buildings and flooding: a risk -response case study · buildings and flooding: a risk ... 2.4...
TRANSCRIPT
Buildings and flooding:
a risk
Aleksandra Kazmierczak and Angela Connelly
Buildings and flooding:
a risk-response case study
Aleksandra Kazmierczak and Angela Connelly
2011
response case study
Aleksandra Kazmierczak and Angela Connelly
2
EcoCities is a joint initiative between the School of Environment and
Development at the University of Manchester and commercial property company
Bruntwood. The project looks at the impacts of climate change and at how we
can adapt our cities and urban areas to the challenges and potential
opportunities that a changing climate presents.
© University of Manchester. 2011.
School of Environment and Development
University of Manchester
Oxford Road
Manchester
M13 9PL
This report should be referenced as:
Kazmierczak, A. and Connelly, A. (2011). Buildings and flooding:a risk-response
case study. EcoCities project, University of Manchester, Manchester, UK.
Please note EcoCities working papers have not been subject to a full external
peer review. The author(s) are solely responsible for the accuracy of the work
reported in this paper and the conclusions that are drawn.
3
Table of Contents
1 Introduction 9
2 Risk of flooding to buildings in Greater Manchester 10
2.1 Overview 10
2.2 Impact of flooding on housing 11
2.3 Hazard of flooding in Greater Manchester 13
2.3.1 Riverine flooding 13
2.3.2 Surface water flooding 15
2.3.3 Past flooding events in Greater Manchester 16
2.4 Residential built environment in Greater Manchester 18
2.4.1 Building types 18
2.4.2 Tenure 19
2.5 Understanding the risk of flooding to buildings 22
2.5.1 Building type and flooding 22
2.5.2 Tenure and flooding 26
2.5.3 Land use as an exposure factor 29
2.5.4 Brownfields and risk of flooding 32
3 Adaptation options and responses 36
3.1 Sustainable urban drainage systems 37
3.1.1 Greener roofs, alleys and gardens 39
3.1.2 Permeable pavements and surfaces 41
3.2 Property-level flood protection measures 43
3.2.1 Retrofitting flood protection measures in existing buildings 43
3.2.2 Flood-proofing new developments 49
4 Neighbourhood case study: damage costs 52
4.1 Selecting the case study area 52
4.2 Calculating the damage cost 54
4.2.1 The exposure index 55
4.2.2 The vulnerability index 56
4.2.3 The hazard index 57
4.2.4 The damage cost 57
4.3 Future damage costs 61
4.4 Potential use of flood resistance and resilience measures 64
4.4.1 Local authority action 64
4.4.2 Potential uptake by individual homeowners 65
5 Conclusion 67
6 References 70
4
List of Figures
Figure 1. The risk triangle. 10
Figure 2. Fluvial flood risk areas in Greater Manchester. 14
Figure 3. Proportion of Lower Super Output Areas susceptible to surface water flooding. 16
Figure 4. Climate events in Greater Manchester. 17
Figure 5. Riverine and surface water flooding events in Greater Manchester. 17
Figure 6. Flood events in Greater Manchester, 1945 – 2008. 18
Figure 7. Proportion of different types of houses in Lower Super Output Areas in Greater Manchester. 20
Figure 8. Proportion of social-rented and private-rented houses in Lower Super Output Areas in Greater Manchester. 21
Figure 9. Proportion of different types of housing within Lower Super Output Areas located within or outside Flood Zone 2 and Flood Zone 3. 23
Figure 10. Proportion of different types of housing within and outside the areas
at risk of surface water flooding exceeding 1.0m depth. 24
Figure 12. Proportion of owner-occupied and social-rented housing in LSOAs
within and outside flood risk areas 27
Figure 13. Hotspots of risk: flooding and social-rented and private-rented housing. 28
Figure 14. Percentage of total green space and gardens in Greater Manchester. 31
Figure 15. Brownfield sites in Greater Manchester. 33
Figure 16. Proposed use of the brownfield land in Greater Manchester (by area). 34
Figure 17. Percentage of the number of brownfield sites that may be affected by flooding. 35
Figure 18. Provision of Flood Storage Capacity within New Development - the opportunity for SUDS. 42
Figure 19. Floor Levels in New Residential Development. 51
Figure 20. Neighbourhoods in the case study area. 53
Figure 21. Surface water flood depth map for the case study area. 58
Figure 22. Flood depth with a probability of 1:100 years. 59
Figure 23. Flood depth with a probability of 1:1000 years (Source: Rahman 2011, 74). 60
Figure 24. Annual damage costs (expressed as HE) for surface water flooding. 62
Figure 25. Average damage cost per building (HE) for surface water flooding. 62
Figure 26. Projected annual damage costs (HE) for river flooding per ‘at risk’ building. 63
5
List of Tables Table 1. Percentage of the Greater Manchester area and individual districts at
the risk of flooding. 14
Table 2. Housing type, condition and floor level in Lower Super Output Areas in Greater Manchester. 19
Table 3. Percentage of different types of tenure in Lower Super Output Areas in
Greater Manchester. 19
Table 4. Spearman’s rank correlation between the proportion of a type of
housing and the proportion of LSOA at risk of flooding. 22
Table 5. Spearman’s rank correlations between the proportion of tenure type in LSOA and the percentage of LSOA at risk of flooding. 26
Table 6. Spearman’s rank correlation between the percentage of green space in LSOA and the percentage of LSOA at risk of surface water flooding. 31
Table 8. Percentage of the number of brownfield sites that may be affected by flooding. 34
Table 10. Flood resilience and resistance measures. 44
Table 11. Indicative costs (£) of flood resilience measures for a three-bedroom semi-detached house. 47
Table 12. Indicators of building vulnerability. 56
6
7
Summary
For the built environment, flooding is recognised as one of the most significant
weather and climate risks for Greater Manchester. Flooding of residential
buildings is a particularly urgent problem; not only causing damage to buildings
and loss of property but also posing risk to the health and life of their occupants.
Recent climatic trends and future scenarios suggest that flooding, particularly
surface water flooding caused by heavy rainfall, is likely to become more
frequent and intense in the future.
This report analyses the magnitude and spatial distribution of flood risk to the
residential built environment in Greater Manchester (GM). Chapter 2 below
outlines the extent to which riverine and surface water flooding is a hazard
within the conurbation. It then describes the character of the residential built
environment in GM, focusing on housing tenure, type and quality. Subsequent
spatial and statistical analyses investigate which building types and forms of
tenure are at the highest risk in order to map the risk ‘hotspots’. The
characteristics of land use and land cover as exposure factors in relation to the
risk of flooding to residential built environment are then investigated. In
particular, it focuses on the spatial distribution of green spaces in relation to
different types of buildings, tenure and areas at risk of surface water flooding.
As brownfield sites (or previously developed land [PDL]) is where the majority of
the new development is likely to take place, the potential impact of flooding on
these is also analysed.
Chapter 3 explores a selection of the adaptation options available to reduce the
risk and impact of flooding to dwellings. This includes sustainable drainage
systems (SUDS), focusing on the provision of green spaces in the existing
environment and the use of permeable surfaces. Next, property-level flood
protection measures to retrofit dwellings are covered, followed by a brief outline
of the options for new residential development in flood risk areas. Barriers to
implementation are briefly considered along with recent policy developments.
In chapter 4, a neighbourhood-level case study looks at the impact of flooding to
buildings in Salford. The case study calculates the damage cost to each building
from various flood events. It considers adaptation measures that can be
introduced before discussing the barriers to successful adaptation. It is based
upon an M. Sc thesis completed at the University of Manchester under the
8
supervision of the EcoCities team (Rahman 2011) and research undertaken at
the University of Salford (Kazmierczak and Birchard 2010).
9
1 Introduction
Flooding is one of the most frequently discussed impacts of the changing climate
in the UK. It is particularly relevant to the built environment: one in six
properties in England and Wales are already threatened by flooding, amounting
to an estimated 5.2 million premises in England (EA 2009). Flooding in the UK is
likely to become more severe and localised in the future due to climate change
(EA 2009; Evans et al. 2004). Already, recent decades have seen an increase in
winter rainfall and heavy precipitation events (Jenkins et al. 2009), and Palmer
and Räisänen (2002) estimate that the total winter precipitation is likely to
increase significantly in the future.1
Greater Manchester is already affected by flooding, which is the most common
recorded type of extreme weather event in GM by some margin (Lawson and
Carter 2009).The climate projections suggest that the precipitation is likely to
become more concentrated (Cavan 2011). One of the main impacts from
flooding is on the built environment: of all the recorded consequences of
weather events impacting on the built environment, one-third related to floods.
(Carter and Lawson 2011).This report focuses on residential buildings and aims
to assess the risks for buildings in Greater Manchester and then to discuss
adaptation options and responses. This is carried out at the Greater Manchester
scale and also at the neighbourhood level.
1 For parts of the UK, the probability of total winter precipitation exceeding two standard deviations above normal will increase by a factor of five (Palmer and Räisänen 2002).
10
2 Risk of flooding to buildings in Greater Manchester 2.1 Overview
EcoCities’ definition of risk is based on the risk assessment framework developed
through the Adaptation Strategies for Climate Change in the Urban Environment
(ASCCUE) project (Lindley et al 2006). It considers three risk components in
relation to their influence on systems: vulnerability, hazard and exposure.
Vulnerability refers to the intrinsic characteristics of the systems (in this case the
residential built environment), which are influenced by climate change or
extreme weather events such as flooding. Thus, vulnerability defines the extent
to which the residential buildings are susceptible to damage from hazards. The
hazard in the risk triangle framework is the extent, severity and probability of a
given phenomenon that can cause damage to the buildings (in this study, this is
riverine and surface water flooding). The term ‘exposure’ relates to the degree
to which the system can come in contact with the hazard. Exposure is a function
of both geographical location (e.g. location within a flood risk area) and physical
context, such as presence of permeable surfaces, which may exacerbate or limit
the hazard (Lindley et al., 2006). The way that each component can lead to a
realisable risk is illustrated in Crichton’s (1999) risk triangle framework (Figure
1). Further discussion on the concept of risk can be found in a report by
Kazmierczak and Handley (2011).
Figure 1. The risk triangle (after Crichton 1999; modified).
MITIGATION ADAPTATION
11
2.2 Impact of flooding on housing
Flood damage in the UK causes more destruction than any other form of natural
disaster (Soetanto et al 2002). Residential buildings tend to have common weak
points and porous structural materials, such as brick and concrete. These
combine to provide minimal resistance to the ingress of water during a flood
(Kenna 2008). The magnitude of damage is related to the depth and velocity of
flood water. For very shallow flooding, where water does not rise above floor
level, damage is unlikely to be significant for most properties. Once water rises
above floor level it can come into contact with furnishings and personal
belongings, causing considerable damage (Soetanto and Proverbs 2004). Kenna
(2008) discusses the following potential impacts in relation to the depth of flood
waters:
• Flooding below ground floor level
o Soil erosion beneath foundations causing subsidence or differential
settlement.
o Expansion of the ground causing uplift forces and subsequent
cracking to the floor immediately above as it fails in tension.
o Saturation of timber components (e.g. wall plates/joists), which
may lead to warping, occurrence of rot and moulds, or corrosion of
metal fixings.
• Flooding above ground level (below 0.5m)
o Damage to services such as water, gas and electricity; low-level
boilers; telecommunications wiring.
o Damage to internal finishes and furnishings: warping and chipping
of plastering and paintwork; debinding of tiles; irreversible damage
to carpets, timber -based kitchen units; saturation of internal
joinery (door frames; skirting boards) causing warping, moulds and
loss of structural integrity, often beyond repair.
• Flooding higher than 0.5m above the floor level
o All damage listed above.
o Higher units affected.
o Damage to electrical services and appliances.
o Potential structural damage to property: cracked masonry, rotation
of walls and other.
12
Velocity, water contamination and flood duration substantially impact on damage
in addition to depth. It is generally accepted that greater velocity leads to a
greater probability of structural damage (Soetanto and Proverbs 2004). High-
velocity floodwaters may increase soil erosion beneath foundations and potential
structural instability. The longer the duration of the flood, the more damage it
will cause to the particularly porous solid materials that most UK properties are
made from (Soetanto and Proverbs 2004).This leads to saturation that may
either increase the upward force of the water (via capillary action) or increases
the probability of frost damage. Drying out times will certainly lengthen (Kenna
2008). Considering floodwater contaminants is equally important when assessing
flood damage. Their presence influences the ability of building materials to
absorb water; alters drying time; transports embryonic forms into the structure
that are difficult to remove without saturation or sterilisation (that may
endanger an occupant’s health); and significantly influence repair costs
depending on the work involved in the removal of physical deposits (Nicholas et
al 2001).
