flood risk assessment hawkins lane, burton on trent

Flood Risk Assessment

Hawkins Lane, Burton on Trent Tesco Stores Ltd

10-Jul-14

lisa.roberts

Text Box

P/2014/01128 Received 27/08/14

Pinnacle Consulting Engineers Limited Flood Risk Assessment – Rev C 131016 -2- Hawkins Lane, Burton

Issue and Revision Record

Rev Date Changes Originator Checker Approver

- 13.09.2010 N/A RK BS NK

A 08.12.2010

Amended to suit new layout

GB CJ NK

B 10.04.2014

Amended to suit new layout

BF NH KE

C 10.07.2014 Executive summary amended

NR KE KE

This document has been prepared by Pinnacle Consulting Engineers Ltd. for the titled project and should not be relied upon or used for any other project. Pinnacle Consulting Engineers Ltd accepts no responsibility or liability for the consequences of this document being used for any purpose other than the purpose for which it was commissioned. Any person using or relying on the document for such other purpose agrees, and will by such use or reliance be taken to confirm his agreement to indemnify Pinnacle Consulting Engineers Ltd for all loss or resultant damage. Pinnacle Consulting Engineers Ltd accepts no responsibility or liability for this document to any party other than the person by whom it was commissioned.


Report Contents

1 EXECUTIVE SUMMARY ................................................................................................................... 4

2 INTRODUCTION ............................................................................................................................. 5

2.1 General .............................................................................................................................................. 5

2.2 Sources of Information ...................................................................................................................... 5

2.3 Existing Site ........................................................................................................................................ 6

2.4 Proposed Development ..................................................................................................................... 7

2.5 Existing and Future Flood Defence .................................................................................................... 8

2.6 Historic Floods ................................................................................................................................... 9

3 FLOOD RISK UNDER EXISTING CONDITIONS ................................................................................. 10

3.1 Policy Basis ...................................................................................................................................... 10

3.2 Flood Zone ....................................................................................................................................... 10

3.3 Flood Sources and Pathways ........................................................................................................... 12

3.4 Risk from Fluvial Sources ................................................................................................................. 13

3.5 Surface Water / Sewer Flooding ...................................................................................................... 17

3.6 Flooding from Groundwater Sources .............................................................................................. 17

3.6.1 Geological ground conditions .......................................................................................................... 17

3.6.2 Source Protection Zone ................................................................................................................... 19

3.6.3 Potentials for SUDS .......................................................................................................................... 19

3.6.4 Soakage tests ................................................................................................................................... 19

3.6.5 Flooding from Groundwater ............................................................................................................ 20

3.7 Flooding from other Sources ........................................................................................................... 20

3.7.1 Flood risk posed by the Trent and Mersey canal ............................................................................. 20

3.8 Climate Change ................................................................................................................................ 20

3.9 Residual Risk .................................................................................................................................... 21

4 FLOOD RISK FOR THE PROPOSED DEVELOPMENT ........................................................................ 22

4.1 Policy Basis ...................................................................................................................................... 22

5 FLOOD RISK MANAGEMENT STRATEGY ....................................................................................... 25

5.1 On-Site Flood Risk ............................................................................................................................ 25

5.3 Surface Water Drainage Strategy .................................................................................................... 25

6 SUSTAINABLE DRAINAGE SYSTEMS (SUDS) .................................................................................. 27

7 CONCLUSIONS ............................................................................................................................. 28

APPENDIX A ........................................................................................................................................... 29

APPENDIX B............................................................................................................................................ 30

APPENDIX C ............................................................................................................................................ 31

APPENDIX D ........................................................................................................................................... 32

APPENDIX E ............................................................................................................................................ 33

APPENDIX F ............................................................................................................................................ 34

APPENDIX G ........................................................................................................................................... 35

APPENDIX H ........................................................................................................................................... 36

APPENDIX I ............................................................................................................................................. 37

APPENDIX J ............................................................................................................................................ 38


1 Executive Summary

Pinnacle Consulting Engineers Ltd have been commissioned by Tesco Stores Ltd to carry out a Flood

Risk Assessment report (FRA) for a proposed new food retail store at the site referred to as Tesco

store at Business Park, Hawkins Lane, Burton upon Trent in the Borough of East Staffordshire (see

Appendix A for an existing site location plan).

