Borough Council of King's Lynn and West Norfolk Strategic Flood Risk Assessment: Annex to Level 1 Final Report April 2010 (Modified October 2010) Creating the environment for business Copyright and Non-Disclosure Notice The contents and layout of this report are subject to copyright owned by Entec (© Entec UK Limited 2010) save to the extent that copyright has been legally assigned by us to another party or is used by Entec under licence. To the extent that we own the copyright in this report, it may not be copied or used without our prior written agreement for any purpose other than the purpose indicated in this report. The methodology (if any) contained in this report is provided to you in confidence and must not be disclosed or copied to third parties without the prior written agreement of Entec. Disclosure of that information may constitute an actionable breach of confidence or may otherwise prejudice our commercial interests. Any third party who obtains access to this report by any means will, in any event, be subject to the Third Party Disclaimer set out below. Third-Party Disclaimer Any disclosure of this report to a third-party is subject to this disclaimer. The report was prepared by Entec at the instruction of, and for use by, our client named on the front of the report. It does not in any way constitute advice to any third-party who is able to access it by any means. Entec excludes to the fullest extent lawfully permitted all liability whatsoever for any loss or damage howsoever arising from reliance on the contents of this report. We do not however exclude our liability (if any) for personal injury or death resulting from our negligence, for fraud or any other matter in relation to which we cannot legally exclude liability. © Entec UK Limited Page ii Doc Reg No. 26655c004 April 2010 (Modified October 2010) Creating the environment for business Notice This report was originally produced in April 2010 and written in the context of the situation which then existed i.e. the recent publication of the Local Development Framework Core Strategy. The Modifications now inserted take account of subsequent suggested revisions identifying the Rural Key Service Centres as discussed in the ‘Background paper to the Settlement Hierarchy (Policy CS02) and changes from the Proposed Submission document (May 2010)’ and ‘Schedule of Focused Changes’. Concurrent with this work the Secretary of State has also revoked the East of England Plan but, in the interests of expediency, the original text has not been revised to reflect this. © Entec UK Limited Page iv Doc Reg No. 26655c004 April 2010 (Modified October 2010) Creating the environment for business Contents 1. Introduction 9 1.1 Background 9 1.2 Previous Studies 9 1.2.1 Level 1 Strategic Flood Risk Assessment (Bullen Consultants Ltd, 2005 and Faber Maunsell Ltd, 2008) 9 1.2.2 Phase 1 Water Cycle Study (Entec, 2009) 10 1.2.3 Phase 2 Water Cycle Study (commenced July 2009, Entec) 10 1.3 Structure of Report 10 2. Planning Context 12 2.1 National Planning Policy 12 2.1.1 PPS 25: Development and Flood Risk 12 2.1.2 PPS 1: Delivering Sustainable Development and the Supplement to PPS1: Planning and Climate Change13 2.1.3 PPS 3: Housing 14 2.2 Regional Policy 14 2.2.1 East of England Regional Spatial Strategy 14 2.3 Local Planning Policy 15 2.3.1 Borough of King’s Lynn and West Norfolk Local Plan 15 2.3.2 Emerging Local Development Framework 16 2.3.3 Growth Point Status 16 2.3.4 Urban Development Strategy 17 3. Flood Zone Mapping 19 3.1 Environment Agency Flood Maps 19 3.2 Level 1 SFRA Flood Maps 20 4. Sustainability and Regeneration Objectives for Development 22 4.1 Development Needs 22 4.2 The Exception Test for Development in King’s Lynn 23 4.3 Emergency Planning 27 5. Flood Risks to Rural Key Service Centres 28 5.1 Development in Rural Areas 28 5.2 Screening of Flood Risk 28 © Entec UK Limited Page v Doc Reg No. 26655c004 April 2010 (Modified October 2010) Creating the environment for business 5.2.1 Tidal Flood Risks 28 5.2.2 Fluvial Flood Risks 29 5.3 Discussion over Impacts of Screening Results on Rural Communities 36 5.4 Summary of Screening Key Service Centres 36 6. The Lynn South Expansion Area 38 6.1 Present Day Flood Risks 38 6.2 Future Flood Risks 39 6.3 Suitable Development 39 7. Flood Defences Policy and Maintenance 44 7.1 Shoreline Management Plans 44 7.1.1 The Draft Wash Shoreline Management Plan 2 (October 2009) 45 7.1.2 Draft North Norfolk Shoreline Management Plan (July 2009) 47 7.2 The Great Ouse Tidal River Strategy (Draft for Consultation September 2009) 48 7.3 Catchment Flood Management 49 7.4 Flood Defence Maintenance Regime 50 8. Sustainable Drainage 51 8.1 Introduction 51 8.2 Adoption of SuDS 53 8.3 