1
Flood Risk
PURPOSE OF THE ASSESSMENT
1.1
The proposals for residential development on land to the north west of Standish village centre
are described in chapter 5.
1.2
This chapter presents information related to surface water (hydrology), groundwater
(hydrogeology) and flood risk.
1.3
The potential environmental impacts associated with the issues covered in this chapter cross
over with other parts of the EIA. In particular it is recommended that this chapter is read in
conjunction with chapter 10 (Ecology and Nature Conservation). The chapter should also
be read in conjunction with the site specific Flood Risk Assessment (FRA) report that forms
an appendix to this chapter (Appendix 14.1).
1.4
Information from a variety of sources has been reviewed to provide an assessment of
baseline hydrological and hydrogeological conditions.
Informed by the baseline
assessment, receptors of potential environmental effects associated with surface and subsurface hydrology arising from the Proposed Development have been identified. Mitigation
measures have been identified and residual effects evaluated.
1.5
The assessment covers both the construction and operational phases of the Proposed
Development.
LEGISLATIVE FRAMEWORK
1.6
There is a wide range of international and national legislation relevant to the assessment of
potential impacts to hydrology and drainage. In addition, there are many guidance
documents concerned with mitigating potential impacts.
1.7
Relevant documents are listed in Table 14.1 and key documents are summarized in the text
that follows.
Water Framework Directive (2000)
1.8
The aim of the WFD (Ref: 14.1) is to establish "good ecological and chemical status in all
surface waters and groundwaters". It also promotes the importance of sustainable water
use. During the implementation process, Local Planning Authorities (LPA) must not act in a
way to compromise the aims of the WFD. The WFD enables LPAs to enforce the control of
diffuse pollution at source. Development proposals must not compromise the potential for
delivering targets or actions set out in River Basin Management Plans (RBMP).
National Planning Policy Framework (2012)
1.9
The National Planning Policy Framework (NPPF) and Technical Guidance (Ref: 14.2) sets out
the government's planning policies for England and how these are expected to be applied.
1.10
The NPPF guides local planning authorities (LPA) and decision-takers both in drawing up
plans and as a material consideration in determining applications. It includes policies to
ensure that flood risk is taken into account at all stages in the planning process to avoid
inappropriate development in areas at risk of flooding, and via the flood risk Sequential Test,
to direct development away from areas of highest risk. In exceptional circumstances where
new development is necessary in areas at risk of flooding, the policy aims to make it safe,
without increasing flood risk elsewhere, and, where possible, reducing flood risk overall.
1.11
As well as steering new development to areas at lowest probability of flooding, the NPPF also
matches the flood risk vulnerability of a development proposal to appropriate Flood Zones.
For example, more sensitive developments, like hospitals, would not be permitted in areas
at high risk of flooding, although leisure and tourism developments may be allowed.
1.12
The NPPF provides details on how to take into account the potential effects of climate change
on development.
1.13
The government's policies on conserving and enhancing the natural environment are included
in the NPPF, and guides LPAs and decision-takers on how major new systems for pollution
control and the management of contaminated land should be taken into account when
considering proposals for development.
Flood and Water Management Act (2010)
1.14
The Flood and Water Management Act 2010 (FWMA) (Ref: 14.3) implements several key
recommendations of Sir Michael Pitt's Review of the Summer 2007 floods. It presents a new
approach to the implementation and management of Sustainable Drainage System (SuDS)
including a new approvals and adoption process (due for Commencement in 2014). Once
implemented, planning applications for new developments would have to be accompanied
by a SuDS application which will be assessed by a SuDS Approval Body.
Water Resources Act (1991)
1.15
The Water Resources Act 1991(Ref: 14.4) sets out the regulatory controls and restrictions
that provide protection to the water environment through controls on abstractions,
impounding and discharges, as well as identifying, amongst other things conservation, water
quality and drought provisions. The Act is supplemented by The Environment Protection Act
1991 which established the Environment Agency and The Environment Act 1995 which
provides for integrated pollution control.
Water Act, 2003
1.16
The Water Act 2003 (Ref: 14.5) formalises Government commitment to the sustainable
management and use of water resources.
Building Regulations (2010) Drainage and Waste Disposal
1.17
The Building Regulations Requirement H3 (Ref: 14.6) stipulates that rainwater from roofs and
paved areas is disposed of by, in order of priority: a soakaway or infiltration system; a
nearby watercourse, or a public sewer.
CIRIA C697 - The SuDS Manual (2007)
1.18
SuDS techniques as described in CIRIA C697 (Ref: 14.7) aim to deal with surface water as
close to the source as possible and reproduce natural drainage patterns to prevent an
increase in the volume and peak discharge from development sites. CIRIA C697 provides
developers with best practice guidance on the planning, design, construction, operation and
maintenance of SuDS.
Sewers for Adoption 7th Edition (2012)
1.19
Sewers for Adoption (Ref: 14.8) provides guidance on the design, construction and
maintenance of drains and sewers outside buildings which are to be adopted by a relevant
public authority.
BS EN 752:2008 - Drain and Sewer Systems Outside Buildings (2008)
1.20
BS EN 752 (Ref: 14.9) provides a framework for the design, construction, rehabilitation,
maintenance and operation of drain and sewer systems outside buildings.
River Basin Management Plan, North West River Basin District (2009)
1.21
The EA North West River Basin Management Plan (North West RBMP) (Ref: 14.10) focuses
on achieving protection, improvement and sustainable use of water and is a requirement of
the WFD. The plan identifies the management of future development as one of the key
aspects which can influence achievement of the WFD requirements.
Local Policy
Wigan Local Plan Core Strategy Development Plan Document 2013 - 2026
(Ref: 14.11)
1.22
The Wigan Local Development Plan is discussed in chapter 7 (Policy Context). With respect
to this chapter, policies CP16, CP9, CP12 and CP17 are particularly relevant.