The FRA has been undertaken with direct reference to, and/or compliance with, a number of

documents including: (i) NPPF: Development and Flood Risk, (ii) a Strategic Flood Risk Assessment

(SFRA) prepared by Royal Haskoning UK Ltd on behalf of East Staffordshire Borough Council and (iii)

guidance from CIRIA C697: The SUDS Manual.

It is stated in NPPF that the developer is responsible for providing a FRA. This FRA report is a site-

specific study and compiles all the necessary data and information to demonstrate the objectives

specifically laid down in NPPF and CIRIA C697 SUDS Manual, as well as other statutory laws, local

bylaws and rules.

There is no particular way to compile FRA reports but the main focus is to identify risks and

mitigate their impacts. The report presents a detailed source-pathways-receptor study of flood risk

from all sources to the site and identifies that the site may be at risk from flooding from fluvial

source, in the event of existing flood defence breaching, and pluvial source. Finished Floor Levels

have been agreed with the Environment Agency to ensure the store remains dry during extreme

events. A Flood Evacuation Plan detailing contingency measures has also been prepared to maximise

the safety of staff and customers during a major flood event.

The site was not considered viable for source control, as the site is located above minor aquifer and

alternative SUDS measures were considered. Surface water discharge rates will however be reduced

to greenfield rate, by means of permeable paving and underground storage.

This FRA has been prepared in accordance with NPPF, which also requires that the FRA be prepared

by competent people. Pinnacle Consulting Engineers Ltd are specialists in flood studies with a track

record of several hundred successful FRA reports and assessments.


2 Introduction

2.1 General

It is stated in NPPF that the developer is responsible for providing a FRA, demonstrating:

whether any proposed development is likely to be affected by current or future flooding

from any source;

satisfying the LPA that the development is safe and where possible reduces flood risk

overall;

whether it will increase flood risk elsewhere; and

the measures proposed to deal with these effects and risks. Any necessary flood risk

management measures should be sufficiently funded to ensure that the site can be

developed and occupied safely throughout its proposed lifetime.

As part of the FRA report, NPPF further requires:

designs which reduce flood risk to the development and elsewhere, by incorporating

sustainable drainage systems and where necessary, flood resilience measures; and

the identification of opportunities to reduce flood risk, enhance biodiversity and amenity,

protect the historic environment and seek collective solutions to managing flood risk.

This FRA report is prepared as per NPPF requirements, stating that “Planning applications for

development proposals of 1 hectare or greater in Flood Zone 1 and all proposals for new

development located in Flood Zones 2 and 3 should be accompanied by a FRA.”

2.2 Sources of Information

This report is compiled by deriving data/information from various sources including:

The Environment Agency’s published information, e.g. Flood Zones and groundwater

Source Protection Maps.

Information published by local planning authorities, such as SFRA

An EnviroCheck report

Various studies carried out specifically for the project, e.g. Geotechnical Ground

Investigations, Engineering Site Assessment and Ecological Site Briefing

Studies commissioned for this FRA, e.g. the CCTV drainage survey

Enquiries made to a number of authorities to understand possible risk of flooding in the area


Specific design works undertaken for the FRA report

2.3 Existing Site

The existing site is approximately 38,009m² and is located at Hawkins Lane, Burton-upon-Trent,

East Staffordshire. The National Grid Reference is 424850, 323850 and this site is bounded by

Network Rail to the north, Hawkins Lane to the south, Horninglow Street to the west and a Business

Park to the east (see Appendices A and B for a site location plan and existing site plan).

The main access to the site is via Hawkins Lane.

Figure 2.1 Aerial View of the Proposed Tesco Store Site

The site has a history of industrial use, having housed several buildings since the end of the 19th

Century, including Union workhouse buildings, railway lines and sidings. These buildings were

recently demolished and the site has been derelict since 2009.

The western boundary is partly formed by a multi-span masonry arched bridge which carries the

Horninglow Street over the railway. The site appears flat and level and at grade with the access

from Hawkins Lane to the south, where ground levels are approximately 44.5m AOD. The majority

of the site is at an elevation of approximately 45.5m AOD but there are some areas of higher ground

(see the topographical survey in Appendix C).


Figure 2.2a Overview of the Site from Horninglow Street

2.4 Proposed Development

As shown in Appendix E and depicted in Figure 2.3, the overall site area is 38,009m² and the

proposed redevelopment comprises:

The construction of a Tesco store and associated service yard in the northern part of the

site

The construction of a non-food retail unit and a hot food restaurant takeaway unit

Car parking to the south of the site

A 6-island Petrol Filling Station unit along the southern boundary of the car park


Figure 2.3 Proposed Developments at Tesco Store

The total site area for proposed redevelopment 38,009m², of which 3,562m² is pervious (approx.

