COLDRA WOODS HOTEL BY CELTIC MANOR AND STARBUCKS DRIVE- THRU RESTAURANT Flood Consequences Assessment

Transcription

1 COLDRA WOODS HOTEL BY CELTIC MANOR AND STARBUCKS DRIVE- THRU RESTAURANT Flood Consequences Assessment APRIL 2017

2 CONTACTS JOSHUA MOORE Graduate Hydrologist dd ++44 (0) Arcadis. 2 Glass Wharf Temple Quay Bristol BS2 0FR United Kingdom APPROVAL AUTHOR Joshua Moore CHECKER Lisa Driscoll APPROVER Lisa Driscoll REPORT NO 5001-UA UU41R-ColdraHotel_FCA-03 DATE 03 April 2017 Arcadis (UK) Limited is a private limited company registered in England registration number: Registered office, Arcadis House, 34 York Way, London, N1 9AB. Part of the Arcadis Group of Companies along with other entities in the UK. Regulated by RICS. Copyright 2015 Arcadis. All rights reserved. arcadis.com

3 VERSION CONTROL Version Date Author Changes 01 08/03/2017 Joshua Moore Draft for comment 02 08/03/2017 Lisa Driscoll Technical Review updates 03 09/03/2017 Joshua Moore Amendments following technical review 04 03/04/2017 For Issue This report dated 03 April 2017 has been prepared for Broadhall (Coldra Woods) Ltd, Coldra Manor Resort and Idris Davies Ltd (the Client ) in accordance with the terms and conditions of appointment dated 16 December 2016 (the Appointment ) between the Client and Arcadis Consulting (UK) Limited ( Arcadis ) for the purposes specified in the Appointment. For avoidance of doubt, no other person(s) may use or rely upon this report or its contents, and Arcadis accepts no responsibility for any such use or reliance thereon by any other third party.

4 CONTENTS 1 INTRODUCTION Background Scope of Works Terminology BACKGROUND Site Location Flood History Natural Resources Wales Flood Map Existing Flood Defences TAN15 DEVELOPMENT AND FLOOD RISK Categorisation of Site within TAN15 Flood Zones Assessment of Flooding Consequences ASSESSMENT OF FLOOD RISK Fluvial Flood Risk Groundwater Surface Water Estimation of Runoff Rates and Storage Volumes Sewers Coastal/Tidal Artificial Sources FLOOD RISK MITIGATION MEASURES FLOOD RISK AND CONSEQUENCES SUMMARY FIGURES Figure 1: Proposed Development Location Figure 2: NRW Risk of Flooding from Rivers and the Sea Figure 3: TAN15 Development & Flood Risk: Development Advice Map Figure 4: Unnamed Watercourse, taken from northeast corner of the Site looking south (downstream) Figure 5: NRW Risk of Flooding from Surface Water... 9

5 TABLES Table 1: Historic Flooding Incidents and Locations... 3 Table 2: Greenfield Peak Runoff Flow Rate for 50%, 3.33% and 1% AEP Events Table 3: Existing and Proposed Development Rainfall-Runoff Volumes APPENDICES Detailed Site Layout Plan

