Flood Risk Assessment

Transcription

1 Flood Risk Assessment Low Whita Swaledale Morrison Utility Services Report Reference: CLE30080/05/01 Clear Environmental Consultants July 2015

2 QUALITY ASSURANCE Client: Morrison Utility Services Report Title: Flood Risk Assessment Project: Low Whita Project No.: CLE30080 REPORT ISSUE REGISTER Name Signature Date Author Martin Spiers BEng (Hons) 15/07/2015 V1 Approved for issue David De Rosa BSc CEng CWe MCIWEM 15/07/2015 V2 Minor changes from client review Martin Spiers BEng (Hons) 20/07/2015 LIABILITY: Clear Environmental Consultants, a trading division of RPS Environmental Management Ltd (Clear) has prepared this report for the sole use of Morrison Utility Services (the client), their agents or other consultants, in accordance with the agreement under which our services were performed. No warranty, express or implied, is made as to the advice in this report or any other service provided by Clear. This report may not be relied upon by any other party except the client or any third party for whom report is intended without the prior written permission of Clear. The content of this report is, at least in part, based upon information provided by secondary data sources and on the assumption that all relevant information has been provided by those parties from whom it has been requested. Information obtained from any third party has not been independently verified by Clear unless otherwise stated in the report. COPYRIGHT: This report is the copyright of Clear. It remains the property of Clear until such time as payment in full for the services conducted as per the contract of Clear s appointment has been compensated. Unauthorised reproduction or usage by any person is prohibited. Clear Environmental Consultants, a trading division of RPS Environmental Management Ltd Low Whita - Flood Risk Assessment July 2015 Morrison Utility Services

3 CONTENTS 1 INTRODUCTION AND BACKGROUND Terms of Reference Approach to the Assessment DETAILS OF THE SITE Site Details Site Description FLOOD RISK ASSESSMENT Possible Flooding Mechanisms Fluvial Flooding Pluvial Flooding Groundwater Flooding Surface Water Runoff Existing Surface Water Runoff Assessment Proposed Surface Water Runoff Management MITIGATION MEASURES Pluvial Flooding Mitigation Surface Water Management CONCLUSIONS... 9 APPENDICES Appendix A Appendix B Appendix C Appendix D Appendix E Existing and Proposed Layout and Levels Information from the Environment Agency Existing Site Runoff Calculations Surface Water Attenuation Calculations Outline Surface Water Drainage Proposal Clear Environmental Consultants, a trading division of RPS Environmental Management Ltd Flood Risk Assessment - Low Whita July 2015 Morrison Utility Services

4 1 Introduction and Background 1.1 Terms of Reference Clear Environmental Consultants, a trading division of RPS Environmental Management Ltd (Clear) was commissioned by Morrison Utility Services to undertake a flood risk assessment to support the proposed water pumping station at Low Whita, Swaledale. The site s location is depicted in Table 1.0. The Environment Agency s mapping shows that part of the site lies within Flood Zone 3 (land assessed as having between a 1 in 100 and 1 in 1000 annual probability of river flooding) and is therefore considered to be at risk of fluvial flooding. The site is currently greenfield land and is used for farming. In terms of the Flood Risk Vulnerability Classification given in Table 2 of the Technical Guidance to the National Planning Policy Framework, Water transmission infrastructure and pumping stations are classed as Water compatible, and are considered compatible with locations in Flood Zones 2 and 3a. 1.2 Approach to the Assessment The site lies within Flood Zone 2 and is therefore at risk of flooding from main rivers. In addition, the surface water flood map shows some areas at risk of pluvial flooding on the site boundary. The assessment is required to demonstrate that the risk of flooding from these, and surface water runoff from the development itself, can be adequately managed within the development. Drawings showing the site location and elevation, and the proposed works, have been provided and are included in Appendix A. The requirements for flood risk assessments are generally as set out in the National Planning Policy Framework (NPPF) and the Technical Guidance to the National Planning Policy Framework. The detail and complexity of the study required should be appropriate to the scale and potential impact of the development. For the purposes of this study, the following have been considered: Available information on historical flooding in the area. Site level information. Details of structures, which may influence hydraulics of the watercourse and consideration of the effect of blockage of structures. Allowances for increased flows resulting from the effects of climate change. Assess the existing runoff characteristics and the potential impact any proposed development will have on the runoff. Further guidance is also provided in the CIRIA Research Project 624 Development and Flood Risk: Guidance for the Construction Industry. Clear Environmental Consultants, a trading division of RPS Environmental Management Ltd Flood Risk Assessment - Low Whita July 2015 Morrison Utility Services

