FLOOD RISK & WATER ENVIRONMENT - East Staffordshire Application...3.6 Surface water flood risk mapping obtained from the Environment Agency indicates that the site is not at risk from

FLOOD RISK & WATER ENVIRONMENT Burton & South Derbyshire College Former College Playing Fields Rolleston on Dove Flood Risk Assessment

lisa.robertsText BoxP/2012/00636

FLOOD RISK & WATER ENVIRONMENT Burton & South Derbyshire College Former College Playing Fields Rolleston on Dove Flood Risk Assessment BWB Consulting Ltd Livery Place 35 Livery Street Birmingham B3 2PB Date: October 2012

Signed

AUTHOR:

B Fleming

CHECKED:

D Harvey

APPROVED:

S Nelmes

REPORT REF:

BMW/2031/FRA

STATUS:

REV B (19/10/2012)

lisa.robertsText Box

Burton & South Derbyshire College former playing fields, Rolleston on Dove Flood Risk Assessment October 2012 BMW2031/FRA/REVB

All comments and proposals contained in this report, including any conclusions, are based on information available to BWB Consulting during investigations. The conclusions drawn by BWB Consulting could therefore differ if the information is found to be inaccurate or misleading. BWB Consulting accepts no liability should this be the case, nor if additional information exists or becomes available with respect to this scheme. a

Except as otherwise requested by the client, BWB Consulting is not obliged to and disclaims any obligation to update the report for events taking place after:- a

(i) The date on which this assessment was undertaken, and (ii) The date on which the final report is delivered

a

BWB Consulting makes no representation whatsoever concerning the legal significance of its findings or the legal matters referred to in the following report. The information presented and conclusions drawn are based on statistical data and are for guidance purposes only. The study provides no guarantee against flooding of the study site or elsewhere, nor of the absolute accuracy of water levels, flow rates and associated probabilities.

CONTENTS PAGE EXECUTIVE SUMMARY ............................................................................................ 1 1.0 SUMMARY INFORMATION ............................................................................ 2

Introduction ........................................................................................................................... 2 Existing Site .......................................................................................................................... 2 Proposed Development ......................................................................................................... 2

2.0 SOURCES OF FLOOD RISK .......................................................................... 4 3.0 FLOOD RISK ASSESSMENT.......................................................................... 5

Risk of Flooding to Proposed Development ........................................................................... 5 Risk of Flooding resulting from the Proposed Development ................................................... 6

4.0 FLOOD RISK MITIGATION AND RESIDUAL IMPACTS ................................. 7 Site Arrangements ................................................................................................................ 7 Outline Surface Water Drainage Assessment ........................................................................ 7 Outline Foul Drainage Assessment ....................................................................................... 8

5.0 CONCLUSIONS AND RECOMMENDATIONS ................................................ 9 List of Figures 1.1 Site Location 1.2 Environment Agency Flood Zones List of Tables 1.1 Site Summary 2.1 Potential Sources of Flood Risk Appendices A Topographical Survey B Proposed Masterplan C Environment Agency Correspondence D Severn Trent Water Correspondence E Surface Water Drainage Details


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EXECUTIVE SUMMARY

This revision B Flood Risk Assessment (FRA) is has been produced on behalf of Burton & South Derbyshire College in respect of a planning application for a residential development on the former playing fields of Burton & South Derbyshire College. This revision has been produced following discussion with the Environment Agency and agreement on a suitable surface water drainage strategy and discharge rate.

The site is located outside the floodplain as shown on Environment Agency Flood Zone Maps. These indicate that the site is in Flood Zone 1 where river flood risk has a low probability.

Sites in Flood Zone 1 are sequentially preferable for development due to the lowest area of flood risk classification. Therefore the principle of the development is entirely appropriate and in accordance with the National Planning Policy Framework (NPPF).

No other forms of flooding are considered to pose a significant risk of flooding to the development site. Mitigation measures can be included to protect the new buildings on site from overland runoff.

For sites in Flood Zone 1, greater than 1ha in size (which the application site is at 6ha) the focus of the Flood Risk Assessment is on surface water drainage proposals to ensure the development does not increase flood risk elsewhere as advised by the Environment Agency.

The development will incorporate sustainable drainage features designed to ensure the volume of runoff generated from a 1 in 100 year return period storm event (plus an allowance for climate change) can be contained on site and discharged at 24l/s which represents a rate lower than the Qbar annual average rainfall event and a 20% reduction on the rate previously proposed following a 5l/s/ha approach. This will ensure that the development does not result in an increased rate of surface water discharge to the local watercourse and will aid reducing localised reported flooding issues in this location not related to the development site.

In compliance with the requirements of the NPPF and subject to the mitigation measures proposed, the development may proceed without being subject to significant flood risk. Moreover, the development will not increase flood risk to the wider catchment area as a result of suitable management of surface water runoff discharging from the site.


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1.0 SUMMARY INFORMATION

Introduction

1.1 This Flood Risk Assessment (FRA) has been produced on behalf of Burton & South Derbyshire College in respect of a planning application for the proposed residential development.