1.23
Policy CP16 Flooding seeks to reduce the risk of flooding from all sources, particularly in flood
zones 2 and 3, critical drainage areas, and other areas vulnerable to surface water flooding,
including areas downstream. This will be achieved by ensuring development follows a
sequential approach, is supported by a detailed site FRA where appropriate, and
incorporates appropriate mitigation and/or management measure to achieve a reduction in
flood risk overall. The policy requires developments to manage surface runoff with no
increase in the rate of surface water runoff on greenfield sites and a reduction of at least
30%, on previously-developed land, rising to a minimum of 50 % in critical drainage areas.
1.24
Policy CP9 Strategic Landscape and Green Infrastructure seeks to improve natural
environments and open spaces within and between towns and dwellings by identifying
appropriate green areas to store flood waters away from residential areas, businesses and
community buildings. Incorporating measures to help reduce the extent of climate change
and/or adapt to changing climates will further help improve natural environments and open
spaces.
1.25
With respect to the water environment, Policy CP12 Wildlife Habitats and Species aims to
protect and enhance regional and local priority habitats and species and other valued
features to wildlife ensuring habitats are part of linked networks. The policy requires
reasonable provision is made for wildlife habitats beneficial to geological conservation as
part of a new development. The impact of climate change must also be taken into account
when enhancing and creating new wildlife habitats.
1.26
Policy CP17 Environmental Protection seeks to maintain, enhance and protect the
environment for the benefit of people and wildlife. In doing so, new developments must not
increase pollution of any watercourse, groundwater or mossland or transfer contaminated
runoff to surface water sewers. The policy supports any strategy, project or plan to improve
water quality within the Rivers Douglas and Mersey and their tributaries. Plans and designs
of new developments must ensure it does not have unacceptable adverse impacts on
amenities and quality of life.
Wigan Borough Hybrid Strategic Flood Risk Assessment (2011)
1.27
The Wigan Borough Hybrid SFRA (Ref: 14.12) was prepared to inform the Council's Local
Development Framework and Sustainability Appraisal (SA) with respect to local flood risk
issues and the location of future development in the Borough.
1.28
The overarching aim of the SFRA is to provide a framework for the management of flood risk
by ensuring that all new development is located in areas of lowest flood risk and where not
possible that there is appropriate justification and that there is sufficient mitigation to prevent
an unacceptable increase in flood risk to people and property. The SFRA was informed by
hydraulic modelling of the River Douglas, Calico Brooks, Wigan Brooks, Leeds Liverpool
Canal and Bridgewater Canal.
Greater Manchester Strategic Flood Risk Assessment (2008)
1.29
The Greater Manchester SFRA (Ref: 14.13) was prepared to inform each District's Local
Development Framework and SA with respect to flood risk, the location of future
development through the application of the sequential test, and to identify information gaps
and anomalies.
Table 14.1 Relevant key legislation, policy and guidance documents
Context
International
National
policy
Legislation, Policies and Guidance Documents
Water Framework Directive 2000/60/EC
EC Dangerous Substances Directive 2006/11/EC and daughter directives
EC Freshwater Fish Directive 76/659/EEC and daughter directives
Drinking Water Directive 98/83/EC
Water Act 2003 (as amended 2003)
Water Environment (Water Framework Directive) (England and Wales)
Regulations 2003
Control of Pollution (Oil Storage) (England) Regulations (2001)
Surface Waters [Dangerous Substances (Classification)] Regulations 1998
Control of Substances Hazardous to Health (COSHH) Regulations (2002)
Environment Act 1995 (as amended)
Surface Water (River Ecosystem) (Classification) Regulations 1994
Context
Local policy
Other
sources of
information
Legislation, Policies and Guidance Documents
Land Drainage Act 1991 (as amended)
Food and Environment Protection Act, 1985
Department for Communities and Local Government, The National Planning
Policy Framework, 2012 (and Technical Guidance)
Making Space for Water – Taking Forward a New Government Strategy for
Flood and Coastal Erosion Risk Management in England, March 2005
WEBTAG Unit 3.3.11 The Water Environment Sub-Objective
CIRIA Report 697 (2003) The SUDS Manual
CIRIA Report 609 (2004) Sustainable Drainage Systems – Hydraulic,
structural and water quality advice
CIRIA Report 532 (2001) Control of water pollution from construction Sites
CIRIA Report 522 (2000) Sustainable urban drainage systems – Design
manual for England and Wales
CIRIA Report 156 (1996) Infiltration Drainage – Manual of good practice
CIRIA Report 142 (1994) Control of Pollution from Highway Drainage
Discharges
Code of Good Agricultural Practice for the Protection of Water (the “Water
Code”) (DEFRA 1998 as amended 2002)
Guidelines for the use of herbicides on weeds in or near watercourses and
lakes (DEFRA 1995 PB2289)
Environment Agency (EA) Pollution Prevention Guidelines (PPG), the most
relevant being: PPG 1 – Good environmental practices; PPG 5 – Works and
maintenance in or near water; PPG 6 - Working at construction and
demolition sites; PPG 21 - Incidence response planning; PPG 22 - Dealing
with spills
Wigan Local Plan Core Strategy Development Plan Document 2013 - 2026,
including Policy CP16 – Flooding; CP9 Strategic Landscape and Green
Infrastructure; CP12 Wildlife Habitats and Species; CP17 Environmental
Protection. Adopted September 2013
Environment Agency, North West River Basin Management Plan, 2009
Wigan Borough Hybrid Strategic Flood Risk Assessment, 2011
Wigan Preliminary Flood Risk Assessment, 2011, with particular reference
to surface water
Greater Manchester Strategic Flood Risk Assessment, 2008
Websites for EA, BGS and Cranfield University
ASSESSMENT METHODOLOGY
Study Area
1.30
For the purposes of this chapter and to provide a robust and comprehensive assessment of
environmental impacts, the Assessment Site (the area contained within the planning
application "red-line") has been extended as shown in Figure 14.1. The total area covered
by the Assessment Site and the Extended Area is referred to as the Assessment Area.