6 1 Introduction 1.1 Background Arcadis Consulting (UK) Limited (Arcadis) has been commissioned by Broadhall (Coldra Woods) Ltd, Coldra Manor Resort and Idris Davies Ltd ( the Client ) to undertake a Flood Consequences Assessment (FCA) in support of the proposed construction of a 160 bedroom hotel and a separate stand-alone A3 Unit and Drive Thru Restaurant ( the proposed Development ). The total site area covers 4.22 hectares (ha), which incorporates the final red line boundary, covering 1.71 ha at the Coldra, Newport ( the Site ). This FCA has been prepared to determine whether the proposed Development would have an acceptable flood risk and to assess the potential for impacts on third party flood risk. 1.2 Scope of Works The scope of works for the FCA comprises the following tasks: Consultation with Natural Resources Wales (NRW) and the Lead Local Flood Authority (Newport City Council (NCC)) to collect up to date flood data (including historic flood records, modelled flood extents and levels); Review of strategic planning information and reports to inform the Technical Advice Note (TAN) 15 precautionary framework; Qualitative assessment of flood risk from all potential sources, informed by the baseline data collected; Calculation of pre and post development rainfall runoff rates and volumes of surface water runoff; Outline identification of potential flood mitigation measures, if required, and recommendations for further investigation, as appropriate; and Preparation of an FCA report, in line with TAN15 requirements Terminology Flood risk is a product of both the likelihood and consequence of flooding. Throughout this FCA, flood events are defined according to their likelihood of occurrence. Floods are described according to an annual chance, meaning the chance of a particular flood occurring in any one year. This is directly linked to the probability of a flood. For example, a flood with an annual chance of 1 in 100 (a 1 in 100 chance of occurring in any one year on average), has an annual exceedance probability (AEP) of 1%. 1 Llywodraeth Cymri Welsh Government (2004). Technical Advice Note 15: Development and Flood Risk Accessed online via: 1

7 2 Background 2.1 Site Location The Site is located at the Coldra in Newport, approximately 150m north of Junction 24 of the M4. The total as shown site area is 4.22 ha, which incorporates the final red line boundary, covering an area of 1.71 ha. The current land use of the Site primarily consists of managed semi-improved grassland, but with some broadleaved woodland in the southeast. The Site is bordered by the A449 to the north and west, the A48 to the south and existing hotel accommodation and commercial buildings to the east. The proposed Development location is illustrated in Figure 1 and a detailed site layout plan is provided in Appendix A. Figure 1: Proposed Development Location, total site area outlined in blue and final red line boundary outlined in red. Contains Ordnance Survey (OS) data Crown copyright and database right As shown in the site layout plan (Appendix A) the proposed Development consists of the creation of a 160- bedroom hotel with a floor area of approximately 5,110 m 2, located in the north of the Site. A separate singlestorey 465 m 2 A3 Unit and Drive-Thru Restaurant, located in the south east of the Site is also proposed, together with car parking provision for the Drive-Thru, and hotel staff and guests. Access to the proposed Development will be from the A48, from the south. 2

8 Existing ground levels have been defined using open source government LiDAR (25cm) datasets 2. The Site has a gentle incline towards the northwest, with ground levels ranging from 40.0m above ordnance datum (AOD) in the northwest to 32.5m AOD in the southeast. The nearest main rivers to the Site are the River Usk, which is located approximately 1.6km to the northwest, and Monks Ditch, 1.6km to the southeast. A minor unnamed watercourse drains southwards, neighbouring the north eastern boundary of the Site and to the downstream extent of the study area drains a hydrological catchment of approximately 1.3km 2 3. A drainage ditch runs along the northern boundary of the Site and joins the unnamed watercourse at the northeast corner of the Site. There are two small ponds located 70m west and 130m southwest of the Site, with surface areas of 350m 2 and 470m 2 respectively. There are no other surface water features in proximity to the Site that could be affected by the proposed Development. 2.2 Flood History Consultation with NCC has confirmed there are no recorded flooding issues in the area, which is confirmed by the NCC Flood Risk Management Plan (FRMP) Historic Flood Incidents Map 4 and the NCC Preliminary Flood Risk Assessment (PFRA) Historic Flood Incidents within Newport 5 map, which indicate there are no records of flooding having affected the Site. There are nine recorded incidents within the vicinity of the Site, from fluvial, surface water and sewer sources, which are detailed below. There are no recorded groundwater flood incidents. Table 1: Historic Flooding Incidents and Locations Flood Type Location Reason Fluvial Ford Farm Lane, 2.3km east of the Site. Blocked debris inlet screen. Surface Water A48 Chepstow Road Magor Road, 2km east of the Site. Recurrent surface water flooding of the road, likely due to upstream culvert inlet arrangement inefficiencies. Surface Water Magor Road Waltwood Road, 3.3km east of the Site. Recurrent surface water flooding of the road, however recent works have seen improvement to the highway drainage, including new gully connections. Sewer A48 Chepstow Road, 300m-500m east of the Site. Six incidences of sewer flooding. 2 UK Government (2006). LiDAR Tiles Digital Terrain Model (DTM). Contains public sector information licensed under the Open Government Licence v3.0. Accessed online via: 3 Centre for Ecology and Hydrology (CEH) (2017), Flood Estimation Handbook (FEH) Web Service. Accessed online via: 4 Newport City Council (2015). Newport City Council Newport, Local Flood Risk Management, Flood Risk Management Plan. Accessed online via: Risk-Management-Plan-Report-Issue-for-Consultation.pdf 5 URS Scott Wilson (2011). Newport City Council Preliminary Flood Risk Assessment, Preliminary Assessment Report. Accessed online via: Assessment-Report-April-2011.pdf 3

