London Borough of Waltham Forest Level 1 SFRA Final Report Project number: 60577135 October 2018 London Borough of Waltham Forest Level 1 SFRA FINAL Project number: 60577135 Quality information Prepared by Checked by Approved by Hannah Booth Emily Craven Sarah Kelly Graduate Water Associate Director, Water Regional Director, Water Consultant Sarah Waite Hydrologist Consultant Revision History Revision Revision date Details Authorized Name Position 01 July 2018 Draft Report for 26 July 2018 Sarah Kelly Regional Director, client comment Water 02 August 2018 Final report 02 October 2018 Sarah Kelly Regional Director, Water AECOM i London Borough of Waltham Forest Level 1 SFRA FINAL Project number: 60577135 Prepared for: London Borough of Waltham Forest Council Prepared by: AECOM Infrastructure & Environment UK Ltd Midpoint, Alencon Link Basingstoke Hampshire RG21 7PP United Kingdom T: +44(0)1256 310200 aecom.com © 2018 AECOM Infrastructure & Environment UK Ltd. All Rights Reserved. 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AECOM ii London Borough of Waltham Forest Level 1 SFRA FINAL Project number: 60577135 Table of Contents Abbreviations ............................................................................................................. v Glossary of Terms ...................................................................................................... vi Executive Summary ................................................................................................... x 1. Introduction ...................................................................................................... 1 1.1 Approach to Flood Risk Management ........................................................................................ 1 1.2 Flood Risk Policy and Guidance ................................................................................................. 4 2. Assessing Flood Risk in Waltham Forest ........................................................ 6 2.1 Study Area .................................................................................................................................. 6 2.2 Topography ................................................................................................................................. 6 2.3 Geology ...................................................................................................................................... 6 2.4 River Network ............................................................................................................................. 7 2.5 Fluvial Flood Risk ....................................................................................................................... 8 2.6 Surface water flood risk ............................................................................................................ 11 2.7 Geology and Groundwater flood risk ........................................................................................ 12 2.8 Sewer Flood Risk ..................................................................................................................... 13 2.9 Risk of Flooding from Reservoirs .............................................................................................. 14 2.10 Historic Flood Events ................................................................................................................ 14 2.11 Flood Risk Management Infrastructure ..................................................................................... 14 2.12 Surface Water Management Schemes- Options Appraisal ....................................................... 15 3. Impact of Climate Change ............................................................................. 17 3.1 Peak River Flow ....................................................................................................................... 17 3.2 Climate change for Surface Water flow .................................................................................... 19 4. Avoiding Flood Risk – Risk Based Approach to Planning .............................. 20 4.1 Sequential Approach ................................................................................................................ 20 4.2 Applying Sequential Test – Plan Making ................................................................................... 20 4.3 Applying Sequential Test – Planning Applications .................................................................... 25 4.4 Exception Test .......................................................................................................................... 27 5. Managing and Mitigating Flood Risk through Spatial Planning and Development Control ..................................................................................... 28 5.1 Overview .................................................................................................................................. 28 5.2 Design Flood Level ................................................................................................................... 28 5.3 Development Layout and Sequential Approach ........................................................................ 28 5.4 Finished Floor Levels ............................................................................................................... 28 5.5 Flood Resistance ‘Water Exclusion Strategy’ ........................................................................... 29 5.6 Flood Resilience ‘Water Entry Strategy’ ................................................................................... 30 5.7 Safe Access/ Egress ................................................................................................................. 31 5.8 Safe Refuge.............................................................................................................................. 31 5.9 Floodplain Compensation Storage ........................................................................................... 31 5.10 Flood Voids ............................................................................................................................... 32 5.11 Car Parks.................................................................................................................................. 32 5.12 Flood Routing ........................................................................................................................... 33 5.13 Riverside Development ............................................................................................................ 33 5.14 Flood Warning Areas ................................................................................................................ 34 5.15 Surface Water Management ..................................................................................................... 34 5.16 Natural Flood Management ...................................................................................................... 34 5.17 Recommendations for Policy and Practice ............................................................................... 35 6. Guidance for Developers ............................................................................... 36 6.1 What is a Flood Risk Assessment? .......................................................................................... 36 AECOM iii London Borough of Waltham Forest Level 1 SFRA FINAL Project number: 60577135 6.2 When is a Flood Risk Assessment required? ........................................................................... 36 6.3 How detailed should a FRA be? ............................................................................................... 36 6.4 What needs to be addressed in a Flood Risk Assessment? ..................................................... 37 6.5 Flood Risk Assessment Checklist ............................................................................................. 38 6.6 Pre-application Advice .............................................................................................................. 40 7. Recommendations for Policy and Practice .................................................... 42 7.1 Strategic Planning .................................................................................................................... 42 7.2 Development Control ................................................................................................................ 43 7.3 Flood Defences ........................................................................................................................ 44 7.4 Sustainable Drainage Systems................................................................................................. 45 7.5 Emergency Planning ................................................................................................................ 45 7.6 Water Environment ..................................................................................................................