5 2 Details of the Site 2.1 Site Details Table 1: Development Location Site Name: Existing Land Use: Proposed Land Use: Site Area: OS NGR: Country: County: Local Planning Authority: Sewerage undertaker: Lead Local Flood Authority Low Whita Greenfield Water pumping station 0.06Ha E,498266N England North Yorkshire Yorkshire Dales National Park Yorkshire Water North Yorkshire Council Location Plan: Site location OpenStreetMap contributors 2015 Clear Environmental Consultants, a trading division of RPS Environmental Management Ltd Flood Risk Assessment - Low Whita July 2015 Morrison Utility Services

6 2.2 Site Description The site is approximately 684 square metres, and consists of part of a field at the junction of Low Lane and Scabba Wath Bridge. The site is greenfield. A drawing of the site and immediate surrounding area is included in Appendix A. Current proposals are to construct a surface water pumping station with associated hardstanding, bordered on the north and west sides by new stone walls and on the east and south sides by the existing stone walls forming the field boundary. The site is located between 192.7m and 192.8m AOD and falls towards the east. The surrounding land falls generally towards the north-east. An aerial photograph of the existing site is shown below in Figure 2.1. Figure 2.1: Site specific aerial photograph Google Earth imagery used under licence 2015 Google 2015 Infoterra Ltd and Bluesky Site boundary Clear Environmental Consultants, a trading division of RPS Environmental Management Ltd Flood Risk Assessment - Low Whita July 2015 Morrison Utility Services

7 3 Flood Risk Assessment 3.1 Possible Flooding Mechanisms Table 2: : Possible Flooding Mechanisms Source/Pathway Significant? Comment/Reason Fluvial Yes The site is shown as lying within Flood Zones 2 and 3 of the Environment Agency detailed flood maps Tidal/Coastal No The site does not lie within close proximity of the sea. Pluvial (urban drainage) Potential Proposals for the site will increase the impermeable area Groundwater Yes The site is located within an area at risk of groundwater flooding Overland flow No The degree of gradient at the site is not significant enough to cause runoff to flow overland towards or from neighbouring land Blockage No No significant watercourse infrastructure likely to have a significant impact on the site. Infrastructure failure No No known infrastructure flood risk Rainfall Ponding No The site slopes such that rainfall will not pond on the site itself. Fluvial flooding from the River Swale is the main source of flood risk associated with the development. 3.2 Fluvial Flooding Consultation with the Environment Agency (EA) shows that parts of the site lies within Flood Zone 2 (land assessed as having between a 1 in 100 and 1 in 1000 annual probability of river flooding) The risk of flooding from main rivers is therefore considered to be medium. This flood risk relates to the River Swale, which lies approximately 60m to the north of the site centroid. Information provided by the EA suggests that the site was affected by the 1995 flood event. This information also confirms that there are flood defences along the right bank of the Swale. These are privately maintained and no information is available on the level of protection provided No flood levels have been provided by the EA, however the site lies towards the edge of Flood Zone 2 and flood depths in the 1 in 1000 flood event are therefore likely to be small, particularly as the ground slopes upwards from the River Swale to the site. The area is covered by the Level 1 Strategic Flood Risk Assessment carried out for the Yorkshire Dales National Park in 2014, however this does not provide any additional information on fluvial flood risk at this location. It is concluded that the site is not at significant risk of fluvial flooding and that, as the plant and equipment are to be located above ground, there is no requirement for additional mitigation measures. 3.3 Pluvial Flooding The risk of flooding to the site has been assessed with reference to the Environment Agency s Risk of Flooding from Surface Water mapping, which shows areas at risk of surface water flooding near to the boundary of the site, predominantly in the fields to the north. Examination of the topography demonstrates that the ground falls to the north of the site, towards the river, and flooding within this area is therefore unlikely to affect the development. Smaller areas of pluvial flooding are indicated within the highway. The topographic data provided shows that finished levels within the compound area are higher than the adjacent road and hence the risk of surface water entering the site from the highway is small. Clear Environmental Consultants, a trading division of RPS Environmental Management Ltd Flood Risk Assessment - Low Whita July 2015 Morrison Utility Services