9 2.3 Natural Resources Wales Flood Map An extract of the NRW Risk of Flooding from Rivers and the Sea map 6, provided in Figure 2, shows that the entire Site is described as Very Low flood risk, which designates land assessed as having a less than 1 in 1000 (0.1%) annual probability of river or sea flooding. Figure 2: NRW Risk of Flooding from Rivers and the Sea, including the red line boundary. Contains OS data Crown Copyright and database right Existing Flood Defences No formal or de facto flood defences have been identified in the vicinity of the Site. 6 Cyfoeth Naturiol Cymru Natural Resources Wales (2017). Risk of Flooding from Rivers and the Sea, virtual map. Accessed online via: /Geocortex/Essentials/REST/sites/Flood_Risk/viewers/Flood_Risk/virtualdirectory/Resources/Config/Default 4

10 3 TAN15 Development and Flood Risk TAN15 summarises the guidance to local planning authorities in determining planning applications with regard to flood risk and provides an interpretation of how this guidance applies specifically to the proposed Development. It provides a framework within which risks arising from both river and coastal flooding, and from additional run-off from the site under development conditions, can be assessed. This precautionary framework should be used for both forward planning and development control purposes. Its operation is governed by TAN15 paragraph 3.2: A development advice map containing three zones (A, B and C, with subdivisions C1 and C2), which should be used to trigger the appropriate planning tests in relation to Sections 6 and 7 in Appendix 1. Definitions of vulnerable development and advice on permissible uses in relation to the location of development and the consequences of flooding. The approach is therefore a stage one: Categorisation of the Site within TAN15 Flood Zones. Application of the TAN15 precautionary framework and determination of whether the proposed development is justified in that location (TAN15 Section 6). Assessment of flooding consequences (TAN15 Section 7 test and Appendix 1) and the production of a FCA report. 3.1 Categorisation of Site within TAN15 Flood Zones The TAN15 Development Advice Map (DAM) 7, provided in Figure 3, shows that the entire Site is located in Zone A, which is land considered to be at little or no risk of fluvial or coastal/tidal flooding. Following TAN15 Guidance, the location of the Site in Zone A indicates that the justification test is not applicable and there is no need to consider flood risk further. 7 Llywodraeth Cymru Welsh Government (2006). TAN15 Development and Flood Risk Development Advice Map. Accessed online via: 5

11 Figure 3: boundary. TAN15 Development & Flood Risk: Development Advice Map, including the red line Contains OS Data Crown Copyright and database right OS There is an area of Zone B, areas known to have been flooded in the past evidenced by sedimentary deposits, located approximately 300m east of the Site. 3.2 Assessment of Flooding Consequences Having established that the proposed Development is justified in its location, there is a need to assess the consequences of flooding. To comply with TAN15 guidance, the FCA must demonstrate that the consequences associated within flooding are manageable and acceptable. TAN15 specifies that flood risk from the following sources should be investigated as part of a FCA: Fluvial Groundwater Surface Water Coastal/Tidal Sewers Artificial Sources The flood risk from each of these sources is assessed in Section 4. 6