Legend
Assessment Site
Extended Area
Primrose Lane Urban
Nature Reserve
Drainage Ditches
Pond
Ponds
© Environment Agency copyright and database rights 2013
© Ordnance Survey Crown copyright. All rights reserved
Environment Agency Wales, 100026380, 2013
Figure 14.1 Assessment Area
Surveys
1.31
Surface and sub-surface receptors potentially susceptible to environmental impact from
flooding and drainage issues associated with the Proposed Development have been
identified. The identification of receptors has been informed by an assessment of baseline
conditions.
1.32
The EIA has been informed by a site specific FRA (Ref: 14.14) undertaken in 2013. The FRA
report is presented in Appendix 14.1. The FRA, prepared in accordance with the NPPF,
assesses the risk of flooding from a variety of potential sources including fluvial flood risk,
the risk of flooding from the failure of water impounding structures such as reservoirs and
canals, groundwater emergence and from surface water.
1.33
A desk-based study and review of available information has been undertaken to determine
the existing baseline conditions within the Study Area.
1.34
Details of the catchment hydrology have been sourced from the Wigan Borough SFRA (Ref:
14.12) and the Greater Manchester SFRA (Ref: 14.13). A review of historical flooding
information within the vicinity of the Assessment Site has been sourced from both the Wigan
Borough and Greater Manchester SFRA, the Wigan Preliminary Flood Risk Assessment
(PFRA), British Hydrological Society (BHS) Chronology of British Flooding Events (Ref:
14.15), the Environment Agency (EA) and from Wigan Borough Council.
1.35
Geological and hydrogeological information for the site has been sourced from the Phase 1
Desk Study Report for the site and associated Enviro-Insight report (Ref: 14.16) (provided in
Appendix 16.1) and from the British Geological Society (BGS) website (Ref: 14.17).
Information on underlying soil conditions from Cranfield University's Soilscapes website
(Ref: 14.18) together with the aforementioned information sources have been used to
assess the risk of groundwater and surface water flooding.
1.36
Ecological information has been sourced from the site Ecological Survey and Assessment
(Ref: 14.19) in addition to findings in chapter 10 of the ES.
Consultation
1.37
Consultation has been undertaken with the EA (regarding groundwater and surface water
flooding), Wigan Borough Council (regarding highways flooding and flooding of ordinary
watercourses), and United Utilities (regarding foul water drainage).
Significance Criteria
1.38
Informed by the baseline assessment, surface and sub-surface hydrology receptors of
potential environmental effects have been identified. The 'importance' of each receptor has
been designated using professional judgment and by reference to the guidance criteria
presented in Table 14.2.
1.39
The potential effects and magnitude of effects on each receptor have been identified using
the criteria presented in Table 14.3 (informed by the baseline assessment), professional
experience and stakeholder consultation.
1.40
In order to assess the impact significance of the Proposed Development on the identified
receptors, the characteristics of each identified impact at the construction and operational
stages have been considered in accordance with the following factors:
 Direction (positive, negative or neutral impact)
 Magnitude (the amount or level of impact)
 Extent (area in hectares, linear metres)
 Duration (in time or related to species life-cycles)
 Reversibility (permanent or temporary impact)
 Timing and frequency (e.g. related to breeding seasons)
 Cumulative impacts (from a number of different sources)
1.41
Identified impacts may be significant at the level of importance defined for the receptor, or at a
lesser geographical scale. For example, limited impacts on a watercourse of County value
might be assessed as being significant at a District level. Thus, the significance of effects
has been determined from the importance of the receptor, the magnitude of the impact and,
where appropriate, the likelihood of the effect occurring using the effect significance matrix
presented in Table 14.4.
1.42
Mitigation measures have been developed for each identified impact using technical
guidance, best practices and professional experience. The magnitude of impacts following
the application of the identified mitigation measures (i.e. the residual impact) has been
assessed with reference to the extent, magnitude and duration of the effect and
performance against environmental quality standards, again with reference to the criteria
presented in Table 14.3. The significance of the residual (i.e. post mitigation) effects has
been assessed as described above.
Table 14.2 Estimating Receptor Importance
Importance
Criteria
Measures
Very High
Receptor has
a high quality
and rarity on a
national or
regional scale
Surface Water:
 Designated Salmonid / Cyprinid fishery
 High WFD Ecological status
 Good WFD Chemical status
 Protected under EU or UK habitat legislation (e.g.
Site of Special Scientific Interest, EA Water
Protection Zone, Ramsar site)
Groundwater:
 Principal aquifer providing a regionally important
resource or supporting site protected under EU and
UK habitat legislation
 Source Protection Zone 1
 WFD status = Good
Flood Risk:
 Highly vulnerable land uses such as essential
transport and utility infrastructure.
Surface Water:
 Major Cyprinid fishery
 Good WFD Ecological status
 Good WFD Chemical status
 Species protected under EU or UK habitat
legislation
Groundwater:
 Principal aquifer providing a locally important
resource or supporting river ecosystem
 Source Protection Zone 2
 Good WFD status
Flood Risk:
 Highly vulnerable land uses such as emergency
services and basement dwellings.