Existing Drainage in the Borough of King’s Lynn and West Norfolk 54 8.4 Suitability of SuDS for Proposed Development 54 8.5 Recommendations for Site-Specific Assessments 56 8.6 Recommendations for Surface Water Management Plans 56 9. Summary and Conclusions 58 10. References 60 Table 4.1 Flood Risk Vulnerability and Flood Zone ‘Compatibility’ (PPS25 Table D.3) 24 Table 4.2 Policy suggestions for Development in King’s Lynn town within Flood Zone 3 (Including Flood Zone 3a with an Allowance for the Potential Impacts of Climate Change) 26 Table 5.1 Results of Flood Risk Screening of Key Rural Service Centres 30 Table 6.1 Summary of Present Day Flood Risks 38 Table 6.2 Summary of Future Flood Risks 39 Table 6.3 Flood Risk Vulnerability and Flood Zone ‘Compatibility’ (PPS25 Table D.3) 40 Table 6.4 Land uses suitable under PPS25 for Lynn (South) 42 Table 7.1 Summary of Issues from The Wash SMP 46 Table 7.2 Summary of Issues from North Norfolk SMP 47 Table 7.3 Proposed Actions from Great Ouse Catchment Flood Management Plan 49 Table 8.1 Examples of SuDS Techniques 51 © Entec UK Limited Page vi Doc Reg No. 26655c004 April 2010 (Modified October 2010) Creating the environment for business Table 8.2 Recommended Discharges for Source Protection Zones 56 Figure 3.1 Extract of Environment Agency’s Flood Mapping, November 2009 (http://maps.environment- agency.gov.uk/wiyby/wiybyController?ep=maptopics&lang=_e) 20 Figure 5.1 Climate Change Flood Risks to Key Service Centres 34 Figure 5.2 Extract of Fluvial Flood Risks Map 35 Figure 6.1 Flood Risks to Lynn South Expansion Area 43 © Entec UK Limited Page vii Doc Reg No. 26655c004 April 2010 (Modified October 2010) Creating the environment for business Glossary Annual Probability. The annual probability of a flood event occurring, so for the 1% AP the chance of a flood occurring AP with that magnitude is 1% in any year. This can also be expressed as a ratio, for example the 1% probability flood is the same as the 1 in 100 year return period. Catchment Flood Management Plans are produced by the Environment Agency to facilitate understanding of the factors CFMP that contribute to flood risk within a catchment, and how to manage flood risk within the catchment for the next 50 to 100 years. CIRIA Construction Industry Research and Information Association. Culvert A watercourse that is channelled beneath a road or railway, usually in drainage pipe. DEFRA Department for Environment, Food and Rural Affairs. DTM Digital Terrain Model. Flood Resistant Measure to prevent flooding or inundation of water. Flood Resilient Measures to reduce the impact of flooding. Fluvial A term relating to rivers. Flood Risk Assessment. A site specific assessment of flood risk from all sources and proposed mitigation to prevent the FRA development and areas downstream from being susceptible to flooding. Geographical Information System, a system for storing, analysing and managing data and associated attributes which GIS are spatially referenced to the earth. Ha Hectare. LiDAR Light Detection and Rada.r LDF Local Development Framework. PDL Previously Developed Land. PPS25 Planning Policy Statement 25: Development and Flood Risk (2006). SAR Synthetic Aperture Radar (surveying technique). Strategic Flood Risk Assessment. The assessment of flood risk at a high level for a local authority unit to guide planning SFRA policy and the Local Development Framework. Special Protection Areas are protected sites classified in accordance with the EC Directive on the conservation of wild SPA birds (79/409/EEC), also known as the Birds Directive. They are classified for rare and vulnerable birds and for regularly occurring migratory species. Source Protection Zone, a zone defined by the Environment Agency to protect groundwater sources of public water SPZ supply. Sustainable Drainage Systems are drainage systems that mimic the natural process of rainfall runoff, which are SUDS advocated as best practice to control flood risk, water quality and enhance groundwater recharge and amenity value, through infiltration and attenuation measures. RFRA Regional Flood Risk Appraisal. A strategic overview of flood risks on a regional scale. Residual Risk The risk which remains after all risk avoidance, reduction and mitigation measures have been implemented. © Entec UK Limited Page viii Doc Reg No. 26655c004 April 2010 (Modified October 2010) Creating the environment for business 1. Introduction 1.1 Background Strategic Flood Risk Assessments (SFRA) are required under Planning Policy Statement 25 “Development and Flood Risk” (PPS25) to be produced by individual planning authorities, in consultation with the Environment Agency, to form part of the authority’s Core Strategy evidence base.