12 4 Assessment of Flood Risk All potential sources of flooding have been considered within the FCA and are discussed below. 4.1 Fluvial Flood Risk The NRW Risk of Flooding from Rivers and the Sea map, provided in Figure 2, illustrates that the Site is located in the very low flood risk zone (Flood Zone 1) and therefore has a risk of annual flooding from Main River sources that is less than 1 in 1,000 (0.1%). It is considered that there is no significant risk of flooding from main river sources. A minor unnamed watercourse flows southwards along the north eastern boundary of the Site and a drainage ditch runs along the northern boundary of the Site. No quantitative data is available for these ordinary watercourses. However, NCC confirm there are no records of historic flooding in this area and given the small size of these catchments, it is considered that there is a low flood risk from these watercourses. Figure 4 shows the channel of the unnamed watercourse, looking downstream from the northeast corner of the Site. The image shows the watercourse has a relatively wide, unconstrained channel, but with potential for large conveyance capacity. It is considered that there is no significance risk of flooding from ordinary watercourse sources. Figure 4: Unnamed Watercourse, taken from northeast corner of the Site looking south (downstream). 7

13 4.2 Groundwater The NCC FRMP and NCC PFRA state that, on a strategic scale, groundwater flooding is not considered to be a significant flood risk to the region and there are no recorded incidents of groundwater flooding in proximity to the Site. It is considered that there is no significant risk of flooding from groundwater sources. 4.3 Surface Water Flooding from this source is a potential risk during short, intense rainstorm events or longer duration storms when the capacity of underlying soils and drainage systems is exceeded and rainfall runs overland to pond in depressions in the landscape. It is important that due consideration is given to changes in surface water runoff patterns as a result of development proposals. The current land use of the entire Site is Greenfield, consisting of semi-improved and managed grassland. Surface water from the Site generally drains naturally to the ground via infiltration or, when the infiltration capacity of the soils is exceeded, flows overland in accordance with local topography towards the southeast corner of the Site and/or the ordinary watercourse. The NRW Risk of Flooding from Surface Water map 8, provided in Figure 5, shows that there are areas designated as at risk of surface water flooding within and in proximity to the Site boundary. The flood map takes a broad account of underground drainage and typical storms that are likely to cause flooding. The map shows four levels of flood risk: High: chance of flooding greater than 1-in-30 year (3.3%); Medium: chance flooding between 1-in-30 year (3.3%) and 1-in-100 year (1%); Low: chance of flooding between 1-in-100 year (1%) and 1-in-1,000 year (0.1%); and Very Low: chance of flooding less than 1-in-1,000 year (0.1%). The map does not contain sufficient information to determine flood risk to individual sites, however it provides an indication of whether, and to what extent, an area may be affected by surface water flooding. The map shows that the central area of the Site is at very low risk of surface water flooding, however land along the southern and eastern boundaries is designated with a low risk of flooding and land along the northern boundary and in the northeast and southeast corners are described as at medium to high risk of surface water flooding. 8 Cyfoeth Naturiol Cymru Natural Resources Wales (2017). Risk of Flooding from Surface Water, virtual map. Accessed online via: /Geocortex/Essentials/REST/sites/Flood_Risk/viewers/Flood_Risk/virtualdirectory/Resources/Config/Default 8

14 Figure 5: NRW Risk of Flooding from Surface Water, including the red line boundary. Contains OS data Crown copyright and database right The current land use of the Site is semi-improved grassland and broadleaved woodland and the proposed Development will increase the area of impermeable land cover which, if not sustainably managed, could lead to increases in flood risk both on Site and to neighbouring third party land. To mitigate any potential impacts of the Development on surface water flood risk, Sustainable Drainage Systems (SuDS), should be integrated into the design of the Site Estimation of Runoff Rates and Storage Volumes The storm water management requirements for a new development are assessed by calculating equivalent Greenfield runoff rates for the area of impermeable surface cover that will be added by the development, and then estimating the storage volume required to restrict runoff from these new impermeable surfaces to the Greenfield rates. 9