Site Name Former College Playing Fields Location Rolleston on Dove NGR (approx) SK245274 Application Site Area (Ha) 6ha Development Type Residential NPPF Vulnerability More Vulnerable Indicative Flood Zone Flood Zone 1 EA Development Control Area Midlands (Central)

Local Planning Authority East Staffordshire Borough Council (ESBC)

Table 1.1 – Site Summary

1.2 The report is based on the following information:

(i) Site Layout Plan (ii) OS Explorer Series mapping (iii) Local Planning Authority consultation (iv) Environment Agency guidance/consultation (v) Strategic Flood Risk Assessment (vi) Site Topographical Survey

Existing Site

1.3 The site is a greenfield plot of land formerly serving Burton & South Derbyshire College as sports fields located on the eastern outskirts of the village as shown outlined in red on Figure 1.1. The site is bound to the north by existing residential development and a children’s play area to the west. The remainder is surrounded by undeveloped, greenfield farmland.

1.4 Ground levels range from 105mAOD falling west to a low point of 97.4mAOD as shown in Appendix A on the Topographical Survey.

Proposed Development

1.5 The proposal is for a residential development on the site with associated access roads, parking and public open space as part of an outline planning application (see Appendix B).


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Figure 1.1 – Site Location

Flood Zones and Vulnerability Classification

1.6 Flood Zone mapping prepared by the Environment Agency identifies areas potentially at risk of flooding from fluvial or tidal sources without taking into account the presence of flood defences or structures such as culverts or minor watercourses. An extract from the mapping outlining the site in red is included as Figure 1.2.

1.7 The Environment Agency Flood Zone mapping shows the site to be located entirely within Flood Zone 1 (Low Probability). This Flood Zone is defined as land assessed as having less than 1 in 1000-year (0.1%) annual probability of river flooding.


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Figure 1.2 – Environment Agency Flood Zones

2.0 SOURCES OF FLOOD RISK

2.1 The table below identifies the potential sources of flood risk to the site. The significance of these sources is investigated further in Section 3.

Flood Source Potential Risk Description High Medium Low None Fluvial X Flood Zone 1 – low risk location Tidal X Not near the sea Canals X Not near a canal Groundwater X No records in SFRA of flooding Reservoirs and waterbodies X

Site not in area at risk of reservoir flooding as shown on EA risk maps

Sewers X In the surrounding built up area

Pluvial runoff X Site elevated above surrounding land Development Drainage X

Increase in impermeable surfaces can lead to an increase in runoff

Table 2.1 – Potential Sources of Flood Risk


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3.0 FLOOD RISK ASSESSMENT

3.1 This section of the Flood Risk Assessment looks at the flood risk to the site before any mitigation measures are put into place and hence identifies where mitigation will be required. Section 4 continues to explain the mitigation measures proposed and the residual risk following implementation of any proposed mitigation.

Risk of Flooding to Proposed Development

River Dove/Mill Fleam

3.2 The site is located well outside the floodplain of the River Dove and Mill Fleam as shown in Figure 1.2. The flood risk from these rivers therefore does not apply to the site.

Other Watercourses

3.3 No other minor watercourses are shown on OS Explorer mapping or Figure 1.1 to be located either within or alongside the site that could present a flood risk. Severn Trent Water sewer records identify that a 450mm diameter culverted watercourse is present adjacent to the north western corner of the site (see Appendix D) directing flows north away from the site. No records of historic river flooding affecting the site are detailed in the ESBC (Level 1 – Oct 2008) Strategic Flood Risk Assessment (SFRA). Therefore the site is not considered to be at a high fluvial flood risk.

Pluvial Runoff, Surface Water and Sewer Flooding

3.4 No records of sewer or surface water flooding affecting the site historically are detailed in the SFRA.

3.5 Ground levels fall west across the site and beyond to Needwood Avenue, which the site is to be accessed from. As levels drop away the risk of overland flows reaching the site through highway drainage surcharge is not believed to present a risk to the site. The site is also elevated compared to undeveloped farm land to the south east so the risk that antecedent runoff could be directed onto the site in the event of extreme rainfall intensity is low.

3.6 Surface water flood risk mapping obtained from the Environment Agency indicates that the site is not at risk from such flooding, although land immediately to the west of the site could be at risk from surface water flows ponding (see Appendix C).

3.7 We have since been informed following production of the revision A FRA that the recreation ground to the west of the watercourse located to the west of the site and alongside the children’s play area has been subject to flooding.


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3.8 No public sewers are located within or immediately adjacent to the development site as shown in Appendix D. Surface and foul water sewers are present within the adjacent residential areas to the north and east but these direct flows north away from the site. Therefore in the unlikely event of sewer surcharge, this source of flood risk is not thought to pose a significant risk to the site.

Groundwater Flooding

3.9 The site is located on Mercia Mudstone (clayey) bedrock and soil material with impeded drainage. This could give rise to relatively poor drainage of rainfall/surface water and a higher water table but would be less responsive to sudden changes in groundwater. The bedrock is classed as a Secondary B aquifer on EA mapping, which are “.predominantly lower permeability layers which may store and yield limited amounts of groundwater due to localised features such as fissures, thin permeable horizons and weathering.”.