A number of factors influence a building’s vulnerability. Houses with the lowest
floor at or below ground level are more exposed than dwellings located on higher
floors; occupants and their belongings may be significantly more affected
(Thieken et al 2005). Structural quality plays a role too. For example, solid
masonry buildings can withstand flooding without suffering major damage, while
lightweight constructions may be more easily damaged (Sanders and Phillipson
2003). Furthermore, the extent of damage depends on the pre-existing condition
of a property before the flood event (Kenna 2008).
Housing type affects the potential damage caused by flooding. In high-density
terraced housing, water can seep under flooring and through walls between
adjacent properties (Bowker 2002). Detached houses are relatively easy to
protect from shallow flooding at property-level with the use of door guards, air
brick covers and waterproof skirts. However, for terraced housing community-
level flood protection measures (for example, structural defences or
landscaping) may be more effective and financially feasible (Johnson and Priest
2008).
Tenure influences the opportunities for occupants to take responsibility for
making changes in and around their home that could reduce the vulnerability of
the building to the flood waters. Whilst homeowners have the right to make
structural alterations to flood-proof their property and its surroundings (Harries
13
2008), tenants in social and private housing are usually more restricted. Since
occupiers of social housing contain higher proportions of the elderly, the
disabled, people with illnesses or on low incomes, amongst others (Kenna
2008), they may be even less able to protect themselves or their possessions
(Pitt 2007).
The insurance industry estimates that the average cost of flood damage
remediation of a building following a flood depth of 1.0m is £22,000. On
average, a further £13,000 will be required to replace personal belongings.
These tangible financial losses are accompanied by intangible losses that are
more arbitrary in nature, such as detriment to health (Kenna 2008). Chapter 4
(the neighbourhood-level case study) discusses a method of quantifying damage
costs that takes into account these multiple losses.
2.3 Hazard of flooding in Greater Manchester
2.3.1 Riverine flooding
Table 1 presents the extent of areas at risk of fluvial (riverine) flooding in
Greater Manchester based on spatial data obtained from the Environment
Agency (EA). The flood zones were developed for the EA Flood Map in 2008 and
are defined by the Government’s Planning Policy Guidance 25 on Development
and Flood Risk (PPG25) as follows:
• Zone 1 – little or no risk with an annual probability of flooding from rivers
and the sea of less than 0.1%
• Zone 2 – low to medium risk with an annual probability of flooding of 0.1-
1.0% from rivers and 0.1-0.5% from the sea.
• Zone 3 – high risk with an annual probability of flooding of 1.0% or
greater from rivers, and 0.5% or greater from the sea.
This report focuses on flood zones 2 and 3 (figure 2).
14
Table 1. Percentage of the Greater Manchester area and individual districts at
the risk of flooding.
Area (km2) River flooding Surface water flooding (depth)
Flood
Zone 2
Flood
Zone 3
>0.1m >0.3m >1.0m
GM 1276.03 6.79 4.75 14.26 7.10 2.17
Bolton 139.80 3.16 2.08 11.46 6.00 2.01
Bury 99.48 7.52 3.01 13.73 7.76 2.63
Manchester 115.65 11.84 8.27 19.77 7.24 1.19
Oldham 142.37 2.37 1.90 8.20 4.71 2.26
Rochdale 158.08 4.24 3.49 11.82 7.61 3.33
Salford 97.19 10.92 8.28 19.03 8.80 1.75
Stockport 126.06 7.60 6.02 12.91 6.20 1.75
Tameside 103.17 3.87 2.69 10.50 5.25 2.07
Trafford 106.04 12.19 8.85 22.37 8.31 1.08
Wigan 188.19 7.35 4.84 15.78 8.92 2.74
Figure 2. Fluvial flood risk areas in Greater Manchester (EA 2009). Base map is
© Crown Copyright/database right (2009). An Ordnance Survey/EDINA
supplied service.
15
2.3.2 Surface water flooding
Surface water (or intra-urban) flooding describes the combined flooding in urban
areas during heavy rainfall. This includes pluvial flooding;2 sewer flooding;
flooding from small open-channel and culverted urban watercourses; and
overland flows from groundwater springs (Falconer et al 2009). Surface water
flooding is predominantly caused by short and intense local rainfall.
Such floods are difficult to forecast and, therefore, to warn against and prepare
for (Falconer et al 2009; Golding 2009). The UK Office of Science and
Technology (Evans et al 2004) estimates that 80,000 urban properties in the UK
are currently at risk from surface water flooding. They project that this yields
average annual damages of £270 million, and that these numbers are likely to
increase in the future as a consequence of climate change. The widespread
character of this hazard suggests that an analysis of surface water flood risk to
people in urban areas is timely and important (Kazmierczak and Cavan 2011).
Over 14.2% of the Greater Manchester (GM) area is susceptible to surface water
flooding, and 2.2% is highly susceptible. The mapping of surface water flooding
against the territorial units suggests that the hazard is widespread (figure 3):
only five of Lower Super Output Areas (LSOAs)3 in GM are not affected by
surface water flooding. Over 78% of LSOAs include areas susceptible to flooding
greater than 1m in depth. The areas exposed to surface water flooding
constitute up to 72.3% of individual LSOAs’ territory (mean=16.3; SD=10.4),
while the percentage of individual LSOAs highly susceptible to flooding range
between 0 and 20.2% (mean=1.9; SD=2.7).
The spatial distribution of the percentage of LSOAs affected by surface water
flooding across GM (figure 3) indicates that the highest proportion of areas
highly susceptible to flooding are located to the north of the conurbation, while
the south-west and areas around urban centres are at lower risk of flooding. This
2 Pluvial flooding results from rainfall-generated overland flow and ponding before the
runoff enters any watercourse, drainage system or sewer, or cannot enter it because the
network is full to capacity. 3 Lower Super Output Areas (LSOAs) are compact areas of homogenous socio-economic
characteristics constrained by the boundaries of the electoral wards used by the Office of
National Statistics to report small area statistics across England and Wales. LSOAs
contain on average a population of around 1500 people (circa 600 households), and a
minimum population of 1000 residents (400 households) (ONS 2008). There are 1646
LSOAs in Greater Manchester.
16
varied distribution suggests that the levels of risk of surface water flooding are
determined by factors associated with topography and land use.
With climate change predicting more frequent, short-duration, high intensity
rainfall as well as more frequent periods of long-duration rainfall, surface water
flooding is likely to be an increasing problem (DCLG 2008a). The Greater
Manchester Surface Water Management Plan (SWMP) is currently in preparation.
This plan will identify, with greater clarity, the extent of properties and critical
infrastructure susceptible to risk from surface water flooding.
Figure 3. Proportion of Lower Super Output Areas susceptible to surface water
flooding (classified using natural breaks) (Kazmierczak and Cavan 2011).
2.3.3 Past flooding events in Greater Manchester
The Greater Manchester Local Climate Impacts Profile (LCLIP) (Lawson and
Carter 2009) suggests that, historically, flooding has been the prevalent
weather-related event reported by the media. Between 1945 and 1997, 38% of
all recorded events were related to flooding; between 1998 and 2007 this
number rose to 48% (figure 4). This is true for both fluvial and surface water
flooding (figure 5). The spatial distribution of past flooding events is presented in
figure 6.
17
Figure 4. Climate events in Greater Manchester (Lawson and Carter 2009).
Figure 5. Riverine (fluvial) and surface water flooding events in Greater
Manchester (Lawson and Carter 2009).
18
Figure 6. Flood events in Greater Manchester 1945 – 2008 (Lawson and Carter
2009).
2.4 Residential built environment in Greater Manchester
2.4.1 Building types
Over half of Greater Manchester’s housing is comprised of semi-detached and
detached housing with terraced housing accounting for one third of the housing
stock (table 2). The vast majority have the lowest floor at or below ground level,
therefore carrying significant flood risk implications. Just over one-quarter of
Greater Manchester’s housing is considered to be in poor condition. Figure 7
presents the spatial distribution of different types of houses in Greater
Manchester. The EcoCities spatial portal can be used to simultaneously view
different types of housing and flood risk areas.
19
Table 2. Housing type, condition and floor level in Lower Super Output Areas in
Greater Manchester (N=1646) (ONS 2001).
Housing type Level of the lowest floor Housing
conditiona
Detached or
semi-
detached
Terraced Flats Ground floor basement Poor
Minimum 0.01 0.00 0.00 20.79 0.00 8.00
Maximum 99.60 95.40 97.22 100.00 46.36 57.00
Mean 53.42 32.01 14.48 88.18 3.18 27.01
Std.
Deviation 27.07 22.09 15.74 11.48 4.85 8.06
a Source: DCLG (2008b)
2.4.2 Tenure
Two-thirds of housing in Greater Manchester is owner-occupied (Table 3). The
remaining one-third comprises of social housing, mainly present in inner-city
areas, and private housing, mainly located close to the universities (figures 7
and Figure 8). The EcoCities spatial portal can be used to view more detailed
distribution of tenure in Greater Manchester.
Table 3. Percentage of different types of tenure in Lower Super Output Areas in
Greater Manchester (N=1646). Based on ONS (2001).
Owner-occupied Social rented Private rented
Mean 66.51 22.96 10.53
Std. Deviation 24.35 21.84 8.23
Figure 7. Proportion of different types of houses in Lower Super Output Areas in Greater Manchester (Based on ONS 2001
and DCLG 2008). Base map is © Crown Copyright/database right (2009). An Ordnance Survey/EDINA supplied service.
Figure 8. Proportion of social-rented and private-rented houses in Lower Super
Output Areas in Greater Manchester (Based on ONS 2001). Base map is ©
Crown Copyright/database right (2009). An Ordnance Survey/EDINA supplied
service.
22
2.5 Understanding the risk of flooding to buildings
2.5.1 Building type and flooding
Only tentative assumptions can be made about any trends in the risk of flooding
to buildings of different types due to the low strength of correlations (table 4).
Areas with larger proportion of housing with basements seem to be slightly more
exposed to river flooding. Detached and semi-detached houses, and those with
the lowest floor at ground level, seem to be more numerous in areas less prone
to shallow surface water flooding. On the other hand, the percentage of flats and
houses in poor condition, in the overall count of residential buildings, seems to
increase with the increased proportion of the area at the risk of shallow surface
water flooding. The proportion of an area at risk of surface water flooding deeper
than 1m is positively associated with the proportion of terraced houses and
houses with the lowest floor at ground level and negatively associated with the
proportion of flats.
Table 4. Spearman’s rank correlation between the proportion of a type of
housing and the proportion of LSOA at risk of flooding.
Housing type Level of the lowest floor
Housing
condition
Detached or
semi-detached Terraced Flats
Ground
floor Basement Poor
Percentage of
LSOA in flood
risk area
Flood Zone 2 ns ns ns ns 0.061* ns
Flood Zone 2 ns ns ns ns 0.073** ns
Surface flood
>0.1m -0.076** ns 0.153*** -0.131*** ns 0.069**
Surface flood
>1.0m ns 0.048* -0.090** 0.064** ns ns
Figure 9 compares the proportion of housing in poor condition, flats and
detached and semi-detached houses in Flood Zones 2 and 3 (the Mann-Whitney
test for these has indicated the presence of statistically significant differences).
For other building types, the difference between the proportion within and
outside of the flood risk areas was non-significant. LSOAs that are exposed to
riverine flooding contain more detached housing, fewer flats and fewer poor
quality housing when compared to the areas not exposed to flooding. Similar
differences in proportion of different types of residential buildings within and
outside flood risk zones have been detected in the case of deep (>1.0m) surface
23
Figure 9. Proportion of different types of housing within Lower Super Output
Areas (N=1646) located within or outside Flood Zone 2 (left column) and
Flood Zone 3 (right column).
The boundaries of the box are Tukey’s hinges. The median is identified by a line inside the box.
