flood risk statement

FLOOD RISK STATEMENT

Job No. 18204

Proposed AD Plant

Land off the A51 Rugeley

Staffordshire

For Wolseley Park Energy

February 2014

18204/SVH 1 February 2014 Rugeley, Staffordshire

CONTENTS 1.0 INTRODUCTION………………………………………………………………………............. 2

2.0 SITE DESCRIPTION…………………………………………………………………................ 2-4

2.1 Location………………………………………………………………….................................. 2 2.2 Existing Site.……….………………………………………………….................................... 2 2.3 Proposed Development.…………………………………………………………….............. 2 2.4 Environment Agency Flood Map................…………………………………….............. 2 2.5 Geology....……………………………………………………………………………….............. 3 2.6 Groundwater........................................................................………….………............ 3 2.7 Surface Water Runoff from the Existing Site..................………….……….............. 3 2.8 Surface Water Runoff from the Proposed Development…………....……............. 3-4

3.0 FLOOD RISK…………………………………………………………………………….............. 4-6

3.1 Sources of Flooding…………………………………………………………………............... 4 3.2 Fluvial Flooding......................................................................................................... 4 3.3 Surface Water Flooding................................…………………………………................ 4-5 3.4 Repairs and Maintenance............................…………………………………................ 5 3.5 Downstream Flooding............................................................................................. 5-6

4.0 SEQUENTIAL TEST…………………………………………………….................................. 6

5.0 SUMMARY………………………………………………………………................................. 6

6.0 CONDITIONS OF INVESTIGATION AND REPORTING………..…………................ 6-7

DRAWINGS APPENDIX Drawing No. 18204/800 - Site Location Plan Drawing No. 18204/001 - Proposed Site Layout Drawing No. 18204/802 - Environment Agency Flood Map Drawing No. 18204/803 - British Geological Survey Superficial Geology Map Drawing No. 18204/804 - British Geological Survey Bedrock Geology Map Drawing No. 18204/805 - Environment Agency Groundwater Map APPENDIX A Greenfield Runoff Rate Calculation Predicted Surface Water Runoff Rates from the Proposed Development Prior to Mitigation


1.0 INTRODUCTION

This Flood Risk Statement is to evaluate the flood risk to the proposed Anaerobic Digestion (AD) Plant on the land off the A51, Rugeley, Staffordshire. The report was prepared for Wolseley Park Energy in February 2014 and has been carried out in accordance with Technical Guidance to the National Planning Policy Framework (TG NPPF) with reference to the former Planning Policy Statement (PPS) 25. A Flood Risk Statement has been prepared to demonstrate how the proposal will impact on the flood risk on-site and in the surrounding area as the site’s area exceeds 1 Hectare.

2.0 SITE DESCRIPTION 2.1 Location

The proposed site is located to the south of the A51 highway, to the north-west of the settlement of Rugeley. The site has an OS Pathfinder Grid Reference of SK 02924 19891, refer to Drawing No. 18204/800 in the Drawings Appendix for the Site Location Plan. The proposed site is located in Stafford Borough Council’s administration area and is within the Environment Agency’s Midlands Central district.

2.2 Existing Site

The Greenfield site occupies 2.26 Hectares. To the north of the site is the A51 highway, beyond this is Greenfield. To the east is Rugeley waste water treatment works. To the west and south of the site is Greenfield. The Ordnance Survey map shows the site to be located between the 70-80m contours where the site falls to the north-east.

2.3 Proposed Development

The proposed development is for a renewable energy AD Plant involving the construction of silage clamps, fermenter, post fermenter, gas to grid processing unit and technical building. Refer to Drawing No. 18204/001 in the Drawings Appendix detailing the proposed site layout. The proposed site will be accessed via the A51 highway. TG NPPF, Table 2 Flood Risk Vulnerability Classification describes the proposed site as having a less vulnerable land-use. TG NPPF Table 3 shows Flood Zone 1, 2 and 3a to be appropriate for less vulnerable developments.

