for the most recent 5 years does not seem to reflect the significant population decrease evident in the longer term national data.
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4000 5000
4000 3000
3000 2000 2000
1000 1000
0 0 0123456789 10111213141516 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16
Figure 5.18 The mean (± SEs) (left) and peak (right) numbers of shelduck on the Orwell (●), Stour (○) and whole SPA (■) in winters 1999-2000 (0) to 2015/2016 (16) (source: Suffolk Wildlife Trust Trading Co, 2016)
5.5.3 Wigeon Frost et al. (2017) report that the 10-year trend (2004/05 to 2014/15) for this species in the UK shows a decline of 18% (compared to a 26% increase over the 25-year period 1989/90 to 2014/15).
The high water data for the Stour and Orwell estuaries (2011/2012 to 2015/2016) appears to show a different pattern of change between the Stour and Orwell estuaries, with an apparent decrease in the Stour and an increase in the Orwell, although the system as a whole does not appear to show a strong trend (Figure 5.5).
The low water data shows a trend of decreasing numbers on the Orwell and for the SPA as a whole, with no statistically significant trend on the Stour (Figure 5.19). The trend for the SPA mirrors the direction of change in the national population over the 10 year period to 2014/15.
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Figure 5.19 The mean (± SEs) (left) and peak (right) numbers of wigeon on the Orwell (●), Stour (○) and whole SPA (■) in winters 1999-2000 (0) to 2015/2016 (16) (source: Suffolk Wildlife Trust Trading Co, 2016)
5.5.4 Pintail The UK population of pintail shows a downward trend; declining by 46% over the 10-year period 2004/05 to 2014/15 (with a 38% decrease over the 25-year period 1989/90 to 2014/15) (Frost et al., 2017).
This decline is not apparent from the high water data for the Stour and Orwell estuaries (2011/2012 to 2015/2016) (Figure 5.6), which show an increase in the population on the Stour and Orwell estuaries over this 5 year period.
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A significant decrease in the low water mean population of pintail is reported for the SPA (with weak confidence), but no statistically significant trend is seen for either estuary individually (Table 5.1 and Figure 5.20).
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Figure 5.20 The mean (± SEs) (left) and peak (right) numbers of pintail on the Orwell (●), Stour (○) and whole SPA (■) in winters 1999-2000 (0) to 2015/2016 (16) (source: Suffolk Wildlife Trust Trading Co, 2016)
5.5.5 Oystercatcher The 10-year trend for the oystercatcher population in the UK shows a decline of 15% (with a 26% decrease over the 25-year period 1989/90 to 2014/15) (Frost et al., 2017). The high water data for the Stour and Orwell estuaries (2011/12 to 2015/16) also appears to show a declining trend (Figure 5.7).
At low water, the mean SPA population does not show a trend, although there is a significant decline in the peak population for the SPA (Table 5.1 and Figure 5.21). The mean and peak oystercatcher numbers on the Stour estuary shows a significant decline, but no statistically significant trend is observed on the Orwell.
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Figure 5.21 The mean (± SEs) (left) and peak (right) numbers of oystercatcher on the Orwell (●), Stour (○) and whole SPA (■) in winters 1999-2000 (0) to 2015/2016 (16) (source: Suffolk Wildlife Trust Trading Co, 2016)
5.5.6 Ringed plover The UK population of ringed plover has declined by 37% for the 10-year period 2004/05 to 2014/15 according to Frost et al. (2017) (with a 59% decrease over the 25-year period 1989/90 to 2014/15). Figure 5.8 also shows an overall decrease in population over the period 2011/2012 to 2015/2016 in the Stour and Orwell estuaries, but there is variability between years. The Orwell population appears relatively stable, with a more obvious decrease in the Stour over this period.
At low water, declines in the ringed plover population are observed in the Stour, Orwell (mean numbers only) and SPA (Table 5.1 and Figure 5.22).
