The University of
Warwick
Development
Masterplan
Flood Risk Assessment
Black
The University of
Warwick
Development
Masterplan
Flood Risk Assessment
June 2007
Ove Arup & Partners Ltd
The Arup Campus, Blythe Gate, Blythe Valley Park,
Solihull, West Midlands. B90 8AE
Tel +44 (0)121 213 3000 Fax +44 (0)121 213 3001
www.arup.com
This report takes into account the
particular instructions and requirements
of our client.
It is not intended for and should not be
relied upon by any third party and no
responsibility is undertaken to any third
party
Job number
115438
The University of Warwick
Development Masterplan
Flood Risk Assessment
Document Verification
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Development Masterplan
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Job number
115438
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Flood Risk Assessment
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FRA 07/01
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David Schofield
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David Schofield
Andy Lloyd
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The University of Warwick
Development Masterplan
Flood Risk Assessment
Contents
Page
1
1
Executive Summary
2
Introduction
2
2.1
Previous Flood Risk Assessments
2
2.2
The Development Proposals
2
2.3
Flood Risk Planning Context
2
2.4
The Sequential and Exception Tests
5
3
Description of the Site
6
3.1
Surrounding Area
6
3.2
Description of the Catchment
6
3.3
Westwood Brook Subcatchment
7
3.4
Whitefield Coppice Subcatchment
8
3.5
Existing Surface Water Infrastructure
9
3.6
Gibbet Hill Subcatchment
10
4
Description of the Proposed Development
11
5
Operating Authorities
12
5.1
Environment Agency
12
5.2
Coventry City Council
12
5.3
Warwickshire County Council
13
5.4
Warwick District Council
13
5.5
Severn Trent Water
13
5.6
Key Infrastructure Requirements
13
6
7
Description of Flooding Mechanisms & Mitigation
15
6.1
Table 1: Potential Flood Risk Summary
15
6.2
Table 2: Flood Risk Identification
16
6.3
Fluvial Flood Risk
16
6.4
Groundwater Flood Risk
17
6.5
Overland Flow Flood Risk
17
6.6
Artificial Drainage System Flood Risk
18
6.7
Infrastructure Failure Flood Risk
18
6.8
Climate Change Flood Risk
18
6.9
Historical Flooding Data
19
6.10
Emergency Access Requirements
19
6.11
Maintenance Requirements
19
Preliminary Surface Water Analysis & Design
20
7.1
Surface Water Management Strategy
20
7.2
Preliminary Surface Water Storage Calculations
21
7.3
Westwood Brook Fluvial Modelling (Refer to Appendix C)
21
The University of Warwick
8
9
Development Masterplan
Flood Risk Assessment
Conclusions and Recommendations
23
8.1
The Sequential and Exception Tests
23
8.2
Approving Authority Consultation
23
8.3
Fluvial Flood Risk Conclusions
23
8.4
Groundwater Flood Risk Conclusions
24
8.5
Overland Flow Flood Risk Conclusions
24
8.6
Artificial Drainage System Flood Risk Conclusions
24
8.7
Infrastructure Failure Flood Risk Conclusions
25
8.8
Climate Change Flood Risk Conclusions
25
8.9
Maintenance and Access Flood Risk Conclusions
25
8.10
Recommendations
26
References
Appendices
Appendix A
Site Photographs
Appendix B
Figures
Appendix C
Westwood Brook Hydraulic Analysis
Appendix D
Record of Consultation
Appendix E
Topographic Survey
27
The University of Warwick
1
Development Masterplan
Flood Risk Assessment
Executive Summary
Arup have been commissioned by the University of Warwick to undertake a Flood Risk
Assessment (FRA), to identify the potential flood risk issues associated with the proposed
new development plan for the University. The FRA will form part of an outline planning
submission for the proposed development and be submitted to the local planning
authorities, Coventry City Council and Warwickshire County Council.
The University of Warwick catchment is located on the south westerly outskirts of Coventry,
close to the A45 trunk road and on the edge of the urbanised conurbation. The overall
catchment area incorporates three developed elements; Westwood Campus, the Central
Campus and Gibbet Hill Campus. Split by Gibbet Hill Road, the eastern side of the
university site lies within the planning jurisdiction of Coventry City Council while the western
side lies within the control of Warwickshire County Council.
The University catchment covers an estimated total area of some 200 hectares, of which
approximately 50% of the catchment is developed and impermeable. The developed area
consists of large and small buildings, which are used for educational, research,
administration or residential purposes. There are also a number of water features. The long
term development masterplanning for the University of Warwick will encompass areas of
new development, areas of redevelopment and extensive areas of hard and soft
landscaping to enhance the amenity value and ecological potential of the Campus.
For the purpose of this FRA and surface water masterplanning, the University catchment
has been split into two main subcatchments; the Westwood Brook Subcatchment and the
Whitefield Coppice Subcatchment. Both subcatchments ultimately drain to the south of the
University and into the Canley Brook, which itself flows in a south westerly direction before
discharging further downstream into the Finham Brook. Both of these watercourses are
designated main rivers by the Environment Agency.
A number of operating authorities have been consulted, including the Environment Agency,
who required that a hydraulic analysis of the Westwood Brook be undertaken. Tables 1 and
2 (adapted from CIRIA document C624: Development and Flood Risk, Guidance for the
3
Construction Industry ) indicates that the potential sources of flood risk to the development
site or adjacent areas to be considered by this development FRA are as follows:
•
Fluvial;
•
Groundwater;
•
Overland flow of surface water;
•
Capacity exceedance of artificial drainage systems;
•
Infrastructure failure.
Flood Risk Conclusions (FRC) for the proposed development were determined and how
they can be removed or reduced to acceptable levels using appropriate Flood Mitigation
Measures (FMM). From consultation with the approving authorities leading up to the
production of this flood risk assessment, the key infrastructure requirements pertaining to
the University development masterplan were also determined.
It is recommended that this Flood Risk Assessment be accepted and that the issues raised
herein are addressed in the future and detailed design stages of the proposed development,
paying careful consideration to the mitigation measures outlined . For specific development
proposals, further bespoke and more detailed flood risk assessments may be required. It is
recommended that the University of Warwick flood risk assessment should be considered
suitable for the proposed main Campus Masterplan, in terms of managing flood risk in a
sustainable manner.
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2
Development Masterplan
Flood Risk Assessment
Introduction
Arup have been commissioned by the University of Warwick to undertake a Flood Risk
Assessment (FRA), to identify the potential flood risk issues associated with the proposed
new development plan for the University. The FRA will form part of an outline planning
submission for the proposed development and be submitted to the local planning
authorities, Coventry City Council and Warwickshire County Council.
1
A University Development Plan Drainage Scoping Study incorporating foul and surface
water sewerage, was undertaken by Arup in September 2004. The Study identified key
drainage strategy issues pertaining to the proposed new development plans and outlined
general concerns related to flood risk.
This FRA has been prepared using the precautionary principle to identify and highlight the
issues associated with flood risk at the site and represents an enhanced quantitative
assessment. This report has been prepared with reference to Planning Policy Statement 25
2
(PPS25): Development and Flood Risk , and follows the Flood Risk Assessment
methodology prescribed in CIRIA document C624: Development and Flood Risk, Guidance
3
for the Construction Industry .
2.1
Previous Flood Risk Assessments
A flood risk assessment was prepared for the site in August 2006 for a preceding master
plan, in accordance with the now superseded Planning Policy Guidance Note 25:
4
Development and Flood Risk (PPG 25) . While this FRA was never formally issued, it was
sent to the Environment Agency for comment. The EA’s comments from this review were
subsequently incorporated ready for future issue.
This FRA is an update of the 2006 FRA to incorporate the changes introduced by PPS 25²
and the small changes made to the university master plan.
2.2
The Development Proposals
Development of the University began some 40 years ago and is now one of the leading
teaching and research establishments in the UK. Over this period the University expansion
has been guided by successive development plans, the last one approved in 1994.
This report covers the proposed expansion of the University over the next 10 years. The
long term development masterplan for the University of Warwick will encompass areas of
new development, areas of redevelopment and extensive areas of hard and soft
landscaping to enhance the amenity value and ecological potential of the Campus.
The works will include improvements to academic, residential and administration facilities.
2.3
Flood Risk Planning Context
Planning policy guidance exists to ensure that flood risk issues are considered when
planning and designing new development. A detailed flood risk assessment is required for
most developments at the time of a planning submission.
2.3.1
Planning Policy Guidance Note 25
Now superseded, Planning Policy Guidance Note 25: Development and Flood Risk
4
(PPG25) was published by the Department of Transport Local Government and the
Regions (DTLR) in July 2001. PPG 25 explained how flooding should be taken into account
when planning for development in England. PPG 25 defined three principal flood risk zones
for fluvial and coastal flooding.
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Flood Risk Assessment
Table 1 from PPG 25 (Flood Zones and degree of flood risk):
Flood Risk •
Flood Zone
1
Little or no risk (Less than 0.1%)
2
Low to medium risk
River: 0.1-1%
Tidal & Coastal: 0.1-0.5%
River: 1% or greater
3
High risk
Tidal & Coastal: 0.5% or greater
Flood Zone 3 was divided into three sections, depending upon the extent of existing
development in an area: 3a (developed areas), 3b (undeveloped & sparsely developed
areas) and 3c (floodplains). Within PPG 25 “floodplain” was defined as “unobstructed or
active areas where water regularly flows in time of flood”.
2.3.2
Planning Policy Statement 25
This FRA has been prepared with reference to Planning Policy Statement 25 (PPS 25):
2
Development and Flood Risk , and follows the methodology prescribed in CIRIA document
3
C624: Development and Flood Risk, Guidance for the Construction Industry . CIRIA
document C624 provides current best practice guidance on the assessment and
management of flood risk in relation the built environment.
The Department for Communities and Local Government (DCLG) intend that PPS 25,
together with the accompanying practice guide, replaces PPG 25. The final version of PPS
25 was formally launched on 7 December 2006.
Planning Policy Statement 25 outlines contemporary government policy on planning to
reduce flood risk and the contribution of best practice drainage techniques to a more
sustainable development.
The aim of PPS 25 is to ensure that flood risk is taken into account at all stages in the
planning process and to avoid inappropriate development in areas at risk of flooding, and to
direct development away from areas at highest risk. It does this by formulating a sequential
risk-based approach towards flooding to be adopted at all levels of planning. Ultimately,
those proposing developments are responsible for:
•
Demonstrating that the proposals are consistent with the policies within PPS 25.
•
Providing a FRA to show:
1. The proposed development is unlikely to be affected by flooding and whether the
development will increase flood risk elsewhere.
2. The development is safe and where possible reduces flood risk.
3. Management and funding arrangements to ensure the site can be developed and
occupied safely throughout its proposed lifetime.
•
Implementing designs which both reduce flood risk for the development and its
surrounding area.
•
Identifying opportunities to reduce flood risk, enhance biodiversity, protect the historic
environment and seek collective solutions to managing flood risk.
•
Flood probability is defined by the annual probability of exceedance of a flood event. A 0.1% annual probability event will be
equalled or exceeded once every thousand years on average (a return period of 1 in 1000 years). A 0.5% annual probability event
has an average return period of 1 in 200 years. A 1% annual probability event has an average return period of 1 in 100 years.
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Flood Risk Assessment
A key difference between PPG 25 and PPS 25 are changes to the definition of flood zones,
the flood risk vulnerability of different land use types has been more clearly defined and the
“Sequential Test” now includes an “Exception Test”.
PPS 25 proposes that where the Sequential Test has been carried out and it is found that
certain types of development may be permitted within a given flood risk zone the Exception
Test may be applied to see whether it is possible to manage flood risk while allowing
necessary development to occur.
PPS 25 does not change the definition of Flood Zones 1 and 2, but does change the
definition of the sub-zones within Flood Zone 3. PPS25 retains the “floodplain” as a subzone within Zone 3, with an amended definition. These Flood Zones are shown overleaf in
Table D.1 from PPS25. Table D.2 of PPS25 (not shown) determines Flood Risk
Vulnerability Classification as; Essential Infrastructure, Highly Vulnerable, More Vulnerable,
Less Vulnerable and Water Compatible Development.
These two key table are then referenced together to show Flood Risk Vulnerability and
Flood Zone Compatibility in Table D.3, shown overleaf.
Table D.1: Flood Zones (as defined by Annex D in PPS 25):
Flood Zone
Definition
Zone 1 Low Probability
This zone comprises land assessed as having a less
than 1 in 1000 annual probability of river or sea
flooding in any year (<0.1%).
Zone 2 Medium Probability
This zone comprises land assessed as having
between a 1 in 100 and 1 in 1000 annual probability of
river flooding (1% - 0.1%) or between a 1 in 200 and 1
in 1000 annual probability of sea flooding (0.5% 0.1%) in any year.
Zone 3a High Probability
This zone comprises land assessed as having a 1 in
100 or greater annual probability of river flooding
(>1%) or a 1 in 200 or greater annual probability of
flooding from the sea (>0.5%) in any year.