8 3.4 Groundwater Flooding A map included in the SFRA shows that the site is located within a 1km square with a susceptibility to groundwater flooding of between 25% and 50%. This indicates that between one quarter and half the square may be at risk of groundwater flooding with an unspecified frequency. 3.5 Surface Water Runoff The existing site is considered as greenfield. Proposals are to construct a water pumping station and to provide hardstanding within the compound. This will increase the impermeability of the site. 3.6 Existing Surface Water Runoff Assessment The existing site is greenfield and wholly permeable. Pre-development runoff rates have therefore been calculated using the IoH124 methodology. The calculated rates are provided in Table 3 below and calculations are included in Appendix D. Return Period Unit Flow in Litres per Second per Hectare (l/s/ha) Flow in Litres per Second (l/s) 1 in 2 year in 30 year in 100 year Table 3: Pre-Development Runoff Rates 3.7 Proposed Surface Water Runoff Management Mapping from the British Geological Survey shows an underlying geology of Dination rocks limestone with subordinate sandstone and argillaceous rocks; and superficial deposits of alluvium and till. The winter rainfall acceptance profile maps included in the Wallingford Procedure show the site as lying within soil class 5, described as Soils of the wet uplands. Both of these datasets indicate that the site is unlikely to be suitable for infiltration drainage. Surface water flows would normally be attenuated to the pre-development 1 in 2 year runoff rate, however due to the small size of the development this may not be practical. A practical limit of 5l/s is usually adopted to allow for practical flow control devices. Using the Wallingford Procedure, Modified Rational Method, the volume to be attenuated for the site has been calculated for the 1 in 2 year, 30 year, 100 year and 100 year plus climate change events based on a restricted discharge rate of 5 l/s. Appendix D contains the calculation spreadsheets used to calculate the required storage volumes on the site for each return period, the results from which are tabulated below in Table 4. This represents a scenario where surface water runoff is discharged from the site with no allowance made for infiltration drainage options. Return Period Volume to be Balanced (m³) 1 in 2 year 0 1 in 30 year 8 1 in 100 year 15 1 in 100 year + Climate Change 20 Table 4: Modified Rational Method Balance Volumes Clear Environmental Consultants, a trading division of RPS Environmental Management Ltd Flood Risk Assessment - Low Whita July 2015 Morrison Utility Services

9 It is normal practice to ensure that the 1 in 30 year event is maintained below the ground in the form of storage and that the difference of 12m 3 between the 1 in 30 year and 1 in 100 year plus climate change events be permitted to flood the surface in a controlled manner as long as there is no flooding to buildings and the flood volume is contained within the site boundary. Due to the small and relatively flat nature of the site, it is likely to be difficult to provide any storage on the surface. It is therefore recommended that the full 1 in 100 year plus climate change event be stored below ground. For example, the required volume of 20m³ could be provided in storage below the compound area. This requirement would be reduced significantly if the material used to provide hardstanding within the compound was such that permeability was maintained. This is discussed further in the following section. Clear Environmental Consultants, a trading division of RPS Environmental Management Ltd Flood Risk Assessment - Low Whita July 2015 Morrison Utility Services

