Level 1 Strategic Flood Risk Assessment
Sedgemoor District Council Strategy and Development October 2015 ldf@Sedgemoor.gov.uk
Level 1 Strategic Flood Risk Assessment Sedgemoor District Council 2015
Revision Schedule
Rev Author Date Status and Descripton
02 AReading October Published version incorporating changes to document and mapping 2015 following consultation feedback.
01 AReading July 2015 DRAFT document for consultation with Risk Management Authorities and other stakeholders. Sedgemoor District Council 2015 Level 1 Strategic Flood Risk Assessment
Contents
1 Introduction 1
2 The Sedgemoor District Council Study Area 5
3 Policy Context 8
4 Data Collection and Methodology 15
5 Broad-scale Assessment 26
6 Focused Assessments 28
7 Developer Guidance 38
8 Development Site Drainage 40
9 Emergency Planning 47
10 Summary & Recommendations 48 Appendix 1 - Mapping 52 Appendix 2 - Wessex Water Sewer Flooding Data 53 Appendix 3 - Emergency Planning Mapping 54 Level 1 Strategic Flood Risk Assessment Sedgemoor District Council 2015 1
Introduction 1
Background
1.1 In 2008 Sedgemoor District Council completed a level 1 Strategic Flood Risk Assessment (SFRA) as part of the evidence base for the Council’s Core Strategy (1). The Core Strategy was later adopted in 2011 and is the current Development Plan for the District. The National Planning Policy Framework (NPPF) states that Local Plans should be supported by an SFRA which should be prepared in consultation with the Environment Agency and other Risk Management Authorities (2). This document therefore updates the previous level 1 SFRA document to provide appropriate information to inform the Council’s Core Strategy (Local Plan) review process (2011-2032). The updated SFRA will form a critical part of the Council’s evidence base in terms of informing the Sustainability Appraisal, identifying appropriate locations for development (by applying the Sequential Test), and preparing the Local Plan’s placemaking and district wide flood risk policies. It will also underpin wider decision making within the District, including assisting the Development Management process. When published it will be an important reference document for applicants preparing Sequential/Exception Test evidence and site specific Flood Risk Assessments to support planning application submissions.
1.2 Given the scale of flood risk in the District it is expected that further level 2 SFRA work may also be required. Level 2 SFRA work is necessary if, taking into account wider sustainability objectives, it is not possible to direct all development outside of medium or high risk areas. The Council intend to scope the need for further SFRA level 2 evidence later in 2015 after the initial Local Plan review consultation. Until this time, for planning application purposes, the current level 2 SFRA available from the Council's website should still be considered as the most up-to-date information on tidal breach and overtopping risk for the Bridgwater and Burnham-on-Sea/Highbridge areas (3).
The Need for an Updated Level 1 SFRA
1.3 Since previous SFRA work there have been a number of significant changes to both flood risk management and planning policy, which means that a comprehensive update to the level 1 SFRA is necessary. These changes include:
1. A number of significant flood events that have occurred in the District since the previous SFRA that need to be taken into account in the updated data. This includes the recent winter 2013-14 flooding on the Somerset Levels. The significant damage and disruption caused by this flood event resulted in Risk Management Authorities coming together to publish of the 20 year Somerset Levels and Moors Flood Action Plan.
2. Changes in the planning system since the publication of the previous SFRA, including the Localism Act (2011) and the NPPF, which replaces Planning Policy Statement 25 (PPS25). The PPS25 companion Practice Guide has also been replaced by the Planning Practice Guidance, published March 2014. While the new planning policy framework retains many of the previous flood risk policy aims of PPS25, an update is required to ensure continued compliance with national planning policy.
3. Many of the provisions of the Flood and Water Management Act 2010 and EU Flood Directive have been implemented, which have significant implications on roles and responsibilities of different organisations in relation to flood risk management.
1 Scott Wilson, 'Sedgemoor District Council Strategic Flood Risk Assessment Level 1 Report', 2008. 2 DCLG, 'National Planning Policy Framework', 2012, p. 24. 3 Scott Wilson, 'Sedgemoor District Council Level 2 Strategic Flood Risk Assessment', 2009. 2 Sedgemoor District Council 2015 Level 1 Strategic Flood Risk Assessment
1 Introduction
4. New and updated mapping in relation to sources of flooding is available, an example being the ‘Updated Flood Map for Surface Water’. It is therefore important to ensure the flood risk evidence base for the Local Plan review is based on the most up to date information.
5. With changes to organisations roles and responsibilities new and updated flood risk policy documents are now available, including for example updated Catchment Flood Management Plans, Local Flood Risk Management Strategies and the County’s Preliminary Flood Risk Assessment.
Aim and Objectives
1.4 The intention is to prepare the document under the requirements of the NPPF and the Flood Risk and Coastal Change section of the accompanying Planning Practice Guidance (4). Following publication of the NPPF the Environment Agency has also published SFRA Guidance detailing key outputs for SFRA’s (5). The aim of an SFRA in general is to provide an assessment of the risk to the District from all sources of flooding (including climate change implications), and to assess the impact that land use changes and new development in the area will have on flood risk. The aim of this level 1 study is to provide comprehensive information to inform policies in the Local Plan relating to flood risk management. It needs to provide a sufficiently detailed assessment so as to allow the Local Planning Authority to apply the Sequential Test to the location of new development, and determine whether development can be allocated outside of high and medium flood risk areas, taking account of all sources of flooding. To achieve this aim the objectives of this level 1 study are:
To produce updated maps for the Sedgemoor area showing Main Rivers, ordinary watercourses and Flood Zones, including defining Flood Zone 3b (functional floodplain) for planning purposes;
To provide an assessment of the implications of climate change on flood risk over an appropriate time period;
Provide information and mapping in relation to other sources of flooding, for example surface water, reservoir and groundwater risk;
Provide details of flood risk management measures, including the location and standard of flood defences, flood warning coverage and emergency plans;
Using the above information on all sources of flooding, undertake a focused assessment of the main settlements to determine the potential to sequentially locate any new development to areas at low risk, or where further level 2 work may be required to accommodate strategic development requirements;
Provide recommendations regarding use of the SFRA for planning policy, including the identification of planning policies that will successfully minimise and manage flood risks; and
Provide any locally specific guidance regarding the preparation of Flood Risk Assessments for new development, including the suitability of different sustainable drainage techniques.
4 DCLG, 'Planning Practice Guidance', 2015. http://planningguidance.planningportal.gov.uk/blog/guidance/flood-risk-and-coastal-change (Accessed 06/05/2015). 5 Environment Agency, 'Strategic Flood Risk Assessments - Guidance to support the National Planning Policy Framework', 2013. Level 1 Strategic Flood Risk Assessment Sedgemoor District Council 2015 3
Introduction 1
Consultation and Cooperation
1.5 Consultation and co-operation with key stakeholders is critical to establishing the evidence base for the new Local Plan, particularly in light of the ‘Duty to Cooperate’ brought in by the Localism Act 2011 (Section 110). This is of key importance for flood risk evidence given different organisations responsibilities, and the fact that river catchments and sources of flood risk do not respect administrative boundaries.
1.6 The Planning Practice Guidance lists the key Risk Management Authorities that need to be involved in the preparation of the SFRA. A description of these organisations, along with other local stakeholders specific to the Sedgemoor area, is detailed in the section 2 of this report. Following the Winter 2013/14 floods a key action from the Flood Action Plan was to improve cooperation between Flood Risk Management Authorities with the establishment of the Somerset Rivers Authority. The Somerset Rivers Authority was launched in January 2015 and will play a key role in bringing together and co-ordinating the Environment Agency, Internal Drainage Boards, Lead Local Flood and Highway Authority and other Somerset authorities, for continued deliver of the Flood Action Plan. The Somerset River Authority should ensure delivery of flood risk management in the County benefits from the collective experience and knowledge of all of its members.
Format and Structure of the Document
1.7 This rest of this SFRA report is split into the following sections:
Section 2:The Sedgemoor District Council Study Area - Provides a summary of the study area and flood risk management responsibilities of key organisations.
Section 3: Policy Context - Provides an overview of plans and strategies relevant to flood risk in the Sedgemoor area.
Section 4: Data Collection and Methodology - Details the consultation, data collection and methods undertaken as part of updating this Level 1 SFRA.
Section 5: Broad-scale Assessment - Provides a high level assessment of flood risk across the District.
Section 6: Focused Assessment - Undertakes a more detailed review of flood risk and implications on development for the Districts larger settlements.
Section 7: Developer Guidance - Updates the guidance to developers in terms of undertaking site specific assessments and Sequential Test evidence, including signposting to detailed guidance.
Section 8: Developer Site Drainage - Provides advice on sustainable drainage from development sites.
Section 9: Emergency Planning - Details the emergency planning procedures in place in the study area.
Section 10: Summary and Recommendations - Summaries the key outputs of the report and recommendations on how the information is used. 4 Sedgemoor District Council 2015 Level 1 Strategic Flood Risk Assessment
1 Introduction
1.8 A key output of a Level 1 SFRA is the production of detailed mapping of catchments, rivers,various sources of flooding, defences, structures and flood warning areas. These are referred to throughout the report and are included in the Appendices. Level 1 Strategic Flood Risk Assessment Sedgemoor District Council 2015 5
The Sedgemoor District Council Study Area 2
Introduction
2.1 Sedgemoor District Council covers an area of approximately 600km2. Its rural areas are principally flat open landscape of wet pasture, arable and wetlands fringed by areas of high ground, including the Mendip and Quantock Hills. Approximately 15 km of Severn Estuary coastline defines the western boundary of the district. In terms of rivers, the sources of the majority of the Council’s river catchments lie beyond Sedgemoor area, with Sedgemoor the last District most rivers pass through before discharging to the Severn Estuary. The major sources of flooding for Sedgemoor are therefore tidal and fluvial.
River Catchments
2.2 The main river Catchments in the Sedgemoor area are described below and shown in Figure 1 (Appendix 1):
2.3 The Axe Catchment – The Axe catchment lies to the north of the District and in some areas forms the administrative boundary with Mendip District Council and North Somerset Council. The River Axe and its tributaries, the Cheddar Yeo and Lox Leo, rise from limestones springs on the Mendips, before flowing through the Somerset Levels and Moors and into the sea just north of Brean Down, via sluice gates at Bleadon level.
2.4 The Brue Catchment – The Brue catchment flows westwards through the Sedgemoor area and incorporates the Huntspill River, North Drain and South Drain. The River Brue rises in the clay uplands to the east before slowly flowing through the Somerset Levels and Moors, via predominantly man made channels. The Brue and Axe catchments are interconnected in several places by rhynes controlled by sluices, forming a complex artificial drainage system to alleviate flooding on the Levels and Moors during times of high flow.
2.5 The Parrett Catchment – The Parrett catchment drains the Quantocks, Blackdown and Polden Hills, with the main tributaries located outside the Sedgemoor area, including the Rivers Tone, Isle, Yeo and Cary. In seeking to alleviate flooding the Parrett catchment has historically been heavily modified in places, for example with the re-routing of floodwaters along the River Sowy and King Sedgemoor Drain. A number of the rivers in the flat lowlands are embanked and perched above the surrounding floodplain. A combination of the steep upland catchments and underlying impermeable geology can generate quick runoff and flooding on the Somerset Levels and Moors, where the gradient reduces and the water slows. This results in the capacity of the embanked channels being exceeded with flood waters overflowing onto the surrounding moors before reaching the estuary. The capacity of the Parrett in the lower reaches can also be significantly reduced through high tide conditions. The Parrett is influenced by the tide for up to 19 miles inland, beyond the district boundary.
Tidal Areas
2.6 In addition to the tide locking effect discussed above a significant amount of the District is also at tidal flood risk in its own right, by virtue of its low lying nature and significant length of coastline. For example the districts second largest group of settlements, Burnham-on-Sea andHighbridge, lies wholly within the tidal floodplain. In reality much of the Districts coastline has tidal flood defences, which provide varying levels of protection. However, breach and overtopping of these defences remains a risk. 6 Sedgemoor District Council 2015 Level 1 Strategic Flood Risk Assessment
2 The Sedgemoor District Council Study Area
Surface Water, Sewer and Groundwater
2.7 Other potential local sources of flooding relevant to the District include surface water, sewer and groundwater flooding. Surface water flooding can result from intense rainfall events and tends to be exacerbated in areas of steeper gradient. Surface water flooding is inextricably linked to issues of poor drainage, including inadequate capacity of drainage systems from blockages. Public sewers themselves have finite capacity and at times of heavy rainfall water entering sewers can overload the system. This can particularly be the case where there are combined sewers with limited capacity, or miss-connections into the foul system.
2.8 Groundwater flooding is caused by the emergence of water from underground at either one point of a number or diffuse locations. It is governed by geological conditions and this type of flooding typically occurs after long periods of rainfall which can result in high water tables and water building up in underground aquifers. A discussed in the previous SFRA there is limited evidence of groundwater flooding in Sedgemoor, however new mapping is available and this will therefore be reconsidered in this update.
Artificial Sources
2.9 Significant volumes of water retained above the natural ground level can pose a flood risk threat if there is a breach of the dam/embankment. The Bridgwater and Taunton Canal links the River Parrett and the River Tone and includes flood control weirs which discharge excess overflow water away from the canal. There are also four reservoirs in the District area used for water resource purposes, as well as others that have a flood storage function. Plans to build a second reservoir at Cheddar have also been given permission, although the OFWAT price review determination for 2015-2020 may mean that construction will not start for some time.