Zone 3b Floodplain
This zone comprises land where water has to flow or
be stored in times of flood. Strategic flood risk
assessments (SFRAs) should identify this flood zone
as land which would flood with an annual probability of
1 in 20 (5%) or greater in any year or is designed to
flood in an extreme (0.1%) flood, or at another
probability to be agreed between the LPA and the
Environment Agency, including water conveyance
routes.
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Table D.3 •: Flood Risk Vulnerability and Flood Zone Compatibility (as defined by
Annex D in PPS25):
Essential
Infrastructure
Water
Compatible
Highly
Vulnerable
More
Vulnerable
Less
Vulnerable
Flood Zone 1
Flood Zone 2
Exception Test
Flood Zone 3a
Exception Test
Exception Test
Flood Zone 3b
“Floodplain”
Exception Test
Development is appropriate.
Development should not be permitted.
2.4
The Sequential and Exception Tests
A sequential risk based approach to determining the suitability of land for development in
flood risk areas is essential at all levels of the planning process. The Sequential Test aims
to ensure preference is given to land within flood zone 1 prior to land in zones 2 and 3 being
considered for the same development. It also ensures that the flood vulnerability of the
proposals is taken into account when locating developments within flood zones 2 and 3.
Should the sequential approach show it is not possible for the development to be located in
zones of lower flood risk due to other wider sustainability objectives, it may be possible to
show using the Exception Test that the development is still feasible by the management of
flood risk.
2.4.1
Sequential Test
The sequential test aims to steer development to the areas of lowest flood risk i.e. flood
zone 1. In this instance, the majority of the University Campus lies outside of any fluvial
floodplain, with the exception of the areas which lie directly adjacent to the Westwood and
Canley Brook.
The type of development being proposed can be classed as ‘less vulnerable’, but also in
instances as ‘more vulnerable’ where development will consist predominantly of student
halls of residents and educational blocks. The intention has been to steer development
clear of any flood zone 3.
The majority of development is suitable for the parts of the university campus which lie
outside of the fluvial floodplain i.e. flood zones 1 and 2 (except the unlikely ‘highly
vulnerable’ development in a flood zone 2). However, if future specific proposals are
proposed for flood zones 3a and 3b, a future Exception Test may required with the
development specific FRA.
2.4.2
Exception Test
Following a review of the floodplain of the Canley Brook and recent Arup modelling of the
Westwood Brook (refer to Appendix C), it can be confirmed that no part of the current
masterplan lies within flood zones 2 or 3 and therefore an exception test is not required for
the University masterplanning proposals.
•
This table does not show the application of the Sequential Test (which guides development to Flood Zone 1 first, then Flood Zone 2
and then Flood Zone 3), FRA requirements, or the policy aims for each Flood Zone.
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Description of the Site
Refer to site photographs in Appendix A and figures within Appendix B.
3.1
Surrounding Area
The University of Warwick catchment is located on the south westerly outskirts of Coventry,
close to the A45 trunk road and on the edge of the urbanised conurbation. The overall
catchment area incorporates three developed elements; Westwood Campus, the Central
Campus and Gibbet Hill Campus. The Westwood Campus is the northernmost part of the
University and is located off Kirby Corner Road. The Central Campus and Gibbet Hill
Campus to the south are located off Gibbet Hill Road.
Split by Gibbet Hill Road, the eastern side of the university site lies within the planning
jurisdiction of Coventry City Council while the western side lies within the control of
Warwickshire County Council. For any planning application relating to the overall
development masterplan, a detailed flood risk assessment (FRA) must be submitted to each
planning authority.
3.2
Description of the Catchment
The University catchment covers an estimated total area of some 200 hectares, of which
approximately 50% of the catchment is developed and impermeable. The developed area
consists of large and small buildings, which are used for educational, research,
administration or residential purposes. There are also a number of water features, large
manicured areas with a permeable natural appearance, complimented by numerous
hedgerows and tree lines that provide valuable natural habitat to flora and fauna. The
remainder of the site lies within the surrounding greenbelt, which is predominately used for
arable farming
The University has a small subcatchment located on Gibbet Hill, with the site being located
close to a residential area. It is connected to the main campus by Gibbet Hill Road and a
separate pedestrian and cycleway that passes through a natural area of significant fluvial
and ecological importance.
However, for the purpose of this FRA and surface water masterplanning, the University
catchment has been split into two main subcatchments; the Westwood Brook Subcatchment
and the Whitefield Coppice Subcatchment. Both subcatchments ultimately drain to the
south of the University and into the Canley Brook, which itself flows in a south westerly
direction before discharging further downstream into the Finham Brook. Both of these
watercourses are designated main rivers by the Environment Agency.
3.2.1
Canley Brook Floodplain
Part of the University catchment lies within the 100 year indicative floodplain of the Canley
Brook (shaded blue below). However, no University above ground infrastructure lies within
this floodplain and this constraint must be adhered to for any future development. Two large
ponds located adjacent to the Tocil Wood are within the indicative 100 year fluvial floodplain
of the Canley Brook. This water body is not believed to be a fluvial attenuation structure
and is not suitable for such a function due to its location within the indicative floodplain.
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100 Year (1%) Fluvial Floodplain (image courtesy of Environment Agency website)
Coventry City
University Campus
Westwood Brook
Canley Brook Floodplain
Confluence with Finham Brook
3.3
Westwood Brook Subcatchment
The Westwood Brook flows from the north through the subcatchment either in open channel
or through a series of culverts. A number of outfalls discharge directly into the Westwood
Brook, which flows through the campus either in open channel or culverted. The pipes,
channels and Westwood Brook all outfall into the Canley Brook, which flows between the
Central Campus and Gibbet Hill site.
The majority of the University’s built environment is located in this subcatchment and it was
important to understand the potential flood risk from the Westwood Brook. Consequently, a
detailed hydraulic analysis was carried out as part of this FRA, in order that the 1 in 100
year floodplain for the Westwood Brook could be determined (refer to section 3.3.2 &
Appendix C).
It should be noted that with the current surface water infrastructure, surface water draining
into the Lakeside water bodies (refer to section 3.4 below), transfers across to the
Westwood Brook subcatchment and discharges into the Westwood Brook via a surface
water pumping station. A potential reduction in this volume from a catchment modification
will be appraised in section 3.4.2.
This subcatchment lies within the planning jurisdiction of Coventry City Council.
3.3.1
Existing Hydraulic Features
There is a water body located adjacent to the Tocil flats (located to the east of the main
campus), although it is not used for the attenuation of surface water runoff. As mentioned
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above, the watercourse flows through a number of culvert and bridge structures on its route
through the subcatchment.
Surface water runoff from the Heronbank and Lakeside ponds is also pumped into the
Westwood Brook via a large pumping station, located in front of the Engineering Block on
University Road. The exact details of this pumping station are currently unknown.
A foul water pumping station, located adjacent to the Tocil Flats collects foul flows from the
whole of the main university campus and discharges them via a rising main which passes
under the Canley Brook into a Severn Trent Sewer located within the housing development
to the East of the site.
3.3.2
Westwood Brook Hydraulic Analysis
The floodplain of this watercourse was unknown, as no previous hydraulic model existed.
The Environment Agency required a detailed hydraulic analysis be carried out as part of this
FRA, in order that the 1 in 100 year floodplain for the Westwood Brook could be determined
and any flood risk understood (the results of this analysis can be found in Appendix C). The
extent of the floodplain will ultimately influence where future buildings in the subcatchment
can be located and drive final engineering solutions. Any encroachment into the floodplain
will require compensation storage on a level-for-level and volume-for-volume basis.
3.4
Whitefield Coppice Subcatchment
This subcatchment is mostly drained by a small watercourse (name unknown) to the east of
Whitefield Coppice, which joins the Canley Brook near Cryfield Grange. The Environment
Agency does not require a fluvial hydraulic modelling exercise to be carried out for this
watercourse due to its minimal flood risk and there are no concerns about floodplain
encroachment, as the subcatchment is elevated above any such constraint.
The subcatchment lies within the planning jurisdiction of Warwickshire County Council.
3.4.1
Existing Hydraulic Features
Within the centre of the Lakeside Residences and Heronbank development there are a
series of three water feature lakes. This significant water body is only partly used for the
attenuation of surface water runoff from some of the Lakeside Residences. The remainder
of the Lakeside Residences and those at Heronbank drain attenuated surface water flows
from below ground surface water infrastructure to the lakes, some of which are pumped
outfalls. All flows from the feature lakes eventually drain to the surface water pumping
station, located in front of the Engineering Block on University Road, before discharging into
Westfield Brook.
Behind the Heronbank buildings on the Hill Top site is a small pond, which is not used for
attenuating surface water runoff. The location of the pond suggests there is a potential flood
risk for the Heronbank buildings during extreme storm events, as there is evidence of
overland flow problems in this area, resulting from surface water shedding from the elevated
Hill Top site.
3.4.2
Modification of Lakeside Water Features
The Lakeside and Heronbank Residences that drain directly to the three lakes or via below
ground proprietary detention tanks, currently discharge to the Westwood Brook via a large
pumping station in front of the Engineering Block on University Road. Initial feasibility
design work has confirmed that it would be possible to reverse the direction of flow of the
upper two lakes and drain them in the direction of Whitefield Coppice, which would both
reduce a potential flood risk from infrastructure failure and reduce the operational costs
associated with the pumping station.
There would be a number of sustainability and flood risk advantages from this engineering
exercise. Firstly it will result in a reduction of flows directed towards the surface water
pumping station on University Road and there will be an operational cost saving for every
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cubic metre of surface water runoff diverted and subsequently drained by gravity. Initial
calculations have indicated there is an estimated 1.75 hectares of impermeable area
connected to the lakes that could be re-directed and provided with a gravity outfall. The
assumed saving (which requires detailed clarification); working on the basis of 700mm
3
average annual rainfall, this translates to an average 12,250m of surface water runoff per
annum that would no longer require pumping into the Westwood Brook.
Secondly, mitigating a flood risk by providing a gravity outfall option rather than the reliance
upon a pumping station discharge would reduce a potential flood risk at both Lakeside and
Engineering Road as a result of infrastructure failure of loss of power for any length of time
or during extreme storm events. There are also two timber construction (possibly with
submerged concrete support structures; no as-built drawings are available) dams separating
the three lakes by providing partitions. In the unlikely event that one of these dams fail, the
sudden loss of water would create a surge of water that could pose a flood risk downstream.
Thirdly, initial feasibility design work has confirmed that the upper two lakes can be modified
to be used as attenuation balancing ponds, saving in infrastructure costs for the proposed
development in this area, although further design work is required to demonstrate that there
will be no increased flood risk to the buildings during extreme storm events. This
modification would require the direction of flow through these ponds to be reversed and the
upper lake permanently drained down to maintain a normal water level identical to the
middle lake (83.37m AOD). Existing control structures will require modification and a new
outfall with flow control designed. As the depth of the lake is not known, this modification
would require additional excavation to maintain a wet feature, or the area could be modified
into a combined shallow wetland and flow balancing feature, with a strong landscape,
ecology and natural habitat bias.
Additional detailed design work is required to confirm the initial feasibility work and also
confirm to the Environment Agency that there will be no detrimental effect to the base flows
in the Westwood Brook once the diversion is made.
3.5
Existing Surface Water Infrastructure
Surface water runoff within the overall catchment is currently collected from both external
paved areas including roads (via gullies and channel drainage) and roof areas (via rainwater
down pipes). These gullies and down pipes are connected locally through numerous piped
systems, some of which discharge into the network of open drainage channels which cross
the University site and some discharge directly to open water features. Within the Lakeside
Residences and Heronbank surface water infrastructure are three below ground detention
3
tanks of 360, 150 and 90m and their respective discharge rates (two of which are pumped)
are 10.6l/s, 8.4l/s and 5.0l/s. These proprietary detention tanks control and attenuate the
surface water flows before discharging into the water feature lakes in that area.
A significant percentage of the site’s surface water runoff is pumped into the Westwood
Brook via a large pumping station, located in front of the Engineering Block on University
Road. This pumping station contains two lift pumps which discharge surface water runoff
into an adjacent breakhead chamber. This is not a storm ancillary and is in operation for all
surface water flows generated during precipitation in that part of the Campus catchment.
Two of the surface water detention tanks serving the Lakeside Residences are thought to
have pumping station ancillaries to lift the attenuated flows into breakhead chambers, for
controlled gravity discharges into the adjacent lakes.
There are no reported flooding problems associated with any of the catchment’s existing
surface water infrastructure.
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3.6
Development Masterplan
Flood Risk Assessment
Gibbet Hill Subcatchment
This small subcatchment is located on Gibbet Hill and is connected to the main campus by
Gibbet Hill Road and a separate pedestrian and cycleway that passes through a natural
area of significant fluvial and ecological importance. It is located well outside of any fluvial
floodplain. The surface water system of pipes and open structures all outfall directly into the
Canley Brook and its key flood risk is to sustainably manage future surface water runoff.