3.10 No historic records of flooding appear to have affected the site from groundwater based on review of the SFRA. It is considered that groundwater would more likely emerge in areas of lower land further north and within the area identified as floodplain land as opposed to on the site.

Reservoirs and Waterbodies

3.11 The site is not located downstream of any reservoirs or major waterbodies. The Environment Agency reservoir flood risk maps show the site is not at risk from this source.

Risk of Flooding resulting from the Proposed Development

3.12 As the development site is currently a greenfield site then the proposed development and introduction of impermeable surfaces will increase the rates of surface water runoff generated. This will increase potential flood risk elsewhere unless managed appropriately in accordance with EA/STW guidance.

3.13 Section 4.0 details the mitigation measures to protect the development from flooding and prevent an increase in flood risk elsewhere.


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4.0 FLOOD RISK MITIGATION AND RESIDUAL IMPACTS

4.1 This section of the FRA sets out the mitigation measures recommended to reduce the risk of flooding to the proposed development and outlines any residual impacts.

Site Arrangements

Finished Floor Levels

4.2 It is recommended that finished floor levels are set a nominal height above finished surrounding ground levels (e.g. 150mm) so as to provide protection to the proposed properties from overland flows of surface water runoff.

Ground Levels

4.3 It is recommended that no buildings be positioned within low spots or hollows on site and external finished levels are appropriately designed to lessen the risk of overland flows or runoff being directed towards them.

Outline Surface Water Drainage Assessment

4.4 The site is a plot of greenfield land so to estimate the rate of greenfield runoff generated at present, the Severn Trent Water advised method of 5l/s/ha was adopted as part of the revision A report. As the site is 6ha then the existing greenfield runoff rate was assessed to equate to 30l/s.

4.5 Following discussion with the Environment Agency, it is now proposed to restrict discharge of surface water from the site to a rate of 24l/s. This represents a 20% reduction on the previous rate proposed and is also lower than the Qbar annual average rainfall rate (26.2l/s – estimated using the Interim Code of Practice Method). This will ensure there is no increase in flood risk elsewhere from surface water leaving the development and is offered to assist reducing localised surface water flooding problems unrelated to the site.

4.6 As the application is at outline stage, the development density has been assumed as approximately 60% for the site equating to an approximate impermeable area of 3.6ha. This will increase the rate of surface water generated from the development site unless managed in accordance with EA guidance.

4.7 To retain the existing greenfield runoff levels from the development to prevent an increase in flooding elsewhere, surface water discharged from the site will be restricted to a rate of 24l/s (subject to approval for connection) to the watercourse 45m to the west of the site (as advised by STW – see Appendix D).

4.8 It is proposed to form a gravity connection from the site to the watercourse west of the site as shown on the topographical survey included within the flood risk assessment. Ground levels on the site are circa 99.5mAOD at the proposed balancing pond and fall west to the watercourse at approximately 97.5mAOD where an outfall point would be constructed allowing sufficient fall to make such a connection.


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4.9 It was intended to use soakaways as a point source control to drain individual plot roof runoff generated as requested by the Client. However, following soil percolation testing the use of soakaways has been discounted due to poor permeability and drain down time (see Appendix E). Therefore it is proposed to drain runoff to an adoptable pipe network and a balancing pond (with fore bay or similar). Using SuDS will provide water storage, water quality treatment and wildlife benefits to be incorporated into the development.

Attenuation Volumes and Sustainable Drainage Systems

4.10 As increasing levels of hardstanding and impermeable areas on the site will increase runoff, then restricting the level of discharge will result in a greater volume of water needing to be retained on site and attenuated. This should be undertaken to account for the volume of runoff generated during up to a 1 in 100 year return period storm event that includes an allowance for climate change (30% increase in rainfall intensity).

4.11 Using the quick storage estimate function in the MicroDrainage package, WinDes, it has been estimated that 2199m3 (representing mean of range calculated) of storage may be required following the above discussed requirements (see Appendix E) so as to retain a 24l/s discharge rate from the site. This will provide betterment to the current situation by retaining more water on site during higher return periods and releasing it at a slower rate.

4.12 Typically, it is recommended to provide up to the 30yr return period storm runoff volume within an adoptable pipe network (subject to detailed design investigation). In this scenario the difference in remaining storage should be provided within a balancing pond (difference between estimate for 30r storage and 100yr+CC). Assuming 1m depth and 1 in 3 side slopes then an approximate area of 2130m2 should be set aside in the north western end of the site for this feature prior to discharge to the culverted watercourse (to be agreed – subject to detailed design review).

4.13 As a further measure, consideration will be given to inclusion of an interceptor drain/feature along the western boundary of the site to intercept any additional or excess overland flows of surface water and direct it into the balancing pond where possible prior to discharge to the watercourse.

Outline Foul Drainage Assessment

4.14 There are two separate 225mm diameter foul sewers near the site where a connection would be feasible (see Appendix D) as advised by STW to drain foul flows from the development. This is subject to Severn Trent Water agreement.


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5.0 CONCLUSIONS AND RECOMMENDATIONS

5.1 This Flood Risk Assessment has been prepared in respect of the proposed residential development.

5.2 The site is located in a low risk area of river flooding and has been established to be at low risk of flooding from other sources.

