Strategic Flood Risk Assessment
Total Page:16
File Type:pdf, Size:1020Kb
Bolton Metropolitan Borough Council Bolton Level 1 Update and Bolton Town Centre Level 2 Strategic Flood Risk Assessment March 2010 Prepared for: Bolton Metropolitan Borough Council Bolton Metropolitan Borough Council Bolton Level 1 Update and Bolton Town Centre Level 2 Strategic Flood Risk Assessment Revision Schedule Bolton Level 1 Update and Bolton Town Centre level 2 Strategic Flood Risk Assessment November 2009 Rev Date Details Prepared by Reviewed by Approved by 01 Dec 2009 Draft Mark Crussell Michael Timmins Jon Robinson Assistant Flood Risk Principal Flood Risk Associate Director Specialist Specialist 02 March 2010 Final Alpha Robinson Michael Timmins Jon Robinson Principal Flood Risk Principal Flood Risk Associate Director Engineer Specialist Lyndsey Regan Anita Longworth Jon Robinson Assistant Planner Principal Planner Associate Director Scott Wilson Brunel House This document has been prepared in accordance with the scope of Scott Wilson's 54 Princess Street appointment with its client and is subject to the terms of that appointment. It is addressed to and for the sole and confidential use and reliance of Scott Wilson's client. Scott Wilson Manchester accepts no liability for any use of this document other than by its client and only for the M1 6HS purposes for which it was prepared and provided. No person other than the client may copy (in whole or in part) use or rely on the contents of this document, without the prior United Kingdom written permission of t he Company Secretary of Scott Wilson Ltd. Any advice, opinions, or recommendations within this document should be read and relied upon only in the Tel +44 (0)161 907 3500 context of the document as a whole. The contents of this document do not provide legal Fax +44 (0)161 907 3501 or tax advice or opinion. © Scott Wilson Ltd 2009 www.scottwilson.com Bolton Metropolitan Borough Council Bolton Level 1 Update and Bolton Town Centre Level 2 Strategic Flood Risk Assessment Table of Contents Abbreviations ...............................................................................................iii Glossary...................................................................................................... iv 1 Introduction ....................................................................................... 1 1.1 Policy Context and Background......................................................................................1 1.2 Study Area...................................................................................................................... 2 1.3 Aims and Objectives of the Level 1 SFRA Update and Level 2 SFRA............................. 4 2 Sequential Approach to Site Allocation.............................................. 6 2.1 The Sequential Test........................................................................................................ 6 2.2 Development Vulnerability .............................................................................................. 6 2.3 Flood Zone Definition...................................................................................................... 7 2.4 The Exception Test......................................................................................................... 8 3 Planning Context............................................................................. 10 4 SFRA Approach .............................................................................. 12 4.1 General Approach......................................................................................................... 12 4.2 Level 1 Update ............................................................................................................. 12 4.3 Level 2 SFRA Requirements ........................................................................................ 13 4.4 Level 2 SFRA Output.................................................................................................... 17 5 Level 1 SFRA Update...................................................................... 18 5.1 Flooding History............................................................................................................ 18 5.2 Level 1 Update of Fluvial Flooding across Bolton ......................................................... 18 5.3 Pluvial Flood Risk (flooding from overland flow)............................................................ 21 5.4 Sewer and Drainage Flood Risk ................................................................................... 22 5.5 Critical Drainage Areas................................................................................................. 23 5.6 Flood Risk from Man-Made/Artificial Sources – Canals ................................................ 25 5.7 Flood Risk from Man-Made/Artificial Sources – Reservoirs........................................... 27 5.8 Groundwater Flood Risk ............................................................................................... 29 6 Bolton Town Centre Level 2 SFRA.................................................. 31 6.1 Bolton Town Centre Development Plans ...................................................................... 31 6.2 Town Centre Level 2 Fluvial Flood Risk Assessment.................................................... 32 6.3 Risk of Flooding from Other Sources ............................................................................ 44 7 SFRA Policies and Flood Risk Management ................................... 46 7.2 District Wide SFRA Policies.......................................................................................... 46 7.3 Town Centre Specific SFRA Policies ............................................................................ 48 7.4 Flood Risk Management Options.................................................................................. 50 (i) Bolton Metropolitan Borough Council Bolton Level 1 Update and Bolton Town Centre Level 2 Strategic Flood Risk Assessment 8 Site Specific Flood Risk Assessment Guidance .............................. 52 8.2 Application of the Sequential Approach ........................................................................ 52 8.3 Building Design............................................................................................................. 53 8.4 Surface Water Management ......................................................................................... 53 8.5 Residual Risk Mitigation................................................................................................ 58 9 Conclusions and Recommendations ............................................... 62 9.1 Conclusions.................................................................................................................. 62 9.2 Recommendations........................................................................................................ 63 Appendix 1 Maps ....................................................................................... 65 Appendix 2 Summary of Planning Data...................................................... 66 Appendix 3 Flood Defence Inspection Report ............................................ 67 Figures Figure 1-1: Bolton Town Centre planned development and Level 2 SFRA Area.......................................3 Figure 4-1: Hierarchical Approach to Flood Risk......................................................................................12 Figure 5-1: Overview of watercourses in Bolton MBC district .................................................................19 Figure 6-1: Representation of trash screen in hydraulic model................................................................35 Figure 6-2: Map showing reach between Central Street and Knowsley Street planned to be culverted as part of the Town Centre Development .....................................................................................................36 Figure 6-3: Map showing reach between Crown Street and Manor Street/Bank Street planned to be culverted as part of the Town Centre Development.................................................................................37 Figure 6-4: Long Section showing water levels in Bolton Town Centre...................................................39 Figure 6-5: Bolton Town Centre Depth Hazard map for the 1% AEP event ............................................40 Figure 6-6 : Bolton Town Centre Depth hazard map for the 1%AEP event plus Climate Change ..........41 Figure 6-7: Flood Zone within Bolton Town Centre..................................................................................42 Figure 6-8: Flood Zone within Bolton Town Centre..................................................................................43 Figure 6-9: Comparison of flows (1%AEP + CC) downstream of St Peter’s Way Culvert .......................44 Figure 7-1: Bolton Town Centre Development with Flood Zones ............................................................49 Tables Table 2-1: Flood Risk Vulnerability Classification ......................................................................................6 Table 2-2: Flood Risk Vulnerability and Flood Zone ‘Compatibility’..........................................................7 Table 4-1: Key to Depth Hazard...............................................................................................................17 Table 5-1: Potential breach vulnerability locations along the Manchester, Bolton and Bury Canal.........26 Table 5-2: