Copyright Travis Baker Limited 2012 All Rights Reserved

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Project Land Off The Long Shoot, Nuneaton title Docum Flood Risk Assessment – Supplementary ent Report type Job 11052 numbe r

Date Rev Comments isio n 29.08. - Issue 2012 Bellway Homes (West Midlands) Ltd

Proposed Residential Pre Checke par d by Development at land off the ed Long Shoot, Nuneaton by

Na Dav Rob Flood Risk Assessment me e Travis Bak Supplementary Report er Date Rev Comments isio n

Pre Checke par d by ed by

Date Rev Comments isio n

This document has been prepared by Travis Baker Limited for the exclusive use by the commissioning party in accordance with the terms and conditions of the contract between Travis Baker Limited and the commissioning party. No other party may use, make use or rely on the contents of this report without the prior written consent of Travis Baker Limited. No liability is accepted by Travis Baker Limited for any use of this report other than for the purpose for which it was originally prepared. This document may contain and rely on information provided by Third Parties; no verification of such information has been undertaken and Travis Baker Limited accept no responsibility for any inaccuracies within such information. No part of this report may be copied or reproduced by any means without written permission from Travis Baker Limited.

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Prepared by Checked by

Date Revision Comments

Prepared by Checked by

This document has been prepared by Travis Baker Limited for the exclusive use by the commissioning party in accordance with the terms and conditions of the contract between Travis Baker Limited and the commissioning party. No other party may use, make use or rely on the contents of this report without the prior written consent of Travis Baker Limited. No liability is accepted by Travis Baker Limited for any use of this report other than for the purpose for which it was originally prepared. This document may contain and rely on information provided by Third Parties; no verification of such information has been undertaken and Travis Baker Limited accept no responsibility for any inaccuracies within such information. No part of this report may be copied or reproduced by any means without written permission from Travis Baker Limited.

BELLWAY HOMES (WEST MIDLANDS) LIMITED Proposed Residential Development, Land off The Long Shoot, Nuneaton Flood Risk Assessment – Supplementary Report

CONTENTS

1.0 INTRODUCTION 1

1.1 Background to Report 1

2.0 CONCERNS RAISED 2

2.1 The Environment Agency 2

2.2 Severn Trent Water 2

3.0 EXISTING RUN-OFF, PROPOSED DRAINAGE SYSTEMS AND SUSTAINABLE MEASURES 3

3.1 Existing Run-off Regime and Proposed Outfall Point 3

3.2 Proposed Surface Water Drainage and SUDS 3

3.3 Proposed Foul Water Drainage 4

4.0 CONCLUSIONS 5

5.0 APPENDICES 6

BELLWAY HOMES (WEST MIDLANDS) LIMITED Proposed Residential Development, Land off The Long Shoot, Nuneaton Flood Risk Assessment – Supplementary Report

1.0 INTRODUCTION

1.1 Background to Report

1.1.1 A Flood Risk assessment was prepared by Travis Baker Ltd in support of a planning application for residential development on land off the Long Shoot in Nuneaton. This is referenced 11052 rev B.

1.1.2 During the consultation process both the Environment Agency (EA) and Severn Trent Water (STW) were consulted and raised concerns with the proposed surface water drainage strategy.

1.1.3 This Supplementary Report has therefore been prepared to address those concerns. It should be read in conjunction with the main report.

Travis Baker Ltd Page No. 1 Project No. 11052 BELLWAY HOMES (WEST MIDLANDS) LIMITED Proposed Residential Development, Land off The Long Shoot, Nuneaton Flood Risk Assessment – Supplementary Report

2.0 CONCERNS RAISED

2.1 The Environment Agency

2.1.1 A copy of the correspondence from the Environment Agency (ref: UT/2012/110619/01-L01) is in the appendices. It raised numerous concerns with the drainage strategy which are summarised as follows:

3.0 Failure to identify a viable point of connection for the surface water outfall

4.0 Existing surface water drainage routes not clarified

5.0 Lack of water quality improvement features and above ground SUDS techniques

6.0 Questions the use of oversized storage pipes and tanks

7.0 Requests information on the disposal of foul water

7.1 Severn Trent Water

7.1.1 STW also raised concerns regarding the available capacity within the public surface water sewers to which the new site system is proposed to outfall.

7.1.2 The developer enquiry response (copy in the appendices) was slightly ambiguous in that it did not specifically state acceptance to an allowable rate of discharge to the public sewer network should an alternative outfall not be found or infiltration testing prove unsatisfactory. It did however allude to greenfield run-off rates of 5 litres per second per hectare.

7.1.3 A meeting was held at the STW offices in Coventry (16 th August 2012) to discuss the concerns and proposed mitigation measures. In attendance were Bill Walton (STW), Julian Lee (Bellway) and Rob Travis (Travis Baker).

