Muse Developments Ltd Mile End Road Development Flood Risk and Surface Water Drainage Strategy

Transcription

1 Muse Developments Ltd Mile End Road Development Flood Risk and Surface Water Drainage Strategy FRSWDS/MER Issue 1 20 October 2016 This report takes into account the particular instructions and requirements of our client. It is not intended for and should not be relied upon by any third party and no responsibility is undertaken to any third party. Job number Ove Arup & Partners Ltd Central Square Forth Street Newcastle upon Tyne NE1 3PL United Kingdom

2 Document Verification Job title Mile End Road Development Job number Document title Flood Risk and Surface Water Drainage Strategy File reference Document ref FRSWDS/MER Revision Date Filename SWDS_Mile End Road_Issue 1.docx Issue 1 20 Oct 2016 Description Issue 1 27 Prepared by Checked by Approved by Name Chris Heath Simon Barugh Simon Barugh Signature Filename Description Name Signature Filename Description Prepared by Checked by Approved by Name Signature Filename Description Prepared by Checked by Approved by Name Signature Prepared by Checked by Approved by Issue Document Verification with Document FRSWDS/MER Issue 1 20 October 2016 \\GLOBAL\EUROPE\NEWCASTLE\JOBS\230000\239812\00 SOUTH SHIELDS INTERCHANGE\DOCS\27- REPORTS\FRA - MILE END ROAD\DOCS\27- REPORTS\SWDS_MILE END ROAD_ISSUE 1.DOCX

3 Muse Developments Ltd Mile End Road Development Flood Risk and Surface Water Drainage Strategy Contents 1 Introduction 1 2 Existing site 1 3 Proposed development 1 4 Potential sources of flooding and mitigation measures Flooding from watercourses and the sea Flooding from surface water and overland flow Flooding from groundwater Flooding from existing and proposed drainage systems 4 5 Surface water management Existing site drainage Proposed site drainage Surface water outfall Surface water flow rate Surface water drainage Allowance for Climate Change Sustainable drainage and surface water management 7 6 Conclusions 8 Page Appendices Appendix A Site Location Appendix B Proposed Site Plan Appendix C Consultation Appendix D Calculations FRSWDS/MER Issue 1 20 October 2016 \\GLOBAL\EUROPE\NEWCASTLE\JOBS\230000\239812\00 SOUTH SHIELDS INTERCHANGE\DOCS\27- REPORTS\FRA - MILE END ROAD\DOCS\27- REPORTS\SWDS_MILE END ROAD_ISSUE 1.DOCX

4 Muse Developments Ltd Mile End Road Development Flood Risk and Surface Water Drainage Strategy 1 Introduction Muse Developments Ltd propose to construct a new two storey office building at South Shields. The development site is currently used for car parking, and is located to the north of South Shields town centre, north west of the junction of Mile End Lane and Queen Street. This report will assess the risk to the proposed development from flooding, and how the management of surface water at the proposed development will impact on others. 2 Existing site The site is currently used as a car park, with an unbound surface and no apparent positive drainage system. The site falls from north to south. The site location is included in Appendix A. 3 Proposed development The proposed development consists of a two storey office building, located to the eastern boundary of the development site. The building footprint is expected to be in the order of 780m 2, with the total site area approximately 2000m 2. The remaining area will be used as car parking and hard and soft landscaping. The proposed development is included in Appendix B. 4 Potential sources of flooding and mitigation measures The risk of flooding to the development has been assessed on readily available information only. No hydraulic modelling has been undertaken on the existing drainage systems. 4.1 Flooding from watercourses and the sea The Environment Agency (EA) has produced flood maps, readily available on their website, that indicate the risk of flooding from rivers and the sea. The flood map for the development site is shown in Figure 1 below. FRSWDS/MER Issue 1 20 October 2016 \\GLOBAL\EUROPE\NEWCASTLE\JOBS\230000\239812\00 SOUTH SHIELDS INTERCHANGE\DOCS\27- REPORTS\FRA - MILE END ROAD\DOCS\27- REPORTS\SWDS_MILE END ROAD_ISSUE 1.DOCX Page 1

