flood risk assessment template - east staffordshire application...table 5.1 - summary of flood risk...

ENVIRONMENT

Goodman International Ltd.

Phase 2, Unit 2

Centrum West

Burton-upon-Trent

FLOOD RISK ASSESSMENT

www.bwbconsulting.com

P/2016/01529Received 21/10/2016

B W B C o n s u l t i n g L t d : R e g i s t e r e d i n E n g l a n d 5 2 6 5 8 6 3

ENVIRONMENT

Goodman International Ltd.

Phase 2, Unit 2

Centrum West

Burton-upon-Trent

FLOOD RISK ASSESSMENT

Birmingham

Livery Place, 35 Livery Street, Colmore Business

District, Birmingham, B3 2PB

T: 0121 233 3322

Leeds

Whitehall Waterfront, 2 Riverside Way, Leeds LS1

4EH

T: 0113 233 8000

London

11 Borough High Street

London

SE1 9SE

T: 020 74073879

Manchester

4th Floor Carvers Warehouse, 77 Dale Street

Manchester, M1 2HG

T: 0161 233 4260

Nottingham

Waterfront House, Station Street, Nottingham

NG2 3DQ

T: 0115 924 1100

PHASE 2, SPECULATIVE UNIT, CENTRUM WEST, BURTON-UPON-TRENT

AUGUST 2016

CWS-BWB-EWE-XX-RP-EN-0001-FRA

Limitations

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.

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:-

(i) The date on which this assessment was undertaken, and

(ii) The date on which the final report is delivered

BWB Consulting makes no representation whatsoever concerning the legal significance of its findings or the legal

matters referred to in the following report.

All Environment Agency mapping data used under special license. Data is current as of August 2016 and is subject

to change.

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.

This report has been prepared for the sole use of Goodman International Ltd. No other third parties may rely upon or

reproduce the contents of this report without the written permission of BWB. If any unauthorised third party comes into

possession of this report they rely on it at their own risk and the authors do not owe them any Duty of Care or Skill

i

DOCUMENT ISSUE RECORD

Document Number CWS-BWB-EWE-XX-RP-EN-0001-FRA

BWB Reference BMW-2575-FRA

Status Revision Date of Issue Author Checked Approved

S2 P1 02/08/16

Julian O’Neill

BSc. MSc.

Keith Alger

BSc (Hons) MSc

Chris Dodd

BEng (Hons) IEng

MICE

S2 P2 09/08/16

Julian O’Neill

BSc. MSc.

Keith Alger

BSc (Hons) MSc

Chris Dodd

BEng (Hons) IEng

MICE


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ii

EXECUTIVE SUMMARY

This Flood Risk Assessment (FRA) is compliant with the requirements set out in the National

Planning Policy Framework (NPPF) and the associated Planning Practice Guidance. It has

been produced on behalf of Goodman International Ltd. in respect of a planning application

for a warehouse development within Phase 2, Centrum West, Burton-upon-Trent (approximate

grid reference: 422460, 322670)

This report demonstrates that the proposed development is not at significant flood risk, subject

to the recommended flood mitigation strategies being implemented.

The site lies within close proximity to three Environment Agency Main Rivers. Correspondence

with the EA has confirmed that the site falls outside of the 1 in 1000 year Shobnall Brook

floodplain. The site is located within Flood Zone 2 of the River Trent (2.4km to the south).

Modelled flood depths are shown to be 0.44m across the formation plateau in the 1 in 1000

year flood event. The Tatenhill Brook, which is 2.1km to the west of the site, is shown to

contribute flood water during high flow events to an Unnamed Ordinary Watercourse (UOW)

which runs through the southern boundary of the site. It was therefore necessary to undertake

a hydraulic flood modelling exercise to understand the risk to the site from these two

watercourses. Results of the modelling show that due to recent realignment works undertaken

within the wider ownership, flood water will not spill onto the site in any event up to and

including the 1 in 1000 year.

Groundwater, canal overtopping, and surface water flooding are shown to pose a medium

risk to the development.

In order to mitigate risk of inundation from any of the sources of flooding the finished floor levels

of the development have been set at 47.30m AOD. This gives 1.3m of freeboard above the 1

in 1000-year event on the UOW, and 10mm of freeboard above the 1 in 1000 year event on

the Trent.

Based upon a drainage strategy undertaken by a 3rd party it is intended that surface water be

attenuated to 17l/s, a prorated rate using previously consented rate for the wider site. The

existing pond to the south west of the development will be used to attenuate surface water in

all events up to an including the 1 in 100 year + 30% allowance for climate change storm.

In compliance with the requirements of National Planning Policy Framework, and subject to

the mitigation measures proposed, the development could 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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CONTENTS PAGE

DOCUMENT ISSUE RECORD i

EXECUTIVE SUMMARY ii

CONTENTS PAGE iii

INTRODUCTION 1 Sources of Data 1 Existing Site 1 Proposed Development 3 Flood Risk Planning Policy 3 Other Relevant Policy and Guidance 4

POTENTIAL SOURCES OF FLOOD RISK 6 Fluvial Flood Risk 6 Flood Risk from Canals 9 Groundwater Flood Risk 10 Flood Risk from Reservoirs & Large Waterbodies 10 Flood Risk from Sewers 11 Pluvial Flood Risk 12 Effect of Development on Wider Catchment 13