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Figure 5.22 The mean (± SEs) (left) and peak (right) numbers of ringed plover on the Orwell (●), Stour (○) and whole SPA (■) in winters 1999-2000 (0) to 2015/2016 (16) (source: Suffolk Wildlife Trust Trading Co, 2016)
5.5.7 Grey plover Frost et al. (2017) report a decline of 19% in the UK grey plover population over the 10-year period 2004/05 to 2014/15 (with a 30% population decrease over the 25-year period 1989/90 to 2014/15).
Based on the high water data for the period 2011/12 to 2015/16 for the Stour and Orwell estuaries combined, grey plover numbers appear to increase to 2013/14, followed by a decline. This appears to be driven by changes in the Stour estuary, with the Orwell population appearing relatively stable (Figure 5.9).
At low water, no statistically significant trend is observed in the Orwell, but declines are observed in the Stour and for the SPA as a whole (Table 5.1 and Figure 5.23).
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Figure 5.23 The mean (± SEs) (left) and peak (right) numbers of grey plover on the Orwell (●), Stour (○) and whole SPA (■) in winters 1999-2000 (0) to 2015/2016 (16) (source: Suffolk Wildlife Trust Trading Co, 2016)
5.5.8 Lapwing According to Frost et al. (2017), the UK population of lapwing has declined by 32% over the 10-year period 2004/05 to 2014/15. The population trend over the 25-year period 1989/90 to 2014/15 has declined by 3%.
The high water data for the Stour and Orwell estuaries (Figure 5.10) shows an increase in numbers to 2014/15, with a decrease in 2015/16 on the Stour and Orwell estuaries combined and in the Orwell estuary. The pattern for the SPA is strongly driven by changes in the Orwell; the population on the Stour has gradually increased during the period to 2015/16.
Suffolk Wildlife Trust Trading Co (2016) no longer reports the trend for lapwing because numbers have been variable since the start of monitoring, it is no longer a species of particular status in the SPA and is not
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necessarily a species characteristic of the low tide community of the SPA (Suffolk Wildlife Trust Trading Co, 2016).
5.5.9 Knot Frost et al. (2017) report that the UK knot population has declined by 16% over both the 10-year period 2004/05 to 2014/15 and the 25-year period 1989/90 to 2014/15.
The high water data for the Stour and Orwell estuaries (Figure 5.11) shows an increase in numbers to 2014/15, with a decrease in 2015/16 on the Stour and Orwell estuaries combined and in the Stour estuary. The pattern for the SPA is strongly driven by changes in the Stour; the population on the Orwell appears relatively stable.
At low water, knot has shown an increase in mean number on the Stour and in the SPA, with an increase in peak number on the Orwell (Table 5.1 and Figure 5.24).
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Figure 5.24 The mean (± SEs) (left) and peak (right) numbers of knot on the Orwell (●), Stour (○) and whole SPA (■) in winters 1999-2000 (0) to 2015/2016 (16) (source: Suffolk Wildlife Trust Trading Co, 2016)
5.5.10 Dunlin The UK dunlin population has declined by 19% over the 10-year period 2004/05 to 2014/15 (with a 40% population decrease over the 25-year period 1989/90 to 2014/15) (Frost et al., 2017).
The high water data for the Stour and Orwell estuaries combined shows fluctuation between years but over the period 2011/12 to 2015/16 the population appears stable. The population on the Orwell has steadily increased over this period, with the Stour population being stable to 2013/14, with a decrease in 2014/15 (Figure 5.12).
At low water, no statistically significant change is observed in the dunlin population (Table 5.1 and Figure 5.25).
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Figure 5.25 The mean (± SEs) (left) and peak (right) numbers of dunlin on the Orwell (●), Stour (○) and whole SPA (■) in winters 1999-2000 (0) to 2015/2016 (16) (source: Suffolk Wildlife Trust Trading Co, 2016)
5.5.11 Black-tailed godwit The 10-year trend for black-tailed godwit shows an increase of 33% over the 10-year period 2004/05 to 2014/15 (with a 300% population increase over the 25-year period 1989/90 to 2014/15) (Frost et al., 2017).
The high water data for the Stour and Orwell estuaries combined shows an increase over the period 2011/12 to 2015/16; the trend closely matches the pattern of change on the Stour. The population on the Orwell appears relatively stable, with an overall increase over this period (Figure 5.13).