10 4 Mitigation Measures The purpose of this section of the report is to provide information for utilisation as part of the planning application for the proposed development site. The mitigation measures outlined below may be adopted to reduce the consequences of flooding to people and property within the proposed development site. 4.1 Pluvial Flooding Mitigation The development does not involve any significant or net changes in ground levels, however the proposed structure does marginally reduce the floodplain storage. Given the location on the edge of the flood zone and the small loss in a broadly undeveloped flood plain, it is considered that compensatory floodplain storage is not required at this location. The proposed pumping station is designed in such a way that the equipment is located above ground level and any floodwater entering will not cause significant damage or affect the operation of the plant within. The structure itself is designed in such a way that the consequences of flooding would be minor. 4.2 Surface Water Management Runoff from the site will require to be discharged to a suitable drain or watercourse. The River Swale lies approximately 40m north-east of the site boundary and may be the most appropriate receptor. Runoff should be attenuated to 5l/s, requiring an attenuation volume of 20m 3 for the 1 in 100 year + climate change event Sustainable Drainage Systems (SuDS) The aim of sustainable drainage systems (SuDS) is to mimic the natural drainage system. In the current case, rain landing on the proposed site of the pumping station either infiltrates into the ground or runs off onto the remainder of the field and eventually into the River Swale. The requirement for attenuation identified above can be reduced significantly if the compound area is finished with permeable surfacing. This could be open-textured soil or granular material - gravel or similar surface on a sub-base reinforced if necessary with a modular interlocking plastic paving system. Given the low frequency of expected maintenance visits to the site, such a system should be capable of retaining permeable throughout the lifetime of the development. The use of an open-graded sub-base will allow any excess runoff including that from the superstructure to be stored in an analogous manner to existing rainfall onto the undeveloped site. Runoff can then be regulated to greenfield rates by suitable openings in the base of the boundary wall and discharged onto the adjacent field as per the existing scenario. Any blockage of the openings may lead to some ponding within the compound area, but this will not affect the operation of the pumping station. With the impermeable area requiring attenuation reduced to the building itself, the volume of attenuation required up to the 1 in 100 year plus climate change event is reduced to 2m 3. This can be easily provided within the sub-base material of the hardstanding area. An outline surface water drainage proposal is shown in Appendix E. Clear Environmental Consultants, a trading division of RPS Environmental Management Ltd Flood Risk Assessment - Low Whita July 2015 Morrison Utility Services

11 5 Conclusions This Flood Risk Assessment has been written in accordance with the requirements set out in the NPPF for the proposed water pumping station. In terms of the Flood Risk Vulnerability Classification given in Table 2 of the Technical Guidance to the National Planning Policy Framework, Water transmission infrastructure and pumping stations are classed as Water compatible, and are considered compatible with locations in Flood Zones 2 and 3a. The EA flood mapping depicts the site as being at risk of flooding from fluvial sources. No flood depths are provided, but the site is towards the edge of floodzone 2 and significantly above the level of the River Swale. The design of the proposed pumping station is such that neither the structure or the equipment would be affected by flooding and the consequences of a flood event on the site itself are therefore small. The pumping station would remain operational during a flooding event. The site is currently greenfield, and the development will increase impermeability and runoff. Attenuation is therefore required to mitigate the potential impacts of increased surface water discharges. It is presumed that surface water flows would be limited to 5l/s as the existing greenfield runoff rate for a site of this size is too small to be achieved without adverse risk of blockage of the flow control device. On this basis it has been calculated that the overall attenuation volumes at the site would be 20³ for the 1 in 100 year + Climate Change event. It is normal practice to store at least the 1 in 30 year event runoff to prevent surface flooding. However, to minimise the risk of overland flooding it is suggested that the 1 in 100 year + Climate Change runoff volume be attenuated. Providing the mitigation measures discussed are implemented it is considered that the risk of flooding to, and from, the site will be minimal. Clear Environmental Consultants, a trading division of RPS Environmental Management Ltd Flood Risk Assessment - Low Whita July 2015 Morrison Utility Services

12 Appendix A: Existing and Proposed Layout and Levels Clear Environmental Consultants, a trading division of RPS Environmental Management Ltd Flood Risk Assessment - Low Whita July 2015 Morrison Utility Services

13 Proposed stone wall in keeping with surrounding wall construction Proposed 3.6m access gate Proposed water pumping station 9.6m x 5.6m Site Location Proposed access road Proposed 2 x 2.8m field access gates Y Area of land = 611.3m 2 Existing access in stone wall to be made good in keeping with surrounding wall construction Location Plan 1:5000 Mott MacDonald Bentley Limited OS Copyright Licence No. WU This document should not be relied on or used in circumstances other than those for which it was originally prepared and for which Mott MacDonald Bentley Ltd was commissioned. Mott MacDonald Bentley Ltd accepts no responsibility for this document to any other party other than the person by whom it was commissioned. Stream: Water Networks Batch No: NQ10 Client Site Plan 1:1000 Scheme Address : Low Whita, Low Lane, Richmond YWS Ref : R0906 North Yorkshire DL11 6NT OS Ref : , Rev Date Designer. CAD Technician. Specialist Check. Drawn Description N.Johns G.Evans Engineering Check. Lead Batch Designer Check. Design Manager Approval. 1:5000 1: m 500m 0 50m 100m Ch'k'd D.Oldfield D.Oldfield App'd P GDE Building relocated, building layout amended DO MS P DO Application outlined in red DO AS P SB Building size and layout ammended A.Stephenson Title AMP6 ES West Stonesdale WTW Low Whita Water Pumping Station Planning Drawing Location Plan Drawing No. Scale at A3 Rev As shown Status NQ P6 PRE