Role and Responsibilities
2.10 Following the Pitt review and Flood and Water Management Act new roles responsibilities for flood risk management have been introduced and clarified. For the Sedgemoor area these are detailed below:
2.11 Environment Agency: Responsible for managed flooding from main river, the sea (including coastal erosion) and reservoirs. The EA also has a strategic overview role in relation to all forms of flooding.
2.12 Somerset County Council: Is the Lead Local Flood Authority for the area and is responsible for managing flooding from local sources (surface water, groundwater and ordinary watercourses).
2.13 Internal Drainage Boards: The Somerset Drainage Boards Consortium operate in Sedgemoor’s low lying areas, managing water levels and providing routine maintenance of Viewed Rhynes for the protection of people, property and the environment. They also have general supervision over all matters relating to the drainage of land in its areas and powers to ensure watercourses are not impeded or obstructed.
2.14 Sedgemoor District Council: As Local Planning Authority Sedgemoor have a critical role in implementing flood risk planning policy, including steering new development to areas at least risk and ensuring development that needs to come forward is safe and incorporates appropriate measures (e.g. SuDS). This is implemented through both its Development Management and Planning Policy (i.e. Local Plan) functions. The Council also have permissive powers to undertake flood risk management works to ordinary watercourses outside of IDB areas and also to serve notice on riparian Level 1 Strategic Flood Risk Assessment Sedgemoor District Council 2015 7
The Sedgemoor District Council Study Area 2 owners to undertake necessary works. This power has been delegated to Sedgemoor Council from the Lead Local Flood Authority. The County Council and District Council also work collectively on Emergency Planning through the Civil Contingencies Partnership.
2.15 Wessex Water: As sewerage undertakers Wessex Water are responsible for flood risk from public sewers in the area. They are also the reservoir undertakers for three of the reservoirs in the District.
2.16 Riparian Owners: Owners of land/property adjacent to watercourses have responsibilities for maintaining them and keeping them clear of debris or other obstructions. In addition private individuals may be responsible for drainage systems that operate prior to discharge either into a watercourse or into a public sewer.
2.17 The Canal & Rivers Trust: Are responsible for the Bridgwater and Taunton canal in Sedgemoor. They are a statutory consultee on development proposals that is likely to affect the canal. They should also be consulted where necessary to determine the impact of surface water discharges on the canal with regard to flood risk.
2.18 Bristol Water: Are the reservoir undertaker for Cheddar reservoir.
2.19 Somerset Rivers Authority: Formed in January 2015 and are specific to the Somerset area. The Somerset Rivers Authority brings together all the Risk Management Authorities under one umbrella. The intention is to promote cooperation and ensure greater control and responsibility over the delivery of water management improvements.
2.20 The diagram below provides an overview of risk management responsibilities and how these relate to planning:
Picture 1 Overview of flood risk management responsibilities (Source: National Flood and Coastal Risk Management Strategy, 2011) 8 Sedgemoor District Council 2015 Level 1 Strategic Flood Risk Assessment
3 Policy Context
Overview
3.1 This section provides an overview of plans and strategies relevant to flood risk in the Sedgemoor area. This intends to give a summary of both national planning policy and the latest flood risk management policy documents from different organisations.
National Planning Policy Framework (NPPF)
3.2 The NPPF was published in May 2012 replacing PPS25 as the principle national planning policy relating to flood risk. Further Planning Practice Guidance has subsequently been published online as a ‘live’ document that is updated when necessary. The online guidance provides addition advice to Planning Authorities and developers on how flood risk planning policy should be implemented.
3.3 The NPPF sought to simplify the larger number of planning policy documents available at the time. While this has resulted in reduced detail (compared to the previous PPS25 and PPS25 Practice Guide), the overall approach to managing flood risk in relation to new development remains the same. Key policy principles remain, including:
Taking a risk based approach, with development steered away from flood risk areas in the first instance (i.e. Sequential Test) and only permitted for certain uses in exception circumstances (i.e. Exception Test);
Ensuring, though the submission of Flood Risk Assessments, that development is safe over its lifetime and does not increase flood risk elsewhere;
That the vulnerability of development is taken into account in decision making.
3.4 Minor changes have been made in relation to the Exception Test, removing the specific requirement that development must be on previously developed land to be capable of passing the Exception Test where it applies. Also some of the advice in the NPPF could be considered more general than previously specified in PPSS25 and its Practice Guide. For example while the need to take into account climate change is still specified in the NPPF, unlike previous guidance specific climate change allowances to be used by planners are not included. Subsequent guidance issued by the Environment Agency has however since clarified climate change allowances (6). Like previous planning policy the NPPF details how Local Plans should be informed by SFRA’s when considering the location of new development and developing policies to manage flood risk. The supporting Planning Practice Guidance provides more information on the scope of SFRA’s and how they should be used in the plan-making process.
National Flood and Coastal Risk Management Strategy for England (2011)
3.5 The Flood and Water Management Act 2010 established that flood risk should be managed within the framework of a National Strategy for England and Local Strategies for each Lead Local Flood Authority area. The Act seeks to address many of the issues identified in the Pitt Review and earlier studies such as the Governments ‘Making Space for Water’. The national strategy prepared by the Environment Agency provides general information on different types of flooding, which organisations are responsible, and sets out principles for how flood risk should be managed.
6 Environment Agency, 'Climate change allowances for planners', 2013. Level 1 Strategic Flood Risk Assessment Sedgemoor District Council 2015 9
Policy Context 3
Somerset Local Flood Risk Management Strategy
3.6 The 2010 Act also introduced the requirement to produce Local Flood Risk Management Strategies. This is the local strategy setting out the approach that Somerset County Council (as Lead Local Flood Authority) will take to manage local sources of flooding across the area. Local sources are considered to be surface water, groundwater and ordinary watercourses. The objectives of the strategy are to (7):
1. Work to achieve a year on year reduction in the impact of flooding from all sources. Any increase in the risk of flooding as a consequence of climate change will be mitigated where practicable.
2. To establish a co-ordinated programme of flood risk and drainage management, including flood risk from all sources, integrating existing strategies, plans and assessments into one Flood Risk Management Plan by 2016.
3. The Somerset Strategic Flood and Water Management Partnership will deliver this strategy and work with local communities to develop and deliver fully integrated flood risk and drainage management services, beginning with a co-ordinated works programme.
4. Local communities will be made more aware of flood risk, and in partnership with risk management authorities they will take informed decisions to minimise that risk through individual and community action and become more resilient.
5. Development across the County will integrate consideration of flood risk and sustainable drainage systems into planning and development management systems and always seek to reduce flood risk; inappropriate development which could increase flood risk will be avoided, as will inappropriate development in areas of significant flood risk.
6. Flood risk management will be fully considered in the local plan development process and identify flood defence infrastructure that development needs to contribute towards.
7. Improved flood risk and drainage management, including taking a catchment wide approach, will contribute towards better water quality and wider environmental benefits.
3.7 The strategy sets out actions on how the County Council will work with individuals, communities and other organisations to reduce the threat of flooding. In relation to new development (objective 6) key actions include the need to improve the evidence base for local flood risk and ensure engagement with the planning process to avoid increased flood risk as a result of inappropriate development. The Planning Practice Guidance is clear that Local Planning Authorities should work with Lead Local Flood Authorities to ensure Local Plan policies are compatible with those in the Local Flood Risk Management Strategy.
Catchment Flood Management Plans (CFMP)
3.8 CFMPs, prepared by the Environment Agency, are high level strategic planning documents that provide a catchment overview of the main sources of flood risk and how these can be managed in a sustainable way for the next 50 to 100 years. The Environment Agency engages with stakeholders within the catchment in order to produce policies in terms of sustainable flood management solutions whilst also considering land use changes and the future effects of climate change. It is important to
7 Somerset County Council, 'Local Flood Risk Management Strategy', 2014, p. 6. 10 Sedgemoor District Council 2015 Level 1 Strategic Flood Risk Assessment
3 Policy Context
be aware CFMP's are likely to be superseded in due course by Flood Risk Management Plans (discussed further below). This will need to be addressed in future SFRA updates. Two CFMPs currently cover the Sedgemoor District area, these are:
North and Mid Somerset CFMP (Environment Agency, 2012)
Parrett CFMP (Environment Agency, 2011)
3.9 Their role is to establish policies that will deliver sustainable flood risk management for the long term. To deliver this aim CFMP’s set out overarching policies for different locations. The different policy options are:
3.10 Policy Option 1: Areas of little or no flood risk where we will continue to monitor and advise.
3.11 Policy Option 2: Areas of low to moderate flood risk where we can generally reduce existing flood risk management actions.
3.12 Policy Option 3: Areas of low to moderate flood risk where we are generally managing existing flood risk effectively.
3.13 Policy Option 4: Areas of low, moderate or high flood risk where we are already managing the flood risk effectively but where we may need to take further actions to keep pace with climate change.
3.14 Policy Option 5: Areas of moderate to high flood risk where we can generally take action to reduce flood risk.
3.15 Policy Option 6: Areas of low to moderate flood risk where we will take action with others to store water or manage run-off in locations that provide overall flood risk reduction and environmental benefits.
3.16 The CFMP catchment areas are separated into sub-areas where these different policy approaches are specified. The sub area policy approaches relevant to the Sedgemoor area are summarised on the following table.
North and Mid Somerset CFMP
Policy Option 1: Areas of little or no flood risk where Sub-area 9: Uplands, including the Mendip we will continue to monitor and advise. Hills Shipham area.
Policy Option 2: Areas of low to moderate flood risk Sub-area 4: River Axe and River Brue. where we can generally reduce existing flood risk management actions.
Policy Option 3: Areas of low to moderate flood risk Sub-area 8: Levels and Moors. where we are generally managing existing flood risk effectively.
Policy Option 4: Areas of low, moderate or high flood Sub-area 5: Coastal Towns, including risk where we are already managing the flood risk Burnham-on-Sea and Highbridge. effectively but where we may need to take further actions to keep pace with climate change. Level 1 Strategic Flood Risk Assessment Sedgemoor District Council 2015 11
Policy Context 3
North and Mid Somerset CFMP
Sub-area 7: Levels and Moors Towns, including Cheddar.
Table 1 North and Mid Somerset CFMP policies by sub-areas.
Parrett CFMP
Policy Option 3: Areas of low to moderate flood risk where Sub-area 3: Upper and North West we are generally managing existing flood risk effectively. Parrett, and Upper Isle.
Sub-area 8: Shoreline, including the area around Steart and Pawlett.
Policy Option 4: Areas of low, moderate or high flood risk Sub-area 7: Bridgwater where we are already managing the flood risk effectively but where we may need to take further actions to keep pace with climate change.
Policy Option 6: Areas of low to moderate flood risk where Sub-area 6: Somerset Levels and we will take action with others to store water or manage Moors. run-off in locations that provide overall flood risk reduction and environmental benefits.
Table 2 Parrett CFMP policies by sub-areas.
South West Flood Risk Management Plan (FRMP)
3.17 The Environment Agency is also in the process of preparing Flood Risk Management Plans across England as part of implementing the European Flood Directive. Sedgemoor Council falls within the South West Flood Risk Management Plan area which was consulted on in October 2014. When completed the plan will draw together information from all Risk Management Authorities on sources of flooding and detail where and how flooding will be managed so that communities and the environment benefit the most. The plans will also aim to better align with river basin planning under the Water Framework Directive.
Shoreline Management Plan (SMP)
3.18 The Sedgemoor District falls under the North Devon and Somerset SMP. In 1998 the first SMP was produced and a review (SMP2) commenced in 2007. The SMP2 sets out a long-term plan for the management of the shoreline between Hartland Point and Anchor Head over the next 100 years. The plan considers four generic policy options for individual sections of coast. These include, 'Hold the line', 'Advance the line', 'Managed realignment' and 'No active intervention'. The loss of land, biodiversity and buildings is considered within each scenario. Four of the Policy Statements are relevant to Sedgemoor: Steart Peninsula, Parrett Estuary, Burnham-on-sea & Highbridge, and Berrow to Brean Down.
3.19 The longer term plan for Steart Peninsula is to return the area to a more natural environment which is likely to involve no active intervention when it is no longer viable to hold the line. Set back defences will be built whilst it is economically viable to do so. The first phase of this has been implemented as part of the Environment Agency’s Steart Marshes project. 12 Sedgemoor District Council 2015 Level 1 Strategic Flood Risk Assessment
3 Policy Context
3.20 The plan for the Parrett Estuary section of the SMP is similar to the Steart Peninsula Plan and so they should be considered together. The short term aim of the plan is to hold the line until further studies are completed regarding the effects of managed realignment and the installation of a surge barrier. In the longer term, set back defences, defence realignment, higher defences and a replacement Huntspill sluice will need to be considered to protect the area. There are a number of assets at risk that will need to be considered if and when the defences are realigned such as the protected habitat sites, the sewage treatment works at Burnham-on-Sea, power-lines from Hinkley Point and non-designated archaeological sites.
3.21 The Burnham-on-Sea stretch of the SMP is considered economically valuable enough to maintain and reduce flood risk to this area and the wider Somerset levels. The short, medium and long-term plan is to hold the line with the eventual aim being to substantially increase the height of the seawall at Burnham-on-Sea which will have an impact on the town’s amenity value.
3.22 The plan for the Berrow to Brean Down section of coast is to actively manage the dunes in the short term whilst further studies are carried out. This hold the line plan may become a managed realignment plan in the medium term which may include the removal of properties to allow the dunes to develop naturally. The fore dunes at Brean are unlikely to provide protection from flooding by the end of the 100 year period.
Somerset Levels and Moors 20 Year Flood Action Plan
3.23 Following the severe floods of winter 2013/14 the Environment Secretary asked for a single overarching plan that will guide water and land management policies and investment on Somerset’s Levels and Moors for the next 20 years. The Flood Action Plan was produced by a range of organisations with involvement of the community and was coordinated by Somerset County Council. Delivery is now the responsibility of the Somerset Rivers Authority which brings together all relevant Risk Management Authorities.