5 Muse Developments Ltd Mile End Road Development Flood Risk and Surface Water Drainage Strategy Site Location Figure 1 - Risk of flooding from rivers and sea The maps indicate that the development is not at risk of flooding from rivers or the sea. 4.2 Flooding from surface water and overland flow The EA has produced maps, readily available on their website, that indicate the potential risk of flooding from surface water. The surface water flood map for the development is shown in Figure 2 below. FRSWDS/MER Issue 1 20 October 2016 \\GLOBAL\EUROPE\NEWCASTLE\JOBS\230000\239812\00 SOUTH SHIELDS INTERCHANGE\DOCS\27- REPORTS\FRA - MILE END ROAD\DOCS\27- REPORTS\SWDS_MILE END ROAD_ISSUE 1.DOCX Page 2

6 Muse Developments Ltd Mile End Road Development Flood Risk and Surface Water Drainage Strategy Site Location Figure 2 - Risk of flooding from surface water The maps indicate that the development site is not currently at risk of flooding from surface water, although some surface water flooding is indicated to Mile End Road, to the eastern boundary. South Tyneside Council (STC), the Lead Local Flood Authority, confirmed in their response of 16 September 2016 that they have no records of flooding in the vicinity of site. STC s consultation response is included in Appendix C. The design of the new surface water drainage system should be in accordance with current design standards, including the Building Regulations 2000 Approved Document H, and BS EN 752:2008. Consideration will be given to flows entering the site from adjacent land. Site levels should be carefully considered to ensure that any surface flooding is directed away from building thresholds, and other vulnerable building openings and infrastructure. FRSWDS/MER Issue 1 20 October 2016 \\GLOBAL\EUROPE\NEWCASTLE\JOBS\230000\239812\00 SOUTH SHIELDS INTERCHANGE\DOCS\27- REPORTS\FRA - MILE END ROAD\DOCS\27- REPORTS\SWDS_MILE END ROAD_ISSUE 1.DOCX Page 3

7 Muse Developments Ltd Mile End Road Development Flood Risk and Surface Water Drainage Strategy 4.3 Flooding from groundwater Ground investigation works are yet to be undertaken, however high groundwater levels may be encountered on the site. Appropriate waterproofing should be provided to areas of the building that may be susceptible to ingress of groundwater, including any proposed pipe work and storage tanks. 4.4 Flooding from existing and proposed drainage systems There are a number of existing drainage systems adjacent to the development site, most notably a public combined sewer and interceptor sewer that are present within Mile End Road, to the east of the site, and public combined sewers to the west and south of the site. Public combined sewers to the west of the site may be subject to easements. Consultation should be undertaken with Northumbrian Water (NW) to establish any constraints that the presence of these sewers may impose. A copy of NW s sewer records is included in Appendix C. There is the potential for flooding from existing and proposed drainage systems to occur when the design standard of the drainage systems is exceeded, or when maintenance issues occur within the drainage systems that prevent them from operating as designed. An extract of NW s sewer records, showing locations within the approximate vicinity of the site where NW have records of flooding from the public sewerage system, is included in Appendix C. No flooding has been recorded within the immediate vicinity of the site. To mitigate the risk of flooding from proposed drainage systems, measures proposed for the management of surface water are outlined in Section 5 below. 5 Surface water management 5.1 Existing site drainage The existing site is surfaced with an unbound material. There is no apparent surface water drainage system, although it is possible that some sub-surface drainage was installed as part of the car park construction. FRSWDS/MER Issue 1 20 October 2016 \\GLOBAL\EUROPE\NEWCASTLE\JOBS\230000\239812\00 SOUTH SHIELDS INTERCHANGE\DOCS\27- REPORTS\FRA - MILE END ROAD\DOCS\27- REPORTS\SWDS_MILE END ROAD_ISSUE 1.DOCX Page 4