10%) and the remaining 34,447m² is impervious (approx. 90%) (Appendix E). Therefore the

impervious area will increase significantly and shall increase surface water runoff compared to

existing conditions.

2.5 Existing and Future Flood Defence

Burton is protected by flood defences depicted in Figure 3.1, which have been implemented through

a series of alleviation schemes since the 1960s. The initial scheme was developed in response to the

1947 floods. These floods alleviation schemes were observed to operate effectively during the

November 2000flood event, although water did seep through weakness in the structures. With the

exception of a short stretch adjacent to the Meadowside Centre, the defences throughout Burton

have now been brought up to the 1 in 200 year standard and the last major improvement works

were carried out in 2006-2007. The Environment Agency has the responsibility for inspection and

routine maintenance of the formal defences.


2.6 Historic Floods

The River Trent flows in an easterly direction, forming the South Eastern boundary of the Borough,

and passes through the town of Burton upon Trent. It carries extreme flows of approximately

468m³sˉ¹ through Burton in a 1 in 100 year event. Burton has suffered on numerous occasions from

fluvial flooding both as a result of rainfall and snowmelt. Due to the location of Burton, moderately

high up in the catchment, there is a relatively quick response time between rainfall and the rise in

river levels. This makes flood forecasting problematic and reduces the viability of temporary and

demountable defences through the town. Following floods in 1947, defences were built through

Burton town centre to a 1 in 100 year standard. Table 2.1 shows the maximum water levels reached

during the various historic events at various locations illustrated by a map, both of which were

purchased from the Environment Agency. The maximum level reached was 45.35 AOD.

2.7 Site History

The site has a history of pervious uses, ranging from a work-house in the late 1800s, an ale store

and timber yard with associated rail sidings, to a barrel works which operated from the 1970s and

has been the most recent use. The barrel works employed processes such as degreasing, acid

pickling and alochrome coating in the refurbishment of beer barrels. The site has also recently been

used for the manufacture of scaffolding products. The area surrounding the site has a similarly

industrial heritage. A small number of residential properties are present at the southeast and

southwest site boundaries but the majority of the surrounding area is under light industrial or

commercial usage.


3 Flood Risk under Existing Conditions

3.1 Policy Basis

The assessment of flood risk in this report is based on the definitions in NPPF, which recognises the

following Flood Zones:

Flood zone 1 – little or no risk, with annual probability of flooding from rivers and the sea of

less than 0.1% (1 in 1000-year)

Flood Zone 2 – low to medium risk, with annual probability of flooding of 0.1% to 1.0% from

rivers and 0.1% to 0.5% from the sea

Flood Zone 3 – high risk of flooding with an annual probability of flooding of 1.0% or greater

from rivers, and 0.5% or greater from the sea.

3.2 Flood Zones

The most recent Flood Zone map by the Environment Agency purchased in July 2010 is reproduced

in Figure 3.1a, which shows that the majority of the site is classified as an Area Benefiting from

Defences (ABD) to the 1:200 year standard, although there is an area to the north-west, which is in

Flood Zone 2.


Figure 3.1 EA Flood Zone Map

Table 3.1 reproduces the requirements of NPPF for these Flood Zones and policy aims. However,

this table is not specific regarding the requirements for Areas Benefiting from Defences.

NPPF Flood Zones

Zone 2 Medium Probability Land assessed as having between a 1 in 100 and 1 in 1000 annual probability of river flooding (1% – 0.1%) or between a 1 in 200 and 1 in 1000 annual probability of sea flooding (0.5% – 0.1%) in any year.

Appropriate uses The water-compatible, less vulnerable and more vulnerable uses of land and essential infrastructure in Table 4.1 are appropriate in this zone. Subject to the Sequential Test being applied, the highly vulnerable uses in Table 4.2 are only appropriate in this zone if the Exception Test is passed.

FRA requirements All development proposals in this zone should be accompanied by a FRA.

Policy aims In this zone, developers and local authorities should seek opportunities to reduce the overall level of flood risk in the area through the layout and form of the development, and the appropriate application of sustainable drainage techniques.


Land assessed as having a 1 in 100 or greater annual probability of river flooding (>1%) or a 1 in 200 or greater annual probability of flooding from the sea (>0.5%) in any year.