FLOOD RISK MITIGATION 14 General Mitigation 14 Finished Levels 14 Safe Access 14 Surface Water Drainage 15

OUTLINE DRAINAGE ASSESSMENT 16 Outline Surface Water Assessment 16

CONCLUSIONS AND RECOMMENDATIONS 17

TABLES

Table 1.1 - Site Summary Table 2.1 - Pre-Mitigation Sources of Flood Risk Table 2.2 – UOW Modelled Flood Levels Table 5.1 - Summary of Flood Risk Assessment

FIGURES

Figure 1.1 - Site Location Figure 1.2 - Environment Agency Flood Map for Planning (Rivers and Sea) Figure 2.1 – 1 in 100 year + 20% modelled Flood Depths (UOW) Figure 2.2 - Environment Agency Reservoir Failure Flood Risk Map Figure 2.3 - Risk of Flooding from Surface Water Mapping

APPENDICES

Appendix 1 - Topographical Survey, Enabling Earthworks/ Diverted Watercourse Drawings

Appendix 2 - Development Proposals and Proposed Level Drawings

Appendix 3 - Environment Agency Correspondence

Appendix 4 - Canal and River Trust Correspondence

Appendix 5 - Drainage Layout (ref: 03-0059-101) and MicroDrainage calculation sheets


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INTRODUCTION

This Flood Risk Assessment (FRA) is compliant with the requirements set out in the

National Planning Policy Framework (NPPF) and the associated Planning Practice

Guidance. The FRA has been produced on behalf of Goodman International Ltd. in

respect of a planning application for the “Phase 2, Centrum West” warehouse

development in Burton-upon-Trent.

Table 1.1 - Site Summary

Site Name Phase 2, Centrum West

Location Burton-upon-Trent

NGR (approx.) 422460, 322670

Application Site Area (ha) 1.9 (Approximately)

Development Type Warehouse / Logistics

NPPF Vulnerability Less Vulnerable

EA Flood Zone Flood Zone 2

EA Office Sentinel House, Staffordshire

Local Planning Authority East Staffordshire Borough Council

Sources of Data

The report is based on the following information:

(i) Site Layout Plan by pHp Architects ref: 3747-3-101

(ii) Topographical Survey by BWB Consulting, ref: BMW/2155/SVY/001

(iii) Enabling earthworks drawings by Hydrock, ref: C14309-208

(iv) Watercourse diversion drawings by BWB, ref: BMW-2155-W100, W101, W102,

W103, W104

(v) Ordnance Survey 1:10000 scale mapping

(vi) Environment Agency consultation and model information

(vii) East Staffordshire Strategic Flood Risk Assessment

(viii) Hydraulic modelling of the Unnamed Ordinary Watercourse undertaken by

BWB Consulting

(ix) Surface Water Drainage Design by THDA ref: 03-0059-102-A

(x) British Geological Survey Drift & Geology Maps

Existing Site

The site is situated off Callister Way within Burton-upon-Trent, East Staffordshire. It is

bound by the A38 to the west, the Trent and Mersey Canal to the south east and a

proposed warehouse building to the north east (known as Centrum West, Phase 2). A

site location plan is included as Figure 1.1, which also includes key water features in

proximity to the site. Topographically the site is flat, as it has been prepared for the

proposed development. These enabling works were conducted after planning consent

was granted by East Staffordshire District Council, ref: P/2015/00891, and included the


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diversion and partial culverting of the Unnamed Ordinary Watercourse (UOW) which

flows on the southern boundary of the site.

Figure 1.1 - Site Location

Appendix 1 includes approved drawings showing the finished levels of the enabling

earthworks and details of the diverted watercourse, including general arrangement

and typical sections. The original topographical survey is also included for reference.

The remainder of this report assumes that the existing conditions on the site are those

which were consented under that enabling works application.

The site is situated upon bedrock geology including the Bromsgrove Sandstone

Formation which is overlain with the Mercia Mudstone Group. There are superficial

deposits recorded which include the Holme Pierrepont Sands and Gravels. The site is

also within an area designated by the Environment Agency as a Groundwater Source

Protection Zone; it is within an Inner zone (Zone 1), Outer zone (Zone 2) and Total

catchment (Zone 3). This designation is likely to be in relation to a groundwater

abstraction just south of the site.

Shobnall Brook

River Trent

Unnamed

Ordinary

Watercourse

Tattenhill Brook Estimated

location.

Eventually

outfalls to Trent

Trent and

Mersey Canal

Approximate Site

Location


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Proposed Development

The proposed development is for a distribution warehouse, with associated

infrastructure; including car parking spaces, and access to the link road which is to be

constructed as part of the ‘Phase 2’ development. A copy of the development layout

is available in Appendix 2.

Flood Risk Planning Policy

National Planning Policy Framework

The NPPF1 sets out the Government’s national policies on different aspects of land use

planning in England in relation to flood risk. Planning Practice Guidance is also

available online2.

The Planning Practice Guidance sets out the vulnerability to flooding of different land

uses. It encourages development to be located in areas of lower flood risk where

possible, and stresses the importance of preventing increases in flood risk off site to the

wider catchment area.

The Planning Practice Guidance also states that alternative sources of flooding, other

than fluvial (river flooding), should also be considered when preparing a Flood Risk

Assessment.

This Flood Risk Assessment is written in accordance with the NPPF and the Planning

Practice Guidance.