14 1: m 25m Proposed stone wall in keeping with surrounding wall construction C Proposed stone wall in keeping with surrounding wall construction 300mm x 300mm Louvre vents, colour matt black Compound surface finish to be weedproof membrane and crushed gritstone or similar approved D Elevation B Low Lane Proposed water pumping station 9.6m x 5.6m SCALE 1: Proposed 3.6m wide timber access gate Area of land = m 2 Security Alarm Proposed entrance to pumping station. Colour of wooden faced steel doors (Dales brown) to be approved by planners B Proposed access track hardstanding to be weedproof membrane and crushed gritstone or similar approved Plan View 1:250 A Brush finish concrete ramp from finish floor level to existing ground level. Existing access to be made good with stone wall in keeping with surrounding wall construction Proposed stone wall in keeping with surrounding wall construction 600mm x 600mm Louvre vents, colour matt black Elevation C SCALE 1: Security alarm Existing stone wall Proposed field access via 2 x 2.8m wide timber gates Water pumping station 9.6m x 5.6m 30 Deg pitch roof with stone slate effect tiles or similar approved External wall in stonework to match surrounding buildings Proposed 3.6m wide timber gate Elevation SCALE 1:200 Mott MacDonald Bentley Limited OS Copyright Licence No. WU This document should not be relied on or used in circumstances other than those for which it was originally prepared and for which Mott MacDonald Bentley Ltd was commissioned. Mott MacDonald Bentley Ltd accepts no responsibility for this document to any other party other than the person by whom it was commissioned. Stream: Water Networks Batch No: NQ10 Client Scheme Address : Low Whita, Low Lane, Richmond YWS Ref : R0906 North Yorkshire DL11 6NT OS Ref : , A mm x 300mm Louvre vent, colour matt black. 600mm x 600mm Louvre vent, colour matt black. Existing access made good with stone wall in keeping with surrounding wall construction Rev Date Designer. CAD Technician. Specialist Check. Drawn Description N.Johns G.Evans Existing GL Engineering Check. Lead Batch Designer Check. Design Manager Approval. Elevation SCALE 1:200 Ch'k'd P GDE Building location and layout amended RG MS P SC Levels added & application area outlined in red DO AS P7 16/07/15 SB Building size and layout ammended D.Oldfield D.Oldfield 1:200 0 App'd A.Stephenson Title Drawing No. D 101 Existing stone wall Proposed entrance to pumping station. Colour of wooden faced steel doors (Dales brown) to be approved by planners NOTE: REFER TO DRAWING NQ FOR DETAILS OF BASE SECTIONS 10m AMP6 ES West Stonesdale WTW Low Whita Water Pumping Station Planning Drawing Plan And Elevations Scale at A3 Rev As shown Status 20m NQ P7 PRE

15 Appendix B: Information from the Environment Agency Clear Environmental Consultants, a trading division of RPS Environmental Management Ltd Flood Risk Assessment - Low Whita July 2015 Morrison Utility Services

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18 Use of Environment Agency Information for Flood Risk / Flood Consequence Assessments Important If you have requested this information to help inform a development proposal, then we recommend that you undertake a formal pre-application enquiry using the form available from our website:- Depending on the enquiry, we may also provide advice on other issues related to our responsibilities including flooding, waste, land contamination, water quality, biodiversity, navigation, pollution, water resources, foul drainage or Environmental Impact Assessment. In England, you should refer to the Environment Agency s Flood Risk Standing Advice, the technical guidance to the National Planning Policy Framework and the existing PPS25 Practice Guide for information about what flood risk assessment is needed for new development in the different Flood Zones. These documents can be accessed via: idance ate You should also consult the Strategic Flood Risk Assessment produced by your local planning authority. In Wales, you should refer to TAN15 for information about what flood consequence assessment is needed for new development in the different flood zones zb3ylczf20xn7lk3zk0nmk! ?orig=/topics/planning/policy/tans/tan15/ You should also consult the Strategic Flood Consequence Assessment if one has been produced by your local planning authority.