Appropriate uses The water-compatible and less vulnerable uses of land in Table 3.3 are appropriate in this zone. The highly vulnerable uses in Table 3.3 should not be permitted in this zone. The more vulnerable and essential infrastructure uses in Table 3.3 should only be permitted in this zone if the Exception Test is passed. FRA requirements All development proposals in this zone should be accompanied by a FRA. Policy aims In this zone, developers and local authorities should seek opportunities to: reduce the overall level of flood risk in the area through the layout

and form of the development and the appropriate application of sustainable drainage techniques

relocate existing development to land in zones with a lower probability of flooding

create space for flooding to occur by restoring functional floodplain and flood flow pathways and by identifying, allocating and safeguarding open space for flood storage.

3.3 Flood Sources and Pathways

This Flood Risk Assessment considers all possible flooding sources and pathways and Table 3.2 below

shows the sources that are normally found in the UK and assesses if they are expected to pose risk

to the proposed site.

Table 3.2 Expected Risk from Possible Flooding Sources

These sources of flooding will be investigated in light of information provided by the SFRA, which

identifies the following possible causes of flooding within East Staffordshire:

Overflow of the River Trent and existing flood defences;

Breaching of flood defences (including flood storage areas);

Flood Sources Risk to Site Further comments

Tidal/Coastal None Remote from tidal reaches

Fluvial Medium The area is benefiting from defences

Urban Drainage Low No specific information is available

Groundwater Low An anecdotal evidence but not on the site

Overland Flow Low No specific information is available

Infrastructure Failure

Reservoir failure As discussed in the report

Artificial Drainage Low Risks from a Canal is discussed


Localised surface water flooding (including sewer flooding and highway drainage flooding);

Manmade waterways such as reservoirs and canals; and

Groundwater flooding.

3.4 Risk from Fluvial Sources

The main body of water near the site is the River Trent. It rises at Staffordshire hills near Stoke-on-

Trent and grows larger as it flows through Burton-upon-Trent, where it becomes navigable. The

history of flooding in the river goes back centuries both as a result of rainfall and snowmelt and

according to the information purchased from the Environment Agency, the site was flooded in

October 1875. This information includes the locations of flood defence walls, as shown in Figure 3.2

and Table 3.3 and the water level that may be reached during design events of various return

periods. According to the SFRA, the Environment Agency upgraded certain sections of the defences,

upgrading the flood protection standard from a 1 in 100year standard to a 1 in 200 year standard.

This confirms the modelling results in Figure 3.1 which indicate that the site is protected against

flood risks to a 1 in 200 year standard.


Table 3.3 Information Product 3, as Purchased from the Environment Agency

Figure 3.2 Flood Defences


Table 3.3 shows that the maximum water level in the River Trent would reach 46.1m AOD but the

defences are largely around 46m AOD. As the site is someway away from the river, it is likely to

remain safe during extreme events. However, Defences 1 and 7 have been identified to be in poor

conditions and therefore susceptible to breaches and thus the risk of breach is not ruled out.

The results of the breach analysis carried out for the SFRA are outlined here in relevance to the

site, E47, which was carried out by the SFRA using best practice guidance not be repeated here.

The results for hazard rating are shown in Table 3.4a and Figure 3.3.

Table 3.4a Flood Hazard Rating

Figure 3.3 Distribution of Flood Hazard Triggered by Breaching


Based on Figure 3.3 and Table 3.4a, the flood hazard at the site in terms of depth of water is

significant and therefore procedures, such as a Flood Evacuation Plan, are needed to be put in place

to manage this risk. This requires a better understanding of the hazard and the information

available on the time of arrival of the breached floodwater to the site. These are given in Table

3.4b and the assessment of access to the site is given in Table 3.4c.

Table 3.4b Flood Hazard Rating – Time to Onset

Table 3.4c Flood Hazard Rating – Availability of Access

The tabular results presented above show that there is only half hour before floodwater from

breaching reaches the site. This does not seem to be high but in reality breaches initially show

certain tell-tale signs and this triggers heightened activities, such as implementing temporary

defence repair works and if these fail, temporary defence works may be implemented to avert the

impacts of a full breach. Knowledge of a possible breach is available significantly in advance of an

actual event and this provides an ample period to implement Flood Evacuation Plans. The modelling

results reflected in Table 3.4c shows that the access to the site remains available, should it be

exposed to such a risk. For extreme events of 1 in 1000 years, no specific contingency measures are

recommended, as it is believed that the Flood Evacuation Plan could still be implemented under

such extreme events and can remain effective during such an event.