8.0 EXISTING RUN-OFF, PROPOSED DRAINAGE SYSTEMS AND SUSTAINABLE MEASURES

8.1 Existing Run-off Regime and Proposed Outfall Point

8.1.1 The drainage strategy drawings put forward in the FRA have been amended and are in the appendices. 8.1.2 Flow arrows have been added which show the current flow routes across the development land. The vast majority of the site falls towards an existing open dry balancing depression beyond the site boundary to the south-west. The position of this has been noted on the drawings. 8.1.3 In recent correspondence from STW dated 21st August 2012 (copy in the appendices) they acknowledge that ‘the area of land to be developed does currently drain into the existing surface water balancing lagoon’. This lagoon is an online feature within the public sewer network. 8.1.4 In the same correspondence they also confirmed that the ‘proposed surface water drainage strategy is acceptable as this replicates the current greenfield run-off’. 8.2 Proposed Surface Water Drainage and SUDS

8.2.1 The surface water drainage strategy proposed in the FRA used the normal 5 litres per second per hectare as the maximum allowable discharge rate for the development. The restriction was set for all critical storm events up to the 100 year + 30% CC. 8.2.2 In order to provide a further level of betterment it has been decided to reduce the maximum allowable discharge rate to 4 l/s/ha (a 20% reduction), leading to a corresponding increase in the required volume of upstream storage. 8.2.3 The FRA concluded that the use of soakaway techniques was not viable due to unsuitable ground conditions. This was accepted by the EA in their letter. An outfall to the public sewer system is therefore proposed and is acceptable to STW. 8.2.4 The concerns raised by the EA regarding a lack of above ground SUDS techniques are noted. 8.2.5 During the preparation of the FRA the local authority were consulted for their comments on the use of open balancing features. A copy of their response is in the appendices. In summary they were reluctant to take on any feature and expected a management company to be engaged to provide future maintenance. 8.2.6 The statement under point 4. V. in the EA letter is not correct. The current STW stance is that any above ground feature that provides balancing storage to the proposed sewer system MUST be adopted by a public body. A management company is not acceptable, even if the facility is placed off-line. 8.2.7 It is therefore still the proposal to provide storage within oversized underground structures. 8.2.8 In order to provide water quality benefits it is proposed to incorporate sustainable drainage measures at source. Where possible these will include the following: 9.0 Lined permeable paving to parking areas and drives

10.0 Filter strips and trenches adjacent to paved areas 11.0 Small local swales 11.1.1 There are also a number of small ditches which cross the site. A survey of these ditches has been undertaken by Travis Baker to establish their functionality. It is proposed that where possible these ditches are retained and incorporated within the development to convey flows. 11.1.2 The WINDES calculations have been updated to reflect the revised maximum allowable discharge rate and the results are in the appendices. 11.2 Proposed Foul Water Drainage

11.2.1 The STW developer enquiry response advises that there is adequate capacity for the connection of foul water flows from the proposed development to the existing public foul water sewer which passes through the site. There is a limit imposed on the number of dwellings at 120. 11.2.2 The current proposals for the site are for the construction of 120 dwellings.

12.0 CONCLUSIONS

12.1.1 An objection was received to the FRA from the EA and concerns were raised by STW. 12.1.2 The proposed drainage strategy has been revised and maximum allowable flow rates reduced, providing betterment over greenfield run-off rates. The point of discharge to the existing public sewer system has been agreed. 12.1.3 The use of above ground balancing features for the provision of attenuation has been investigated and proved unviable due to issues with future adoption and maintenance. 12.1.4 Suitable at-source SUDS features will be incorporated to improve the quality of surface water run-off. 12.1.5 It is therefore considered that the proposed drainage scheme will neither result in nor cause an increase flood risk to surrounding properties or the development site itself. 12.1.6 The principles for the disposal of foul water are acceptable to STW.

13.0 APPENDICES

 Correspondence  Drainage Strategy Drawings  WINDES calculations

Correspondence

Environment Agency letter ref : UT/2012/110619/0-L01

Severn Trent Water developer enquiry response

Severn Trent Water letter ref : WT26822, dated 21st August 2012

Email from Helena Lidgate – Nuneaton and Bedworth BC, dated 30th March 2012

Travis Baker Ltd Project No. 11052 BELLWAY HOMES (WEST MIDLANDS) LIMITED Proposed Residential Development, Land off The Long Shoot, Nuneaton Flood Risk Assessment – Supplementary Report

Drainage Strategy Drawings

Travis Baker Ltd Project No. 11052 BELLWAY HOMES (WEST MIDLANDS) LIMITED Proposed Residential Development, Land off The Long Shoot, Nuneaton Flood Risk Assessment – Supplementary Report

WINDES calculations

Travis Baker Ltd Project No. 11052