2.4 Environment Agency Flood Map

The Environment Agency flood map indicates that the site is not located in an area of flood risk as the proposed development is located within Flood Zone 1, refer to Drawing 18204/802 in the Drawings Appendix.


2.5 Geology The geological map for the area indicates there are no superficial deposits on-site. The bedrock comprises of Bromsgrove Sandstone Formation. Refer to Drawing No. 18204/803 & 804 in the Drawings Appendix showing an extract of the British Geological Survey (BGS) Superficial and Bedrock Geology Map.

2.6 Groundwater The site is not located within a Groundwater Source Protection Zone, refer to Drawing No. 18204/805 in the Drawings Appendix.

2.7 Surface Water Runoff from the Existing Site

The proposed site for the AD Plant is currently Greenfield. The Greenfield runoff rates for the area of site which is proposed to be made impermeable (1.0825 Hectares) are shown below in Table 1.

Storm Event 1 in 1

year event 1 in 30

year event 1 in 100

year event

2014 0.4 l/s 1.0 l/s 1.3 l/s

Table 1. Predicted Greenfield runoff rates from the existing site. The Greenfield runoff rates shown above were calculated using the IH 124 method, refer to Appendix A.

2.8 Surface Water Runoff from the Proposed Development

The proposed facility will create an impermeable area of 1.0825 Hectares and will result in an increased amount of surface water runoff discharging from the site. Table 2 below details the predicted amount of surface water runoff from this area now and for the lifetime of the development prior to mitigation. The following values are calculated using the Modified Rational formula with average rainfall intensities based on the FSR/FEH rainfall parameters for the site with a Cv value of 0.75 and a Cr value of 1.30. As recommended in Flood Estimate Handbook, Volume 2 FSR rainfall parameters were used for storm durations that were less than 30 minute duration, whereas storm events exceeding this were calculated using FEH rainfall data. Storm durations of 15 and 360 minutes were used for comparison.


2.8 Continued…

Storm Event 1 in 1 year event

1 in 30 year event

1 in 100 year event

2014 (15 min)

85.49 l/s 209.50 l/s 271.29 l/s

2014 (360 min)

11.09 l/s 26.41 l/s 36.07 l/s

Storm Event (including CC)

1 in 1 year event

1 in 30 year event

1 in 100 year event

2074 (15 min)

102.58 l/s 251.40 l/s 325.55 l/s

2074 (360 min)

13.31 l/s 31.69 l/s 43.29 l/s

Table 2. Predicted surface water runoff rates from the proposed facility including climate change prior to mitigation. To allow for an increase in rainfall due to the effects of climate change over the lifetime of the development (60 years for a renewable energy facility) the rainfall intensities have been increased by 20% (as detailed in Table 5 of TG NPPF). Refer to Appendix A for surface water runoff rate calculations.

3.0 FLOOD RISK

3.1 Sources of Flooding

The proposed development could be at possible risk from the following sources of flooding:

• Fluvial flooding • Surface water flooding

3.2 Fluvial Flooding

The Environment Agency flood map shows the site to be located within Flood Zone 1, refer to Drawing No. 18204/802 in the Drawings Appendix. The map shows the site is not located within Flood Zones 2 or 3, therefore the annual probability of the site being flooded by a fluvial flood event is less than 0.1% (equivalent to a storm event with a greater than 1 in 1000 year annual probability).

3.3 Surface Water Flooding

Building Regulations Part H recommend that surface water drainage should discharge into an infiltration drainage system where practical. Should infiltration drainage not be possible the next preferred option is to discharge to a watercourse at a restricted rate, following this restricted discharge to the sewer.