8 Muse Developments Ltd Mile End Road Development Flood Risk and Surface Water Drainage Strategy 5.2 Proposed site drainage Surface water outfall The Building Regulations 2000, Approved Document H (H3) requires that surface water be discharged to one of the following, in order of priority: a) An adequate soakaway or some other adequate infiltration system; or, where that is not reasonably practicable, b) A watercourse; or, where that is not reasonably practicable, c) A sewer. Arup have undertaken a Geo-Environmental Desk Study for the site. The study indicates that the site is indicated to be underlain by thick glacial drift deposits overlying Coal Measures bedrock at approximately 35m to 40m below ground level. The glacial deposits near the ground surface are indicated to comprise glacial till in the form of stiff silty clays, which are considered likely to be of low permeability. Whilst layers and pockets of more permeable sand and gravels are indicated to be present locally in the wider area, such deposits can often vary substantially in their thickness and lateral extent. Based upon the available information it is therefore currently considered that the site is unlikely to be suitable for the use of soakaway drainage systems. Viability should be further assessed based upon the findings of any intrusive ground investigation. There are no watercourses local to the development site. An outfall to the local public sewerage system is therefore required Surface water flow rate To ensure that the risk of flooding to others is not increased, the post development flow rate should be restricted to the pre-development flow rate. The site is not currently paved, and there is no apparent existing surface water drainage system. STC confirmed in their consultation response that the site should be treated as an undeveloped site and that a greenfield runoff rate should be used. The site area is approximately 0.2 ha. Equivalent greenfield runoff rates, calculated in accordance with the recommendations set out in The Institute of Hydrology Report 124, Flood Estimation for Small Catchments, are shown in Table 1 below. FRSWDS/MER Issue 1 20 October 2016 \\GLOBAL\EUROPE\NEWCASTLE\JOBS\230000\239812\00 SOUTH SHIELDS INTERCHANGE\DOCS\27- REPORTS\FRA - MILE END ROAD\DOCS\27- REPORTS\SWDS_MILE END ROAD_ISSUE 1.DOCX Page 5

9 Muse Developments Ltd Mile End Road Development Flood Risk and Surface Water Drainage Strategy Return Period Flow Q bar Table 1 - Greenfield Runoff Rates (IH124) Given the low flow rates, STC agreed in their consultation response that a practical minimum of 5 l/s can be adopted. To restrict surface water flow rates lower than 5 l/s, a small flow control device that would be susceptible to blockage would be required. A pre-development enquiry was submitted to NW. A copy of the predevelopment enquiry response is included in Appendix C. NW confirm that foul water may be discharged to the public sewerage system unrestricted. In addition, NW confirm that, should an outfall to a soakaway or watercourse be unachievable, surface water may be discharged to the public sewerage system at a restricted rate of 5 l/s. A positive surface water drainage system will be provided, connected to the existing public sewerage system to the south of the development site. In accordance with STC and NW requirements, surface water flows will be restricted to 5 l/s, for all events up to and including the 1 in 100 year storm Surface water drainage The surface water drainage system is subject to detailed design. The surface water drainage system will be designed in accordance with the recommendations set out in BS EN 752:2008, and the Building Regulations 2000, Approved Document H. An outline drainage layout is included in Appendix D Allowance for Climate Change The EA has produced guidance, available on the gov.uk website, relating to allowances that should be made for climate change. Climate change allowances relating to increased peak rainfalls intensity are outlined in Table 2 below. FRSWDS/MER Issue 1 20 October 2016 \\GLOBAL\EUROPE\NEWCASTLE\JOBS\230000\239812\00 SOUTH SHIELDS INTERCHANGE\DOCS\27- REPORTS\FRA - MILE END ROAD\DOCS\27- REPORTS\SWDS_MILE END ROAD_ISSUE 1.DOCX Page 6

