THE HIDEAWAY, HEATH END ROAD, BAUGHURST, RG26 5ND FLOOD RISK ASSESSMENT AND DRAINAGE STRATEGY FOR NEW RESIDENTIAL DEVELOPMENT ON BEHALF OF GRAPHENE ARCHITECTS 34 GLOUCESTER ROAD RICHMOND, TW9 3BU GRAR/20-0018/FRA01 APRIL 2020 DOCUMENT CONTROL Project: The Hideaway, Heath End Road, Baughurst, RG26 5ND New Residential Development Document: Flood Risk Assessment and Drainage Strategy Client: Graphene Architects Reference: GRAR/20-0018/FRA01 Document Checking: Name Date Signature Author: Chris Williams 24.04.2020 Checked by: Gregory Schmidt 24.04.2020 Approved by: Gregory Schmidt 24.04.2020 Status: Issue Date Status Issued by 1. 24.04.2020 First Issue Gregory Schmidt 2. 3. 4. 5. © Copyright Russell Giles Partnership Limited 2020 No part of this publication may be reproduced by any means without the prior permission of Russell Giles Partnership Limited. GRAR/20-0018/FRA01 TABLE of CONTENTS 1 INTRODUCTION .................................................................................................................................... 1 2 PLANNING POLICY .............................................................................................................................. 2 2.1 National Planning Policy Framework (NPPF) ......................................................................... 2 2.2 Local Policies ............................................................................................................................. 3 2.3 Statutory Authority Consultation ............................................................................................. 3 3 PLANNING POLICY CONTEXT ............................................................................................................. 4 3.1 Flood Zones ............................................................................................................................... 4 3.2 Flood Risk Vulnerability Classification .................................................................................... 4 3.3 Flood Risk Vulnerability and Flood Zone Compatibility ....................................................... 6 3.4 Sequential test and Exception Test ......................................................................................... 6 4 EXISTING SITE INFORMATION .............................................................................................................. 7 4.1 Site Location .............................................................................................................................. 7 4.2 Existing Site Description ............................................................................................................ 7 4.3 Source Protection Zone ............................................................................................................ 8 4.4 Existing Geology and Hydrogeology ..................................................................................... 9 4.5 Surrounding Hydrology .......................................................................................................... 10 5 PROPOSED DEVELOPMENT INFORMATION ...................................................................................... 11 5.1 Proposed Development Description .................................................................................... 11 6 FLOOD RISK ........................................................................................................................................ 12 6.1 Flooding from Seas (Tidal) ..................................................................................................... 12 6.2 Flooding from Rivers (Fluvial)................................................................................................. 12 6.3 Flooding from Surface Water (Pluvial) .................................................................................. 13 6.4 Flooding from Groundwater .................................................................................................. 14 6.5 Flooding from Public Sewers/Highway Drains ..................................................................... 14 6.6 Flooding from Artificial Sources ............................................................................................ 15 6.7 Peak Rainfall Intensity Allowance for Climate Change ..................................................... 15 7 PROPOSED DRAINAGE STRATEGY AND SUDS .................................................................................. 16 7.1 Existing Surface Water Run-off ............................................................................................... 16 7.2 Surface Water Option 1 – Infiltration Scheme and Soakaway Design Estimate .............. 16 7.3 Surface Water Option 2 – Attenuation Scheme and Tank Design Estimate..................... 17 7.4 Sustainable Drainage Systems (SuDS) .................................................................................. 18 7.5 Proposed Foul Drainage Strategy ......................................................................................... 24 8 SAFE ACCESS ..................................................................................................................................... 25 9 CONCLUSION ..................................................................................................................................... 26 APPENDIX 1 Site Plans APPENDIX 2 Topo Survey APPENDIX 3 Basingstoke and Deane Borough Council SFRA APPENDIX 4 Thames Water Sewer Records and Correspondance APPENDIX 5 Hampshire CC Guidance for Developers, Designers and Planners. APPENDIX 6 RGP Drainage Calculations GRAR/20-0018/FRA01 List of Tables Table 1 – Flood Zones .................................................................................................................................... 4 Table 2 - Flood Risk Vulnerability Classification ........................................................................................ 4 Table 3 - Flood Risk Vulnerability and Flood Zone Compatibility ............................................................ 6 Table 4 – Existing Site Surface Coverage ................................................................................................... 8 Table 5 - Existing Permeable and Impermeable Surface Areas ............................................................. 8 Table 6 – Proposed Development Surface Coverage ............................................................................ 11 Table 7 – Proposed Permeable and Impermeable Surface Areas ....................................................... 11 Table 8 - Existing Site Surface Water Runoff Rates – IH 124 Method ...................................................... 16 Table 9 - Proposed Soakaway Summary ................................................................................................. 17 Table 10 - Proposed Attenuation Summary ............................................................................................. 18 Table 11 - SuDS Assessment ....................................................................................................................... 20 List of Figures Figure 1 - SFRA Update May 2012, Basingstoke and Deane Historic Flooding - Area 2 ....................... 2 Figure 2 - Site Location Plan showing approx. Redline Boundary ........................................................... 7 Figure 3 - Source Protection Zone Layout .................................................................................................. 9 Figure 4 - Aquifer Designation Map (Defra) ............................................................................................... 9 Figure 5 - Underlying Bedrock Formation ................................................................................................. 10 Figure 6 - Underlying Superficial Deposits ................................................................................................ 10 Figure 7 – EA Flood Map – Wider Area ...................................................................................................... 12 Figure 8 - EA Flood Map ............................................................................................................................. 13 Figure 9 - EA Surface Water Flood Risk Map ............................................................................................ 13 Figure 10 - EA Flood Risk from Reservoir Map .......................................................................................... 15 GRAR/20-0018/FRA01 The Hideaway, Heath End Road, Baughurst, RG26 5ND April 2020 1 INTRODUCTION 1.1 RGP has been commissioned by Graphene Architects (the ‘Client’) to consider the flood risk associated with the proposed development at The Hideaway, Heath End Road, Baughurst, RG26 5ND, from all potential sources of flooding, as defined by the National Planning Policy Framework (NPPF). RGP has also been commissioned to provide a Drainage Strategy for the proposed development, which is included with this FRA. 1.2 In compiling this Flood Risk Assessment and Drainage Strategy, reference has also been made to the Basingstoke and Deane Borough Council Strategic Flood Risk Assessment, updated in 2012, and Hampshire County Council Guidance for Developers, Designers and Planners. 1.3 The aim of this FRA is to review the potential flooding impact on the proposed development site due to tidal, fluvial (Rivers), pluvial (Overland), sewer, reservoir, canal and other artificial flooding sources. The FRA will also review the potential