The SFRA report notes that due to the relative location of Burton being moderately high up in the

catchment, the response time between rainfall and the rise in river levels can be quick, making

flood forecasting problematic and reducing the viability of temporary and demountable defences

through the town. However, it is probably due to the recognition of this factor that the Environment

Agency is providing a standard of protection of 1 in 200 years rather than the usual 1 in 100 year.

3.5 Surface Water / Sewer Flooding

The SFRA presents information on the past sewer flooding and areas at potential risk in Burton upon

Trent, following consultation with Severn Trent Water based on DG5 records (which captures

reported incidents of sewer flooding and reports them to the Ofwat). Full information was withheld

due to the Data Protection Act but indicative maps were published in the SFRA, showing that the

scale of sewer / surface flooding to be localised. No specific information on flood risk from surface

water and sewer sources has been identified and therefore it is assumed that these are not

significant.

3.6 Flooding from groundwater sources

Groundwater and geological formations related to the site can potentially: (i) act as a source of

flooding, exposing the site to flood risk and (ii) accommodate source control methods through

surface water management to reduce flooding risks both within the site and elsewhere by reducing

runoff.

3.6.1 Geological ground conditions

Geological conditions at the site are detailed in Appendix H, which are based on a British Geological

Survey (BGS) report. The focus is on Made Ground, Drift Geology and Solid geology and these are

outlined in Table 3.5 and depicted in Figure 3.4. This evidence demonstrates that the site is

situated in an environmentally sensitive location, underlain by sand and gravel deposits associated

with the River Trent. As discussed below, groundwater within the sand and gravel deposits is

classified by the Environment Agency as a Minor Aquifer. The water table is between 1.5m and 3.0m

below ground level. A number of wells used to abstract groundwater from the Minor Aquifer are

situated to the South West of the site. The River Trent, which is in hydraulic continuity with the

Minor Aquifer, is situated the east of the site. Due to the relatively shallow water and sensitivity of

the underlying Aquifer, infiltration methods of surface water disposal are not considered viable.


Table 3.5 Site Geology

Figure 3.4 Geological Long Section of the Formation in the Vicinity of the Site

Formation Description

Artificial round (Made Ground)

Artificial Ground of unknown thickness and composition is likely to be

present across the site.

Superficial Deposits (Drift Deposits)

The site is underlain by the Holme Pierrepont Sand and Gravel Member (1st river terrace of the River Trent) of the Trent Valley Formation.

The deposit comprises fine to medium grained sand and gravel with occasional cobbles. The cobbles are mainly of ‘Bunter’ quartzite,

although other lithologies are present - all derived from the local

occurrences of glacial till. The thickness of the Member beneath the site is unknown but sand and gravel is proven to at least 6m in a

nearby borehole. A 1m thick peat deposit has been recorded 80m to the south east and this, or similar deposits, could also be present

beneath the site. Peat is a highly compressible material with a very high moisture content, presenting engineering ground hazards.

Rockhead

Depth

The depth to rockhead is estimated to be 5-10m and may vary across

the site.

Bedrock

The bedrock is the Triassic, Edwalton Member (of the Sidmouth Mudstone Formation, Mercia Mudstone Group). The sequence

comprises mainly red-brown to dark-red mudstone and silty mudstone with subordinate bands (skerries) of pale greenish grey siltstone and

sandstone.

The maximum thickness is around 400m in the centre of the Needwood Basin, though the thickness here, at the edge of the

feature is likely to be somewhat less. 500m east of the site, the bedrock sequence is faulted.


3.6.2 Source Protection Zone

The Source Protection Zone map of the Environment Agency identifies possible aquifers within the

site and its vicinity. Figure 3.5a shows that the site is located within the catchment of Groundwater

Source Protection Zone 3. From 1 April 2010 the Environment Agency requires compliance with their

Groundwater Protection Policy using aquifer designations that are consistent with the Water

Framework Directive. The Aquifer maps for superficial deposits and bedrock and published by the

Environment Agency collectively confirm the aquifer sensitivity of the site. This signifies that the

use of infiltration drainage systems is unlikely to be acceptable.