10 Muse Developments Ltd Mile End Road Development Flood Risk and Surface Water Drainage Strategy Applies across all of England Total potential change anticipated for the 2020s (2015 to 2039) Total potential change anticipated for the 2050s (2040 to 2069) Total potential change anticipated for the 2080s (2070 to 2115) Upper end 10% 20% 40% Central 5% 10% 20% Table 2 - Peak rainfall intensity allowance in small and urban catchments EA guidance is to assess both the central and upper end allowances to understand the range of impact Sustainable drainage and surface water management Sustainable drainage (SuDS) techniques aim to manage surface water close to where it falls, and may comprise above ground features such as swales, ponds and basins, and below ground features such as infiltration systems and buried storage tanks. SuDS features should be integrated into the surface water drainage system where possible, and will be considered as part of the detailed design. SuDS should be designed in accordance with CIRIA Report C753, The SuDS Manual. MicroDrainage Quick Storage Estimate (QSE) has been used to assess the storage volume required in order to restrict surface water flows to 5 l/s for all events up to an including the 1 in 100 year storm. 40% increased rainfall intensity has been included to allow for potential climate change. Results from QSE are included in Appendix D. Between 48 and 78m 3 of storage will be required. The proposed site layout does not lend itself to extensive above ground features such as swales and basins, as limited space to site these features is available. As such, it is likely that underground storage will be required for part or all of this volume. Surface SuDS, such as filter drains and permeable surfacing, should be considered as part of the detailed design. Potential SuDS are included on drawing C.960.SK.001, included within Appendix D. In their consultation response, STC also state that the post-development volume of surface water should be restricted to the pre-development volume. The design of the drainage system should ensure that, during the 100 year 6 hour storm, any surface water volume in excess of the pre-development volume should be discharged to an infiltration system, or discharged from the site at a very low rate (2 l/s/ha). With a site area of approximately 0.2 ha, this would result in a restricted flow rate for the surplus surface water volume of 0.4 l/s. Given the practical limitations of providing a flow control device to restrict surface water to such low flow rates, it is proposed that all volume is restricted to 5 l/s. SuDS FRSWDS/MER Issue 1 20 October 2016 \\GLOBAL\EUROPE\NEWCASTLE\JOBS\230000\239812\00 SOUTH SHIELDS INTERCHANGE\DOCS\27- REPORTS\FRA - MILE END ROAD\DOCS\27- REPORTS\SWDS_MILE END ROAD_ISSUE 1.DOCX Page 7

11 Muse Developments Ltd Mile End Road Development Flood Risk and Surface Water Drainage Strategy features that have the potential to reduce surface water volumes, such as green roofs and rainwater recycling, should be considered as part of the detailed design. 6 Conclusions EA flood maps confirm that the site is not at risk of flooding from the sea, watercourses, or surface water. STC have no record of surface water flooding at the site. NW have no record of sewer flooding at the site. Ground conditions are unlikely to be suitable for infiltrating surface water. There are no watercourses local to the site. It is therefore currently considered that a positive outfall for surface water into the local sewerage system will be required. STC has been consulted, and accept that surface water flow rates can be restricted to a practical minimum of 5 l/s. Ground conditions, and the small site area, mean that it will be impractical to restrict the post-development volume of surface water to the pre-development volume. NW has been consulted and confirm that, should an outfall to a soakaway or watercourse be unachievable, surface water may be discharged to the public sewerage system at a restricted rate of 5 l/s. Between 48 and 78m 3 of surface water storage will be required to restrict surface water flow to 5 l/s. Because space for surface SuDS features such as swales and basins is limited, it is likely that part or all of this will be provided as underground storage. Other SuDS features should be considered as part of detailed design. These are surface features such filter drains and permeable surfaces, and features that may reduce surface water volume such as green roofs and rainwater recycling. FRSWDS/MER Issue 1 20 October 2016 \\GLOBAL\EUROPE\NEWCASTLE\JOBS\230000\239812\00 SOUTH SHIELDS INTERCHANGE\DOCS\27- REPORTS\FRA - MILE END ROAD\DOCS\27- REPORTS\SWDS_MILE END ROAD_ISSUE 1.DOCX Page 8

