Suffolk Coastal and Waveney District Councils Suffolk Coastal and Waveney District Strategic Flood Risk Assessment Main Report Report February 2008 Prepared for: Suffolk Coastal …where quality of life counts Suffolk Coastal and Waveney District Councils Strategic Flood Risk Assessment Revision Schedule Strategic Flood Risk Assessment February 2008 Rev Date Details Prepared by Reviewed by Approved by 01 May 2007 Draft SFRA Elizabeth Williams Elizabeth Williams Jon Robinson Senior Consultant Senior Consultant Principal Consultant Eleanor Cole Graduate Hydrologist 02 January 2008 Final SFRA Eleanor Cole Elizabeth Williams Jon Robinson Graduate Hydrologist Senior Consultant Principal Consultant 03 February Final SFRA Eleanor Cole Elizabeth Williams 2008 Graduate Hydrologist Senior Consultant This document has been prepared in accordance with the scope of Scott Wilson's appointment with its client and is subject to the terms of that appointment. 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Tel 0207 7985000 © Scott Wilson Group PLC 2006 Fax 0207 7985001 www.scottwilson.com Scott Wilson I February 2008 Suffolk Coastal and Waveney District Councils Strategic Flood Risk Assessment Table of Contents List of Tables ................................................................................................IV List of Figures................................................................................................V 1 Introduction.........................................................................................1 1.1 Background .......................................................................................................................1 1.2 Suffolk Coastal and Waveney SFRA ................................................................................2 1.3 Scope and Objectives .......................................................................................................2 1.4 SFRA Approach ................................................................................................................3 1.5 Synopsis............................................................................................................................4 2 Background ........................................................................................8 2.2 History of Flooding ............................................................................................................9 3 Flooding and Planning Policy ...........................................................11 3.2 Overview of the English Planning System.......................................................................11 3.3 Introduction to Flooding and Planning Policy ..................................................................12 3.4 Statutory National Planning Policy and Guidance...........................................................12 3.5 Non-Statutory National Planning Documents..................................................................18 3.6 Regional Planning Policy and Guidance .........................................................................19 3.7 Sub-Regional Planning Policy and Guidance .................................................................22 3.8 Local Planning Policy and Guidance...............................................................................24 4 Flood Sources, Defences and Mechanisms .....................................28 4.2 Coastal Flood Sources in the study area ........................................................................28 4.3 Fluvial Flood Sources in Waveney..................................................................................29 4.4 Fluvial Flood Sources in Suffolk Coastal.........................................................................30 4.5 Flood Defences in Suffolk Coastal and Waveney ...........................................................32 4.6 Flood Warnings ...............................................................................................................41 4.7 Flood Mechanisms for Suffolk & Waveney......................................................................43 4.8 Localised Flooding ..........................................................................................................45 5 Methodology .....................................................................................50 5.2 Digital Terrain Map (DTM) Generation............................................................................50 5.3 Flood Cell Definition ........................................................................................................50 5.4 Extreme Water Level Derivation......................................................................................53 5.5 Breach Modelling ............................................................................................................56 5.6 Definition of Tidal Hazard Categories .............................................................................61 5.7 Definition of Fluvial Hazard Categories...........................................................................61 5.8 Functional Floodplain ......................................................................................................62 6 Flood Mapping and Application ........................................................65 6.1 Introduction .....................................................................................................................65 Scott Wilson II February 2008 Suffolk Coastal and Waveney District Councils Strategic Flood Risk Assessment 6.2 Flood Zone Mapping .......................................................................................................65 6.3 Hazard Zones..................................................................................................................66 6.4 Rapid Inundation Zone....................................................................................................67 6.5 Using the Hazard Maps...................................................................................................67 7 Residual Risk Management..............................................................69 7.2 Managing Residual Risk .................................................................................................69 8 Sustainable Drainage systems .........................................................73 8.2 What are Sustainable Drainage Systems?......................................................................73 8.3 SuDS Techniques ...........................................................................................................75 8.4 Infiltration SuDS ..............................................................................................................75 8.5 Attenuation SuDS............................................................................................................76 8.6 Alternative Forms of Attenuation.....................................................................................76 8.7 Combined Infiltration / Attenuation Systems ...................................................................77 8.8 SuDS Suitability in the Suffolk Coastal and Waveney Areas ..........................................77 8.9 Further Information..........................................................................................................84 9 Conclusions and Recommendations ................................................86 9.1 Summary.........................................................................................................................86 9.2 Recommendations ..........................................................................................................86 9.3 Local Flood Risk Assessment Recommendations ..........................................................87 10 References .......................................................................................90 Annex 1 - PPS25 Extracts...........................................................................92 Annex 2 Data Collection and Sources.........................................................97 Introduction ...................................................................................................................................97 Topographic Data/Base Mapping..................................................................................................97 Flood Defences.............................................................................................................................98 Drainage........................................................................................................................................99 Flood History.................................................................................................................................99 Hydrometric Data