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4
Development Masterplan
Flood Risk Assessment
Description of the Proposed Development
Development of the University began some 40 years ago and is now one of the leading
teaching and research establishments in the UK. Over this period the University expansion
has been guided by successive development plans, the last one approved in 1994.
This report covers the proposed expansion of the University over the next 10 years. The
long term development masterplan for the University of Warwick will encompass areas of
new development, areas of redevelopment and extensive areas of hard and soft
landscaping to enhance the amenity value and ecological potential of the Campus.
The works will include improvements to academic, residential and administration facilities;
refer to figures 1, 2 and 3 in Appendix B. The approximate areas of new development are
detailed below:
Approximate Gross External Floor Areas (m²)
Academic
Other
Admin
Residential
Totals
Area 1
5,000
0
4,600
0
9,600
Area 2
36,300
14,900
10,400
12,400
74,000
Area 3
0
0
0
3,500
3,500
Area 4
0
0
2,700
26,650
29,350
Area 5
8,600
8,100
6,950
6,650
30,300
Area 6
7,600
0
650
7,800
16,050
Area 7
3,300
0
-1,300
0
2,000
Area 8
4,200
0
2,000
0
6,200
Totals
65,000
23,000
26,000
57,000
171,000
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5
Development Masterplan
Flood Risk Assessment
Operating Authorities
Throughout the design development, consultation and input has been sought from the
following key stakeholders and this will continue through the planning process:
5.1
Environment Agency
The Environment Agency (EA) has wide-ranging responsibilities including the management
of water resources, control of pollution in inland waters, and flood defence including water
level management. A principle duty of the Agency is to ‘contribute towards the achievement
of sustainable development.’ It is therefore, essential that the Environment Agency is
consulted throughout the design development of the site.
5.1.1
Consultation and Requirements
Meetings with the EA have been held in 2004 and 2005 (refer to the minutes of meetings in
Appendix D) to clarify their requirements relating to flood risk and surface water
management with respect to the development plan. There was also consultation in 2006
when the original draft PPG 25 FRA for this development was submitted for comment only
and the Agency responded in writing; those comments have been addressed by this PPS 25
FRA and a copy of that letter can be found in Appendix D.
The key EA requirements are summarised as follows:
•
The EA will require the submission of a detailed flood risk assessment for any planning
submission. The FRA content will have to be undertaken to a level of detail that a
preliminary design and outline masterplan can be submitted to the two planning
authorities. This will include sewerage and fluvial modelling where applicable to
determine flood risk and acceptable mitigation measures. An assessment of climate
change should be included.
•
The master plan FRA must include a detailed hydraulic analysis of the Westwood
Brook, in terms of flood risk and 100 year floodplain definition (refer to Appendix C).
Hydraulic modelling of the Canley Brook will not be required.
•
There should be no above ground building in any fluvial floodplain; any impingement will
require volume-for-volume and level-for-level compensation.
•
All surface water attenuation structures shall be designed with a 100 year return period,
plus 20% to 30% for climate change (dependent upon design life). All surface water
runoff from the proposed development draining to the watercourse shall be managed in
a sustainable manner. This will include the equivalent rate of greenfield runoff
discharge constraint for all new build (typically 5 litres per second per hectare).
•
The EA will not approve any culverting of watercourses and would support de-culverting
where feasible.
•
The Whitefield Coppice subcatchment will be required to include an analysis of surface
water management in accordance with the parameters detailed above. This
infrastructure will drain to an unnamed watercourse running through Whitefield Coppice,
although the EA will not require a hydraulic analysis of this watercourse.
•
Surface water quality issues will be to standard requirements. This shall include
proprietary separators for significant car parking areas and to maximise the water
quality improvement potential from natural sustainable drainage techniques.
5.2
Coventry City Council
Coventry City Council is the Local Planning Authority (LPA) for the Westfield Brook
subcatchment and is responsible for the preparation and development of local plans and the
controlling of development within the area.
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Coventry City Council as an LPA will be consulted throughout the future design process to
ensure the proposals do not conflict with any existing or proposed developments in terms of
flooding and drainage.
After scoping study consultation, it was determined that the Council do not want any further
increases in runoff entering watercourses, and therefore would like to see the use of
sustainable drainage and attenuation devices within any new developments. The Council
have also been liaising with the EA.
5.3
Warwickshire County Council
Warwickshire County Council is the Local Planning Authority (LPA) for the Whitefield
Coppice subcatchment and is responsible for the preparation and development of local
plans and the controlling of development within the area.
Warwickshire County Council as an LPA will be consulted throughout the future design
process to ensure the proposals do not conflict with any existing or proposed developments
in terms of flooding and drainage.
At the scoping study consultation, the Council did not have any key issues.
5.4
Warwick District Council
Warwick District Council were contacted during the scoping study, and will be consulted
throughout the future design process, to determine if they had any drainage issues or
concerns within this area. No such issues were raised.
5.5
Severn Trent Water
Severn Trent Water is the local sewerage undertaker, responsible for all the public foul and
surface water infrastructure in this area. Severn Trent Water should be consulted
throughout the future design process regarding existing capacities and likely flooding of
public sewers and any proposed connections to them.
Any proposed connection to a public sewer should be subject to an early submission of a
Severn Trent “Developer Enquiry”, to determine the correct location and permissible
discharge rate of the connection. Where there is an existing connection being reused, the
discharge rate should be no greater than existing and reduced if feasible. Where there is a
requirement for a new connection, Severn Trent Water will determine the discharge rate.
Severn Trent has no knowledge of any surface water discharge consents for the University
drainage, but provided details for two foul water effluent discharge consents.
5.6
Key Infrastructure Requirements
From consultation with the approving authorities leading up to the production of this flood
risk assessment, the key infrastructure requirements pertaining to the University
development plan are as follows:
•
There should be no above ground building in any fluvial floodplain; any impingement will
require volume-for-volume and level-for-level compensation and extensive flood risk
mitigation measures implemented to the structure.
•
All buildings should be designed and constructed with full regard for flood risk issues
and mitigation measures implemented where required. This shall include consideration
of overland flow paths.
•
Flood risk elsewhere (downstream) as a result of the development plan should be
considered and not increased.
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•
All surface water attenuation structures shall be designed with a 100 year return period,
plus 20% or 30% allowance for climate change, level of protection. All surface water
runoff from the proposed development draining to watercourses shall be managed in a
sustainable manner. This will include the equivalent rate of greenfield runoff discharge
constraint for all new build (typically 5 litres per second per hectare).
•
The design of sewerage infrastructure shall be in accordance with the current edition of
5
Sewers For Adoption .
•
Where connections to public sewerage are to be made (foul and surface water sewers),
they should be subject to an early submission of a Severn Trent Water “Developer
Enquiry”, to determine the correct location and permissible discharge rate of the
connection. For existing sewer connections to be reused, flow rates should be agreed
with Severn Trent Water; this will likely be maintained to existing levels and reduced if
possible.
•
Surface water quality issues, although not directly related to flood risk, will be to
standard requirements. This shall include proprietary separators for significant car
parking areas and to maximise the water quality improvement potential from natural
sustainable drainage techniques.
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Description of Flooding Mechanisms & Mitigation
Table 1: Potential Flood Risk Summary
Is the development site protected by a flood control structure (eg flap valve,
sluice gate, tidal barrier etc)?
Is the development site located upstream of a culvert which may be prone to
blockage?
Are water levels in a watercourse/body located in or next to a development
site controlled by a pumping station?
Is the development site downstream/downslope of a reservoir or other
significant water body?
Infrastructure Failure
Is the development site next to any watercourse shown on Ordnance Survey
maps?
Is the development site, or part of the development site, identified as being at
risk of flooding within available documentation?
If a strategic flood risk assessment is available, is the development site, or
part of the development site, identified as being at risk of flooding?
If a flood zone map is available, is the development site, or part of the
development site, within a Flood Risk Zone?
If there is an existing property on, or next to the site at the same level, is the
property within a flood warning area?
Are the LPA/FDA aware of any existing, historical or potential flooding
problems that may affect the site?
Do the physical characteristics of the site suggest that it may be prone to
flooding?
If a flood zone map is not available, is the development site, or part of the
development site below 10m AOD AND does the FDA consider the
development to be at risk from tidal flooding?
Is the development located within a natural or artificial hollow, or at the base
of a valley or at the bottom of a hill slope?
Does examination of historical maps indicate any likelihood of flood risk at
the site?
Do the names of surrounding roads, areas or houses suggest the possibility
of seasonal or historical flooding?
Is the site likely to involve excavation / construction below existing ground
levels (excluding foundations)?
Is the land use upslope of the site such that the generation of overland flow
may be encouraged, and can water from this area flow onto the site?
Are there any artificial drainage systems on or next to the site, at the same
level, or upslope of, the site?
Is the development site protected by an existing flood defence?
Overland flow
Fluvial
Key:
= Yes,
= No,
? = Unconfirmed but possible.
Artificial Drainage
Systems
Flood Hazard
Sea
Question
?
Groundwater
6.1
Estuaries
6
Development Masterplan
Flood Risk Assessment
No SFRA currently available
?
?
?
?
?
?
?
?
?
?
The outputs from Table 1 have been optimised and specific flood hazards identified in the
following Table 2.
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6.2
Development Masterplan
Flood Risk Assessment
Table 2: Flood Risk Identification
Potential Flood Hazard
Fluvial flooding
Flooding from the sea
Flooding from estuaries/watercourses
affected by tide locking
Groundwater flooding
Overland flow flooding
Flooding from artificial drainage systems
Flooding due to infrastructure failure
Flood risk
to the
development?
Increased
upstream
flood risk?
Increased
downstream
*
flood risk?
Tables 1 and 2 (adapted from CIRIA document C624: Development and Flood Risk,
3
Guidance for the Construction Industry ) indicates that the potential sources of flood risk to
the development site or adjacent areas to be considered by this development FRA are as
follows:
•
Fluvial;
•
Groundwater;
•
Overland flow of surface water;
•
Capacity exceedance of artificial drainage systems;
•
Infrastructure failure.
The tabulated approach has indicated that there may be a potential for increased flood risk
from fluvial, groundwater, overland flow, artificial drainage systems and infrastructure failure.
6.3
Fluvial Flood Risk
Flooding from rivers, streams and other natural inland watercourses is usually caused by
prolonged or intense rainfall generating high rates of surface water runoff throughout the
catchment, which overwhelms the capacity of the fluvial system as a flood flow and as a
result, spills into available floodplain storage areas.
Part of the University catchment lies within the 100 year floodplain of the Canley Brook
(refer to section 3.2.1). However, no University above ground infrastructure lies within this
floodplain and this constraint must be adhered to for any future development. During
consultation with the Environment Agency it was agreed that no fluvial hydraulic modelling
would be required for the Canley Brook, as a previous study had adequately mapped the
floodplain
The Environment Agency did require fluvial modelling of the Westwood Brook as part of this
FRA, along its reach where it might influence development on the University Campus.
Refer to section 7.3 and Appendix C for details of the fluvial modelling exercise. The results
of this modelling show that parts of the existing University campus lies immediately adjacent
the modelled 1 in 100 year floodplain (with and without climate change).
Any future buildings should be located outside the direct influence or flood risk (i.e. overland
flow paths) of the Westwood Brook floodplain. No actual finished floor levels have yet been
set in the Westwood Brook sub-catchment, but they should be a minimum of the 100 year
fluvial flood level with a 20% allowance for climate change, plus a freeboard level which is to
be agreed with the EA.
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Provision for emergency access during extreme flood events should be considered and
expressly maintained where close to a fluvial floodplain extents.
6.4
Groundwater Flood Risk
Flooding can occur in locations where groundwater naturally occurs at shallow depths.
Prolonged periods of rainfall can result in elevated groundwater levels that can lead to the
groundwater level reaching the surface. This can pose a flood risk to developments
particularly basements and cellars but also the emergence of groundwater will prevent
infiltration occurring and so will promote the occurrence of overland flow. In addition,
groundwater may leak into existing surface water drainage systems of poor integrity,
reducing their ability to accommodate surface water run off.
(8-13)
Previous site investigations undertaken on the Central Main Campus
area have failed
to find significant evidence of water in near surface materials. Below the surface, superficial
materials tend to be dominated by sandy silty clay, presumably formed from weathered
mudstone and alluvial deposits, extending between 2 and 6m below ground level to the Tile
Hill mudstones and sandstones. Owing to the predominance of clay and silt and to its
grading distribution, flow in these superficial materials is expected to be poor and not waterbearing.
