Land to the rear of the Black Bull Public House Flood Risk Assessment March 10, 2014 Version 1.0 Ref: RAB 148

Transcription

1 Land to the rear of the Black Bull Public House Flood Risk Assessment March 10, 2014 Ref: RAB 148 Lindsey Phillips Turnbull Tweedale Ltd 61 Oaken Lanes Codsall South Staffordshire WV8 2AW R A B C O N S U L T A N T S F L O O D R I S K A N D I N C I D E N T M A N A G E M E N T L I C H F I E L D B U S I N E S S V I L L A G E, T H E F R I A R Y, L I C H F I E L D, S T A F F O R D S H I R E W S Q G P H O N E : F A X : E M A I L : e n q u i r i e r a b c o n s u l t a n t s. c o. u k W E B S I T E : w w w. r a b c o n s u l t a n t s. c o. u k

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3 Revision History Version Date Amendments Issued to /11/09 Gemma Jackson (EA) Quality Control Action Signature Date Prepared Andy McHugh 03/11/09 Checked Gavin Wilson 04/11/09 Approved Bryan Nelson 05/11/09

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5 Table of Contents REVISION HISTORY... I QUALITY CONTROL... I TABLE OF CONTENTS... III 1.0 INTRODUCTION SITE LOCATION DEVELOPMENT PROPOSALS FLOOD RISK BOYCE S BROOK PREVIOUS FLOOD HISTORY FLOOD MITIGATION MEASURES RECOMMENDED FINISHED FLOOR LEVELS SAFE ACCESS AND EXIT SURFACE WATER RUNOFF SUDS SUSTAINABLE DRAINAGE SOLUTIONS CONCLUSION RECOMMENDATIONS... 7 APPENDIX A EA FLOOD MAP... 1 APPENDIX B DEVELOPMENT PROPOSAL... 2 APPENDIX C - ENVIRONMENT AGENCY S RIBCHESTER SFRM STUDY, APPENDIX D TOPOGRAPHIC SURVEY... 4 APPENDIX E FLOOD WARNING AND EVACUATION PLAN... 5

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7 1.0 Introduction This flood risk assessment has been prepared by RAB Consultants, in support of the proposed development on land to the rear of the Black Bull Public House, Ribchester, Lancashire, PR3 3YE. Planning Policy Statement 25: Development and Flood Risk (PPS25) requires a flood risk assessment to be carried out to ensure that the development is safe from flooding and will not increase the risk from flooding. 2.0 Site Location The proposed site is the land to the rear of the Black Bull Public House, Ribchester, Lancashire, PR3 3YE. (see Environment Agency Flood Map in appendix A). The site is currently used as a car parking facility to the Black Bull Public House and neighbouring properties. On the eastern border of the site are grassed areas, on the southern boundary is the Black Bull Public House, on the western boundary are residential developments and to the north of the car park is the B6245. Photographs 1 and 2 Existing land behind Black Bull Public House 3.0 Development Proposals The planning proposal is to convert an existing bunkhouse into 2no dwellings, re-develop number 49 Blackburn Road, erect 2no semi detached dwellings fronting Blackburn Road and erect 5no three storey terraced cottages on an area of hard standing currently used as car parking for the Black Bull Hotel, Ribchester. (See development plans in appendix B). The site is approximately 250m North West of the Ribble and 150m south of Boyce s Brook. The location of the development is within flood zone 2 (see Appendix A) which is described in PPS 25 below:

