Environmental Statement for Port of Southampton: Southampton Approach Channel Dredge Updated by Further Information 15. Coastal Defences Executive Summary: Chapter 15. Coastal Defences The proposed channel dredge is consistent with the policies set out in National Planning Policy Framework Planning Policy Statement (PPS) 25, which sets out the Government’s national policies on development and flood risk in England. None of the proposed works are planned to take place upon land and, therefore, this chapter can be considered to be a stand alone Flood Risk Assessment (FRA). There will be no direct effects on any of the coastal defences in the study area as a result of the proposed works. The potential indirect impacts that will arise from the proposed scheme, either through changes to the hydrodynamic or sediment regime, were assessed as: 1) Potential Impact Due to Changes in Water Levels The predicted changes in high water (HW) levels across Southampton Water and the Solent are millimetric and negligible in the context of natural variability in the wind-wave environment and would be nearly impossible to measure or observe in the field. Therefore, the impact of changes in water levels across the study area is considered to be insignificant. With respect to flood risk assessment, there will be no change to the risk of flooding as a result of the proposed dredge. 2) Potential Impact Due to Changes in the Flow and Sediment Transport Regime In Southampton Water, there will be a marginal change in the flow dynamics that will result in minor changes to existing erosion and sedimentation patterns. The predicted level of these changes would not be measurable from natural variation and would be close to the accuracy of any recording instrument. In the Solent, the pattern of flow speed and directions are largely unaffected and the only changes evident occur within the areas proposed to be dredged (i.e. not along the coast). Although the changes to flows and sedimentary processes that are predicted in Southampton Water will potentially improve the situation with respect to coastal flood protection, the overall impact across the study area is considered to be insignificant. 3) Potential Impacts Due to Ship Wash The total energy reaching the shore and seabed from vessel generated wave activity, water surface drawdown, backflow and vessel propeller wash will be marginally reduced. These changes in ship wash have the potential to marginally reduce intertidal erosion from existing conditions and the risk of overtopping existing sea defences, although this is unlikely to be discernable from background wind-wave energies reaching the shore. Therefore, the overall impact of ship wash is considered to be minor beneficial significant to the integrity of coastal defences, albeit marginal. Conclusion There will be no direct impact to coastal protection levels as a result of the proposed Southampton Approach Channel Dredge. Following completion of the capital works, the indirect impacts on flood risk will be insignificant. There will be a marginal reduction in the existing impacts to coastal defences from ship wash, which is considered to be minor beneficial significant. R/3742/8 232 R.2015 Environmental Statement for Port of Southampton: Southampton Approach Channel Dredge Updated by Further Information Coastal Defence Management 15.1 Operational management of coastal protection structures lies largely with District and Unitary Councils. Under the Water Resources Act 1991, the Environment Agency is responsible for supervision of all matters relating to flood defence and has permissive powers to maintain and improve water levels on main rivers. Natural England has a role in assessing the impact of coastal defence on nature conservation interests and Defra has a supervisory role, which includes providing an overarching policy framework and administering grant aid. Organisations with responsibilities and interests in shoreline protection along the south-central coast of England formed the Standing Conference on Problems Associated with the Coastline (SCOPAC) in 1986, providing a forum for debate on the difficulties relating to coastal defence and protection. 15.2 The Government’s national policies on development and flood risk in England are set out in National Planning Policy Framework (NPPF). The NPPF Planning Policy Statement (PPS) 25. This NPPF PPS aims to ensure that flood risk is taken into account at all stages in the planning process to avoid inappropriate development in areas at risk of flooding and to direct developments away from areas of highest risk. This chapter demonstrates that the proposed development is consistent with the policies set out in NPPF PPS25, and on the basis that none of the development is planned to take place upon land, can be considered to be a stand alone Flood Risk Assessment (FRA). In this way, the risk of flooding arising from the development has been considered and the impacts of climate change according to Defra’s latest guidelines (2006) have been taken into account in the impact assessment. 