5.3 The following mitigation measures have been recommended:

• Finished floor levels set above finished surrounding ground levels to provide protection against any overland flood flows

• New buildings should not be positioned in any low spots or hollows and external finished levels designed to lessen the risk of being affected by flows of runoff

5.4 Surface water runoff generated by the development will be restricted to a greenfield discharge rate of 24l/s to ensure flood risk is not increased elsewhere.

5.5 Attenuation on site will be provided incorporating sustainable drainage in the form of a balancing pond and permeable paving where appropriate.

5.6 Attenuation on site will be designed to store the volume of runoff generated up to the 1 in 100 yr return period including an allowance for the potential effects of climate change.

5.7 Subject to the mitigation measures proposed, the development may proceed without being subject to significant flood risk. Moreover, the development will not increase flood risk to the wider catchment area as a result of suitable management of surface water runoff discharging from the site.

APPENDIX A

Topographical Survey

lisa.robertsText Box

AXIS SURVEYSTHE BRETBY BUSINESS PARK

STANHOPE BRETBYASHBY ROAD

BURTON ON TRENTSTAFFS

FAX. 01283 2210911:500 6 APRIL 2001

1438.DWG

LEVELS ARE RELATIVE TO AN ARBITRARY DATUM

ROLLESTON COLLEGE

BURTON COLLEGE

THE GRID IS LOCAL

email [email protected]

PLAYING FIELDS

mailto:[email protected]

APPENDIX B

Proposed Masterplan

APPENDIX C

Environment Agency Correspondence

Environment Agency,Sentinel House, 9 Wellington Crescent, Fradley Park, Lichfield Staffordshire, WS13 8RRCustomer Service Line: 03708 506 506Email: [email protected]

Our Ref: 1237/DE

Your Ref: BMW2031

Date: 18 November 2011

Mr J PickeringBWB Consulting Ltd

Dear Mr Pickering

RE: ROLLESTON ON DOVE

Thank you for your enquiry of 02 November 2011 requesting informationrelating to the above.

Flood Map

I can confirm that according to our published Flood Map, which providesa general estimate of the likelihood of flooding across England, the siteis shown to be outside of the Extreme Flood Outline. This refers toland where the indicative annual probability of flooding is less than 0.1%(1 in 1000) from rivers.

Surface Water

Please find attached the Flood Map for Surface Water Flooding and theAreas Susceptible to Surface Water Flooding maps as well as a briefoutline letter providing information on the datasets underlying thesemaps.

A site inspection has not been carried out in relation to your request forinformation. This information is provided under the conditions for use ofdata or information attached.

Yours sincerely

Diane EdwardsExternal Relations AssistantMidlands – Central AreaDirect Line 01543 404971Email: [email protected]

mailto:[email protected]://www.environment-agency.gov.ukmailto:Email:[email protected]

Contact: [email protected] 03708 506506

Standard Notice [not for use with Special Data, Personal Data or unlicensed 3rd party rights]Information warningWe (The Environment Agency) do not promise that the Information supplied to You will always beaccurate, free from viruses and other malicious or damaging code (if electronic), complete or up todate or that the Information will provide any particular facilities or functions or be suitable for anyparticular purpose. You must ensure that the Information meets your needs and are entirelyresponsible for the consequences of using the Information. Please also note any specific informationwarning or guidance supplied to you.

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The Information is protected by intellectual property rights and whilst you have certain statutoryrights which include the right to read the Information, you are granted no additional use rightswhatsoever unless you agree to the licence set out below.Commercial use is subject to payment of a £50 licence fee (+VAT) for each person seeking thebenefit of the licence, except for use as an Environment Agency contractor or for approved mediause.To activate this licence you do not need to contact us (unless you need to pay us a Commerciallicence fee) but if you make any use in excess of your statutory rights you are deemed to acceptthe terms below.

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You are free to:

copy, publish, distribute and transmit the Information

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exploit the Information commercially, for example, by combining it with other Information, orby including it in your own product or application

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“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 thatWe endorse you or your use of the Informationensure that you do not mislead others or misrepresent the Information or its source or usethe Information in a way that is detrimental to the environment, including the risk of reducedfuture enhancementensure that your use of the Information does not breach the Data Protection Act 1998 or thePrivacy and Electronic Communications (EC Directive) Regulations 2003

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Mr J PickeringBWB Consulting Ltd3-4 Kayes WalkThe Lace MarketNottinghamNG1 1PY

Our ref: 1237/DEYour ref:

Date: 18 November 2011

Dear Sir

Request for Surface Water Flooding Information

Further to your request for information I am writing to explain the Environment Agency’s rolewith respect to surface water flooding.

We have provided two national maps, under our Strategic Overview for flooding, to yourLead Local Flood Authority, Staffordshire County Council, who are responsible for local floodrisk, (i.e. surface runoff, ground water and ordinary watercourse), which alongside theirexisting local information will help them to determine what best represents surface waterflood risk in your area.

We are not able to confirm if the Lead Local Flood Authority for your area has decided whatbest represents surface water flood risk. You should contact Staffordshire County Council toconfirm the latest position.