3.24 The six key objectives of the plan are (8):
Reduce the frequency, depth and duration of flooding;
Maintain access for communities and businesses;
Increase resilience to flooding;
Make the most of the special characteristics of the Somerset Levels and Moors;
Ensure strategic transport connectivity; and
Promote business confidence and growth.
3.25 In helping to deliver these objectives it is considered the local planning authorities will have an important role to play and are identified in a number of the actions in the plan. These include:
Helping with developer funding and delivery of a Bridgwater tidal barrier/sluice through plan making and developer contributions;
Ensuring effectively planning policies are in place in relation to floodplain avoidance and mitigation;
8 Somerset County Council, 'The Somerset Levels & Moors Flood Action Plan - Executive Summary', 2014, p.2. Level 1 Strategic Flood Risk Assessment Sedgemoor District Council 2015 13
Policy Context 3
Ensuring flood mitigation measures are secured by condition/Section 106 agreement and are delivered;
Securing the delivery of sustainable drainage systems (SuDS) in new development.
Severn Estuary Flood Risk Management Strategy
3.26 This strategy will set out the Environment Agency’s plan to manage tidal flood risks in the Severn Estuary, including Sedgemoor’s coastline. The three main objectives of the strategy are:
To define a 100 year plan of investment for flood defences by the Environment Agency and local authorities, including withdrawal where it is uneconomic to continue defences;
To prioritise other flood risk management measures such as providing advice to utility companies to protect critical infrastructure, development control advice and flood warning investment
To decide where we should create new inter-tidal wildlife habitats to compensate for losses of habitat caused by rising sea levels.
3.27 The strategy is important in highlighting the likely limited ability over the long term to maintain defences in some locations of Steart Peninsula and Brean, where management realignment is likely to be required. A consultation was undertaken 2013 and the strategy is currently with Defra and the Welsh Government for approval prior to publication.
Other Relevant Policy and Legislation
3.28 In addition to the above main policy documents the following legislation and policies are also important in managing flood risk in the District.
Flood Defence Consents for works on main rivers
3.29 The Water Resources Act 1991 and associated byelaws requires developers to apply for formal consent from the Environment Agency for works in, over, under or adjacent to main rivers. Consent is required to ensure works do not increase flood risk, damage flood defences, or harm the environment, fisheries, or wildlife. For the Sedgemoor area consent is required for works within 8 m of the top of bank of a main river.
Land Drainage Consent for works on ordinary watercourses
3.30 Under the Land Drainage Act 1991, consent is also needed from either the local authority or Internal Drainage Board when culverting or obstructing a watercourse. The Somerset Drainage Board Consortium has also made Land Drainage byelaws to put in place further restrictions and requirements in the interest of managing drainage effectively. In relation to new development these include the requirement for consent for discharge into watercourses in their area and the requirement for consent for any works within 9 m of the edge of a watercourse. 14 Sedgemoor District Council 2015 Level 1 Strategic Flood Risk Assessment
3 Policy Context
Sustainable drainage systems non-statutory technical standards
3.31 Published by Defra in March 2015 this document sets out standards for the design, maintenance and operation of sustainable drainage systems (SuDS). Following Government consultation it is now intended that SuDS will be delivered through the planning system rather than under separate legislation, with the LLFA (Somerset CC) now a statutory consultee on major applications. The technical standards should therefore be read in conjunction with the NPPF and Practice Guidance advice on SuDS.
Sewers for Adoption (7th Edition, 2012)
3.32 Provides industry standard guidelines for the planning, design and construction of foul and surface water infrastructure for adoption by Wessex Water through a Section 104 Agreement (of the Water industry Act 1991). This includes guidance on the design criteria for the adoption of SuDS. Level 1 Strategic Flood Risk Assessment Sedgemoor District Council 2015 15
Data Collection and Methodology 4
Overview
4.1 This section provides details of the data collection and methodology undertaken to update the Level 1 SFRA. As data is received from a variety of different sources it is important to review its accuracy and relevance to assess with what confidence it can contribute to the SFRA. Risk Management Authorities importantly highlight a number of limitations for use of different dataset in order to avoid it being misused. An overview of the core datasets, including their source and their applicability to the SFRA is therefore outlined here.
4.2 It should be noted that best available information on flood risk is continually changing as a result of flood events occurring and improvements in mappings. Therefore, whilst the datasets used are the best available at the time of publication the SFRA will need to be reviewed regularly. This section also describes the approach taken to the delineation of Flood Zone 3b and consideration of climate change impacts.
Programme
4.3 The programme of tasks undertaken in the preparation of this Level 1 SFRA is detailed below:
Inception meeting between Sedgemoor District Council and the Environment Agency on 14th January 2015 to discuss the SFRA scope, format, and new data available;
Identification of key organisations with a flood risk management role (see section 2 for summary);
Where applicable, requests sent to key organisations requesting updated data/information (February 2015);
Follow-up data requested where required (March 2015);
Collation and review of available data (March/April 2015);
Meeting with Environment Agency to agree delineation of Flood Zone 3b (April 2015);
Update to GIS mapping, SFRA reporting and focused assessments for individual settlements (April/May 2015).
Consultation of draft report and mapping with Risk Management Authorities and other stakeholders (July/August 2015).
GIS Layers and Mapping
4.4 Geographical data such as flood extents and recorded flood incidents that can be used to inform planning policy and other planning decisions have been presented as maps using the MapInfo Geographical Information System (GIS). These are included in the Appendices to this document and will be referred to throughout this section when discussing the various sources of flooding.
4.5 GIS acts as an effective management tool for the coordinated capture, storage, and analysis of data of a geographical nature. GIS handles data in a hierarchical manner by storing spatial features within various layers, which are allied to an underlying database. GIS is a recognised tool for the efficient collation, storage and analysis of information and is also an increasingly valuable resource for local planning authorities. 16 Sedgemoor District Council 2015 Level 1 Strategic Flood Risk Assessment
4 Data Collection and Methodology
4.6 In addition to the fixed maps published in the appendices to this document the intention is, subject to relevant licencing restrictions, to display a number of the layers on the Council’s web based GIS mapping, allowing easier access for planning agents and other members of the public. While the majority of the information mapped is available via the individual Risk Management Authorities, Sedgemoor's web based mapping will be particularly useful for displaying Flood Zone 3b, given the delineation of this is a key output of the level 1 SFRA.
Flood Map for Planning (Rivers and Sea)
4.7 To inform the level 1 update the latest extents of Flood Zone 2 and 3 were obtained for the study area. These are available to LPA's via the Environment Agency DataShare website.
4.8 Together, Flood Zone 2 and 3 form the Flood Map for Planning (Rivers and Sea) and identifies areas at risk of both fluvial and tidal flooding. The Flood Map for Planning ignores the presence of flood defences and covers all Main Rivers and Ordinary Watercourses with catchment areas greater than 3km2. As if ignores defences the mapping forms the starting point for the applying the Sequential and Exception Tests and requiring site specific Flood Risk Assessments for planning application. The definition of Flood Zones 1, 2 and 3 are included in the table below.
Flood Zone Definition
Flood Zone 1 Low probability – Defined as zone where there is less than 0.1% (1 in 1000 year) probability of flooding each year.
Flood Zone 2 Medium probability – Defined as having between 0.1% and 1% (between 1 in 1000 and 1 in 100 year) probability of fluvial flooding each year or a 0.1% and 0.5% (between 1 in 1000 and 1 in 200 year) probability of tidal flooding each year.
Flood Zone 3 High probability – Defined as having a 1% or greater (1 in 100 year or greater) probability of fluvial flooding each year and a 0.5% or greater (1 in 200 year or greater) probability of tidal flooding each year.
Table 3 Flood Zone descriptions.
4.9 Given better information and modelling is always becoming available the Environment Agency undertakes quarterly updates of the Flood Map for Planning to make sure the most up to date and relevant flooding information is used to inform planning decisions. It is however important to understand the limitations of the data. It only considers tidal and fluvial risk and does not take into account other sources. It also does not consider risk for catchments smaller than 3km2. The mapping is largely based on modelled data that makes necessary assumptions and generalisations, meaning that for the majority of areas the data is indicative rather than site specific. While it can give an indication that an area of land is at flood risk it cannot be used to determine whether an individual property is at flood risk. Nor does it give an indication of the depth or velocity of flood waters, only extent. It is for these reasons that the Flood Map only acts as a trigger for site specific Flood Risk Assessments to ensure developers undertake a more detailed assessment at the local level. The Flood Map for Planning, including the definition of Flood Zone 3b is shown in Figure 2. Level 1 Strategic Flood Risk Assessment Sedgemoor District Council 2015 17
Data Collection and Methodology 4
Functional Floodplain
4.10 The Planning Practice Guidance describes that Local Planning Authorities should identify in their SFRA's areas of functional floodplain (or Flood Zone 3b), in agreement with the Environment Agency. This is therefore a key output of this SFRA update and an important planning tool in ensuring that development is directed to the most appropriate locations.
4.11 Functional floodplain is defined as comprising land where water has to flow or be stored in times of flood. Further the Practice Guidance advises that its identification should take account of local circumstances and not be defined solely on rigid probability parameters. Land that would flood with an annual probability of 1 in 20 or greater in any one year is offered only as a general guide. For example in contrast it is also advised that areas designed to flood (e.g. flood storage reservoirs) in more extreme events could also be considered as functional floodplain, even if they might not flood that often. It is also advised that defences should be taken into account and areas that are prevented from flooding due to defences, structures or solid buildings would not normally be identified as functional floodplain.
4.12 National policy therefore provides considerable flexibility in identifying functional floodplain areas. The Environment Agency's Flood Map for Planning does not differentiate between Flood Zone 3a and Flood Zone 3b and it is therefore the role of the SFRA to identify this. A meeting was held with the Environment Agency in April 2015 to discuss the methodology for the delineation of functional floodplain, agreeing where changes are required compared to the previous level 1 SFRA. The previous SFRA principally took the approach of analysing the Environment Agency's flood map to identify areas of undefended fluvially influenced floodplain and considering these areas to be functional floodplain, with the exception of some built up areas.
4.13 The extents of Flood Zone 2 and 3 have changed since the previous SFRA in 2008 as data and modelling techniques have improved. This has also influenced the interface between areas at principally tidal risk and those areas at fluvial risk, where the role of floodplain storage is important. The functional floodplain was therefore reviewed in light of this updated mapping, with reference also to the Environment Agency's 'Risk of Flooding from the Rivers and Sea' (previously NAFRA), which shows undefended areas considered to be at high risk.
4.14 Reference was also made historic flood records, particularly flood outlines from the Winter 2013/14 event in considering updates to the functional floodplain across the Levels and Moors. Local Environment Agency Officer knowledge was also used in identifying potential changes and agreeing the final mapping. The result of this review is that functional floodplain remains similar to that of the previous SFRA, but with some changes. The mapping can be viewed in Figure 2 and the main changes are detailed further in the table below.
Location and Nature of Reason Change
Steart Marshes - Changed to The recently completed project delivering new inter-tidal habitat Flood Zone 3b is purposely designed to flood during high tide. This has therefore been changed to Flood Zone 3b up to the set-back defences.
Durleigh Brook, east of For the majority of the Durleigh Brook the functional floodplain Taunton-Bridgwater canal - has been kept the same. The exception to this is the built up area Changed to Flood Zone 3a east of the canal. Here it is considered appropriate to change it to Flood Zone 3a in line with national guidance regarding the effect of solid buildings/structures. 18 Sedgemoor District Council 2015 Level 1 Strategic Flood Risk Assessment
4 Data Collection and Methodology
Location and Nature of Reason Change
Stockmoor/Wilstock Country One of the key roles of the country park is to act as a flood Park - Change to Flood Zone 3b storage area when required, ensuring the adjacent urban extensions remain safe. A change to Flood Zone 3b is therefore considered justified.
Moorland and Fordgate - Changes to Flood Zone 3b were made to the south and around Redefine the Flood Zone 3b Moorland and Fordgate to be consistent with the 'Risk of Flooding extent from the Rivers and Sea' mapping and the flood outline of the winter 13/14 event. Main built up areas are excluded from functional floodplain in line with national guidance.
Area west of Chedzoy and east There is an area which falls within 'tidal only' Flood Zone 3. of the M5 - changed from Flood Therefore it is considered appropriate to change this from Flood Zone 3b to 3a Zone 3b to Flood Zone 3a. This is consistent with the flood extents from the winter 13/14 event. The rest of the King Sedgemoor Drain corridor remains as Flood Zone 3b given its important role in storing and conveying floodwaters.
Levels and Moors north of the Flood Zone 3b has been redefined in this area to take into River Huntspill - Some account changes to fluvial Flood Zone 3 indicated on the extensions to Flood Zone 3b Environment Agency's Flood Map for Planning. This is also consistent with areas identified as high risk in the Environment Agency's 'Risk of Flooding from the Rivers and Sea' mapping.
Table 4 Key change to Functional Floodplain (Flood Zone 3b) as part of SFRA update
4.15 The new functional floodplain mapping will be an important tool for the Local Plan Review in identifying areas where certain development is not considered appropriate in principle. Applicants and agents should also refer to it when considering sites for development given that it significantly constrains what uses are appropriate.
4.16 The functional floodplain has been updated using the best available data and local knowledge at the time of this update. Developers, through site specific Flood Risk Assessments, may be able to challenge the designation if site level information or more detailed modelling agreed with the Environment Agency suggests it should not be considered functional. This will be considered on a case by case basis. The Council will also keep the functional floodplain under regular review as updated information and mapping becomes available from the Environment Agency and other Risk Management Authorities.