15.3 The characteristics of the coastal defences and their management types and practices protecting the coastline in the study area are presented in Figure 15.1. New coastal defences and changes to existing coastal defences are designed with future changes to sea level and the potential for overtopping taken into account. The timescale over which designed defences provide protection is typically in the order of 10 to 50 years depending on the coastal area. The saltmarshes and mudflats of the study area act as an additional natural block to wave energy and inhibit erosion of the backing coast and any manmade defences. The presence of these natural features, therefore, enhances the effectiveness of manmade protection works and effectively provides a two-tier coastal defence. The baseline distribution of marine and coastal habitats in the study area has been reviewed in Chapter 11 and the status of the saltmarsh, with respect to erosion and accretion patterns, is reviewed in Chapter 8. 15.4 Coastal defence strategies that cover the coastline of the study area are currently set out in the Western Solent and Southampton Water Shoreline Management Plan (SMP) North Solent Shoreline Management Plan, the East Solent SMP and the Isle of Wight SMP. These management plans are being revised and are expected to be completed by the end of 2009 (see Chapter 5). In addition to these SMPs, there is an Estuary Management Plan (EMP) for the Hamble Estuary. ABPmer have also undertaken an estuary processes study on behalf of Mouchel Parkman for Southampton City Council and backed by Eastleigh and Fareham Borough Councils in support of the coastal defence strategy for the River Itchen, Weston Shore, Netley and Hamble (ABPmer, 2006). The study describes the key issues and problems facing the study area based on current information, supported through the use of the photographs taken during a survey of the study frontage. R/3742/8 233 R.2015 Environmental Statement for Port of Southampton: Southampton Approach Channel Dredge Updated by Further Information 15.5 The following baseline sections review the levels of protection along the key areas of coastline in the context of existing coastal defence strategies and associated studies, as well as additional information provided on the SCOPAC website. Baseline Information Southampton Water and Test, Itchen and Hamble Estuaries 15.6 Over 26km of the shoreline in Southampton Water and its component tributaries is protected by a wide range of coastal protection works. Prevailing south-westerlies mean that the estuary is relatively sheltered with slightly more energy reaching the eastern shore than the western shore. Coastal protection works include steel piling and concrete sea walls, stone, rock armour and rubble revetments, shingle ridges, stone walls, gabion baskets, concrete revetments, steel pipes, concrete and timber piles, and sandbanks. Table 15.1 summarises the lengths of coastline in Southampton Water and its component tributaries protected by various engineering structures. Southampton City Council and the Port of Southampton own the majority of these defences. However, defences are also owned by the New Forest District Council, Fareham Borough Council, commercial organisations and private owners. Table 15.1 Summary of manmade coastal defences in Southampton Water and its tributaries Southampton Southampton % Length (m) River Test River Itchen River Hamble Total Water West Water East of Total Concrete wall 1640 290 430 1610 1030 5000 19 Shingle ridge 0 890 0 270 0 1160 4.4 Rock armour 2200 0 0 0 0 2200 8.3 Steel pipe 420 0 0 0 0 420 1.16 Steel piling 3510 0 665 2710 1450 8335 31.6 Gabion basket 50 0 160 110 290 610 2.3 Concrete pile 280 0 0 90 0 370 1.4 Concrete revetment 50 0 0 400 90 540 2 Rubble revetment 1150 0 0 120 520 1790 6.8 Timber pile 0 0 75 20 200 295 1.1 Stone revetment 0 0 0 1940 2490 4430 16.8 Sand bags 0 0 250 0 0 250 1 Stone wall 0 0 550 0 420 970 3.7 Total 9300 1180 1880 7270 6490 26370 100 (Source: Western Solent and Southampton Water SMP) 15.7 With respect to natural defences, the majority of the lower intertidal shoreline in Southampton Water and its tributaries comprises mudflat, the western side of the estuary being largely backed by saltmarsh and the eastern side backed by natural low cliffs, such as Netley Cliff. Over 32km of the shoreline is currently not protected by manmade coastal defences (i.e. it is protected by existing natural habitat), which constitutes over