Please find attached the maps we provided to your Lead Local Flood Authority for yourlocation:

Flood Map for Surface Water (2010)Areas Susceptible to Surface Water Flooding (2009).

Flood Map for Surface Water is our new surface water flood map and provides a generalindication of areas that may be at risk of surface water flooding. It takes broad account ofunderground drainage and typical storms which are likely to cause flooding, but these areonly typical national figures and are not appropriate everywhere. The map indicates twodepths of flooding: greater than 0.1m deep, and greater than 0.3m deep.

Areas Susceptible to Surface Water Flooding was produced in 2009 using a simplemethod that assumes that underground sewerage and drainage systems, and smaller overground drainage systems are full to capacity. Generally these assumptions areoversimplifications, but in a few locations these assumptions are realistic. It shows threebands, indicating which are 'less to more' at risk of flooding from surface water.

Which map is right?Generally the Flood Map for Surface Water is the more realistic dataset as it takes betteraccount of typical conditions that lead to surface water flooding.

Lead Local Flood Authorities, will consider all the available data and agree, with theEnvironment Agency, Water Companies, Internal Drainage Boards and other interestedparties, what surface water flood data best represents local conditions. This is known aslocally agreed surface water information.

Environment Agency, 9 Wellington Crescent, Fradley Park, Lichfield, Staffs WS13 8RRCustomer services line: 03708 506 506Email: [email protected]

mailto:Email:[email protected]://www.environment-agency.gov.uk

2

It’s very important to remember that neither map can be considered accurate down to anindividual property level. Our surface water flood mapping is useful for identifying broadareas at risk of surface water flooding, but it’s vital that local knowledge and information isused to interpret the maps.

As a rule of thumb the types of locations where the Areas Susceptible map might be a betterrepresentation of surface water flood risk that the Flood Map for Surface Water are where:

local sewer capacity is able to drain closer to 0mm/hr than 12mm/hr in the 1.1hr stormevent;

or areas are very flat and longer storm durations are more likely to cause flooding thanshorter durations.

As a rule of thumb the types of locations where the Flood Map for Surface Water might be abetter representation of the surface water flood risk that the Areas Susceptible are where:

local sewer capacity is able to drain closer to 12mm/hr than 0mm/hr in the 1.1hr stormevent;

or areas are steeper and flooding is more likely to be caused by short duration stormsrather than longer durations.

Is my location at risk?

Each map can only give an indication of areas at risk from surface water flooding from anational assessment. They cannot provide detail on individual properties. Therefore theinformation above should not be interpreted as stating that the location you are interestedin will or won't actually flood, but simply that it is in or not in an area shown at risk on themaps.

Who else is using this data?We have already provided these maps to our other partners (such as emergency services,local authorities, water companies) to use for emergency planning purposes. We have alsoprovided this map to Local Planning Authorities for land use planning purposes. We haveadvised all our partners that they will need to make a local decision as to what informationbest represents local conditions.

Limitations of usePlease read the attached copyright statement and disclaimer which explains what youcan/cannot do with the data. If you have requested this map for use in a Flood Risk orConsequence Assessment please speak with your local Environment Agency Development& Flood Risk team who will advise on its use.

For more information about how surface water flood risk is managed in your area, pleasecontact your local authority.

If you have any queries please contact Michael Adams at the Environment Agency.

Yours faithfully

Michael AdamsFlood Risk Mapping & Data TeamDirect dial 01543 405013Direct fax 01543 444161Direct e-mail [email protected]


APPENDIX D

Severn Trent Water Correspondence

Sewer Capacity Assessment

Hydraulic Modelling Summary Report

Rolleston On Dove, Staffordshire

DE-1112-017

Final

04/2012

Mouchel Knights House 2 The Parade Sutton Coldfield Birmingham B72 1PH 0121-355-8949

Rolleston On Dove, Staffordshire Sewer Capacity Assessment Severn Trent Water

Mouchel April 2012

Executive Summary

The site is located to the east of Rolleston on Dove to the south of Twentylands (NGR 424608 327492).

The site is currently Greenfield and does not drain to the public sewer network. The developer is proposing to construct between 120 and 150 dwellings on site. The developer has not specified a preferred connection location.

Hydraulic modelling was used to assess the impact of the proposed development. Two possible connections to the public sewerage network were modelled. A connection at Forest Scholl Road has the least impact on the performance of the receiving network

Severn Trent Water are aware of capacity issues within the existing sewer system and will seek to rectify these issues in line with our priorities and funding covered in our business plan. The addition of this new development has a negligible impact on these issues and therefore we do not require additional capacity to cater for the flows from this development.


Mouchel 2 April 2012

Table of Contents Executive Summary ............................................................................................................................................. 1

Table of Contents ................................................................................................................................................ 2

1 Introduction ................................................................................................................................................. 3

1.1 Site Details ........................................................................................................................................... 3

1.2 Proposed Development ....................................................................................................................... 4

1.3 Study Aims and Objectives .................................................................................................................. 5

2 Sewer Capacity Assessment ........................................................................................................................ 6

2.1 Modelling Methodology ...................................................................................................................... 6

2.2 Assumptions and Limitations .............................................................................................................. 6

2.3 System Performance ........................................................................................................................... 7

3 Conclusions and Recommendations ........................................................................................................... 8

3.1 Conclusions .......................................................................................................................................... 8

3.2 Recommendations ............................................................................................................................... 8

Appendix A: Sensitive Information ...................................................................................................................... A

Appendix B: Proposed Development Plans ......................................................................................................... B

Appendix C: Model Review Proforma ................................................................................................................. C



1 Introduction

1.1 Site Details The site is located to the east of Rolleston on Dove to the south of Twentylands (NGR 424608 327492). The site is currently Greenfield and does not drain to the public sewer network.