Flood Zones

The Flood Map for Planning has been prepared by the Environment Agency. This

identifies areas potentially at risk of flooding from fluvial or tidal sources. An extract from

the mapping is included as Figure 1.2.

The Environment Agency mapping shows the site to be located entirely within Flood

Zone 2 (Medium Probability) of the River Trent. This Flood Zone is defined in the NPPF as

land assessed as having between a 1 in 100-year and a 1 in 1000-year annual

probability of river flooding.

Environment Agency correspondence and model information confirm that the site is

outside of the 1 in 1000-year floodplain of the Shobnall Brook, which is discussed further

in Section 2.

A hydraulic modelling exercise to understand the risk to the site from the Unnamed

Ordinary Watercourse and catchment transfer flows from the Tatenhill Brook is

discussed in Section 2.

Table 2 of the Planning Practice Guidance classifies land use. Under these

classifications the proposed development use; storage and distribution and associated

infrastructure is considered to be ‘Less Vulnerable’.

1 National Planning Policy Framework, CLG, March 2012

2 Planning Practice Guidance. http://planningguidance.planningportal.gov.uk/.


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Table 3 of the Planning Practice Guidance identifies that a ‘Less Vulnerable’

development within Flood Zone 2 is considered to be ‘appropriate’.

Figure 1.2 - Environment Agency Flood Map for Planning (Rivers and Sea)

Other Relevant Policy and Guidance

Strategic Flood Risk Assessment

East Staffordshire Borough Council commissioned the production of two strategic flood

risk assessments for the borough in 2008, both of which contain information relevant to

the site location.

The Level 1 SFRA3 states that severe flooding along the entire length of the Shobnall

Brook occurred in July 1999. It indicates that much of the flooding in recent years in the

area has been attributable to blocking of grills/culverts. Extreme events in 1999/2000

caused overtopping of non-main rivers within the suburbs, mostly through the

3 East Staffordshire Borough Council Level 1 Strategic Flood Risk Assessment February 2008


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surcharging of culvert entrances. It does not however relate this information directly to

the site in question.

It also states that no problems have been observed on the Trent and Mersey Canal

and that locks regulate water level through the use of both fixed and manually

operated sluices and weirs. This maintains a freeboard of 300mm between normal

water level and top of bank. The SFRA does identify that although no problems have

been observed, any interaction with the Trent could increase flood risk from this source.

Flood mapping of the Shobnall Brook included as part of the SFRA is believed to have

been superseded by more recent Environment Agency hydraulic modelling –

discussed in Section 2.0.

Sequential Testing

The site is shown to lie within Flood Zone 2, so under the National Planning Practice

Guidance it is required to undergo a Sequential Test.

A Sequential Test was undertaken for a previously consented planning application for

a similar warehouse unit on the site (ref: PA/25617/023/JPM/PO), demonstrating the

development was suitable and as such passed the Sequential Test as part of the

permission which was granted.

Furthermore, the August 2008 East Staffordshire Borough Council SFRA identifies the site

as being suitable for employment purposes under reference ‘E26’.

Therefore, based on the history and precedent of previous applications on the site and

supporting detail from the SFRA it is not necessary to undertake the process again for

this application.


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POTENTIAL SOURCES OF FLOOD RISK

The table below identifies the potential sources of flood risk to the site, and the impacts

which the development could have in the wider catchment prior to mitigation. These

are discussed in greater detail in the forthcoming section. The mitigation measures

proposed to address flood risk issues and ensure the development is appropriate for its

location are discussed within Section 3.0.

Table 2.1 - Pre-Mitigation Sources of Flood Risk

Flood Source Potential Risk

Description High Medium Low None

Fluvial

X The site is located in Flood Zone 2 of

the River Trent.

X

The site is located outside of the

Shobnall Brook 1 in 1000-year

floodplain.

X

The Tatenahll Brook and the

Unnamed Ordinary Watercourse on

the site is shown to pose a low risk to

the site.

Canals X

The Trent and Mersey Canal

maintains a freeboard of 300mm

between the normal water level

and top of bank. There have been

no records of overtopping on this

section.

Groundwater X

Groundwater emergence from

bedrock is unlikely however there is

a risk that perched water may

bepresent within superficial

deposits.

Reservoirs and

waterbodies X

The site is shown to fall inside of the

area at risk of reservoir failure;

though the probability of this

occurring is very low.

Sewers X No sewers present within the site.

Pluvial runoff X Surface water flow routes are

present within the site.

Effect of

Development

on Wider

Catchment

X

The development will increase the

area of impermeable surfaces

leading to a potential increase in

runoff

Fluvial Flood Risk

There are three main rivers which are in proximity to the development site. The flood risk

from each of these has been confirmed through correspondence with the Environment

Agency. The Burton Tributaries flood modelling exercise was published in 2014; both the


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Shobnall and Tatenhill Brooks were part of that study. Correspondence from the

Environment Agency confirming flood levels is available in Appendix 3.

River Trent

The site lies in Flood Zone 2 (extreme flood extent) of The River Trent which is

approximately 2.4km south east of the site. Product 4 information from the Environment

Agency shows that the 1 in 1000-year flood level on the site is 47.29m AOD. The plateau

created by the above mention previous consented planning application (ref.

P/2015/00891) is identified to be at 46.85m AOD. Flood depths during that event would

therefore be approximately 0.44m in the external areas of the site.