8 This zone comprises land assessed as having between a 1 in 100 and 1 in 1000 annual probability (a.p) of river flooding (1% - 0.1%) or between a 1 in 200 and 1 in 1000 year a.p of sea flooding (0.5% - 0.1%) in an year. 4.0 Flood Risk 4.1 Boyce s Brook Table 1 below shows flood levels of Boyce s Brook taken from the Environment Agency s Ribchester SFRM Study, 2009 (see Appendix C). In making an assessment of the impacts of climate change on flooding from rivers, table B.2 of PPS25 recommends a 20% increase on peak river flows. The Ribchester SFRM Study of 2009 has modelled a 1% & climate change event and this level of 27.78mAOD shall be used for this assessment. For this flood risk assessment, we will use the 1% & CC flood level from cross section ea01210boyc01_0487 to the north of the site. Return periods (yr) modelled levels maod & CC ea01210boyc01_ ea01210boyc01_ ea01210boyc01_0343u Table 1 Ribchester SFRM Study, 2009 modelled flood levels A topographic survey was undertaken by CPS Surveys Ltd in November 2008 (see Appendix D). Levels across the site range from mAOD at the site entrance from Blackburn Road to on the area of hardstanding behind the Black Bull Public House. The lowest level on site (27.673mAOD) is 107mm below the 1% & a.p. & CC flood event level of 27.78mAOD. It is understood that there are non-formal flood defences along the banks of Boyce s Brook offering an unspecified level of protection Ribchester to the south. 4.2 Previous Flood History There have been a number of historic flooding events in Ribchester (see Environment Agency Flood Map in Appendix A for flood outline and Appendix C Table 2 for flood history details, taken from Ribchester SFRM 2009 Study). Environment Agency records indicate that in October 2000, Blackburn Road was

9 flooded as a result of Boyce s Brook channel capacity being exceeded following an intense rainfall event coinciding with a blockage of Boyce s Bridge. Further information on this flooding event was provided by a member of the Ribchester community who was as a volunteer community flood warden for Ribchester between 2000 and He confirmed that in the 2000 Ribchester flood Boyce's bridge (over Boyce's Brook on Ribblesdale Road) experienced substantial blockage. This led to flooding upstream of the bridge. The flood route came across the fields on the right bank of Boyce's Brook and separately flooded onto Ribblesdale Road and Blackburn Road where it entered the Black Bull car park. It came approximately half way across the car park to the rear of the Black Bull Public House to a depth of no more than 27.80mAOD. Discussions with a member of the Environment Agency s Flood Mapping Team confirmed that this flood event occurred as a result of a blockage of this Boyce s bridge. The former Flood Warden also stated that a significant surface water flood event occurred in August Flood water came down Preston Road and off the surrounding fields due to an intense local downpour. Approximately 20 houses in the village were affected to a greater or lesser degree; these were on Preston Road (including Bill Mill Garage) the end of Church Street closest to Longridge, Blackburn Road and Ribblesdale Road (photos 3 & 4 below). No flooding occurred at the proposed development site as a result of this event. Photographs 3 & 4 Flooding of Ribblesdale Road during 2004 event. United Utilities have confirmed that there are no sewer flooding events on their frequent flood list in the surrounding area of the site.

10 5.0 Flood Mitigation Measures 5.1 Recommended Finished Floor Levels In order to afford a level of protection against flooding it is normally recommended that finished floor levels are set 600mm above the 1% a.p. plus climate change flood level (27.78mAOD from section 4.2). Local knowledge of the Autumn 2000 flood event caused by the blockage of Boyce s Bridge suggests that flood waters came approximately half way across the proposed development site which would indicate a flood level of no more than 27.80mAOD. Floor levels for the 2 semi detached dwellings fronting Blackburn Road and the 5 three storey terraced cottages should be constructed at a minimum of 28.38mAOD. This is 600mm above the 1% a.p. plus climate change level and 580mm above the flood level caused by the blockage of Boyce s Bridge. 5.2 Safe Access and Exit Tan access/egress route will exist from the south of the site onto Church Street with levels in the range of 27.90mAOD. From Church Road a safe route exists on Preston Road to the West of the site where levels rise above 35mAOD. A dry and safe access/egress is expected at all times. The Environment Agency provides a flood warning service for Ribchester as a result of Boyce s Brook backing up due to high levels in the Ribble. A Flood Warning will be issued, with a lead time in excess of two hours. Appendix E provides a flood warning and evacuation plan for the site. 6.0 Surface Water Runoff PPS 25 states that surface water arising from a developed site should as far as practicable, be managed in a sustainable manner to mimic the surface water flows arising from the site prior to the proposed development, while reducing the flood risk to the site itself and elsewhere, taking climate change into account. 6.1 SuDS Sustainable Drainage Solutions Paragraph from the SUDS manual (C697) discusses the SUDS management train which is intended to mimic the natural catchment process as closely as possible. The hierarchy of techniques used to achieve the management train include;

