Water Boston Borough Council October 2010 Strategic Flood Risk Assessment Water Boston Borough Council October 2010 Prepared by: ................................ Checked by: .............................. Roy Lobley Richard Ramsden Associate Director Senior Engineer Approved by: ........................... Andy Yarde Regional Director Strategic Flood Risk Assessment Rev No Comments Checked by Approved Date by 1 Final to client RR AY April 2011 5th Floor, 2 City Walk, Leeds, LS11 9AR Telephone: 0113 391 6800 Website: http://www.aecom.com Job No 60034187 Reference RE01 Date Created October 2010 This document is confidential and the copyright of AECOM Limited. Any unauthorised reproduction or usage by any person other than the addressee is strictly prohibited. f:\projects\50016i boston sfra (revision)\reports\boston sfra final march11.docx Table of Contents Executive Summary ........................................................................................................................................................................ 1 1 Introduction ....................................................................................................................................................................... 7 2 Development Planning...................................................................................................................................................... 9 East Midlands Regional Spatial Strategy ............................................................................................................................ 9 3 Level 1 SFRA - Introduction ........................................................................................................................................... 11 Planning Policy Statement 25 ........................................................................................................................................... 11 Sequential Test ................................................................................................................................................................. 11 Flood Zones ...................................................................................................................................................................... 11 4 Causes of Flooding ......................................................................................................................................................... 13 Functional Floodplains and Washlands ............................................................................................................................. 13 Overflowing of Watercourses ............................................................................................................................................ 13 Breaching of Embankments .............................................................................................................................................. 14 Mechanical, Structural or Operational Failure ................................................................................................................... 15 Floodlocking and Tidelocking ............................................................................................................................................ 15 Localised Flooding ............................................................................................................................................................ 16 5 Sources of Flooding in Boston Borough ...................................................................................................................... 17 Introduction to Boston Borough ......................................................................................................................................... 17 Tidal Flooding .................................................................................................................................................................... 17 Fluvial Flooding ................................................................................................................................................................. 17 Potential Sources of Flooding ........................................................................................................................................... 17 Internal Drainage Board Arterial Drains............................................................................................................................. 18 Flood Risk in Pump-Drained Systems ............................................................................................................................... 18 Minor Sources of Flooding ................................................................................................................................................ 22 Critical Ordinary Watercourses ......................................................................................................................................... 22 Groundwater Flooding ....................................................................................................................................................... 23 Surface Water Flooding..................................................................................................................................................... 23 Areas Susceptible to Surface Water Flooding ................................................................................................................... 23 Sewer Flooding ................................................................................................................................................................. 24 River Witham Catchment Flood Management Plan .......................................................................................................... 24 The Wash Shoreline Management Plan ............................................................................................................................ 26 6 Flood Risk Management ................................................................................................................................................. 27 Inappropriate Development in the Floodplain .................................................................................................................... 27 Flood Storage Areas ......................................................................................................................................................... 27 Raised Defences ............................................................................................................................................................... 27 CFMP Policies ................................................................................................................................................................... 29 SMP Policies ..................................................................................................................................................................... 29 Operational and Emergency Planning ............................................................................................................................... 29 7 Sequential Test ................................................................................................................................................................ 31 Development Planning Sequential Test ............................................................................................................................ 31 Development Control Sequential Test ............................................................................................................................... 31 8 Flood Hazard ................................................................................................................................................................... 33 Flood Hazard Zones .......................................................................................................................................................... 33 Impact of Climate Change ................................................................................................................................................. 34 Topographical Survey Data Available For Hazard Mapping .............................................................................................. 34 9 Relative Probability Of Flooding .................................................................................................................................... 35 Introduction ....................................................................................................................................................................... 35 Man Made Flood Risk Sources ......................................................................................................................................... 36 Residual Risk Flooding...................................................................................................................................................... 37 Relative Probability of Flooding General Methodology ...................................................................................................... 38 Relative Probability of Flooding ......................................................................................................................................... 38 10 Exception Test ................................................................................................................................................................