Surface Water:
 Moderate WFD Ecological status
 Good WFD Chemical status
Groundwater:
 Secondary aquifer with limited connection to
surface water
 Good/Poor WFD status
 Source Protection Zone 3
Flood Risk:
 More vulnerable land uses such as hospitals,
residential units, educational facilities and waste
management sites.
Surface Water:
 Poor/Bad WFD Ecological status
 Poor WFD Chemical status
Groundwater:
 Unproductive strata
 Poor WFD status
Flood Risk:
International
to National
High
County to
Regional
Medium /
Local to
District
Low
Site
Receptor has
a high quality
on a local
scale
Receptor has
a medium
quality on a
local scale
Receptor has
a low quality
and rarity on a
local scale
Importance
Criteria
Measures

Less vulnerable land uses such as watercompatible developments, retail, commercial and
general industrial units, agricultural/forestry sites
and water/sewage treatment plants.
Table 14.3 Criteria for Estimating the Magnitude of an Effect on a Receptor
Magnitude
Criteria
Descriptor
Substantial
Adverse
Loss of
receptor or
loss of quality
and /or
integrity of
receptor
Moderate
Adverse
Effect on
integrity of
receptor or
loss of part of
receptor
Minor
Adverse
Measurable
change in
receptor
quality or
vulnerability
Negligible
Effect on
receptor but of
insufficient
Surface Water:
 Reduction in WFD class
 High risk of pollution from a spillage
 Loss or extensive change to a fishery
 Loss or extensive change to a designated Nature
Conservation Site
Groundwater:
 Reduction in WFD class
 Loss of, or extensive change to an aquifer
 High risk of contamination of groundwater from
polluted runoff
 Loss of, or extensive change to groundwater
supported wetlands
 Reduction in aquifer recharge
Flood Risk:
 Significant increase in flood risk. This may be an
increase in flood depth, flood flow velocities or
extent of flooding
Surface Water:
 Reduction in WFD class
 Medium risk of pollution from a spillage
 Partial loss of productivity of a fishery
Groundwater:
 Reduction in WFD class
 Partial loss, or change to aquifer
 Medium risk of contamination of groundwater from
polluted runoff
 Partial loss of integrity of groundwater supported
wetlands
Flood Risk:
 Moderate increase in flood risk. This may be an
increase in flood depth, flood flow velocities or
extent of flooding
Surface Water:
 Minor risk of pollution from a spillage
Groundwater:
 Low risk of contamination of groundwater from
polluted runoff
 Minor effects on groundwater supported wetlands
Flood Risk:
 Minor increase in flood risk. This may be an
increase in flood depth, flood flow velocities or
extent of flooding
Surface Water:
 Negligible or no risk of pollution from a spillage
Groundwater:
Magnitude
Criteria
Descriptor
magnitude to
affect the use
or integrity
 No measurable impact on aquifer
 Negligible risk of pollution from spillages
Flood Risk:
 Negligible change in flood risk
Surface Water:
 Improvement in WFD class
Groundwater:
 Significant reduction in risk of pollution of
groundwater by spillage
Flood Risk:
 Minor reduction in flood risk. This may be a
reduction in flood depth, flood flow velocities or
extent of flooding
Surface Water:
 Improvement in WFD class
Groundwater:
 Improvement in WFD class
 Major reduction in risk of pollution of groundwater
by spillage
Flood Risk:
 Moderate reduction in flood risk. This may be a
reduction in flood depth, flood flow velocities or
extent of flooding
Surface Water:
 Improvement in WFD class
 Removal of existing polluting discharge to or
removal of likelihood of polluting discharge
occurring
Groundwater:
 Improvement in WFD class
 Removal of existing polluting discharge to aquifer or
removal of likelihood of polluting discharge
occurring
 Increase in aquifer recharge
Flood Risk:
 Substantial reduction in flood risk. This may be a
reduction in flood depth, flood flow velocities or
extent of flooding
Minor
Beneficial
Some
beneficial
effect on
receptor or a
reduced risk of
negative effect
occurring
Moderate
Beneficial
Moderate
improvement
of receptor
quality
Substantial
Beneficial
Major
improvement
in receptor
quality
Importance
of Receptor
Table 14.4 Estimating the Significance of Potential Effects
Very high
Not Significant
Minor/Moderate
Major
Severe
High
Not Significant
Minor
Moderate
Major
Medium
Not Significant
Not Significant
Minor
Moderate
Low
Not Significant
Not Significant
Not Significant
Minor
Negligible
Minor
Moderate
Substantial
Magnitude of Impact
BASELINE CONDITIONS
Site Description and Context
1.43
There are no significant watercourses in the vicinity of the Assessment Area. There is a small
unnamed pond within the western portion of the Assessment Area, and four small unnamed
ponds within Primrose Lane Urban Nature Reserve in the north-east section of the
Assessment Area (Figure 14.1). Drainage ditches are located throughout the Assessment
Site, extending into the western portion of the Assessment Area (Figure 14.1). These
surface water features are known to be dry at times (Ref: 14.16). No EA water quality data is
available for the drainage ditches.
1.44
The topography of the Assessment Area generally slopes from north to south with levels
ranging from approximately 110 m Above Ordnance Datum (AOD) to 95 m AOD.
Baseline Survey Information
Ground Conditions and Hydrogeology
1.45
According to the Phase 1 Geo-Environmental Desk Study Report (Ref: 14.16), the solid
geology comprises alternating sequences of mudstone, siltstone, sandstone and occasional
coal seams (Carboniferous Pennine Middle Coal Measures Formation). BGS mapping
indicates that the superficial deposits consist of glacial till across the Assessment Area.
1.46
The EA uses aquifer designations consistent with the WFD. These reflect the importance of
aquifers in terms of groundwater as a resource for drinking water and its role in supporting
rivers, lakes and wetland ecosystems. The aquifer designation is in two categories superficial (drift) and bedrock, and aquifers are then classified according to whether they are
principal or secondary.