15 The proposed development will convert approximately 80% of the Site to impermeable surface cover and NCC have confirmed that runoff rates from the Site should be restricted to Greenfield rates. Equivalent Greenfield rainfall runoff rates and associated attenuation storage requirements have been estimated for this area using the Revitalised Flood Hydrograph method (ReFH) 9, part of a suite of techniques within the Flood Estimation Handbook 10. Greenfield runoff rates have been calculated for the 50%, 3.33% and 1% AEP events and are presented in Table 2 below. Table 2: Greenfield Peak Runoff Flow Rate for 50%, 3.33% and 1% AEP Events. Return Period Event (Annual Exceedance Probability) Greenfield Peak Flow Rate (l/s/ha) 50% % 7.7 1% 10.2 Storage volumes have been estimated for a rainstorm over the development Site with a 6-hour storm duration and 1% AEP inclusive of a 40% allowance for climate change, in line with CIRIA C609 and current NRW climate change guidelines. The Design Rainfall is the amount of rain that is predicted to fall on the proposed development Site during the event. The Net Rainfall is the portion of the Design Rainfall that contributes to surface water runoff, after accounting for losses due to evaporation, soil moisture retention and depression storage. To quantify the effect of the proposed Development on rainfall-runoff volumes, it has been assumed that no losses would occur when rain falls on the impervious services, such as roofs and hardstanding (these contribute to Net Rainfall). Those areas not covered by impermeable surfaces would encourage losses, with rainfall volume contributions calculated from Net Rainfall depths. The results of the calculations for the existing situation and the proposed Development option are presented in Table 3 below. Table 3: Existing and Proposed Development Rainfall-Runoff Volumes (1% AEP with Climate Change for 6-hour Storm). Option Total Volume of rainfall runoff (m³) (difference with respect to existing situation) Total Volume of rainfall runoff with Climate Change (m³) (difference with respect to existing situation) Existing Proposed Development 721 (+346) 1009 (+484) 9 Wallingford Hydrosolutions and Centre for Ecology and Hydrology (2016). Revitalised Hydrograph Model Version 2.2 Technical Guidance Report. Accessed online via: 10 Centre for Ecology and Hydrology (2016). Flood Estimation Handbook. Accessed online via: 10

16 The proposed development and the associated conversion of permeable to impermeable surfacing results in a significant increase in rainfall-runoff volume of 346m 3 and 484m 3 for the current and climate change (future) scenarios respectively. A comprehensive drainage strategy is therefore required so that the induced changes to the rainfall runoff regime does not impact on surface water flood risk on Site or on neighbouring third party land. The drainage strategy will incorporate appropriate Sustainable Drainage Solutions (SuDS) techniques that provide attenuation as well as treatment of surface water runoff. With an appropriate drainage strategy in place, it is considered that there would be no significant risk from surface water flooding on Site or to third party areas. 4.4 Sewers The NCC PFRA states that sewer flooding within Newport does not have significant consequences at a strategic scale and is instead limited to several small sewer flooding hotspots. The NCC PFRA and NCC LFRMS indicate that the flooding incidents in closest proximity to the Site have been from sewer flooding, however none of the extents from these events have included any areas within the Site boundary. It is considered that there is no significant risk of flooding from sewer sources. 4.5 Coastal/Tidal The Site is located over 7km from the coast and at an elevation of over 35m AOD, there is no risk of flooding at the proposed Development Site from tidal sources. 4.6 Artificial Sources The NRW Risk of Flooding from Reservoirs 11 map illustrates areas that could flood following the failure of a large reservoir and the subsequent release of any contained waters. The map shows that the entire Site is not considered at risk of reservoir flooding. No other potential sources of artificial flooding, including canals or lakes, have been identified in the area. It is considered that there is no risk of flooding from artificial sources. 11 Cyfoeth Naturiol Cymru Natural Resources Wales (2017). Risk of Flooding from Reservoirs, virtual map. Accessed online via: /Geocortex/Essentials/REST/sites/Flood_Risk/viewers/Flood_Risk/virtualdirectory/Resources/Config/Default 11

