Jaguar Land Rover – Flood Consequence Assessment May 2021 www.jbaconsulting.com Jones Brother (Henllan) Ltd, Heol Parc Mawr, Cross Hands, Llanelli SA14 6RE DQH-JBAU-XX-XX-RP-Z-0001-S1-P02.02-FCA_Report.docx i JBA Project Manager Faye Tomalin JBA Consulting Kings Chambers 8 High Street NEWPORT UNITED KINGDOM NP20 1FQ Revision History Revision Ref/Date Amendments Issued to May 2021 First Issue James Player – Jones Brothers Contract This report describes work commissioned by Jones Brother (Henllan) Ltd. Prepared by .................................. Nia Vines BSc .................................................... Technical Assistant .................................................... Faye Tomalin BSc (Hons) MSc MCIWEM C.WEM .................................................... Chartered Senior Analyst Reviewed by .................................. George Baker BEng AIEMA CEnv IEng MCIWEM C.WEM Associate Director Purpose This document has been prepared for Jones Brothers (Henllan) Limited. 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 Jones Brothers (Henllan) Limited. Copyright © Jeremy Benn Associates Limited 2021. DQH-JBAU-XX-XX-RP-Z-0001-S1-P02.02-FCA_Report.docx i Contents 1 Introduction 1 1.1 FCA requirements 1 2 Site description 2 2.1 Site topography 2 2.2 Soils and geology 3 2.3 Watercourses and Flood Defences 3 2.4 Development proposal 4 3 Planning Policy and flood risk 6 3.1 Planning context 6 3.2 DAM Zoning and Vulnerability classification Error! Bookmark not defined. 3.3 Local Development Plan 7 3.4 Justification test 7 4 Flood Risk Assessment 9 4.1 Historical flooding 9 4.2 Fluvial Flood Risk 10 4.3 Tidal Flood Risk 10 4.4 Surface Water and Small Watercourse Flood Risk 10 4.5 Groundwater Flood Risk 11 4.6 Reservoirs Flood Risk 11 5 Detailed Fluvial Flood Risk Assessment 12 5.1 Hydraulic modelling availability 12 5.2 JBA Flood Model Updates (2019) Hydraulic Modelling 12 5.3 Hydrology 12 5.4 Baseline Model Results 13 5.4.1 1% AEP + Climate Change 13 5.4.2 0.1% AEP Event 13 5.5 Post-Development Model Results 14 5.5.1 0.1% AEP Event – Post-Development 15 5.6 Third Party Impacts 15 6 The Acceptability of Consequences 17 7 Conclusions 19 A Proposed development site plan Error! Bookmark not defined. B Proposed development layout II DQH-JBAU-XX-XX-RP-Z-0001-S1-P02.02-FCA_Report.docx ii List of Figures Figure 2-1 Site Location Plan 2 Figure 2-2 Watercourses and flood defences around the site 4 Figure 2-3 Proposed development design 5 Figure 3-1 Development Advice Map 7 Figure 4-1 NRW Historic Flooding records 9 Figure 4-2 NRW FRAW Risk from Rivers 10 Figure 4-3 FRAW- Risk of Flooding from Surface Water and Small Watercourses 11 Figure 5-1 1% AEP + CC Baseline Predicted Flood Depths 13 Figure 5-2 0.1% AEP Baseline Predicted Flood Depths 14 Figure 5-3 0.1% AEP Event Post-Development Predicted Flood Depths 15 Figure 5-4 0.1% AEP Depth Comparison Grid 16 List of Tables Table 2-1 Site summary 2 Table 3-1 Development categories defined by TAN-15 6 Table 3-2 Justification Test applied to the proposed development 8 Table 4-1 Existing Flood Risk Data for the Site 9 Table 6-1 Assessment of accessibility criteria 17 DQH-JBAU-XX-XX-RP-Z-0001-S1-P02.02-FCA_Report.docx iii 1 Introduction JBA Consulting (JBA) were commissioned by Jones Brothers (Henllan) Limited on behalf of Sinclair Garages Port Talbot Ltd. to undertake a Flood Consequence Assessment (FCA) for a proposed commercial development at Heron Drive, Llansamlet, Swansea. 1.1 FCA requirements This FCA follows Welsh Government guidance on development and flood risk set out in the Technical Advice Note 15: Development and Flood Risk (TAN15). Where appropriate, the following aspects of flood risk will be addressed in all planning applications over its expected lifetime in flood risk areas: • The likely mechanisms of flooding • The likely source of flooding • The depths of flooding through the site • The speed of inundation of the site • The rate of rise of flood water through the site • Velocities of flood water across the site • Overland flow routes • The effect of access and egress and infrastructure, for example, public sewer outfalls, combined sewer outflows, surface water sewers and effluent discharge pipes from wastewater treatment works • The impacts of the development in terms of flood risk on neighbouring properties and elsewhere on the floodplain DQH-JBAU-XX-XX-RP-Z-0001-S1-P02.02-FCA_Report.docx 1 2 Site description The site is located on the outskirts of Swansea, within Swansea Enterprise Park in the Llansamlet area. The site is bound to the north, east and south by existing highways, as shown in Figure 2-1. The western boundary of the site is comprised