1.47
According to the EA Groundwater Vulnerability Map (Figure 14.2) the Assessment Site is
underlain by a Secondary A bedrock aquifer. Secondary A aquifers are defined as
consisting of permeable layers capable of supporting water supplies at a local rather than
strategic scale.
Legend
Principal
Secondary A
Secondary B
Secondary
(undifferentiated)
© Environment Agency copyright and database rights 2013
© Ordnance Survey Crown copyright. All rights reserved
Environment Agency Wales, 100026380, 2013
Figure 14.2 Bedrock Aquifers
Groundwater Quality
1.48
The achievement of good status in groundwater involves meeting a series of conditions which
are defined in the WFD. In order to assess whether these conditions are being met, a series
of tests have been designed for each of the quality elements defining good (chemical and
quantitative) groundwater status.
1.49
There are five chemical and four "quantitative" tests, the latter being an expression of the
degree to which a body of groundwater is affected by direct and indirect abstractions. Each
test is applied independently and the results combined to give an overall assessment of
groundwater body chemical and quantitative status. The worst case classification from the
relevant chemical status tests is reported as the overall chemical status for the groundwater
body and the worst case classification of the quantitative tests reported as the overall
quantitative status for the groundwater body. The worst result of these two is reported as the
overall groundwater body status. Groundwater is classed as having good or poor status.
1.50
According to the North West RBMP (Appendix 14.3), the underlying groundwater body, the
Douglas, Darwen and Calder Carboniferous Aquifers unit (reference GB41202G100300) is
assessed to have a current poor overall status based on both its quantitative and its
qualitative status.
1.51
According to the RBMP the main pressures facing the aquifer are due to hazardous
substances, nutrients and other pollutants.
Groundwater Abstractions
1.52
The Assessment Site is not within a Source Protection Zone and according to the EnviroInsight report (Ref: 14.16) there are no existing licences for groundwater abstractions within
2,000 m of the Assessment Site.
Flood Risk
Fluvial Flood Risk
1.53
A site specific FRA has been undertaken to assess flood risk at the Assessment Site from all
identified sources to the site, to demonstrate that the development would be safe for its
lifetime and to ensure that the Proposed Development would not increase flood risk
elsewhere. The FRA report is attached as Appendix 14.1.
1.54
The NPPF provides the following definitions for each of the flood zones:
 Flood Zone 1: Low Probability. Land assessed as having a less than 1 in 1000 annual
probability of river or sea flooding in any year.
 Flood Zone 2: Medium Probability. Land assessed as having between a 1 in 100 and 1 in
1000 annual probability of river flooding or between a 1 in 200 and 1 in 1000 annual
probability of flooding from the sea in any year.
 Flood Zone 3a: High Probability. 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.
 Flood Zone 3b: The Functional Floodplain. Land where water has to flow or be stored in
times of flood. The identification of the functional floodplain should take account of local
circumstance and not be defined solely on rigid probability parameters. However, land
which would flood with an annual probability of 1 in 20 or greater in any year should
provide a starting point for consideration and discussion.
1.55
According to the EA flood map (Figure 14.3) the Assessment Site is in Flood Zone 1. As
such, the site is not considered to be at significant risk of fluvial flooding although localised
flooding associated with the drainage ditches cannot be completely ruled out.
Legend
FZ3 (1 in 100 yr / 200yr)
FZ2 (1 in 1,000 yr)
FZ1 (>1 in 1,000 year)
Flood defences
Areas benefiting from
flood defences
Main River
© Environment Agency copyright and database rights 2013
© Ordnance Survey Crown copyright. All rights reserved
Environment Agency, 100026380, 2013
Figure 14.3 EA Flood Map
Groundwater Flooding
1.56
Groundwater flooding generally occurs during intense, long-duration rainfall events, when
infiltration of rainwater into the ground raises the level of the water table until it exceeds
ground levels. It is most common in low-lying areas overlain by permeable soils and
permeable geology, or in areas with a naturally high water table.
Phase 1
1.57
The Geo-Environmental Desk Study Report (Ref 14.16 and Appendix 16.1) stated:
"Groundwater flooding is also considered to represent a low possibility, though the
initial walkover survey has certainly confirmed the presence of standing surface water
in a number of locations where topographical low spots are present. Localised minor
flooding of gardens and associated areas may occur within this site in low areas"
(Para 3.4.2).
1.58
According to the Soilscapes maps produced by the National Soils Research Institute (Ref:
14.18) soil conditions at the Assessment Site and within the surrounding area are described
as 'Slowly permeable seasonally wet slightly acid but base-rich loamy and clayey soils'. The
permeability of the underlying soil conditions and the subsequent propensity for groundwater
flooding may therefore be considered low.
1.59
According to the British Geological Survey (BGS) Groundwater Flooding Hazard map (Ref:
14.17, Figure 14.4) the susceptibility to groundwater flooding varies across the Assessment
Site but is generally low to moderate with an area considered to be at significant
susceptibility towards the north-west.
Legend
Susceptibility to flooding
from groundwater
Significant
Moderate
Low
© Crown Copyright 20011. All rights reserved. Licence number 100047514
Derived from 1:50 000 scale BGS Digital Data, British Geological Survey - NERC
Figure 14.4 BGS Groundwater Flooding Hazard Map
Flood Risk from Surface Water
1.60
Pluvial flooding results from rainfall-generated overland flow, before the runoff enters any
watercourse or sewer, or where the sewerage/drainage systems and watercourses are
overwhelmed and therefore unable to accept surface water. Pluvial flooding is usually
associated with high intensity rainfall events but may also occur with lower intensity rainfall
where the ground is saturated, developed or otherwise has low permeability resulting in
overland flow and ponding within depressions in the topography.
1.61
As detailed previously, according to the Soilscapes maps, soil conditions are described as
'Slowly permeable seasonally wet slightly acid but base-rich loamy and clayey soils'. There
may therefore be the propensity for surface water flooding at the Assessment Site.
However, the site slopes down in a northerly direction which would naturally promote gravity
drainage, and surface water would not be expected to accumulate to any significant depth or
extent.
1.62
Wigan Borough Council has confirmed that it does not hold any records of highway flooding at
this location.
Risk of Flooding from Other Sources
1.63
Reservoir or canal flooding may occur as a result of the facility being overwhelmed and/or as
a result of dam or bank failure. In the unlikely event that a reservoir dam failed, a large
volume of water would escape at once and flooding could happen with little or no warning.
1.64
There are no canals within the vicinity of the Assessment Site and the EA Risk of Flooding
from Reservoirs Map (Figure 14.5) indicates the site is not at risk of flooding from such
sources.
Legend
Flooding from reservoirs
© Environment Agency copyright and database rights 2013
© Ordnance Survey Crown copyright. All rights reserved
Environment Agency, 100026380, 2013
Figure 14.5 Risk of Flooding from Reservoirs
Historic Flooding
1.65
Figure 4-2 of the Wigan PFRA provides a map of historic flood events throughout Wigan.
According to this map, the site has not historically been affected by flooding.
1.66
The BHS Chronology of British Flood Events (Ref: 14.15) and the EA do not hold any details
of historic flood events affecting the Assessment Site.
Development Receptors
1.67
Table 14.5 lists the identified environmental receptors and their assessed importance/scale
using criteria presented in Table 14.2 as guidance.
Table 14.5 Development Receptors
Receptor
Nature of Impact
Receptor Importance
Pond
Drainage ditches
Aquifer
Water quality
Water quality
Water quality
Low
Low
Medium
PREDICTED SIGNIFICANT EFFECTS (THE ASSESSMENT)
1.68
This section summarises the likely impacts of the Proposed Development during the
construction phase and the operational phase. The assessment of effects is prior to the
implementation of mitigation measures.
Impact during Construction Phase: short to medium term
1.69
During the construction phase there will be a number of activities which could reduce surface
water quality with respect to physical contaminants. These include:
 Materials handling, storage, stockpiling, spillage and disposal;
 Earthworks involving manipulation of ground levels and re-engineering of existing made
ground if/as necessary;
 Excavation and foundation construction within the site and site preparation;
 Installation of temporary and permanent infrastructure and roads;
 Installation of temporary site accommodation and sanitary facilities;
 Construction of proposed dwellings;
 Construction of drainage runs and utilities duct runs;
 Formation of public spaces, public realm and associated restoration and landscaping;
 Movement and use of static and mobile plant/construction vehicles.
1.70
The construction activities may lead to the disturbance and mobilisation of physical
contaminants (i.e. dust, sediments and muds). In particular, during periods of heavy rainfall,
vehicle movements resulting in damage to soil structure may generate increased
sedimentation within surface water runoff. In addition, during periods of dry, windy weather,
wind-blown dusts may be generated by the excavation of soils.
1.71
These activities may result in sediments directly or indirectly entering surface water features,
impacting on the physical, chemical and biological quality of the surface water receptors in
the Assessment Area.
1.72
Contaminants, spilled contaminants and suspended sediments have the potential to affect
surface and ground water bodies via surface runoff, shallow interflow and infiltration.
1.73
Construction activities such as ground excavation or piling may create new pollutant
pathways from the surface to the underlying aquifer.
1.74
There is a risk of pollution from foul water from site worker accommodation and sanitary
facilities.
1.75
On and off-site flood risk may increase due to increased runoff due to soil compaction on site.
1.76
The likely effects of the Proposed Development during the construction phase prior to the
implementation of mitigation measures are summarised in Table 14.6.
Table 14.6 Impact Significance during Construction Phase (Pre-Mitigation)
Receptor
Value
Potential Impact
Magnitude of Impact
Significance of Impact
Ponds
Drainage
ditches
Aquifer
Low
Low
Pollution risk
Pollution risk
Substantial adverse
Substantial adverse
Minor adverse
Minor adverse
Medium
Pollution risk
Moderate adverse
Minor adverse
Impact during Operational Phase: long term
1.77
The possible effects of the Proposed Development during the operational phase are
summarised below:
 The increase in impermeable area and in traffic volumes would increase the risk of
contamination of surface runoff due to spillage of contaminants and from flushing of
pollutants from the impermeable surfaces. Contaminated surface runoff could enter local
water bodies via overland flow;
 The large number of residents and users of the Proposed Development will increase the
risk of drainage ditches becoming blocked due to build-up of debris, tipping of rubbish
etc, potentially causing localised flooding; and
 Foul water from the developed site could pollute the receptor water bodies.
1.78
The likely effects of the Proposed Development during the operational phase prior to the
implementation of mitigation measures are summarised in Table 14.7.
Table 14.7 Impact Significance during Operational Phase (Pre-Mitigation)
Receptor
Value
Potential Impact
Magnitude of Impact
Significance of Impact
Ponds
Drainage
ditches
Aquifer
Low
Low
Pollution risk
Pollution risk
Substantial adverse
Substantial adverse
Minor adverse
Minor adverse
Medium
Pollution risk
Moderate adverse
Minor adverse
SCOPE OF MITIGATION
Construction Phase
1.79
Potential impacts on the water environment through the construction phase would be
managed by a range of operational, control and monitoring measures as set out below.