The low water count data indicates stability in the population of black-tailed godwit, with peak numbers in the Orwell showing an increase (Table 5.1 and Figure 5.26).
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Figure 5.26 The mean (± SEs) (left) and peak (right) numbers of black-tailed godwit on the Orwell (●), Stour (○) and whole SPA (■) in winters 1999-2000 (0) to 2015/2016 (16) (source: Suffolk Wildlife Trust Trading Co, 2016)
5.5.12 Curlew Curlew populations in the UK have declined by 13% in the 10-year period 2004/05 to 2014/15 (with a 15% decline over the 25-year period 1989/90 to 2014/15) (Frost et al., 2017).
The high water data for the Stour and Orwell estuaries (2011/12 to 2015/16) appear to show stability in numbers, with a small increase in numbers to 2014/15, but a decline in 2015/16 largely due to a decrease in numbers on the Stour (Figure 5.14).
At low water, a decline in mean and peak numbers on the Orwell estuary and in the SPA is observed, with no statistically significant change in the Stour (Table 5.1 and Figure 5.27).
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Figure 5.27 The mean (± SEs) (left) and peak (right) numbers of curlew on the Orwell (●), Stour (○) and whole SPA (■) in winters 1999-2000 (0) to 2015/2016 (16) (source: Suffolk Wildlife Trust Trading Co, 2016)
5.5.13 Redshank The UK redshank population has declined by 18% over the 10-year period 2004/05 to 2014/15 (with a 20% decline over the 25-year period 1989/90 to 2014/15) (Frost et al., 2017).
The high water data for the Stour and Orwell estuaries show an increase in population over the period 2011/12 to 2015/16, although a minor decline is apparent from 2013/14 (Figure 5.15).
The numbers of redshank at low water have declined in both the Stour and Orwell estuaries and the SPA as a whole (Table 5.1 and Figure 5.28).
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Figure 5.28 The mean (± SEs) (left) and peak (right) numbers of redshank on the Orwell (●), Stour (○) and whole SPA (■) in winters 1999-2000 (0) to 2015/2016 (16) (source: Suffolk Wildlife Trust Trading Co, 2016)
5.5.14 Turnstone Frost et al. (2017) report a 24% decrease in the UK turnstone population over the 10-year period 2004/05 to 2014/15 (with a 47% decline over the 25-year period 1989/90 to 2014/15).
The high water data for the Stour and Orwell estuaries (2011/12 to 2015/16) shows an increase in the turnstone population over the period, notably in the Stour estuary (Figure 5.16).
At low water, no trend in turnstone numbers is apparent in the Stour estuary and in the SPA, with a decline in mean numbers in the Orwell (Table 5.1 and Figure 5.29).
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Figure 5.29 The mean (± SEs) (left) and peak (right) numbers of turnstone on the Orwell (●), Stour (○) and whole SPA (■) in winters 1999-2000 (0) to 2015/2016 (16) (source: Suffolk Wildlife Trust Trading Co, 2016)
5.6 Summary of trends from all data sources Table 5.2 presents a summary of the population trends for the key species of the Stour and Orwell Estuaries SPA, including the national population trends for these species.
It can be seen from Table 5.2 that the UK population of many of the key species have declined over the 10- year period 2004/05 to 2014/15 (based on WeBS Core Count data). In nearly every case where a decrease in the UK population has been observed, there has either been a decrease in the population in the Stour and Orwell estuaries or no trend has been detected (based on low water counts). The exception to this is knot; for this species, the UK population has declined whereas an increase in the mean numbers in the SPA has been observed.
The UK population of dark-bellied Brent goose has increased over the period 2004/05 to 2014/15 and the mean numbers of this species in the Stour and Orwell estuaries at low water have shown an increasing trend. The national population of black-tailed godwit has increased, but no trend in the WeBS core count data is observed in the SPA.