Given the dominance of the Tile Hill Mudstone formation across the site, together with its
mix of relatively impermeable mudstone and sandstone bands, groundwater flow is
expected to be dominated by horizontal flow within the more permeable sandstone bands
and to follow the local surface topography. The Tile Hill Mudstone formation is reported to
comprise a high proportion of silt and, though classified by the Environment Agency as a
Minor Aquifer, is not expected to support significant groundwater flows given the
composition in terms of silt and fine sand. Although ultimately underlain by sandstones of
the Coventry Formation and the Keele Formation, which are considered capable of
supporting significant groundwater flows, the thickness of the Tile Hill Formation is
described as varying between 250m and 300m, and vertical migration to these sandstone
layers is not expected.
It is therefore expected that at the northern Westwood campus there would be a local flow of
groundwater to the southeast. Similarly the outcrop of Kenilworth Sandstone, located to the
Central Campus West is expected to result in localised flow again to the southeast while
groundwater from Gibbet Hill is expected to flow to the northeast.
The design and construction of any substructures will have to consider high groundwater
and implement mitigation measures (waterproofing) where required, as there are historical
problems recorded within the catchment. Building services should be located above
underlying groundwater levels where possible and where not feasible, they should be
designed to prevent the ingress of water and resist any water inflicted damage. Existing
groundwater flowpaths must be understood and any substructure proposed should consider
the effects and residual risk of flooding problems elsewhere.
6.5
Overland Flow Flood Risk
Overland flow is a description for water flowing over the surface, which has yet to enter a
natural drainage channel, an artificial drainage system or the natural substrate. It is often a
result of very intense short lived rainfall events but can also be produced during mild rainfall
events when drainage systems are at capacity or the ground is already saturated. This can
result in the inundation of low-lying areas. It is also related to sewer flooding, excessive
groundwater and infrastructure failure.
Wherever proposed University buildings are to be located at the base of a significant slope
or along the route of a potential flood path, consideration and mitigation from overland flow
flood risk should be undertaken. Finished floor levels and building thresholds should be set
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with due regard for potential overland flow paths. This may also require provision of
physical drainage structures such as swales, berms or cut-off trenches.
Behind the Heronbank buildings on the Hill Top site is a small pond, which is not used for
attenuating surface water runoff. The location of the pond suggests there is potential flood
risk from overland flow for the Heronbank buildings during extreme storm events. There is
already evidence of overland flow problems in this area from the presence of cut-off filter
drains and a swale at the toe of the slope, as a result of surface water shedding from the
elevated Hill Top site. The flood risk mitigation these structures provide should be
replicated by the development proposals, as they are shown to be beneath a main area for
development.
6.6
Artificial Drainage System Flood Risk
Artificial drainage systems designed to manage surface water run off can pose a flood risk if
the system is overwhelmed. This may occur if the amount of surface water run off exceeds
the systems capacity or if the system becomes blocked or surcharged by the receiving
watercourse. Artificial drainage systems designed to manage foul water (and combined
effluent) can pose a flood risk and public health risk if the system is overwhelmed. This may
occur if the amount of foul water allowed to discharge, exceeds the systems capacity.
Wherever proposed buildings are to be located downstream of a significant sewer line or
along the route of a potential overland flow from sewer flooding (foul or surface water),
consideration and mitigation from flow flood risk should be undertaken. Finished floor levels
and building thresholds should be set with due regard for potential overland flow paths.
6.7
Infrastructure Failure Flood Risk
Where significant infrastructure exists that retains, transmits or controls the flow of water,
flooding may result if there is a structural, hydraulic, geotechnical, mechanical or operational
failure. This may not be infrastructure that has been specifically designed and implemented
as a water controlling structure, such as a mater main or a dam. It may also be a structure
such a road or rail embankment that acts an informal flood defence during severe storm
events.
Wherever proposed buildings are to be located downstream of a significant water main or
along the route of a potential overland flow path resulting from water main failure flooding,
consideration and mitigation from flood risk should be undertaken. Finished floor levels and
building thresholds should be set with due regard for potential overland flow paths.
There are also two timber dams separating the three Lakeside/Heronbank lakes by
providing partitions to facilitate differing water levels between the water features. In the
event of an abrupt dam failure, the sudden loss of water would create a flood wave that
would pose a significant flood risk to the downstream built environment.
6.7.1
Surface Water Pumping
By providing a gravity outfall options rather than the reliance upon a pumping station
discharge would reduce a potential flood risk at both Lakeside/Heronbank and Engineering
Road, as a result of infrastructure failure, of loss of power for any length of time or during
extreme storm events.
6.8
Climate Change Flood Risk
Increasing global temperatures and changing weather patterns indicate that climate change
is a reality. Therefore, an allowance of the impact of climate change is a critical part of any
assessment of flood risk and assessment of design mitigation measures. In accordance
with PPS 25, the following climate change allowances have been included in the
infrastructure design for this FRA:
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•
Surface Water Drainage: Peak rainfall intensity added 20% or 30% (Table B.2).
•
Fluvial Modelling: Peak river flow added 20% (Table B.2).
6.9
Historical Flooding Data
In order to ascertain the precise extent of any flood risk, Arup undertook a number of site
visits and verbal or written requests to validate any historical flooding data. Of the
approving authority sources questioned, none identified any known major flooding or flood
risks in the vicinity of the development site.
6.10
Emergency Access Requirements
In terms of emergency access and egress, all of the local external main highway and
pedestrian routes serving the site are elevated well above any fluvial floodplain. The routing
of the main access route into and out of the development site is also located outside of any
fluvial floodplain and hence, any restriction of access from flood risk is deemed negligible
and no specific mitigation measures are required.
Furthermore, it is mandatory that emergency access to and from the buildings on the
application site is maintained during extreme storm conditions. There will also be a need to
consider flood risk mitigation to any new buildings proposed in future, in close proximity to a
floodplain.
6.11
Maintenance Requirements
Specific maintenance or access requirements have not yet been discussed in detail with the
appropriate parties during preparation of this flood risk assessment, as the project is at
masterplan stage. On this basis, the only key requirements identified thus far are that the
drainage infrastructure (existing and proposed) and riparian fluvial structures should be
adequately maintained by the University throughout their operational life to ensure a
sustainable level of service. This is especially relevant to the existing and proposed
attenuation and flow control structures.
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7
Development Masterplan
Flood Risk Assessment
Preliminary Surface Water Analysis & Design
7.1
Surface Water Management Strategy
The widespread implementation of sustainable drainage system (SUDS) best management
practices (BMPs) to contemporary standards, will be integral to the University surface water
management strategy. This will provide the platform to mimic the response of the existing
catchment and its surfaces and ultimately, negating any increased off-site flood risk.
A contemporary sustainable drainage methodology for managing surface water runoff will
use BMPs to focus on three key areas; controlling surface water quantity, improving surface
water quality and providing added development amenity value. It is anticipated that
contemporary sustainable drainage techniques shall be used throughout the University
future development plan to manage and control surface water runoff. Three key tenets will
be developed as part of an integrated University surface water management strategy:
•
Maximise natural runoff losses through infiltration techniques;
•
Maximise surface water runoff quality improvements through natural BMP techniques
such as bioremediation;
•
Attempt to reduce the yearly volume of surface water runoff pumped to discharge.
In an attempt to ensure that the future University sustainable drainage system is designed to
mimic the natural characteristics of the catchment and attain the key tenets above, the
surface water management train will ensure that storm runoff is addressed through a
number of key stages during conveyance to the regional fluvial system; these are prevention
– source control – site control. This will be achieved by designing and implementing a blend
of natural and proprietary sustainable drainage BMPs, complemented by traditional
drainage techniques. Such techniques may include, although not be limited to the following:
•
Natural BMP structures are formed with natural materials and integrated into the
landscape. They include swales, infiltration trenches, open channels, detention
basins (dry features) and balancing ponds (wet features). They can be designed to
operate with or without infiltration and all will afford excellent attenuation properties
and bioremediation.
•
Proprietary BMP are a range of manufactured techniques that include porous or
pervious surfacing, cellular below ground storage systems, rainwater harvesting
systems, traditional detention tanks, flow control devices and pipework.
It should also be noted that the seamless integration with the proposed landscape
architecture is essential for the successful implementation of contemporary sustainable
drainage on any development site and this will be inherent to the University sustainable
drainage implementation. Techniques may include although not be limited to, the following
additional BMPs:
•
Successfully integrating natural but engineered BMP structures into the landscape
proposals, to maximise the amenity value and overall aesthetics.
•
Adopting pervious or porous surface finishes to designated paved areas where
technically feasible and/or aesthetically required.
•
Integrating landscape features into the sustainable drainage infrastructure; this will
include a series of natural swales acting as primary drainage channels, the use of
strategic planting to provide source control and promoting extended grass blade
growth to reduce both the rate and amount of surface water runoff and promote
natural filtration and bioremediation.
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The University of Warwick
7.2
Development Masterplan
Flood Risk Assessment
Preliminary Surface Water Storage Calculations
Preliminary hydraulic modelling storage calculations undertaken during the flood risk
assessment have indicated the required estimated storage volumes (tabulated below) for
the individual development area plot references, which may be subject to variance if the
development proposals change (please note: detailed design hydraulic modelling may also
alter the volumes).
These storage volumes are based on the current masterplan (refer to Appendix B)
additional impermeable areas, an existing equivalent greenfield runoff discharge rate of the
1 in 1 year return period (assumed at 5 litres per second per hectare), against the 1 in 100
year return period storm event (1%) storage volumes. In accordance with Planning and
Policy Statement 25, volumes have been provided for both 20% and 30% allowance for
climate change. The actual allowance for climate change will depend upon the design life of
each of the developments, and this will be agreed with the Environment Agency during
detailed design.
A preliminary layout of how the key structures may be implemented across the catchment
can be viewed on figure 3 in Appendix B:
Masterplan
Development
Area
Estimated 1% Storage Volume
3
Required Inc Climate Change (m )
20% CC
Subcatchment
Identification
Preferred BMP
Attenuation
Technique
30% CC
1
950
1020
Westwood Brook
Natural &
Proprietary
2
2070
2175
Westwood Brook
Natural &
Proprietary
3
150
160
Westwood Brook
Natural
4
1440
1520
Whitefield Coppice
Natural
5
990
1060
Whitefield Coppice
Natural &
Proprietary
6
660
725
Whitefield Coppice
Proprietary
7
180
195
Gibbet Hill
Natural &
Proprietary
8
145
155
Whitefield Coppice
Natural
7.3
Westwood Brook Fluvial Modelling (Refer to Appendix C)
A detailed fluvial modelling exercise of the Westwood Brook was undertaken as part of this
FRA and this required a bespoke topographical survey to be commissioned by the
University, to obtain the required cross sections for the model build. The steady state flow
approach was selected for this study since there is no storage facility within the study reach
and the floodplain was not significant relative to the main channel, using the HEC-RAS
steady state modelling software package.
The model results indicated that the 1 in 100 year event flows can be expected to remain
within bank for the conditions tested. However, when the flow is increased by 20% to allow
for climate change water begins to overtop the banks. This occurs in the vicinity of the
junction between University Road and Library Road. The flow will be out of the left bank
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The University of Warwick
Development Masterplan
Flood Risk Assessment
and may affect the Existing Academic Square. The fluvial flood outline figures are shown on
figures 4 and 5 in Appendix B.
Any future buildings should be located outside the direct influence or flood risk (i.e. overland
flow paths) of the Westwood Brook floodplain. No actual finished floor levels have been set
by the Environment Agency in the Westwood Brook subcatchment, but they should be a
minimum of the 100 year fluvial flood level plus an agreed freeboard allowance and a
minimum of 20% for climate change.
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Issue 1 18 June 2007
The University of Warwick
8
Development Masterplan
Flood Risk Assessment
Conclusions and Recommendations
The following section summarises the identified key Flood Risk Conclusions (FRC) of the
proposed development and how they have been removed or reduced to acceptable levels
using appropriate Flood Mitigation Measures (FMM), determined from the key infrastructure
requirements discussed in Section 6 and 7.
8.1
The Sequential and Exception Tests
FRC:
The majority of development is suitable for the parts of the University Campus
which lie outside of the fluvial floodplain i.e. flood zones 1 and 2.
FMM:
No part of the current masterplan lies within flood zones 2 or 3 and therefore an
exception test is not required for the University masterplanning proposals.
However, if future specific proposals are proposed for flood zones 3a and 3b, a
future Exception Test may required with the development specific FRA.
8.2
Approving Authority Consultation
FRC:
The infrastructure design development should be undertaken in conjunction with
consultation with all relevant approving authorities.
FMM:
The masterplan design development has been undertaken thus far after
consultation with the Environment Agency, Severn Tent Water and Coventry City
Council, Warwickshire County Council and Warwick District Council.
8.3
Fluvial Flood Risk Conclusions
FRC:
The Canley Brook and Westwood Brook flow adjacent to and through the
development site and indicative floodplain mapping suggests a flood risk to parts
of the development site.
FMM:
Detailed fluvial modelling has confirmed that the developed site lies outside of the
Westwood Brook fluvial floodplain and is not at risk from flooding. Building within
any fluvial floodplain will be avoided. Where impingement into the fluvial
floodplain is unavoidable, impingement will require volume-for-volume and levelfor-level compensation.