11 Technique Prevention Source control Site control Regional control Description The use good house design and housekeeping measures to prevent run off and pollution; rainwater reuse/harvesting Soakaways, porous and pervious surfaces, water butts, green roofs Routing water to large soakaways, infiltration or detention basins Balancing pond, wetlands, swales, retention ponds, There are a number of techniques which would be feasible to use for this type of development which are summarised in table 2 below. Table 2 Hierarchy of techniques and their descriptions Technique Issues Feasible? Y / N / Possible Prevention Good house design and rainwater harvesting Ensuring that drains and guttering are properly laid, located and maintained will enable water butts to be used for activities such as garden irrigation. Water harvesting systems could be installed to re-use rainwater as greywater. Y Y Source Control Porous and pervious materials The proposed development incorportes the use of porous and pervious materials on the driveway. This will enable infiltration of surface water hence reducing the volume leaving the site. Some garden areas are to be created which will also reduce the impermeable surface area. Y Soakaways The underlying bedrock material is thick boulder clay from previous River Ribble deposits which may reduce the effectiveness of soakaways. If this approach is considered then infiltration P

12 tests will be required to determine their usefulness. Green Roof Although a green roof could offer a certain level of runoff betterment, it is not in keeping with the scene of the surrounding area. N Site and Regional Control Infiltration / detention basins / balancing ponds / wetlands / swales / retention ponds These techniques will be too large, costly and would not hold a great benefit to the surrounding area. They are not considered appropriate for the small scale of the development. N The total area of the site is approximately 2400 of which approximately amount of permeable areas to approximately 1200 te considering rooftops, paving stones and tarmac (see Development Plans in Appendix B). The impermeable area will therefore be reduced by 37% and therefore the runoff rate and volume from the site can be expected to reduce by 37%. 7.0 Conclusion The location of the development is within flood zone 2 of the Environment Agency flood map. The proposal is to convert an existing bunkhouse into 2no dwellings, re-develop number 49 Blackburn Road, erect 2no semi detached dwellings fronting Blackburn Road and erect 5no three storey terraced cottages on an area of hard standing currently used as car parking for the Black Bull Hotel, Ribchester. The fluvial flood risk at the site is primarily influenced by Boyce s Brook. It has been shown that approximately half of the site is below 1% a.p. (plus climate change) flood level following the Ribchester SFRM Study There are some defences on the banks of Boyce s Brook which offer some protection to Ribchester to the south. Approximately half of the proposed development site flooded during the October 2000 flood event caused by a blockage of Boyce s Bridge north east of the site. Flood depths across half of the site were no more than a few centimetres as a result of this 2000 event. A recommended finished floor level of 28.38mAOD will provide 580mm of freeboard above the October 2000 flood level. The development will not increase the rate and volume of surface water runoff from the site and will provide a reduction by an increase of permeable area. It can be concluded therefore that the proposed development is appropriate for the flood risk and is not expected to increase the risk of flooding elsewhere.

13 8.0 Recommendations It is recommended that the finished floor levels are set at 28.38m AOD, 600mm above the 1% plus climate change flood level. The drainage design for the site should make best use of SUDS techniques e.g. porous block paving surfaces and water butts, where appropriate, to provide some betterment of surface water runoff at the site. Future tenants should sign up for the Environment Agency s flood warning service for Ribchester by registering to receieve the Severe Flood Warning (ref code 012FSFL5D) and implement the flood warning and evacuation plan provided in Appendix E.