of the River Tawe Flood Defence and associated footpath. The River Tawe flows 17m to the west of the site in a southerly direction. Table 2-1 Site summary Site name Land at Heron Drive, Llansamlet Site area 1.90 Ha Existing land use Greenfield Purpose of development Commercial development OS NGR SS 67677 98677 Local Planning Authorities Swansea Council Lead Local Flood Authority Swansea Council Figure 2-1 Site Location Plan 2.1 Site topography The proposed development site is located within the Swansea Enterprise Park, Llansamlet. A topographic survey undertaken by Senior Surveys Land Survey Consultants in June 2020 indicates that the majority of the site is relatively flat, with ground levels between 10.0mAOD to 11mAOD. The topographic survey is contained in Appendix A. The site is protected from the River Tawe by a flood embankment which forms the western boundary of the site. DQH-JBAU-XX-XX-RP-Z-0001-S1-P02.02-FCA_Report.docx 2 Figure 2-2 identifies the key heights across the proposed site. Points A and B are located along the river embankment, with levels of 13.3mAOD and 12.4mAOD respectively. The lowest ground level within the proposed site is in the north east corner of the site; point C, 9.8mAOD. The highest point within the site boundary is point D, 12.1mAOD. The average height across the site is identified by point E at 10.2mAOD. Figure 2-2 1m DTM LiDAR 2.2 Soils and geology The British Geological Survey (BGS)1 shows that the area’s geology forms part of the Grovesend Mudstone Group, which consists of mudstone and sedimentary bedrock. The superficial deposits on site are alluvium which consist of clay, silt, sand and gravel. The Cranfield University Soilscape viewer2 describes the site’s soil as loamy, typical of wet carr woodlands in old river meanders. 2.3 Watercourses and Flood Defences As shown in Figure 2-3, the River Tawe flows 17m to the west of the site in a southerly direction and is an NRW designated Main River. The site is protected from the River Tawe by a flood embankment which forms the western boundary of the site, as shown in Figure 2-3. These flood defences form part of the Lower Swansea Valley flood scheme completed by NRW in 2014. ———————————————————————————————————————————— 1 Geology of Britain Viewer. http://mapapps.bgs.ac.uk/geologyofbritain/home.html 2 Cranfield Soil Scapes Viewer. http://www.landis.org.uk/soilscapes/ DQH-JBAU-XX-XX-RP-Z-0001-S1-P02.02-FCA_Report.docx 3 Figure 2-2 Watercourses and flood defences around the site 2.4 Development proposal A proposed site layout has been provided, as shown in Figure 2-4. The proposal is to develop the site for Class B8 (Storage or distribution) use. The site will be comprised of two buildings, the Jaguar Land Rover main sales building and associated valet building located towards the centre of the site, with the remaining area used for car parking. The main access to and from the site will be via an entrance created on Heron Drive with an additional second entrance via Moorhen Close. Proposed ground levels across the site shall be set to an average of 10.7mAOD, with Finished Floor Levels of the building set to 10.85mAOD. The proposed development layout is contained in Appendix B. DQH-JBAU-XX-XX-RP-Z-0001-S1-P02.02-FCA_Report.docx 4 Figure 2-3 Proposed development design DQH-JBAU-XX-XX-RP-Z-0001-S1-P02.02-FCA_Report.docx 5 3 Planning Policy and flood risk 3.1 Planning context TAN-15 was introduced in 2004 by the Welsh Assembly Government. It is technical guidance related to development planning and flood risk using a sequential characterisation of risk based on the Welsh Government's Development and Flood Risk Advice Map (DAM). Its initial requirement is to identify the flood zones and vulnerability classification relevant to the proposed development, based on an assessment of current and future conditions. 3.2 Development vulnerability classification TAN-15 assigns one of three flood risk vulnerability classifications to a development, as shown in Table 3-1. The proposed development at Heron Drive is classed as commercial. Consequently, the development is classified as less vulnerable. Table 3-1 Development categories defined by TAN-15 Development category Types Emergency services Hospitals, ambulance stations, fire stations, police stations, coastguard stations, command centres, emergency depots and buildings used to provide emergency shelter in time of flood. Highly vulnerable All residential premises (including hotels and caravan development parks), public buildings, (e.g. schools, libraries, leisure centres), especially vulnerable industrial development (e.g. power stations, chemical plants, incinerators), and waste disposal sites.