12 Appendix A Site Location

13 DISABL STAFF ONLY ONLY LOADING Salem Street Shrubs Shrubs Paving Stones Paving Stones Paving Stones Grass ONLY Grass ONLY Grass No Access Grass Grass Grass TB Grass Note: Surrounding contextual buildings and information are based on received ordinance survey drawings and are shown for illustrative purposes only. Assumed site boundary is subject to confirmation. Drawing subject to any easements and underground services. NORTH Paving Stones Paving Stones Paving Stones Beam Paving Stones Paving Stones 7.5 Block Paving LOADING LOADING 8.5 Paving Stones Paving Stones Block Paving Block Paving Block Paving Smithy Street Paving Stones Planter DELIVERY ONLY GOODS Fowler Street Block Paving B Red line boundary amended in HP CB accordance with Client comments A Second red line boundary removed in accordance with Client comments Rev Date Description Rev By Chk'd By HP CB Project Title DWP Building South Shields 365 Mile End Road South Shields Town Centre Drawing Title Job-Dwg No Red Line Plan 12569H St. Johns North, Wakefield, WF1 3QA t Rev B Client Muse Developments / STC Carvers Warehouse, 77 Dale Street, Manchester, M1 2HG t Status PLANNING The Old Rectory, 79 High Street, Newport Pagnell, MK16 8AB t LOADING ONLY Scale 1:1250 Drawing Size A3 101 London Road, Reading, RG1 5BY t CAD file reference J:\ \12569\12569H Job Centre Mile End Road This drawing is copyright and may not be reproduced in whole or part without written authority. Do not scale off this drawing. Date 20/09/2016 Drawn By ASR Checked CB 10 Gees Court, St Christophers Place, London, W1U 1JJ t A R C H I T E C T S

14 Appendix B Proposed Site Plan

15 Note: Surrounding contextual buildings and information are based on received ordinance survey drawings and are shown for illustrative purposes only. Assumed site boundary is subject to confirmation. Drawing subject to any easements and underground services. NORTH Proposed 2 Storey Office Building 8300sqft (771sqm) GEA Footprint core Access 23 proposed car parking spaces Illustrative service manouvre subject to highways design New access created into the site subject to LA Approval A Red line boundary amended in HP CB accordance with Client comments Rev Date Description Rev By Chk'd By Project Title DWP Building South Shields 365 Mile End Road South Shields Town Centre Drawing Title Job-Dwg No Parameter Plan 2 - Site Plan 12569H St. Johns North, Wakefield, WF1 3QA t Rev A Client Muse Developments / STC Carvers Warehouse, 77 Dale Street, Manchester, M1 2HG t Status PLANNING The Old Rectory, 79 High Street, Newport Pagnell, MK16 8AB t Scale 1:500 Drawing Size A3 101 London Road, Reading, RG1 5BY t CAD file reference CAD FILE REFERENCE This drawing is copyright and may not be reproduced in whole or part without written authority. Do not scale off this drawing. Date 22/09/2016 Drawn By ASR Checked A 10 Gees Court, St Christophers Place, London, W1U 1JJ t A R C H I T E C T S

16 Appendix C Consultation

17 Chris Heath From: Flood Enquiries Sent: 16 September :57 To: Chris Heath Subject: RE: Office Development, Mile End Road, South Shields [NOT PROTECTIVELY MARKED] This has been classified as: NOT PROTECTIVELY MARKED Hello Chris Please see on the my responses in red but please feel free to come back if you have any questions or give me a ring Thanks Michelle Michelle Hogg Environmental Protection Officer Environmental Health and Resilience Team South Tyneside Council Town Hall and Civic Offices Westoe Road South Shields NE33 2RL Tel: Fax: michelle.hogg@southtyneside.gov.uk From: Chris Heath [mailto:chris.heath@arup.com] Sent: 15 September :36 To: Flood Enquiries Cc: Simon Barugh Subject: Office Development, Mile End Road, South Shields Dear Flood Risk Management Team, Arup have been commissioned to prepare a Flood Risk and Surface Water Drainage Strategy in support of a forthcoming outline planning application for a development in South Shields. The current development proposals are for a two storey office building, with associated external car parking, and hard and soft landscaping. The site is located at the existing car park located to the north west of the Mile End Road/Queen Street Junction. The attached plan shows the site boundary in red. We would be grateful if you could confirm if there have been recorded instances of surface water flooding at or adjacent to the development site. South Tyneside Council have received no reports of problems at this location or in the vicinity. 1