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16 Appendix C - Environment Agency s Ribchester SFRM Study, 2009 This page intentionally left blank

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18 Appendix E Flood Warning and Evacuation Plan Flood Risk The site is approximately 250m north west of the Ribble and 150m south of Boyce s Brook within flood zone 2. Planning policy statement 25 describes this zone as This zone comprises land assessed as having between a 1 in 100 and 1 in 1000 annual probability (a.p) of river flooding (1% - 0.1%) or between a 1 in 200 and 1 in 1000 year a.p of sea flooding (0.5% - 0.1%) in an year. How Flood Warnings will be provided Businesses/householders in these areas can sign up for telephone flood warnings by ringing Floodline ( ) or alternatively registering online at Once registered customers will receive a direct warning via a telephone recorded message. In addition, customers can call the Environment Agency s Flood dial & listen service on for further information. The quick dial code for the Ribchester area is The Environment Agency issue flood warnings using Flood Warning Codes to identify and highlight the severity and likelihood of flooding, there are four in total, each with specific public information and advice relating to it: FLOOD WATCH Environment Agency Definition: Flooding of low lying land and roads expected. What this means for The Black Bull Public House. Boyce s Brook is not expected to burst its banks What you should do: Monitor the local news and weather forecasts (including the local radio networks). Be aware of water levels near you. Call Floodline on for updates. FLOOD WARNING Environment Agency Definition: Flooding of homes and businesses is expected. Act Now! Properties on Blackburn Road are not affected at this Flood Warning level. What you should do: Monitor local news and weather forecasts (including

19 local radio networks). Be aware of water levels near you. Call Floodline on for updates. SEVERE FLOOD WARNING (ref code 012FSFL5D) Environment Agency Definition: Act now! Severe flooding is expected with extreme danger to life and property. What this means for The Black Bull Public House. The defences and/or river banks may be overtopped or breached; the probability of flooding in Blackburn Road is high. What you should do: Ring Floodline and monitor water levels. Collect things you need * and evacuate the site. The building should be locked to prevent anyone entering during a flood and a sign warning people that a flood may occur should be placed at the entrance. Turn off gas, electricity and water supplies if it is safe to do so. If Blackburn Road is flooded and evacuation is not possible, stay in a high place with means of an escape. Avoid walking or driving through flood water. If anyone is in danger, call 999 immediately. Listen to the emergency services and follow their advice. If the emergency services recommend evacuation, it is highly likely that Blackburn Road is going to flood. ALL CLEAR Definition: No further flooding is expected. Water levels will start to go down. What to do: Keep listening to the local news and weather reports for updates. Only return to evacuated buildings if you are advised to do so and have been assured it is safe. Beware of sharp and hidden objects and pollution in flood water. If your property or belongings are damaged, contact

20 your insurance company. Ask their advice before starting to clean up. *Emergency Flood Plan What is to be included: A list of useful telephone numbers: Environment Agency: Floodline Environment Agency General Enquires Emergency Services: Ribble Valley Fire and Rescue Ribchester Police Lancashire Ambulance Service (In an emergency, dial 999) (08708) Ribble Valley Borough Council Personal numbers (for residents to include): Insurance Company Users of the nursery Neighbours A Flood Kit: (This should be collected and stored in a place where it can be easily accessed). Medication: Valuable and This should include: Any key documents (accounts, insurance details, etc) Torch (with spare batteries), Battery or wind-up radio, A mobile phone (with the useful telephone numbers already stored and a full battery), Rubber gloves, Wellington boots, Waterproof clothing, First aid kit, Blankets. Does anyone need regular medication? Get into the habit of storing these upstairs or in a

21 sentimental belongings: Flood boards / sandbags: Gas, Electricity and Water: Motor Vehicles: Evacuation: high place downstairs. Have a few flood boards and sandbags prepared to block doorways and airbricks. Ensure that you know how to turn these off, be aware that you may need to do this in the dark. Is there anywhere that the vehicle(s) could be stored (garage?) so that they do not cause any damage if they are moved by flood waters. If flooding is severe, you may be evacuated. Think about what you need to take with you. Make provisions for your pets. DON T WAIT FOR A FLOOD TO SEE IF YOUR FLOOD PLAN WORKS, TEST IT NOW!