FRC:
Fluvial flood risk to buildings from overland flows.
FMM:
Building within any fluvial floodplain will be avoided. For any building at negligible
flood risk, comprehensive flood risk mitigation measures will be implemented to
the structure, such as finished floor levels (they should be a minimum of the 100
year fluvial flood level plus freeboard and 20% climate change in the Westwood
Brook subcatchment) and thresholds above flood levels. Overland flow paths will
be provided to divert flood water away from buildings.
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Issue 1 18 June 2007
The University of Warwick
Development Masterplan
Flood Risk Assessment
FRC:
Increased flood risk elsewhere (typically downstream).
FMM:
The development plan shall not increase flood risk elsewhere, through increased
surface water discharge, loss of floodplain volume or restriction of existing channel
flows.
8.4
Groundwater Flood Risk Conclusions
FRC:
High groundwater levels could affect subsurface infrastructure such as
basements, and services.
FMM:
High groundwater is not considered to be a significant flood risk but will have to be
considered in the design of the buildings and especially any substructures.
8.5
Overland Flow Flood Risk Conclusions
FRC:
Buildings generally at flood risk from overland fluvial flood flows.
FMM:
The topography of the site and drainage system will be designed so that overland
flow can be controlled and directed away from future development locations and
encouraged to drain to a designated area or outfall.
FRC:
Buildings located at the base of a hill slope.
FMM:
The topography of the site and above ground drainage structures will be designed
so that overland flow can be controlled and directed away from surrounding
locations and encouraged to drain to a designated area or outfall
8.6
Artificial Drainage System Flood Risk Conclusions
FRC:
The capacity of the new surface water drainage system may be exceeded at times
of intense rainfall and/or extreme antecedent conditions.
FMM:
The on site drainage system will be designed to ensure flooding does not occur on
site up to and including the 1% storm event plus 20% climate change. This is a
requirement of the Environment Agency and beyond the design requirements of
Sewers For Adoption.
FRC:
The capacity of the offsite public sewers may be exceeded, due to increases of
both foul and surface water flows from the site.
FMM:
Surface water will be attenuated on site to ensure discharge is not increased from
existing rates and will largely discharge to local watercourses. Any future
discharge rate to a public surface water sewer will be agreed in principle with
Severn Trent Water.
Any proposed connection, foul or surface water, to a public sewer should be
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Issue 1 18 June 2007
The University of Warwick
Development Masterplan
Flood Risk Assessment
subject to an early submission of a Severn Trent “Developer Enquiry”, to
determine the correct location and permissible discharge rate of the connection.
8.7
Infrastructure Failure Flood Risk Conclusions
FRC:
On or off-site water main failure could lead to flooding of site infrastructure.
FMM:
The unlikely failure of a water main would not cause a significant flood risk, as any
resulting flood waters would flow down the highways away from the site.
FRC:
Pumping station failure at either/or Lakeside/Heronbank and Engineering Road as
a result of loss of power for any length of time or during extreme storm events.
FMM:
Reduce future reliance upon pumped surface water discharge to reduce flood risk
and ensure essential maintenance and mechanical replacement is carried out.
FRC:
Failure of wooden dam construction at Lakeside/Heronbank lakes.
FMM:
Consider a future modification to the configuration and the direction of flow at two
of the lakes to reduce flood risk. Ensure essential maintenance and checks are
carried out.
8.8
Climate Change Flood Risk Conclusions
FRC:
Future climate change may increase the frequency of flood risk to the
development site
FMM:
In accordance with PPS 25, the following climate change allowances have been
included in the infrastructure design:
8.9
•
Surface Water Drainage: Peak rainfall intensity added 20% and 30% (Table
B2).
•
Fluvial Modelling: Peak river flow added 20% (Table B.2).
Maintenance and Access Flood Risk Conclusions
FRC:
Maintain external access routes for emergency vehicles during flood risk events.
FMM:
The site and its main access routes lie outside of the 1% and 0.1% fluvial
floodplains in a flood zone 3 and is not at risk from fluvial flooding; no mitigation
measures required.
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Issue 1 18 June 2007
The University of Warwick
8.10
Development Masterplan
Flood Risk Assessment
Recommendations
On the basis of this Flood Risk Assessment and the suggested mitigation measures, it is
concluded that the proposed development will not adversely affect onsite, neighbouring or
downstream developments and their flood risk.
Having identified and categorised the potential sources of flood risk, it has also been
possible to identify mitigation measures for each of the sources of potential flooding. If
these measures are incorporated into the design and implementation of the proposed
masterplan development, it should be possible to drastically reduce the flood risks
associated with the site to acceptable levels, such that the residual risks can be judged low
to zero risk.
It is recommended that this detailed masterplanning Flood Risk Assessment be accepted on
the basis of an outline planning consent for the redevelopment of this previously developed
University of Warwick campus in Coventry and that the issues raised herein are integral and
optimised in the future detailed design stages of the proposed development, paying careful
consideration to the key infrastructure design requirements outlined. It is also essential that
future consultation with the operating authorities is maintained.
If the documented mitigation measures are adhered to, it is recommended that the site is
considered suitable for the proposed masterplan development.
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The University of Warwick
9
Development Masterplan
Flood Risk Assessment
References
[1] The University of Warwick Development Plan Drainage Scoping Study, Arup, August 2004.
[2] Planning and Policy Statement 25 (PPS 25): Development and Flood Risk, Communities and
Local Government, Dec 2006.
[3] CIRIA C624: Development and Flood Risk, Guidance for the Construction Industry, 2004.
[4] Planning and Policy Guidance Note 25 (PPG 25): Development and Flood Risk, Department
of Local Government and the Regions, July 2001.
th
[5] Sewers For Adoption 6 Edition, WRc, March 2006.
[6] Hydrological summary for the United Kingdom – December 2000, Centre for Ecology and
Hydrology, January 2001.
[7] Effects of Climate Change on Flood Frequency, The Environment Agency, September 2000.
[8] University of Warwick, Report on Site Investigation, Felix J Samuely and Partners, 1964
[9] Warwick University Estates Office: Extensions to Arts Centre Phase III and Social Studies
Building, Factual Report, Exploration Associates Ltd, 1983
[10] New Post Graduate Residences, University of Warwick, Factual Report on Ground
Investigation (H1174-A), Exploration Associates, June 1991
[11] New Manufacturing Systems Engineering Building, University of Warwick, Interpretive Report
on Ground Investigation (112422), Exploration Associates, November 1992
[12] Proposed New Car Park: Geotechnical Appraisal – Factual Report, Integrated Geotechnical
and Environmental Services Ltd, December 1995
[13] Ground Investigation for Lakeside Residences II at University of Warwick, Coventry, Report
No. 238, Peel and Fowler, April 2002
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Issue 1 18 June 2007
Appendix A
Site Photographs
1. Westwood Brook opposite the Engineering Block.
2. Westwood Brook downstream of main Campus.
3. Timber dam at upper Lakeside/Heronbank water feature.
4. View downstream at middle Lakeside/Heronbank water feature.
5. The surface water pumping station outside the Engineering Block.
6. Typical view of the Canley Brook
Appendix B
Figures
A
B
C
D
E
F
G
J:\115000\115438-00\4 Internal Project Data\4-03 Drawings\0_Drawings\FRA Figure 1.dgn
A3
Legend
University Boundary
Administrative Boundary
Westwood Campus
Indicative Line of
1
Subcatchments
SQUIRES WAY
CDN
358
.000
CDN173,
Surface Water Pumping Station
2
LB
CDN
359
360
361
362
363
80.777
CDN(45),
CDN(46),
CDN(47),
CDN(48),
CDN(49),
Westwood Brook
Tocil Flats
Heronbank / Lakeside
Foul Water P.S.
Main Campus
3
02
19/
06/
07
JW
AW
DS
DS
DS
Chkd
Appd
Issued For FRA
Canley Brook
01
21/
08/
06
AW
Issued for Information
Issue
Hill Top Pond
Date
By
WATER VALVE
WATER VALVE
WV G24
WV G17
WATER VALVE
WV G16
WV G21
WV G22
WV G23
WV G19
WV G18
WATERVALVE
WATER VALVE
WATER VALVE
CLUSTER (6)
WATERVALVE
WATER VALVE
G13, G14, G15
WATER VALVE
CLUSTER (4)
G10, G11, G12
Westwood
Whitefield
Brook Subcatchment.
WV G26
WV G09
WV G08
WV G07
WV G05
WV G06
WV G04
Brook Subcatchment.
WATER VALVE
PIT FULL OF MUD
4
WV G03
Gibbet Hill
WV G02
WATER VALVE (M)
WV G01
Subcatchment
The Arup Campus, Blythe Gate, Blythe Valley Park
Solihull, West Midlands B90 8AE
Tel +44(0)121 213 3000 Fax +44(0)121 213 3001
www.arup.com
Client
THE
UNIVERSITY
OF
Job Title
Development Masterplan
5
97.5m
Drawing Title
Existing Layout
Scale at A3
1:12500
Plot ID
The Bungalow
6
Dunns Pitts Cott
Dunns Pitts Farm
Drawing Status
X=431000000
Y=274000000
N
FRA
Job No
Drawing No
Issue
115438-00
Figure 1
02
' Arup
A
B
C
D
E
F
G
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A3
Legend
University Boundary
Administrative Boundary
Proposed Building
1
SQUIRES WAY
CDN
358
.000
CDN173,
2
LB
CDN
359
360
361
362
363
80.777
CDN(45),
CDN(46),
CDN(47),
CDN(48),
CDN(49),
3
02
19/
06/
07
JW
AW
DS
DS
DS
Chkd
Appd
Issued for FRA
01
21/
08/
06
AW
Issued for Information
Issue
Date
By
WATER VALVE
WATER VALVE
WV G24
WV G17
WATER VALVE
WV G16
WV G21
WV G22
WV G23
WV G19
WV G18
WATERVALVE
WATER VALVE
WATER VALVE
CLUSTER (6)
WATERVALVE
WATER VALVE
G13, G14, G15
WATER VALVE
CLUSTER (4)
G10, G11, G12
WV G26
WV G09
WV G08
WV G07
WV G05
WV G06
WV G04
WATER VALVE
PIT FULL OF MUD
4
WV G03
WV G02
WATER VALVE (M)
WV G01
The Arup Campus, Blythe Gate, Blythe Valley Park
Solihull, West Midlands B90 8AE
Tel +44(0)121 213 3000 Fax +44(0)121 213 3001
www.arup.com
Client
THE
UNIVERSITY
OF
Job Title
Development Masterplan
5
97.5m
Drawing Title
Proposed Layout
Scale at A3
1:12500
Plot ID
The Bungalow
6
Dunns Pitts Cott
Dunns Pitts Farm
Drawing Status
X=431000000
Y=274000000
N
FRA
Job No
Drawing No
Issue
115438-00
Figure 2
02
' Arup
A
B
C
D
E
F
G
N 277000
N 276500
N 276000
N 275500
N 275000
Notes:
1. Reproduced from drawing supplied
by MJP Architects.
2. Do not scale from this drawing.
1
3. Existing sewerage infrastructure not
shown.
4. Location and selection of SUDS
E 429000
E 429000
structure type subject to change and
Area 4
addition.
5. Surface water runoff to be balance
to pre-development flows and
volumes.
Legend
2
Subcatchment boundary
Constructed wetland
Local watercourse
Culverted watercourse
Area 6
Overland flow defence
Natural SUDS structure
Westwood
(open structure)
Brook
Proprietary SUDS structure
E 429500
E 429500
(closed structure)
3
Principal connecting conduit
(open or closed structure)
Area 5
02
19/
06/
07
RW
AW
DS
Chkd
Appd
Issued for FRA
Area 8
Issue
Date
By
Area 1
4
The Arup Campus, Blythe Gate, Blythe Valley Park
Solihull, West Midlands B90 8AE
Tel +44(0)121 213 3000 Fax +44(0)121 213 3001
www.arup.com
Client
1
E 430000
E 430000
THE
UNIVERSITY
OF
Area 2
Job Title
Development Masterplan
5
Drawing Title
CDN
359
360
361
362
363
80.777
CDN(45),
CDN(46),
CDN(47),
CDN(48),
CDN(49),
Area 3
Sustainable Drainage (SUDS)
Strategy (Indicative)
CDN
358
.000
CDN173,
Canley
Brook
Scale at A3
1:7000
Plot ID
Westwood Brook
6
E 430500
E 430500
Drawing Status
FRA
N 277000
SQUIRES WAY
N 276500
N 276000
WATER VALVE
WATER VALVE
WV G22
WV G26
N 275500
WV G23
WV G02
WATER VALVE (M)
WV G24
WV G01
WV G03
N 275000
Area 7
Job No
Drawing No
Issue
115438-00
Figure 3
02
' Arup
J:\115000\115438-00\4 Internal Project Data\4-03 Drawings\0_Drawings\FRA Figure 3.dgn
A3
A
B
C
D
E
F
G
Pond
Notes:
1.Refer to the University of Warwick
Institute House
El Sub Sta
Development Plan Flood Risk
Ponds
Viscount Centre
Viscount Centre
1&2
Pond
1
Assessment for hydraulic model details
2. Floodplain extent has yet to be
approved by the Environment Agency
3.The flood outline is based on the flood
width for each cross-section and by
directly joining these points with those
University of Warwick Science Park
for adjacent cross-sections.
