Strategic Flood Risk Assessment (Level 1 SFRA) a Technical Report Supporting the Royal Borough of Windsor and Maidenhead Borough Local Plan
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Strategic Flood Risk Assessment (Level 1 SFRA) A Technical Report Supporting the Royal Borough of Windsor and Maidenhead Borough Local Plan September 2016 (Revision 07) DRAFT Royal Borough of Windsor and Maidenhead Planning and Property Services Town Hall St Ives Road Maidenhead SL6 1RF STRATEGIC FLOOD RISK ASSESSMENT (SFRA) A Technical Report Supporting the Royal Borough of Windsor and Maidenhead Borough Local Plan EXECUTIVE SUMMARY Introduction The Royal Borough of Windsor and Maidenhead (RBWM) is located in the east of Berkshire, between Slough, Wokingham and Bracknell. The River Thames forms the northern and eastern boundaries of the Royal Borough and is a major source of flood risk to properties within the Royal Borough, including core centres of future growth, such as Maidenhead, Windsor and Wraysbury). Tributaries of the River Thames including The Cut, the River Colne, the Bourne and Twyford Brook (a tributary of the River Loddon) also pose a flood risk to the Royal Borough. A considerable proportion of the Royal Borough is at risk of flooding from a number of sources including river flooding, localised runoff, sewer and groundwater flooding. Flooding can result not only in costly damage to property, but can also pose a risk to life, health and livelihood. It is therefore, essential that the Royal Borough of Windsor and Maidenhead in its role as the Local Planning Authority, Lead Local Flood Authority and Emergency Planning Authority is in a position where it is able to make informed decisions to ensure future development proposals are steered away from areas that are at the greatest risk from flooding, and ensuring that it does not exacerbate existing known flooding problems. The Royal Borough must also be in a position to make an informed decision on how best to balance flood risk with other planning constraints. The Royal Borough of Windsor and Maidenhead Strategic Flood Risk Assessment (SFRA) provides specific guidance and flood risk policy recommendations which should be adhered to by both developers and council officers in order to assist the Royal Borough in making informed decisions on future development to minimise and manage flood risk. The SFRA for the Royal Borough of Windsor and Maidenhead is divided into two documents; the Level 1 SFRA and the Level 2 SFRA. This report (and supporting mapping) represents the Level 1 SFRA (2016). The report provides the background information on flood risk and flood risk policy in the Royal Borough, along with requirements and guidance on assessing flood risk for site-specific development proposals. The report also provides guidance on land use planning and flood risk mitigation options for sites where flood risk has been identified as a potential constraint to future development. The accompanying Level 2 SFRA considers potential development allocation sites in more detail through the application of the National Planning Policy Framework (NPPF) Sequential Test and, where necessary, the need to apply the Exception Test. The Level 2 report sets out the methodology for applying the Sequential Test and the Exception Test in the Royal Borough, which has been applied in the testing of potential development allocation sites, and should also be used to inform the application of the tests to non-allocated development sites. The Level 1 and Level 2 SFRA should be read in conjunction when a potential site is being considered for development. Policy Context The NPPF requires local planning authorities to review the variation in flood risk across their district, and to steer vulnerable development (e.g. housing) towards areas of lowest risk. Where this cannot be achieved and development is to be permitted in areas that may be subject to some degree of flood risk, the NPPF requires the Council to demonstrate that there are sustainable mitigation solutions available that will ensure that the risk to property and life is minimised (throughout the lifetime of the development) should flooding occur. This information should be provided by a Strategic Flood Risk Assessment (SFRA); a study conducted by one or more local planning authorities to assess the risk of flooding to an area from all sources, now and in the future, taking into account the effects of climate change. At a more local scale, this SFRA forms an intrinsic part of the evidence base that informs the production of the Royal Borough of Windsor and Maidenhead Borough Local Plan. The Borough Local Plan is currently in draft and is anticipated to be adopted in 2017. The Borough Local Plan will set the overarching, long-term, spatial development strategy to support sustainable development in Borough up to 2032. The Borough Local Plan will also STRATEGIC FLOOD RISK ASSESSMENT (SFRA) A Technical Report Supporting the Royal Borough of Windsor and Maidenhead Borough Local Plan include a number of allocated sites, on which the potential for development has been assessed through the various evidence documents that support the Royal Borough Local Plan, which include the SFRA. Flood Risk in the Royal Borough of Windsor and Maidenhead The existing flood risk to the Royal Borough has been assessed thorough review of the data sources held by the Environment Agency (which include hydraulic model outputs), Royal Borough of Windsor and Maidenhead and Thames Water. The Level 1 SFRA identifies where there are significant areas of flood risk within the Royal Borough from all sources, including fluvial, surface water, groundwater and sewer and drainage infrastructure. The Level 1 SFRA provides a number of maps which demonstrate the fluvial flood risk in the Royal Borough, including Flood Zone 3a, Flood Zone 3b developed and Flood Zone 3b functional floodplain extents. Maps are also provided showing the extent of flood risk from other sources, the effect of climate change and other supporting information. The principles behind the Royal Borough Local Plan Policy 45: Managing Flood Risk and Waterways are detailed, as well as guidance on the requirements that should be adhered to when producing site-specific Flood Risk Assessments (FRA). The report also provides information on reducing flood risk and making development safe, including Sustainable Drainage Systems (SuDS) and mitigation measures. The Level 1 SFRA was updated in September 2016. Both the Level 1 and Level 2 SFRA reports are living documents and will be periodically updated to reflect changes to flood risk in the Royal Borough. STRATEGIC FLOOD RISK ASSESSMENT (SFRA) A Technical Report Supporting the Royal Borough of Windsor and Maidenhead Borough Local Plan Table of Contents 1 Introduction .................................................................................................. 1 1.1 Context and Purpose ......................................................................... 1 1.2 Aim and Objectives ............................................................................ 1 1.3 Document Structure ........................................................................... 2 2 Legislative and Policy Framework ............................................................... 4 2.1 National Legislative and Policy Context ............................................. 4 2.2 Local Policy Context .......................................................................... 4 3 Data Collection ............................................................................................ 5 3.1 Overview............................................................................................ 5 3.2 Flood Map for Planning (Rivers and Sea) .......................................... 5 3.3 Detailed Hydraulic Modelling ............................................................. 5 3.4 Flood Defences ................................................................................. 6 3.5 Updated Flood Map for Surface Water .............................................. 6 3.6 Records of Historic Flooding .............................................................. 7 3.7 Additional Information ........................................................................ 7 Royal Borough of Windsor and Maidenhead ................................................ 7 4 Understanding Flood Risk in RBWM ........................................................... 9 4.2 Overview of Flood Risk in RBWM ...................................................... 9 4.3 Climate Change ............................................................................... 15 5 Assessing Flood Risk in RBWM ................................................................ 17 5.1 Fluvial Flooding - Delineation of the NPPF Flood Risk Zones ......... 17 5.2 Assessment of Flood Hazard ........................................................... 19 5.3 Residual Risk of Flooding ................................................................ 20 6 Flood Risk Policy in RBWM ....................................................................... 22 6.2 Managing Flood Risk for New Development and Applying the Sequential Approach .................................................................................. 22 6.3 Assessing Vulnerability and Flood Risk ........................................... 23 6.4 Site Evacuation Plan........................................................................ 24 6.5 Maintain Existing Overland Flowpaths ............................................. 24 6.6 Floodplain Storage Capacity............................................................ 24 6.7 Ecological Habitat ...........................................................................