West Suffolk Level 1 Strategic Flood Risk Assessment
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WEST SUFFOLK COUNCIL STRATEGIC FLOOD RISK ASSESSMENT Level 1 10039526-ARC-EWE-S1-RP-DH-00003 APRIL 2021 CONTACTS RENUKA GUNASEKARA Technical Director m +44 (0) 7793 187 700 Arcadis. e [email protected] 2 Cornwall Street, Birmingham B3 2DX Arcadis Consulting (UK) Limited is a private limited company registered in England & Wales (registered number 02212959). Registered Office at Arcadis House, 34 York Way, London, N1 9AB, UK. Part of the Arcadis Group of Companies along with other entities in the UK. Copyright © 2018 Arcadis. All rights reserved. arcadis.com VERSION CONTROL Version Date Author Checker Approver Changes 01 18/12/20 SH CG RG Draft for Client Comment 02 04/03/21 SH CG RG Final Draft for Client Review 03 13/04/21 SH AH RG For Issue This report dated 13 April 2021 has been prepared for West Suffolk Council(the “Client”) in accordance with the terms and conditions of appointment dated 17 March 2020 (the “Appointment”) between the Client and Arcadis Consulting (UK) Limited (“Arcadis”) for the purposes specified in the Appointment. For avoidance of doubt, no other person(s) may use or rely upon this report or its contents, and Arcadis accepts no responsibility for any such use or reliance thereon by any other third party. CONTENTS 1 INTRODUCTION ....................................................................................................... 1 1.1 Project Context ..................................................................................................................................... 1 1.2 Policy Context ....................................................................................................................................... 1 1.2.1 National ............................................................................................................................................... 1 1.2.2 Local ................................................................................................................................................... 2 1.3 Data Collection ...................................................................................................................................... 3 1.4 Study Area ............................................................................................................................................. 3 1.4.1 West Suffolk Council ........................................................................................................................... 3 1.4.2 Watercourses ...................................................................................................................................... 4 1.4.3 Risk Management Authorities / Stakeholders..................................................................................... 6 2 USER GUIDANCE ..................................................................................................... 8 3 FUTURE DEVELOPMENT ...................................................................................... 10 4 HISTORIC FLOODING ............................................................................................ 14 4.1 Section 19 Flood Investigation Reports ........................................................................................... 16 4.2 Settlement Specific Reports from Other Sources of Historic Flooding Information ................... 17 4.2.1 Newmarket ........................................................................................................................................ 17 4.2.2 Haverhill and Clare ........................................................................................................................... 17 4.2.3 Bury St Edmunds .............................................................................................................................. 17 4.3 Historic Sewer Flooding ..................................................................................................................... 18 5 SOURCES OF FLOOD RISK .................................................................................. 20 5.1 Rivers ................................................................................................................................................... 20 5.1.1 Flood Zone 2 ..................................................................................................................................... 20 5.1.2 Flood Zone 3a ................................................................................................................................... 20 5.1.3 Flood Zone 3b ................................................................................................................................... 21 5.1.4 Approach to Mapping Flood Zones .................................................................................................. 21 5.2 Reservoirs ........................................................................................................................................... 23 5.3 Groundwater ....................................................................................................................................... 23 5.4 Surface Water ...................................................................................................................................... 23 5.4.1 Environment Agency Flood Map for Surface Water ......................................................................... 23 5.4.2 Surface Water Management Plans ................................................................................................... 24 5.4.3 Critical Drainage Areas ..................................................................................................................... 24 5.5 Sewers ................................................................................................................................................. 24 6 IMPACT OF CLIMATE CHANGE ............................................................................ 26 6.1 Context ................................................................................................................................................. 26 6.2 Rivers ................................................................................................................................................... 26 6.2.1 Modelled flood outlines ..................................................................................................................... 27 6.3 Surface Water ...................................................................................................................................... 28 6.4 Reservoirs ........................................................................................................................................... 29 6.5 Groundwater ....................................................................................................................................... 29 7 FLOOD RISK MANAGEMENT ................................................................................ 30 7.1 Flood warning ..................................................................................................................................... 30 7.2 Features and Structures .................................................................................................................... 34 7.2.1 Existing Environment Agency Assets ............................................................................................... 34 7.2.2 Existing Suffolk County Council Assets ............................................................................................ 35 7.2.3 Future Flood Risk Management Features ........................................................................................ 35 7.2.4 Flood Risk Management Opportunities ............................................................................................ 38 8 ADDRESSING FLOOD RISK IN DEVELOPMENT ................................................. 46 8.1 Site Specific Flood Risk Assessments ............................................................................................. 46 8.2 Cumulative Impacts of Development ................................................................................................ 48 8.3 Emergency Flood Management Plans .............................................................................................. 48 8.4 Additional Recommendations Identified during the SFRA Process ............................................. 49 IMAGES Figure 1 - Flow diagram showing the process of site allocation using the Sequential Test .............................. 1 Figure 2 - Flow diagram showing how to apply the Exception Test .................................................................. 2 Figure 3 - West Suffolk Study Area ................................................................................................................... 4 Figure 4 - Main Rivers, Ordinary Watercourses and IDB Drainage Channels .................................................. 5 Figure 5 - Risk Management Authorities ........................................................................................................... 7 Figure 6 - Distribution of ‘included’ housing sites over the 15-year trajectory. ................................................ 12 Figure 7 - Distribution of ‘included’ economic sites over the 15-year trajectory. ............................................. 13 Figure 8 - Bunds and Basins recommended as part of the Newmarket SWMP modelled mitigation Option