BRIDGE 11
The topography between two
cross-sections was therefore not
2
considered on this outline.
Approximate Line of Culvert
Key:
BRIDGE 10
Indicative 1 in 100 Year
PIPE 16
The New Varsity
(PH)
Floodplain
Indicative 1 in 100 Year
Floodplain + 20% allowance
for climate change
Toar Cottage
3
02
19/
06/
07
AW
AW
DS
AW
AW
DS
By
Chkd
Appd
Issued for FRA
01
18/
08/
06
BRIDGE 10
First issue
BRIDGE 9
PIPE 15
Issue
Date
PIPE 14
PIPE 13
PIPE 12
BRIDGE 9
PIPE 11
PIPE 10
PIPE 05
4
PIPE 04
PIPE 09
The Arup Campus, Blythe Gate, Blythe Valley Park
BRIDGE 4
BRIDGE 8
PIPE 08
Solihull, West Midlands B90 8AE
BRIDGE 5
BRIDGE 3
PIPE 07
Tel +44(0)121 213 3000 Fax +44(0)121 213 3001
BRIDGE 7
BRIDGE 2
www.arup.com
PIPE 06
BRIDGE 6
Client
PIPE 03
THE
UNIVERSITY
OF
Job Title
Development Masterplan
Pond
5
El Sub Sta
Pond
Drawing Title
Westwood Brook
El Sub Sta
1 in 100 Year Floodplain
1 of 2
Pond
Scale at A3
1:2500
Plot ID
6
Drawing Status
Multistorey Car Park
Pond
FRA
Radcliffe House
Pond
El
Sub
Sta
Job No
Drawing No
Issue
115438-00
Figure 4
02
' Arup
J:\115000\115438-00\4 Internal Project Data\4-03 Drawings\0_Drawings\FRA Figure 4.dgn
A3
A
B
C
D
E
F
G
Notes:
Pond
1.Refer to the University of Warwick
Development Plan Flood Risk
Assessment for hydraulic model details
1
2. Floodplain extent has yet to be
PIPE 05
approved by the Environment Agency
PIPE 04
BRIDGE 4
BRIDGE 5
3.The flood outline is based on the flood
BRIDGE 3
BRIDGE 7
BRIDGE 2
PIPE 06
width for each cross-section and by
BRIDGE 6
directly joining these points with those
PIPE 03
for adjacent cross-sections.
The topography between two
cross-sections was therefore not
2
considered on this outline.
Pond
Pond
El Sub Sta
Key:
Indicative 1 in 100 Year
Floodplain
El Sub Sta
Indicative 1 in 100 Year
Pond
Floodplain + 20% allowance
for climate change
3
02
BRIDGE 1
19/
06/
07
AW
AW
DS
AW
DS
Chkd
Appd
Issued for FRA
Multistorey Car Park
01
18/
08/
06
AW
First Issue
Issue
Date
By
The Lodge
4
The Arup Campus, Blythe Gate, Blythe Valley Park
Solihull, West Midlands B90 8AE
Tel +44(0)121 213 3000 Fax +44(0)121 213 3001
www.arup.com
PIPE 02
Pond
Client
THE
El Sub Sta
UNIVERSITY
OF
PIPE 01
Pond
Job Title
Development Masterplan
5
Drawing Title
Westwood Brook
Drain
1 in 100 Year Floodplain
2 of 2
Scale at A3
1:2500
Pond
Plot ID
6
Drawing Status
FRA
Job No
Drawing No
Issue
115438-00
Figure 5
02
' Arup
J:\115000\115438-00\4 Internal Project Data\4-03 Drawings\0_Drawings\FRA Figure 5.dgn
A3
Appendix C
Westwood Brook
Hydraulic Analysis
Technical Note
Page 1 of 8
Job title
University of Warwick - Development Masterplan
Job number
115438
cc
David Schofield, Serter Atabay
File reference
4-04-01 Water\Fluvial
Prepared by
John Ravening x 3 3271 (Campus)
Date
14 March 2006
Subject
Flow Estimation
1.
HYDRAULIC MODELLING OF THE WESTWOOD BROOK
1.1
Introduction
It has been agreed with the Environment Agency (EA) that the extent of the 1 in 100 year return
period floodplain occupied by the West wood Brook should be mapped as part of the University
of Warwick Development Masterplan flood risk assessment. In order to do this it is necessary to
simulate range of flows, up to the 1 in 100 year return period flood event, using hydraulic
modelling computer software such as HEC-Ras.
In order to successfully replicate the flood event conditions 2 main components are required.
These are:
1.2
•
Topographical survey information of the existing river channel and the area either side of the
channel that may be occupied by water overtopping the banks. This information can then be
used to construct an accurate model of the existing channel conditions within the hydraulic
modelling software.
•
Estimations of the magnitude of flood events with different return periods
Topographical Survey and Hydraulic Model construction
In order to ascertain the existing conditions within the Westwood Brook, a topographical survey
of the watercourse and it tributaries was commissioned. A detailed specification document was
issued to the successful survey company and the route of the watercourse was inspected by the
consultant and the survey company, in order to identify the exact points to be surveyed both
within the channel and either side of the channel.
The detailed topographical survey has been returned. This includes levels for the points identified
in the specification and the site walkover. This information has been input into HEC-Ras along
with additional information obtained from the Estates Office at the University of Warwick. The
supplementary information is related to the existing culvert that links the northern end of the
watercourse, behind the Varsity Public House, with the main channel through the Central
Campus.
This information has enabled an accurate hydraulic model of the existing channel to be
constructed. This model extends from a point approximately 100m upstream of the Kirby Road,
road bridge to the confluence with the Canley Brook.
After initial model construction, arbitrary flows have been simulated to identify any errors or
warning messages. This process has not identified any serious errors in the model construction
and so the model is considered able to accurately simulate water levels for a given flow.
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ESTIMATION TECHNIQUES AND RESULTS 18-06-07 .DOC
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Rev 9.4, 15 March 2004
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Technical Note
14 March 2006
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The downstream boundary condition of the model has been set as the confluence of the Canley
Brook. The water level for different flow conditions has been established at this location using
the single section method. Sensitivity analysis identified that the boundary conditions have a
small backwater effect that extends for approximately 200m upstream, however, this effect does
not influence the water levels within the area of the proposed development. As the Westwood
Brook is an ungauged catchment it has not been possible to calibrate the model using existing
data. In the absence of this, the model has been verified using additional sensitivity analysis. In
particular the roughness value has been examined to determine the range of water level
fluctuation influenced by this variable.
1.3
Hydrological investigation
In order to accurately model a range of return period flood events, it is necessary to obtain
accurate estimates for a range of different of different flows. The Westwood Brook is a totally
ungauged catchment and for this reason the methods available for deriving a flow estimate are
limited. However, methods do exist, as prescribed within the industry standard document, the
Flood Estimation Handbook (FEH).
Different flow estimation methods can produce flow values that vary dramatically. For this
reason, it is recommended that a range of different estimates are calculated and then a final value
chosen based on conservative judgement.
The two methods available in this instance are;
•
The statistical method using pooling group analysis.
•
Rainfall Run off method.
1.3.1
Statistical Method Using Pooling Group analysis
Pooled group analysis is a method of using observed data from similar catchments to determine
the magnitude of return period of flows.
1.3.1.1
Qmed Derivation
The first step required to estimate flow values for a given return period flood is to estimate the
Median Flood (Qmed). For a gauged catchment, with in excess of 13 years worth of flow data the
Median Flood is simply the median annual maxima flow value. For a gauged catchment, with
less that 13 years worth of annual maximum series data, peak overt threshold data has to be
examined in order to derive the Qmed. For an ungauged catchment there are two methods that
can be used.
•
Catchment Descriptors;
•
Analogue Sites.
1.3.1.2
Catchment Descriptors
The FEH CD-ROM enables the user to identify the physical extent of the study catchment by
using the Digital Terrain Map (DTM) contained within the CD. The CD also contains
information regarding the hydrological and meteorological characteristics of the catchment.
Using the catchment descriptors the Qmed can be estimated by solving the following equation.
Qmedrural = 1.172AREAAE (SAAR/1000)1.560 FARL2.642 (SPRHOST/100)1.211 0.0198RESHOST
Where:
AREA = Catchment drainage area (km2 ) = 2.99
SAAR = Standard Period Average Annual Rainfall (mm) = 680
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FARL = Index of Flood Attenuation = 1
SPRHOST = Standard Percentage Runoff from the Hydrology of Soil Types classification = 32.2
AE = 1 – 0.015 In(AREA/0.5)
RESHOST = BFIHOST +b 1.30(SPRHOST/100) - 0.987
BFIHOST = Baseflow Index derived from the Hydrology of Soil Types Classification = 0.599
Qmedurban = Qmedrural x Urban Adjustment Factor (UAF)
UAF = (1+URBEXT)0.83 PRUAF
PRUAF = 1 + 0.615 x URBEXT(70/SPRHOST-1)
The UAF is required for catchments with an urban extent factor in excess of 0.025. According to
the FEH CD-ROM, the urban extent of the Westwood Brook catchment is 0.071.
For the Westwood Brook the Qmed calculated using catchment descriptors is 0.466m3 /s.
1.3.1.3
Analogue Site.
For ungauged catchments it is recommended to identify an analogue site and to use a calculated
Qmed for that site, rather than rely on a Qmed calculated using the catchment descriptors. In
order to identify a site that can be used as an analogue for the study catchment, the catchment
descriptors can be used. The easiest way to do this is to create an initial pooling group using the
WINFAP-FEH software. This identifies the catchments in the UK with similar characteristics.
These catchments can then be analysed individually to identify the catchment that is most alike to
the study catchment.
Once an analogue catchment has been identified, the calculated Qmed for that site can be
discovered either from the WINFAP-FEH software or using another data source such as the
HiFlows website.
In this case the analogue site chosen was the River Wey at Broadwey Station. The Qmed from
observed events at this site is 1.683m3 /s.
In addition the catchment descriptors for the analogue site have also been used to calculate a
Qmed, using the same equation as shown in Secition 1.3.1.1. This has produced a Qmed of
1.41m3 /s
1.3.1.4
Final Qmed Derivation
The process required to derive a final Qmed for the study site is to use the following equation to
adjust the Qmed s cds (Qmed derived using catchment descriptors for the study site), based on the
Qmed g obs (Qmed derived from observed data for the analogue site) and Qmed g cds (Qmed derived
using catchment descriptors for the analogue site).
Qmed = Qmed s cds x [Qmed g obs/ Qmed g cds]
Using this equation the final Qmed = 0.556 m3 /s.
1.3.2
Pooled Group Analysis
This process assembles a list of gauged sites that are hydrologically similar to the study site.
Using this list, the magnitude of return period floods can be estimated by deriving a growth curve.
The growth curve can then be used to derive a factor that can be used to scale up the Qmed, to the
required return period, for the study site.
The pooled group analysis is undertaken using the WINFAP-FEH software. The first step in the
process is to identify the catchment using the FEH CD-ROM and export a file containing the
catchment descriptors information into the WINFAP-FEH. The WINFAP-FEH is able to compile
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an initial group of hydrologically similar catchments based on the catchment descriptors.
However, it informs the user of the heterogeneity of the pooled group and the discordance of each
of the pooled catchments, compared to the study catchment. Each catchment within the pooled
group is then examined to decide whether there are reasons why the catchment should not remain
in the pooled group.
The initial pooled group for the Westwood Brook included the following catchments.
