Strategic Flood Risk Assessment - Wiltshire Council

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Wiltshire CouncilSFRA High Level Executive Summary1 Introduction1.1 Background1.1 Scott Wilson Ltd was commissioned in December 2008 to provide a high level executivesummary for the commencement of Wiltshire Council (April 2009). This summary drawstogether the information provided in the Level 1 Strategic Flood Risk Assessments (SFRAs)produced for the individual Local Planning Authorities (LPAs) that are being integrated toform a single unitary authority of Wiltshire Council. The LPAs being integrated are:• North Wiltshire District Council (NWDC);• Kennet District Council (KDC);• West Wiltshire District Council (WWDC); and• Salisbury District Council (SDC).1.2 This report summarises information on the application of the Sequential Test, a broad scaleassessment of flood risk for potential strategic developments, flood risk managementmeasures for consideration for new developments, recommendations for flood risk policyand site specific Flood Risk Assessment (FRA) guidance.1.3 In addition, there will be a brief overview of the collation of the datasets and theaccompanying Geographical Information System (GIS) layers for use by Wiltshire Councilalong with recommendations on the maintenance and update of data sources for futuredecision making.1.4 The accompanying GIS layers will also be used to inform the Minerals and Waste LocalDevelopment Framework and the Minerals and Waste Level 1 SFRA is being updated intandem with this document. This will ensure that the available data is consistent across theWiltshire Council administrative area, providing continuity in the decision making process.3 June 2009
Wiltshire CouncilSFRA High Level Executive Summary2 Sequential Test2.1 What is the Sequential Test?2.1.1 The Sequential Test refers to the application of the sequential approach by LPAs. Thisallows the determination of site allocations based on flood risk and vulnerability (see Table2-1 and Table 2-2, provided below). Development should be directed to Flood Zone 1wherever possible, and then sequentially to Flood Zone 2 and then Flood Zone 3. Where asite lies spans different flood zones, a sequential approach based on vulnerability ofdevelopment should be undertaken steering development to the areas of least risk.Table 2-1: PPS25 Flood Zone Definitions (These ignore the presence of defences)Flood ZoneFlood Zone 1DefinitionLow probability - less than 0.1% (1 in 1000 year) probability of floodingeach year from fluvial or tidal flooding.Flood Zone 2 Medium probability - between 0.1% and 1% (between 1 in 1000 and 1in 100 year) probability of fluvial flooding each year and between 0.1%and 0.5% (between 1 in 1000 and 1 in 200 year) probability of tidalflooding each year .Flood Zone 3aFlood Zone 3bHigh probability - 1% or greater (1 in 100 year or greater) probability offluvial flooding each year and a 0.5% or greater (1 in 200 year orgreater) probability of tidal flooding each year.Functional floodplain - land where water has to flow or be stored intimes of flood. Defined as the 5% (1 in 20 year) annual probabilityfloodplain or an area designed to flood in an extreme (0.1%) flood, oranother probability agreed between the LPA and the EnvironmentAgency. (The Environment Agency do not currently produce FloodZone 3b mapping for England and Wales).2.1.2 The application of the Sequential Test aims to manage the risk from flooding by avoidance.This avoids the promotion of sites that are inappropriate on flood risk grounds. Theapplication of the Exception Test, where required, through a Level 2 SFRA will ensure thatnew developments in flood risk areas will only occur where flood risk is clearly outweighedby other sustainability drivers.2.1.3 The LPA must demonstrate that it has considered a range of possible sites in conjunctionwith the Flood Zone information from the SFRA and applied the Sequential Test, and wherenecessary, the Exception Test, in the site allocation process.2.1.4 PPS25 acknowledges that some areas will (also) be at risk of flooding from flood sourcesother than fluvial or tidal systems. Consequently all sources of flooding must be consideredwhen looking to locate development in any of the flood zones. The other sources of floodingrequiring consideration when situating new development allocations include:• Surface water;• Groundwater;• Sewers; and,• Artificial sources.4 June 2009
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Strategic Flood Risk Assessment - Wiltshire Council

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