Flood Consequence Assessment (Level 1) Y Bwthyn Palliative Care Unit, PontPontyyyyclunclun MMMaMaaarrrrcccchhhh 2012017777 Prepared by: Giuliano Guadagnino BEng Reviewed by: Dimitris Linardatos BEng (Hons) MSc CEng MICE Reference: 25364 Revisions Ver Date ByByBy Notes 1 Sept 2016 GG Draft for comment 2 Oct 2016 GG Draft for comment 3 Mar 2017 GG Issued as Supporting document for Planning Application Page 1 of 23 Y BWTHYN PALLIATIVE CARE UNIT Contents 1 Introduction 2 Site Context Site Description & Location 3 Development Proposals 4 Flood Consequence Assessment Flood Risk from Watercourses/Sea Flood Risk from Groundwater Flood Risk from Sewers and Overland Flows Flood Risk from Reservoirs Flood Mitigation Measures 5 Warning and Flood Evacuation Plan 6 SuDS Assessment 7 Surface Water Management Existing Run-off Proposed Run-off 8 Conclusions & Recommendations Appendix A - Topographical Plans Appendix B - Correspondence Appendix C - Drawings Appendix D - Calculations Abbreviations AOD Above Ordnance Datum NRW Natural Resources Wales FFL Finished Floor Level FCA Flood Consequence Assessment TAN 15 Technical Advice Note 15 SFRA Strategic Flood Risk Assessment FRMP Flood Risk Management Plan 25364 - Flood Consequence Assessment Page 2 of 23 Y BWTHYN PALLIATIVE CARE UNIT 1.1.1. Introduction Price & Myers have been commissioned to undertake a Flood Consequence Assessment (FCA) for the proposed development of the Y Bwthyn Palliative Care Unit at The Royal Glamoran Hospital in Ynysmaerdy, Pontyclun. This FCA has been carried out in accordance with the Planning Policy Wales (PPW), Rhonnda Cynon Taf County Borough Council Flood Risk Management Plan (FRMP), Technical Advice Note 15 (TAN 15), along with advice and guidance from Natural Resources Wales (NRW) and CIRIA documents to support the outline planning application for the proposed development at the above site. The TAN 15 states that an appropriate FCA is required for all development proposals within a tidal or fluvial floodplain. The Natural Resource Wales (NRW) indicative map shows that the site is within the River Ely’s floodplain. Therefore, the flood risk must be focused on flood risk from the River Ely as well as assessing the flood risk from other sources. This report is based on a desk-top review of published information. The objectives of this FCA are to: • Identify and assess the risks of all forms of flooding to the development and demonstrate how these flood risks will be managed. • Establish whether the proposed development will be safe from all sources of flooding. Assess the Risk of flooding from the proposed works to the surrounding areas. Figure 1 --- Location Map 25364 - Flood Consequence Assessment Page 3 of 23 2.2.2. Site Context Site Description & Location The site is currently fully developed and occupies an area of approximately 0.48 Ha. An existing carpark, an access road, soft and hard landscaped areas currently cover the site, as seen in Figure 2. Access is available from an access road coming off the Ely Valley Road which is approximately 60m east of the site’s eastern boundary. The River Ely runs approximately 200m west of the site’s western boundary in a southerly direction. The existing Royal Glamoran Hospital buildings bound the site to the north and west. The site falls to the south, having a maximum ground level difference of approximately 1m. The average ground level is 59.5m AOD. A topographical survey drawing showing the existing site levels can be found in Appendix A. Figure 2 --- Existing Site Arrangements The site has approximate OS coordinates of 303649/184110 at Grid Reference ST036841, and the postcode is CF72 8XR. 23528 – Flood Risk Assessment Page 4 of 2123 Y BWTHYN PALLIATIVE CARE UNIT 3.3.3. Development Proposals The site will be redeveloped for a new single storey hospital building consisting of a new palliative care unit, providing inpatient based care, specialist day centre care and palliative outpatient services. The development will have a carpark on the eastern side of the site, as can be seen in Figure 3. It is proposed that the site of the new building be raised to match the existing hospital platform which has a Finished Floor Level (FFL) of approximately 60.12m AOD. The existing carpark levels will be retained with new additional carpark areas tying into these levels. Figure 3 --- Proposed Development 25364 - Flood Consequence Assessment Page 5 of 23 Y BWTHYN PALLIATIVE CARE UNIT 444 Flood Consequence Assessment Flood Risk from Watercourses/Sea There is a risk of flooding from watercourses as identified on the Natural Resources Wales (NRW) indicative flood outline map. The map shows that the site lies partly within Flood Zone 2 (1 in 1000 year undefended flood event) and is at risk of flooding from the River Ely and the Nant Muchudd. Land in this flood