Pooling Group 1
Station
Years
L-CV
L-Skewne
L-Kurtosis
Discordancy
Distance
25019 R. Leven @ Easby
26
0.376
0.421
0.336
1.273
1.167
29009 R. Ancholme @
Toff Newton
28
0.334
0.190
0.274
1.002
1.240
32029 Flore Experimental
@ Flore
5
0.374
0.054
0.127
1.111
1.309
44801 R. Hooke @
Hooke
11
0.232
0.269
0.063
1.840
1.316
33045 R. Whiddle @
Quidenham
35
0.351
0.169
0.117
0.273
1.322
54034 Dowles Brook @
Oak Cottage
32
0.238
0.188
0.071
0.983
1.406
44009 R. Wey @
Broadwey
26
0.359
0.251
0.153
0.297
1.474
40006 R. Bourne @
Hadlow
39
0.372
0.437
0.349
1.453
1.498
20002 West Peffer Burn
@ Luffness
38
0.287
-0.014
0.155
1.978
1.511
45817 Trib of R. Haddeo
@ Upton
10
0.333
0.238
0.131
0.2
1.539
45816 R.Haddeo @
Upton
10
0.352
0.417
0.327
1.17
1.586
30004 R. Lymn @
Partney
41
0.246
0.045
0.070
0.99
1.610
36003 R. Box @ Polstead
40
0.356
0.197
0.232
0.416
1.674
20006 Biel Water @
Belton Water
28
0.375
0.128
0.058
1.159
1.685
53017 R. Boyd @ Bittton
30
0.260
0.125
0.116
0.514
1.718
36007 Belchamp Brook
@ Bardfield Bridge
39
0.407
0.140
0.075
1.696
1.756
39003 R. Winterbourne
@ Bagnor
41
0.247
0.189
0.157
0.742
1.759
44003 R. Asker @ East
Bridge Bridport
21
0.318
0.306
0.110
0.903
1.762
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In the first instance station 32029 Flore Experimental @ Flore, has been removed from the
pooling group due to the fact that this station comprised a very short record (5 years). The rest of
the pooling group has then been analysed to determine whether there are reasons why sites should
not be used in the pooling group. The result of this analysis has removed the following stations:
•
44801 R. Hooke @ Hooke due to a short record, discordance in terms of FARL and SAAR,
compared to the study site.
•
44003 R. Asker @ East Bridge Bridport due to change in gauging station location and discordancy in
terms of SAAR, PROPWET and AREA, compared to the study site.
•
33045 R. Whiddle @ Quidenham due to concerns over high flow measurement capability of this
station.
•
44009 R. Wey @ Broadwey concern with flow estimation in excess of the Qmed.
•
45817 Trib of R. Haddeo @ Upton and 45816 R.Haddeo @ Upton due to a short record.
The following guidelines have been adopted when considering how suitable the pooling ghroup
sites are:
AREA – Should be within a factor of 4 – 5.
BFIHOST – The difference should not exceed 0.18
SPRHOST – The difference should not exceed 15
SAAR – Should be within a factor of 1.25
FARL – The difference should not exceed 0.05.
It should be noted that almost all the pooling group sites exceed the study site catchment area by
more than a factor of 5.
It is recommended that the total number of years of data used in pooling group analysis is 5 times
the most extreme flood flow required, in this case the 1 in 100 year return period flow. Therefore,
a total of 500 years is required. By removing these sites from the pooling group the total number
of years of gauging data available has dropped to below 500 years. In this situation a new pooling
group is assembled but with an aim of retaining in excess of 500 years of data, even after the
removal of inappropriate gauging stations from the pooling group. This has been done by
inputting the 1 in 200 year return period flow as the most extreme event.
The second pooling group generated comprised the following sites:
Pooling Group 2
Station
Years
L-CV
L-Skewne
L-Kurtosis
Discordancy
Distance
25019 R. Leven @ Easby
26
0.376
0.421
0.336
1.273
1.167
29009 R. Ancholme @
Toff Newton
28
0.334
0.190
0.274
1.002
1.240
32029 Flore Experimental
@ Flore
5
0.374
0.054
0.127
1.111
1.309
44801 R. Hooke @
Hooke
11
0.232
0.269
0.063
1.840
1.316
33045 R. Whiddle @
Quidenham
35
0.351
0.169
0.117
0.273
1.322
54034 Dowles Brook @
Oak Cottage
32
0.238
0.188
0.071
0.983
1.406
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44009 R. Wey @
Broadwey
26
0.359
0.251
0.153
0.297
1.474
40006 R. Bourne @
Hadlow
39
0.372
0.437
0.349
1.453
1.498
20002 West Peffer Burn
@ Luffness
38
0.287
-0.014
0.155
1.978
1.511
45817 Trib of R. Haddeo
@ Upton
10
0.333
0.238
0.131
0.2
1.539
45816 R.Haddeo @
Upton
10
0.352
0.417
0.327
1.17
1.586
30004 R. Lymn @
Partney
41
0.246
0.045
0.070
0.99
1.610
36003 R. Box @ Polstead
40
0.356
0.197
0.232
0.416
1.674
20006 Biel Water @
Belton Water
28
0.375
0.128
0.058
1.159
1.685
53017 R. Boyd @ Bittton
30
0.260
0.125
0.116
0.514
1.718
36007 Belchamp Brook
@ Bardfield Bridge
39
0.407
0.140
0.075
1.696
1.756
39003 R. Winterbourne
@ Bagnor
41
0.247
0.189
0.157
0.742
1.759
44003 R. Asker @ East
Bridge Bridport
21
0.318
0.306
0.110
0.903
1.762
20007 Gifford Water @
Lennoxlove
30
0.436
0.310
0.149
1.865
1.778
49004 R.Ganel @ Gwills
34
0.250
0.116
0.018
0.970
1.787
29002 Great Eau @
Claythorpe Great Eau
40
0.313
0.325
0.278
0.453
1.856
From this pooling group the sites identified for removal in the initial run were removed and site
20002 was also removed due to discrepancy in terms of PROPWET. This left the sites shown
below. This pooling group had a heterogeneity value of 2.6593. There was no valid reason to
remove any of the remaining sites, although some of the sites still displayed high discordance
values. However, this is the difference between the catchment area of the pooling group sites and
the study site, which has a very small catchment area.
Final Pooling Group
25019 R. Leven @ Easby
26
0.376
0.421
0.336
1.273
1.167
29009 R. Ancholme @
Toff Newton
28
0.334
0.190
0.274
1.002
1.240
54034 Dowles Brook @
Oak Cottage
32
0.238
0.188
0.071
0.983
1.406
44009 R. Wey @
Broadwey
26
0.359
0.251
0.153
0.297
1.474
40006 R. Bourne @
Hadlow
39
0.372
0.437
0.349
1.453
1.498
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20002 West Peffer Burn
@ Luffness
38
0.287
-0.014
0.155
1.978
1.511
30004 R. Lymn @
Partney
41
0.246
0.045
0.070
0.99
1.610
36003 R. Box @ Polstead
40
0.356
0.197
0.232
0.416
1.674
20006 Biel Water @
Belton Water
28
0.375
0.128
0.058
1.159
1.685
53017 R. Boyd @ Bittton
30
0.260
0.125
0.116
0.514
1.718
36007 Belchamp Brook
@ Bardfield Bridge
39
0.407
0.140
0.075
1.696
1.756
39003 R. Winterbourne
@ Bagnor
41
0.247
0.189
0.157
0.742
1.759
20007 Gifford Water @
Lennoxlove
30
0.436
0.310
0.149
1.865
1.778
49004 R.Ganel @ Gwills
34
0.250
0.116
0.018
0.970
1.787
29002 Great Eau @
Claythorpe Great Eau
40
0.313
0.325
0.278
0.453
1.856
Using the Goodness of fit function within the WINFAP-FEH, the Generalised Logistic (GL) and
Generalised Extreme Value (GEV) distributions have been utilised to derive the growth and flood
frequency curves required for the pooling group based on a user defined Qmed of 0.556 m3 /s.
This analysis has produced the following results.
Return Period
Flood
GL
Q
GEV
Q
2 (Qmed)
1
0.556
1
0.556
5
1.533
0.852
1.588
0.883
10
1.920
1.068
1.998
1.111
25
2.481
1.380
2.539
1.412
50
2.966
1.649
2.959
1.645
100
3.518
1.959
3.393
1.886
Assuming a worst case scenario the higher estimate for each return period has been assumed.
1.3.2.1
Rainfall Run Off
In addition to pooling group analysis to determine the return period flows the restatemented
rainfall run off method as described with volume 4 of the FEH has also been applied to the
Westwood Brook catchment. This analysis has been undertaken within the Rainfall Run off
module of the Isis hydraulic model. The recently issued revitalised method has not been used in
this case.
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The results of the rainfall run off method are shown below:
1.4
Return Period Flood
Q
5
1.464
10
1.875
25
2.502
50
3.054
100
3.616
Conclusions
On the basis that the study catchment is far smaller and has a larger urban extent than the majority
of the sites within the pooling group it is preferred to use the flow estimates derived using the
rainfall run off methodology. In addition, these estimates are higher and so more conservative.
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1
Westwood Brook Fluvial Modelling
1.1
Hydraulic Model & Methodology
The steady-state flow approach is generally considered conservative in its determination of
water surface elevation, in that this method of flow analysis generally tends to overestimate.
This overestimation is due to the assumption that flow is constant within the river reach since
the steady-state flow approach ignores the effects of channel storage on the shape and peak of
the flow hydrograph.
The steady state flow approach was selected for this study since there is no storage facility
within the study reach and the floodplain was not significant relative to the main channel. HECRAS steady state modelling software package is therefore capable of modelling all the key
features required for this study. These include friction effects, bridge afflux losses, and overbank conveyance. HEC-RAS will also resolve the transition from super-critical to sub-critical
flow, i.e. hydraulic jumps, which might occur in places along the watercourse including the long
culvert.
1.2
Climate Change
The period from October to December 2000 ranks as the second wettest three-month sequence
6.
for England and Wales in the last 200 years Although recent climate patterns have been
unusual, several broadly comparable wet episodes can be identified. These include the
October to January periods of 1960/61, 1929/30 and 1852/53. In addition, although the high
storm rainfall totals recorded, are rare, they are by no means unprecedented. The recorded
rainfalls are well within the envelope of meteorological fluctuations that characterise the climate
of England and Wales.
7
Recent research by the Environment Agency suggests that over the next 30 to 50 years the
probability of occurrence of severe flood flows will increase. Unfortunately, this increase in
severity cannot as yet be accurately quantified, and analyses of the annual maximum flood
series at the longer term gauging stations do not provide compelling evidence for any climate
driven trend.
1.3
Assumptions
The representation of any complex system by a 1-dimensional hydraulic model requires a
number of assumptions to be made. These assumptions are as follows:
•
•
•
•
•
1.4
The cross-sections accurately represent the watercourse and level water surface across the
entire cross-section;
The flow is primarily perpendicular to the entire cross-section;
Discharge distributed within a cross-section based on the conveyance distribution;
The energy slope is uniform across the entire cross-section;
The design flows are an accurate representation of flows of a given return period.
Main Channel and Floodplain Sections
In total the model contains 67 open channel cross sections, labelled from 1 to 88 from the
downstream extent up. Floodplains are represented in the model by the extent of the cross
sections taken across the watercourse and the adjoining land on both sides.
The predicted water levels are then defined within these conveyance points. In addition, the
model contains 14 cross sections where the cross section upstream of a structure has been
copied to the downstream of a structure for modelling purposes.
1.5
Structures
The model contains a total of 10 culverts and four bridges along the Westwood Brook.
It has been necessary to include additional cross-sections at some locations to model the
downstream face of hydraulic structures or to ensure model stability. These cross-sections
have been copied or interpolated from the surveyed cross-sections as appropriate.
1.6
Roughness Coefficients
Channel and floodplain roughness is represented by Manning’s ‘n’ values in the model.
Channel roughness parameters were derived for each model cross-section from a combination
of site inspections and comparison of survey photographs with published values (e.g. Chow
1
1959 ). The initial values were chosen following a walkover survey by an experienced modeller.
The values chosen were 0.04 and 0.05 for the channel and the floodplains respectively.
1.7
Other Coefficients
For the Westwood Brook, modelled using the HEC-RAS software, contraction and expansion
coefficients needed to be determined. Contraction and expansion coefficients are essential in
the hydraulic model computations, to determine the energy losses due to the expansion and
contraction of flow, between two adjacent cross-sections during the standard step profile
calculations.
These coefficients were determined using the HEC-RAS manual. The manual suggests that
typical values of contraction and expansion coefficients are 0.1 and 0.3 respectively for a
gradual transition along an open channel. These values therefore have been adopted for the
open channel section. However, the values 0.3 and 0.5 are recommended for the bridge
contraction and expansion coefficients respectively in all the relevant HEC-RAS publications.
The same values were therefore used in this study.
1.8
Unit Referencing
Labelling rules in HEC-RAS require that cross sections are ordered in the reach from highest
river station upstream to lowest river station downstream (in ascending order from downstream
to upstream with) with no allowance for the use of text.
1.9
Hydraulic Model Boundaries
A hydraulic model requires boundaries at each end point in the model, i.e. at the upstream
extent of every watercourse, at each inflow point and also at the downstream extent of the
model.
Each inflow to the HEC-RAS model for the steady state condition is introduced to the model as
a peak flow calculated for different flood return period.
1.10
Model Calibration
No calibration procedure has been carried out for this study due to the absence of suitable
simultaneous river gauging and rainfall data for the study area. In these cases specific
sensitivity analyses should be undertaken to verify the operation of the hydraulic model. The
sensitivity analysis has been carried out on the downstream boundary condition as well as
roughness coefficients and blockage of the structures.