3.3 Continued… The permeable Sandstone bedrock formation shown on the BGS geology map to underlie the site shows the use of an infiltration drainage system to be feasible onsite. It is therefore proposed that the surface water from the site will discharge into an infiltration lagoon located in the northern area of the site, as shown on Drawing No. 18204/001 in the Drawings Appendix. To ensure there is no risk of surface water flooding, the sustainable system will be designed to contain up to and including the 1 in 100 year storm event including the effects of climate change. The surface water runoff along the access road will be collected in filter drains and discharge into the infiltration lagoon via a silt trap. Surface water which lands on the silage clamp covers will be collected within drainage channels on top of the clamps and channel drains across the ends, which will discharge into the lagoon via a sample chamber and silt trap. On obtaining planning permission permeability tests will be undertaken to confirm the site specific infiltration rate. The infiltration drainage system will be designed in accordance with C697 “The Suds Manual” and Part H of the Building Regulations. The infiltration lagoon will drain surface water only, leachate collected within the concrete silage clamps will discharge into a separate drainage system and be contained within a leachate tank, prior to being fed into the fermenter tank to be used within the process. In the event of a leachate spillage a shut off valve will divert surface water to the leachate tank to prevent pollution to the infiltration lagoon. In the event where the surface water system fails consideration has been given, routing surface water away from vulnerable areas through the natural landscape of the site towards the infiltration lagoon. The increase in hardstanding areas will create an increase in the current volume of surface water runoff generated within the site. However through the incorporation of a surface water drainage system the increased surface water runoff will be entirely contained within an on-site soakage drainage system, therefore the proposal will not increase the risk of flooding on-site or to the surrounding area.

3.4 Repairs & Maintenance The long term maintenance and repair of the proposed surface water drainage system shall be the responsibility of site owner. The maintenance and repair will be included within their general maintenance regime.

3.5 Downstream Flooding

It is evident that any hydrological change within the catchment will have an effect downstream.


3.5 Continued… The increase in surface water runoff resulting from the development will not increase the risk of flooding to the surrounding area as the runoff will be contained onsite within a drainage scheme designed to cope up to and including the 1 in 100 year storm event plus climate change. The proposal is located within Flood Zone 1 and therefore will not occupy any critical flood plain storage or cause any obstruction to the natural flow of water.

4.0 SEQUENTIAL TEST

It is the Local Planning Authority’s responsibility to apply the Sequential Test to steer proposed new development away from areas at risk of flooding. However the proposed development will be located within Flood Zone 1. Table 1, 2 and 3 of TG NPPF states that this is the preferred Flood Zone for all new development. Therefore the Local Planning Authority will not be required to apply the Sequential Test to the proposed development in this instance.

5.0 SUMMARY

The proposed development at Rugeley will result in part of the permeable site becoming impermeable creating an increase in the surface water runoff. Through the creation of an infiltration system the additional surface water will be contained within a sustainable drainage system. The drainage system will be designed to provide storage to contain up to and including the 1 in 100 year storm event plus climate change. The site is not at risk from fluvial flooding or surface water flooding, nor will it increase the risk of flooding to the surrounding area.

6.0 CONDITIONS OF INVESTIGATION AND REPORTING Report Prepared by:-

Sally Hare ………….………………………………………..................(Environmental Consultant)

S Hare B.Sc (Hons) MCIWEM

Report Authorised by:-

Julian Riley …...…………………………………………………………………..............…… (Director)

Eur Ing J R Riley B.Sc (Hons), C.Eng., MICE., C.WEM MCIWEM For and on behalf of Plandescil Ltd.

Plandescil Ltd are only able to work on information available at the time the Flood Risk Statement is carried out which have been applied to the Flood Risk Statement in accordance with current best practice. Plandescil Ltd cannot be held responsible for any subsequent flooding to the development or surrounding area. The Flood Risk Statement may indicate that the development requires the Local Planning Authority to carry out a sequential test. Plandescil Ltd has no influence over the decision of the sequential test.


6.0 Continued… This report was prepared and provided for the sole and specific use of the client. Plandescil Ltd shall not be responsible for any use of the report or its contents for any other purpose. Copies of the report to other parties for information should be copied in full but Plandescil Ltd shall extend no professional liability or warranty to other parties in this connection without written consent. The copyright of this report and other plans and documents prepared by Plandescil Ltd are owned by them.