Figure 3.5a EA Groundwater Source Protection Zone Map

3.6.3 Potentials for SUDS

The provision of SUDS is an East Staffordshire Borough Council Policy and is the first method of

disposal to be considered for surface water runoff. However, Infiltration methods of source control

are not considered feasible at this site due to restrictions stemming from the protection of

groundwater aquifer resources and a relatively shallow ground water table.

3.6.4 Soakage tests

As the site is not considered viable for infiltration, no soakage tests have been commissioned.


3.6.5 Flooding From Groundwater

The SFRA report includes references to the Environment Agency’s groundwater team but has very

few reported incidences of groundwater flooding within East Staffordshire. The only events that

have occurred were a result of the cessation of the quarrying of gravel and sand in the area and

thus the abstraction of water from the pits. Once the abstraction operations ceased, groundwater

levels rose and filled some of the pits, hence the existence of the Branston Water Park on the right

banks of the River Trent before entering Burton upon Trent. As a result of this, there has been one

report regarding the occurrence of minor cellar flooding.

3.7 Flooding from Other Sources

3.7.1 Flood risk posed by the Trent and Mersey Canal

The Trent and Mersey Canal is as a body of water with hydraulic connectivity to the River Trent but

will not pose flooding risk to the site of the proposed development. This is because in the vicinity of

the site, the canal is on the far side of the adjacent railway embankments. Furthermore, it is

effectively a self-regulating system, with water levels controlled through a system of sluices and

weirs, aiming to maintain a freeboard of 300mm. In isolation, the canal system operates effectively

and is able to accommodate the flows that enter it from feeder streams and its own small

catchment areas. The combined operation of the canal and the River Trent is likely to reduce the

overall flooding risk, as it provides extra storage capacity.

3.7.2 Flood risk posed by the Blithfield Reservoir dam failure

Blithfield Reservoir, a significant reservoir for which the Reservoir Act 1975 is applicable, is located

upstream of Burton upon Trent. A dam failure occurred in the 1930s and resulted in a loss of life.

Any failure would result in the rapid release of a large volume of water down the River Blithe to the

River Trent with a possible impact on Burton upon Trent. The SFRA notes that the operation of

reservoirs is strictly managed, complying with appropriate legislation (Reservoirs Act 1975) enforced

by the Environment Agency. This Act was overhauled in the in Draft Flood and Water Act 2009,

putting in place a risk-based approach to reservoir management. No Flood Maps have yet been

published and whilst the implications on the site are unknown, they are not expected to be

significant.

3.8 Climate Change

The various modelling works reported by competent authorities are normally inclusive of an

appropriate allowance for climate change. The proposed drainage system will include a 20%

allowance for climate change in any capacity and attenuation calculations.


3.9 Residual Risk

Although the site is located in a Flood Zone 2 area, there remains potential residual risk of flooding

from fluvial River Trent due to a breach failure. To cope with such a possibility, an Evacuation Plan

has been included in Appendix J.


4 Flood Risk for the Proposed Development

4.1 Policy Basis

The status of the proposed development in respect to planning permission should be based on

vulnerability class and flood zone as stated in NPPF. These are discussed as follows.

Central Government has identified East Staffordshire as a potential New Growth Point and as such,

East Staffordshire Borough Council has ambitions for growth, subject to the statutory regional and

local planning process. East Staffordshire Borough Council is preparing its Local Development

Framework (LDF) and to this end, a Level 2 SFRA report has been published. This SFRA report refers

to the site as Site E47 and identifies it as an area suitable to Employment Retail.

This is shown in Figure 4.1.

Figure 4.1 The SFRA Determination of the Status of Development for the

Proposed Site, E47


Table 4.1 Flood Risk Vulnerability Classification

The proposed development is classified as ‘Less Venerable’ in NPPF

Essential Infrastructure

Essential transport infrastructure (including mass evacuation routes) which has to cross the area at risk, and strategic utility infrastructure, including electricity generating power stations and grid and primary substations

Highly Vulnerable

Police stations, Ambulance stations, Fire stations, Command Centres and telecommunications installations required to be operational during flooding

Emergency dispersal points Basement dwellings, caravans, mobile homes and park homes intended for permanent

residential use

Installations requiring hazardous substances consent

More Vulnerable

Hospitals, residential institutions such as residential care homes, children’s homes, social services homes, prisons and hostels

Buildings used for dwelling houses; student halls of residence, drinking establishments, nightclubs and hotels.

Non–residential uses for health services, nurseries and educational establishments

Landfill and sites used for waste management facilities for hazardous waste.