Burton-upon-Trent is afforded protection from River Trent flooding due to the

Environment Agency maintained flood defences present (details in Appendix 3).

Breach analysis of the defences has been undertaken by the EA at several locations

for the 1 in 100-year event to identify the residual risk of flooding in such an eventuality.

Extents are shown not to reach the site, and therefore this risk pathway can be

excluded.

On the above basis the site is only considered to be at medium risk of flooding, from

extreme river flood events.

Shobnall Brook

The Shobnall Brook is the closest Environment Agency main river to the site, located

approximately 500m to the north. It flows in a south easterly direction before entering

culvert and being diverted along the canal in a north eastern direction away from the

site. Figure 1.1 shows its location.

As noted above, the EA have recently completed detailed modelling of the Shobnall

Brook which shows that the site is outside of the 1 in 1000-year floodplain.

Tatenhill Brook & Unnamed Ordinary Watercourse

The Tatenhill Brook is 2.5km to the south west of the site, and is shown by the Burton

Tributaries Study to have an extensive floodplain – associated with it being tide locked

by water levels on the Trent during high flow events. Mapping shows this floodplain to

potentially interact with that of the UOW. The UOW flows along the southern boundary

of the site and enters a culvert beneath the Trent and Mersey Canal at the north

eastern corner of the site, immediately south of the existing attenuation feature.

In order to determine the flood risk to the development from the UOW and Tatenhill

Brook, a 1 Dimensional – 2 Dimensional (1D-2D) hydraulic flood model was created. This

was undertaken using the Flood Modeller Pro, ESTRY and TUFLOW software packages.

The model links the existing Environment Agency ESTRY-TUFLOW representation of the

Tatenhill Brook produced as part of the Burton Tributaries Study (2014) with a Flood

Modeller Pro – TUFLOW model of the UOW created by BWB (2015/16). This connection

was created using the TUFLOW multi-domain link.

The “Adapting to Climate Change: Guidance for Risk Management Authorities4”

document has been used to ascertain the potential impact of climate change on the

proposed development. The site is within the Humber river basin district and is a ‘less

4 Adapting to Climate Change: Advice for Flood and Coastal Erosion Risk Management Authorities (2016), Environment Agency.


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vulnerable’ development in Flood Zone 2. It is therefore required for river flows to use

the ‘central allowance’ for climate change. Given the expected lifespan of the

development is in excess of 50 years; a 20% uplift on the 1 in 100 year flows should be

used as the design standard scenario.

Results of subsequent modelling show that while the floodplain from the Tatenhill Brook

spills into the upstream catchment of the UOW, peak flows are not significantly

impacted, but the hydrograph is extended. Flood levels from key events are available

in Table 2.1, interrogation locations are illustrated within Figure 2.1.

Given that the formation plateau level is 46.85m AOD, and the 1 in 1000 flood level at

the upstream node is 46.02m AOD, there is 0.83m of freeboard to the ground level of

the site even in the most extreme event. A sensitivity scenario also undertaken where

the UOW culvert beneath the Trent & Mersey Canal was blocked by 50% shows that

flood flows remain in bank, and levels are 20mm higher than the 1 in 1000-year event.

Figure 2.1 – 1 in 100 year + 20% modelled Flood Depths (UOW)


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Table 2.2 – UOW Modelled Flood Levels

FMP Model

Node

Return Period (years)

20 100 100+20%

100

(50% Blockage of

D/S Culvert)

1000

ConsWC_9 46.24 46.36 46.43 46.39 46.60

ConsWC_8 46.24 46.36 46.43 46.39 46.61

ConsWC_7 46.23 46.36 46.43 46.39 46.61

ConsWC_6 45.92 45.96 45.99 46.07 46.05

ConsWC_5 45.90 45.94 45.97 46.07 46.02

ConsWC_4 45.88 45.92 45.95 46.06 46.01

ConsWC_3 45.86 45.90 45.94 46.05 46.00

ConsWC_2 45.83 45.89 45.92 46.05 45.98

Flood risk from the UOW and Tatenhill Brook is therefore thought to pose a low risk to

the site.

Flood Risk from Canals

The Trent and Mersey Canal runs directly adjacent to the south eastern boundary of

the site. The SFRA states that no problems have been observed on the Trent and Mersey

Canal and that locks regulate the water level through both fixed and manually

operated sluices and weirs. This maintains a freeboard of 300mm between normal

water level and top of bank.

The Canal and Rivers Trust were previously contacted in relation to the full planning

application for the site to provide any relevant information on the relevant section of

the Mersey and Trent Canal (see Appendix 4).

The Canal and Rivers Trust confirmed that:

(i) All water for this navigation is passed down through the locks from the River

Trent at Wychnor, Alrewas, located approximately 9km south of the site

location.

(ii) There are no feeders or uncontrolled discharges into this section of the

navigation.

(iii) They are not aware of any records of overtopping from this section of the

waterway. Generally this section of the canal is protected by a 300mm

freeboard.

With the provision of 300mm of freeboard, the risk from the canal to the development

is considered low.

There is a residual risk that the canal could spill into the site, where upon flood water

would be intercepted by the unnamed ordinary watercourse. This residual risk should

be considered within the developments mitigation strategy.


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Groundwater Flood Risk

The site is situated upon bedrock geology including the Bromsgrove Sandstone

Formation which is in turn overlain with the Mercia Mudstone Group. There are

superficial deposits recorded which include the Holme Pierrepont Sands and Gravels.

