March 2014 LEVEL 2 STRATEGIC FLOOD RISK ASSESSMENT CHULEY ROAD, ASHBURTON Dartmoor National Park Authority 3512820A-SSR Final Level 2 Strategic Flood Risk Assessment 3512820A-SSR Prepared for Dartmoor National Park Authority Parke Bovey Tracey Newton Abbot Devon TQ13 9JG Prepared by Parsons Brinckerhoff Queen Victoria House Redland Hill Bristol BS6 6US 0117 933 9300 www.pbworld.com Report Title : Level 2 Strategic Flood Risk Assessment Chuley Road, Ashburton Report Status : Draft Job No : 3512820A-SSR Date : March 2014 DOCUMENT HISTORY AND STATUS Document control Checked by Prepared by Charles Bennett Joanna Goodwin (technical) Checked by Approved by Jonathan Ralph Joanna Goodwin (quality assurance) Revision details Pages Version Date Comments affected August 0.1 - First draft 2013 December 0.2 - Updated following revision of hydraulic modelling 2013 March 1.0 Updated following EA and DNPA review 2014 Level 2 Strategic Flood Risk Assessment CONTENTS Page List of Abbreviations 5 Executive Summary 6 INTRODUCTION 9 1 Introduction 10 1.1 Project Background 10 1.2 Aims and Objectives 11 1.3 Sources of Flood Risk 11 1.4 Approach 12 1.5 Stakeholders 12 1.6 Flood Risk Management Roles and Responsibilities 12 1.7 Future Level 2 SFRA Updates 14 STUDY AREA AND LOCATION 15 2 Study Area and Location 16 2.1 Study Area 16 2.2 Hydrology 16 2.3 Geology 18 2.4 Flood Defence Infrastructure 18 LEVEL 2 SFRA APPROACH AND METHODOLOGY 20 3 Level 2 SFRA Approach and Methodology 21 3.1 Overview 21 3.2 Consultation 21 3.3 Desk Based Study 21 3.4 Hydraulic Modelling 22 3.5 Sequential Approach 23 PLANNING FRAMEWORK AND FLOOD RISK POLICY REVIEW 28 4 Planning Framework and Flood Risk Policy Review 29 4.1 Introduction 29 4.2 National Planning Policy Framework 29 4.3 Flood and Water Management Act 2010 29 4.4 Flood Risk Regulations 2009 30 4.5 Water Framework Directive 2000 / 60 / EC 30 4.6 South Devon Catchment Flood Management Plan 30 4.7 Devon Preliminary Flood Risk Assessment 30 4.8 Devon Local Flood Risk Management Strategy 31 4.9 Dartmoor National Park Level 1 Strategic Flood Risk Assessment 31 4.10 Dartmoor National Park Local Development Framework 31 4.11 Ashburton Town Plan 32 4.12 Implications of Planning Policy for Ashburton 32 Level 2 Strategic Flood Risk Assessment_v1.0.docx Prepared by Parsons Brinckerhoff March 2014 for Dartmoor National Park Authority - 1 - Level 2 Strategic Flood Risk Assessment ASSESSMENT OF FLOOD RISK 33 5 Assessment of Flood Risk 34 5.1 Introduction 34 5.2 Historic Flooding 34 5.3 Fluvial Flooding 40 5.4 Updated assessment of EA Flood Zones 45 5.5 Surface Water Flooding 48 5.6 Sewer Flooding 49 5.7 Groundwater Flooding 50 5.8 Flood Risks from Other Sources 50 5.9 Potential Impact of Development on Existing Flood Risk 50 5.10 Summary of Key Risks 50 SPATIAL PLANNING AND DEVELOPMENT GUIDELINES 52 6 Spatial Planning and Development Guidelines 53 6.1 Introduction 53 6.2 Spatial Planning and Development Guidelines 53 6.3 Application of the Exception Test 54 6.4 Measures to Reduce Flood Risk 56 6.5 Sustainable Drainage Systems (SUDS) 56 6.6 Water Sensitive Urban Design 60 6.7 Summary of Guidance 61 APPROACHES TO REDUCE FLOOD RISK 63 7 Approaches to reduce flood risk 64 7.1 Introduction 64 7.2 Reducing Flood Risk from River Ashburn 64 7.3 Reducing Flood Risk from Balland Stream 66 7.4 Summary of options considered 69 7.5 Partnership Funding Opportunities 70 SUMMARY AND CONCLUSIONS 72 8 Summary and Conclusions 73 8.1 Summary 73 BIBLIOGRAPHY 74 9 Bibliography 75 APPENDIX A: FIGURES APPENDIX B: HYDRAULIC MODELLING REPORT APPENDIX C: CORRESPONDENCE APPENDIX D: HISTORICAL FLOODING INFORMATION APPENDIX E: RESULTS OF HYDRAULIC MODELLING APPENDIX F: DEVELOPER GUIDANCE AND FLOOD RISK REDUCTION MEASURES APPENDIX G: EA NATIONAL FLOOD AND COASTAL DEFENCE DATABASE RECORDS Level 2 Strategic Flood Risk Assessment_v1.0.docx Prepared by Parsons Brinckerhoff March 2014 for Dartmoor National Park Authority - 2 - Level 2 Strategic Flood Risk Assessment Figure 1 Chuley Road Level 2 SFRA study area (dotted pink outline) with Chuley Road site 14 (solid red outline). Figure 2 River Ashburn upstream of Chuley Road site 22 Figure 3 River Ashburn in south of Chuley Road site 22 Figure 4 Inlet to Balland Stream culvert 22 Figure 5 Extract of video showing flooding in Love Lane from adjacent to Swimming Pool 43 entrance on 22.3.2013. Figure 6 Flooding adjacent to former Cattle Market in Vealenia Terrace. 7.2.1990. 45 Figure 7 Flooding in Chuley Road outside of Station Garage. 7.2.1990. 45 Figure 8 Flooding at south of Chuley Road site adjacent to Auction House. 7.2.1990. 45 Figure 9 Flooding in Chuley Road to south of Caravan Park, 7.2.1990 45 Figure 10 Flooding in Chuley Road adjacent to Station Garage. 