19 In both England and Wales you should note that: 1. Information supplied by the Environment Agency may be used to assist in producing a Flood Risk / Consequence Assessment (FRA / FCA) where one is required, but does not constitute such an assessment on its own. 2. This information covers flood risk from main rivers and the sea, and you will need to consider other potential sources of flooding, such as groundwater or overland runoff. The information produced by the local planning authority referred to above may assist here. 3. Where a planning application requires a FRA / FCA and this is not submitted or deficient, the Environment Agency may well raise an objection. 4. For more significant proposals in higher flood risk areas, we would be pleased to discuss details with you ahead of making any planning application, and you should also discuss the matter with your local planning authority.

20 89_07_SD02, Version 6 Standard notice [not for use with Special Data, Personal Data or unlicensed 3 rd party rights] Information warning We (The Environment Agency) do not promise that the Information supplied to You will always be accurate, free from viruses and other malicious or damaging code (if electronic), complete or up to date or that the Information will provide any particular facilities or functions or be suitable for any particular purpose. You must ensure that the Information meets your needs and are entirely responsible for the consequences of using the Information. Please also note any specific information warning or guidance supplied to you. Permitted use The Information is protected by intellectual property rights and whilst you have certain statutory rights which include the right to read the Information, you are granted no additional use rights whatsoever unless you agree to the licence set out below. Commercial use of anything except EA OpenData is subject to payment of a 50 licence fee (+VAT) for each person seeking the benefit of the licence, except for use as an Environment Agency contractor or for approved media use. To activate this licence you do not need to contact us (unless you need to pay us a Commercial licence fee) but if you make any use in excess of your statutory rights you are deemed to accept the terms below. Licence We grant you a worldwide, royalty-free (apart from the 50 licence fee for commercial use), perpetual, nonexclusive licence to use the Information subject to the conditions below. You are free to: copy, publish, distribute and transmit the Information adapt the Information exploit the Information commercially, for example, by combining it with other Information, or by including it in your own product or application You must (where you do any of the above): acknowledge the source of the Information by including the following attribution statement: Contains Environment Agency information Environment Agency and database right ensure that you do not use the Information in a way that suggests any official status or that We endorse you or your use of the Information ensure that you do not mislead others or misrepresent the Information or its source or use the Information in a way that is detrimental to the environment, including the risk of reduced future enhancement ensure that your use of the Information does not breach the Data Protection Act 1998 or the Privacy and Electronic Communications (EC Directive) Regulations 2003 These are important conditions and if you fail to comply with them the rights granted to you under this licence, or any similar licence granted by us will end automatically. No warranty The Information is licensed as is and We exclude all representations, warranties, obligations and liabilities in relation to the Information to the maximum extent permitted by law. We are not liable for any errors or omissions in the Information and shall not be liable for any loss, injury or damage of any kind caused by its use. We do not guarantee the continued supply of the Information. Governing Law This licence is governed by the laws of England and Wales. Definitions Information means the information that is protected by copyright or by database right (for example, literary and artistic works, content, data and source code) offered for use under the terms of this licence. Commercial means: offering a product or service containing the Information, or any adaptation of it, for a charge, or internal use for any purpose, or offering a product or service based on the Information for indirect commercial advantage, by an organisation that is primarily engaged in trade, commerce or a profession. Contact: enquiries@environment-agency.gov.uk

21 North East Region - Yorkshire Area Coverdale House Amy Johnson Way Aviator Court York YO30 4GZ 2014 FLOOD ZONE DATA FOR ENGLAND Information - User Note The Flood Zones have been produced in accordance with the requirements of Government Planning Policy on Development and Flood Risk). Flood Zones are for planning consultation. As the information is indicative rather than specific Local Planning Authorities will need to consult the Environment Agency in accordance with our standing advice for planning consultations. The flood zones are based on information available at the time, and will benefit from updates as better information becomes available. For example changes in hydrological river response, observations following flood events or improved modelling techniques. No consideration has been given to climate change at this time. It should be noted that locations adjacent to rivers, not included at this stage of the survey, may be at risk of flooding. When in doubt the Environment Agency should be consulted. These maps may be also used by Local Authority Emergency Planners when producing Major Incident Flood Response Plans. The extents of any Flood Warning Service provided by the Agency is contained in the Local Flood Warning Plan. Zone 3 (England) and Zone C (Wales) is the Agency's best estimate of the areas of land with a 100 to 1 (1%) chance or greater of flooding each year from rivers in catchments greater than 3 sq.km, or with 200 to 1 (0.5%) chance or greater of flooding each year from the sea without the presence of any defences. Zone 2 (England) and Zone B (Wales) is the Agency's best estimate of the areas of land that could flood under extreme conditions with a 1000 to 1 (0.1%) chance of flooding each year from rivers or the sea, without the presence of defences. Legend Flood Zone 3 Flood Zone 2 Scale: 1:10,000 This map is reproduced from Ordnance Survey material with the permission of Ordnance Survey on behalf of the Controller of Her Majesty's Stationery Office Crown copyright. Unauthorised reproduction infringes Crown copyright and may lead to prosecution or civil proceedings. Environment Agency, , 2014.