It is acknowledged that the above comparison of UK and SPA population trends is using two different data sets (i.e. high water WeBS core counts and low water coordinated counts in the Stour and Orwell estuaries). However, it is reasonable to infer that a change in the UK population as recorded by WeBS would be likely to be reflected in counts of waterbirds recorded at low water in estuaries.
A visual interpretation of the WeBS core count data (2011/12 to 2015/16) for the Stour and Orwell estuaries in the context of the WeBS core count data for the UK shows that for the majority of species that are declining in the national context, this trend is either mirrored in the Stour and Orwell estuaries, the population appears stable or no trend is apparent. For pintail, lapwing, redshank and turnstone, the UK population is declining while apparently increasing in the Stour and Orwell estuaries (over the period 2011/12 to 2015/16). The increasing national trend for black-tailed godwit appears to be reflected by an increase in the Stour and Orwell estuaries.
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Table 5.2 Summary of national and SPA population trends for key waterbird species UK population trend (% change based on WeBS Core Counts (high Stour and Orwell SPA population trend (low water) water)) Stour and Orwell Estuaries SPA population trend (based on WeBS (1999/00-2015/16) Species Core Counts (2011/12 - 2015/16) (description of change is based on Peak numbers (with Mean numbers (with 10-year (2004/05-2014/15) 25-year (1989/90-2014/15) visual (as opposed to statistical) analysis of data) statistical trend statistical trend confidence) confidence) Brent Goose (Dark-bellied) 42 17 Apparent stability High No trend Shelduck -27 -32 No clear trend No trend No trend Wigeon -18 26 No clear trend Weak Medium Pintail -46 -38 Apparent increase Weak No trend Oystercatcher -15 -26 Apparent decline No trend High Ringed plover -37 -59 Apparent decline High High Grey plover -19 -30 Variability in numbers, no obvious trend High High Lapwing -32 -3 Apparent increase Not assessed Not assessed Knot -16 -16 Variability in numbers, no obvious trend Medium No trend Dunlin -19 -40 Apparent stability No trend No trend Black-tailed godwit 33 300 Apparent increase No trend No trend Curlew -13 -15 Apparent stability High High Redshank -18 -20 Apparent increase High High Turnstone -24 -47 Apparent increase No trend No trend
Increasing trend Decreasing trend No trend
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5.7 Waterbird distribution
5.7.1 Introduction In February 2016, the HHA and Natural England published a report describing changes in the distribution of birds at low water based on data gathered over the period 1996 to 2015 (HHA and Natural England, 2016) (Appendix G). The aim of the report was to contribute towards an understanding of changes in the pattern of bird distribution in the estuaries and to attempt to understand the potential causes of any changes, but the report itself does not attempt to interpret any changes in bird distribution.
HHA and Natural England (2016) presents the results of two analyses:
1) The trend in the mean winter population in each section (count area) between 1996/97 and 2014/15 (i.e. the absolute numbers of birds using each section in isolation). 2) The trend in the proportion of the whole estuary population using each section between 1996/97 and 2014/15.
An example of the results of the above two analyses (for dark-bellied Brent goose) is shown in Figure 5.30.
5.7.2 Results Figures presenting the results of the two analyses listed in Section 5.7.1 for each bird species individually are presented in Appendix G. A cumulative analysis has been undertaken with increases and decreases in the number of species presented (Figure 5.31).
On analysis of the results presented in Appendix G, there does not appear to be any notable pattern of change. For example, there is no count sector or zone of either estuary which has experienced a consistent increase or decrease for several species which could indicate a general problem with supporting habitat in that sector or zone. It is likely that there are a number of complex, interacting factors affecting the distribution of each waterbird species and it would be necessary to analyse each species in detail and to understand site-specific influences across the system in order to interpret the results of the distribution analysis.
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Figure 5.30 Trends in winter section populations (1996-2015) (upper) and trends in section proportions of winter estuary populations (1996-2015) (lower) for dark-bellied Brent goose
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Decreasing population Decreasing proportion of estuary population
Increasing population Increasing proportion of estuary population
Figure 5.31 Cumulative trends
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6 STOUR AND ORWELL CONDITION ASSESSMENT
This section of the annual report discusses the current condition of the Stour and Orwell Estuaries in the context of the anthropogenic impacts that may lead to ‘unfavourable no change’ or ‘unfavourable declining’ assessments.