Rolleston on Dove is within in Hatton Drainage Area Plan. Rolleston on Dove is served by a mixture of foul/combined systems, surface water sewers and soakaway drains.

The site location and boundary are shown in Figure 1-1. There are two separate 225mm diameter public foul sewers close to the site which drain via gravity to the Station Road pumping station (PS) via a 225mm diameter combined sewer in Station Road.

The foul/combined sewers in Rolleston on Dove all gravitate to Station Road PS which serves Rolleston on Dove, north of the site. The Station Road PS delivers flows to Rolleston Green Tank. Rolleston Green Tank receives all pumping flows from Hatton, Rolleston on Dove and Hilton and then conveys the flows to Clay Mills Sewage Treatment Works (STW). South Hill Combined Sewer Overflow (CSO) is located upstream of the development site in Station Road on the east side of Rolleston on Dove.

There are known capacity issues at Rolleston Green Tank during times of high flows.

Severn Trent Water has 14 records of flooding in Rolleston on Dove. One record is in the vicinity of the proposed development site whilst the others are mainly in the west side of Rolleston on Dove.



Figure 1-1: Proposed development site location

© Crown Copyright 2004. All rights reserved. Ordnance Survey licence number 100018202.

1.2 Proposed Development The site is located to the east of Rolleston on Dove and is currently Greenfield. The developer is proposing to construct between 120 and 150 dwellings on the site. The proposed development is summarised in Table 1-1. Development plans are included in Appendix B.

At this stage the developer has not specified a preferred connection location. The site location plan and relevant correspondence have been received from the developer, and the following plans were used to inform the study:

111120 STW Development Enquiry Response.pdf DE-1112-017_Rolleston.tab 1438.dwg Rolleston Housing Sketch Scheme.dwg



Table 1-1: Summary of proposed development

Development Type Units

Dwellings 120 - 150 units

Employment 0000 m2

Include additional development as required 0

1.3 Study Aims and Objectives The aim of the study is to identify potential impact on the sewer system of flows from the proposed development. This will be achieved through modelling the development and assessing the impact at key points on the sewer network.



2 Sewer Capacity Assessment

2.1 Modelling Methodology The modelling methodology used to assess the impacts of the proposed development is summarised below:

The development proposals of 150 dwellings were included in the model.

There are two separate 225mm diameter public foul sewers close to the site where a foul connection from the site may be possible: One is in Forest Scholl Road (SK24274504) and the other is in Fairfield Avenue (SK24277501). Both potential connection locations were modelled to identify the most suitable location.

The connection in Forest Scholl Road had the least impact on the public sewerage network and a full analysis was undertaken on this connection location.

2.2 Assumptions and Limitations The Model Review Proforma is included in Appendix C.


Mouchel 8 04/2012

3 Conclusions and Recommendations

3.1 Conclusions There are known flooding issues in Rolleston on Dove, which was reflected in the hydraulic model.

Inclusion of the development proposal is predicted to have no impact on the known capacity issues.

Two possible connections were tested using hydraulic modelling. Connecting the development to the public sewerage network at Forest Scholl Road provides the best option with regards to post-development performance of the sewerage network.

Overall, there is limited capacity in the current sewer network. However, the impact of the proposed development on the sewerage network is considered negligible.

3.2 Recommendations No specific additional capacity will be required to cater for this proposed development. There are existing issues on the sewer network of which Severn Trent Water are aware and will seek to address where appropriate.


Mouchel A 04/2012

Appendix A: Sensitive Information

Plan 1-2: Reported flooding locations

This information has been removed for external circulation as it contains sensitive information.


Mouchel B April 2012

Appendix B: Proposed Development Plans

1438.dwg

Rolleston Housing Sketch Scheme.dwg


Mouchel C April 2012

Appendix C: Model Review Proforma

Sewer Capacity Assessment - Existing Model Review Checklist

Date of Model 03/2012 Date of Model Verification 25/02/2012

Confirm Name of Model Network Reviewed 523-039_Clay Mills Current As-Built model#28

List Associated Modelling Files

Model Status (Verified, Needs, Options) Verified

Key factor assessed in vicinity of site Comments Impact on Model Accuracy (H/M/L)

Software Suitability Is model in HydroWorks or

non-InfoWorks Software? No - InfoWorks v10.5 L

Software Suitability Does model require upgrading to more recent version of InfoWorks?

No needs. Model was built and verified by InfoWorks v10.5

L

Suitability of Modelling Specification Does model

require converting to current modelling specification (Procedure 264 AMP3 Model Conversion Process)?