Climate Change
4.17 It is predicted that climate change will bring milder wetter winters that are characterised by periods of long duration rainfall. In contrast, frequent and short duration, high-intensity rainfall linked with longer drier summers is predicted. This is likely to cause increased flooding from fluvial, surface water and sewer sources. In addition, the effects of climate change on sea level will increase the likelihood of tidal flooding in low lying areas such as Sedgemoor.
4.18 The NPPF and Environment Agency guidance requires SFRA’s to undertake an assessment of the implications of climate change on development sites over an appropriate time period. The Practice Guidance identifies an indicative lifetime for residential developments of 100 years; Level 1 Strategic Flood Risk Assessment Sedgemoor District Council 2015 19
Data Collection and Methodology 4 consequently Flood Zones should be defined accounting for the effects of at least 100 years of climate change. A 60 year development lifetime is generally accepted as the indicative lifetime for other forms of development, such as commercial/agricultural buildings and infrastructure.
4.19 Where hydraulic modelling exists and allowances have been made for the predicted effects of climate change, then these can be used to provide flood extents for future scenarios. However, it is noted than the existing Flood Map for Planning available for the level 1 SFRA does not incorporate an allowance for climate change. This was also the situation for the previous level 1 SFRA and a pragmatic approach was taken to consider Flood Zone 2 (1 in 1000 year return period) as an indicative extent for climate change Flood Zone 3a. It is noted that due to the low lying nature of the Somerset Levels and Moors, the spatial extent of Flood Zone 3a is widespread. Therefore, the impact of climate change is likely to have a limited impact on the spatial extent of Flood Zone 3a, but may cause slight increases in the floodwater depths.
4.20 The approach to assessing climate change implications was discussed with the Environment Agency at the inception meeting for this SFRA update. The previous approach, of considering Flood Zone 2 as climate change Flood Zone 3a was agreed as still being fit for purpose. To validate this approach it was however considered sensible to compare Flood Zone 2 with the 100 year climate change scenarios modelled as part of the Somerset WAVE project, a European funded project addressing climate change resilience. Review of the WAVE project mapping indicates that the undefended climate change scenarios for both the 1 in 100 year fluvial and 1 in 200 year tidal produce very similar extents to the current Flood Zone 2. For planning purposes it is therefore considered appropriate to continue the approach of considering Flood Zone 2 as climate change Flood Zone 3a.
Historic Flooding Records
4.21 The 2008 level 1 SFRA compiled a dataset from different stakeholder’s records of the location and nature of flood events. A key task of the SFRA update has therefore been to update this dataset, particularly given the number of flood events that have occurred in the area since the previous SFRA. Key sources of historic flood data included:
The Environment Agency Flood Reconnaissance Information System (FRIS);
Sedgemoor District Council Land Drainage historical records;
Section 105 flood data - point data from Section 105 Water Act Section 24 (5) Survey of Land Drainage.
Somerset Council Historic Flooding Database, which incorporates where relevant information from Somerset Highways Confirm system relating to highway flooding.
Environment Agency recorded flood outlines and historic flood map.
4.22 This data was collated together and mapped using GIS with the point data shown in Figure 3 and polygon data shown in Figure 4. Where the background data has given an indication the mapping has sought to show the identified source of the flooding recorded (e.g. surface water, tidal etc.). This should however only be taken as a general indication as for a number of records the flooding experienced was attributed to more than one source.
4.23 The reliability of the records should be taken on a case by case basis. While some are based on aerial photography and validated by the Environment Agency the majority are anecdotal with no records of the antecedent conditions giving rise to the flooding. This causes difficulties in both attributing 20 Sedgemoor District Council 2015 Level 1 Strategic Flood Risk Assessment
4 Data Collection and Methodology
it to specific source or return period. The data should also be considered to only represent approximate locations that have been flooded in the past and should not be considered to indicate that specific properties were internally flooded. In a number of areas the flooding may have also occurred prior to flood infrastructure improvements which means that the area no longer floods or floods under different circumstances. An example of this is the 1981 tidal event which occurred prior to significant improvements to tidal defences along Sedgemoor's coastline. Nevertheless, provided it is used with the knowledge of these limitations the historic flood records are a very useful source of information that complements the other mapping.
4.24 The previous level 1 SFRA included a table summarising a selection of the larger historical flood events that have affected the Sedgemoor area (9). These are detailed in Table 3 below and has also been updated to include significant flood events since 2008 when the previous SFRA was published.
Location Year of flood Details of affected area
Levels and Moors December Heavy prolonged rainfall led to extensive flooding across the 2013 to Levels an Moors affecting property and agricultural land. During February 2014 January Southern England experienced the highest rainfall since records began in 1910. The extent of the flooding led to a major incident being declared by Somerset County Council and Sedgemoor District Council. Key settlements affected included Moorland, Fordgate and Westonzoyland. The flooding had a significant affect on transport routes with many communities cut off due to road flooding and disruption to railway services on the Bristol to Exeter line between Bridgwater and Taunton. Extensive areas of low lying agricultural land were inundated throughout the event including North Moor, Curry and Hay Moors, and Greylake.
Levels and Moors November Wet weather throughout April to October had led to saturated and surrounding 2012 ground and exceptionally high groundwater levels. Up to villages 150mm fell across some areas through late November leading to extensive flooding across the Levels and Moors with associated road closures. Significant property flooding also occurred in Cannington in the area to the south of the brook. Flooding was also reported in other settlements including Otterhampton and Combwich.
Wedmore and September A month's worth of rain fell overnight on the 24th September surrounding 2012 resulting in flooding to extensive communities in the Cheddar villages valley. In Wedmore flooding occurred on Guildhall and Gramball Lanes with 3ft of water reported in some properties. Flooding also affected some areas of Cheddar, Blackford, Brent Knoll and Mark.
9 Scott Wilson, 'Sedgemoor District Council Level 1 Strategic Flood Risk Assessment', 2008, p.24. Level 1 Strategic Flood Risk Assessment Sedgemoor District Council 2015 21
Data Collection and Methodology 4
Location Year of flood Details of affected area
Nether Stowey 2000 Surface water from roads affected properties on Mount Road and St Mary’s Street.
Nether Stowey 2000 Fluvial flooding from the brook affected properties on Castle Street and Pooles Close.
Bridgwater April 1998 Tidal and fluvial flooding affected properties and land. Number and location of properties affected unknown.
Levels and Moors August 1997 Dramatic summer flooding not seen in Somerset since July 1968. Curry Moor, West Moor and Hay Moor suffered damage to grassland. Trapped floodwater caused vegetation to rot causing serious pollution.
Burnham-on-Sea January 1983, Tidal flooding from overtopping affected buildings and transport January and routes. Oxford Street, North Esplanade and South Esplanade February 1990 specifically affected. Number of properties affected unknown.
Levels and Moors December Very high tidal levels resulted in overtopping of sea defences 1981 at Pawlett, Combwich, Burnham-on-Sea. Approximately 3570 hectares were inundated with 1072 dwellings and commercial properties flooded (in the then 'Somerset Land Drainage District'). Most severe tidal event in this location in the 20th Century.
Cheddar July 1968 Summer storm affecting Somerset, in particular Cheddar Gorge became a raging torrent of water, mud and rocks leaving a 9m hole in the road and causing 35 people to lose their homes.
Levels and Moors October/ Prolonged rainfall caused widespread flooding across the November Levels and Moors. Floodwater remained for approximately 86 1960 days.
Table 5 Significant historic flood events.
Flood Defences
4.25 The flood defence data from the previous level 1 SFRA was updated using information from the Risk Management Authorities. The location of structures and flood defence assets within Sedgemoor District are shown in Figure 5.
4.26 Since the previous SFRA new flood mapping has also been undertaken that takes into account flood defences. The 'Risk of Flooding from Rivers and Sea' (previously known as NAFRA) shows the chance of flooding taking to account defences, split in 50m by 50m squares (cells). Each cell is 22 Sedgemoor District Council 2015 Level 1 Strategic Flood Risk Assessment
4 Data Collection and Methodology
allocated one of four risk likelihood categories, ranging from high (1 in 30 or greater return period) to very low (less than 1 in 1000 return period). This mapping is particularly useful as it considers the height, type and condition of each defence, validated using local expertise. Each cell is also assigned a suitability rating to indicate at what scale is it generally appropriate to use the data, given that the quality of the modelling and input data varies across the country.
4.27 The 'Risk of Flood from Rivers and Sea' mapping has therefore been included in Figure 5 to give a useful indication of the standard of protection and the condition of defences. It is important to highlight that as this mapping takes into account defences it should not be used for Sequential Test purposes. In the first instance the Sequential Test should ignore the presence of defences as it should not be assumed that defences can be maintained in perpetuity. The 'Flood Map for Planning' (Figure 2) should be used for undertaking the Sequential Test in the first instance.
Residual Risk
4.28 Figure 5 therefore shows the location of defences and structures within Sedgemoor District Council that provide mitigation from flood risk and/or have a role in water level management. The structures shown range from natural embankments to man-made embankments reinforced with sheet piling or concrete structures. It is important to be aware that railway and major roads may also provide de facto flood defence structures that are not necessarily maintained as flood management structures.
4.29 A detailed assessment of residual risk that remains behind defences has not been undertaken and is beyond the scope of a level 1 SFRA. Although the ‘Risk of Flooding from Rivers and Sea’ mapping included on Figure 5 does take into account the condition of defences. The requirements for a detailed assessment of residual risk as part of a level 2 SFRA update will be scoped after the Council has initially used the level 1 SFRA to Sequential Test different strategic development options. Where strategic development cannot be directed outside of the Flood Zones further level 2 SFRA work is likely to be necessary.
Surface Water Flooding
4.30 Since the previous SFRA there has been significant additional mapping that has been undertaken in relation to surface water flooding, largely implementing the recommendations of the Pitt Review.
4.31 The latest version of this is called the 'Updated Flood Map for Surface Water' which was produced in 2013 by the Environment Agency, working with Lead Local Flood Authorities. This was the third national surface water map produced by the Environment Agency as part of their Strategic Overview role in flood risk management. The main aim was to help establish a consistent understanding of surface water flooding across England and Wales.
4.32 The new mapping improves significantly upon previous maps in terms of using better data and modelling techniques and using local information where available. The mapping provides information on extent, depth, velocity and hazard of for a range of return periods (1 in 30, 1 in 100 and 1 in 1000).
4.33 Although the mapping is an improvement it is important to be a aware of the limitation of the mapping. For example assumptions are made regarding the representation of buildings and structures in the model and as it is based principally on a digital terrain model it may not be accurate in some urban areas where the drainage regime is heavily influenced by the man-made sub-surface drainage network. Nor does the model take into account any affects from tide-locking which is particularly relevant in Sedgemoor. Essentially the modelling picks out natural drainage channels, rivers and low Level 1 Strategic Flood Risk Assessment Sedgemoor District Council 2015 23
Data Collection and Methodology 4 areas in floodplains to indicate where flooding is most likely to occur as a result of local rainfall. It does not show flooding that occurs from overflowing watercourses, drainage systems or public sewers caused by catchment-wide rainfall events or river flows.
4.34 Given these limitations the mapping includes a suitability category which gives an indication of the scale that the data can be used reliably at. Across the majority of the Sedgemoor area the suitability category is 'county to town'. This means that the mapping can be used for comparing risks between settlements and identifying the approximate extend of flooding, however it is unlikely to be reliable at the local level and very unlikely to be reliable for identifying individual properties at risk. Overall in Sedgemoor the mapping is not suitable for use at the individual property scale.
4.35 Given the above it is important that this surface water mapping is not used in isolation and instead used in conjunction with other evidence such as the historic point and polygon data described previously. Users should apply local knowledge to assess how suitable the map is for their needs. The mapping is however useful for SFRA purposes in providing the Council with a strategic overview of surface water flooding for planning purposes, as well as assisting the Lead Local Flood Authority in their duties relating to surface water flood risk.
Flood from Public Sewers
4.36 Wessex Water is the statutory water undertaker and is responsible for the public sewer systems within Sedgemoor District. To meet legal commitments set by OFWAT Wessex Water maintains a register of historical sewer flooding events called the DG5 register. This defines internal flooding as 'flooding that enters a building or passes below a suspended floor'. Properties registered are those that have suffered or are likely to suffer internal flooding from public foul, combined or surface water sewers, due to the sewerage system being overloaded. The DG5 register seeks to capture those properties subject to frequent internal flooding due to hydraulic overload (i.e. 1 in 10 return period).
4.37 To help inform this SFRA update Wessex Water have reviewed the register to help identify any problematic areas affected by sewer flooding within the study area. This mapping is available in Appendix 2. This shows a number of locations in Bridgwater, Cannington and Highbridge that are on the register. For information it is not possible to make the data available at a more detailed level given the need to avoid property blight. The mapping therefore indicates the settlement location of properties but does not identify the number of properties, actual location within the settlement or frequency/timing of flooding.
4.38 The DG5 register as well as other data Wessex Water collects helps to inform their extensive improvement program to address existing problems in the system. The DG5 register should also be used in conjunction with any sewer flood records provided within FRIS and Section 105 databases provided by the Environment Agency (as shown in Figure 3).
Groundwater
4.39 Groundwater flooding occurs when water levels rise above surface water elevations and causes spring resurgence. This type of flooding is dependent on the underlying geological strata and the antecedent conditions. Groundwater flooding may occur days to weeks after a rainfall event due to the time taken for water to flow through underlying aquifers. Conversely, it may also take weeks or months to dissipate because groundwater flows are typically less than surface water flows and water levels will take a greater time period to return to normal conditions.
