Greater Nottingham Strategic Flood Risk Assessment Summary of Key
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Greater Nottingham Strategic Flood Risk Assessment Summary of Key Findings for Nottingham City Council July 2008 This page is intentionally left blank. GREATER NOTTINGHAM STRATEGIC FLOOD RISK ASSESSMENT Summary of Key Findings Document issue details: B&V project no. 120986 Client’s reference no. BV-N2/MDC/00026 Version no. Issue date Issue status Distribution Nottingham City Council Draft Report (Electronic Environment Agency 1 October 2007 copy only) Nottingham Regeneration Ltd. (digital copy only) Nottingham City Council 2 July 2008 Final Report Environment Agency Nottingham Regeneration Ltd. Version no. Principal Authors Principal Checker Principal Reviewer Naomi Wing, EA Naomi Wing, EA 1 Lisa Roche, NCC Jenny Palmer, B&V Lisa Roche, NCC Ian Vernalls, NCC Ian Vernalls, NCC Naomi Wing, EA Naomi Wing, EA 2 Lisa Roche, NCC Peter Savill, EA Lisa Roche, NCC Ian Vernalls, NCC Ian Vernalls, NCC Notice: This report was prepared by the Environment Agency and Nottingham City Council solely for use by Broxtowe Borough Council, Environment Agency, Erewash Borough Council, Gedling Borough Council, Nottingham City Council, Nottingham Regeneration Limited, Nottinghamshire County Council, Rushcliffe Borough Council and Severn Trent Water (the Greater Nottingham SFRA Partnership). This report is not addressed to and may not be relied upon by any person or entity other than the Greater Nottingham SFRA Partnership for any purpose without the prior written permission of BVL. BVL, its directors, employees and affiliated companies accept no responsibility or liability for reliance upon or use of this report (whether or not permitted) other than by the Greater Nottingham SFRA Partnership for the purposes for which it was originally commissioned and prepared. Whilst all reasonable care has been taken in this assessment we cannot guarantee that during the lifetime of the flood risk assessment water levels may not exceed those stated. The report has addressed the risk of flooding from the River Trent, River Erewash, River Derwent, River Leen, Fairham Brook, Nethergate Brook, Day Brook and other watercourses/sources specifically mentioned only, and the conclusions stated in it are based on our best estimate using available data with a precautionary approach taken where possible. We have not assessed flood risks from sources other than those specifically referred to. We must make it clear that the assessment of weather generated flooding is inexact and that analysis is limited by the accuracy and availability of recorded data. Higher water levels may occur in the future due to the actions or omissions of third parties, or to poor maintenance, blockage, storm events in excess of the design standard quoted, inaccuracy or unavailability of data. Flooding beyond that estimated in this report may also occur due to climate change. In producing this report, BVL has relied upon information provided by others. The completeness or accuracy of this information is not guaranteed by BVL. This page is intentionally left blank. Note for Developers/Landowners The Greater Nottingham Strategic Flood Risk Assessment (SFRA) and River Leen SFRA represent the best currently available flooding information for the City of Nottingham. They should be read in conjunction with the Environment Agency’s Flood Zone Maps as described in Paragraph 5.3 of this document. Together these two documents should be the starting point for establishing the risk of flooding to sites in the City. However, the SFRA does not replace the need for a site-specific flood risk assessment to look at the flood risk and mitigation options for your individual site. Further advice on the process for undertaking a site-specific flood risk assessment is included in Section 4 of this document. It is important that when considering flooding to your individual site, you give due regard to climate change and the impact of proposed flood mitigation measures on flood risk to land elsewhere. Further advice on flood protection measures can be found in the Department of Communities and Local Government (DCLG) publication entitled ‘Improving the Flood Performance of New buildings’ available at http://www.planningportal.gov.uk/uploads/br/flood_performance.pdf and Office of the Deputy Prime Minister (ODPM) publication ‘Preparing for Floods’ available at http://www.planningportal.gov.uk/uploads/odpm/4000000009282.pdf?lang=_e The Environment Agency will expect a site-specific flood risk assessment to consider sustainable forms of surface water management (e.g. SUDS) in preference to traditional forms of drainage. Further advice can be found in the Construction Industry Research and Information Association (CIRIA) publication ‘SUDS Design Manual for England and Wales ’ or www.ciria.org/suds/ A site specific flood risk assessment will need to conform with the advice contained in Planning Policy Statement 25: Development and Flood Risk (PPS 25). Excerpts of PPS 25 are included in Appendix B of this document. The Environment Agency encourages pre-planning discussions, in particular of major developments, in order to establish the constraints to delivery of sites at the earliest opportunity. You should also discuss application of the flood risk Sequential Test with the Planning Case Officer at Nottingham City Council. i This page is intentionally left blank. ii GREATER NOTTINGHAM STRATEGIC FLOOD RISK ASSESSMENT Summary of Key Findings Contents 1. Introduction 1 1.1 Project Outline 1 1.2. Planning and Legislative Context 3 2. Study Area and Methodology 4 2.1. Study Area 4 2.2. Existing Flooding Information 4 2.3. Methodology 6 3. Results 8 3.1 Executive Summary 8 3.2. River Trent Corridor 9 3.3 Fairham and Nethergate Brooks 13 3.4 Other Sources of Flooding 13 3.5 River Leen and Day Brook 14 4. Site-Specific Flood Risk Assessments 14 4.1 Advice for Undertaking a Flood Risk Assessment 14 5. Development Control Guide 16 5.1 Guidance 16 6. Glossary of Terms and Abbreviations 18 7. Related Documentation 23 Appendix A – Detailed Methodology 30 Appendix B – Planning Policy Extracts 32 iii This page is intentionally left blank. iv 1. Introduction 1.1 Project Outline 1.1.1 This document is designed to communicate to planners, landowners and developers the key findings of the study as they relate to land use planning within Nottingham City Council area. Background and Partnership 1.1.2 In December 2006, Black and Veatch (B&V) commenced a study into flood risk from the River Trent and its key tributaries through the Nottingham Core Housing Market Area on behalf of the Greater Nottingham Strategic Flood Risk Assessment Partnership (GNSFRA), which comprises: • Broxtowe Borough Council • Environment Agency • Erewash Borough Council • Gedling Borough Council • Nottingham City Council • Nottingham Regeneration Limited • Nottinghamshire County Council • Rushcliffe Borough Council • Severn Trent Water. 1.1.3 The Strategic Flood Risk Assessment (SFRA) draws upon updated river modelling and survey data to predict how the River Trent and its key tributaries will react during various storm events, including the key planning benchmark - the 1 in 100 annual chance flood event1. 1.1.4 For Nottingham City Council, the SFRA primarily consolidates and expands upon existing flooding information to provide a more complete picture of flood risk and its impact on planning. Project Purpose 1.1.5 The purpose of the SFRA is to: • provide a map-based planning tool that can be used by planning officers to inform the Local Development Framework (LDF) process and individual planning applications; • inform and anticipate the Environment Agency’s response to the various stages of the planning process; 1 Probability of flooding is expressed in terms of the statistical likelihood of an event being exceeded in a given year, such as “the 1 in 100 annual chance flood event” or similar. This is often abbreviated as the 1 in 100 year flood. It is essential to appreciate that the 1 in 100 chance flood may re-occur in less than 100 years. 1 • help steer new development away from areas of highest risk; and • assist with emergency planning. Primary Outputs 1.1.6 The primary outputs of the SFRA are: • more accurate flood maps indicating areas of flooding at the 1 in 20, 1 in 100, 1 in 100 plus climate change and 1 in 1000 annual chance flood events with both the existing and proposed defences; • flood dynamic plans illustrating depths and direction of anticipated flows shown on Maps 4–NCC–01 to 06; • flood hazard maps providing information on the varying degrees of risk within the floodplain based upon the predicted depths and velocities of flood water (see Table 2.1 for further information on flood hazard ratings) shown on Maps 4–NCC–07 to 18; • breach maps showing the impact of failure of the flood defences on flood risk shown on Maps 1–FDP–30 and Map 1–FDP–33; and • other sources of flooding map consolidating factual and anecdotal evidence held by a variety of organisations on sources of flooding other than from rivers within the Nottingham City Council area e.g. sewer flooding, drainage issues, groundwater flooding etc. shown on Map 1–OTH- 03 and Table 6.1 at the end of the report. 1.1.7 The SFRA will be reviewed when significant events occur, which require updates to the mapping (e.g. flood event, changes to planning policy, defence works or development affecting major floodplain compensation/ storage areas etc). Relationship between the SFRA and Existing Flood Zone Mapping 1.1.8 The SFRA differs from the Environment Agency’s Flood Zone Maps by providing flood mapping taking into account existing flood defences. The Flood Zone Maps (as published on the Environment Agency’s web site) ignore the presence of man made structures (e.g. flood defences, railway embankments etc.). 1.1.9 The SFRA provides more refined flooding information for the River Trent and its key tributaries and the SFRA should be used to compliment the Flood Zone Maps.