The length of the box is the interquartile range (IQR) computed from Tukey’s hinges. Values
more than 1.5 IQRs but less than 3 IQRs from the end of the box are labelled as outliers
(circle). Values more than three IQRs from the end of a box are labelled as extreme, denoted
with an asterisk (*).
Figure 10. Proportion of different types of housing within and outside the
Lower Super Output Areas (N=1646) at risk of surface water flooding
exceeding 1.0m depth.
The boundaries of the box are Tukey’s hinges. The median is identified by a line inside the box.
The length of the box is the interquartile range (IQR) computed from Tukey’s hinges. Values more
than 1.5 IQRs but less than 3 IQRs from the end of the box are labelled as outliers (circle). Values
more than three IQRs from the end of a box are labelled as extreme, denoted with an asterisk (*).
Figure 11.Concentrations of poor quality housing and housing with
basements (hatched areas) (based on ONS 2001 and DCLG 2008) in
relation to flooding (EA 2009). Base map is © Crown
Copyright/database right (2009). An Ordnance Survey/EDINA
supplied service.
water flooding (figure 10).4 Nevertheless, the differences are very small. So,
actions that aim to adapt residential buildings in flood risk areas can be based on
the average numbers for Greater Manchester.
Figure 11 presents the ‘hotspots’ of risk. Spatially, flood risk seldom coincides
with a high proportion of housing in poor quality and a high proportion of houses
with basements; those LSOAs characterised by a larger proportion of dwellings
at risk of river or surface water flooding do not contain high percentages of
houses in poor condition or with the lowest floor at basement level. The analysis
suggests that policy-makers and practitioners can direct resources towards other
issues when addressing the risk of flooding to residential buildings. Next, we
consider links between tenure and flooding.
2.5.2 Tenure and flooding
In the case of river flooding, there are no clear associations between the
percentage of the LSOA that is located in flood risk areas and the percentage of
different types of tenure. This suggests that flood risk areas contain a similar
mix of tenure to other areas in Greater Manchester. Responsibility for protection
of properties will rest predominantly with owner-occupiers, followed by social
and private landlords. This means that policies and initiatives will be more
effective when directed towards these groups.
Areas that are, to a larger extent, exposed to shallow surface water flooding
(>0.1m) tend to have slightly more social- and private-rented properties, and
fewer owner-occupied properties (table 5). However, areas where surface water
flooding may occur at greater depths, very weak opposite associations occur:
more owner-occupied and fewer privately-rented housing is present
Table 4. Spearman’s rank correlations between the proportion of tenure type in
LSOA and the percentage of LSOA at risk of flooding (N=1646).
Tenure
Owner-occupied Social rented Private rented
Percentage
of LSOA in
flood risk
area
Flood Zone 2 ns ns ns
Flood Zone 2 ns ns ns
Surface flood >0.1m -0.140*** 0.095*** 0.181***
Surface flood >1.0m 0.071** ns -0.068**
4 This analysis was not possible for the areas at risk of shallow (>0.1m) surface flooding,
as only one LSOA in Greater Manchester is not even partially at risk of shallow surface
water flooding.
27
The boundaries of the box are Tukey’s hinges. The median is identified by a line inside the box.
The length of the box is the interquartile range (IQR) computed from Tukey’s hinges. Values more
than 1.5 IQRs but less than 3 IQRs from the end of the box are labelled as outliers (circle).
Figure 12. Proportion of owner-occupied and social-rented housing in LSOAs
within and outside flood risk areas (N=1646).
Flood Zone 2
Flood Zone 3
Surface water flooding > 1.0m
Figure 13. Concentrations of social-rented and private-rented housing (hatched areas; based on ONS, 2001) in relation to
flooding (EA, 2009).Base map is © Crown Copyright/database right
(2009). An Ordnance Survey/EDINA supplied service.
Figure 12 compares the proportion of owner-occupied and social-rented housing
within and outside flood risk areas (Flood Zone 2, Flood Zone 3 and areas
exposed to surface water flooding exceeding 1m). In all cases, the percentage of
owner-occupied housing is slightly higher in areas at the risk of flooding than in
places not at the risk of flooding; the situation is reversed in the case of social-
and private-rented housing. Whilst the differences are small, the Mann-Whitney
test suggests that they are statistically significant.
Figure 13 presents ‘hotspots’ of risk, where the high proportion of social-rented
and private-rented housing coincides with flood risk areas. This data can be
viewed in more detail in the EcoCities spatial portal.
2.5.3 Land use as an exposure factor
The presence of large sealed surfaces in urban areas (such as buildings, roads
and car parks) raises the volume of surface water runoff and, consequently,
increases the risk of flooding (Ripl 1995; Sanders and Phillipson 2003). Both
large new developments and an accumulation of minor works, such as driveways
and paving, are exacerbating the problem (Pitt 2007). Conversely, highly
permeable surfaces, such as vegetated areas and bare soil, reduce the volume
and rate of runoff by facilitating the infiltration of water into the ground, and
through evapotranspiration of water back into the air (Ripl 1995). Therefore,
increasing the permeability of land cover is thought to limit the risk of surface
water flooding in a given area. It can also slow down the water cycle to ensure
that the drainage system is not overwhelmed and that flooding is not caused in
another location.
Gill et al (2007) modelled surface water runoff from different types of land use
and found that it increases with the proportion of built-up areas. For the north
west of England, an 18 mm precipitation event in low-density residential areas
built on sandy soil (with 66% vegetated cover) were characterised by 32%
runoff, compared with 74% runoff in town centres (with 20% vegetated cover).
An empirical study investigating the proportion of surface water runoff from
different surfaces (Ennos 2011) suggests that runoff from a grass surface can be
as little as 5% of the rainfall volume; runoff from a tarmac plot with a tree is
35%; and runoff from a fully tarmaced surface is about 80%. Consequently, land
use, and the proportion of evapotranspiring surfaces in particular, has a
significant influence on surface water behaviour and, therefore, the exposure of
an area to flooding (Kazmierczak and Cavan 2011).
30
The total green space cover in Greater Manchester, calculated as the percentage
of green and open space in different land use types, is 71.7%, ranging between
20.1 and 94.1% (mean=58.7; SD=14.6) in individual LSOAs. The highest
percentage areas of green space are associated with peripheral areas of Greater
Manchester (Figure 14). Specifically, private gardens constitute 17.7% of the
total Greater Manchester area, and their proportion in LSOAs ranges between
0.2 and 63.7% (mean=25.9; SD=14.2). The highest proportion of gardens is
present in the suburban parts of GM, particularly to the south of the conurbation
(figure 14).
Table 5 suggests that the areas with a large proportion of land susceptible to
surface water flooding >0.1m tended to have less green space. This may
suggest that providing some greening in such areas may resolve some of the
surface water flooding problems. The larger the proportion of a LSOA that is
susceptible to flooding >1m, the more green space is present; however, the
gardens are fewer. This may suggest that in these areas the green space can
perform the role of flood water storage; this role to a much lesser extent could
be performed by private gardens.
The associations between the proportion of area at risk of flooding and the
proportion of green space are also shown for individual green space types.
Whilst the percentage of woodland and farmland in LSOAs decreases with the
increasing proportion areas of risk of surface water flooding >1m, the
association is positive for derelict and disused land, formal recreation sites and
informal open spaces. This may suggest that the urban types of green spaces:
brownfield land; recreation sites and informal greenery surrounding housing
estates could be potentially used as water storage areas.
As intuitively expected, areas with higher proportions of low-density detached
and semi-detached houses tend to have more green space and gardens. The
situation reverses for areas comprising terraced housing and flats (table 7).
Thus, the areas with semi-detached and detached housing may have much
higher infiltration rates, and therefore be less exposed to surface water flooding
than areas of higher density.
31
Figure 14. Percentage of total green space and gardens in Greater Manchester
(Kazmierczak and Cavan 2011).
Table 5. Spearman’s rank correlation between the percentage of green space in
LSOA and the percentage of LSOA at risk of surface water flooding (N=1646).
Percentage of green space % LSOA at risk of surface water flooding
Depth >0.1m Depth >1m
Total green space -0.152*** 0.237***
Gardens Ns -0.365***
Urban Morphology Types
Improved farmland -0.239*** 0.181***
Unimproved farmland -0.152*** 0.078**
Disused/derelict land 0.073** 0.215***
Remnant countryside Ns 0.148***
Woodland -0.171*** 0.228***
Formal recreation 0.049* 0.057*
Formal open space Ns Ns
Informal open space 0.074** 0.106***
Allotments 0.055* Ns
*** Significant at 0.001 level; ** Significant at 0.01 level; * Significant at 0.05 level; Ns
- not significant.
32
Table 6. Spearman’s rank correlation between the percentage of green space
and the proportion of types of housing and tenure in LSOAs (N=1646).
Type of housing/tenure Percentage of green space in LSOA
Total green space Gardens
Detached and semi-detached 0.469*** 0.368***
Terraced -0.323*** -0.376***
Flats -0.336*** -0.110***
Housing in poor condition -0.448*** -0.257***
Housing with the lowest level at the ground floor 0.346*** 0.145***
Housing with the lowest floor at basement level -0.144*** -0.084**
Owner-occupied housing 0.351*** 0.193***
Social-rented housing -0.264*** -0.193***
Private-rented housing -0.465*** -0.213***
*** Significant at 0.001 level; ** Significant at 0.01 level.
Areas characterised by high proportions of social- and private-rented housing
tend to have less green space and less garden area compared to the areas with
a lower percentage of rented housing and higher proportion of owner-occupiers.
This could suggest that in the areas of renting, provision of additional green
space may be necessary to facilitate infiltration and reduce the risk of flooding.
Interestingly, the proportion of houses with basements is also negatively
associated with the proportion of green space. This increases the risk of damage
to these properties because of the reduced infiltration rates and, therefore, they
have increased exposure.
2.5.4 Brownfields and risk of flooding
Reducing flood risk needs to be considered for future residential areas as well as
existing dwellings. Between 1996 and 2005, 133,600 homes in the UK were
constructed on flood risk sites despite the known threat of flooding, and an
unknown number was built against EA advice during the same period (Kenna
2008). The land use implications of the EcoCities scenarios (Carter 2011; Carter
and Ravetz 2012) suggest that a wide range of drivers of change will influence
where new development takes place. The level of protection afforded to the
green belt and strong spatial planning regulations make it likely that most of this
development will take place on brownfield sites (previously developed land).
33
According to National Land Use Database of Previously Developed Land (NLUD-
PLD), there are more than 2,200 brownfield sites in Greater Manchester,
occupying an area of 4,200 ha, or 3.3% of the conurbation (HCA 2011).
Individual sites vary in size, ranging from 0.02 ha up to 268 ha (Figure 15). A
considerable proportion of brownfield sites may be affected by flooding (table 8);
shallow, surface water flooding in particular. Around one-quarter of brownfield
land in GM includes housing as the proposed use (figure 16). Hence, it is
important to analyse whether flooding is likely to affect the planned residential
development in Greater Manchester. This was done by investigating the spatial
distribution of brownfields with different proposed uses against the spatial
distribution of flood risk.
Figure 15. Brownfield sites in Greater Manchester (Polyakova 2011: 30).
Figure 16. Proposed use of the brownfield land in Greater Manchester (by area;
Table 7. Percentage of the number of brownfield sites that may be affected by
Flood Zone 2
% brownfield sites
at the risk of
flooding
34
. Proposed use of the brownfield land in Greater Manchester (by area;
based on HCA 2011).
Percentage of the number of brownfield sites that may be affected by
flooding
River flooding Surface water flooding
Flood Zone 2 Flood Zone 3 depth>0.1m
25.52 21.27 76.40
Open Space
Housing
Mixed with housing
Mixed without housing
Employment
Retail
Other
None/unknown
. Proposed use of the brownfield land in Greater Manchester (by area;
Percentage of the number of brownfield sites that may be affected by
Surface water flooding
depth>0.1m depth>1.0m
32.58
Mixed with housing
Mixed without housing
None/unknown
35
Figure 17. Percentage of the number of brownfield sites that may be affected
by flooding.