The Mercia Mudstone Group is classified by the Environment Agency as a Secondary B

aquifer. Secondary B aquifers are considered to be 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.

The sands and gravels overlaying the Mudstone are classified as a Secondary A aquifer

and are considered to be permeable layers capable of supporting water supplies at a

local rather than strategic scale, and in some cases forming an important source of

base flow to rivers.

There is a borehole log available via the BGS GeoIndex web app within proximity to

the site. The borehole log describes the geology to include; 15m of Sands and Gravel,

183m of Mercia Mudstone Group and 132m of the Bromsgrove Sandstone Formation

(base not proven). There is the potential for perched water to be present within the

sands and gravels which are likely to be in continuity with the watercourses. During

periods of high flows and intense rainfall water levels within the sands and gravels may

rise to pose a risk to underground structures or construction methods.

The risk from this source is considered to be medium and further mitigation measures

for the proposed development are outlined within Section 3.0.

Flood Risk from Reservoirs & Large Waterbodies

Reservoir failure flood risk mapping has been prepared by the Environment Agency,

this shows the largest area that might be flooded if a reservoir were to fail and release

the water it holds. The map displays a worst case scenario and is only intended as a

guide. An extract from the mapping is included as Figure 2.2.


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Figure 2.2 - Environment Agency Reservoir Failure Flood Risk Map

This data indicates that the site is located within the reservoir failure floodplain (as

indicated within Figure 2.2). The modelled flood extent relates to Blithfield reservoir

which is operated by South Staffordshire Water Plc.

Given the stringent controls and legislation on reservoirs the Environment Agency have

stated a flood to the extent shown is extremely unlikely. Reservoirs are also inspected

regularly insuring safety works are carried out. As such it is considered that the site is not

at significant flood risk from this source in spite of the mapping, especially considering

the ‘Less Vulnerable’ status of the proposed development.

The overall risk posed by the source is considered to be low.

Flood Risk from Sewers

There are no sewers within the site, however, the topographical survey (Appendix 2)

shows that there is a surface water sewer network within Callister Way which was

provided with the infrastructure to serve the wider site.


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It is understood that the sewers that have been provided in the wider infrastructure

have been sized appropriately and the residual risk of sewer flooding would therefore

be the result of an extreme rainfall event or blocked gullies. In this event flood flows

would be in a south easterly direction following the topography of the site. The diverted

watercourse would intercept these flows and therefore minimise disruption to users or

areas outside the site.

The overall risk posed from the sewer source is considered to be low.

Pluvial Flood Risk

Risk of flooding from surface water mapping has been prepared by the Environment

Agency, this shows the potential flooding which could occur when rainwater does not

drain away through the normal drainage systems or soak into the ground, but lies on or

flows over the ground instead. An extract from the mapping is included as Figure 2.3.

Figure 2.3 - Risk of Flooding from Surface Water Mapping


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The Environment Agency Surface Water flood maps show there to be a ‘low risk’

surface water flood route which runs through the site, as shown in Figure 2.3. There is

also an area of ‘medium risk’, where surface water may pond within the site. Though it

should be noted that this mapping exercise was undertaken prior to the enabling

earthworks. There is therefore unlikely to be any significant ponding on site, as it has

been flattened in preparation for the proposed development.

Hazard mapping of this low probability event shows that the majority of the surface

water flooding shown is low in nature, and could be managed using suitable mitigation

measures during construction of the development. Further mitigation measures are

recommended in Section 3.0.

Effect of Development on Wider Catchment

Displacement of Floodplain

There is no displacement of high risk fluvial floodplain. As the site lies within Flood Zone

2, there is a residual risk that there will be displacement of flood water in high

magnitude events. Under current NPPF guidelines there is no requirement to

compensate for that lost volume.

Development Drainage

The proposed development will have a modern standard of surface water drainage

which will ensure that no additional flow will be passed on to others within the

catchment.


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FLOOD RISK MITIGATION

Section 2.0 has identified the sources of flooding which could potentially pose a risk to

the site and the proposed development. This section of the FRA sets out the mitigation

measures which are to be incorporated within the proposed development to address

and reduce the risk of flooding to within acceptable levels.

General Mitigation

Temporary outfalls into the rivers during the construction phase will require discharge

consents from the LLFA. The discharge location points, the date when the discharge

will start, the duration of the discharge and the method of their installation will need to

be submitted. The flows from these outfalls would also need to be agreed.

Due to the location of the site within a Groundwater Source Protection Zone it will be

necessary during the construction for onsite refuelling facilities to take place in a

bunded area over an impermeable surface to prevent runoff and infiltration. Refuelling

activities should comply with the Environment Agency’s Pollution Prevention Guidance

by regular testing of the storage tanks and pipes. Any surface water runoff from these

areas will need to be routed through an oil separator before disposal.

There is the potential for groundwater to be encountered during construction. Where

significant groundwater is encountered within excavations alternative dewatering

system will need to be employed. The advice of a suitably experienced contractor

should be sought to determine the most viable option.

Finished Levels

Finished floor levels of the proposed warehouse are shown as 47.30m AOD. This provides

1.3m of freeboard above the UOW 1 in 1000-year flood level. This is also sufficient to

raise it nominally above 1 in 1000-year River Trent flood level. Drawings showing the

proposed development levels are available in Appendix 2.