Less Vulnerable

Buildings used for shops; financial, professional and other services, restaurants and cafes, hot food takeaways, offices, general industry, storage and distribution and assembly and leisure.

Land and buildings used for agriculture and forestry. Waste treatment (except landfill and hazardous waste facilities). Minerals working and processing (except for sand and gravel working). Water treatment plants and sewage treatment plants (if adequate pollution

control measures are in place).

Water-compatible

Development

Flood control infrastructure, water transmission infrastructure, pumping stations. Sewage transmission infrastructure and pumping stations. Sand and gravel workings. Docks, marinas, wharves and navigation facilities. MOD defence installations. Ship building, repairing and dismantling, dockside fish processing and refrigeration

and compatible activities requiring a waterside location. Water-based recreation (excluding sleeping accommodation). Lifeguard and coastguard stations. Amenity open space, nature conservation and biodiversity, outdoor sports and

recreation and essential facilities such as changing rooms. Essential ancillary sleeping or residential accommodation for staff required by uses

in this category, subject to a specific warning and evacuation plan.

Notes 1) This classification is based partly on Defra/Environment Agency research on Flood Risks to People

(FD2321/TR2)21 and also on the need of some uses to keep functioning during flooding. 2) Buildings that combine a mixture of uses should be placed into the higher of the relevant classes of

flood risk sensitivity. Developments that allow uses to be distributed over the site may fall within several classes of flood risk sensitivity.

3) The impact of a flood on the particular uses identified within this flood risk vulnerability classification will vary within each vulnerability class. Therefore, the flood risk management infrastructure and other risk mitigation measures needed to ensure the development is safe may differ between uses within a particular vulnerability classification.

Source: PPS25 Table D2


Table 4.2 – Flood Risk Vulnerability and Flood Zone ‘Compatibility’

It has been concluded that the majority of the site is in an AREA Benefitting from Defences, which

are built to a design standard of 1:200 years. A small part of the site is located in Flood Risk Zone 2.

In summary, Table 3.1 (Flood Zones) within NPPF classifies the flood zone for the site as ‘Zone 2 –

Medium Probability’, with the site being classified as ‘Less Vulnerable’ within Table 4.1 (Flood Risk

Vulnerability Classification). Therefore, from Table 4.2 the development is classified as

‘appropriate’.

Vulnerability Classification

Essential Infrastructure

Water-compatible

Highly Vulnerable More Vulnerable Less

Vulnerable

Flo

od Z

one

Zone 1

Zone 2 Exception Test

Zone 3a

Exception Test Exception Test

Zone 3b

Exception Test

Key

Development is appropriate

Development should not be permitted

Source: PPS25 Table D3


5 Flood Risk Management Strategy

5.1 On-Site flood Risk

Having considered the risk of flooding to the site from all sources, it has been concluded that the

majority of the site is in an Area Benefitting from Defences, which are built to a design standard of

1:200 years. A small part of the site is located in Flood Risk Zone 2.

5.2 Finished Floor Levels

Modelled levels have been provided from both the River Trent Strategy study (2005) and the Burton

Hydraulic and Economic study (2005). The Trent Hydraulic and Economic Study model 2005 divides

the defended area of Burton on Trent into 10 reservoirs units. A series of ten 100m long breach

scenarios were considered at various locations along the length of the defences. The model

considers these results and calculates a 1 in 200-year flood level applicable to each reservoir unit.

The Environment Agency have confirmed that the applicable reservoir breach reservoir unit at this

location is 45.54m AOD (see Appendix I). In consultation with the EA, it has been recommended that

finished floor levels be set with a minimum freeboard of 600m above this level i.e. 46.14m AOD.

5.3 Surface water Drainage Strategy

The existing and proposed impermeable areas have been assessed to determine the extent of any

potential increase in surface water runoff. This corresponds to NPPF which states, “Surface water

arising from a developed site should, as far as is practicable, be managed in a sustainable manner to

mimic the surface water flows arising from the site prior to the proposed development, while

reducing the flood risk to the site itself and elsewhere, taking climate change into account. This

should be demonstrated as part of the flood risk assessment.”

