Level 2 Strategic Flood Risk Assessment (.pdf ... - Wigan Council

direction in Future Water3, Making Space for Water4, the Pitt Review5 and the Flood andWater Management Act6 that provides for more sustainable management of the water cycle,working in partnership across different agencies and new responsibilities for local flood riskmanagement. In particular, the Flood and Water Management Act requires developers wherepractical, to include sustainable drainage in new developments to reduce flood risk andimprove water quality. It includes ‘a requirement on developers to demonstrate that theyhave met national standards for the application of SUDS techniques before they can connectany residual surface water drainage to a public sewer (amending section 106 of the WaterIndustry Act 1991).’ As part of their new responsibility for local flood risk management, localauthorities will be responsible for approving SUDS for new developments and adopting andmaintaining them. Table E-1 and Table E-2 (Appendix E) outline the suitability of WiganBorough Council's proposed development sites for SUDs suitability schemes.The choice of SUDs within a proposed development site will be determined by local groundconditions (including groundwater levels). Whilst infiltration SUDS may be the most suitablefor new development, developers must also consider the risk of contamination to underlyingaquifers as part of a detailed site specific FRA.5.3.1 River Douglas CFMP Groundwater Flooding"In the Douglas catchment there has been groundwater pumping for many years, but this hasmostly ceased now. Some local flooding of property in Appley Bridge has been reported sincepumping stopped. There is flood risk from the Rufford aquifer as the groundwater level wouldnaturally be above the surface but the aquifer is covered by a thin layer of clay, whichprevents the groundwater flowing to the surface."http://publications.environment-agency.gov.uk/pdf/GENW0309BPTQ-E-E.pdf5.4 Surface Water and Sewer Capacity Mapping5.4.1 Surface Water MappingThe national Areas Susceptible to Surface Water Flooding (ASTSWF) map provides a usefulreference in identifying areas that could be at risk from surface water flooding. The SFRAsurface water flooding results are shown in Appendix C.5.4.2 Sewer MappingMost new sewers are designed to a 1 in 30 year design standard and hence sewer floodingproblems will often be associated with more frequent storm events when a sewer becomesblocked or fails. In the larger events that are less frequent but have a higher consequence,surface water will exceed the sewer system and flow across the surface of the land. Surfacewater mapping highlights these overland flow routes.5.4.3 Combined Surface Water and Sewer MappingConsidering both sewer and surface water flooding together is considered an appropriatemethodology when assessing surface water flooding at a strategic level. More detailedconsideration of the mechanisms and locations of sewer flooding are beyond the scope of theSFRA. However, the historical mapping provides supporting evidence and patterns offlooding within Wigan. Where surface water is identified as being a significant issue, thendevelopment planning needs to focus on managing the impact of development, or to avoiddevelopment where the risk of surface water flooding is considered too high.5.4.4 Critical Drainage Areas3 Defra (2008) Future Water4 Defra, Department for Transport, HM Treasury and Office of the Deputy Prime Minister (2005) Making Space forwater: Taking forward a new Government strategy for flood and coastal erosion risk management in England; FirstGovernment response to the autumn 2004 Making space for water consultation exercise5 The Pitt Review (2008) Learning lessons from the 2007 floods6 Defra (2009) Draft Flood and Water Management Act © Crown Copyright2009s0578 Final SFRA with Environment Agency Comments - L2 Ver5 Wigan.doc 24