17 5 Flood Risk Mitigation Measures The entire Site and its proposed access/egress routes are designated as within TAN15 Zone A and the Site is considered to be at little or no risk of fluvial or tidal/coastal flooding and the justification test is not applicable and no need to consider flood risk further. As such, no additional mitigation measures are required to manage flood risk from rivers, the sea, groundwater or artificial sources. With regards to flood risk from surface water runoff and sewers, as the Development will convert semiimproved grassland to impermeable land cover, the design of a suitable surface water drainage system, incorporating SuDS is a key requirement. In addition, consultation with Dwr Cymru Welsh Water, as the statutory sewerage undertaker, is recommended to agree appropriate rates of foul water discharge. 12

18 6 Flood Risk and Consequences Summary All potential sources of flood risk to the proposed Development have been investigated using a desk study approach. Flood risk from fluvial, groundwater, artificial and coastal/ tidal sources have been assessed as low. Surface water flooding has been confirmed as the main source of flood risk to the Site. The centre of the Site is designated with a very low risk of surface water flooding, however the boundaries of the site, in particular the southern, northern and eastern edges are designated with medium-high surface water flood risk. The proposed Development will result in an increase in impermeable land cover, with approximately 80% of the Site being turned from greenfield land to built development. Calculations have confirmed that this change in land cover results in impacts on the existing rainfall runoff regime, which if not managed, poses an increased surface water flood risk, to the Site and third party areas. A drainage strategy would be produced for the proposed Development, which ensures that surface water runoff rates and volumes match existing (Greenfield) rates. The drainage strategy would incorporate a number of SuDS techniques, selected to accommodate site specific ground conditions and constraints. Access and egress to the proposed Development Site would be flood free in events up to and including the 0.1% AEP flood event. It is concluded that the development proposals satisfy the development and flood risk policy requirements of TAN15. 13

19 Appendix A Detailed Site Layout Plan

20 General Notes 1. Contractor to verify all dimensions and check level datums on site 2. All of the designs are the sole property of TACP Architects Ltd and may not be used without their written agreement 3. All prints, specifications and their copyright are the property of TACP Architects Ltd North 4. Do not scale off drawings 5. All dimensions shall be checked on site before commencment of shop drawings, manufacture and all discrepencies must be reported to TACP Architects Ltd STAFF CAR PARKING 7 Spaces Staff Entrance HOTEL DEVELOPMENT Entrance DROP-OFF ZONE CAR PARKING 7 Spaces Outdoor Seating Area Hotel Car Parking Barrier Risk Assessments Starbucks Drive-Thru 4 Wheelchair Users Spaces CAR PARKING 143 Spaces Revisions Rev A B COLDRA WOOD Date 22/02/17 23/02/17 Description By Site context added KA Area around Starbucks revised in accordance with client's AW comments. Check KA CAR PARKING 15 Spaces Consultants Client Lewis & Lewis Project Title Langstone Hotel Drawing Title Site layout Scale 1 : 200@A0 Date Drawn By Checked By 03/02/17 JH DM Job Number Drawing Number ST-01 Office Wrexham Revision B TACP Architects Ltd Pembroke House Ellice Way, Wrexham Technology Park, Wrexham, LL13 7YT admin@tacparchitects.co.uk Architecture Interior Design Healthcare Planning Conservation Masterplanning Sustainable Design

21 Arcadis Consulting (UK) Limited 2 Glass Wharf Temple Quay Bristol BS2 0FR United Kingdom T: +44 (0) arcadis.com