Cheshire East Council Strategic Flood Risk Assessment
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Cheshire East Council Strategic Flood Risk Assessment Final Report August 2013 Cheshire East Council Spatial Planning Team 1st Floor Westfields Sandbach CW11 1HZ JBA Project Manager Chris Isherwood JBA Consulting Bank Quay House Sankey Street WARRINGTON WA1 1NN Revision History Revision Ref / Date Issued Amendments Issued to Draft (Level 1 SFRA) Report Cheshire East Council Version 1.1 Environment Agency 05 February 2013 United Utilities Draft (Level 2 SFRA) Report Inclusions of comments made by Cheshire East Council Version 2.2 Cheshire East Council Environment Agency 30 April 2013 19/02/2013 and United Utilities United Utilities 21/02/2013 on report version 1.1. Final SFRA Report Inclusions of comments made by Cheshire East Council Version 3.0 Cheshire East Council Environment Agency 19 June 2013 05/06/2013 on report version 2.2. United Utilities Final SFRA Report Final comments by Council Cheshire East Council Version 4.0 Members 02/08/2013 on report Environment Agency 19 August 2013 version 3.0. United Utilities Contract This report describes work commissioned by Stuart Penny, on behalf of Cheshire East Council, by a letter dated 9 October 2012. Cheshire East Council’s representative for the contract was Stuart Penny of the Spatial Planning Team. Chris Isherwood of JBA Consulting carried out this work. Prepared by ................................................ Chris Isherwood BSc DipWEM MSc CEnv MCIWEM C.WEM Chartered Senior Analyst Reviewed by ............................................... Howard Keeble MPhil BEng BSc CertBusStud CEng CEnv CSci MICE MCIWEM C.WEM Principal Engineer Approved by ................................................ Gary Deakin BSc CEng MICE Director Cheshire East Council SFRA - Final Report - v4.0.doc i Purpose This document has been prepared as a draft report for Cheshire East 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. JBA Consulting has no liability regarding the use of this report except to Cheshire East Council. Acknowledgements JBA would like to thank all Council, Environment Agency and United Utilities' staff for their time and commitment to providing data and discussing the issues identified during the course of this study. Particular thanks is given to Allan Clarke, as the Project Manager, for his valuable guidance and direction throughout the study process. Copyright © Jeremy Benn Associates Limited 2013 Carbon Footprint 472g A printed copy of the main text in this document will result in a carbon footprint of 371g if 100% post-consumer recycled paper is used and 472g if primary-source paper is used. These figures assume the report is printed in black and white on A4 paper and in duplex. JBA is aiming to achieve carbon neutrality. Cheshire East Council SFRA - Final Report - v4.0.doc ii Executive Summary As set out in the NPPF and its supporting Technical Guidance, Cheshire East Council as a Local Planning Authority are required to undertake a Strategic Flood Risk Assessment (SFRA) to support the preparation of their Local Plan. The SFRA forms an essential reference tool providing the building blocks for future strategic planning. Cheshire East Council should use the evidence provided in this SFRA to inform their knowledge of flooding, refine information on the Flood Map and determine the variations in flood risk from all sources of flooding. The SFRA should form the basis for preparing appropriate policies for flood risk management within the area. The primary objective of the SFRA is to enable Cheshire East Council to apply the Sequential and Exception Test in the development allocation and development management process set out in the NPPF. The NPPF requires that all development is steered to areas of lowest flood risk, where possible. Development is only permissible in areas at risk of flooding in exceptional circumstances where it can be demonstrated that there are no reasonable available sites in areas of lower risk and that the benefits of that development outweigh the risks from flooding. Such development is required to include mitigation and management measures to minimise risk to life and property should flooding occur. The original SFRAs were prepared by the former Districts of Crewe and Nantwich, Macclesfield, Congleton and Cheshire County Council under Planning Policy Statement 25 (PPS25). However, since their production new legislation, policies, strategies and flood risk evidence have emerged. In October 2012, Cheshire East Council commissioned JBA Consulting to review, update and consolidate each of the SFRAs into one document in accordance with Government’s development planning guidance. The Level 1 SFRA builds upon existing District SFRAs collating all flood risk evidence into one document. The core output of this study is a series of maps and GIS datasets, which include a narrative of flood risk issues across the District. The Level 2 SFRA includes a community flood risk review focusing on Principal Towns, Key Service Centres and New Settlements outlined in the Councils Local Plan document ‘Shaping our future: A Development Strategy for Jobs and Sustainable Communities’. The community review provides a detailed but high level overview of flood risk for each community and Strategic Sites proposed. Using this analysis, development recommendations have been provided on site-specific FRAs and appropriate flood risk management within that community. The SFRA study area predominantly covers the Cheshire Plain, a flat, lowland area, which is characterised by watercourses running in well-defined floodplains and localised areas of hilly terrain. To the northeast, the study area covers part of the western Peak District, an upland area forming the southern end of the Pennines. This area has steep topography, and is characterised by steep sided valleys and large numbers of minor watercourses. The main source of flood risk in the study area is from main rivers and Ordinary Watercourses. Whilst the overall level of risk from these sources is low, there are a number of major town centres such as Crewe, Macclesfield and Congleton where risk is greater due to the presence of a densely urban population. In these urban areas, watercourses can often be modified with straightened and culverted sections common, especially where rivers flow underneath major railway and road infrastructure. The Environment Agency has hydraulically modelled the majority of main rivers in the study area providing detailed flood risk information in the form of Flood Zones. There is however, a vast number of rivers and small Ordinary Watercourses not modelled or have indicative Flood Zones based on broad scale modelling outputs. In these locations, flood risk information is poor or incomplete. Due to the flat nature of the topography there is likely to be extensive surface water flood risks across the District resulting from an extreme rainfall event. To the north east, steeper topography is likely to result in surface water flooding along well defined flow-paths. Flooding in Cheshire East Council SFRA - Final Report - v4.0.doc iii these areas has the potential to represent a significant hazard to people due to its velocity and depth. The complex hydraulic interactions in the urban environment also increase the risk of surface water flooding. Urban watercourse connectivity, sewer capacity, and the location and condition of highway gullies all have a major role to play and in many cases urban watercourses have been culverted over and are likely to be in poor condition. A blockage or collapse of one of these culverts could represent a significant flood risk to adjacent properties. There is very little detailed information on these flood mechanisms. The Council has produced a Surface Water Management Plan that identifies high risk areas throughout the District, however further detailed analysis is required going forward. Cheshire East Council SFRA - Final Report - v4.0.doc iv Contents 1 Introduction............................................................................................................. 1 1.1 Commission .............................................................................................................. 1 1.2 Cheshire East SFRA ................................................................................................. 1 2 Understanding Flood Risk ...................................................................................... 3 2.1 Sources of Flooding .................................................................................................. 3 2.2 Likelihood and Consequence .................................................................................... 4 2.3 Risk .......................................................................................................................... 5 3 The Planning Framework and Flood Risk Policy .................................................. 6 3.1 Introduction ............................................................................................................... 6 3.2 Legislation ................................................................................................................ 7 3.3 Planning Policy ......................................................................................................... 9 3.4 Flood Risk Management Policy ................................................................................. 11 3.5 Roles and