4.40 Information on groundwater flooding is limited within Sedgemoor District, in part, due to the underlying substrate. It is noted that the Parrett Catchment Flood Management Plan and the North and Mid Somerset Catchment Flood Management Plans do not identify groundwater as being a 24 Sedgemoor District Council 2015 Level 1 Strategic Flood Risk Assessment
4 Data Collection and Methodology
significant source of flooding within the study area. Groundwater flooding from springs emerging at the foot of permeable geology slopes have the potential to cause problems in the Cheddar area. This is associated with the Mendip escarpment. However apart from this area reference to Goundwater and Source Protection Zone mapping produced by the Environment Agency indicate that Sedgemoor is predominantly underlain by low permeability aquifers which are unlikely to be a source of significant groundwater flood risk.
4.41 Since the previous SFRA new 'Areas Susceptible to Groundwater Flooding' mapping has become available. This can be viewed in Figure 7. This mapping is a strategic scale map showing groundwater flood areas on a 1km square grid. It was developed specifically by the Environment Agency for use by Lead Local Flood Authorities in Preliminary Flood Risk Assessments, required under the Flood Risk Regulations. The mapping shows the proportion of each 1km grid square where geological and hydrogeological conditions show that groundwater might emerge. As shown on Figure 7 the susceptible areas are represented by a percentage split into 4 separate categories.
4.42 In terms of use of this new mapping it is important to state that it only shows the areas susceptibility to groundwater emergence. It does not show the likelihood of groundwater flooding actually occurring. The Environment Agency has not assessed the mapping as appropriate for any use other than information for Preliminary Flood Risk Assessments. It is therefore provided as part this SFRA update from completeness, but should not be relied upon as an indicator of groundwater flooding for planning purposes in the absence of any other local of historical evidence. Overall, as concluded by the previous SFRA, the risk from groundwater flooding is relatively minor in Sedgemoor when considered in proportion to other risks such as fluvial and tidal flooding.
Artificial Sources (Infrastructure Failure)
4.43 Flooding from artificial sources occurs when raised channels such as canals or storage features including reservoirs become overwhelmed as a result of dam or bank failure. Regular inspection and maintenance means that the likelihood of failure is low. However, in the event of a breach, the consequences can be significant.
4.44 No records of flooding associated with artificial sources have been identified however it is still important to map the risk where possible given the high consequence in the event of a failure.
4.45 The previous level 1 SFRA identified the Bridgwater-Taunton canal and reservoirs as the principle artificial sources of flooding. Since then as one of the actions of the Pitt Review the Environment Agency has produced reservoir inundation maps for all raised reservoirs registered under the Reservoirs Act 1975. The maps provide an indication of the area that could be affected by reservoir flooding.
4.46 There are seven operational impounding reservoirs located in Sedgemoor’s area that may present a flood risk due to failure or overtopping. These are a mixture of reservoirs that are used for water resources/supply purposes and ones which perform a flood risk management role. They are summarised in the following table.
Reservoir Reservoir Undertaker Maximum Capacity (m3) Surface Area Height (m2)
Ashford Wessex Water 5.62 50,000 29,000
Cheddar Bristol Water 14 6,137,000 956,000 Level 1 Strategic Flood Risk Assessment Sedgemoor District Council 2015 25
Data Collection and Methodology 4
Reservoir Reservoir Undertaker Maximum Capacity (m3) Surface Area Height (m2)
Durleigh Wessex Water 9.82 959,000 314,000
Hawkridge Wessex Water 22.42 864,000 129,600
Beer Wall/North Environment Agency 0.70 1,130,800 2,542,100 Moor
Curry Moor Environment Agency 3.40 11,283,000 8,240,000
South Lake Environment Agency 1.60 785,000 1,630,000
Table 6 Reservoirs in Sedgemoor registered under the Reservoirs Act 1975.
4.47 The extent of potential inundation from these sources are indicated by the Environment Agency’s reservoir mapping is shown in Figure 8. The mapping was originally produced for Local Resilience Forums to aid emergency planners but are also relevant to planning in terms of considering all sources of flooding. It is however important to be aware of the limitation. For example the breach modelled represents a credible worst case scenario and is therefore a generic dam failure to ensure consistency in the mapping. In reality there are in fact a range of dam failure scenario’s which would result in differing flood extents. It is important to also highlight that the maps do not show risk to individual properties. Nor do the maps reflect the structural integrity of the dam or the chance of it failing. They therefore cannot be used to assess likelihood or probability, bearing in mind however that these can be considered very low probability events given the requirements for undertakers to maintain the structures in accordance with the Reservoir Act 1975. It is also not possible to fully assess the accuracy of the maps given that there are no historic records to validate the mapping against.
4.48 It is worth noting from review of the mapping that given the route of reservoir inundation essentially follows the topography of the area, the majority of areas shown as being within the inundation areas are already considered to fall within either Flood Zone 3a or 3b. The exceptions to this are the inundation areas for Cheddar and Hawkridge reservoirs where the inundation areas spread slightly wider than the Environment Agency Flood Map for Planning. Given site specific Flood Risk Assessments need to consider all sources of flooding developers should use the available mapping and table 6 above to liaise with reservoir undertakers where necessary.
4.49 For information Cheddar reservoir two received consent recently and may be constructed in due course. The mapping may therefore need to be updated in the future if and when this is delivered. 26 Sedgemoor District Council 2015 Level 1 Strategic Flood Risk Assessment
5 Broad-scale Assessment
Overview
5.1 The updated mapping described in the previous section has been used to undertake a broad-scale flood risk review within the study area. This is followed by more focused settlement specific assessments in the next section. The broad-scale flood risk is detailed in the matrix below and is intended to provide an initial 'at a glance' overview of flood risk within the study areas main settlements. The flood risk matrix indicates if the settlement has any land that falls within Flood Zone 1, 2, 3a or 3b and identifies if any other sources of flooding have been experienced. It should be used with caution given flood risk can vary significantly within an individual settlement, therefore further information is available in the focused assessments. Where a settlement transcends a number of different Flood Zones the highest risk classification has been used.
5.2 This broad-scale assessment has been undertaken based on the settlement hierarchy and boundaries detailed in the current Core Strategy, including the main Towns, Key Rural Settlements and Other Sustainable Settlements. Further updates to the matrix will be undertaken if the settlement hierarchy changes significantly as part of the Local Plan Review.
Settlement Settlement Flood Zone Classification Other Sources Classification
Principal Bridgwater Flood Zone 3a Yes Town
Town Burnham-on Sea & Highbridge Flood Zone 3a Yes
Key Rural Ashcott No No Settlement Axbridge No Yes
Berrow Flood Zone 3a Yes
Brent Knoll Flood Zone 3a Yes
Cannington Flood Zone 3b Yes
Cheddar Flood Zone 3a Yes
East Huntspill Flood Zone 3a Yes
Lympsham Flood Zone 3a Yes
Mark Flood Zone 3b No
Nether Stowey No Yes
North Petherton Flood Zone 3b Yes
Pawlett No Yes
Puriton Flood Zone 2 No
Wedmore No Yes
Wembdon Flood Zone 3a Yes Level 1 Strategic Flood Risk Assessment Sedgemoor District Council 2015 27
Broad-scale Assessment 5
Settlement Settlement Flood Zone Classification Other Sources Classification
Westonzoyland Flood Zone 3a No
Woolavington No Yes
Other Catcott No Yes Sustainable Settlement Chilton Polden No Yes Combwich Flood Zone 3b No
Cossington No Yes
East Brent Flood Zone 3a Yes
Edington No No
Middlezoy Flood Zone 2 No
Othery Flood Zone 3a No
Shipham No No
Spaxton No Yes
Weare Flood Zone 3b No
West Huntspill Flood Zone 3a No
Table 7 Broad-scale Assessment Matrix
5.3 The broad-scale assessment alongside the mapping illustrates the scale of flood risk in Sedgemoor District. Of the 31 settlements detailed above over half (19) have part of the settlement falling within either Flood Zone 2, 3a, or 3b. The vast majority of the settlements (20) have also experienced some other form of flooding other than tidal and fluvial. 28 Sedgemoor District Council 2015 Level 1 Strategic Flood Risk Assessment
6 Focused Assessments
Overview
6.1 Focused assessments have been undertaken for the Districts main towns and Key Rural Settlements. These are locations which are most likely to be considered for accommodating strategic development over the plan period, based on the range and depth of services, facilities and employment opportunities they provide.
6.2 While the role and function of the District’s settlements is being comprehensively reviewed as part of the Local Plan Review, the main towns and some of the Key Rural Settlements identified below are likely to continue to be identified as the locations where strategic growth can most sustainably be accommodated. These focused assessments will therefore provide a summary of the flood risk in these locations and provide an indication of its likely implications for development. Used in conjunction with the mapping this will therefore be useful in allowing the Council to undertake the Sequential Test of development options that are identified, as well as scope any further SFRA level 2 requirements. For information Ashcott has not been included in the focused assessments given the broad-scale assessment identified it as being in Flood Zone 1 and with no evidence of other sources of flooding.
Bridgwater
6.3 The tidal River Parrett flows through the District’s Principle Town before discharging into the Severn Estuary. Tidal flood risk is by far the most significant source of flooding to the town, with all of the town east of the Parrett and much of the town to the north lying in Flood Zone 3a. To the west land is higher with much of this area located in Flood Zone 1. Functional floodplain associated with the Stockmoor Rhyne and Durleigh Brook is located to the west, however the majority of these areas are identified as green space, including the Wilstock/Stockmoor country park and the Meads transformational project. Further to the north the Reedmoor Rhyne and King Sedgemoor Drain also discharge into the Parrett.
6.4 Despite the scale of the undefended floodplain in Bridgwater the Environment Agency's 'Risk of Flooding from Rivers and Sea' mapping indicates that the majority of the town is at 'low' risk present day taking into account defences. This has also previously been shown by SFRA level 2 work undertaken in 2009. There are also long term plans in place to address climate change flood risk to the town, with the construction of a tidal surge barrier identified as the most sustainable option. It's delivery is identified as a priority in the Somerset Levels and Moors Flood Action Plan. Development has also already been contributing towards the cost of a barrier since 2009, firstly through a Section 106 tariff system, and now via the the Council's Community Infrastructure Levy. Level 1 Strategic Flood Risk Assessment Sedgemoor District Council 2015 29
Focused Assessments 6
6.5 In terms of historic events significant tidal flood events are recorded in 1957, 1974 and 1981, when flood defences offered a poorer standard of protection. A notable event was also recorded on 15/04/1998 where both fluvial and tidal flooding sources affected the Broadway and Salmon Parade areas, although the number of people and properties affected is unknown. Some fluvial flood risk also affected some areas of the town during the November 2012 and Winter 13/14 events, including the Somerset Bridge area. Picture 2 Flooding on Broadway 1974 (Source: Environment Implications on development Agency) potential
6.6 While being at flood risk Bridgwater is the District's Principle Town and will therefore certainly be expected to accommodate a significant proportion of strategic development to meet other sustainability objectives of the plan. Sequentially, opportunities still remain to direct new development to low risk areas in the west of the town, but even with this it is highly likely that a proportion of new development may still need to be located in the towns tidal flood risk areas. This is due to the need to balance flood risk with other sustainable development objectives. For example the Bridgwater Vision sets out a framework for regeneration of the town and what needs to be done to meet the needs of people and business going forward.
6.7 In this respect Bridgwater is in a relatively good position in generally having a good standard of protection present day and a longer term solution to address climate change risk in the form of the Bridgwater barrier. New development in Bridgwater has previously contributed towards delivery of the barrier through a tariff approach and will continue to do so in the future through CIL. Any development options taken forward in flood risk areas would still need to be with a thorough understanding of climate change implications and residual risks to enable the Council to undertake the Exception Test. Once development options are Sequentially Tested the need to understand this through any further SFRA level 2 work will be considered in consultation with the Environment Agency.
Burnham-on-Sea & Highbridge
6.8 Like Bridgwater, tidal flood risk is the main source of flooding to Burnham-on-Sea & Highbridge. All of Highbridge and almost all of Burnham-on-Sea fall within tidal Flood Zone 3a. The River Brue is located along the southerly edge of Highbridge, which is tidal only up to Highbridge Clyse. Due to the benefit of tidal defences much of the built up area of the settlement is currently identified as 'low risk' according to the Environment Agency's 'Risk of Flooding from Rivers and Sea' mapping. The previous SFRA Level 2 undetaken for the area does however highlight the significant inundation that could result for breach of defences, and the level of overtopping that may occur in the long term if defences are not improved sufficiently to keep pace with climate change. 30 Sedgemoor District Council 2015 Level 1 Strategic Flood Risk Assessment
6 Focused Assessments
6.9 In terms of historic events there are several recorded flood incidents that are from both tidal and surface water sources. Notable events of tidal flooding include 1979, 1981,1983 and 1990. These typically affected Oxford Street and North/South Esplanade. Surface water incidents have been recorded on North/South Esplanade, Highbridge Road and near to the hospital. Extent, depth and duration of these events is unknown.
Implications on development potential
6.10 While currently well defended tidal flood risk is clearly a major Picture 3 Burnham-on-Sea during the 1981 event (Source: constraint on development in this Environment Agency) settlement. There are little or no opportunities to sequentially direct new development outside of Flood Zone 3a. In terms of future climate change risk to any new development the current Shoreline Management Plan commits to a 'hold the line' approach in the short, medium and long term, given the towns important role and economic value. Flood risk improvements are also expected to be delivered through the Boatyard and Brue Farm development sites. However unlike Bridgwater there is not yet a clear coherent strategy in place for the town in terms of what long term flood defence improvements will actually entail and in what way any future development proposals would need to contribute. It is likely that a substantial increase in the seawall would be required which would clearly also have implications on the towns amenity value. The above considerations will need to be taken into account when considering what proportion of the District's development requirements should be directed to Burnham-on-Sea & Highbridge, as well as Sequentially Testing specific development options that come forward. Any strategic development taken forward may require an update to the SFRA level 2 to understand residual and climate change risk, as well as establishing an understanding of future improvements to defences required to ensure the development remains safe over its lifetime.
