West Cheshire SFRA Chester City Council Main Report May 2008 Prepared by: ............. Approved by: Sam Wingfield Graham Knott Environmental Engineer Regional Director West Cheshire SFRA Rev No Comments Date 1 Updated from LPA comments 2 Updated from final LPA comments 18th April 2008 38 Woodside Business Park, Birkenhead, Merseyside, CH41 1EL Telephone: 0151 647 2312 Fax: 0151 647 4742 Website: http://www.fabermaunsell.com Job No: 53726IBKR Date Created April 2008 This contains confidential and commercially sensitive information, which shall not be disclosed to third parties. f:\projects\53726ibkr_chester_sfra\reports\v3\chester\chester main report final 16.04.08.doc Faber Maunsell West Cheshire SFRA 0 Table of Contents Abbreviations / Acronyms.......................................................................................................... 0 1 Introduction ..................................................................................................................... 4 Background ....................................................................................................................... 4 The need for a SFRA ........................................................................................................ 4 SFRA Objectives............................................................................................................... 5 Planning and flood risk...................................................................................................... 5 Methodology.................................................................................................................... 10 2 Flood Risk...................................................................................................................... 14 Introduction...................................................................................................................... 14 Responsibilities ............................................................................................................... 14 Planning Policy Statement 25 ......................................................................................... 17 Flood Mapping ................................................................................................................ 22 3 Data Collection .............................................................................................................. 28 Flood Zone maps ............................................................................................................ 28 Topography ..................................................................................................................... 28 Hydraulic Models............................................................................................................. 28 Historic flooding............................................................................................................... 29 Defences ......................................................................................................................... 29 Flood warning.................................................................................................................. 31 Other related plans and strategies.................................................................................. 32 Data deficiencies............................................................................................................. 34 4 Causes of Flooding....................................................................................................... 38 Introduction...................................................................................................................... 38 Overflowing of watercourses (including Breach)............................................................. 38 Tidal Flooding.................................................................................................................. 39 Mechanical, Structural or Operational Failure................................................................. 40 Groundwater Flooding..................................................................................................... 41 Land drainage, sewer and ordinary watercourse flooding .............................................. 41 Catchment characteristics............................................................................................... 44 5 Flooding in West Cheshire........................................................................................... 48 Historic flooding............................................................................................................... 48 River Dee and associated watercourses ........................................................................ 49 River Gowy catchment and associated watercourses .................................................... 50 Sewer Flooding in Chester District.................................................................................. 50 Other sources of flooding................................................................................................ 51 6 Strategic Assessment of Flood Risk........................................................................... 54 Plans produced and mapping ......................................................................................... 54 Flood risk profile.............................................................................................................. 55 Climate change ............................................................................................................... 58 Land use changes for West Cheshire............................................................................. 60 Land use changes on the River Dee catchment............................................................. 60 Risk from abandonment of assets .................................................................................. 62 Mitigation for Flood Zones............................................................................................... 63 Defences not at the required standard............................................................................ 65 7 Development in Chester District ................................................................................. 68 Summary of Regional Flood Risk Assessment Figures.................................................. 68 Chester District................................................................................................................ 70 8 Assessment of Flood Risk in Study Areas................................................................. 74 Faber Maunsell West Cheshire SFRA 1 The Sequential Test ........................................................................................................ 74 Application of the Sequential Test .................................................................................. 75 Flood risk matrix explanation .......................................................................................... 77 Sequential Test summary ............................................................................................... 78 General summary............................................................................................................ 78 Generic requirements for planning applications.............................................................. 80 How to use the SFRA to apply the Sequential Test........................................................ 86 9 Flood Risk Policies ....................................................................................................... 93 Current Planning policy................................................................................................... 93 LDF Draft flood risk policies ............................................................................................ 94 Advice on the use of SuDS and sustainable development ............................................. 97 10 Conclusions and Recommendations........................................................................ 104 Conclusions................................................................................................................... 104 Recommendations ........................................................................................................ 105 Glossary ................................................................................................................................... 107 References ............................................................................................................................... 113 Sources of Information ........................................................................................................... 113 Appendix .................................................................................................................................. 115 Appendix A: Flood Risk Problem Location Database Appendix B: Data provided by LPA Appendix C: Flood Risk Matrix for sites Appendix D: Data Register List of Tables Table 1: Key development planning tools in PPS25 (taken from PPS25)..............................6 Table 2: PPS25 Flood Zones (taken from PPS251).................................................................18 Table 3: Flood Risk Vulnerability Classification from PPS25 (taken from PPS251) ...........19 Table 4: Recommended contingency allowances for net sea level rise (taken from PPS251)...........................................................................................................................29