Stockport Metropolitan Borough Council Stockport Level 1 Update and Stockport Town Centre Level 2 Strategic Flood Risk Assessment March 2010 Prepared for Stockport Metropolitan Borough Council Stockport Level 1 Update and Stockport Town Centre Level 2 Strategic Flood Risk Assessment Revision Schedule Stockport Level 1 Update and Stockport Town Centre Level 2 Strategic Flood Risk Assessment March 2010 Rev Date Details Prepared by Reviewed by Approved by 01 Nov 2009 Draft Mark Crussell Michael Timmins Jon Robinson Assistant Flood Risk Principal Flood Risk Associate Director Specialist Specialist Alpha Robinson Principal Flood Risk Engineer Sam Rosillo Anita Longworth Graduate Planner Principal Planner 02 Dec 2009 Draft Rev2 Alpha Robinson Michael Timmins Jon Robinson Principal Flood Risk Principal Flood Risk Associate Director Engineer Specialist 03 March 2010 Final Alpha Robinson Michael Timmins Jon Robinson Principal Flood Risk Principal Flood Risk Associate Director Engineer Specialist Scott Wilson Brunel House 54 Princess Street Manchester M1 6HS United Kingdom Tel +44 (0)161 907 3500 Fax +44 (0)161 907 3501 www.scottwilson.com Stockport Metropolitan Borough Council Stockport Level 1 Update and Stockport Town Centre Level 2 Strategic Flood Risk Assessment Table of Contents 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.......................................2 2 Sequential Approach to Site Allocation....................................................... 4 2.1 The Sequential Test....................................................................................................................4 2.2 Development Vulnerability ..........................................................................................................4 2.3 Flood Zone Definition ..................................................................................................................6 2.4 The Exception Test .....................................................................................................................7 3 Planning Context ........................................................................................... 8 4 SFRA Approach ............................................................................................. 9 4.1 General Approach .......................................................................................................................9 4.2 Level 1 Update ............................................................................................................................9 4.3 Level 2 SFRA Requirements ....................................................................................................10 4.4 Level 2 SFRA Output ................................................................................................................15 5 Level 1 SFRA Update................................................................................... 16 5.1 Flooding History ........................................................................................................................16 5.2 Level 1 Update of Fluvial Flooding across Stockport................................................................16 5.3 Pluvial Flood Risk (flooding from overland flow).......................................................................19 5.4 Sewer and Drainage Flood Risk ...............................................................................................20 5.5 Critical Drainage Areas .............................................................................................................22 5.6 Flood Risk from Man-Made/Artificial Sources – Canals ...........................................................23 5.7 Flood Risk from Man-Made/Artificial Sources – Reservoirs .....................................................25 5.8 Groundwater Flood Risk ...........................................................................................................27 6 Stockport Town Centre Level 2 SFRA........................................................ 29 6.1 Stockport Town Centre Development Plans.............................................................................29 6.2 Town Centre Level 2 Fluvial Flood Risk Assessment...............................................................30 6.3 Risk of Flooding from Other Sources........................................................................................36 7 SFRA Policies and Flood Risk Management ............................................. 37 7.2 District Wide SFRA Policies......................................................................................................37 7.3 Town Centre Specific SFRA Policies........................................................................................39 7.4 Flood Risk Management Options..............................................................................................42 8 Site Specific Flood Risk Assessment Guidance....................................... 45 8.2 Application of the Sequential Approach....................................................................................45 8.3 Building Design .........................................................................................................................46 8.4 Surface Water Management .....................................................................................................46 8.5 Residual Risk Mitigation............................................................................................................51 Stockport Metropolitan Borough Council Stockport Level 1 Update and Stockport Town Centre Level 2 Strategic Flood Risk Assessment 9 Conclusions and Recommendations ......................................................... 55 9.1 Conclusions...............................................................................................................................55 9.2 Recommendations ....................................................................................................................56 Appendix 1 Maps ...................................................................................................... 57 Appendix 2 Summary of Planning Data.................................................................. 58 Appendix 3 Flood Defence Inspection Report ....................................................... 59 Figures Figure 4-1: Hierarchical Approach to Flood Risk........................................................................................9 Figure 5-1: Overview of watercourses in the district ...............................................................................17 Figure 6-1: Long Section showing water levels along the Tame, Goyt and Mersey................................32 Figure 6-2: Stockport Town Centre Depth Hazard map for the 1% AEP event .......................................34 Figure 6-3 : Stockport Town Centre Depth Hazard map for the 1% AEP event plus Climate Change....35 Figure 6-4: Stockport Town Centre Depth Hazard map for the 0.1% AEP event ....................................36 Figure 7-1: Key Town Centre Regeneration Activity (Source: Future Stockport Review) ......................40 Figure 7-2: Comparison of flow hydrographs downstream of the Town Centre development boundary (defended and defended scenarios).........................................................................................................43 Tables Table 2-1: Flood Risk Vulnerability Classification ......................................................................................4 Table 2-2: Flood Risk Vulnerability and Flood Zone ‘Compatibility’..........................................................5 Table 4-1: Key to Depth Hazard...............................................................................................................15 Table 5-1: Potential breach vulnerability locations along canals within Stockport...................................24 Table 5-2: Watercourses where reservoirs are located upstream outside of the study area...................26 Table 5-3: Key Hydro geological Units in the Stockport MBC District......................................................28 Table 6-1: Examples of key developments and appropriate flood zones ................................................29 Table 8-1: Typical SuDS Components .....................................................................................................47 Table 8-2: Flood Proofing Options ..........................................................................................................52 Stockport Metropolitan Borough Council Stockport Level 1 Update and Stockport Town Centre Level 2 Strategic Flood Risk Assessment Abbreviations ACRONYM DEFINITION AEP Annual Exceedance Probability AOD Above Ordnance Datum AONB Area of Outstanding Natural Beauty ASTSWF Areas Susceptible To Surface Water Flooding BW British Waterways CDA Critical Drainage Area CFMP Catchment Flood Management Plan DEM Digital Elevation Model DPD Development Plan Documents EA Environment Agency EP English Partnerships FRA Flood Risk Assessment GIS Geographical Information