1.80
As a matter of course:
 A Construction Environmental Management Plan (CEMP) would be prepared and agreed
with the LPA. The CEMP will set out the methods by which construction will be managed
to avoid, minimise and mitigate any adverse effects on the water environment;
 The principal contractor would take regard of the relevant EA Pollution Prevention
Guidelines (PPG) in preparation of the CEMP;
 All construction works would be designed in accordance with the latest relevant EA
guidelines and the ADAS Technical Note on Workmanship and Materials for Drainage
Schemes (1995) (Ref: 14.20);
 Method statements would be agreed with the EA to ensure compliance with PPGs prior
to the commencement of construction works to ensure that surface runoff quality is
managed during the construction process;
 Contractors undertaking earthworks would develop risk assessments and method
statements covering all aspects of their work that have the potential to cause physical
damage to structures (e.g. water supply and sewerage infrastructure), mobilise large
quantities soil/sediments or block open water bodies. Earth moving operations would be
undertaken in accordance with BS 6031: 2009 Code of Practice for Earthworks (Ref:
14.21);
 Works affecting soils would follow MAFF's Good Practice Guide for Handling Soils (2000)
(Ref: 14.22) which provides comprehensive advice on soil handling including stripping,
soil stockpiling and reinstatement;
 Works would comply with DEFRA guidance in the Construction Code of Practice for the
Sustainable Use of Soils on Construction Sites (2009) (Ref: 14.23) which provides
guidance on the use, management and movement of soil on site. This action should
prevent the mobilisation of sediment and prevent pollution of water bodies;
 Good practice guidance on erosion and pollution control would be followed, e.g. CIRIA
Environmental Good Practice on Site (C692) (Ref: 14.24) and Control of Water Pollution
from Construction Sites (C532) (Ref: 14.25);
 The principal contractor would avoid the storage of plant, machinery fuel or materials
(including soil stockpiles) alongside water bodies unless unavoidable. Construction
works should be programmed as far as is practicable to minimise soil handling and
temporary soil storage; and
 The refuelling of plant, storage of fuels and chemicals and overnight storage of mobile
plant would be within the designated contractors compound areas. The compounds
would contain appropriate facilities for the storage of fuels and chemicals i.e. bunded and
locked storage containers, and would also be equipped with spill kits.
1.81
The adoption of best practice construction methods and construction management processes
would significantly mitigate the identified potential environmental effects of the construction
phase of the Proposed Development.
1.82
The principal contractor may use alternative procedures compliant with their own
Environmental Management System. However, the broad approach and content would as a
minimum be comparable.
1.83
Foul water from temporary staff welfare facilities would be contained within sealed storage
vessels and disposed of off-site to minimise the risk of surface or groundwater
contamination.
Operational Phase
Finished Floor Levels
1.84
To mitigate flood risk from all identified sources, finished floor levels (FFL) of residential
dwellings would be a minimum of 0.15 m above adjacent ground levels. This measure
would, subject to the implementation of an appropriately designed surface water drainage
scheme, (see below) enable any potential surface water to be conveyed safely across the
Assessment Site without affecting property in accordance with the approach promoted
within DEFRAs Making Space for Water (2005) (Ref: 14.26).
Water Body Maintenance
1.85
A maintenance regime would be implemented to prevent the build-up of debris and/or rubbish
in drainage ditches which would have the potential to become blocked and cause localised
flooding.
Surface Water Drainage Scheme
1.86
Further details on the surface water drainage system are presented within the FRA report
(Appendix 14.1) with key features summarised below:
 The extent of impermeable area at the site will increase by over 4.88 ha following
development;
 It is proposed to limit the peak runoff rates from impermeable areas to greenfield runoff
rates;
 The surface water drainage scheme for the development would utilise source, site and
regional controls to manage post development runoff rates and provide quality treatment
via a SuDS treatment train;
 It is expected that the attenuation storage would be provided by above ground storage
such as detention basins, retention basins, swales and filter strips. The final decision will
be taken during detailed design, informed by site investigations to confirm sub-surface
conditions (permeability); and
 Initial calculations indicate that approximately 3,131 m3 of storage would be required.
This can be accommodated in the pipe system and detention basins (approximate land
requirement of 0.16 ha). The potential size and location of detention basins is indicated
on the illustrative masterplan.
RESIDUAL EFFECT ASSESSMENT
1.87
The magnitude of effects during the construction and operational phases following the
application of the identified mitigation measures (i.e. the residual impact) has been
assessed with reference to the extent, magnitude and duration of the effect; its nature (direct
or indirect; reversible or irreversible); potential interactions between effects; performance
against environmental quality standards and other relevant criteria; receptor sensitivity and
compatibility with environmental policies.
Impact during Construction Phase
1.88
Table 14.8 sets out a summary of magnitude of effects.
Potential
Impact
Significance of
Impact (PreMitigation)
Minor adverse
Receptor
Value
Ponds
Low
Pollution
risk
Drainage
ditches
Low
Pollution
risk
Minor adverse
Aquifer
Mediu
m
Pollution
risk
Minor adverse
Mitigation
Operational,
control and
monitoring
measures
Operational,
control and
monitoring
measures
Operational,
control and
monitoring
measures
Residual
Significance of
Impact
Not significant
Not significant
Not significant
Table 14.8 Post Mitigation (Residual) Impacts - Construction Phase
Impact during Operational Phase
1.89
Table 14.9 sets out a summary of magnitude of effects.