It can be seen from enclosed drawings (Appendix D) that the existing impervious area of the site and

therefore the existing positively drained area is 1,440m². The proposed impervious area is 34,447m²

resulting in an increase of 33,007m². It should be noted however, that the site was previously

brownfield and therefore surface water runoff would have been significantly greater than the figure

provided above. To ensure that betterment is provided, surface water discharge will be reduced to

a greenfield rate of 5l/s/ha. Based on a proposed impermeable area of 34,447m², the discharge

rate from the site will be restricted to 18.5l/s. An a additional 7.0l/s


Will be discharged from the two small public car parks south of the site adjacent to Hawkins Lane as

part of the pre commencement works agreed with Severn Trent.

As discussed previously, infiltration methods of surface water disposal are not considered feasible

due to restrictions relating to the protection of groundwater aquifer resources and a relatively

shallow ground water table. It is proposed that a lined permeable paving system be installed to

reduce surface water runoff to greenfield rates from the majority of the site and thus improvement

in water quality will be provided. The runoff from roof areas will be directed to an underground

attenuation system which will restrict runoff to 5l/s via a suitable flow control device, such as a

hydro-brake or orifice plate.

Public sewer records indicate that a surface water sewer is located within the site, as shown in

Appendix G. the existing pipe is a 225mm diameter pipe with a gradient of 1 in 470 and has a

capacity of approximately 23.5l/s. it is proposed that with the approval of Severn Water, existing

outfall routes be reused to convey flows from the permeable pavement system to receiving public

sewers. Full details of existing outfalls will be established during the detailed design stage, and

approval sought from Severn Trent Water under through a 106 application.

It should be noted that regardless of the methods of attenuation, the proposed drainage system will

be designed for the 1:100 year + 20% climate change event with no flooding on site.

Permeable pavement systems will treat receiving runoff from car park areas and where applicable,

precautions relating to regarding water quality will be observed by the provision of appropriate

petrol interceptors, deep silt trapped gullies and silt boxes to all channel drains.


6 Sustainable Drainage Systems (SUDS)

A permeable pavement system will be installed to receive runoff from proposed parking areas. In

addition to attenuating runoff to greenfield rates, this option will provide a notable improvement in

water quality when compared to the previous industrial uses at this site.

The use of a greenroof has been assessed. The proposed retail store is a relatively lightweight

structure and therefore, the effect on the structural design of the building when the roof is holding

water would be to increase loads by approximately 71% (from 1.1kN/sqm to 1.86kN/sqm). This

impact will increase the size of the rafters, purlins, beams and columns which in turn will increase

foundation sizes by approx. 71% with the associated increase in excavation and disposal that would

be required. In terms of sustainability, any potential benefits would have to be offset against the

required increase in steel production and other natural reserves. There will also be increase

disposal of excavated arising to landfill; with the added vehicle movements that this would bring.

There would also clearly be a significant increase in the cost of the project and the construction

programme would also be lengthened.


7 Conclusions

A detailed source-pathway-receptor study was carried out to identify the level of flood risk at the

site of the proposed development. The proposed development is indicated as being located within

Flood Zone 3a on the Environment Agency’s Flood Zone Map, if defences are not taken into account.

The Environment Agency has confirmed that the majority of the site is in an Area Benefitting from

Defences, which are built to a design standard of 1:200 years. A small part of the site is located in

Flood Risk Zone 2. No Significant risks from other sources have been identified, such as groundwater

or sewers.

The site is classified as ‘Less Vulnerable’ (Flood Risk Vulnerability Classification) and the

development classified as ‘appropriate’, both of which are based on information specified by NPPF.

Finished Floor Levels have been agreed with the Environment Agency to ensure the store remains

dry during extreme events. Although the proposed development is considered appropriate for the

risk level, it is still exposed to a residual risk of flooding and hence a Flood Evacuation Plan has

been prepared and included Appendix J.

The proposed development will increase the impervious area and whilst infiltration methods of

surface water disposal are not considered feasible, it is proposed to install a lined permeable paving

system, to provide water quality improvements and reduce surface water discharge rate to

greenfield rates. The normal precautions regarding water quality will be observed by the provision

of appropriate petrol interceptors, deep silt trapped gullies and silt boxes to all channel drains.


Appendix A – Site Location Plan


Appendix B – Existing Site Plan


Appendix C – Topographical Survey


Appendix D – Proposed and

Existing Pervious and Impervious Areas


Appendix E – Proposed Development Plan


Appendix F – Envirocheck Flood Map


Appendix G – Water Sewer Records


Appendix H – BGS Extract


Appendix I – Enviroment Agency

Correspondence


Appendix J – Evacuation Plan

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flood risk assessment hawkins lane, burton on trent

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