Figure 17 indicates that brownfield sites where housing is the only proposed land
use are the least exposed to both riverine and surface water flooding. This
suggests that flooding is taken into consideration when deciding future uses for
vacant sites. Nevertheless, 30% of brownfield sites proposed as mixed use (with
or without housing) should incorporate some flood protection measures due to
the considerable risk of surface water flooding. A slightly lower proportion should
also consider riverine flood risk. Brownfield sites where the proposed use is open
space tend to be the most exposed to flooding. It is recommended that they are
at least partially used as water storage areas, which can help to alleviate the
flood risk in other locations. This analysis is clearly valuable to planners and
developers when taking decisions on development location and flood risk
management strategies.
0%
10%
20%
30%
40%
50%
60%
70%
80%
90%
100%
Flood Zone 2
Flood Zone 3
SWF depth> 0.1m
SWF depth>1.0m
36
3 Adaptation options and responses
Government efforts to reduce the impact of flooding have recently focused n
flood risk assessment, forecasting, provision of defences and warnings and
awareness raising (DEFRA 2004; EA 2009). To date, almost 70% of England and
Wales has been assessed for flood risk and the EA informs residents each time a
new flood risk area has been defined (EA 2009). However, Flood forecasting,
which is based on measurements of river and sea levels (EA 2009), is not
available for all flood risk areas. Moreover, over half of the 5.2 million properties
at risk of flooding are threatened by surface water flooding (EA 2009), which is
presently difficult to accurately forecast (Falconer et al 2009). The EA provides
online flood risk maps and free information about approaching flooding by
telephone and email through Floodline Warnings Direct. In 2007/08, 61% of
properties at risk of river and sea flooding across England and Wales were
covered by this service and the EA is aiming to increase this to 80% by 2013 (EA
2009).
Whilst £500 million is spent annually on the maintenance and new construction
of structural flood defences (EA 2009), it is estimated that about half of the
households in areas of significant risk of flooding are undefended (DEFRA
2008a). Also, flood risk may be affected by the public spending reviews, which
are likely to lead to a reduction in flood defence budget (ABI 2010). The UK
Government’s Foresight: future flooding (Evans et al 2004) explained that, given
climate change, a varied portfolio of responses (other than engineering works)
was the most effective way to keep flood exposure in check.
Adequate insurance cover can minimise the financial cost of damage from
flooding for property owners. However, it does little to alleviate associated
trauma and intangible losses. Furthermore, insurance is designed to cover only
occasional damage. Where the likelihood of flooding is high, flood insurance
should be accompanied by preventive adaptation measures (ABI, no date).
This chapter considers additional options that limit flood risk to the residential
built environment. These include: land use and land cover changes; retrofitting
of existing houses with property-level flood protection measures; and flood-proof
design for new developments.
37
3.1 Sustainable urban drainage systems
Sustainable urban drainage systems (SUDS) aim to mimic natural drainage.
They are a sequence of management practices and control structures designed
to drain surface water in a more sustainable fashion than some conventional
techniques (DCLG 2008a). SUDS can achieve multiple objectives. They remove
pollutants from urban run-off at source, control surface water run-off from
developments, ensure that flood risk does not increase further downstream and,
by combining water management with green space, they can increase amenity
and biodiversity value (DCLG 2008a). For these reasons, SUDS are included in
the Code for Sustainable Homes (DCLG 2006).Their benefits and issues for
planning are summarised in table 9.
The Flood and Water Management Act (FWMA) 2010 introduced significant new
responsibilities for local authorities around SUDS, likely to come in force in 2012.
Unitary and county councils will be responsible for forming SUDS Approval
Bodies (SABs) to evaluate and approve SUDS in all new developments and to
adopt and maintain SUDS that serve more than one property. National
Standards are currently being developed and are likely to mirror information
found in The SUDs manual (Woods-Ballard et al 2007), including basic principles
and design guidance on run-off destination, peak flow rate and volume and
water quality (CIRIA 2011).
Salford City Council (2008) promotes the use of SUDS in new developments, in
particular focusing on the following measures:
• Porous materials - such as permeable concrete blocks, crushed stone and
porous asphalt can be used for pavements, driveways and car parks. They
encourage rainwater to infiltrate into the ground.
• Infiltration trenches and soakaways – are stone-filled trenches which
promote the slow movement of surface water into the ground. They can
be effective for draining highways and are able to remove water pollutants
by absorption, filtering and microbial decomposition in the surrounding
soil. Rainwater harvesting systems – collect rainwater from roofs for it to
be used for flushing toilets, urinals and for watering plants in gardens.
Ponds and wetlands – are designed to attenuate surface water by storing
peak flows and releasing to the sewer network or watercourse at a
controlled rate during and after the peak flow has passed. Ponds and
38
Table 8. Sustainable Drainage Systems: benefits and issues for planning (DCLG
2008a).
Feature Benefits Issues for planning
Green roofs Attenuated run-off, improved aesthetics,
climate change adaptation.
Visual appearance.
Dissemination of ongoing
management requirements.
Water butts Attenuated run-off. Design in space for water
butts.
Porous and
pervious paving
Infiltration to promote attenuation and
groundwater recharge, treatment by
detention, treatment by filtration. Can
also be used as storage before
discharging downstream, if infiltration
not appropriate.
Using the right material for
the use. Visual appearance.
Traffic loading.
Rainwater
harvesting
Attenuated run-off, water
conservation
Building design.
Filter strips Green links/corridors through a
development, run-off attenuation,
filtering of contaminants.
Land take and visual
integration into
development.Multi-
functionality. Adequate for
predicted run-off.
Swales Can be planted with trees and shrubs,
provides green links/corridors, improved
visual amenity, conveyance of storm
water.
Land take; Multi-
functionality.
Adequate for predicted run-
off. Health and safety.
Improved amenity value.
Infiltration basins Potentially compatible with dual-use
e.g. sports pitches, play areas, wildlife
habitat. Treatment by detention and
filtration.
Land take; Multi-functionality
– provision of open space in
development. Health and
safety.
Detention basins Can be designed as an amenity or
wildlife habitat. Treatment by detention.
Land take. Multi-
functionality.
Health and safety.
Retention ponds Open water bodies which can
significantly enhance the visual amenity
of a development. Treatment by
detention. Wildlife habitat. Can abstract
water for re-use e.g. irrigation. Fishing,
boating and other water sports.
Land take. Multi-
functionality.
Health and safety. Improve
amenity value, including the
restoration of habitat and/or
environmental enhancement.
Wetlands Provide a range of habitats for plants
and wildlife. Biological treatment linear
wetlands can also provide green
corridors.
Land take; multifunctionality.
Health and Safety. Strategic
planning for biodiversity.
Improve amenity value,
including restoration of
habitat and/or environmental
enforcement.
39
wetlands have value for biodiversity and should be designed and
maintained for this purpose as for their value in dealing with surface water
drainage.
The following paragraphs describe different forms of greening and provision of
permeable surfaces as SUDS for various types of residential buildings.
3.1.1 Greener roofs, alleys and gardens
Green spaces are considered to be an important measure for reducing the
surface water runoff (Gill et al 2007). Greening may include conservation of
existing and development of new parks and woodlands, with a particular
attention to planting of moisture-retaining tree and shrub species (Williams et al
2010). The positive associations between the susceptibility to flooding and the
proportion of informal open spaces and formal recreation sites in LSOAs in
Greater Manchester (table 6) suggest that these types of green spaces could
potentially be used to provide the functions which help to manage surface water
flooding.
Where green space is absent, and the density of development does not allow for
the provision of new green areas (e.g. terraced housing; flats), green roofs could
provide an additional measure to reduce surface water flooding. Green roofs are
one of the SUDS options, as they act as storage units by imitating the
hydrological behaviour of the upper soil layer. Storage is provided mainly by the
substrate and drainage layer and the surface of the vegetation. Runoff is
generally delayed with significant reductions in peak flows and volume. An
investigation into the runoff volume from a selection of different types of green
roofs suggests that the annual runoff is, on average, 32%, with a range of 23%
to 39%, depending on the subtract depth (Uhl and Schiedt 2008). Gill et al
(2007) estimate that adding green roofs in high density residential areas can
reduce total runoff (from all surfaces in the area) by up to 20%. Another option
in areas of high-density terraced houses is to green the ginnels between
buildings. Vegetated strips allow natural water infiltration, provide cooling during
summer months and can be aesthetically pleasing (see Kazmierczak 2012).
In suburban areas (with their majority of semi-detached and detached houses),
urban densification may be exacerbating the risk of surface water flooding. Perry
and Nawaz (2008) mapped the changes in impervious surfaces in a suburban
area of Leeds. They observed a 13% increase in impervious surfaces between
1971 and 2004; 75% of this was due to the paving of residential front gardens,
40
mainly to create off-street car parking space. Modelling showed a 12% increase
in the average annual surface water run-off in that area.
This is particularly relevant in GM, where domestic gardens account for around
one-fifth of the entire conurbation. In many suburban areas they are the main
type of green space (Gill et al 2007). While the paving over of gardens attracts
little attention due to the small scale of each change, it could have far-reaching
consequences (Perry and Nawaz 2008). Williams et al (2010) recommend
removing non-porous driveways and restoring green front gardens to reduce
surface water flood risk. Currently, UK legislation to specifically manage this
problem is limited. The Civic Amenities Act (1967), that allows local planning
authorities to define areas of special architectural or historic interest, could be
used to prevent garden walls being removed to create driveways (Perry and
Nawaz 2008). However, Article 3 (f) of the UK Town and Country Planning
(General Permitted Development) Order (1995) permits hard surfacing within
the curtilage ‘for any purpose incidental to the enjoyment of the dwelling’, as
this change is excluded from the definition of development and does not require
planning permission.
Increasing levels of impervious surfaces can also be a result of ‘garden-grabbing’
by developers: where one or two large houses with attached gardens are
purchased by property developers and then converted into many new flats and
houses to cover most of the plot with hard surfaces. For example, Pauleit et al
(2005) observed a 5% loss in vegetation in Merseyside between 1975 and 2000,
mainly due to infill densification of urban areas. Until recently, gardens were
classified as brownfield land in the list of land use types, where development is
encouraged (DCLG 2010). Changing this classification may potentially slow down
the garden loss trend. However, it remains unclear the extent to which the draft
National Planning Policy Framework (2011) could be at odds. It aims to simplify
planning and favours ‘sustainable development'; a phrase that could easily be
interpreted as a potential endorsement of developers’ current practices.
In order to reverse the trend of garden paving, policy-makers need to become
more aware of the environmental implications of domestic garden paving.
Secondly, education could raise the general public’s knowledge and response to
the problem. A pertinent example is the Royal Horticultural Society’s campaign
(2005) to highlight the value of domestic gardens for societal well-being and
with suggested alternatives to hard surfacing. Thirdly, the Civic Amenities Act
(1967) and the UK Town and Country Planning (General Permitted Development)
41
Order (1995) should be updated and enforced with greater rigour to protect
gardens (Perry and Nawaz 2008).
To become even more effective at managing stormwater and reducing the risk of
flooding, gardens can also be utilised as retention basins, replacing traditional
drainage systems with a natural process of infiltration for individual properties.
Scholz (2003) describes a case study of a property disconnected from the public
drainage system in which a domestic garden was transformed to contain water
retention ponds. This reduced water load on the public drainage system, and
thus reduce the risk of flooding elsewhere, and also provided some storage for
water and reduced the risk of surface water flooding to the property.
Opportunities for green spaces performing as SUDS should also be incorporated
in the layout of the new developments. Salford City Council (2008) requires that
new development in Flood Risk Zone 3 should not result in a net loss of flood
storage capacity. If ground levels on which new development is situated have to
be raised, it will be necessary to lower ground levels either within the curtilage
of the development or elsewhere in the floodplain, in order to maintain at least
the same volume of flood storage capacity within the floodplain for the 1:100
year flood event. This policy provides an excellent opportunity for creation of
SUDS in form of wetlands and ponds in the ground hollows (figure 18).
3.1.2 Permeable pavements and surfaces
The majority of impervious surfaces in urban areas are roads. However, a
significant portion of these impervious areas (particularly parking bays,
driveways and road shoulders) experience only minimal traffic loading. Car parks
are typically sized to accommodate occasional peak traffic usage leaving most of
the area unused for a majority of the time. Other car parks, such as those for
businesses and schools, may be at full capacity nearly every day but with only
once-in and once-out traffic that imposes little long-term wear (Brattebo and
Booth 2003). Here, permeable paving can reduce the amount of stormwater
entering the drainage system. They can be divided into non-vegetated and
vegetated pavements (EPA no date 2):
• Non-vegetated pavements are usually resilient to traffic. Examples of non-
vegetated permeable pavements include porous asphalt; rubberized asphalt,
made by mixing shredded rubber into asphalt; pervious concrete; brick or
block pavers, made from clay or concrete, and filled with rocks, gravel, or
soil.
