Cwrt Sart Comprehensive School, Neath Level 1 Flood Consequence Assessment February 2017 Neath Port Talbot County Borough Council The Quays Brunel Way Baglan Energy Park Neath SA11 2GG JBA Project Manager Jack Southon JBA Consulting 35 Perrymount Road Haywards Heath West Sussex England RH16 3BW Revision History Revision Ref / Date Issued Amendments Issued to V1.0 / February 2017 Draft Report Jonathan Morris V2.0 / April 2017 N/A issued as Final Jonathan Morris Contract This report describes work commissioned by Jonathan Morris, on behalf of Neath Port Talbot County Borough Council, by an email dated 16th January 2017. Neath Port Talbot County Borough Council's representative for the contract was Jonathan Morris of Neath Port Talbot County Borough Council. Aaron Barber and Jack Southon of JBA Consulting carried out this work. Prepared by .................................................. Aaron Barber BSc Technical Assistant Reviewed by ................................................. Jack Southon BSc MSc FRGS MCIWEM C.WEM CSci CEnv Chartered Senior Analyst, Team Leader Purpose This document has been prepared as a Final Report for Neath Port Talbot County Borough Council. JBA Consulting accepts no responsibility or liability for any use that is made of this document other than by the Client for the purposes for which it was originally commissioned and prepared. JBA Consulting has no liability regarding the use of this report except to Neath Port Talbot County Borough Council. 2017s5510 - FCA Cwrt Sart School (v1 April 2017).docx i Acknowledgements We would like to acknowledge and thank Jonathan Morris from Neath Port Talbot County Borough Council as well as Natural Resources Wales for their provision of the relevant information required for this assessment. Copyright © Jeremy Benn Associates Limited 2017 Carbon Footprint A printed copy of the main text in this document will result in a carbon footprint of 99g if 100% post- consumer recycled paper is used and 126g if primary-source paper is used. These figures assume the report is printed in black and white on A4 paper and in duplex. JBA is aiming to reduce its per capita carbon emissions. 2017s5510 - FCA Cwrt Sart School (v1 April 2017).docx ii Executive Summary Background JBA Consulting was commissioned by Jonathan Morris from Neath Port Talbot County Borough Council to prepare a Flood Consequence Assessment to support the redevelopment of the Cwrt Sart Comprehensive School site, Old Road, Briton Ferry, Neath, SA11 2ET. This Flood Consequence Assessment provides information pertaining to the nature of flood risk as the site and follows the Technical Advice Note 15 with regards to development and flood risk. It also considers potential next steps appropriate for mitigation options available for the development. The site area is approximately 3.71 hectares, and currently hosts the existing Cwrt Sart Comprehensive School buildings, now disused. The site is now considered to be a site for the demolition of the existing buildings and the development of a new primary school, with associated playgrounds, playing fields, sports pitches, parking, ancillary buildings and soft landscaping. Flood risk Natural Resources Wales' Development Advice Map indicated that the site is partially within both flood zones B and C2, and therefore is at risk of flooding. Flood Zone B indicates areas previously known to have flooded through examination of sediment records, and Flood Zone C2 indicates areas of floodplain not benefitting from significant flood defences. The River Neath is the source of the fluvial and tidal flooding. Tidal flooding is modelled to provide risk to the site in a 1 in 200-year scenario. Updated modelling by JBA for NRW has recently been completed for the Neath area, and part of the model covers the Cwrt Sart site. Pre-application comments submitted by NRW recommends that the site levels are compared to the modelled tidal levels of the 0.5%AEP with climate change and 0.1%AEP scenarios. As the model only partially covers the site, tidal levels were extrapolated across the remainder of the site to determine potential flood risk for the remainder of the site. It is estimated that: • The 1 in 200-year plus climate change tidal event will generate a peak water level of 7.45mAOD • The 1 in 1000-year plus climate change tidal event will generate a peak water level of 7.53mAOD When compared to the current ground levels of the site (sourced from Natural Resource Wales' 1m LIDAR dataset), it is considered that: • The site is at risk from the 1 in 200-year plus climate change event, as well as the 1 in 1000- year plus climate change event. • Maximum flood depths could potentially reach 0.75m above current ground level in the area of the planned school buildings during the 1 in 200-year plus climate change event. The site is also at risk from surface water flooding, with a depression in the site allowing water to flow and pool. Recommendations TAN15 policy A1.14 states that a highly vulnerable development such as a school should be designed to be flood free during a 0.5% AEP tidal flood event. This condition is met with the current site plan for current day tidal levels. However A1.5 states that development should be flood free for the lifetime of the development. The site is found to be within the 0.5% AEP tidal flood event including climate change (assuming development lifetime of 100 years), based on the extrapolation of the updated modelling of the River Neath, therefore finished floor levels or ground raising above the projected flood level should be considered to account for the impacts of climate change. It is recommended that, at the detailed design stage, the existing Neath model is extended to include the entire site and surrounding properties, to confirm the results of the extrapolation performed for this FCA. The model can be run to include raised site levels, to confirm impacts on flooding and surface water on the site and nearby third party land, and to review flood velocities and inundation rates (A1.15). As the planned building is located within a depression in the landscape, it is recommended that landscaping is confirmed in line with predicted tidal flood levels, and modelling run to confirm the 2017s5510 - FCA Cwrt Sart School (v1 April 2017).docx iii impacts of surface water no longer flowing into this area, and flowing off of the impermeable structures. A Surface Water Drainage Strategy is advised in this case, in conjunction with the FCA. 2017s5510 - FCA Cwrt Sart School (v1 April 2017).docx ii Contents Executive Summary ............................................................................................................ iii 1 Introduction ............................................................................................................ 1 1.1 Terms of Reference ........................................................................................................... 1 1.2 FCA Requirements ............................................................................................................. 1 2 Site Description ...................................................................................................... 2 2.1 Site description................................................................................................................... 2 2.2 Site Topography ................................................................................................................. 2 2.3 Site soils and geology ........................................................................................................ 3 2.4 Watercourses ..................................................................................................................... 3 2.5 Drainage Network .............................................................................................................. 4 2.6 Development Proposal ....................................................................................................... 4 3 Planning Policy and Flood Risk ............................................................................. 5 3.1 Planning context................................................................................................................. 5 3.2 DAM Zone & Vulnerability Classification ............................................................................ 5 3.3 TAN-15 Flood Zones .......................................................................................................... 5 3.4 Policy and Guidance Review ............................................................................................. 6 4 Flood risk assessment ........................................................................................... 8 4.1 Historical flooding ............................................................................................................... 8 4.2 Existing fluvial flood risk data ............................................................................................. 8 4.3 Surface water flood risk ...................................................................................................... 13 4.4 Risk of flooding from reservoirs .......................................................................................... 13 5 Conclusions and recommendations ...................................................................... 15 Appendices ......................................................................................................................... I A NRW - Pre-application comments