18204/SVH February 2014 Rugeley, Staffordshire

DRAWINGS APPENDIX

CONTENTS Drawing No. 18204/800 - Site Location Plan Drawing No. 18204/001 - Proposed Site Layout Drawing No. 18204/802 - Environment Agency Flood Map Drawing No. 18204/803 - British Geological Survey Superficial Geology Map Drawing No. 18204/804 - British Geological Survey Bedrock Geology Map Drawing No. 18204/805 - Environment Agency Groundwater Map

Wolseley Park Energy

Land off the A51 Rugeley Staffordshire

Site Location Plan

N.T.S

18204/800 0

February 2014 SVH

N Source: Bing Maps

N

Environment Agency Flood Map

N.T.S

18204/802 0

February 2014 SVH



Flood Zone 1 (less than 0.1% annual probability of flooding)

Flood Zone 2 (0.1% annual probability of flooding)

Flood Zone 3 (1.0% annual probability of flooding)

Legend

Source: Environment Agency

British Geological Survey Superficial Geology Map

N.T.S

18204/803 0

SVH


N

February 2014


Legend

Alluvium (Clay, Silt, Sand & Gravel)

Glaciofluvial Deposits (Sand & Gravel)

Till, Mid Pleistocene (Diamicton)

River Terrace Deposits

Source: British Geological Survey

British Geological Survey Bedrock Geology Map

N.T.S

18204/804 0

SVH


N

February 2014


Source: British Geological Survey

Legend

Mercia Mudstone Group

Bromsgrove Sandstone Formation (Sandstone Pebbly (gravelly)) Kidderminster Formation (Sandstone & Conglom-erate, Interbedded)

Environment Agency Groundwater Map

N.T.S

18204/805 0

SVH


N

February 2014

Legend

Source Protection Zone 1 (Inner Zone)

Source Protection Zone 2 (Outer Zone)

Source Protection Zone 3 (Total Catchment)

None


Source: Environment Agency

18204/SVH February 2014 Rugeley, Staffordshire

APPENDIX A

CONTENTS Greenfield Runoff Rate Calculation…………………………………………...………………………….. 1 Predicted Surface Water Runoff Rates from the Proposed Development Prior to Mitigation…. 2

Plandescil Limited Page 142-44 Connaught Road 18204AttleboroughNorfolk NR17 2BWDate February 2014 Designed by SVHFile Checked byMicro Drainage Source Control 2013.1.1

ICP SUDS Mean Annual Flood

©1982-2013 Micro Drainage Ltd

Input

Return Period (years) 2 SAAR (mm) 779 Urban 0.000Area (ha) 1.083 Soil 0.150 Region Number Region 4

Results l/s

QBAR Rural 0.5QBAR Urban 0.5

Q2 years 0.4

Q1 year 0.4Q30 years 1.0Q100 years 1.3

18204/SVHRugeley, Staffordshire 2 February 2014

Storm EventAverage Rainfall

Intensities (i) (mm/hr)1 year 15 mins 29.135

30 year 15 mins 71.401100 year 15 mins 92.4611 year 360 mins 3.779

30 year 360 mins 9.001100 year 360 mins 12.295

1.0825Cv: 0.75, CR: 1.3


1 in 30year event

1 in 100year event

2014 85.49 209.50 271.29(15 mins)

2014 11.09 26.41 36.07(360 mins)


1 in 30year event

1 in 100year event

2074 102.58 251.40 325.55(15 mins)

2074 13.31 31.69 43.29(360 mins)

Predicted Surface Water Runoff Rates (Including 20% Climate Change)

Predicted Surface Water Runoff Rates from the Proposed Development Prior to Mitigation

Average Rainfall Intensities (i) for Listed Storm Events

Qp = 2.78 Cv CR i A

Predicted Surface Water Runoff Rates

Proposed Impermeable Area (A) (hectares):

flood risk statement

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