42
Figure 18. Provision of flood storage capacity within a new development - the
opportunity for SUDS (Salford City Council 2008).
• Vegetated permeable pavements include grass pavers and concrete grid
pavers. They use plastic, metal or concrete lattices for support and allow
grass or other vegetation to grow in the interstices. Although the
structural integrity can support vehicle weights comparable to
conventional pavements, these materials are most often used in areas
where lower traffic volumes are expected to minimise damage to the
vegetation (EPA no date 2).
According to Pratt et al (1995) concrete block paving filled with gravel retained
between 53% and 66% of the rainfall, depending on the types of base. Studies
suggest that permeable pavements are quite resilient to wear from traffic, with
some of the types appearing as durable as asphalt under small volume of traffic
(Brattebo and Booth 2003). Porous surfaces of permeable pavements can clog
over time (Pratt et al 1995). They require regular maintenance, either by a
vacuum sweeper or pressure washing, which may result in additional costs. This
is one reason why there has thus far been limited uptake of SUDS in both new
builds and as a retrofit measure (Mott MacDonald 2008).
Other barriers include: unclear legislation to demarcate who responsibility for
maintenance lies with, particularly where tenure is short-term; fears over health
and safety (particularly in the case of retention ponds and detention basins);
lack of expertise in planning departments to test the robustness of SUDS plans;
43
lack of guidance especially for retrofit SUDS; and insufficient tools to definitively
work out the costs and benefits (Mott MacDonald 2008). Legislation is believed
to be one measure that can allay the uncertainty. The FWMA was discussed in
section 36. The introduction of SWMPs also addresses this as they can be used
to coordinate and strategically plan drainage provision, particularly to support
consistent ownership and maintenance for SUDS where these do not exist
(DEFRA 2010: i.24). Detailed guidance on retrofit SUDS (that deals with a
number of the barriers mentioned above) will be published by CIRIA early in
2012.
3.2 Property-level flood protection measures
3.2.1 Retrofitting flood protection measures in existing buildings
Technology has moved far beyond providing sandbags to protect buildings
during floods. Property-level flood-protection measures may be classified into
those that increase the resistance of the house, and those that improve its
resilience (DEFRA 2008a). Resistance measures are designed to keep water out
of the property by preventing floodwater from entering the curtilage of a building
(Kenna 2008) or by sealing potential water entry points. These measures are
either temporary, applied shortly before a flood, or else permanent changes to
the building (Bowker 2002). Resilience measures aim for the quickest possible
recovery to minimise damage to the house structure, including the interior and
furnishings, in the likely event that water will enter the premises (Pitt 2008).
These measures are largely permanent (Bowker 2002). These two types of
measures are summarised in table 10 and discussed below.
Resistance measures provide a watertight building envelope to restrict
floodwater from the building interior via entry routes such as permeable
brickwork, weathered / damaged mortar joints, air bricks, gaps and cracks in
joint sealant around doors and windows, backflow through overloaded drainage /
sewage systems and openings for service pipes and cables (Kenna, 2008).
Temporary solutions to pre-empt a flood event include flood gates, house-
wrapping, toilet plugs, and air brick covers. Permanent improvements to
waterproof a dwelling include raised thresholds and floors, waterproof doors,
automatically sealing airbricks, external wall rendering/facing, remedial works to
seal water entry points and valves on wastewater pipes.
44
Table 9. Flood resilience and resistance measures (Bichard and Kazmierczak
2009).
Measure Temporary Permanent
Resistance Resilience Resistance Resilience
Door guards +
Air brick covers + +
Sump and pump + +
Sandbags (or other sacks) +
House wrapping +
Temporary barriers +
Toilet plugs +
Furniture bags +
Drainage channels (where the driveway or
garden slope towards the house)
+
Flood-proof external doors +
External wall rendering/facing +
Raised door thresholds +
Floors raised above the most likely flood
level (where ceiling height allows it)
+
Back flow valve on sewage pipe +
Dishwasher and washing machine fitted
with valves to prevent flood water backing
up
+
Carpet/wooden floor replaced with
concrete flooring covered in tiles or treated
timber
+
Plastic skirting boards/tiling +
Skirting boards made of solid timber
painted with waterproof paint on both
sides
+
Resilient plaster/timber panels on the
walls; dado rail above them
+
Lightweight internal doors (easily
removed)
+
Waterproof (plastic/uPVC/fibreglass) door
frames
+
Doors and frames painted with oil-based
or waterproof paint
+
Resilient windows and window frames
(plastic, fibreglass)
+
Resilient kitchen (Waterproof cupboards;
Appliances on plinths; Raised, built-in
oven)
+
Raised electricity sockets, phone and TV
points
+
Raised fuse box and electricity meter +
Bottom part of staircase made of concrete
instead of timber
+
Change bath from plastic (with a
stabilising chipboard) to a ceramic one
+
Move washing machine to the first floor +
45
The average cost of temporary property-level resistance measures is currently
estimated at £4, 000. A package of permanent resistance measures is valued at
£8, 000 (DEFRA 2008a). If properly deployed prior to a flood, temporary
resistance measures can reduce the cost (£) of damage by about 50%.
Additional investment in permanent resistance increases prevented damage to
between 65% and 84%. However, due to higher investment costs, this is not as
financially beneficial as temporary resistance measures; estimated to be only
economically worthwhile for properties with an annual chance of flooding at 2%
or above (DEFRA 2008a).
Flood resistance products, either temporary or permanent, perform well at
keeping water out of buildings during shallow floods (up to 0.3-0.6m; Kenna
2008; DCLG and EA 2007). They can protect the house from shallow flooding, in
the case of deeper or longer events, they can at least buy time for occupants to
move possessions from ground floor to safer heights. However, during sustained
exposure to floodwaters, water will eventually penetrate porous masonry walls
and floors. Furthermore, such products should not be used where flood depths
exceed 0.3m since they will magnify the differential head exerted upon the
structure to cause damage (Kenna 2008). Here, the integration of flood resilient
measures may have to be considered in order to reduce the impacts of flooding
on domestic property.
Resilience measures aim to minimise damage to the structure, interior and
furnishings of a building when floodwaters enter the premises (Pitt 2008).
Predominantly permanent measures, they include replacing floor, wall, and
furnishing materials with waterproof alternatives, and raising electrical fixtures
above the expected flood level (table 10). Implementing resilience measures is
more effective than property-level resistance for deeper floods (above 0.6m),
that can overwhelm temporary barriers and cause structural damage to the
property if the water was held back. However, it is less effective at reducing
damage to personal possessions because it does not slow the ingress of water so
there is little time for householders to move possessions to safety (DEFRA
2008a).
These measures are commonly integrated with repairs following a flood, but
could be installed in anticipation of damage or during refurbishment (Proverbs
and Soetanto 2004). There is also an opportunity to integrate flood resilience
46
measures with the work carried out by social housing providers to comply with
the Decent Homes Standard (Kenna 2008).
According to DEFRA (2008a), a package of resilience measures (consisting of
flood resilient plaster and waterproof kitchens and flooring) can exceed £30,
000. This makes it economically worthwhile only when installed in a building that
has a greater than 4% annual risk of flooding or that has a greater than 2%
annual risk and is in need of repair or refurbishment. The extra costs of
implementing flood resilient repairs over like-for-like repairs are easily
recuperated after a single flood event (Kenna 2008). Table 11 shows the
comparative cost of resilience measures against an unprotected dwelling as
calculated by the Association of British Insurers. Flood resilient measures also
limit the length of time that a home is out-of-bounds. The Pitt Review described
a case study where a householder was out of their home for seven months
during the floods of 2000. The property was fitted with resilience measures
including choice of building materials, repositioning of services and the
replacement of a timber ground floor with a solid concrete ground floor. When
flooded again in 2007, the householder was back in their home within four
weeks (Kenna 2008).
Policymakers increasingly believe that householders bear some personal
responsibility to protect their dwellings against the effects of flooding (Pitt
2008). In Making Space for Water, DEFRA (2004) shifted the flood risk
management paradigm away from the previously state-centred approach
towards a more prominent role for other organisations and individuals (Johnson
and Priest 2008). Pitt’s interim review (Pitt 2007) recommended that local
authorities and housing associations assumed an active role to increase the
uptake of flood resistance and resilience measures; leading by example by
repairing their properties with appropriate materials.
By 2008, fewer than 5, 000 homes had adopted resistance or resilience
measures in the UK (DEFRA 2008a). To increase the uptake DEFRA announced
the £5.5 million Property-Level Flood Protection Grant Scheme in December
2008.Local authorities in England have the opportunity to apply for funding to
identify and subsidise appropriate measures for individual properties in areas of
frequent flooding and without structural defences (DEFRA 2009). The pilot
project in 2008 provided flood-protection measures to 177 residential properties
(DEFRA 2008b).
47
Table 10. Indicative costs (£) of flood resilience measures for a three-bedroom
semi-detached house (ABI no date).
Measure
Cost of
restoration
(no flood
resilience)
Extra cost
of installing
flood
resilience
Costs saved
each
deep flood
(<1m)
Costs saved
each
shallow
flood
(<5cm)
FLOORS
Replace sand-cement screeds
on solid concrete slabs 585 115 390 390
Replace chipboard flooring with
treated timber floorboards 470 505 370 370
Replace floor including joints
with treated timber 3100 520 2735 2735
Replace timber floor with solid
concrete 3100 6150 2350 2350
Raise floor above most likely
flood level 20300 12000 15800 13500
WALLS
Replace mineral insulation
within walls with closed cell
insulation
430 270 360 360
Replace gypsum plaster with
water resistant material, e.g.
lime plaster
3875 2925 3375 3375
Install chemical damp-proof
course below joist level 3100 3445 2450 3450
Replace doors, windows,
frames with water-resistant
alternatives
5800 4670 5150 3450
INTERIORS
Mount boilers on wall 850 150 700 700
Replace ovens with raised,
built-under type 450 200 350 350
Move electrics well above likely
flood level 500 300 400 None
Move service meters well
above likely flood level 1000 500 850 300
Replace chipboard kitchen and
bathroom units with plastic
units
1750 1650 1550 1550
48
Some of the issues associated with increasing the uptake of the flood resistance
and resilience measures include as follows:
• Little incentive to repair flood-damaged properties with resilient materials
since insurance companies refuse to pay for betterment (Kenna 2008).
• Little information about the available options and their effectiveness.
However, the EA has a number of useful publications setting out
recommended flood-protection products on their website. The British
Standards Institute (BSI) has developed a ‘Kitemark’ Certification Scheme
for flood protection products (ABI, no date).
• Before undertaking major renovations, advice from a specialist flood
surveyor is suggested. Whilst the surveyor can recommend an appropriate
set of measures for the property, taking into account the type of flooding
that occurs locally, the construction of the property, and other factors,
such as local geology (ABI, no date), this service is likely to be quite
expensive.
• Lack of building regulations ensuring the provision of resistance and
resilience measures. The Pitt Review (2008) suggested that building
regulations should be revised to ensure that all new or refurbished
buildings in high flood-risk areas are flood resistant or resilient.
• Attitudes and perceptions of homeowners: whilst in general people are
aware of living in flood risk areas, they tend to underestimate the risk of
flooding. Also, in general the responsibility for flood protection is
attributed to local authorities or other public agencies. This means that
homeowners do not see a reason to pay for the flood-proofing of their
property (Bichard and Kazmierczak 2011).
• Lack of encouragement for social landlords. The Decent Homes
Programme is ineffective to motivate RSLs to make flood-protection
improvements. Therefore, either the Decent Homes criteria need to be
tightened, or a new performance measure needs to be established to
cover the issues of property-level flood protection. RSLs should be
required to identify all stock under their management that is in a flood risk
area. Further, the nature of remedial work for each unit should be
assessed using a qualified surveyor. In order to identify the housing stock
within flood risk areas, improvements in the flow of information about
flooding between City Councils and their RSLs are necessary in order for
housing managers to identify properties at risk and take necessary
actions. There is a high level of support for flood-proofing and energy-
saving initiatives among the tenants and they were not perturbed by
additional work to their houses (Bichard and Kazmierczak 2009).