No needs. Already completed as part of SMP study

L

Is adequate Model Build Documentation available identifying modelling process and any limitations in

model?

Yes, previous DAP and current SMP L

Have all relevant documented limitations been assessed and identified?

Yes, documented limitations do not impact this study

L

Does the model require upgrading to improve the

representation of extents, detail or known ancillaries?

Station Road operational regime

(staff or instrumentation) L

Are there any significant changes to the catchment since model build that require including in the

model?

No. The model was verified and

signed off in 02/2012. L

Are there any significant changes to the sewer

network or ancillaries that need to be included in the model?

No. model is up to date. L

Is the existing model flow survey and verification

adequate?

Yes, the model was verified against

2007 and 2011 flow survey data. L

Is there a need to combine a number of DAP models to create a single model to assess this site?

No, already completed as part of SMP

L

Other issues?


Mouchel D April 2012

APPENDIX E

Surface Water Drainage Details

APPENDIX 5BMW2031E/01/V1/A5

Our Ref: BMW2031/DW/LC/120308Contact: Mr Luke CrossDirect Dial: 01159 241100

Date: 8 March 2012

SOIL INFILTRATION TESTING, FORMER PLAYING FIELDS, BURTON & SOUTHDERBYSHIRE COLLEGE

BWB Consulting Limited (BWB) carried out Soil Infiltration Testing at the site known asthe former playing fields, Burton and South Derbyshire College, Rolleston on Dove,Burton on Trent. The works were carried out in accordance with the fee proposalIDN/KH/BMW2031E dated November 2011.

This factual report aims to provide:• The soil testing strategy employed,• The soil infiltration rate results.

SCOPE OF ASSESSMENTS

A total of two soakage trial pits (TP01 & TP02) were excavated across the site to enablesoil infiltration testing. In addition, two further trial pits (TP03 & TP04) were excavated toconfirm that similar geology is found across the whole site. All trial pits were excavatedusing a JCB 3CX type excavator on Tuesday 28th February 2012. The trial pits wereexcavated ensuring vertical sides and were trimmed square to a maximum depth of2.1m.

A plan showing the approximate locations of the trial pits is presented as Figure 2 withinthe Main BWB Report ref: BMW2031E/01/V1 dated March 2012.

SOIL TESTING STRATEGY

A BWB Engineer directed and logged the infiltration testing of the soakage trial pit underthe guidance of BRE Digest 365 ‘Soakaway Design’ and in accordance withBS5930:1999+A2:2010 ‘Code of Practice for Site Investigations’. Using a water bowser,all soakage trial pits were filled with water, ensuring a rapid inflow and that the flow didnot cause the collapse of the side walls. The water level and the time were recorded asthe pits drained. This process was carried out simultaneously at trial pits TP01 & TP02due to the length of time the water took to dissipate.

GROUND CONDITIONS

It was noted that the ground conditions remained similar across the entire site, typicallycomprising of turf and topsoil over weathered clay overlying extremely weak weatheredmudstone. No groundwater strikes were noted during the excavations. Full details of thematerials encountered are presented on the trial pit logs included as Enclosure 2.

SOIL INFILTRATION RESULTS

Due to the slow dissipation of the water, it was not possible to conduct a full depthinfiltration test at either of the two locations. At location TP02 water levels in the test pitfell by 9cm in 3hrs, remaining within the topsoil horizon, and the results were notsuitable to carry out an infiltration rate calculation.

At location TP01 water level fell by 34cm over a 3hr period, within the very weatheredupper clay horizon of the Mercia Mudstone. A potential infiltration rate for this horizonwas calculated, however, as recommended in the BRE document, the determination ofthis infiltration rate has used the design method adopting the results determined fromthe 75% to 25% effective depth of the actual water level drop. A result of 1.01E-05 m/shas been calculated for TP01 within the upper 75cm of soil.

The infiltration results show that the geology of the site has generally poor drainagecharacteristics, and while the very small amount of weathered clay immediately belowthe topsoil may allow a small degree of infiltration in general the site should beconsidered as having a very low permeability.

No assessment has been made of the suitability of a potential permanent soak awaydesign or other potential environmental contamination issues which should be consideredwith respect to draining through potentially contaminated soil materials.

Yours faithfully

Luke Cross (BSc Hons)Monitoring Technician

Project Title Hole Ref.Client Project No.Plant used

Start Date

REMARKS

EASTING

LOGGED BY SCALE

NORTHING GROUND LEVEL

SHEETFax : 0115 9503966Tel : 0115 9241100

NG1 1PYNottingham

The Lace Market3-4 Kayes Walk

Groundwater

Strike Well

Depth(m)

Description of Strata Level(mAOD)

Legend Samples In-situ TestingType From To

Depth Depth (m)(SPT Type) Result

SOIL SAMPLE TYPED - 500g to 1kg DisturbedB - 5kg to 20kg DisturbedU - 100mm dia. UndisturbedJ - 250ml Amber Glass JarV - Glass Vial

GROUNDWATERGroundwater

Standing

IN-SITU TESTSSV - Hand Shear Vane

N = SPT blows over 300mm

PID - Photo IonisationDetector (ppm)

strike

groundwater level

Environmental Division

End Date

HP - Hand Penetrometer

S = Split Spoon SamplerC = Solid Cone

No groundwater encountered.1.Excavation stable throughout.2.Excavation backfilled with arisings on completion.3.