zone is assessed as having an annual probability of river flooding between 0.1% and 1%. The NRW’s map suggests that the site is not located in an area which benefits from flood defences. Refer to Figure 4 for the NRW’s flood map for planning purposes. The River Ely flows through Tonyrefail, and then through the grounds of the Royal Glamoran Hospital at Ynysmaerdy, west of the site. The Nant Muchudd stream flows past the eastern side of the site before flowing into the River Ely at the Llantrisant & Pontyclun Golf Club. These sections of the rivers are fluvial only as the local topography indicates and therefore pose no tidal risk in the local area, including the site. NRW have provided modelled flood level information for this area. The site is located between cross sections NtMchdd1641U and NtMchdd1774D which are taken along the Nant Muchudd, and cross sections ELY06170 and ELY06380 which are taken along the River Ely, as can be seen in Figure 5. The flood map indicates that flooding will most likely occur from the River Ely at cross section ELY06170 and the Nant Muchudd at NtMchdd1641U. Therefore, ELY06170 and NtMchdd1641U will be used to assess the flood risk to the proposed development as it is located upstream of the site and represents the worst case scenario. The 1 in 100 year, 1 in 100 year plus climate change for the River Ely and the Nant Muchudd are 59.61 AOD and 60.00m AOD respectively. Refer to Appendix B for NRW plans to scale. Price & Myers have done further modelling based on the Product 7 information received from NRW, as seen in Figure 7.1 and Figure 7.2. Structures along the watercourses have been incorporated into the model to more accurately mimic flood conditions. The Welsh Government’s policy clarification letter for ‘Flood Consequence Assessments: Climate change allowances’ (issued 23 rd August 2016) states,” it is recommended that the central estimate, or change factor, for the 2080s for the relevant river basin district should be used to assess the potential impact of climate change as part of a flood consequence assessment ”. The LPA has expressed that, as the proposed building is a stand-alone unit and non-hospital/emergency unit, the building should be classified as Highly Vulnerable and therefore designed to 1 in 100 year plus climate change standards. A 1 in 100 year plus 25% climate change storm event was used for the model. Additionally, a 1 in 1000 year storm event was used to determine the worst case flood scenario. Refer to Appendix C for the River Model Plan to scale. The results show that the entire site is at risk of flooding from both the River Ely and the Nant Muchudd. The model shows that, for the developed site, the highest flood water level will be approximately 59.544m AOD at the north east corner of the site for the 1 in 100 year plus 25% climate change storm event. The level of flood water at the proposed building location will vary from 59.470m AOD on the southern side to 59.544m AOD on the northern side. The model shows that the proposed building will not increase the flood risk to third party land. Additionally, the flood model for the 1 in 1000 year storm event shows that the proposed building will reduce flooding in the neighbouring property to the south by acting as a barrier steering a portion of the flood water on the site back towards the main watercourse before the flood water reached the southern properties. 25364 - Flood Consequence Assessment Page 6 of 23 Y BWTHYN PALLIATIVE CARE UNIT Figure 4 --- Natural Resources Wales Indicative Floodplain Map for Planning Figure 5 --- Natural Resources Wales Cross Sections for Flood MoModellingdelling NRW’s maps show the extent of historical flooding, as seen in Figure 6. However, NRW’s flood maps confirm that the specific site has not been flooded since records began. 25364 - Flood Consequence Assessment Page 7 of 23 Y BWTHYN PALLIATIVE CARE UNIT Figure 6 --- Historic Flooding Map (extract from Natural Resources Wales website) Figure 77.1.1 --- 1 in 100 year plus 25% climate change allowance ffloloodod mmmodelmodel without the proposed building (Price & Myers model based on NRW Product 7 information) 25364 - Flood Consequence Assessment Page 8 of 23 Y BWTHYN PALLIATIVE CARE UNIT Figure 7.2 --- 1 in 100 year plus 25% climate change allowance flofloodod model with the proposed building (Price & Myers model based on NRW Product 7 information) Existing Flood Defences The NRW’s Flood Defences map shows that there are flood defences along the eastern bank of the River Ely, as seen in Figure 8. The NRW flood map (Figure 4) does not indicate that the site benefits from these defences. However, it should be noted that the site is bounded by the existing hospital building to the west and that this building will act as a barrier for flood waters from the River Ely.