22 Flood Event Outline Map centred on Low Whita, DL11 6NT. [RFI/2015/33482] Scale 1:10,000 Please note that the supplied map is not considered by the Environment Agency to constitute a flood risk assessment on its own and may not be accepted by local planning authorities for that purpose. Using an inappropriate scale can in some instances result in a different indication of whether a particular point is within a flood zone. Legend FEO_122JAN1995 Environment Agency copyright and / or database rights All rights reserved. Crown Copyright and database right. All rights reserved. Environment Agency, , Contact Us: National Customer Contact Centre, PO Box 544, Rotherham, S60 1BY. Tel: (Mon-Fri 8-6). enquiries@environment-agency.gov.uk

23 Flood Defence Asset Location Map centred on Low Whita, DL11 6NT. [RFI/2015/33482] Scale 1:10,000 Please note that the supplied map is not considered by the Environment Agency to constitute a flood risk assessment on its own and may not be accepted by local planning authorities for that purpose. Using an inappropriate scale can in some instances result in a different indication of whether a particular point is within a flood zone. Legend Defence <all other values> ASSETREFER R R01 Environment Agency copyright and / or database rights All rights reserved. Crown Copyright and database right. All rights reserved. Environment Agency, , Contact Us: National Customer Contact Centre, PO Box 544, Rotherham, S60 1BY. Tel: (Mon-Fri 8-6). enquiries@environment-agency.gov.uk

24 Easimap Legend m. Environment Agency copyright and / or database rights All rights reserved. Crown Copyright and database right Ordnance Survey licence number

25 Appendix C: Existing Site Runoff Calculations Clear Environmental Consultants, a trading division of RPS Environmental Management Ltd Flood Risk Assessment - Low Whita July 2015 Morrison Utility Services

26 Project: Part: Low Whita IoH greenfield runoff Cals by: Date: M A Spiers 01/07/2015 INSTITUTE OF HYDROLOGY REPORT 124 FLOOD ESTIMATION ON SMALL CATCHMENTS This spreadsheet is suitable for estimating design flows on small rural catchments (less than 25 km 2 ) using the IH Report 124 equation for QBAR plus the FSR regional growth curves. Rural can be taken as meaning URBAN less than 0.05, or equivalently URBEXT < Step 1: Enter catchment descriptors and calculate QBAR AREA From site plans 0.06 Ha AREA km2 SAAR4170 From FEH CD-ROM 1110 mm SOIL From FSR WRAP maps 0.50 Enter fraction of catchment covered by each WRAP class: Key User Input Header (do not change) Formula cell (do not change) QBAR m3/s Scaled down from 50Ha equivalent catchment as per recommendations of "Preliminary rainfall runoff management for developments", Defra/EA, Step 2: Use a FSR regional growth curve to estimate design flows Choose your region from the map. Enter a number, or I for Ireland or GB for Great Britain 3 Return period (Design flow (m 3 /s) Specific runoff (l/s/ha) Design flow l/s

27 Appendix D: Surface Water Attenuation Calculations Clear Environmental Consultants, a trading division of RPS Environmental Management Ltd Flood Risk Assessment - Low Whita July 2015 Morrison Utility Services

28 Full site area considered as impermeable, runoff limited to 5l/s Clear Environmental Consultants, a trading division of RPS Environmental Management Ltd Flood Risk Assessment - Low Whita July 2015 Morrison Utility Services