11.2.1974. 46 Figure 11 Flooding in centre of Ashburton at Kings Bridge. 11.2.1974. 46 Figure 12 Flooding in the Bullring, August 1938 47 Figure 13 Flooding at London Inn in 1939 or 1946 47 Figure 14 Flooding in central Ashburton, 1950 47 Figure 15 1 in 10 year flood extent 49 Figure 16 1 in 100 year flood extent 49 Figure 17 1 in 100 year +cc flood depth 50 Figure 18 1 in 1000 year flood depth 50 Figure 19 1 in 10 year flood velocity 51 Figure 20 1 in 100 year flood velocity 51 Figure 21 1 in 100 year +cc flood velocity 51 Figure 22 1 in 1000 year flood velocity 51 Figure 23 1 in 10 year flood hazard 52 Figure 24 1 in 100 year flood hazard 52 Figure 25 1 in 100 year +cc flood hazard 53 Figure 26 1 in 1000 year flood hazard 53 Figure 27 Revised flood zone map based on detailed 1D-2D hydraulic model. 54 Figure 28 Revised flood zone map based on detailed 1D-2D hydraulic model with 100 year 54 flow increased by 20% to allow for potential climate change impact. Figure 29 Revised flood zone map based on detailed 1D-2D hydraulic model 56 Figure 30 Existing indicative EA flood zone map 56 Figure 31 First of two bridges adjacent to Auction House at south of Chuley Road site. 57 Figure 32 Second of two bridges adjacent to Auction House at south of Chuley Road site. 57 Figure 33 Old Totnes Road bridge 57 Figure 34 Small arch bridge 20m upstream of Castle Bridge 57 Level 2 Strategic Flood Risk Assessment_v1.0.docx Prepared by Parsons Brinckerhoff March 2014 for Dartmoor National Park Authority - 3 - Level 2 Strategic Flood Risk Assessment Figure 35 Small privately owned footbridges at south of Stonepark Crescent 57 Figure 36 Small privately owned footbridges at south of Stonepark Crescent 57 Figure 37 Example of swale in residential street 67 Figure 38 Example of wetland attenuation 67 Figure 39 SUDS management train 68 Figure 40 Illustrative example of a SUDS rain garden 69 Figure 41 Illustrative example of a SUDS wetland 70 Figure 42 Indicative sketch showing potential re-profiling options in River Ashburn 76 Level 2 Strategic Flood Risk Assessment_v1.0.docx Prepared by Parsons Brinckerhoff March 2014 for Dartmoor National Park Authority - 4 - Level 2 Strategic Flood Risk Assessment LIST OF ABBREVIATIONS AEP Annual Exceedance Probability AOD Above Ordnance Datum BGS British Geological Survey CFMP Catchment Flood Management Plan DCC Devon County Council DHS Devon Hydrology Study DPD Development Plan Document DNPA Dartmoor National Park Authority EA Environment Agency FCERM Flood and Coastal Erosion Risk Management FDGIA Flood Defence Grant in Aid FMfSW Flood Map for Surface Water FRR Flood Risk Regulations 2009 FWMA Flood and Water Management Act 2010 LDF Local Development Framework LFRMS Local Flood Risk Management Strategy LLFA Lead Local Flood Authority NFCDD National Food and Coastal Defence Database NPPF National Planning Policy Framework PB Parsons Brinckerhoff PPS25 Planning Policy Statement 25: Development and Flood Risk (superseded) PFRA Preliminary Flood Risk Assessment SAB SUDS Approval Body SFRA Strategic Flood Risk Assessment SUDS Sustainable Drainage Systems SWW South West Water TDC Teignbridge District Council TGNPPF Technical Guidance to the National Planning Policy Framework WaSC Water and Sewerage Company WFD Water Framework Directive WSUD Water Sensitive Urban Design Level 2 Strategic Flood Risk Assessment_v1.0.docx Prepared by Parsons Brinckerhoff March 2014 for Dartmoor National Park Authority - 5 - Level 2 Strategic Flood Risk Assessment EXECUTIVE SUMMARY Background Parsons Brinckerhoff was commissioned by Dartmoor National Park Authority to undertake a Level 2 Strategic Flood Risk Assessment for the Chuley Road area of Ashburton. The purpose of the report is to provide a detailed understanding of flood risk and hazard from flooding that can be used to inform future planning decisions in Ashburton. The report builds upon the findings of the 2010 Dartmoor Level 1 Strategic Flood Risk Assessment and should be reviewed alongside this document. Existing Existing Environment Agency indicative flood mapping showed the study area assessment of flood to be at high risk of fluvial flooding from the River Ashburn and the Balland risk Stream. Much of the Chuley Road site was shown to be in the high risk Flood Zone 3, with an annual probability of flooding of greater than 1%. The indicative assessment was based on broad-scale mapping which did not consider the impact of existing flood defences or the complex overland flow paths in urban flood events. Importantly, a flood relief culvert was constructed on the River Ashburn in the 1980s to divert peak flows away from the centre of Ashburton and reduce flood risk.