Potential
Impact
Significance of
Impact (PreMitigation)
Minor adverse
Receptor
Value
Ponds
Low
Pollution
risk
Drainage
ditches
Low
Pollution
risk
Minor adverse
Aquifer
Mediu
m
Pollution
risk
Minor adverse
Mitigation
Operational,
control and
monitoring
measures
Operational,
control and
monitoring
measures
Operational,
control and
monitoring
measures
Residual
Significance of
Impact
Not significant
Not significant
Not significant
Table 14.9 Post Mitigation (Residual) Impacts - Operational Phase
MONITORING
1.90
The following monitoring works are likely to be implemented as part of the construction phase
activities:
 Monitoring of practice construction methods and construction management processes in
respect to physical contaminants (i.e. dust, sediments and muds) in accordance with
good practice procedures;
 Regular visual inspection of water bodies in the Assessment Area.
1.91
The following monitoring works are likely to be implemented as part of the operational phase
activities:
 Routine maintenance of the completed development, to include any drainage ditches and
SuDS features.
ASSUMPTIONS
1.92
The following assumptions have been made for this assessment:
 This chapter has been prepared to support the planning application based on the
illustrative masterplan provided by DGL Associates Ltd;
 Baseline information sourced online and within the Phase 1 Geo-Environmental Desk
Study Report (including the Enviro-Insight Report) is accurate and up to date.
References
14.1
EC (2000), 'Directive 2000/60/EC of the European Parliament and of the Council
of 23 October 2000 establishing a framework for Community action in the field of
water
policy'.
Available
at:
http://ec.europa.eu/environment/water/waterframework/index_en.html
14.2
Department of Community and Local Government (2012), 'National Planning
Policy
Framework'.
Available
at:
https://www.gov.uk/government/uploads/system/uploads/attachment_data/file/607
7/2116950.pdf
14.3
Flood
and
Water
Management
Act,
2010.
Available
www.legislation.gov.uk/ukpga/2010/29/pdfs/ukpga_20100029_en.pdf
at:
14.4
Water
Resources
Act,
1991.
www.opsi.gov.uk/ACTS/acts1991/ukpga_19910057_en_1
at:
14.5
Water
Act,
2003.
Available
at:
www.opsi.gov.uk/acts/acts2003/ukpga_20030037_en_1
14.6
Office of Deputy Prime Minister (2010). The Building Regulations 2010 Drainage
and
Waste
Disposal,
Approved
Document
H,
Available
from:
www.planningportal.gov.uk/uploads/br/BR_PDF_ADH_2002.pdf
14.7
Woods Ballard B, Kellagher R (2007), 'The SuDS Manual'. CIRIA C697
14.8
Water Research Centre (2012), Sewers for Adoption 7th Edition (2012).
14.9
BS EN 752 2008 - Drain and Sewer Systems Outside Buildings (2008)
14.10
Environment Agency (2009), 'Water for Life and Livelihood - River Basin
Management Plan North West River Basin District'
14.11
Wigan Borough Council (2013), 'Wigan Local Plan Core Strategy Development
Plan Document'
Available
Available
at:
14.12
Wigan Borough Council (2011), 'Wigan Borough Hybrid SFRA. Volume 1: SFRA
Report'. JBA Consulting
14.13
Association of Greater Manchester Authorities (2008), 'Strategic Flood Risk
Assessment for Greater Manchester - Sub-Regional Assessment'
14.14
Weetwood (2013), 'Almond Brook Road, Standish - Flood Risk Assessment'
Report ref. 2521/FRA
14.15
British Hydrological Society Chronology of British Flood Events. Available at:
www.dundee.ac.uk/geography/cbhe/
14.16
REFA (2013), 'Proposed Residential Development CAT I'TH Window Farm,
Almond Brook Road, Standish, Wigan. For Wainhomes (NW) Limited. Phase 1
Geo-Environmental Desk Study Report'
14.17
British
Geological
Society
website.
http://www.bgs.ac.uk/data/mapViewers/home.html
14.18
Cranfield University, National Soil Research Institute, Soil Viewer. Available at:
www.landis.org.uk/soilscapes/
14.19
ERAP Ltd (2013), 'Ecological Survey and Assessment'. ERAP Ltd Ref: 2013_093
14.20
Redrup A (1995), 'Technical Note on Workmanship and Materials for Drainage
Schemes', ADAS
14.21
BS 6031: 2009 Code of Practice for Earthworks, December 2009. Available for
purchase
from:
http://shop.bsigroup.com/en/ProductDetail/?pid=000000000030234058
14.22
Ministry of Agriculture Fisheries and Food (2000), 'Good Practice Guide for
Handling
Soils'.
Available
at:
http://webarchive.nationalarchives.gov.uk/20090306103114/http:/www.defra.gov.u
k/farm/environment/land-use/soilguid/index.htm
14.23
Department for Environment, Food and Rural Affairs (2009), 'Code of Practice for
the Sustainable Use of Soils on Construction Sites'. Available at:
https://www.gov.uk/government/publications/code-of-practice-for-the-sustainableuse-of-soils-on-construction-sites
14.24
Audus I, Charles P, Evans S (2010), 'Environmental Good Practice on Site'. CIRIA
C692,
3rd
Edition.
Available
at:
www.ciria.org/service/Web_Site/AM/ContentManagerNet/ContentDisplay.aspx?Se
ction=Web_Site&ContentID=8982
14.25
Masters-Williams H, Heap A, Kitts H, Greenshaw L, Davis S, Fisher P, Hendrie M,
Owens D (2001), 'Control of Water Pollution from Construction Sites'. CIRIA C532.
Available
at:
http://www.orkneywind.co.uk/advice/SEPA%20Pollution%20Advice/ciria%20c532.
pdf
Available
at:
14.26
Department for Environment, Food and Rural Affairs (2005), 'Making space for
water - Taking forward a new Government strategy for flood and coastal erosion
risk management in England, First Government response to the autumn 2004
consultation
exercise'.
Available
at:
http://archive.defra.gov.uk/environment/flooding/documents/policy/strategy/strateg
y-response1.pdf