The current assessment of the SSSI condition for the Stour and Orwell estuaries is available from Natural England (https://designatedsites.naturalengland.org.uk/SiteSearch.aspx). The Stour and Orwell Estuaries SPA covers the same area as the combined Stour and Orwell Estuary SSSIs. The condition assessments were undertaken between 2009 and 2010.
Within the Stour Estuary (see Figure 6.1), 8 out of 9 units are deemed to be in ‘favourable’ condition. The unit which is in ‘unfavourable declining’ condition (Unit 1) is adjacent to Manningtree in the upper estuary. The condition assessment states that there is some upper foreshore erosion and evidence of active erosion of saltmarsh types associated with the notified feature, Limonium humile (lax-flowered sea lavender), and notes that coastal squeeze may be a key contributory factor to the unfavourable declining condition.
Within the Orwell Estuary (see Figure 6.2 and Figure 6.3), there are 21 units of which 3 are in ‘unfavourable declining’ condition, 4 are ‘unfavourable no change’ and the remaining 14 are considered to be in ‘favourable’ condition. The units in ‘unfavourable declining’ condition are: • Unit 1 (in the upper estuary), deemed to be due to coastal squeeze; • Unit 8 (east of Chelmondiston) which is cited as experiencing coastal squeeze, causing the loss of saltmarsh; and, • Unit 13 (Trimley) where coastal squeeze is cited as the cause, leading to loss of saltmarsh vegetation.
Figure 6.1 Upper reaches of the Stour Estuary
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The units classified as ‘unfavourable no change’ are 12, 15 and 16 around the mouth of the Orwell and Unit 11 on the east side of the estuary south of Levington. Each of these units is considered to be in ‘unfavourable no change’ condition due to the presence of sea walls causing coastal squeeze, thereby constraining the natural development of saltmarsh.
Figure 6.2 Lower reaches of the Orwell Estuary
Figure 6.3 Upper reaches of the Orwell Estuary
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In conclusion, for all units that are not in favourable condition, there is no apparent link to the effects of port development or dredging. Coastal squeeze is cited as being the reason for the unfavourable condition of a number of units throughout within the estuaries.
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7 COMPLETED MONITORING STUDIES
7.1 Trimley Marshes managed realignment monitoring The monitoring of the Trimley Marshes managed realignment site was undertaken for a period of 10 years between 2001 and 2010. The monitoring has shown that the site has an established intertidal benthic community which supports a wide range of waterfowl and contributes to maintaining the integrity of the internationally designated sites.
Saltmarsh at the site has thrived and, in line with the design criteria for the site, a diverse community has developed but is unlikely to exceed the 30% threshold for vegetative growth.
The required period of monitoring, as specified within the Mitigation and Monitoring Package, was completed in 2010 and provided a clear indication of the development and successional changes within the site, a clear sign of the success of this managed realignment site.
7.2 Trinity III Terminal habitat enhancement monitoring Monitoring of the habitat enhancements on the Trimley and Shotley foreshores ceased in 2013 as the HHA has met its commitments for monitoring these sites, which have fulfilled their objectives. Consequently, no benthic monitoring was undertaken for these aspects during 2015.
Waterbird population monitoring at these sites continues as part of the system-wide monitoring (see Section 5). This will continue as long as the estuary-wide counts are undertaken.
The habitat enhancement sites were also covered as part of the LiDAR survey undertaken in 2015 (see Section 3).
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8 SUMMARY AND CONCLUSIONS
8.1 Introduction The HHA has carried out a comprehensive programme of environmental monitoring since 1999 in accordance with the original consents, modified over time after discussion with key statutory bodies. With the exception of aspects of the monitoring programme that have now ceased, monitoring was undertaken for all ‘live’ aspects of the monitoring programme in 2015. The current report presents the findings of the monitoring programme up to 2015/2016 and includes the results of monitoring:
• bathymetric and topographic data (including saltmarsh extent); • benthic invertebrate communities; and, • bird distribution and abundance.