Axbridge
6.11 The development boundary of Axebridge falls within Flood Zone 1. To the south of the settlement lies Flood Zone 3b associated with the floodplains of the River Axe and Cheddar Yeo, however this does not extend as far as the built up area. There are a couple of reported incidence of flooding from fluvial sources in the area of 'The Square' in Axebridge in 1995 and November 2012. However there are not details of depth, extent or duration. Level 1 Strategic Flood Risk Assessment Sedgemoor District Council 2015 31
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Implications on development potential
6.12 Other than the lower moorland south of the settlement Axebridge is relatively unconstrained in terms of flood risk compared to other settlements in the District. Any development options that are considered are likely to fall within Flood Zone 1.
Berrow
6.13 Given its location north of Burnham-on-Sea the principle flood risk remains tidal flooding from the Severn Estuary. Much of the existing built up area of Berrow actual falls within Flood Zone 1, being built essentially on the landward side of Berrow Dunes which offer flood protection. The village is however heavily constrained with Flood Zone 3a to the east, where the land is lower, and the dunes system to the west. In terms of other sources of Picture 4 Flooding to the south of Axebridge during 2012 flooding their is one report of surface (Source: Environment Agency) flooding to Red Road in 1979, due to blocked gullies.
Implications on development potential
6.14 While the built up area is in Flood Zone 1 the settlement is essentially surrounded by high flood risk areas. The dunes do currently offer a standard of protection but it is important to highlight that while the Shoreline Management Plan policy is to actively manage the dunes and 'hold the line' in the short term, this may in the long term become a management realignment policy subject to further studies. Given the dunes do offer a standard of protection there is however still potential for development of an appropriate scale to come forward where justified based on local need. It would need to be understood how development would remain safe throughout its lifetime given the long term Shoreline Management Plan policy.
Brent Knoll
6.15 Located further inland Brent Knoll is a linear shaped village stretching along both sides of Brent Street and Burton Row, lying at the foot of the hill of the same name. Much of the low lying areas of Brent Knoll fall within Flood Zone 3a, bordered by some areas of Flood Zone 2. To the south end of the village there are however a number of properties located in Flood Zone 1 where the settlement has started to extend onto high ground at the base of the hill.
6.16 While further inland, the principle source of flood risk in Brent Knoll is still tidal flooding. There are however a number of records of surface water flooding in 1996 along Brent street and Crooked Lane. 32 Sedgemoor District Council 2015 Level 1 Strategic Flood Risk Assessment
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Implications on development potential
6.17 Brent Knoll is a relatively small settlement but a popular commuter and retirement village with a number of services for local residents. While still heavily constrained by the tidal floodplain it does benefit from the tidal defences, therefore there may still be some opportunities for small scale development to come forward in the lower risk areas of the settlement.
Cannington
6.18 Located to the west of Bridgwater Cannington is located on higher ground and therefore not at tidal risk like the Districts towns. The Cannington Brook and an associated functional floodplain does however flow through the village and has resulted is significant flood events in the south half of the village. Most notable flooding in November 2012 which resulted in road and property flooding including in the areas of Main Road, Lonsdale, Southbrook and Southbrook Close.
6.19 In terms of other sources of flooding there are also a number of reports of surface water flooding, most likely as a result of drainage being unable to discharge into the Brook. For example there are five recorded incidents from 2002 that indicate water was unable to enter the existing flood relief channel, causing problems for traffic. In addition, storm sewers were also noted as surcharged on the same date.
6.20 For information following the November 2012 flooding the Environment Agency has recently received planning permission for an improved flood relief scheme that should address the existing fluvial flooding problems in Cannington.
Implications on development potential
6.21 In terms of accommodating development Cannington has a good range of services and facilities for its size. Whilst flood risk from the Cannington Brook is a constraint for some areas of the village the floodplain is relatively narrow meaning there are still plenty of opportunities to locate development in Flood Zone 1 areas.
Cheddar
6.22 The Cheddar Yeo's source is to the north east of Cheddar from Springs near Charterhouse. It then disappears under the Mendip Hills before reappearing at Gough's Cave. It then flows down the gorge and through the village. An area of floodplain is therefore associated with the river, with a number of properties either side of the channel falling within Flood Zone 3a. It is however a relatively narrow floodplain in the context of the wider settlement, located principally Flood Zone 1.
6.23 The most significant flood event in Cheddar was during the summer storms of 1968. Torrential rain led to a flow of water that swept large boulders down the gorge, damaging property and washing away vehicles. Other historical incidents include a number of reports of surface water flooding in various locations and two incidents of sewer flooding in 1995. The November 2012 flooding led to the closure of both Gough's Cave and the road up the gorge.
Implications on development potential
6.24 Whilst there is clearly a risk from the Cheddar Yeo and flood flows travelling down the gorge during heavy rain much of the village lies outside of the floodplain in Flood Zone 1. Sequentially there are therefore significant opportunities to locate any strategic growth away from flood risk areas. Given numerous historical reports in relation to surface water and sewer flooding the use of sustainable drainage methods in any new development is likely to be a priority. Level 1 Strategic Flood Risk Assessment Sedgemoor District Council 2015 33
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East Huntspill
6.25 Situated on the low lying Huntspill level the village of East Huntspill lies wholly within Flood Zone 3a. It is considered to be at both tidal and fluvial flood risk although the Environment Agency's 'Risk of Flooding from Rivers and Sea' shows it to fall within a 'low' category taking into account existing flood defences and structures. The village therefore benefits significantly from the coastal defences and the numerous assets (e.g. Gold Corner pumping station) that manage water levels across this area of the Levels and Moors.
6.26 In terms of historical flood events the only records are from the 2012 event. This includes some fluvial flooding in the Bason Bridge area near the river Brue, and some road flooding from blocked gullies around Nut Tree Close.
Implications on development potential
6.27 Whilst defended East Huntspill still lies wholly in Flood Zone 3a. It may therefore be difficult to justify any significant development in this location over more sequentially preferable locations. That said East Huntspill is well-connected and offers a reasonable level of services and facilities given its size. Smaller scale development, justified based on meeting local needs, may therefore be appropriate.
Lympsham
6.28 Lympsham falls wholly within the tidal floodplain, designated Flood Zone 3a. The only exception to this is the area near St Christopher's Church which is located on slightly higher ground. Like East Huntspill however the Environment Agency's 'Risk of Flooding from Rivers and Sea' shows it to fall within a 'low' category taking into account existing flood defences and structures.
6.29 In terms of historical records there were reports of some houses flooded during the 1968 event, although there are no details of the scale and location of the flooding. There were also some reports of surface water flooding around the entrance of the First School during the November 2012 event.
Implications on development potential
6.30 Like with East Huntspill the scale of Flood Zone 3a in Lympsham is likely to make it difficult to justify significant development on Sequential test grounds. However an active community and a number of local services mean smaller scale development to meet local needs may be justified.
Mark & Mark Causeway
6.31 Mark and Mark Causeway lie on the Levels and Moors. The Mark Yeo runs through the main village and acts as a connection between the River Brue to the south and River Axe to the North. Some parts of the village are heavily constrained by areas of Flood Zone 3b. These areas are also classified as 'high' risk by the Environment Agency's 'Risk of Flooding from Rivers and Sea' mapping, even taking into account defences. Other areas of the village however do lie within Flood Zone 2 and Flood Zone 1, particularly to the west where grounds levels are slightly higher in the area of the Church.
6.32 In terms of other sources of flooding surface water flooding along Vole Road and in isolated parts of Mark Causeway were recorded during the November 2012 flood event. 34 Sedgemoor District Council 2015 Level 1 Strategic Flood Risk Assessment
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Implications on development potential
6.33 Despite the flood risk in the area Mark is a key settlement along the B3139 route and has a range of basic facilities and local employment opportunities. Significant areas of the settlement are still identified as falling within Flood Zone 1 and therefore there is potential to accommodate an appropriate scale of development.
Nether Stowey
6.34 Unlike the majority of the District's settlement Nether Stowey is well located in terms of avoiding fluvial and tidal risk, lying on higher ground in the foothills of the Quantock Hills AONB. It therefore falls wholly within Flood Zone 1.
6.35 The principal flood risk in Nether Stowey is instead from other sources, mainly from surface water flooding and ordinary watercourse fluvial flooding from the small brook that runs through the village. Figure 3 shows a significant cluster of recorded incidents in the settlement. These are mainly attributed to the Autumn 2000 events although a number were also recorded during the November 2012 event. The main areas affected were St Mary's Street, Castle Street and Mount Road, although the extent and duration of property flooding is unknown.
Implications on development potential
6.36 Flood risk is unlikely to be a significant constraint to development given that the majority of recorded incidents are located in the main built up area in the centre of the village. There may however be the opportunity for any new development to improve or at least not exacerbate existing flood risk problems elsewhere in the village. For example through the use of Sustainable Drainage Systems. This should therefore be seen as a particular priority for development coming forward in the area.
North Petherton
6.37 North Petherton has an ordinary watercourse that runs west to east through the settlement past a number of residential properties, St Mary's Church and the Community Primary School, before discharging into Hay Moor. An area of Flood Zone 3b is associated with the stream affecting properties in close proximity. There are no raised defences associated with the watercourse and there are reports of its channel capacity being exceeded and flooding surrounding areas, including in the Chruch Walk area near Hammet Street. In 1984 bank failure resulted in a bockage at Fore Street bridge, causing fluvial flooding upstream in the Watery Lane area.
6.38 In terms of other sources of flooding there is a recurring incident of flooding on Mill Street over a 20 year period caused by a sewer blockage. This incident looks to have been last reported in 1995 therefore the sewerage undertaker may well have since addressed this problem.
Implications on development potential
6.39 North Petherton is one of the District's larger Key Rural Settlements and offers a significant range and depth of facilities for its population as well as surrounding smaller villages such as North Newton. While a number of areas of the town are at risk from fluvial flooding the vast majority of the rest of the built up area is located in Flood Zone 1. Flood risk is therefore not expected to be a significant constraint on any future development. Level 1 Strategic Flood Risk Assessment Sedgemoor District Council 2015 35
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Pawlett
6.40 The village a Pawlett just north of Bridgwater is located the slightly higher ground of Pawlett Hill, and therefore falls within Flood Zone 1. The area around the village, including the A38 access is however located in tidal Flood Zone 3a.
6.41 In terms of other recorded incidents no major flooding has been reported. There are some reports of surface water flooding on Chapel Road during heavy rain at various times, but no properties were affected.
Implications on development potential
6.42 Pawlett is located in Flood Zone 1 and therefore there are no significant flood risk constraints on bringing development forward within the settlement boundary. The tidal Flood Zone 3a areas surrounding the village may however constrain further development adjacent to the development boundary in certain locations. In terms of the Local Plan review the fact that Pawlett could potentially become a 'dry island' during a major tidal flood event, with limited access of Picture 5 Flooding at Stretcholt just north of Pawlett during the egress, should also be considered 1981 tidal event (Source: Environment Agency) in terms of the scale of development that may be appropriate.
Puriton
6.43 Located on the westerly end of the Polden Hills almost all of the village of Puriton is located within Flood Zone 1. The only exception to this is in the north west corner of the village where it drops down onto Puriton level in the direction of the Royal Ordnance Factory. In this location there are small areas of Flood Zone 2, these are however unlikely to be a significant constraint on development in the context of the wider village. Other than some minor road flooding due to blocked gullies there are no reported incidents of flooding from other sources in the village.
Implications on development potential
6.44 Puriton is a popular residential village with a good range of facilities and very well connected to surrounding settlements and the strategic road network. Flood risk should not be a significant constraint on bringing new development forward either within or adjacent the development boundary. 36 Sedgemoor District Council 2015 Level 1 Strategic Flood Risk Assessment
6 Focused Assessments
Wedmore
6.45 Wedmore is situated on raised higher ground in the Somerset Levels, between the River Axe and River Brue. This area is often called the Isle of Wedmore. The settlement is therefore located in Flood Zone 1 according to the Environment Agency's Flood Map for Planning.
6.46 The village has however experienced flooding from other sources, including fluvial flooding from an ordinary watercourse and surface water flooding. A stream runs from south west to north east through the centre of the village, passing over a number of weirs and is culverted in some places. Fluvial flooding from this watercourse has been reported in 1979, 1995, 1996, 1997 and 2012 in the Guildhall Lane area of the village. Other areas affected include the eastern end of Church Street where channel capacity was exceeded where the stream enters a culvert. Numerous occurrences of surface water flood have been reported elsewhere in the village, the majority pre-2000.
Implications on development potential
6.47 While located in Flood Zone 1 other local sources of flooding are clearly an important issue in Wedmore. Most of the areas affected are in the built-up centre of the village. Therefore while flood risk it is unlikely to be a constraint on bringing development forward in principle, close attention should be given to historical events and the advice of the Lead Local Flood Authority to ensure development does not exacerbate any existing local flooding problems.
Wembdon
6.48 Wembdon village adjoins Bridgwater but still retains a sense of separate identify even with the recent housing development along the Northern Distributor Road. Rising up onto higher ground to the west the majority of the Wembdon is located within Flood Zone 1. However the east of the village in the area of Wembdon Common and St George's Church does fall within Flood Zone 3a where ground levels are lower. There are a number of recorded flood incidents associated with this from 1958, 1994 and 1995 at the bottom of Wembdon Hill and along Church Road.
