Swindon Borough Council Strategic Flood Risk Assessment Level 1 SFRA - Final Report (Volume I) August 2008
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Swindon Borough Council Strategic Flood Risk Assessment Level 1 SFRA - Final Report (Volume I) August 2008 Halcrow Group Limited Halcrow Group Limited Burderop Park Swindon Wiltshire SN4 0QD Tel +44 (0)1793 812479 Fax +44 (0)1793 812089 www.halcrow.com © Halcrow Group Limited 2008 Swindon Borough Council Strategic Flood Risk Assessment Level 1 SFRA - Final Report (Volume I) August 2008 Halcrow Group Limited Halcrow Group Limited Burderop Park Swindon Wiltshire SN4 0QD Tel +44 (0)1793 812479 Fax +44 (0)1793 812089 www.halcrow.com © Halcrow Group Limited 2008 Halcrow Group Limited Burderop Park Swindon Wiltshire SN4 0QD Tel +44 (0)1793 812479 Fax +44 (0)1793 812089 www.halcrow.com Swindon Borough Council Strategic Flood Risk Assessment Level 1 SFRA - Final Report (Volume I) Contents Amendment Record This report has been issued and amended as follows: Issue Revision Description Date Signed 1 0 First draft 12 September 2007 T Houghton 2 1 Second draft 7 February 2008 CJ Weeks 3 2 Third draft 14 March 2008 D Kensett 4 3 Fourth draft 8 May 2008 A Corner 5 4 Final 28 August 2008 A McConkey M Barker P Crozier D Wilson PS Rayner Swindon Borough Council Strategic Flood Risk Assessment Table of Contents Executive Summary Volume I - Final Report (contents list below) Volume II - SFRA Flood Maps 1 Introduction.................................................................................................... 1 2 The Swindon SFRA Area .............................................................................. 2 2.1 Overview ..................................................................................................................... 2 2.2 Planning Context......................................................................................................... 2 2.3 Thames Corridor Catchment....................................................................................... 3 2.4 Swindon Rivers ........................................................................................................... 3 2.5 Geology....................................................................................................................... 3 3 SFRA Approach & Methodology .................................................................. 5 3.1 Overview ..................................................................................................................... 5 3.2 Outcomes of the SFRA Process ................................................................................. 6 3.3 The Sequential Test .................................................................................................... 6 3.4 The Exception Test ..................................................................................................... 8 3.5 Level 1 SFRA methodology ........................................................................................ 8 3.6 The need for Level 2 SFRA......................................................................................... 9 4 Policy framework......................................................................................... 11 4.1 Overview ................................................................................................................... 11 4.2 Planning policy framework ........................................................................................ 11 4.3 National policy........................................................................................................... 11 4.4 Regional planning policy ........................................................................................... 13 5 Data sources................................................................................................ 16 5.1 Overview ................................................................................................................... 16 5.2 Consultation process................................................................................................. 16 5.3 Environment agency Flood Zone maps .................................................................... 17 5.4 Detailed hydraulic modelling ..................................................................................... 17 5.5 Localised flooding ..................................................................................................... 17 6 Assessment of potential causes of flooding............................................. 19 6.1 Overview ................................................................................................................... 19 6.2 SFRA flood maps ...................................................................................................... 19 6.3 Localised flooding ..................................................................................................... 19 6.4 PPS25 Flood zones .................................................................................................. 28 6.5 Existing services/infrastructure within PPS25 Flood zones....................................... 30 7 Assessment of flood risk management practices .................................... 32 7.1 Overview ................................................................................................................... 32 7.2 Flood risk managment responsibilities ...................................................................... 32 7.3 Existing flood defences ............................................................................................. 32 7.4 Flood warning areas.................................................................................................. 34 7.5 Variation in actual flood risk ...................................................................................... 35 Swindon Borough Council Strategic Flood Risk Assessment 8 Assessment of the capacity for the use of SUDS..................................... 36 8.1 Overview ................................................................................................................... 36 8.2 Types of SUDS systems ........................................................................................... 36 8.3 SUDS at the planning stage...................................................................................... 36 8.4 Application of SUDS within Swindon......................................................................... 37 9 Flood risk & climate change....................................................................... 40 9.1 Overview ................................................................................................................... 40 9.2 Flood risk & climate change ...................................................................................... 40 9.3 Integrated urban drainage......................................................................................... 41 9.4 Potential increase in flood risk caused by future development ................................. 42 9.5 Potential effect of flood defence failure (residual risk) .............................................. 42 9.6 Extent and costs required to raise flood defence standard to 1%............................. 43 9.7 Sustainability of land use in medium and high risk flood areas................................. 44 10 Appropriate planning responses for low, medium & high risk areas ..... 45 10.1 Overview ................................................................................................................... 45 10.2 Strategic flood risk management studies – Environment Agency ............................. 45 10.3 Indicative Sites .......................................................................................................... 46 10.4 Policy Recommendations.......................................................................................... 47 10.5 Planning Response Matrix ........................................................................................ 49 10.6 Development within areas affected by surface water and sewer flooding................. 50 11 Measures to make development permissible in higher risk flood zones51 11.1 Overview ................................................................................................................... 51 11.2 Potential measures ................................................................................................... 51 11.3 Recommendations for reducing existing flood risks.................................................. 52 11.4 Need for flood risk assessment................................................................................. 52 11.5 Monitoring post development runoff.......................................................................... 55 12 Conclusions & Recommendations ............................................................ 56 References.............................................................................................................. 59 APPENDIX A Audit trail database APPENDIX B Geology & soils APPENDIX C Model reviews APPENDIX D Locations with blockage potential APPENDIX E July 2007 flood study of Whitehill Stream, Swindon APPENDIX F Localised flooding database APPENDIX G Sewer flooding APPENDIX H Site visit APPENDIX I Main defences APPENDIX J PPS25 flood risk vulnerability classification APPENDIX K Using computer river modelling as part of a FRA Best practice guidance APPENDIX L Swindon’s Flood Review: July 2007 An investigation into the causes and flood risk management options Swindon Borough Council Strategic Flood Risk Assessment