The 47.3mAOD floor level is approximately 300mm above the downstream canal tow

path level. Therefore, should the canal spill into the site, it would overflow into the

downstream floodplain before it exceeded the floor levels.

The proposed finished level is 0.45m above the development plateau which will help

to mitigate and residual risk of ingress via pluvial runoff or groundwater. It is also

recommended to profile exterior ground levels away from the development towards

the closest drainage point.

Safe Access

Safe, dry pedestrian access to and from the proposed development can be provided

via the proposed access onto Callister Way on land outside the high risk floodplain of

watercourses in proximity to the site.


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Surface Water Drainage

To mitigate the development’s impact on the current runoff regime it is proposed to

incorporate surface water attenuation and storage as part of the development

proposals, discussed in detail within Section 4.0


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OUTLINE DRAINAGE ASSESSMENT

Outline Surface Water Assessment

This section of the report has been prepared in conjunction with THDA Consulting

Engineers, who have provided the strategy, including calculations and drawings, which

are available in Appendix 5.

Existing Site Runoff

Previously the wider site (including this application area) gained consent to discharge

at a rate of 86.8l/s that was based upon a site area of 9.93ha. This application concerns

a smaller portion of that wider site (1.9ha) therefore, the consented discharge rate for

this plot is worked out as 17l/s. (MicroDrainage calculation available within Appendix

5).

Drainage Hierarchy

Although infiltration testing has not been undertaken it is not thought soakaways are

viable due to ground water levels on the site.

Proposed Site Runoff

It is intended that the site runoff is limited to discharge at 17l/s in all events up to and

including the 1 in 100 + 30% allowance for climate change.

The vast majority of surface water will be routed through the existing pond to the south

west of the site, which was constructed for this purpose under a previous application.

It is proposed discharge will be limited using an orifice control.

The site has been split into several drainage catchments, with the parking area to the

north draining to one discharge point in the attenuation pond with an appropriately

sized oil separator. The HGV parking loading area and siphonic drainage system from

the warehouse roof drain to an alternative piped connection to the attenuation basin.

Again, an appropriately sized oil separator will be used to prevent pollution entering

the basin from the yard.

The proposed access road has been identified as a separate catchment, which

discharges via a drainage ditch towards the UOW, details of which can be seen in the

strategy drawing.

Detailed MicroDrainage simulations have been carried out and are available in

Appendix 5.

Exceedance Events

Exceedance events should be designed to route towards the attenuation basin or

UOW.


AUGUST 2016


17

CONCLUSIONS AND RECOMMENDATIONS

This Flood Risk Assessment (FRA) is compliant with the requirements set out in the

National Planning Policy Framework (NPPF) and the associated Planning Practice

Guidance. The FRA has been produced on behalf of Goodman International Ltd. in

respect of a planning application for the Phase 2, Centrum West, Burton-upon-Trent.

This report demonstrates that the proposed development is at an acceptable level of

flood risk, subject to the recommended flood mitigation strategies being implemented.

The identified risks and mitigation measures are summarised within Table 5.1:

Table 5.1 - Summary of Flood Risk Assessment

Flood Source Proposed Mitigation Measures

Fluvial

Development finished floor levels and thresholds are set above the 1 in 1000

year flood level for all watercourses that are shown to have a potential

impact on the site.

Groundwater Any residual flood risk from groundwater sources will be mitigated by raising

the development above surrounding ground levels. Detailed mitigation

maybe required during construction, as outlined in Section 3.0 of this report. Canals

Sewers The risk of the external sewer capacity being exceeded and any residual risk

of pluvial runoff affecting the site will be mitigated through creation of a flow

route through the site into the attenuation pond and positively drained areas Pluvial runoff

Impact of the

Development

The proposed drainage network on the site will not increase surface water

discharge from the site.

This summary should be read in conjunction with BWB’s full report. It reflects an assessment of

the Site based on information received by BWB at the time of production.

In compliance with the requirements of National Planning Policy Framework, and

subject to the mitigation measures proposed, the development could 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 1

Topographical Survey

Enabling Earthworks Drawings &

Diverted Watercourse Alignments

P/2015/00891Received 16/06/2015

47.1

0

46.2

7

So

46.66

46.65

46.03

47.11

47.20

45.95

45.9

8 46.8

446

.87

46.1

2

46.1

8

46.8

646

.80

45.9

1

47.00

47.02

46.8

847

.05

45.3

345

.37

45.23 45.3

5

45.80 45

.91

45.77

45.89

45.99

45.97

46.00

46.63

46.0

045

.86

Head

wall

Grass

Post and rai

l fence h

t 1.2m

LOW FLOW/ BASE

FLOW CHANNEL

0.3m DEEP

PROPOSED BACKWATER

0.5m DEEP

ROCK ARMOR

EROSION

PROTECTION

B

B

Trent and Mersey Canal

46.18

46.80

45.9146.01

46.9646.93

46.11 45.90

46.83

46.81

46.22 46.75

47.0546.91

46.1146.38

46.8047.26

46.99 47.15

47.7446.93

46.6946.75

47.67

47.68

46.97 47.12

47.79

47.64

46.73

45.9945.94

46.00 45.97

46.50 46.94 47.12 47.00

46.93

46.81

46.64

Pillar

Raised pipe

PROPOSED

RIFFLE

PROPOSED

ONLINE POOL

0.8m DEEP

2.5m WIDE

FLOOD FLOW

BED

A

A

C

C

I

I

I

I

50.00m

47.12

47.79

47.64

46.73 46.34

47.39

47.62

47.0947.00

47.36

47.05

46.4646.37

47.29

47.44

46.9946.98

47.38

47.11

46.40

46.9347.07

46.47 47.03

46.95

46.7846.80

46.85

46.6246.81

46.64Grass

1:3 EMBANKMENTS

1:3 EMBANKMENTS

4

5

.