Implications on development potential
6.49 While some parts of the village fall within Flood Zone 3a there is little potential for development in these areas. The main development opportunities exist to high ground to the west of the village. Flood risk is therefore not considered to be a significant constraint on any further growth. Level 1 Strategic Flood Risk Assessment Sedgemoor District Council 2015 37
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Westonzoyland
6.50 Westonzoyland is located on the Somerset Levels four miles east of Bridgwater. The village is significantly constrained by both tidal and fluvial flood risk. The north edge of the village is designated as Flood Zone 3b associated with the King Sedgemoor Drain which has an important flood risk management role in storing and conveying flood water from the levels towards the Severn Estuary. The majority of the remainder of the village lies with Flood Zone 3a although there are some pockets of higher ground designated as Flood Zone 1, Picture 6 Flood Defences in place in Westonzoyland during the particularly in the centre and west of Winter 2013/14 event (Source: Environment Agency) the village.
6.51 The impact of fluvial risk was shown during the Winter 2013/14 event when rising waters levels posed a risk to the Grays Avenue area to the west of the village. Through the Flood Action Plan this has led to an Environment Agency scheme to provide a flood defence bund in this location to protect against future events. Flooding was also reported along Liney Road towards the airfield, and in the South Moor area along Lake Wall where the Horsey Moor Drain (also known as the River Penzoy) came out of bank.
6.52 There are no other reported incidence of flooding from other sources.
Implications on development potential
6.53 The land around Westonzoyland is constrained by floodplain and therefore there are limited opportunities to accommodate significant additional growth. There are a number of pockets of Flood Zone 1 within the settlement boundary and to the east of the village which may present some opportunities for smaller scale developments that meet local needs.
Woolavington
6.54 Woolavington is a popular commuter village located on the Polden Hills between Puriton and Cossington. Since the previous SFRA the Environment Agency Flood Map for Planning has been revised which now shows the whole of the settlement falling within Flood Zone 1. To the north of the village lies Woolavington Level which falls within Flood Zone 3a, associated with the River Huntspill.
6.55 In terms of other sources of flooding there is a report of surface water flooding in 1968 in the Lower Road area. At the time this looks to have been attributed to a inadequate culvert under the road.
Implications on development potential
6.56 Woolavingon falls on higher ground in Flood Zone 1 and flood risk is not considered to be a significant constraint on development. 38 Sedgemoor District Council 2015 Level 1 Strategic Flood Risk Assessment
7 Developer Guidance
Overview
7.1 The assessment of flood risk at the planning application stage is a fundamental consideration and needs to take into account the scale and type of development proposed. Understanding the flood risk to and arising from development is important in managing the risk to people and property. The effects of climate change are expected to exacerbate future flood risk, therefore developers need to demonstrate how their proposals will remain safe throughout the lifetime of the development.
7.2 A site specific Flood Risk Assessment (FRA) should aim to refine the more strategic information available through either the SFRA or from Risk Management Authorities. This should inform the location, layout and design of development, including incorporating mitigation measures where necessary.
Sequential Test Requirements
7.3 Utilising the SFRA the Local Plan review will undertake a Sequential Test for strategic development sites that it looks to allocate for different uses. For developments brought forward by developers on unallocated sites the Local Planning Authority will undertake the Sequential Test when determining the planning application, using evidence provided by the developer. For developers progressing sites in flood risk areas it is their responsibility to demonstrate that there are no reasonably available sites at lower flood risk where the development could alternatively be located.
7.4 Like policy D1 in the current Core Strategy the new Local Plan will set the context for undertaking the Sequential Test at the planning application stage, taking into account wider sustainability considerations. This will therefore include, for example, limiting the area of search for undertaking the Sequential Test where this is justified in line with the wider spatial strategy and other sustainability considerations.
FRA Requirements
7.5 The NPPF (footnote 20) indicates clearly in what instance FRA’s are required. The associated Practice Guidance provides guidance on the scope and content of FRA’s, including links to further guidance on the Environment Agency’s website. Developers should pay particular attention to the vulnerability classifications detailed in the Practice Guidance. This indicates for different development vulnerabilities where the Exception Test needs to be passed and in what locations development is not permitted in principle.
7.6 In terms of additional local guidance developers in Sedgemoor should be aware that the Environment Agency has issued Local Flood Risk Standing Advice (LFRSA) to the Council. This was issued given the specific flood risk issues in the Sedgemoor area, allowing a pragmatic approach to the assessment and mitigation of flood risk for specific areas of the District. This Local Standing Advice is published on the Council’s website and should be referred to instead of the National Flood Risk Standing Advice. Using the LFRSA helps to:
decide when and why to consult the Environment Agency on a planning application;
identify the types and locations of development for which the Environment Agency has provided Local Standing Advice;
assess the particular Local Standing Advice which is applicable (the Council will not need to consult the Environment Agency in such cases). Level 1 Strategic Flood Risk Assessment Sedgemoor District Council 2015 39
Developer Guidance 7
7.7 The Environment Agency continues to provide case-by-case advice to the Development Management team at Sedgemoor District Council when the LFRSA indicates the need for consultation.
Other Consent requirements
7.8 Developers should be aware that in addition to obtaining planning permission other consents relevant to flood risk management may also be required directly from the Risk Management Authorities. This includes, for example, Flood Defence Consent from the Environment Agency for works within 8m of the top of bank of a Main River, and Land Drainage Consent from the Internal Drainage Board for any works within 9m of the top of the bank of an ordinary watercourse in their area.
7.9 Developers should ensure that any planning work, including preparing FRA's and determining the layout and design of development, is undertaken in parallel with an understanding of other consent requirements. This helps to avoid abortive work and delays in bringing developments forward. 40 Sedgemoor District Council 2015 Level 1 Strategic Flood Risk Assessment
8 Development Site Drainage
Principles
8.1 Traditionally, built developments have utilised piped drainage systems to manage storm water and convey surface water run-off away from developed areas as quickly as possible. Typically these systems connect to the public sewer system for disposal to local watercourses and/or treatment. Whilst this approach rapidly transfers storm water from developed areas, the alteration of natural drainage processes can potentially impact on downstream areas by increasing flood risk and reducing water quality. Receiving watercourses are therefore much more sensitive to rainfall intensity, volume and catchment land uses after a catchment or areas of a catchment have been developed.
8.2 Due to the difficulties associated with up grading sewer systems it is uncommon for sewer and drainage systems to keep pace with the rate of development/re-development and there are increasingly stringent controls placed on discharges to watercourses. As development progresses and/or urban areas expand these systems become inadequate for the volumes and rates of storm water they receive, resulting in increased flood risk and/or pollution of watercourses. Allied to this are the implications of climate change on rainfall intensities, leading to flashier catchment/site responses and surcharging of piped systems.
8.3 In addition, as flood risk has increased in importance within planning policy, a disparity has emerged between the design standard of conventional sewer systems (1 in 30 year) and the typical design standard flood (1 in 100 year). This results in drainage inadequacies for the flood return period developments need to consider, often resulting in potential flood risk from surface water/combined sewer systems.
8.4 A sustainable solution to these issues is to reduce the volume and/or rate of water entering the sewer system and watercourses.
What are SuDS?
8.5 Sustainable Drainage Systems (SUDS) are the Government's preferred method of managing surface water run-off generated by development sites. Improving the use of SuDS and there ongoing maintenance was a key recommendation of the Pitt Review following the summer 2007 floods. It is also picked up as a key theme in the Somerset Levels and Moors Flood Action Plan where a number of actions are identified to promote SuDS and reduce downstream flooding.
8.6 SuDS seek to manage surface water as close to its source as possible, mimmicking natural surface water flows arising from the site prior to development taking place. They provide opportunities to reduce the adverse impacts of traditional surface water systems, including removing pollutants from urban run-off at source and combining water management with green space and wider benefits of amenity, recreation and wildlife.
8.7 In general the cost of constructing SuDS is cheaper than conventional drainage. Above ground SuDS can usually be integrated into the urban realm as part of multi-functional space. Green infrastructure SuDS provide additional benefits which can increase adjacent property appeal and value.
8.8 A sustainable approach to surface water drainage therefore:
Manages rainfall runoff as near to where it lands as possible;
Stores surface water runoff and realises it slowly; Level 1 Strategic Flood Risk Assessment Sedgemoor District Council 2015 41
Development Site Drainage 8
Allows the runoff water to soak into the ground if suitable, slowly transporting excess water and filtering out pollutants;
Follows a hierarchy of discharge to to deal with excess runoff water; and
Requires a different design approach to traditional drainage systems.
Current Approach to SuDS
8.9 Following Pitt Review recommendations the Governments initial intention was for a separate approval to be required for SuDS from the Lead Local Flooding Authority. In 2014 the Government however consulted on a alternative planning-led approach that has since been implemented. From April 2015 the Lead Local Flood Authority are now a statutory consultee on drainage matters for planning applications for major development proposals (10+ dwellings, > 1000m2 or 0.5ha).
8.10 Alongside these change the Practice Guidance was also updated to include further advice on sustainable drainage (10). This includes guidance on operation and maintenance and that developers should aim to discharge surface water runoff as far up the hierarchy of drainage options as is reasonably practicable. For example the first option should be to infiltrate to ground, with discharge by less sustainable methods (e.g. combined sewer) only considered as a last resort.
8.11 Local Planning Authorities therefore need to now consult the Lead Local Flood Authority and satisfy themselves that the proposed minimum standards of operation are appropriate and secure through planning conditions and/or obligations the arrangements for ongoing maintenance.
8.12 In addition to changes to the Practice Guidance DEFRA has also released technical standards for the design, maintenance and operation of SuDS (11). The document provides useful guidance, including, for example, expectations in relation to peak flow and volume control. Compliance with the technical standards is expected unless there are overriding viability reasons that make compliance impractical. Developers should also be aware of the extensive guidance available from the www.susdrain.org website, including useful case studies and the comprehensive SuDS manual (12).
8.13 Surface water drainage should therefore be evaluated at the start of the design process as surface water drainage constraints and opportunities are likely to influence site layout. With the new planning led approach to SuDS the Government has encouraged Lead Local Flood Authorities to produce Local Standing Advice and guidance where appropriate to compliment the national guidance. This is particularly relevant to the Somerset area where the Flood Action Plan also identified the need to produce an easy to use online resources on SuDS, ensuring that appropriately robust standards are implemented given local circumstances (13). Given this it is likely that through the Local Plan review flood risk policies will be strengthened with regards to sustainable drainage. Somerset County Council has also been working with West of England Unitary Authorities to produce a Sustainable Drainage Developers Guide. This includes two sections. Section one provides general advice on
10 DCLG, Planning Practice Guidance, 2015, http://planningguidance.planningportal.gov.uk/blog/guidance/flood-risk-and- coastal-change/reducing-the-causes-and-impacts-of-flooding/why-are-sustainable-drainage-systems-important/ (Accessed June 2015). 11 DEFRA, Non-statutory technical standards for sustainable drainage systems, 2015. 12 CIRIA, The SuDS Manual (C697), 2007. http://www.susdrain.org/resources/ciria-guidance.html (Accessed June 2015). 13 Somerset County Council, The Somerset Levels and Moors Flood Action Plan, 2014, p. 9. 42 Sedgemoor District Council 2015 Level 1 Strategic Flood Risk Assessment
8 Development Site Drainage
SuDS best practice, while section two, prepared individual by each Lead Local Flood Authority, will provide authority-specific local advice and requirements. Somerset County Council are in the process of drafting section two which will be published in due course.
8.14 Given that local advice and requirements are in the process of being drafted it is not intended to repeat this process or provide significant detailed local SuDS advice through this SFRA. When published developers should have full regard to the local requirements identified in the Sustainable Drainage Developers Guide and any other Standing Advice that Somerset County Council issue in their role as statutory consultee on drainage.
Where can SuDS be Utilised?
8.15 The Practice Guidance sets out the hierarchy of drainage options (e.g. infiltration, surface water body, sewer) and that developers should use the most sustainable methods in the first instance. The Practice Guidance does however state that it would be helpful for Local Planning Authorities to set out those local situations where they anticipate particular SuDS systems may not be appropriate. The previous SFRA set out the suitability of different SuDS techniques across the District dependent on geology and soil type (14). These tables are included again below for information. Please be aware however that this information may soon be superseded when the Lead Local Flood Authority publishes local requirements as part of their Sustainable Drainage Developers Guide.
SuDS Permeability Geology Description Technique
Infiltration Moderate Clifton Down Interbedded sandstones, limestones and shales. or Group - Permeability is likely to be Combined Carboniferous Infiltration Limestone moderate depending on the depth to formation and Series and extent of weathering. Located in the north Attenuation of the Sedgemoor District around Cheddar/Axbridge.
Moderate Burtle Beds Islands of sands and gravels raised a few metres above the surrounding alluvium. Likely to be of moderate permeability. Dispersed locations including Westonzoyland.
Low/Moderate Blue Lias Interbedded limestones, shales, mudstones and clays. Permeability is likely to vary locally depending on the exposed geology. Located around Pawlett, Puriton and Woolavington.
Low/Moderate Blue Anchor Green, greenish-grey and dark grey siltstones, Formation mudstones and marls. Permeability is likely to vary locally depending on the exposed geology and extent of weathered material. Located around Wedmore.