Burton & South Derbyshire CollegeBurton & South Derbyshire CollegeJCB

0.00

AM

0.00 0.00

28/02/2012

BMW2031

TP01

28/02/2012

0.20

0.75

1.80

2.10

-0.20

-0.75

-1.80

-2.10

Turf over dark brown sandy clayeyTOPSOIL with frequent fine rootlets.

Soft to firm reddish brown silty CLAYwith fine to coarse angular gravel ofsiltstone and pockets of grey silt.[WEATHERED MUDSTONE]

Red friable slightly silty gravellyCLAY. Gravel is angular to subangularfine to medium lithorelicts of extremelyweak mudstone. [WEATHEREDMUDSTONE]

Red and occasionally grey slightlyclayey GRAVEL of fine to coarse angularto sub rounded mudstone and siltstone.Mudstone/siltstone fragments areextremely weak to moderately strong withoccasional pockets of grey silt.(WEATHERED MUDSTONE)End of hole at 2.10 m

1:50 Sheet 1 of 1


Start Date

REMARKS

EASTING

LOGGED BY SCALE


SHEETFax : 0115 9503966Tel : 0115 9241100

NG1 1PYNottingham


Groundwater

Strike Well

Depth(m)






Standing




strike

groundwater level


End Date





0.00

AM

0.00 0.00

28/02/2012

BMW2031

TP02

28/02/2012

0.25

1.50

-0.25

-1.50

MADE GROUND: Turf over dark brownsandy clayey TOPSOIL with occasionalgravel of fine to coarse angular brick andsub rounded quartz.

Red to red brown silty clayey GRAVEL.Gravel is fine to medium lithorelicts ofweak angular mudstone and extremelyweak tabular mudstone. Becoming fine tocoarse from 1.2m and becomingoccasionally grey by 1.4m.[WEATHERED MUDSTONE]End of hole at 1.50 m

1:50 Sheet 1 of 1


Start Date

REMARKS

EASTING

LOGGED BY SCALE


SHEETFax : 0115 9503966Tel : 0115 9241100

NG1 1PYNottingham


Groundwater

Strike Well

Depth(m)






Standing




strike

groundwater level


End Date





0.00

AM

0.00 0.00

28/02/2012

BMW2031

TP03

28/02/2012

0.30

0.600.68

1.80

2.60

3.50

-0.30

-0.60-0.68

-1.80

-2.60

-3.50

Turf over brown to dark brown sandyclayey TOPSOIL with frequent finerootlets.

Soft to firm reddish brown andoccasionally grey mottled silty CLAYwith occasional black charcoal pockets(0-5mm). (ALLUVIUM)

Yellow brown sandy silty CLAY withoccasional gravel of fine to coarsesubrounded quartz. [ALLUVIUM]

Soft red brown occasionally grey friablesilty CLAY with occasional pockets ofgrey silt. Becoming firm and veryfriable by 1.2m. (WEATHEREDMUDSTONE)

Red clayey GRAVEL of fine to coarse,angular to sub angular mudstone.(WEATHERED MUDSTONE).

Red occasionally grey tabular andangular extremely weak siltstoneGRAVEL and occasional cobbles.(WEATHERED MUDSTONE)End of hole at 3.50 m

1:50 Sheet 1 of 1


Start Date

REMARKS

EASTING

LOGGED BY SCALE


SHEETFax : 0115 9503966Tel : 0115 9241100

NG1 1PYNottingham


Groundwater

Strike Well

Depth(m)






Standing




strike

groundwater level


End Date





0.00

AM

0.00 0.00

28/02/2012

BMW2031

TP04

28/02/2012

0.15

1.10

3.50

-0.15

-1.10

-3.50

MADE GROUND: Turf over dark brownsandy gravelly TOPSOIL. Gravel issubrounded fine to course quartz andpockets of grey black fine to coarse gravelof slag.

Soft to firm red to red brown silty CLAYwith occasional pockets of grey silt.Becoming slightly gravelly by 0.7m.(WEATHERED MUDSTONE)

Grey fine to coarse angular to subangular GRAVEL of siltstone.(WEATHERED MUDSTONE)

End of hole at 3.50 m

1:50 Sheet 1 of 1

ICP SUDS Mean Annual Flood

Input

Return Period (years) 100 Soil 0.450Area (ha) 5.975 Urban 0.000SAAR (mm) 700 Region Number Region 4

Results l/s

QBAR Rural 26.2QBAR Urban 26.2

Q100 years 67.5

Q1 year 21.8Q30 years 51.4Q100 years 67.5

BWB Partnership 30 St Pauls Square Birmingham B3 1QZ Date 28/06/2012 15:39 File Micro Drainage

Designed By ben.fleming Checked By Source Control W.12.5

Page 1

©1982-2010 Micro Drainage Ltd

Documents

FLOOD RISK & WATER ENVIRONMENT - East Staffordshire Application...3.6 Surface water flood risk mapping obtained from the Environment Agency indicates that the site is not at risk from