Flood Smart Plus Site address Aver House Nursery Road Waltham Abbey EN9 2JE Site coordinates 538661, 206404 Report prepared for DPA (London) Ltd 25 Tudor Hall Brewery Road Hoddesdon Herefordshire EN11 8FP Report reference 65590R1 Report status Final report Date issued July 2017 Report author Jessica Bayliff Consultant Report checker Mike Piotrowski Project Consultant Report reviewer Bob Sargent Associate Consultant GeoSmart Information Ltd New Zealand House t. +44(0)1743 276150 160 Foregate e. [email protected] Shrewsbury SY2 6FD www.geosmartinfo.co.uk Registered office: New Zealand House, 160 Abbey Foregate, Shrewsbury SY2 6FD. Registered in England and Wales, number 5475394. 1. Executive summary The National Planning Policy Framework (2012) and Planning Practice Guidance (2015) requires that flood risk assessments review flooding from all potential sources. A review has been undertaken of national environmental data sets to assess the potential flood risk to the Site. The review is provided within this concise interpretative report written by an experienced GeoSmart flood risk consultant. Site analysis Source of Flood risk Baseline After Mitigation River and coastal Moderate Low Surface water (pluvial) flooding Low to Very Low Very Low Groundwater flooding Moderate Low Other flood risk factors present No N/A Is any other further work Yes (Please Yes recommended? see below) N/A = mitigation not required The proposed development will comprise the change of use from an existing storage building to a residential dwelling. According to the Environment Agency’s Flood Map for Planning Purposes, the Site is located within fluvial Flood Zone 2. As the Site is located within Flood Zone 2, modelled flood data was obtained from the Environment Agency to confirm the flood levels at the Site. Further analysis of the modelled flood level data, including the most up to date guidance on the allowance for climate change, confirms the 1 in 100 year plus a 35% Climate Change allowance flood level at the site to be 25.67 mAOD. A comparison of the Site specific topographic survey (SJ Geomatics ,2017) and both modelled and estimated flood levels, indicate flood flows in all events up to the 1 in 1000 year event would not impact the Site. Flood depths during the 1 in 1000 year event within Nursery Road, outside of the Site boundary, would be 0 and 0.1m. Although the areas of the Site proposed for development would not be impacted. According to the Environment Agency’s Risk of Flooding from Surface Water mapping, parts of the Site to the north and the east are at low risk of pluvial flooding however the majority FloodSmart Plus Ref 65590R1 t. +44(0)1743 276150 e. [email protected] www.geosmartinfo.co.uk 2 of the Site is at very low risk of pluvial flooding. According to GeoSmart’s Groundwater (GW5) Flood Risk Mapping, the Site is also at moderate risk of groundwater flooding, due to the underlying permeable superficial geology, in response to river events. The Site is not at risk of Reservoir Flooding. Recommendations • It is recommended that minimum floor levels for the Site are set no lower than 26.27 mAOD. Where raising the finished floor levels within the majority of the development cannot be achieved, flood resistance measures such as barriers for flood depths are recommended up to 0.3m. • Resilience measures such as raising electrical sockets, tiling or using a similar waterproof material for the development floor and non-return flap valves should be considered for any proposed foul and surface water discharge pipes. • A Sustainable Drainage scheme should be considered for the Site and specific groundwater measures should be implemented on the Site. We recommend that mitigation measures that have been discussed within this report are considered as part of the proposed development where possible and evidence of this is provided to the Local Authority as part of the planning application. FloodSmart Plus Ref 65590R1 t. +44(0)1743 276150 e. [email protected] www.geosmartinfo.co.uk 3 2. Introduction Background and purpose This assessment has been undertaken by firstly compiling information concerning the Site and the surrounding area. The information which is gathered is then used to construct a ‘conceptual site model’, including an understanding of the appropriateness of the development as defined in the NPPF (2012) and the source(s) of any flood risk present. Finally, a preliminary assessment of the steps that can be taken to manage any flood risk to the development is undertaken. This report has been prepared with reference to the National Planning Policy Framework (NPPF, 2012). “The National Planning Policy Framework set out the Government’s planning policies for England and how these are expected to be applied” (NPPF, 2012). The National Planning Policy Framework promotes a sequential, risk based approach to