18 The site currently has an unbound surface, with no apparent positive drainage system. In accordance with the hierarchy set out within the Building Regulations Approved Document H, we would look to discharge surface water to an infiltration system as a preference. However, underlying ground conditions and the proximity of existing and/or proposed buildings may preclude this approach. If a positive outfall for surface water is required then, in the absence of a local watercourse or surface water sewer, we would look to connect to the adjacent public combined sewerage system. This would be by prior agreement and in accordance with the requirements of Northumbrian Water Ltd. Yes you must follow the hierarchy and ensure that you demonstrate its been followed in your document. If a positive outfall is required, we would look to reduce surface water flows to the equivalent green field rates. As the site area is in the order of 0.2 ha, we propose that a practical minimum of 5 l/s, or the use of a 75mm diameter flow control device, is adopted. Please could you confirm that this approach is acceptable? Agree it would not be practical to achieve the actual greenfield run off which would be much lower. We are currently discussing the potential to incorporate sustainable drainage features into the development with our client. The report will outline which features should be considered as part of any forthcoming detailed design. The report will also assess the likely storage volume required in order to restrict surface water to the rate above, and how this storage may be provided. Allowances for climate change in accordance with current planning guidance will be made. Due to the nature of this urban development and available space, it is likely that storage would be provided underground, with surface and sub-surface SuDS features provided to offer additional attenuation and water quality benefits. We would be grateful if you could confirm if this approach is acceptable? Yes, but additionally please also be aware that as well as restricting rates volumes should also be restricted too (i.e. runoff volume should be as close as practical for the 100 year 6 hour storm). We follow the LASOO guidance which I am sure you are familiar with so I would refer to this when drafting your submission. As it is an outline we would expect the following to be included in the strategy: Preliminary layout drawings Preliminary outline hydraulic calculations Preliminary landscape proposals Ground condition information(including infiltration testing if ground is likely suitable) Evidence of third party agreement in principle If you need any additional information in order to respond, please do not hesitate to contact me. Regards, Chris -- Chris Heath Senior Technician Infrastructure EngTech TMICE Arup Central Square Forth Street Newcastle upon Tyne NE1 3PL United Kingdom t: d: Connect with Arup on LinkedIn 2

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24 Appendix D Calculations

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26 A A 3311 Key Site Boundary Existing Combined Sewer Existing Surface Water Sewer Proposed Foul Drain Proposed Surface Water Drain Permeable surface (TBC during detailed design) B C D E F G H 12. Potential rainwater recycling tank (TBC as part of detailed design) Proposed 2 storey office building Green roof TBC as part of detailed design 3308 Moo 3302 Ø225 H New connection to NWL sewer Ø225 Warehouse N \\global\europe\newcastle\jobs\230000\239812\00 South Shields Interchange\Docs\27- Reports\FRA - Mile End Road\Acad\Civils\C.960.SK.001.dwg 19 Oct :24:22 4 Ø Ø225 El Sub Sta Ø225 80m³ Surface water storage. Type, dimensions and volume to be confirmed as part of detailed design Control manhole with HydroBrake. Flow limited to 5 l/s for 100 year storm, 40% climate change reated using CADplot Notes 1. All SuDS features are indicative and to be considered and incorporated as appropriate as part of detailed design. Do not scale P1 18/ 10/ 16 CDH SFB SFB For Information Issue Date By Chkd Appd Central Square, Forth Street Newcastle upon Tyne NE1 3PL Tel +44 (0) Fax +44 (0) Job Title Mile End Road South Shields Client Muse Developments Ltd Drawing Title Concept Drainage Layout Scale at A3 Discipline Drawing Status Job No Drawing No 1:250 Drainage C.960.SK.001 For Information Issue P1 Arup