2

9

3

D

D

O

rd

in

a

ry

B

ro

o

k

WL

46.9146.26

46.88

So

47.22

47.34

46.77

46.83

47.35

47.57

46.40

46.39

46.79

46.71

46.9146.96

46.36

46.31

46.93

47.1047.06

46.29

45.79

46.49

46.77

46.51

46.56

46.6446.74 46.88

45.37

46.73

46.38

46.5346.55 46.71

47.10

46.75

46.79

46.91

46.9045.34

45.11

45.3645.17 44.95

46.58

Headwall

Grass

Grass

BWB846.905

BWB946.750

EXISTING BED TO

BE DE-SILTED

REDUNDANT WATER COURSE

CHANNEL TO BE BACKFILL

AFTER DIVERSION IS

COMPLETE

NOTES

1. DO NOT SCALE THIS DRAWING. ALL DIMENSIONS MUST BE

CHECKED/ VERIFIED ON SITE. IF IN DOUBT ASK.

2. THIS DRAWING IS TO BE READ IN CONJUNCTION WITH ALL

RELEVANT ARCHITECTS, ENGINEERS AND SPECIALISTS

DRAWINGS AND SPECIFICATIONS.

3. ALL DIMENSIONS IN MILLIMETRES UNLESS NOTED

OTHERWISE. ALL LEVELS IN METRES UNLESS NOTED

OTHERWISE.

4. ANY DISCREPANCIES NOTED ON SITE ARE TO BE REPORTED

TO THE ENGINEER IMMEDIATELY.

5. EXCAVATED MATERIAL TO BACKFILL EXISTING CHANNEL

AFTER THE WATER VOLE HABITAT TO WHERE THE NEW

CHANNEL DISCHARGES.

KEY

c Copyright BWB Consulting Ltd

Drawing No. Revision

Drawing Status

Size

Drawing Title

Project Title

Scale

Reviewed

Drawn

A1

ISSUES & REVISIONS

Rev Date Details of issue / revision RevDrw

Client

Birmingham | 0121 233 3322

Leeds | 0113 233 8000

London | 020 7234 9122

Manchester | 0161 233 4260

Nottingham | 0115 924 1100


Birmingham | 0121 233 3322

Leeds | 0113 233 8000

London | 020 7234 9122

Manchester | 0161 233 4260

Nottingham | 0115 924 1100


Birmingham | 0121 233 3322

Leeds | 0113 233 8000

London | 020 7234 9122

Manchester | 0161 233 4260

Nottingham | 0115 924 1100


Birmingham | 0121 233 3322

Leeds | 0113 233 8000

London | 020 7234 9122

Manchester | 0161 233 4260

Nottingham | 0115 924 1100


Birmingham | 0121 233 3322

Leeds | 0113 233 8000

London | 020 7234 9122

Manchester | 0161 233 4260

Nottingham | 0115 924 1100


Birmingham | 0121 233 3322

Leeds | 0113 233 8000

London | 020 7234 9122

Manchester | 0161 233 4260

Nottingham | 0115 924 1100


Birmingham | 0121 233 3322

Leeds | 0113 233 8000

London | 020 7234 9122

Manchester | 0161 233 4260

Nottingham | 0115 924 1100


Birmingham | 0121 233 3322

Leeds | 0113 233 8000

London | 020 7234 9122

Manchester | 0161 233 4260

Nottingham | 0115 924 1100


P4BMW/2155/W100

PRELIMINARY

G. Littlewood

R. Green

1:200

WATERCOURSE

DIVERSION GENERAL

ARRANGEMENT

CENTRUM WEST

ENABLING WORKS

50m LONG CULVERT 750mm Ø

ALTHON H10_C_A HEADWALL WITH TRASH

SCREENS OR APPROVED EQUIVALENT

PIPE CONNECTI0N 450mm Ø CAPPED (PROPOSED OUTFALL FROM DEVELOPMENT

ALTHON H6C A HEADWALL WITH ALTHON HDPE 500mm

FLAP VALVE (580 X 610mm) OR APPROVED EQUIVALENT

TYPICAL CROSS SECTION WITH LOW FLOW

CHANNEL AND "BACK WATER"

100 YEAR PLUS CLIMATE

CHANGE FLOOD LEVEL.

NORMAL WATER LEVEL

(BASE FLOW)

PROPOSED GROUND PROFILE

NOT STEEPER THAN 1 IN 3



0.40

0.3

TYPICAL CROSS SECTION WITH LOW FLOW

CHANNEL

NORMAL WATER LEVEL

(BASE FLOW)


CHANGE FLOOD LEVEL.





EXISTING

BOUNDARY

FENCE LINE

0.3


CHANGE FLOOD LEVEL.

NORMAL WATER LEVEL

(BASE FLOW)

TYPICAL CROSS SECTION OF RIFFLE





EXISTING

BOUNDARY

FENCE LINE


CHANGE FLOOD LEVEL.

