Spelthorne Borough Council Strategic Flood Risk Assessment Spelthorne Borough Council Project number: 60559796 Draft February 2018 DRAFT Spelthorne Borough Council DRAFT Project number: 60559796 Quality information Prepared by Checked by Approved by Fraser O’Halloran Sarah Littlewood Sarah Kelly Graduate Consultant Senior Consultant Regional Director Revision History Revision Revision date Details Authorized Name Position 1 Feb 2018 Draft for Client Comment 14/02/2018 Sarah Kelly Regional Director Distribution List # Hard Copies PDF Required Association / Company Name Prepared for: Spelthorne Borough Council Prepared by: AECOM Infrastructure and Environment UK Limited Midpoint, Alencon Link Basingstoke Hampshire RG21 7PP United Kingdom T: +44(0)1256 310200 aecom.com © 2018 AECOM Infrastructure and Environment UK Limited. All Rights Reserved. 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Prepared for: Spelthorne Borough Council AECOM Spelthorne Borough Council DRAFT Project number: 60559796 Table of Contents Abbreviations ...................................................................................................................................................5 Glossary of Terms .............................................................................................................................................6 Executive Summary ..........................................................................................................................................8 1 Introduction and User Guide ............................................................................ 9 1.1 Introduction .........................................................................................................................................9 1.2 Approach to Flood Risk Management ..................................................................................................9 1.3 Purpose of the SFRA ........................................................................................................................ 11 1.4 Flood Risk Policy and Guidance ........................................................................................................ 11 1.5 User Guide .......................................................................................................................................12 1.6 Living Document ...............................................................................................................................13 2 Methodology .................................................................................................. 14 2.1 Consultation ......................................................................................................................................14 2.2 Data Collection and Mapping .............................................................................................................15 3 Strategic Assessment of Flood Risk .............................................................. 16 3.1 Overview ..........................................................................................................................................16 3.2 Flooding From Rivers ........................................................................................................................18 3.3 Flooding From Surface Water ............................................................................................................25 3.4 Flooding From Groundwater ..............................................................................................................27 3.5 Flooding From Sewers ......................................................................................................................29 3.6 Flooding From Artificial Sources.........................................................................................................30 4 Avoiding Flood Risk – Applying the Sequential and Exception Tests ............. 32 4.1 Overview ..........................................................................................................................................32 4.2 Applying the Sequential Test for the Local Plan ..................................................................................32 4.3 Applying the Sequential Test for Planning Applications .......................................................................35 4.4 Exception Test...................................................................................................................................36 5 Managing and Mitigating Flood Risk.............................................................. 38 5.1 Overview ..........................................................................................................................................38 5.2 Development Layout and Sequential Approach ..................................................................................38 5.3 Finished Floor Levels ........................................................................................................................38 5.4 Flood Resistance ‘Water Exclusion Strategy’ ......................................................................................39 5.5 Flood Resilience ‘Water Entry Strategy’ .............................................................................................41 5.6 Safe Access and Egress ....................................................................................................................41 5.7 Flood Compensation Storage ............................................................................................................42 5.8 Flood Routing ...................................................................................................................................44 5.9 Riverside Development .....................................................................................................................44 5.10 Surface Water Management ..............................................................................................................45 5.11 Flood Warning and Evacuation Plans................................................................................................. 48 5.12 Flood Warning Areas .........................................................................................................................49 6 Preparing Site Specific FRAs ........................................................................ 51 6.1 What is a Flood Risk Assessment? ....................................................................................................51 6.2 When is a Flood Risk Assessment required? ......................................................................................51 6.3 How detailed should a FRA be? .........................................................................................................51 6.4 What needs to be addressed in a Flood Risk Assessment? ................................................................53 6.5 Flood Risk Assessment Checklist ......................................................................................................53 6.6 Pre-application Advice .......................................................................................................................56 Appendix A Data Register ........................................................................................ 57 Appendix B Figures .................................................................................................. 58 Prepared for: Spelthorne Borough Council AECOM Spelthorne Borough Council DRAFT Project number: 60559796 Appendix C Surface Water Conditions Report ......................................................... 59 Figures Figure 1-1 Taking flood risk into account in the preparation of a Local Plan (Planning Practice Guidance for Flood Risk and Coastal Change) ..............................................................................................................................10 Figure 4-1 Application of Sequential Test for Local Plan preparation (Planning and Practice Guidance for Flood Risk and Coastal Change) ..............................................................................................................................32 Figure 5-1 Flood Resistant / Resilient Design Strategies, Improving Flood Performance, CLG 2007 ..................40 Figure 5-2 Example of Floodplain Compensation Storage (Environment Agency 2009) .....................................43 Tables Table 1-1 Flood Risk Policy and Guidance Documents ..................................................................................... 11 Table 2-1 SFRA Stakeholder Organisations and Roles .....................................................................................14 Table 3-1 Fluvial Flood Zones (extracted from the PPG, 2014) .........................................................................18 Table 3-2 Peak river flow allowances for Thames river basin district (use 1961 to 1990 baseline) ......................20 Table