The report also describes the maintenance dredging, disposal and sediment replacement activity undertaken in the Haven in 2015.
The condition assessment for the Stour and Orwell estuary SSSI units is summarised; but this assessment has not been updated by Natural England and is therefore unchanged from previous annual reports.
8.2 Bathymetric and topographic data A comparison of bathymetry and LiDAR data sets measured in 2005/2006, 2010/2011 and 2015/2016 has been undertaken and a calculation of intertidal and subtidal levels, surface areas and volume differences has been carried out.
Analysis of the combined bathymetric and topographic data shows that both the intertidal and subtidal zones of the Stour and Orwell estuaries have accreted over the period 2005 to 2015.
Comparison of the saltmarsh extent within the estuary system, based on the 2015 survey with the results of the 2005 and 2010 surveys, shows an increase in saltmarsh extent within the estuary system of 15.8ha over the monitoring period, equating to approximately 1.6ha/year on average.
8.3 Benthic invertebrate communities In 2015, the annual benthic monitoring and a review of the macrobenthic data for the whole monitoring period (1997 to 2015) was undertaken. The review concluded the following:
• Abundance, diversity and biomass generally have been stable over the monitoring period. • Abundance has increased in the Stour estuary in the subtidal sites, with abundance being stable in the intertidal sites. • In the Orwell estuary, an increase in abundance has been observed at intertidal sites, while it remained relatively stable in subtidal sites. • Intertidal and subtidal diversity has remained stable in the Orwell estuary and increased in the Stour estuary. • Biomass has remained relatively constant over the monitoring period. • Biotopes have been observed to shift between years; the most abundant biotope in all survey years is the LS.LMu.MEst.HedMac biotope.
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A review of non-native invasive species was also undertaken. This review concluded that there has been a slight increase in the total number of invasive individuals recorded over the 5 year period since 2010, but the pattern is not consistent across all species, with some species reducing in abundance and others increasing over the period.
8.4 Bird distribution and abundance Generally, the population trend for waterbird species in the Stour and Orwell estuaries (based on low water data) reflects the trend in the UK population (which is typically declining); although in a number of cases the Stour and Orwell estuaries population shows no trend when the UK population is declining. The exception is knot; for this species, the UK population has declined whereas an increase in the mean numbers in the SPA has been observed.
The UK population of dark-bellied Brent goose has increased over the period 2004/05 to 2014/15 and the mean numbers of this species at low water have shown an increasing trend. The national population of black-tailed godwit has increased, but no trend is observed in the WeBS core count data in the SPA.
The WeBS core count data for the most recent 5 years for the Stour and Orwell estuaries shows that for the majority of those species that are declining in the national context, this trend is either mirrored in the Stour and Orwell estuaries, the population appears stable or no trend is apparent. For pintail, lapwing, redshank and turnstone, the UK population is declining while apparently increasing in the Stour and Orwell estuaries. The increasing national trend for black-tailed godwit appears to be reflected by an increase in the Stour and Orwell estuaries.
8.5 Conclusion On the basis of the evidence gathered through the monitoring programme, it is concluded that the HHA has met the primary objectives of the compensation, mitigation and monitoring (set out in Section 1.2) and the detailed objectives related to the approach channel deepening (Section 1.3.1) and the Trinity III Terminal (Phase 2) Extension (Section 1.3.2). In summary, and with regard to these objectives, it can be concluded that:
1) Impacts on the favourable conservation status of habitats and species have been avoided. 2) Adverse effects predicted to be associated with the approach channel deepening and the Trinity III Terminal (Phase 2) Extension are not evident and have been effectively mitigated. 3) Effective intertidal habitat creation – the Trimley Marshes managed realignment site – has been provided to compensate for the predicted effect of the approach channel deepening. 4) The predicted increase in the background rate of erosion of intertidal habitat is not apparent. 5) There is no evidence of any effect on habitats within Hamford Water (as reported in previous annual reports). 6) The habitat enhancement measures on the Shotley and Trimley foreshores have been effective in meeting their stated objectives of providing enhanced protection to the seawalls along the Shotley and Trimley frontages and increasing their stability, enhancing the ecological value of the foreshores, providing valuable feeding habitat for waterbirds while not constraining future options for sustainable management of flood defences.