49
• Absence of pressure/ incentives for private landlords to flood-proof their
properties. Landlords are responsible for repairing the damage to the
structure of the property and keeping the installations for the supply of
water, gas, electricity, sanitation and heating in working order, but there
is no requirement for them to secure the property from flooding.
Consequently, the increased adoption of flood resilience and resistance
measures is largely associated with the changes in policy beyond Greater
Manchester’s (GM) boundaries. However, recommendation 24 of the Pitt Review
suggests that the government should develop a scheme which allows and
encourages local communities to invest in flood-risk management measures (Pitt
2008). It is therefore conceivable that policy-makers at local and GM level can
identify pilot projects that incorporate the resilience and resistance measures;
identify the sources of funding for such projects and work with social landlords to
ensure the exchange of knowledge and promote flood protection as part of the
Decent Homes Standard.
3.2.2 Flood-proofing new developments
The construction of new developments provides more flexibility for flood-proof
design and solutions than retrofitting options. Technology is far enough
advanced to allow for the construction of flood-proof houses in risk areas. Dutch
examples (Zevenbergen et al 2007) of different construction approaches include:
• Houses on posts or columns made of wood, steel, masonry or precast
reinforced concrete. The posts are not founded deep in the ground and are
suited for low to moderate flood depth and velocity.
• Houses on piles, which are founded to greater depths than posts or
columns, made from precast reinforced concrete and more suited for high
velocity floods.
• Amphibious structure. Floating homes in the Netherlands can
accommodate a difference in water level of 5.5m, but is the most costly
flood proofing technology.
The Code for Sustainable Homes (DCLG 2006) suggests an appropriate
assessment: how a building will react to flooding (including the use of resilient
construction where necessary) to mitigate the risk of flooding remaining after
the application of other measures. Salford City Council (2008) advocates the use
of flood resilient materials and construction techniques that reduce the
consequences of flooding and facilitate recovery from its effects sooner than
50
buildings that use conventional construction methods. Flood resilient design
includes:
• Using solid rather than suspended floors.
• Using treated timber to resist waterlogging, and/or marine plywood for
shelves and fittings.
• Fitting electric, gas and phone circuits above expected flood levels.
• Fitting one-way auto-seal valves on WCs.
• Using water-resistant alternatives to traditional plaster or plaster-boarding
for internal wall finishes.
• Avoiding the use of chip board or MDF.
• Concentrating living accommodation on the upper floors.
• Avoiding fitted carpets.
Salford City Council’s (2008) Planning Guidance: Flood Risk and Development
suggests providing a safety margin for new developments in flood risk areas,
accommodating even highly unlikely events. For example, new residential
development proposed in Flood Risk Zone 3 should be designed and built such
that floor levels for habitable rooms and kitchens would be no more than 600mm
below the flood level predicted for the 1:1,000 year flood event and no floor
level for habitable rooms and kitchens should be below the flood level predicted
for the 1:100 year flood event (figure 19).
New developments in flood risk areas should also be flood resilient up to the
flood level predicted for the 1:1,000 year flood event. The principles of flood-
proofing new developments and making sure that they include a safety margin
should be extended to other areas in GM that are at risk of flooding. Findings
from the emerging GM SWMP should be taken into consideration so that these
policies can also be extended to areas at risk of surface water flooding.
Having considered flood risk in GM, and potential adaptation options, chapter 4
provides the results of a case study that uses a holistic method of weighing up
the costs and benefits of various flood-proofing measures at neighbourhood
level.
51
Figure 19. Floor Levels in New Residential Development (Salford City Council
2008).
52
4 Neighbourhood case study: damage costs
4.1 Selecting the case study area
This case study is to calculate the average cost of damage from various flood
events at neighbourhood scale (Rahman 2011). We selected an area within GM
that is at high risk from flooding and with high levels of social vulnerability (see
also Kazmierczak and Cavan 2011). From a social and environmental justice
perspective, such areas are a priority for climate change adaptation actions. The
selected case study area is located in the City of Salford within the floodplain of
the River Irwell (Flood Zone 2) and significantly affected by floods in the past.
The severest incidents occurred in 1866, when 450 ha of land were flooded, and
1946, when 5,300 properties were inundated. Less widespread flooding also
occurred in 1954 (600 properties flooded); and, more recently, in 1980 and
2007 (Douglas 1998).
The selected area consists of five LSOAs across the wards of Kersal, Irwell
Riverside (including Charlestown) and Broughton (including the Spike Island
estate) (figure 20). At present, the River Irwell Flood Control Scheme protects
Lower Kersal (A), Charlestown (B, C) and Lower Broughton (D, E) from river
flooding to a 1:75 year standard. Operated and maintained by the EA, the
scheme contains floodwalls, embankments, and a flood storage basin (Salford
City Council 2009). However, the area remains at risk from the overtopping or
breaching of the flood defences along the riverbank of the Irwell (Salford City
Council 2008).
Lower Kersal sits in the meander loop of the River Irwell and is at a relatively
low elevation compared to the surrounding land. Depths of flooding of up to
0.5m would be expected for a 1:100 year flood event. In an extreme flood,
simulated to the 1:1,000 year flood event, maximum depths of flooding of up to
3m are expected. Charlestown is situated on the opposite side of the River Irwell
to Lower Kersal. Depths of flooding are expected up to 0.5m in a 1:100 year
flood event and up to a depth of 2m in a 1:1,000 year flood event. Lower
Broughton is situated opposite Charlestown on the eastern side of the River
Irwell. Lower Broughton also has a relatively low elevation compared to the
surrounding land. It is, in effect, the lowest point in the Lower Irwell floodplain
system and acts as a collecting point for floodwaters. Consequently, depths of
flooding maybe particularly high in some areas, with depths of up to 2m in a
53
Figure 20. Neighbourhoods in the case study area. © Crown copyright/database
right 2011. An Ordnance Survey/ EDINA supplied service (Source: Rahman
2011: 49).
54
1:100 flood year event and 3.5m in a 1:1,000 year flood event (Salford City
Council 2008).
A significant proportion of the housing in the areas most at risk of flooding is
social-rented accommodation (over 50%). During the 1980s and 1990s, the
housing stock was cleared or transformed of unpopular public sector housing.
Kersal and Charlestown received stimulus under the New Deal for Communities
(2000 - 2010) and Broughton was designated a neighbourhood renewal area
under the Single Regeneration Budget 2 Programme between 1996 and 2003.
While significant investment has been undertaken, much of the area comprises
traditional redbrick terrace houses (pre-1919) that have fallen in demand and
are in disrepair. Mass-produced, post-war social housing constructed using
porous ‘no fines’ concrete in a single wall structure is common to the Spike
Island Estate in Lower Broughton. Although the available evidence is insufficient,
it is believed to be a particularly problematic building type for flood proofing (EA
and Salford City Council 2009: 19). A visual property condition survey,
undertaken by Urban Vision on behalf of Salford City Council, identified a
‘considerable’ range of building defects and poor maintenance on buildings in
Lower Kersal and on Spike Island (EA and Salford City Council 2009).
4.2 Calculating the damage cost
The cost of flood damage was calculated using a GIS-based risk assessment
successfully piloted in the town of Lewes (Fedeski and Gwilliam 2007). The
assessment incorporates the severity of a hazard and the level of exposure and
vulnerability (Crichton 1999; see section 2.1 for an explanation). It is expressed
as the equation:
Risk = ƒ {Hazard, Exposure, Vulnerability}
This is integrated with the calculation damage index developed by Blong (2003)
to quantify the damage to buildings following a natural disaster. The ‘Damage
Cost’ is expressed in ‘Housing Equivalents’ (HE) that measure both the building’s
value and the magnitude of the damage. It is represented in the following
equation:
55
Damage Cost (HE) = Replacement Ratio [cost of replacing a
median sized family home] x Damage Value [proportion of the
building value lost due to natural hazard]
The replacement ratio represents exposure and the damage value represents
hazard and vulnerability. The calculations needed to reach the HE involve
determining the three indices of exposure, vulnerability and hazard. These are
described in subsequent sections.
4.2.1 The exposure index
The Replacement Ratio (RR) is an expression of exposure and is relative to the
cost of replacing an average family-sized house. It can be used and compared to
present and future calculations because it does not need to be adjusted for the
inflation rate. The average house is assigned a unit of 1 and the RR for all other
buildings is relative to this. To calculate the RR for another building the cost of
the building is multiplied by its area. The sum is divided by the cost of an
average house. Fedeski and Gwilliam (2007: 52) give the example of a 600m2
library that costs the same to construct as 21 average houses. The RR does not
include other external factors such as landscaping, roads, service facilities and
so on (Blong 2003: 3). RR is expressed in the following equation:
RR = Cost of the building/ Cost of an average house (Blong 2003: 4)
We drew on Building Cost Information Service data to calculate construction
costs for a number of building types in the case study area (BCIS 2011). These
were identified using OS MasterMap data (2005), supplemented by a visual
inspection. The mean surface area was calculated after determining the total
surface area and dividing it by the number of buildings. This allowed us to
calculate the cost of an average building using the following calculation:
Cost of the average building = Average price per m2x Mean
surface area x Number of storeys
The same formula was used to calculate the cost of an average house. We used
BCIS information on ‘estate houses’ and estimated the number of storeys as 2.
This yielded a figure of £74, 035. The replacement ratio of all other buildings is
56
considered as a proportion of this where the HE of an average house is assigned
the value of 1.
4.2.2 The vulnerability index
Other factors compromise a building’s vulnerability including the type; age;
construction method; state of repair; openings such as windows, doors and air
bricks; and relationship to service roads (See Gwilliam et al 2006: 251). Given
the limited scope of the study, the focus is on the most pressing issues of age,
state of repair and openings (table 12).
Our field survey was cross-referenced against two surveys prepared for Salford
City Council on housing stock condition and townscape quality (Salford City
Council 2007; Berry 2009). In Lower Kersal and Charlestown, the buildings are
considered to be more vulnerable because of age and poor quality construction.
The quality indicator ranges between 0 and 1, where 0 indicates the lowest
impact and 1 indicates the highest impact.
Table 11. Indicators of building vulnerability (Source: Rahman 2011: 34–5)
Standardised
Measurement
Very low
impact
Low
impact
Medium
Impact
High
Impact
Very High
Impact
Opening 0.2 0.35 0.5 0.65 0.8
Building quality 0.2 0.35 0.5 0.65 0.8
Age 0.2 < 40
yrs
- 0.5 40 –
80 yrs
- 0.8 > 80
yrs
The vulnerability index assigns equal importance to these criteria for each
building and is therefore calculated using the following equation:
Vulnerability index = (⅓ x age index) + (⅓ x quality index) + (⅓
x opening index)
57
4.2.3 The hazard index
Using detailed and up-to-date flood zone and depth maps developed for the
Strategic Flood Risk Assessment plan for Manchester, Salford and Trafford (JBA
Consulting 2011), we developed the hazard maps that were superimposed on a
detailed distribution of buildings in Salford derived from the MasterMap
topographical data set. The hazard index was calculated separately for:
• Surface water flooding (figure 21).
• Flood depth with a probability of 1:1000 years without flood defence
(figure 22).
• Flood depth with a probability of 1:1000 years (figure 23).
Each building in the case study area was assigned a Central Damage Value
(CDV) dependent on flood depth. Those likely to experience depths of less than
0.3 m were assigned 0.1; between 0.3m and 1m were assigned 0.4; and those
over 1m were assigned 0.75.
4.2.4 The damage cost
The damage value was calculated by multiplying the vulnerability and severity
indices. To determine the damage cost, expressed by House Equivalent (HE), the
replacement ratio (exposure index) is multiplied by the function of the
vulnerability and hazard indices (Blong 2003).
For this case study, the damage cost was calculated separately for each type of
flood event. A total of 2, 360 buildings are located in the five neighbourhoods. In
order to extract a summary, buildings at risk were identified by overlaying the
neighbourhood map on the flood depth maps prepared for the Manchester,
Salford and Trafford Strategic Flood Risk Assessment (JBA Consulting 2011).
