Strategic Flood Risk Assessment - Wiltshire Council

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Wiltshire CouncilSFRA High Level Executive SummarySettlementPotentialdevelopmentsites intersectwith Flood Zone1Potentialdevelopmentsites intersectwith ClimateChange FloodZone 3bPotentialdevelopmentsites intersectwith ClimateChange FloodZone 3aOther floodsourceswithinurban areaMelksham Trowbridge Warminster Westbury 4.3 The Location of Future Development4.3.1 The broad-scale assessment of flood risk, provided in Section 4.2, indicates that within eachdistrict there are available sites for development located within Flood Zone 1. Where a siteconsists of land located in more than one flood zone the development should besequentially located within the site boundary to ensure those developments that arevulnerable are located within the lowest risk flood zones.4.3.2 Under certain circumstances other sustainability objectives considered by Wiltshire Councilmay result in sites located in Flood Zones 2, 3a and 3b being taken into account. In suchcases, further work at the Level 2 SFRA stage may be required to satisfy the ExceptionTest.4.3.3 Level 2 SFRA work is currently being undertaken for two specific sites within Salisbury(Churchfields Industrial Estate and Central Car Park / the Maltings). These sites are partiallylocated within Flood Zones 2 and 3. The Level 2 SFRA work will provide detailed informationon flood risk and flood risk management at the potential development sites.4.3.4 Based on the information presented within the existing Level 1 SFRAs together with theEnvironment Agency Catchment Flood Management Plans (CFMPs) Existing areas inChippenham, Salisbury and Malmesbury may require further information through additionalhydraulic modelling to inform potential flood alleviation options, to mitigate against theanticipated effects of climate change.4.3.5 To investigate feasible options to reduce flood risk these in urban areas a joint approachworking with the Environment Agency should be adopted. In addition, within the settlementsof Warminster and Britford SWMPs are likely to be required to manage the risk of surfacewater flooding.4.3.6 It is noted that the Swindon Water Cycle Strategy is emerging and includes the ‘west ofSwindon growth area’. This growth area is undergoing a site selection process where fromten initial sites, three preferred sites have been identified. In some instances, thesepreferred sites lay within the administrative boundary of Wiltshire Council and it is thoughtthat development can be fully accommodated within Flood zone 1. The Environment Agencyhas identified that a Level 2 SFRA may be required due to the size of the development(3000 houses) to consider other sources of flooding.19 June 2009
Wiltshire CouncilSFRA High Level Executive Summary5 Flood Risk Management5.1 Overview5.1.1 This section provides an overview of flood risk management practices including commentaryon flood defence infrastructure, flood warning and Sustainable Drainage Systems (SuDS).5.2 Existing Flood Defences5.2.1 Flooding may occur across areas of the study area with minimal effect to people, buildings,infrastructure or the economy, however, in some areas there may be a significant effect.Where required, flood defences are usually focused in and around the urban areas wherefor social, economic and sustainability reasons these are required to minimise disruption toindividuals, businesses and the wider community.5.2.2 Environment Agency Flood Maps do not account for the presence of flood defences whendelineating the Flood Zone extent and therefore areas of land situated behind thesedefences are still attributed with a flood risk. The presence of flood defences does notremove the risk for the areas protected as failure through overtopping or breaching mayoccur, therefore, a residual flood risk remains.5.2.3 Flood defences generally fall into one of two categories: ‘formal’ or ‘defacto’. A ‘formal’defence (termed ‘raised defence (man-made) in NFCDD) is a structure which has beenspecifically built to control floodwater. It is maintained by its owner (this is not necessarilythe Environment Agency) so that it remains in the necessary condition to function.5.2.4 A ‘defacto’ defence includes road and rail embankments and other linear infrastructure(buildings and boundary walls) which may act as water retaining structures or createenclosures to form flood storage areas in addition to their primary function. Other structuresare identified on the Environment Agency database, but these have not necessarily beenbuilt to control floodwater and are not maintained for this purpose.5.2.5 Mapping of the formal flood defences held within the NFCDD database has been providedwithin the existing Level 1 SFRAs. Integrated NFCDD man-made defence and structure GISdatasets have been produced as part of this high level executive summary covering theWiltshire Council administrative area.5.3 Flood Warning Procedures5.3.1 The Environment Agency undertakes a considerable amount of work in terms of floodwarning procedures. The Environment Agency operates a flood warning service in all areasat risk of flooding, which is available on their website 4 .5.3.2 Within the study area there are a number of flood watch areas. Flood watch areas arehydrologically similar (or groups of catchments). Within each flood watch area are focussedareas, known as flood warning areas, where flooding is known to occur during larger floodevents.4 http://www.environment-agency.gov.uk/homeandleisure/floods/31618.aspx20 June 2009
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Strategic Flood Risk Assessment - Wiltshire Council

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