29 Project: Low Whita Part: Modified Rational Method Attenuation - 2yr return period Cals by: Date: M A Spiers 14/07/2015 Return Period 2 years Length (m) 48 m Rainfall Duration Rainfall Duration Rainfall Depth Effective Rainfall Intensity FLOW RUN-OFF Allowable Difference FLOW (l/s) Area (ha) 0.06 Ha (hours) (days) (mm) Depth (mm) (mm/hr) (l/s/ha) FLOW (m 3 ) RAIN (m 3 ) Outflow (m 3 ) (m 3 ) Max Height maod Min Height maod DeltaH Slope (%) Te (mins) mins ARF SAAR 1110 mm UCWI 121 mm PIMP 100 % SOIL Percentage Runoff PR Depression storage Cv Cr allowable outflow 5.0 l/s m 3 /s m Storage RT years Storage

30 Project: Low Whita Part: Modified Rational Method Attenuation - 30yr return period Cals by: Date: M A Spiers 14/07/2015 Return Period 30 years Length (m) 48 m Rainfall Duration Rainfall Duration Rainfall Depth Effective Rainfall Intensity FLOW RUN-OFF Allowable Difference FLOW (l/s) Area (ha) Ha (hours) (days) (mm) Depth (mm) (mm/hr) (l/s/ha) FLOW (m 3 ) RAIN (m 3 ) Outflow (m 3 ) (m 3 ) Max Height maod Min Height maod DeltaH Slope (%) Te (mins) mins ARF SAAR 1110 mm UCWI 121 mm PIMP 100 % SOIL Percentage Runoff PR Depression storage Cv Cr allowable outflow 5.0 l/s m 3 /s m Storage RT years Storage

31 Project: Low Whita Part: Modified Rational Method Attenuation - 100yr return period Cals by: Date: M A Spiers 14/07/2015 Return Period 100 years Length (m) 48 m Rainfall Duration Rainfall Duration Rainfall Depth Effective Rainfall Intensity FLOW RUN-OFF Allowable Difference FLOW (l/s) Area (ha) Ha (hours) (days) (mm) Depth (mm) (mm/hr) (l/s/ha) FLOW (m 3 ) RAIN (m 3 ) Outflow (m 3 ) (m 3 ) Max Height maod Min Height maod DeltaH Slope (%) Te (mins) mins ARF SAAR 1110 mm UCWI 121 mm PIMP 100 % SOIL Percentage Runoff PR Depression storage Cv Cr allowable outflow 5.0 l/s m 3 /s m Storage RT years Storage

32 Project: Low Whita Part: Modified Rational Method Attenuation - 100yr return period + 20% climate change Cals by: Date: M A Spiers 14/07/2015 Return Period years + 20 % climate change Length (m) 48 m Rainfall Duration Rainfall Duration Rainfall Depth Rainfall depth + Effective Depth Rainfall Intensity FLOW RUN-OFF Allowable Difference FLOW (l/s) Area (ha) Ha (hours) (days) (mm) Climate change (mm) (mm/hr) (l/s/ha) FLOW (m 3 ) RAIN (m 3 ) Outflow (m 3 ) (m 3 ) Max Height maod Min Height maod DeltaH Slope (%) Te (mins) mins ARF SAAR 1110 mm UCWI 121 mm PIMP 100 % SOIL Percentage Runoff PR Depression storage Cv Cr allowable outflow 5.0 l/s m 3 /s m Storage RT years Storage

33 Roof area considered as impermeable, runoff limited to greenfield rate Clear Environmental Consultants, a trading division of RPS Environmental Management Ltd Flood Risk Assessment - Low Whita July 2015 Morrison Utility Services

34 Project: Low Whita Part: Modified Rational Method Attenuation - 2yr return period Cals by: Date: M A Spiers 14/07/2015 Return Period 2 years Length (m) 12 m Rainfall Duration Rainfall Duration Rainfall Depth Effective Rainfall Intensity FLOW RUN-OFF Allowable Difference FLOW (l/s) Area (ha) 0.01 Ha (hours) (days) (mm) Depth (mm) (mm/hr) (l/s/ha) FLOW (m 3 ) RAIN (m 3 ) Outflow (m 3 ) (m 3 ) Max Height maod Min Height maod DeltaH Slope (%) Te (mins) mins ARF SAAR 1110 mm UCWI 121 mm PIMP 100 % SOIL Percentage Runoff PR Depression storage Cv Cr allowable outflow 0.6 l/s m 3 /s m Storage RT years Storage