Report Template
Total Page:16
File Type:pdf, Size:1020Kb
Babergh District Council Strategic Flood Risk Assessment March 2009 FINAL REPORT JBA Consulting Babergh District Council 100 Crowmarsh Battle Barns Corks Lane Preston Crowmarsh Hadleigh WALLINGFORD IPSWICH Oxfordshire Suffolk OX10 6SL IP7 6SJ UK t: +44 (0)1491 836688 f: +44 (0)8700 519307 www.jbaconsulting.co.uk This page is intentionally left blank. JBA Consulting www.jbaconsulting.co.uk N:\2008\Projects\2008s3779 - Babergh District Council - Babergh and Tendring District Councils Stage 2 SFRA\Reports\Final Report\Babergh\2008s3779 - Babergh DC SFRA Final Report v3.2.doc: 20/04/2009 i REVISION HISTORY Revision Ref./ Amendments Issued to Date Issued Draft Report Naomi Allen (Babergh DC) January 2009 One digital copy Nicole Ager (Environment Agency) One digital copy Draft Final Report Complete report with appendices Naomi Allen (Babergh DC) 17 February 2009 One digital copy Nicole Ager (Environment Agency) One digital copy Final Report Including comments from Babergh DC Naomi Allen (Babergh DC) March 2009 and Environment Agency, aswell as Two paper copies inclusion of DG5 information. One digital copy Nicole Ager (Environment Agency) One paper copy One digital copy CONTRACT This report describes work commissioned by Babergh District Council under Order (No. 2003600). Babergh District Council‟s representative for the contract was Naomi Allen. Tony Green, Paul Eccleston, Liu Yang, Philip Emonson, Claire Gardner and Jenny Hill of JBA Consulting carried out the work. Prepared by: Philip Emonson, BSc, MSc, FRGS Analyst Reviewed by: Paul Eccleston, BA, CEnv, MCIWEM Senior Analyst PURPOSE This document has been prepared solely as a Strategic Flood Risk Assessment for Babergh District Council. JBA Consulting accepts no responsibility or liability for any use that is made of this document other than by the Client for the purposes for which it was originally commissioned and prepared. ACKNOWLEDGMENTS JBA would like to thank Babergh District Council, the Environment Agency and Anglian Water for the timely supply of data and for co-operation on the project. JBA Consulting www.jbaconsulting.co.uk N:\2008\Projects\2008s3779 - Babergh District Council - Babergh and Tendring District Councils Stage 2 SFRA\Reports\Final Report\Babergh\2008s3779 - Babergh DC SFRA Final Report v3.2.doc: 20/04/2009 ii EXECUTIVE SUMMARY This report constitutes the Final report for the Strategic Flood Risk Assessment (SFRA) for the district of Babergh, Suffolk. This fulfils the requirements of a Level 1 and Level 2 SFRA. This SFRA has been prepared in accordance with current best practice, Planning Policy Statement 25: Development and Flood Risk (PPS25). The SFRA is a planning tool that will assist the Council to make the spatial planning decisions required to inform the Local Development Framework (LDF). The assessment focuses on existing site allocations within the district, together with known areas of search, but also sets out the procedure to be followed when assessing additional sites for development in the future. High level planning, policy and guidance documents have been identified, which have been taken into account in preparing this SFRA. The documents which have been reviewed include national, regional and local planning legislation and guidance (including the Babergh Local Plan, Alteration No. 2, June 2006), together with Environment Agency policy documents. A thorough review of existing information, and additional modelling work, has identified the level of flood risk at present within the district from fluvial, tidal and other sources. This final report introduces the SFRA, sets the context in light of the existing planning framework, describes the approach taken to undertake the assessment, and reviews the different data sources used. It also provides details of fluvial and tidal flood risk (and the flood hazard associated with the breach of flood defences), as well as the risk from other sources. The details of the breach modelling, allowing the Exception Test to be undertaken, are displayed in Appendix C, and Appendix D summarises the risk to the development sites in Babergh. Fluvial flood risk across the district affects areas along the main river corridors of the Rivers Stour, Brett, Box, Gipping, their associated tributaries and the Belstead Brook. Some defences do exist along fluvial rivers such as the embankments at Stratford St Mary, although more commonly flood risk is managed through river and structure maintenance. There is risk of tidal flooding along the Stour and Orwell Estuaries including Shotley, Wherstead and Ipswich along the Orwell estuary, and Harkstead and Cattawade along the Stour. However, the significant tidal embankments and walls and the Cattawade tidal barrier protect this area up to a 0.5% annual exceedance probability flood