NORMAL WATER LEVEL

(BASE FLOW)

TYPICAL CROSS SECTION OF ON-LINE

POOL





EXISTING

BOUNDARY

FENCE LINE

0.8

1.3

2.2

2.0

0.75

0.6

1.5

PIPE 750mm ø

PRECAST HEADWALL WITH

TRASHCREEN (ALTHON H10 _C_A)

PIPE

SURROUNDS

TRASH

SCREEN

Note:

Where pipework is located

under footpaths, verges and

other non-trafficked areas,

backfill material to be

agreed on site. Use of

struck material subject to

Engineer and Local

Authority approval.

Min. Trench Widths Vary According

To Pipe Dia. See Table Opposite.

Pipe Dia.

Varies See

Plan.

Note:

Applicable where pipework has more than

1200mm cover under trafficked areas or more

than 600mm under non-trafficked areas.

DOT Type 1 granular

backfill laid and compacted

in 150mm max. layers.

External Works construction

10mm dia. nom size

Pea gravel bedding

and surround.

Pipe Bedding Detail Type S

100

100

min.

min.

Min. Trench Widths Vary According

To Pipe Dia. See Table Opposite.

Min. Trench

Width (mm)

Pipe Dia. (mm)

Mass concrete encasement to be interrupted over

it's entire cross section @ each pipe joint using

'Korkpak' filler board by 'Servicised' or similar

approved.

Note:

No Mechanical compaction

techniques to be used within 300mm

of the crown of all pipework.

See Structural Engineers details for

pipework laid under buildings /

through foundations etc.

Pipe Bedding Detail Type A

Note:

Applicable where pipework has less than

1200mm cover under trafficked areas or less

than 600mm under non-trafficked areas.

150

150

Pipe Dia.

Varies See

Plan.

min.

min.

Grade ST4 mass concrete bed

and surround, 150mm thk min.

20mm nom. aggregate size.

DOT Type 1 granular

backfill laid and compacted

in 150mm max. layers.

External Works construction

Over 1200 Pipe Dia. + 1000

1050

1200

975

900

825

750

675

600

2300

2300

2000

1900

1600

1500

1450

1350

525

450

300

375

100

150

225

1200

1150

750

1050

550

600

700

Trench Widths:

Note:

Where pipework is located

under footpaths, verges and

other non-trafficked areas,

backfill material to be

agreed on site. Use of

struck material subject to

Engineer and Local

Authority approval.

NOTES

1. DO NOT SCALE THIS DRAWING. ALL DIMENSIONS MUST BE

CHECKED/ VERIFIED ON SITE. IF IN DOUBT ASK.

2. THIS DRAWING IS TO BE READ IN CONJUNCTION WITH ALL

RELEVANT ARCHITECTS, ENGINEERS AND SPECIALISTS

DRAWINGS AND SPECIFICATIONS.

3. ALL DIMENSIONS IN MILLIMETRES UNLESS NOTED

OTHERWISE. ALL LEVELS IN METRES UNLESS NOTED

OTHERWISE.

4. ANY DISCREPANCIES NOTED ON SITE ARE TO BE REPORTED

TO THE ENGINEER IMMEDIATELY.

c Copyright BWB Consulting Ltd

Drawing No. Revision

Drawing Status

Size

Drawing Title

Project Title

Scale

Reviewed

Drawn

A1

ISSUES & REVISIONS

Rev Date Details of issue / revision RevDrw

Client

Birmingham | 0121 233 3322

Leeds | 0113 233 8000

London | 020 7234 9122

Manchester | 0161 233 4260

Nottingham | 0115 924 1100


Birmingham | 0121 233 3322

Leeds | 0113 233 8000

London | 020 7234 9122

Manchester | 0161 233 4260

Nottingham | 0115 924 1100


Birmingham | 0121 233 3322

Leeds | 0113 233 8000

London | 020 7234 9122

Manchester | 0161 233 4260

Nottingham | 0115 924 1100


Birmingham | 0121 233 3322

Leeds | 0113 233 8000

London | 020 7234 9122

Manchester | 0161 233 4260

Nottingham | 0115 924 1100


Birmingham | 0121 233 3322

Leeds | 0113 233 8000

London | 020 7234 9122

Manchester | 0161 233 4260

Nottingham | 0115 924 1100


Birmingham | 0121 233 3322

Leeds | 0113 233 8000

London | 020 7234 9122

Manchester | 0161 233 4260

Nottingham | 0115 924 1100


Birmingham | 0121 233 3322

Leeds | 0113 233 8000

London | 020 7234 9122

Manchester | 0161 233 4260

Nottingham | 0115 924 1100


Birmingham | 0121 233 3322

Leeds | 0113 233 8000

London | 020 7234 9122

Manchester | 0161 233 4260

Nottingham | 0115 924 1100


P2BMW/2155/W101

PRELIMINARY

A. Clifford

1:25

WATERCOURSE

DIVERSION TYPICAL

CROSS SECTION

CENTRUM WEST

ENABLING WORKS

REFER TO DRAWING

BMW/2155/W100 GENERAL

ARRANGEMENT FOR

SECTION LOCATIONS

HEADWALL ELEVATION SECTION HEADWALL CONSTRUCTION DETAIL

PIPE SURROUND DETAILS

flood risk assessment template - east staffordshire application...table 5.1 - summary of flood risk...

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