the location of development. “This general approach is designed to ensure that areas at little or no risk of flooding from any source are developed in preference to areas at higher risk. The aim should be to keep development out of medium and high risk flood areas (Flood Zones 2 and 3) and other areas affected by other sources of flooding where possible” (NPPG, 2014). The purpose of this report is to provide clear and pragmatic advice regarding the nature and potential significance of flood hazards which may be present at the Site. Report scope A thorough review of a commercially available flood risk report and Environment Agency supplied data indicating potential sources of flood risk to the Site from rivers and coastal sources, surface run-off (pluvial), groundwater and reservoirs, including historical flood information and modelled flood extent. Appropriate measures are recommended to manage and mitigate the flood risk to the property. Local rainfall data for the 1 in 100 year rainfall event is used to support site run-off calculations if there is an increase in impermeable area as a result of the development. The effects of climate change are also included in these calculations, using industry standard advice. Information obtained from the Environment Agency and a review of Epping Forest District Council Level 1 Strategic Flood Risk Assessment (SFRA) (URS, 2015) is used to ascertain local flooding issues and, where appropriate, identify information to support a Sequential and/or Exception test required as part of the National Planning Policy Framework (NPPF, 2012). Using the available data the existing and future flood risks to and from the Site from all flood sources will be assessed in line with current best practice. FloodSmart Plus Ref 65590R1 t. +44(0)1743 276150 e. [email protected] www.geosmartinfo.co.uk 4 An indication of potential flood risk from the Site to downstream receptors is provided where the proposed development increases run-off from the Site. Report limitations It is noted that the findings presented in this report are based on a desk study of information supplied by third parties. Whilst we assume that all information is representative of past and present conditions we can offer no guarantee as to its validity and a proportionate programme of site investigations would be required to fully verify these findings. This report excludes consideration of potential hazards arising from any activities at the Site other than normal use and occupancy for the intended land uses. Hazards associated with any other activities have not been assessed and must be subject to a specific risk assessment by the parties responsible for those activities. Datasets The following table shows the sources of information that have been consulted as part of this report: Datasets consulted Thames Commercial Environment Source of flooding Water Flood Report SFRA* Agency OS Data (Appendix (Appendix B) (Appendix C) D) Historical X X X Fluvial/tidal X X X Surface water X X X (pluvial) Groundwater X X Sewer X X Culvert/bridges X X Reservoir X X *Epping Forest District Council Level 1 Strategic Flood Risk Assessment (SFRA) (URS, 2015) *Supporting information on the datasets used is provided in the relevant appendix FloodSmart Plus Ref 65590R1 t. +44(0)1743 276150 e. [email protected] www.geosmartinfo.co.uk 5 3. Site analysis Site information The Site is located in Lower Nazing in a setting of commercial and residential land use, National Grid Reference TL 38661 06404 (see Figure 1). According to OS data the immediate area surrounding the Site is relatively flat between 20 - 30 mAOD. Using a 1 km buffer around the Site, it is noted that to the north land falls between 20-25 mAOD. To the west land remains between 20-30 mAOD, to the east land rises between 45-50 mAOD and to the south is between 25-30 mAOD. The general level of the Site is between 25.13 and 25.95 mAOD with the Site falling gradually in an easterly direction. This is based on EA elevation data obtained for the Site to a 1m resolution with a vertical accuracy of ±150 mm. Site plans and drawings are provided in Appendix A. Figure 1 Site Location Contains Ordnance Survey data © Crown copyright and database right 2017 FloodSmart Plus Ref 65590R1 t. +44(0)1743 276150 e. [email protected] www.geosmartinfo.co.uk 6 Development The Site is currently used as a storage unit. The proposed development will comprise the change of use of the building to a residential dwelling. The effect of the overall development will result in an increase in number of occupants and/or users of the building and will result in the change of use, nature or times of occupation. The estimated lifespan of the development is 100 years. Hydrological features Watercourses/surface water features within 1km of the Site: There is a drain located approximately 10 m east of the Site.