event (1 in 200 year event) and a new barrier for Ipswich is proposed. Surface water flood risk has been assessed for the district. The impacts of the 0.5% annual exceedance probability storm event has been mapped, showing that the most vulnerable areas to surface water flooding include Sudbury, areas near Hadleigh and near Boxted. Sewer flooding is recorded by Anglian Water via their DG5 register. Anglian Water have supplied their DG5 register and from previous studies it is known that this is not a significant problem in the Babergh area compared with elsewhere in the country. Groundwater flooding is primarily controlled by the underlying geology. Chalk aquifers dominate parts of the Upper Stour catchment, in which following heavy rainfall the water table has the potential to rise above the ground surface and cause groundwater flooding. However in many parts of the district the chalk is overlaid by impermeable drift deposits which restrict this. There are very few reported incidents of groundwater flooding in the district and flooding from this source is not considered as high risk. Maps have been provided with the report showing the Flood Zones, the effect of climate change, residual risk, together with other supporting information. A thorough review of flood risk at each of the site specific allocations and for broader development areas has been undertaken, allowing the LPA to apply the Sequential Test. It provides advice on any site specific requirements for a Flood Risk Assessment for each site, and should inform the LPA on the use of the Exception Test should the Sequential Test be passed. In addition, an outline has been given of requirements for developers for Flood Risk Assessments (FRAs), with supporting guidance on reducing flood risk and making development safe, including Sustainable Drainage Systems (SuDS) and mitigation measures. JBA Consulting www.jbaconsulting.co.uk N:\2008\Projects\2008s3779 - Babergh District Council - Babergh and Tendring District Councils Stage 2 SFRA\Reports\Final Report\Babergh\2008s3779 - Babergh DC SFRA Final Report v3.2.doc: 20/04/2009 iii CONTENTS Page REVISION HISTORY ii CONTRACT ii PURPOSE ii ACKNOWLEDGEMENTS ii EXECUTIVE SUMMARY iii CONTENTS iv GLOSSARY AND ABBREVIATIONS viii 1 INTRODUCTION ----------------------------------------------------------------------------------------------------- 1 1.1 Introduction ..................................................................................................................................... 1 1.2 Objectives ....................................................................................................................................... 1 1.3 Study Area ...................................................................................................................................... 1 1.4 Background to the study ................................................................................................................ 2 2 THE PLANNING FRAMEWORK --------------------------------------------------------------------------------- 3 2.1 Introduction ..................................................................................................................................... 3 2.2 National planning policy ................................................................................................................. 3 2.3 Regional planning policy ................................................................................................................ 4 2.4 Local planning policy ...................................................................................................................... 6 2.5 Environment Agency policy ............................................................................................................ 8 2.6 Additional documents of relevance .............................................................................................. 10 3 APPROACH TO STRATEGIC FLOOD RISK ASSESSMENT ------------------------------------------ 13 3.1 Overview ...................................................................................................................................... 13 3.2 Level 1 – Scoping Study SFRA .................................................................................................... 17 3.3 Level 2 – Increased Scope SFRA ................................................................................................ 18 4 DATA SOURCES -------------------------------------------------------------------------------------------------- 19 4.1 Flood Zones ................................................................................................................................. 19 4.2 Flood defences ............................................................................................................................