PREC Red Lion Propco 2 Site at Lombard Wall, Charlton Flood Risk Assessment & Indicative Surface Water Drainage Strategy 134026-R1(2)-FRA APRIL 2021 RSK GENERAL NOTES Project No.: 134026-R1(2)-FRA Site: Site at Lombard Wall, Charlton Title: Flood Risk Assessment & Indicative Surface Water Drainage Strategy Client: PREC Red Lion Propco 2 Date: 30th April 2021 Office: Hemel Hempstead Status: Final Technical Author S Thorpe reviewer M Cheeseman Signature Signature Date: 30th April 2021 Date: 30th April 2021 Quality reviewer C Whittingham Signature Date: 30th April 2021 Date Reviewed Approved Issue No Version/Details Author issued by by R1(0) Draft 31.03.21 ST MEC CW R1(1) Final 27.04.21 ST MEC CW R1(2) Updated site layout plan 30.04.21 ST CW CW RSK LDE Ltd (RSK) has prepared this report for the sole use of the client, showing reasonable skill and care, for the intended purposes as stated in the agreement under which this work was completed. The report may not be relied upon by any other party without the express agreement of the client and RSK. No other warranty, expressed or implied, is made as to the professional advice included in this report. Where any data supplied by the client or from other sources have been used, it has been assumed that the information is correct. No responsibility can be accepted by RSK for inaccuracies in the data supplied by any other party. The conclusions and recommendations in this report are based on the assumption that all relevant information has been supplied by those bodies from whom it was requested. No part of this report may be copied or duplicated without the express permission of RSK and the party for whom it was prepared. Where field investigations have been carried out, these have been restricted to a level of detail required to achieve the stated objectives of the work. This work has been undertaken in accordance with the quality management system of RSK LDE Ltd. PREC Red Lion Propco 2 Site at Lombard Wall, Charlton Flood Risk Assessment & Indicative Surface Water Drainage Strategy 134026-R1(2)-FRA CONTENTS 1 INTRODUCTION .............................................................................................................................. 1 2 SITE DESCRIPTION & PROPOSALS ............................................................................................. 2 2.1 Existing site .............................................................................................................................. 2 2.2 Development Proposals ........................................................................................................... 3 3 ENVIRONMENTAL SETTING .......................................................................................................... 4 3.1 Hydrology ................................................................................................................................. 4 3.2 Geology .................................................................................................................................... 4 3.3 Hydrogeology ........................................................................................................................... 4 4 SOURCES OF FLOOD RISK ........................................................................................................... 5 4.1 Criteria ...................................................................................................................................... 5 4.2 Flooding from rivers (fluvial flood risk) ...................................................................................... 5 4.3 Flooding from the sea (tidal flood risk) ..................................................................................... 6 4.4 Flooding from the land (overland pluvial flood risk) .................................................................. 7 4.5 Flooding from groundwater ...................................................................................................... 8 4.6 Flooding from sewers ............................................................................................................... 9 4.7 Other sources of flooding ....................................................................................................... 10 5 MITIGATION MEASURES AND RESIDUAL RISK ....................................................................... 12 5.1 Overland flood flow ................................................................................................................. 12 5.2 Finished floor levels ................................................................................................................ 12 5.3 Flood compensation ............................................................................................................... 12 5.4 Safe access/egress ................................................................................................................ 12 6 PLANNING CONTEXT ................................................................................................................... 13 6.1 Application of planning policy ................................................................................................. 13 6.2 Land use vulnerability ............................................................................................................. 13 7 SURFACE WATER DRAINAGE ASSESSMENT .......................................................................... 14 7.1 Scope ..................................................................................................................................... 14 7.2 Pre-development situation ...................................................................................................... 14 7.3 Off site discharge options and limits....................................................................................... 15 7.4 Post-development situation .................................................................................................... 16 7.5 Water quality ........................................................................................................................... 18 7.6 Foul drainage provision .......................................................................................................... 20 8 CONCLUSIONS AND RECOMMENDATIONS ............................................................................. 21 9 REFERENCES ............................................................................................................................... 23 TABLES Table 6.1: Flood risk vulnerability and flood zone ‘compatibility’ .......................................................... 13 Table 7.1: Existing and proposed site areas ......................................................................................... 14 Table 7.2: IOH 124 surface water runoff (greenfield) ........................................................................... 14 Table 7.3: Modified Rational Method pre-development surface water runoff ....................................... 15 Table 7.4: Quick storage estimates ...................................................................................................... 17 Table 7.5: Extract of SuDS Manual Table 26.2: Pollution hazard indices for different land use classifications ........................................................................................................................................ 19 PREC Red Lion Propco 2. i Site at Lombard Wall, Charlton Flood Risk Assessment & Indicative Surface Water Drainage Strategy 134026-R1(2)-FRA Table 7.6: Extract of Table 26.3: Indicative SuDS mitigation indices for discharges to surface waters .............................................................................................................................................................. 19 Table 8.1: Flood risk summary .............................................................................................................. 21 FIGURES Figure 2.1: Site location plan................................................................................................................... 2 Figure 4.1: Environment Agency ‘Flood map for planning’ ..................................................................... 6 Figure 4.2: Environment Agency ‘Flood risk from surface water’ map ................................................... 8 Figure 4.3: Environment Agency ‘Flood risk from reservoirs’ map ....................................................... 10 APPENDICES APPENDIX A RSK GROUP SERVICE CONSTRAINTS APPENDIX B TOPOGRAPHIC SURVEY APPENDIX C THAMES WATER ASSET PLANS APPENDIX D PROPOSALS APPENDIX E ENVIRONMENT AGENCY DATA APPENDIX F GREENWICH COUNCIL PRE-APPLICATION RESPONSE APPENDIX G CALCULATIONS APPENDIX H INDICATIVE SURFACE WATER DRAINAGE STRATEGY APPENDIX I GREENWICH SUDS PRO-FORMA PREC Red Lion Propco 2. ii Site at Lombard Wall, Charlton Flood Risk Assessment & Indicative Surface Water Drainage Strategy 134026-R1(2)-FRA 1 INTRODUCTION RSK Land and Development Engineering Ltd were commissioned by PREC Red Lion Propco 2 (the client) to provide a Flood Risk Assessment (FRA) and Indicative Surface Water Drainage Strategy to support the planning application at Lombard Wall, Charlton (the site). Development proposals include the demolition of the existing building and the construction of a new flexible B2/B8 unit and associated car parking and servicing areas. The purpose of the FRA is to establish the risk associated with the proposed development and