Detailed neighbourhood analyses shows the variation in cost and impact; not all
areas are at risk and flood frequency varies.
With river flooding, the neighbourhood areas located in and around the River
Irwell contain homes that are at high risk of flooding (liable to flood during a
1:100 year event), particularly in Lower Kersal and Lower Broughton. Fewer
buildings are at risk but the damage from these events will be greater. The other
three neighbourhoods are at risk from surface water flooding – over half of
buildings were considered to be at risk – but the damage here will be lower. The
58
Figure 21. Surface water flood depth map for the case study area (Source:
Rahman 2011: 71).
59
59
Figure 22. Flood depth with a probability of 1:100 years (Source: Rahman 2011:
73).
Figure 23. Flood depth with a probability of 1:1000 years (Source: Rahman
2011: 74).
61
total damage cost from surface water flooding varied according to the
neighbourhood. Damage costs for those neighbourhoods located in medium-risk
flood zones (water depth between 0.3m–0.6m), such as Lower Kersal, are likely
to be higher although for the other neighbourhoods at lower risk, more buildings
are exposed. For flood events occurring 1:1000 years, the severity is much
greater and affects all but 40 of the buildings in the case study area.
The annual damage cost can be calculated by multiplying the final damage cost
with the annual frequency of a particular flood event. This should not be taken
as an accurate value of the resources that need to be expended each year. It is
a comparative tool to evaluate increases in damage costs between baseline and
future projections.
4.3 Future damage costs
Future damage costs were calculated by multiplying the baseline figures from
the preceding sections by the annual frequency of threshold rainfall events under
different emissions scenarios.
Annual Damage Cost = Damage Cost x Annual Frequency
The data used for these calculations is based on UKCP’s Weather Generator.
Under all of the emission scenarios, flooding becomes more frequent but does
not significantly differ between them (figure 24). Therefore, the figures reported
for future annual damage cost are based on the medium emissions scenario.
Under a medium emissions scenario, the annual damage cost for surface water
flooding may rise from a baseline figure of 222 HE to 291 HE by 2020 (31%). A
further increase, 44% above the baseline figure, is anticipated by 2050 (321
HE). Of the 1,186 at risk buildings in the case study area, this equates to almost
0.19 HE per building, rising to 0.24 HE by 2020 and just over 0.27 HE by 2050
(figure 25). This figure represents the mean; the annual damage costs per
building may range between a minimum of 0.09 HE to a maximum of 0.41 HE by
the 2020s (107 HE to 491 HE for the entire area).
62
Figure 24. Annual damage costs (expressed as HE) for surface water flooding in
the case study area under different emissions scenarios.
Figure 25. Average damage cost per building (HE) for surface water flooding in
each neighbourhood in the case study area.
Damage costs were also worked out for river flood events at two thresholds
indicating the depth of flooding: 60 to 80 mm and greater than 100 mm. Under
200
220
240
260
280
300
320
340
1990s 2020s 2050s
An
nu
al D
amag
e C
ost
(H
E)
Year
Low
Medium
High
0
0.05
0.1
0.15
0.2
0.25
0.3
0.35
0.4
1990s 2020s 2050s
Da
ma
ge
Co
st (
HE
) A
B
C
D
E
All
Neighbourhood
63
a medium emissions scenario, these events significantly varied in the percentage
increases. While the mean increased by 300% for 1:100 years flood events, the
maximum may be to 1600%. By 2050, the mean increase is projected to be
370%.
For 1:1000 river flood events, the increase by 2020 under a medium emissions
scenario could be 600%. However, although the damage cost is higher, these
events are much less frequent resulting in a lower annual damage cost (figure
26). By occurring on a more regular basis, albeit with less severity, the annual
damage cost for surface water flooding is greater. Moreover, the neighbourhood
analysis of flooding here shows that river flood events only happen in specific
neighbourhoods whereas surface water flooding happens across all
neighbourhoods and is unpredictable and localized (see figures 21 – 23).
Figure 26. Projected annual damage costs (HE) for river flooding per ‘at risk’
building in the case study area.
0
0.002
0.004
0.006
0.008
0.01
0.012
0.014
0.016
1990s 2020s 2050s
Da
ma
ge
Co
st (
HE
)
Year
River flooding 60 - 100 mm
River flooding > 100mm
64
4.4 Potential use of flood resistance and resilience measures
4.4.1 Local authority action
Assessing the physical costs in the manner demonstrated above will allow local
authorities to consider the benefits of introducing property-level flood protection
measures. If a council chooses to instigate property-level flood protection
measures, the strategy depends on the flood depth anticipated. In areas where
surface water flooding is likely to occur at depths below 1 m, such as Lower
Kersal, the strategy should aim to minimise water ingress through primary
access points in a building; a water exclusion strategy. At higher depths, a water
entry strategy may be required that places an emphasis on materials and
products that can assist in draining and consequent drying (DCLG 2007, 65).
Using the information above, a water exclusion strategy would be of greater
benefit to the area, particularly in Lower Kersal and Lower Broughton where
surface water flooding causes more damage.
There are a number of temporary measures that can easily be introduced to
protect doors, windows and airbricks from flood water. These are discussed in
greater depth in section 3.2.1. Individual property assessments may be needed
to ensure there are no other water access points could reduce the effectiveness
of these measures. The average cost of these measures are:
• Door Guards vary in cost from £60 to £500. Flood guards consisting of
strong baffles, which are fitted over door and air vent openings, can
prevent flood water entering the property. There are normally two main
doors in the houses in the case study area.
• Air brick seals also prevent water from entering the building. They cost
from £7.50 to £100 fitted for automatic air-brick covers (that can be
installed in advance). The number of airbricks on each property will vary.
• Stop valves can be fitted onto the main waste water outlet pipe to
minimise the sewer flooding after a particularly heavy rainfall. These can
be purchased for £150 with an estimated fitting cost of £100. In the case
study area, there is normally only one main waste water outlet pipe
(information courtesy of Salford City Council 2009).
Salford City Council considers 268 properties to be at a greater risk than
average and would particularly benefit from flood resistance measures.
65
Introducing the water exclusion methods described above, their estimated cost
for each property (factoring in costs such as community engagement and FRA’s)
is between £1,280 and £2,900. Even at the minimum increase of damage cost
cited in section 2.6 above, this outlay amounts to one third of the anticipated
minimum damage costs from surface water flooding by the 2020s. Taking a
long-term perspective means that installing flood protection measures is an
intuitive and rational use of resources.
Other councils have set a precedent. The Moray Council in northern Scotland was
the first such initiative: a total of £500, 000 provided 237 council-owned
properties with flood guards following severe flooding in 2002. The average price
per home was £2, 305. Council staff are trained in ‘flood response’ to fit flood
guards and provide targeted assistance to enable local residents to evacuate.
The initiative was partly funded through a Communities Scotland Grant (CSG) to
which individual households applied for means tested grants (providing 75% of
the total fund). The remaining 25% was paid by individual households who did
not pass the means test (Flood Protection Association 2004). Leeds City Council
was the first DEFRA pilot scheme to follow the same measure on a 1930’s
council house estate, protecting doors, windows and airbricks of 68 properties at
an average price of £2, 305 per home (Flood Protection Association 2007).
4.4.2 Potential uptake by individual homeowners
Whilst the local authorities can provide some funding for the implementation of
the flood-protection measures in private homes, the responsibility ultimately
rests with the homeowners. Kazmierczak and Bichard (2010) aimed to assess
the potential for uptake of flood-protection measures in part of the area
investigated by Rahman (2011). They interviewed 43 homeowners living in
Lower Kersal and Spike Island area. Over half of the respondents agreed or
strongly agreed that they were concerned by how climate change could affect
their properties. Nearly all (93%) respondents were aware that their properties
were located within a flood-risk zone, and 42% have been affected by flooding
before. However, nearly 90% assessed the risk of flooding as very low or low.
This suggests that whilst the respondents understand the climate change risk
and the nature of the area they live in, more effort is required to communicate
the risk of flooding. This may be difficult as the inhabitants are aware of the
existing flood-protection scheme; therefore, it is easier for them to deny the
residual risks of flooding.
66
There was a very low awareness of the types of resistance and resilience
measures that are available to homeowners. After hearing a description of the
measures, the respondents were asked to select the flood protection measures
that they would consider installing in their house. The list included door guards,
air-brick covers, tiled floors, raised electric fixtures and the replacement of a
timber staircase with a concrete one. The most popular measure considered by
the respondents was raising the electric fixtures even though this measure is
intrusive and could be costly. The least popular solutions were concrete
staircases and replacing timber or carpet flooring with ceramic tiles. Concern
was expressed over most of the listed measures: air-brick covers were seen as
source of condensation and dampness; tiled floors and concrete staircases were
rejected because they would make the house feel cold; and door guards were
considered to be difficult to fit (Kazmierczak and Bichard 2010). Detailed
information about the measures available and demonstrating what they look like
and how to use them could change some of these misconceptions.
Nearly half of the respondents were not prepared to contribute to the cost of
flood protection measures for their home, and only one-fifth would be prepared
to pay over £500. When this is compared against the prices of flood-protection
measures (see table 11) it is clear that there is a significant discrepancy
between the sum homeowners were willing to pay and the real cost of
adaptation measures. However, cost is not the only barrier as in Lower Kersal
and Spike Island, where there has been limited up-take by residents of cost free
flood protection measures (Salford City Council 2011). Underlying issues of
unawareness and risk denial may need to be addressed here.
Nevertheless, to ensure wider uptake the existing financial barriers must be
removed. In the areas of high material deprivation, such as the one described in
this study, a system of financial support to obtain the resistance and resilience
measures in the form of grants (similar to currently existing schemes for energy
saving measures) should result in a higher percentage of protected houses. In
more affluent areas, homeowners could be incentivised to invest in property-
level flood protection (Kazmierczak and Bichard 2010).
67
5 Conclusion
Climate change will happen and requires adaptation to moderate its most
hazardous effects. This risk-response report has considered increased flooding
and the potential consequences for residential buildings at conurbation and
neighbourhood scale.
Mapping the flood risk at conurbation scale allowed us to identified those areas
in GM most likely to suffer. Looking at the characteristics of those areas shows
that there are very small statistical differences between types and tenure of
housing. While owner-occupiers and landlords may have to bear the brunt of
costs to insure their property against flood risk, there are vulnerable groups who
may not have the capacity to enact these measures due to other pressures. We
suggest that local authorities and social housing landlords take some
responsibility for alleviating the risk to vulnerable populations. To that end, our
‘hotspots’ of risk (figure 13) identifies social housing with significant flood risks.
However, there has to be a strong case made to facilitate this kind of response
from statutory service providers. Going beyond simple financial calculations, the
neighbourhood-level case study in chapter 4 uses a tried-and-tested method of
calculating overall damage values that can be compared to future flood risk
under projected climate change for the area.
The key messages from the case study are that although the impact of surface
water flooding is less severe, there is a greater likelihood that flooding will occur
at neighbourhood level. Given the small variations between these
neighbourhoods in the severity and scope of surface water flooding, this means
that a larger number of vulnerable people will be affected with adverse effects
on their physical and mental health (Tapsell et al 2002). There is a strong
incentive for an intervention in making those properties flood resilient.
When compared against the average damage costs per building at risk for
various types of flooding, the cost of adopting flood proofing measures is far
below the total cost of rectifying the physical damage to buildings. When
weighed up against the current and projected damage costs of flooding, enacting
preventive rather than reactive measures may have the net effect of reducing
the financial burden to local authorities.
68
One issue remains in persuading property owners, landlords and local authorities
to invest in flood protection measures. The financial costs of implementing flood
resilience measures can be shared between the local authority and the local
residents. However, sustained awareness-raising, risk communication and the
removal of existing financial barriers are necessary.
69
Acknowledgements
The authors would like to acknowledge the Environment Agency for providing
river flooding and surface water flooding data, and Ordnance Survey for the use
of spatial data, including MasterMap. Many thanks go to the Homes and
Communities Agency for the permission to use the National Land Use Database
of Previously Developed Land (NLUD-PDL) dataset in the EcoCities project.
Thanks go to Anastasia Polyakova, who digitised a part of the brownfield
dataset.
The neighbourhood case study draws extensively on the M. Sc dissertation by
Asif Rahman (2011). We acknowledge Salford City Council for sharing the data
and information with us for the purposes of this dissertation.