The MMP and CMMA for the 1998/2000 approach channel deepening and for the Trinity III Terminal (Phase 2) Extension required monitoring to be carried out for periods of no less than ten years, which have now expired. Consequently the 2015/16 monitoring is the last which HHA is obliged to carry out and HHA will now cease monitoring under the agreements.
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Nevertheless, HHA intends to continue with the bathymetric and LiDAR surveys and analysis of intertidal and subtidal areas and volume on the existing five year cycle. Waterbird counts at low water will also continue on a three yearly cycle, with the next counts taken in 2018 / 2019. Until a new regime of benthic monitoring is designed and put in place, HHA intends to continue the sediment and benthic analysis (as is currently undertaken) every three years. A sediment and benthic survey was carried out on this basis in 2018.
In 2017 HHA commissioned HR Wallingford to construct a three dimensional computer model of water flow and sediment movement covering the estuary and offshore area in order to better analyse a range of topics including the impacts of ongoing maintenance work to the harbour. The initial modelling has been completed and calibrates well with existing and new data. The results from this modelling work will be used to produce an updated tidal atlas of the harbour, to design a new and more focused benthic monitoring regime and to investigate possible improvements to the sediment replacement and maintenance dredging works.
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9 REFERENCES
Frost, T.M., Austin. G.E., Calbrade, N.A., Hall, C, Mellan, H.J., Hearn, R.D., Stroud, D.A., Wotton, S.R. and Balmer, D.E. (2017). Waterbirds in the UK 2015/16: The Wetland Bird Survey. BTO, RSPB and JNCC, in association with WWT. British Trust for Ornithology, Thetford.
HHA and Natural England (2016). Changes in the distribution of birds at low water in the Stour and Orwell Estuaries SPA 1996-2015. February 2016.
PDE and HR Wallingford (1998). Harwich Haven Approach Channel Deepening – Mitigation and Monitoring Package.
PDE and HR Wallingford (2001). Mitigation and Monitoring for the Stour and Orwell Estuaries SPA (and Hamford Water). June 2001.
Royal HaskoningDHV (2013). Stour and Orwell Estuaries Annual Monitoring: Analysis of saltmarsh extent. February 2013
Royal HaskoningDHV (2015a). Mitigation and Monitoring for the Stour and Orwell Estuaries SPA and Hamford Water SPA Annual Review 2014. March 2015.
Royal HaskoningDHV (2015b). Monitoring of Saltmarsh in the Stour and Orwell Estuaries. October 2015.
Suffolk Wildlife Trust Trading Co (2016). Ornithological Monitoring of the Stour and Orwell Estuaries Special Protection Area: Winters 1999/2000 to 2015/2016.
Thomson Unicomarine (2016a). Stour and Orwell Estuaries Annual Benthic Monitoring Report: 2015 survey. June 2016.
Thomson Unicomarine (2016b). Stour and Orwell Estuaries benthic monitoring programme: review of macrobenthic data from 1997 to 2015. June 2016.
Thomson Unicomarine (2016c). Distribution of Marine Invasive Species in Harwich Haven (2010-2015). February 2016.
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Appendix A Comparison of LiDAR and bathymetry data sets (HR Wallingford)
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Appendix B Monitoring of Saltmarsh in the Stour and Orwell Estuaries
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Appendix C Stour and Orwell Estuaries Annual Benthic Monitoring Report: 2015 survey
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Appendix D Stour and Orwell Estuaries benthic monitoring programme: Review of macrobenthic data from 1997 to 2015
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Appendix E Distribution of Marine Invasive Species in Harwich Haven (2010-2015)
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Appendix F Ornithological monitoring of the Stour and Orwell Estuaries Special Protection Area: winters 1999/2000 to 2015/2016
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Appendix G Changes in the distribution of birds at low water in the Stour and Orwell Estuaries SPA 1996-2015