Kings Lynn & West Norfolk Strategic Flood Risk
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Kings Lynn & West Norfolk Strategic Flood Risk Assessment (2007/8 Revision) Final Report Kings Lynn & West Norfolk Borough Council December 2008 Faber Maunsell Kings Lynn & West Norfolk Strategic Flood Risk Assessment (2007/8 Revision) i Table of Contents Contents .................................................................................................................................i List of Tables and Figures..................................................................................................iii Executive Summary .............................................................................................................v 1 Introduction ..............................................................................................................1 2 Flood Risk.................................................................................................................5 Planning Policy Statement 25 ....................................................................................5 Indicative Floodplain Maps.........................................................................................6 Flood Zone Maps .......................................................................................................7 The Flood Map ...........................................................................................................7 3 Causes of Flooding..................................................................................................9 Overflowing of Watercourses.....................................................................................9 Breaching of Embankments.....................................................................................10 Mechanical, Structural or Operational Failure..........................................................11 Floodlocking and Tidelocking...................................................................................12 Localised Flooding ...................................................................................................13 Critical Ordinary Watercourses ................................................................................13 Functional Floodplains and Washlands ...................................................................14 4 Flooding in Kings Lynn & West Norfolk ..............................................................15 Classes of Flooding..................................................................................................15 Potential Sources of Flooding ..................................................................................17 Residual Risk Flooding ............................................................................................17 Flood Risk in Pump-Drained Systems .....................................................................18 Records of Flooding .................................................................................................18 Flood Alleviation Measures......................................................................................19 Operational and Emergency Planning .....................................................................20 5 Strategic Assessment of Flood Risk....................................................................21 General Methodology...............................................................................................21 Topographic Divisions..............................................................................................22 Anthropogenic Influences.........................................................................................22 Flood Risk Mapping .................................................................................................24 Flood Hazard Mapping - General...........................................................................25 Flood Hazard Mapping - Kings Lynn & West Lynn ................................................27 6 Assessment of Flood Risk in the Study Areas ...................................................29 7 Study Areas in Kings Lynn & West Norfolk ........................................................31 SOUTH LYNN & LYNN SOUTH EXPANSION AREA (KL1) ................................35 WEST LYNN (KL2) .................................................................................................39 HISTORIC CORE (OLD LYNN) (KL3) ....................................................................43 NORTH LYNN (KL4) ...............................................................................................47 GAYWOOD (KL5) ...................................................................................................51 HARDWICK (KL6)...................................................................................................55 EASTERN EXPANSION AREA (KL7) ....................................................................59 NORTH & SOUTH WOOTTON (KL8).....................................................................61 DOWNHAM NORTH WEST (DM1).........................................................................67 DOWNHAM SOUTH WEST (DM2).........................................................................71 HUNSTANTON (HN1).............................................................................................75 Continued over .... Faber Maunsell Kings Lynn & West Norfolk Strategic Flood Risk Assessment (2007/8 Revision) ii Continued …. 8 Planning Policy and Flood Risk............................................................................79 East of England Regional Strategy ..........................................................................79 Sustainable Urban Drainage Systems .....................................................................80 9 Conclusions............................................................................................................83 10 Recommendations .................................................................................................85 References ..........................................................................................................................87 FIGURES PHOTOGRAPHS APPENDICES Appendix A The Brief Appendix B Conclusions & Recommendations in the 2005 Report Appendix C Strategic Flood Risk Mapping Methodology Faber Maunsell Kings Lynn & West Norfolk Strategic Flood Risk Assessment (2007/8 Revision) iii List of Tables and Figures LIST OF TABLES Table 1.1 Study Areas in Kings Lynn & West Norfolk Table 2.1 PPS 25 Flood Risk Zones Table 9.1 Future Housing Provision in the East of England Table 9.2 Future Housing Provision in Norfolk Appendix C Table C.1 Breach Widths and Time to Close Table C.2 Mannings ‘n’ Coefficients used in Breach Modelling Table C.3 Extreme Tide Levels in the Study Area (2007 Estimates) LIST OF FIGURES Figure 1.1 Borough of Kings Lynn & West Norfolk - General Location Plan Figure 1.2.1 Study Areas - Kings Lynn Location Plan Figure 1.2.2 Study Areas - Downham Market Location Plan Figure 1.2.3 Study Areas - Hunstanton Location Plan Figure 3.1 Principal Drainage Features of Kings Lynn & West Norfolk Strategic Flood Risk Maps of Kings Lynn & West Norfolk Figure 5.1 Present Day Situation (Flood Risk Zones) (Eleven sheets) Figure 5.1A Present Day Situation (F R Zones in Kings Lynn) Figure 5.2 Predicted Situation in Year 2115 (Flood Risk Zones) (Eleven sheets) Figure 5.2A Predicted Situation in Year 2115 (F R Zones in Kings Lynn) Figure 5.3 Present Day Situation (Hazard Zones) (Eleven sheets) Figure 5.4.1 Kings Lynn Breaches - Flood Extent Figure 5.4.2 Kings Lynn Breaches - Flood Depth Figure 5.4.3 Kings Lynn Breaches - Flood Velocity Figure 5.5.1 West Lynn Breaches - Flood Extent Figure 5.5.2 West Lynn Breaches - Flood Depth Figure 5.5.3 West Lynn Breaches - Flood Velocity Study Area Plans Figure 7.1 KL1 South Lynn Figure 7.2 KL2 West Lynn Figure 7.3 KL3 Historic Core (Old Lynn) Figure 7.4 KL4 North Lynn Figure 7.5 KL5 Gaywood Figure 7.6 KL6 Hardwick Continued over …. Faber Maunsell Kings Lynn & West Norfolk Strategic Flood Risk Assessment (2007/8 Revision) iv Continued …. Figure 7.7 KL7 Eastern Expansion Area Figure 7.8 KL8 North & South Wootton Figure 7.9 DM1 Downham North West Figure 7.10 DM2 Downham South West Figure 7.11 HN1 Hunstanton Appendix C Figure C.1 LiDAR Data Coverage Figure C.2 Breach Locations Selected for Modelling Faber Maunsell Kings Lynn & West Norfolk Strategic Flood Risk Assessment (2007/8 Revision) v Executive Summary The Department for Communities and Local Government's Planning Policy Statement 25 entitled "Development and Flood Risk" outlines how flood risk issues should be addressed in both Regional and Local Authority development plans as well as in the planning guidance issued to developers by planning authorities. The Planning Policy Statement (and its accompanying Practice Guide) also provides guidance on how flood risk assessments should be undertaken at regional, district (strategic) and development site level. Bullen Consultants Ltd, now part of Faber Maunsell, were originally commissioned by Kings Lynn & West Norfolk Borough Council in April 2003 to undertake a Strategic Flood Risk Assessment of the Borough based on a Brief issued by the Borough Council. The purpose of that study was to provide a reference and policy document to inform the Borough Council’s Local Plan. Kings Lynn & West Norfolk was one of the earliest local planning authorities in the country to undertake a strategic flood risk assessment and the Kings Lynn & West Norfolk Strategic Flood Risk Assessment