70
6 References
ABI. 2010. Spending Review – ABI comments on flood investment plans. ABI
News Release 52/10, 20 October. Association of British Insurers, London.
ABI (no date) Flood Resilient Homes. What homeowners can do to reduce flood
damage. Association of British Insurers.
BCIS. 2011. Average price for different buildings [Online Resource].
Berry, K. 2004. Visual Condition Survey: Flood Protection Measures in Lower
Kersal and Spike Island Housing Estates. Eccles, Urban Vision.
Bichard, E. and Kazmierczak, A. 2009. Resilient Homes: Reward-based methods
to motivate householders to address dangerous climate change
Bichard, E. and Kazmierczak, A. 2011. Are homeowners willing to adapt to and
mitigate the effects of climate change? Climatic Change.
Blong, R. 2003. A new damage index. Natural Hazards. 30, 1 – 23.
Bowker, P. 2002. Making properties more resistant to floods. Municipal Engineer.
151, 197-205.
Brattebo, B.O. and Booth, D.B. 2003. Long-term stormwater quantity and
quality performance of permeable pavement systems. Water Research, 37,
4369-4376.
Carter, J. 2011. One city, multiple futures. Two scenarios for exploring the future
of Greater Manchester. EcoCities project, University of Manchester,
Manchester, UK
Carter, J. and Lawson, N. 2011. Looking back to inform the future: Greater
Manchester’s weather and climate. EcoCities project, University of
Manchester, Manchester, UK
Carter, J. and Ravetz, J. 2012. Climate change in Greater Manchester:
deepening and lengthening the consideration of adaptation responses,
EcoCities project, University of Manchester, Manchester, UK.
Cavan, G. 2011. Climate change projections for Greater Manchester. EcoCities
project, University of Manchester, Manchester, UK.
CIRIA. 2011. SuDS and SABs: Implications of new legislation for local
authorities. Evolution, 16-19.
Civic Amenities Act. 1967. London: HMSO.
Crichton, D. 1999. The risk triangle. In Natural Disaster Management, ed. J.
Ingleton. London, Tudor Rose, 102 – 3.
71
DCLG. 2006. Code for Sustainable Homes. A step-change in sustainable home
building practice. Department for Communities and Local Government,
London.
DCLG/ Environment Agency 2007. Improving the flood performance of new
buildings: flood resilient construction. London, H.M.S.O.
DCLG. 2008a. Planning Policy Statement 25: Development and Flood Risk
Practice Guide. Department for Communities and Local Government, London.
DCLG. 2008b. The English Indices of Deprivation 2007. Department for
Communities and Local Government, London.
DCLG. 2010. Planning Policy Statement 3: Housing. Communities and Local
Government. Department for Communities and Local Government, London.
DEFRA. 2004. Making Space for Water: Developing a New Government Strategy
for Flood and Coastal Erosion Risk Management in England: A Consultation
Exercise. Department for Environment, Food and Rural Affairs, London.
DEFRA. 2008a. Developing the evidence base for flood resistance and resilience. R&D
Technical Report FD2607/TR1. Department for Environment, Food and Rural
Affairs, London
DEFRA. 2008b. Resilience grants pilot projects. Department for Environment,
Food and Rural Affairs, London.
DEFRA. 2009. Government grants to local authorities for household-level flood
mitigation. Department for Environment, Food and Rural Affairs, London.
DEFRA. 2010. Surface Water Management Plan Technical Guidance. Department
for Environment, Food and Rural Affairs, London.
Douglas, I. 1998. Urban floodplains and slopes: the human impact on the
environment in the built-up area. In Exploring Greater Manchester: A
Fieldwork Guide. Eds. Gardiner, A., Hindle, P., McKendrick, J. and Perkins, C.
Eds. Manchester Geographical Society, Manchester.
EA. 2009. Flooding in England. A national assessment of flood risk. Environment
Agency, Bristol.
Environment Agency. 2009. Flood Risk dataset and surface water flooding
dataset.
Environment Agency and Salford City Council. 2009. Climate Action, Lower
Kersal and Spike Island Project, phase one project report.
Environment Agency. 2004. Flood zones for England. Environment Agency, Flood
Mapping Programme.
72
EPA (no date) Reducing urban heat islands: compendium of strategies. United
States Environmental Protection Agency.
Evans, E., Ashley, R., Hall, J., Penning-Rowsell, E., Saul, A., Sayers, P., Tjorne,
C., Watkinson, A. 2004. Foresight. Future Flooding. Scientific summary:
Volume 1 - Future risks and their drivers. Office of Science and Technology,
London.
Falconer, R.H., Cobby, D., Smyth, P., Astle, G., Dent, J., Golding, B. 2009.
Pluvial flooding: new approaches in flood warning, mapping and risk
management. Journal of Flood Risk Management, 2, 198-208.
Fedeski, M. and Gwilliam, J. 2007. Urban sustainability in the presence of flood
and geological hazards: the development of a GIS-based vulnerability and
risk assessment methodology. Landscape and Urban Planning, 83, 50 – 61.
Flood Protection Association. 2004. Case Study – Leeds City Council.
Flood Protection Association. 2004. Case Study – The Moray Council.
Fordham Research Group. 2007. Private Sector Stock Condition Survey. Salford:
Salford City Council.
Golding, B.W. 2009. Long lead time flood warnings: reality or fantasy?
Meteorological Applications, 16, 3–12.
Gwilliam, J., Fedeski, M., Theuray, N., Lindley, S. and Handley, J. 2006. Methods
for Assessing Risk from Climate Hazards in Urban Areas. Municipal Engineer,
159 (4), 245 – 55.
Harries, T. (2008) Feeling secure or being secure? Why it can seem better not to
protect yourself against a natural hazard. Health, Risk and Society, 10 (5),
479-90.
HCA. 2011. National Land Use Database of Previously Developed Land. Homes
and Communities Agency
JBA Consultancy. 2011. Manchester City, Salford City and Trafford Councils
Level 2 Hybrid SFRA.
Jenkins, G. J., Perry, M. C., Prior, M. J. 2009. The climate of the United Kingdom
and recent trends. Revised edition. Met Office Hadley Centre, Exeter
Johnson, C., and Priest, S. 2008. Flood risk management in England: a changing
landscape of risk responsibility? International Journalof Water Resources D,
24, 513-25
Kazmierczak, A., and Bichard, E. 2010. Investigating homeowners’ interest in
property-level flood protection. International Journal of Disaster Resilience in
the Built Environment, 1(2), 157-172.
73
Kazmierczak, A. and Cavan, G. 2011. Surface water flooding risk to urban
communities: Analysis of vulnerability, hazard and exposure. Landscape and
Urban Planning, 103 (2), 185-97
Kazmierczak, A. and Handley, J. 2011. The vulnerability concept: use within
GRaBS.
Kazmierczak, A. 2012. Heat and social vulnerability in Greater Manchester: a
risk-response case study. EcoCities, The University of Manchester.
Kenna, S. 2008. Do social housing providers across Yorkshire and the East
midlands have effective flood risk management in place when maintaining
and repairing their housing stock? Journal of Building Appraisal, 4, 71-85.
Kurtz, T. 2007. Peak flow and flow volume reductions for urban retrofit projects
in Portland, Oregon. Presentation to 2nd National Low Impact Development
(LID) Conference.
Lawson, N. and Carter, J. 2009. Greater Manchester Local Climate Impacts
Profile (GMLCIP). A report on the development of a LCLIP for Greater
Manchester, The University of Manchester.
Lindley, S. J., Handley, J. F., Theuray, N., Peet, E., McEvoy, D .2006. Adaptation
Strategies for Climate Change in the Urban Environment - assessing climate
change related risk in UK urban areas. Journal of Risk Research, 9 (5), 543-
68.
Mott MacDonald. 2008.Review of regulatory and legal options for reducing
surface water in sewers: final report. OFWAT.
Nicholas, J., Holt, G.D., Proverbs, D.G. 2001. Towards standardizing the
assessment of flood damaged properties in the UK. Structural Survey, 19 (4),
163-72.
Office for National Statistics. 2001. Census 2001 dataset. London, Office of
National Statistics.
Palmer, T.N. and Räisänen, J. 2002. Quantifying the risk of extreme seasonal
precipitation events in a changing climate. Nature, 415, 512-514
Pauleit, S., Ennos, R., Golding, Y. 2005. Modelling the environmental impacts of
urban land use and land cover change - a study in Merseyside, UK. Landscape
and Urban Planning, 71 (2-4), 295-310.
Perry, T. and Nawaz, R. 2008. An investigation into the extent and impacts of
hard surfacing of domestic gardens in an area of Leeds, United Kingdom.
Landscape and Urban Planning 86 (1), 1-13.
Pitt, M. 2007. Learning lessons from the 2007 floods, an independent review by
Sir Michael Pitt. Interim report. Cabinet Office, London
74
Pitt, M. 2008. Learning lessons from the 2007 floods, an independent review by
Sir Michael Pitt. Cabinet Office, London
Polyakova, A. 2011. Assessing the Potential Climate Change Adaptation
Functions of Green Spaces Redeveloped from Brownfields in Greater
Manchester. Unpublished M.Sc thesis, University of Manchester.
Pratt, C. J. 1995. A review of source control of urban stormwater runoff. Journal
of the Chartered Institution of Water and Environmental Management, 9(2),
132-9.
Rahman. A. 2011. Assessing social and physical flood risk in an urban area: the
case of Greater Manchester. Unpublished M.Sc thesis, University of
Manchester.
Ripl, W. 1995. Management of water cycle and energy flow for ecosystem
control: the energy-transport-reaction (ETR) model. Ecological Modelling, 78,
61-76.
Royal Horticultural Society. 2005. Front gardens: are we parking on our
gardens? Gardening Matters Series, Royal Horticultural Society.
Salford City Council. 2008. Planning Guidance: Flood Risk and Development.
Salford City Council. 2009. Draft Core Strategy.
Salford City Council. 2011. Completion Of The Resilient Homes Community
Climate Change Action Plan For Lower Kersal And Spike Island 2009/11. Lead
Member Report, 8 March.
Sanders, C.H., Phillipson, M.C., 2003. UK adaptation strategy and technical
measures: the impacts of climate change on buildings. Building Research &
Information, 31, 210-221.
Scholz, M. 2003. Sustainable operation of a small-scale flood-attenuation
wetland and dry pond system. Water and Environment Journal. 19 (3), 171-
5.
Soetanto , R . , Proverbs , G . D., Nicholas , J. 2002. Assessment of flood
damage to domestic properties: surveyors’ perceptions of flood
characteristics. RICS Foundation construction and building research
conference, The Royal Institution of Chartered Surveyors, Nottingham Trent
University.
Soetanto, R. and Proverbs, D.G. 2004. Impact of flood characteristics on
damage caused to UK domestic properties: the perceptions of building
surveyors. Structural Survey, 22 (2), 95-104.
75
Tapsell, S.M., Penning‐Rowsell, E.C. Tunstall, S.M., Wilson, T.L. 2002.
Vulnerability to flooding: health and social dimensions. Philosophical
Transactions of the Royal Society A, 360, 1511‐25.
Thieken, A.H., Muller, M., Kreibich, H., Merz, B. 2005. Flood damage and
influencing factors: new insights from the August 2002 flood in Germany.
Water Resoures Research. 41.
Uhl, M. and Scheidt, L. 2008. Green roof storm water retention – monitoring
results. 11th International Conference on Urban Drainage, Edinburgh,
Scotland, UK.
UK Town and Country Planning Order, 1995. General Permitted Development
Order, Statutory Instrument No. 418, Article 4.
Williams, K., Joynt, J.L.R., Hopkins, D. 2010. Adapting to climate change in the
compact city: the suburban challenge. Built Environment, 36, 105-15.
Woods-Ballard, B., Kellagher, R., Martin, P., Jefferies, C., Bray, R. Shaffer, P.
2007. The SuDS Manual C697. CIRIA, London.
Zevenbergen, C., Gersonius, B., Puyan, N., van Herk, S. 2007. Economic
feasibility study of flood proofing domestic dwellings. In Advances in urban
flood water management. Eds. Ashley, R., Garvin, S., Pasche, E.,
Vassilopoulos, A. and Zevenbergen, C. Taylor and Francis, London, 299-319.