14 Scott Wilson, Sedgemoor District Council Level 1 Strategic Flood Risk Assessment, 2008, p. 54. Level 1 Strategic Flood Risk Assessment Sedgemoor District Council 2015 43
Development Site Drainage 8
SuDS Permeability Geology Description Technique
Low/Moderate Mercia Predominantly red, less commonly green-grey, Mudstone Group mudstones and subordinate siltstones with thick (Keuper Marls) halite-bearing units in some basinal areas. Thin beds of gypsum/anhydrite widespread; sandstones are also present. Underlies large areas of Sedgemoor including Nether Stowey, Cannington. Within the Levels and Moors, this is overlain predominantly by alluvium.
Low Penarth Group Dark grey/black mudstones with lenticular limestones, sandstones and bone beds. Permeability will be variable depending on depth and extent of weathering. Located in the Wedmore area on higher ground.
Low Morte Slates Silvery grey slates with thin bands of sandstone. Permeability will be variable depending on the extent of weathering. West of North Petherton.
Attenuation Low Alluvium/Marine Permeability is typically low but depends on the Alluvium content of sand, silt and clay. Increased content of silt and clay will reduce effective permeability. Superficial deposits located within the floodplain. Predominates across the Levels and Moors.
Table 8 Suitable techniques dependant on geology.
SuDS Permeability Soil Geology Description Technique Association
Infiltration Moderate Blacktoft Marine Deep stoneless permeable or Alluvium calcareous fine and coarse silty Combined soils. Some calcareous clayey Infiltration soils. Flat land. Groundwater and controlled by ditches and pumps. Attenuation Moderate Crediton Permian and Well drained gritty reddish loamy Carboniferous soils over breccia, locally less Reddish stony. Steep slopes in places. Breccia
Moderate Crwbin Carboniferous Very shallow and shallow well Limestones drained loamy soils over limestone, often on steep slopes. Limestone pavement, and other rock exposures common.
Low/ Curtisden Cretaceous Silty soils over siltstone with slowly Moderate and Jurassic permeable subsoils and slight 44 Sedgemoor District Council 2015 Level 1 Strategic Flood Risk Assessment
8 Development Site Drainage
SuDS Permeability Soil Geology Description Technique Association
siltstone and seasonal waterlogging. Some sandstone similar well drained soils. Some well drained coarse loamy soils over sandstone.
Moderate Larkbarrow Devonian Reddish very acid permeable reddish loamy upland soils over sandstone. sandstone Associated loamy soils, some with a seasonal wet thin peaty surface horizon and some with thin ironpan but otherwise permeable subsoils.
Moderate Milford Devonian Well drained fine loamy reddish sandstone, soils over rock. Some steep slopes. siltstone, mudstone and slate
Moderate Newham River terrace Well drained reddish coarse and drift fine loamy soils over gravel, locally deep. Some similar soils affected by groundwater.
Moderate Nordrach Aeolian silty Well drained fine silty over clayey drift over soils, stoneless or with chert Carboniferous stones, often deep. Shallow silty limestone soils over limestone in places. Mainly on flat or gently sloping ground. Bare rock in places on brows or steeper in valley sides.
Moderate Sherborne Jurassic Shallow well drained brashy limestone and calcareous clayey soils over clay limestone, associated with slowly permeable calcareous clayey soils.
Attenuation Low Altcar 1 Fen Peat Deep peat soils with earthy topsoil. Groundwater usually controlled by ditches and pumps.
Low Brockhurst 1 Permo-Triassic Slowly permeable seasonally reddish waterlogged reddish fine loamy mudstone and over clayey soils. Some similar till soils with slowly permeable subsoils and slight seasonal waterlogging.
Low Compton Reddish River Stoneless mostly reddish clayey Alluvium soils affected by groundwater. Flat land. Risk of flooding. Level 1 Strategic Flood Risk Assessment Sedgemoor District Council 2015 45
Development Site Drainage 8
SuDS Permeability Soil Geology Description Technique Association
Low Denchworth Jurassic and Slowly Permeable seasonally Cretaceous waterlogged clayey soils with Clay similar fine loamy over clayey soils. Some fine loamy over clayey soils with only slight seasonal waterlogging and some slowly permeable calcareous clayey soils.
Low Downholland Marine Deep stoneless humose clayey Alluvium and soils, calcareous in places. Some fen peat peat soils and deep humose calcareous silty soils. Flat land. Groundwater usually controlled by ditches and pumps.
Low Evesham 3 Jurrassic and Slowly permeable calcareous Cretaceous clayey, and fine loamy over clayey Clay soils. Some slowly permeable seasonally waterlogged non-calcareous clayey soils.
Low Newchurch 2 Marine Deep Stoneless mainly calcareous Clayey soils. Groundwater Alluvium controlled by ditches and pumps. Flat land. Risk of flooding in places.
Low Turbary Moor Raised bog Deep earth peat soils. Groundwater peat usually controlled by ditches and pumps. Very acid with high groundwater levels where uncultivated. Risk of wind erosion.
Low Whimple 1 Drift over Reddish fine loamy over clayey Permo Triassic soils with slowly permeable reddish subsoils and slight seasonal mudstone waterlogging. Associated with similar well drained soils, some over gravel.
Low Whimple 3 Drift over Reddish fine loamy or fine silty over Permo Triassic clayey soils with slowly permeable and subsoils and slightly seasonal Carboniferous waterlogging. Some similar clayey reddish soils on brows. Slowly permeable mudstone seasonal waterlogging fine loamy and fine silty over clayey soils on lower slopes. 46 Sedgemoor District Council 2015 Level 1 Strategic Flood Risk Assessment
8 Development Site Drainage
SuDS Permeability Soil Geology Description Technique Association
Low Worcester Permo-Triassic Slowly permeable noncalcareous Reddish and calcareous reddish clayey soils Mudstone over mudstone, shallow on steeper slopes. Associated with similar non-calcareous fine loamy over clayey soils.
Table 9 Suitable SuDS techniques dependant on soil type. Level 1 Strategic Flood Risk Assessment Sedgemoor District Council 2015 47
Emergency Planning 9
Multi-Agency Response Plan
9.1 When extreme flood events occur it is essential to have an emergency plan in place to provide clear procedural instructions. The mobilisation and organisation of the emergency services and supporting agencies is required to rescue, treat and transport potentially large numbers of people. During and after a flood event the role of the Local Authority includes providing transport for the evacuees and safe rest centres to house people in the event of homes being flooded. Further health and welfare issues are inevitable as a result of serious flood events.
9.2 Somerset Local Authorities have a Somerset Major Incident Co-ordination Group (SMICG) and have prepared a Somerset Flood Multi-agency Response Plan (15). Copies can be obtained from Somerset County Council. This plan deals with flood emergencies that are of a scale that cannot be dealt with by the Emergency Services, Local Authorities and other agencies as part of their normal day-to-day operations. It therefore provides a framework for responding to all forms of major flooding events across the area. In includes an overview of tactical/operations actions, and roles and responsibilities specific to flooding in Somerset. The plan therefore details the multi-agency operational response.
9.3 In consultation with the Environment Agency the plan also identifies six sites where there is a need for a specific flood response plan. These are identified either because of their potential for large numbers of people to be at risk in a single location, or where there is such a short time between warning and actual flooding that affected communities and responding agencies need to react immediately. For Sedgemoor both Bridgwater and Burnham-on-Sea/Highbridge are identified as requiring a specific flood response plan. These include details such as the potential location for Silver Control, Traffic Management requirements and the provision of rest centres. Mapping associated with the the response plan, including the extent of flood warning areas, is included in Appendix 3.
Site Level Emergency Planning Considerations
9.4 Emergency planning and evacuation arrangements are important considerations in ensuring that any new development is safe, including where there are residual risks of flooding. This should therefore be addressed in site specific FRA's in consultation with Council emergency planning staff. It is recommended that detailed flood warning and evacuation plans are undertaken for development in flood risk areas. In some instances the Council may secure this requirement through condition where it is necessary to ensure development is safe. Plans should include consideration of the availability of flood warnings, the location strategic rest centres, and safe refuge within the development site. Developers should be aware that the Practice Guidance advises safe access and egress should be maintained for the lifetime of development. It is important that emergency planning considerations are considered at an early stage as requirements can significantly influence scheme design. For example, if it is required to ensure development is two-storey.
15 Somerset Somerset Local Authorities Civil Contingencies Unit, Somerset Flood Multi-agency Response Plan, 2012. 48 Sedgemoor District Council 2015 Level 1 Strategic Flood Risk Assessment
10 Summary & Recommendations
Overview
10.1 This final section seeks to draw together the appendices mapping and information in previous sections to summarise the key outputs of the level 1 SFRA. It then provides a list of key recommendations on how the information should be used.
Local Plan Review - District Wide Flood Risk Policy
10.2 Sedgemoor's current Core Strategy flood policy (Policy D1) pre-dates this SFRA update. Since 2008 there has been significant changes in national planning policy in the NPPF as well as new flood risk management policy documents that have been published. Changes in mapping and different organisations roles and responsibilities in relation to flood risk have taken place and significant flood events that have affected the District have led to key local actions to address flood risk (Somerset Levels and Moors Flood Action Plan). The Local Plan Review District wide policies in relation to flood risk therefore need to be updated to reflect these changes.
Recommendation 1
District Wide Flood Risk Policy
Sedgemoor Council should review local planning policy in relation to flooding to ensure it is consistent with the NPPF, Practice Guidance and other local flood risk management strategies. This is likely to include the need for additional policy working on specific topics based on the actions identified in the Somerset Levels and Moors Flood Action Plan (e.g. Sustainable drainage). District wide policy should provide clear location specific policies on Sequential and Exception Test requirements for unallocated development that comes forward within the District.
Local Plan - Site Allocations
10.3 The ideal solution to addressing flood risk through the planning system is to steer new development away from areas at flood risk, taking into account all sources of flooding (i.e. Sequential Test). As this report has identified extensive parts of Sedgemoor are at fluvial and tidal risk. Even in areas of Flood Zone 1 other local sources of flooding need to be taken into account. That said there are still clear opportunities to apply the Sequential Test to direct significant proportions of the Districts growth requirements to Flood Zone 1. Where flood risk cannot be avoided due to other sustainability consideration the level 1 mapping will be important in scoping any further SFRA level 2 requirements in consultation with the Risk Management Authorities. A more detailed understanding of residual and climate change risk will then allow the Council to consider whether the Exception Test can be passed for different development location.
Recommendation 2
Site Allocations
Sedgemoor Planning Policy should use the updated level 1 mapping alongside the Sustainability Appraisal to Sequentially Test different distribution options of development across the District and potential development sites within each settlement. Through this process flood risk will be Level 1 Strategic Flood Risk Assessment Sedgemoor District Council 2015 49
Summary & Recommendations 10
balanced with other planning considerations. Where development cannot be located outside of Flood Zone 2 or 3 the need for any further level 2 SFRA work should be scoped in consultation with the Environment Agency and other Risk Management Authorities.
Safeguarding
10.4 Paragraph 100 of the NPPF states that Local Planning Authorities should safeguard land from development that is required for current and future flood risk management.
10.5 Within Sedgemoor the main flood risk management infrastructure required over the new plan period will be delivery of the Parrett barrier in Bridgwater, addressing climate change risk to the site and helping to address fluvial risk on the Somerset Levels and Moors. The Local Planning Authority will need to ensure the appropriate areas for delivery of the Parrett barrier are secured through the plan-making process.
Recommendation 3
Safeguarding
In consultation with the Environment Agency Sedgemoor Council should safeguard in the new Local Plan the preferred location for construction and delivery of the Parrett barrier. In consultation with all Risk Management Authorities the Council should consider the need to safeguard other areas for flood risk management infrastructure where these are identified as priorities in the Somerset Levels and Moors Flood Action Plan.
Planning Application Requirements
10.6 The consideration of flood risk at the planning application stage is of critical importance to ensuring safe development. This SFRA updates the previous SFRA mapping and signposts developers to specific requirements and guidance in relation to the Sequential Test, site level FRA's, sustainable drainage and emergency planning. While the Council will endeavour to keep the SFRA as up-to-date as possible developers should also refer to mapping and information available directly from the Risk Management Authorities to ensure FRA are informed by the latest information.
Recommendation 4
Planning Application Requirements
Developers should use the information available in the SFRA and from Risk Management Authorities to inform site specific Sequential Test and FRA requirements. Particular attention should be given to the delineation of Flood Zone 3b identified in the SFRA given its implications for what uses are appropriate in principle. 50 Sedgemoor District Council 2015 Level 1 Strategic Flood Risk Assessment
10 Summary & Recommendations
Monitoring and Updating
10.7 Flood risk mapping and information is always being updated as flood events occur, defences are constructed and mapping techniques improve. The risk across the District is also expected to change given the affects of climate change. The Council should ensure the SFRA is kept as up to date as possible as new mapping is published. This is particularly important in relation to Flood Zone 3b to ensure that it is remains consistent with the Environment Agency's Flood Map for Planning, which is updated on a quarterly basis. Changes may also be requires where developers have successfully challenged the Flood Zone 3b designation based on robust site level information.
Recommendation 5
Monitoring and Updating
The Council should seek to ensure the SFRA is kept as up to date as possible as new information becomes available, ensuring the document remains useful and relevant for planning purposes. Particular attention should be given to ensuring Flood Zone 3b is updated in consultation with the Environment Agency when new information is released which justifies amendments. The Council should explore different ways (e.g. web-based mapping) of making SFRA information available to make it easily accessible to developers and the public. Level 1 Strategic Flood Risk Assessment Sedgemoor District Council 2015
Appendix 1 - Mapping Level 1 Strategic Flood Risk Assessment Sedgemoor District Council 2015
Appendix 2 - Wessex Water Sewer Flooding Data Level 1 Strategic Flood Risk Assessment Sedgemoor District Council 2015
Appendix 3 - Emergency Planning Mapping