1.11
Model Design Runs
The hydraulic model under steady state condition was run for the existing conditions with the 5year, 10-year, 25-year, 50-year, and 1 in 100-year peak flows (20%, 10%, 4%, 2% and 1%
annual exceedance probability) estimates. In addition to these peak flows the model was also
tested for the effect of climate change by increasing the flow of 100-year by 20%.
1
Open Channel Hydraulics – Chow V T 1959
2
Hydraulic Modelling Results
2.1
Hydraulic Model Results
A HEC-RAS steady state model was constructed of the Westwood Brook, across and
downstream of the site. The Schematic for the model is shown in Figure -1.
Figure -1: Westwood Brook Hydraulic Model Schematic
The model results indicate that the 1 in 100 year flow can be expected to remain within bank.
This can be easily seen in the long section of the model in Figure -2. HEC-RAS model results
in terms of maximum water level along the Westwood Brook for the designs flows are given in
Table -1.
Selected cross-section views for the 1 in 100-year flow are also shown in Figure -3.
Figure -2: Long section of Westwood Brook for the 100-year return period
Table -1: Westwood HEC-RAS Model Result in terms of the maximum water surface elevation
for design flows
Model
Node
5 year
10 year
25 year
50 year
100 year
100 yr +
20%
88
87
86
85
84
83
82
81
80
79
78
77
76
75
74.9
74.5
71.5
71
70
69
68
67
66
65
64
63
62
61
60
59
58
57
56
55
54
53
52
51
50
49
48
47
46
45
44
43
42
41
40
39
38
37
36
35
82.7
82.63
82.19
82.16
82.16
82.15
82.14
82.05
81.97
81.97
81.91
81.92
81.57
80.82
80.82
80.2
79.3
79.72
79.7
79.35
79.36
79.35
79.32
79.11
79.11
79.08
78.99
78.91
78.9
78.72
78.67
78.35
78.36
78.34
78.34
78.29
78.28
78.29
78.28
78.26
78.25
78.2
78.2
78.21
78.06
77.73
77.52
77.49
77.48
77.45
77.44
77.41
77.38
77.36
82.76
82.68
82.26
82.24
82.24
82.23
82.22
82.12
82.04
82.05
81.96
81.98
81.61
80.92
80.93
80.28
79.34
79.8
79.79
79.44
79.44
79.44
79.41
79.19
79.19
79.16
79.06
78.98
78.97
78.78
78.76
78.49
78.49
78.46
78.47
78.4
78.4
78.41
78.41
78.39
78.36
78.3
78.31
78.31
78.15
77.82
77.64
77.61
77.59
77.55
77.55
77.51
77.46
77.45
82.84
82.73
82.36
82.35
82.36
82.33
82.32
82.23
82.14
82.15
82.02
82.06
81.67
81.05
81.07
80.37
79.4
79.91
79.91
79.55
79.55
79.55
79.52
79.3
79.3
79.26
79.16
79.08
79.07
78.88
78.9
78.67
78.67
78.64
78.64
78.56
78.57
78.58
78.57
78.55
78.52
78.44
78.45
78.46
78.27
77.96
77.81
77.76
77.74
77.69
77.69
77.65
77.57
77.57
82.9
82.78
82.44
82.44
82.44
82.4
82.39
82.3
82.21
82.22
82.04
82.1
81.72
81.18
81.19
80.44
79.45
80
80
79.64
79.64
79.64
79.61
79.38
79.38
79.34
79.23
79.15
79.14
79
79.01
78.81
78.81
78.79
78.78
78.69
78.69
78.71
78.7
78.68
78.64
78.54
78.56
78.56
78.37
78.07
77.94
77.89
77.87
77.81
77.82
77.76
77.66
77.66
82.95
82.81
82.54
82.54
82.55
82.47
82.47
82.37
82.29
82.29
82.1
82.16
81.77
81.31
81.3
80.52
79.49
80.07
80.08
79.72
79.72
79.72
79.68
79.46
79.46
79.41
79.3
79.23
79.22
79.11
79.12
78.95
78.95
78.93
78.91
78.8
78.82
78.83
78.82
78.81
78.76
78.63
78.66
78.66
78.45
78.18
78.07
78
77.97
77.92
77.93
77.86
77.74
77.74
83.02
82.87
82.68
82.68
82.68
82.55
82.55
82.46
82.37
82.38
82.15
82.22
81.82
81.48
81.43
80.6
79.55
80.16
80.17
79.82
79.81
79.81
79.77
79.55
79.56
79.5
79.39
79.33
79.32
79.21
79.22
79.08
79.08
79.07
79.02
78.93
78.95
78.96
78.96
78.94
78.88
78.73
78.76
78.76
78.56
78.32
78.22
78.16
78.08
78.05
78.06
77.97
77.82
77.83
Model
Node
5 year
10 year
25 year
50 year
100 year
100 yr +
20%
34
28
27
26
25
24
23
22
21
20
19
18
17
16
15
14
13
12
11
10
9
8
7
5
4
3
2
1
77.05
76.97
76.82
76.74
76.69
76.54
76.27
76.06
75.99
75.88
75.8
75.79
75.76
75.76
75.67
75.64
75.63
75.63
75.6
75.6
75.6
75.59
75.57
75.57
75.57
75.57
74.91
74.33
77.13
77.05
76.89
76.81
76.76
76.6
76.33
76.13
76.06
75.94
75.86
75.85
75.83
75.83
75.74
75.7
75.69
75.69
75.66
75.65
75.65
75.65
75.62
75.62
75.62
75.62
74.94
74.38
77.24
77.16
76.98
76.9
76.85
76.68
76.41
76.22
76.14
76.03
75.94
75.93
75.91
75.91
75.83
75.78
75.77
75.77
75.72
75.71
75.71
75.7
75.69
75.69
75.69
75.69
74.98
74.44
77.32
77.24
77.05
76.97
76.92
76.75
76.47
76.3
76.22
76.1
76.01
76
75.97
75.98
75.9
75.85
75.83
75.83
75.78
75.77
75.77
75.76
75.75
75.74
75.74
75.74
75.01
74.48
77.39
77.32
77.12
77.04
76.98
76.81
76.53
76.38
76.29
76.15
76.07
76.06
76.03
76.03
75.95
75.89
75.87
75.88
75.81
75.79
75.79
75.78
75.77
75.76
75.76
75.76
75.05
74.51
77.48
77.4
77.19
77.11
77.04
76.88
76.61
76.45
76.36
76.23
76.14
76.13
76.1
76.11
76.03
75.96
75.95
75.95
75.87
75.86
75.86
75.85
75.84
75.83
75.84
75.83
75.08
74.55
The fluvial flood outline, for the 1 in 100 year flood events and for the climate change effect
were produced for the Westwood Brook catchment as the flooding occurs for the flow calculated
for the 1 in 100-year plus 20% increase in flow. The flood outline is based on the flood width for
each cross-section and by directly joining these points with those for adjacent cross-sections.
The topography between two cross-sections was therefore not considered on this outline.
Figure -3: Selected cross-section views along the Westwood Brook for design flows
2.2
Sensitivity Analysis
As there is no water level or flow data available for calibration in the study area, it is necessary
to rely on sensitivity tests on increases in parameters to judge how sensitive the results
obtained are to the assumptions made covering flow, roughness of the channel and
downstream water level.
Checks were made on water level variation with channel roughness varying ±0.005 from the
‘design’ values (1 in 100-year). Manning’s ‘n’ values in the model were taken as 0.040 for the
main channel and 0.05 for the floodplains. The sensitivity analyses carried out for this study
were as follows:
Sensitivity 1: Manning’s ‘n’ values were reduced by 0.005 for both the main channel and the
floodplains (nmc=0.035 and nfp=0.045).
Decreasing the Manning’s ‘n’ roughness values by 0.005 gave an average decrease in water
levels of 0.046m along the length of the Westwood Brook, with a maximum decrease of 0.14m.
This maximum decrease in the water level is at the downstream face of the bridge at model
node 59.5.
Sensitivity 2: Manning’s ‘n’ values were increased by 0.005 for both the main channel and the
floodplain (nmc=0.045 and nfp=0.055).
Increasing the Manning’s ‘n’ roughness values by 0.034 gave an average increase in water
levels of 0.035m along the length of the Westwood Brook, with a maximum increase of 0.070m.
The model gave the maximum decrease or increase in water levels of within ±0.08 m for some
sections, especially at structures. However the results for sensitivity run and design run along
the length of the watercourse are not affected.
The results show that in general all models appear to be fairly insensitive to channel roughness
changes of this magnitude.
Downstream Boundary Conditions and Climate Change
Sensitivity analysis to downstream boundary conditions for the Westwood Brook has been
undertaken by altering the downstream boundary for normal depth computation. The different
downstream slopes and critical depth have been taken for normal depth computation.
Altering the downstream boundary using the critical depth (Sensitivity 3) in the model did not
affect the water levels along the watercourse. The altering effects can only be seen at the
downstream section as expected. The results are shown in Appendix F for the selected
sections as Sensitivity 3.
A sensitivity analysis was also undertaken to consider climate change by increasing the flow by
20% for each model (Sensitivity 4). Increasing the flow by 20% gave an average increase in
water level of 0.09m along the length of the Westwood Brook. Full results are given in Table
3.2 and relevant nodes are summarised below. Flows along the Westwood Brook are generally
in bank. However, flow starts to come out of bank in the area of the proposed development
(between the model nodes 57-55) by increasing the level approximately by 0.19m.
It is considered that possible variations in water level tested by sensitivity analysis will not affect
the accuracy of the floodplain maps.
Sensitivity to Blockages of the Structure
Sensitivity to blockage (Sensitivity 5) on the structures has been undertaken for the 1 in 100year flow by blocking the cross-section areas of the selected structures. These structures were
assumed to be blocked by approximately 30% and are listed in.
Comparison between water surface elevations with and without blockage of structure is also
shown in Table 2 for immediate upstream cross-section. This table shows that the water levels
increase by 0.14m from 78.91m AOD to 79.05m AOD at model nodes 53.5. Water surface
elevation for the model node of 40.5 also increase by 0.16m from 78.0m to 78.16m. However,
the effect of a blockage at these locations for the smaller return periods will be more significant
since the blockage ratio will be higher.
Table 2: Summary of structures which were assumed to be blocked
Watercourse
Westwood
Brook
Westwood
Brook
Model
Node
OS NGR
Level without
Blockage
(m AOD)
Level with
Blockage
(m AOD)
53.5
430063 276148
78.91
79.09
40.5
430179 276162
78.00
78.14
This concludes that the blockage of structures along the watercourse will increase the water
level significantly and may create a flood risk.
Summary results for the sensitivity analysis in terms of water surface elevation are shown in
Table -3.
Table -3: Sensitivity Result in terms of the maximum water surface elevation for the 1 in 100year return period
Model
Node
100 year
Sensitivity
1
Sensitivity
2
Sensitivity
3
Sensitivity
4
Sensitivity
5
88
87
86
85
84
83
82
81
80
79
78
77
76
75
74.9
74.5
71.5
71
70
69
68
67
66
65
64
63
62
61
60
59
58
57
56
55
54
53
52
82.95
82.81
82.54
82.54
82.55
82.47
82.47
82.37
82.29
82.29
82.1
82.16
81.77
81.31
81.3
80.52
79.49
80.07
80.08
79.72
79.72
79.72
79.68
79.46
79.46
79.41
79.3
79.23
79.22
79.11
79.12
78.95
78.95
78.93
78.91
78.8
78.82
82.91
82.78
82.48
82.5
82.5
82.44
82.43
82.35
82.28
82.29
82.05
82.11
81.76
81.31
81.3
80.52
79.49
80.02
80.02
79.67
79.68
79.68
79.63
79.44
79.45
79.4
79.25
79.2
79.2
79.04
79.06
78.91
78.91
78.9
78.87
78.76
78.77
82.99
82.85
82.59
82.58
82.59
82.51
82.5
82.4
82.29
82.29
82.09
82.15
81.81
81.32
81.3
80.52
79.49
80.13
80.14
79.77
79.77
79.77
79.73
79.49
79.49
79.44
79.35
79.26
79.25
79.17
79.17
78.98
78.98
78.97
78.94
78.85
78.86
82.95
82.81
82.54
82.54
82.55
82.47
82.47
82.37
82.29
82.29
82.1
82.16
81.77
81.31
81.3
80.52
79.49
80.07
80.08
79.72
79.72
79.72
79.68
79.46
79.46
79.41
79.3
79.23
79.22
79.11
79.12
78.95
78.95
78.93
78.91
78.8
78.82
83.02
82.87
82.68
82.68
82.68
82.55
82.55
82.46
82.37
82.38
82.15
82.22
81.82
81.48
81.43
80.6
79.55
80.16
80.17
79.82
79.81
79.81
79.77
79.55
79.56
79.5
79.39
79.33
79.32
79.21
79.22
79.08
79.08
79.07
79.02
78.93
78.95
82.95
82.81
82.54
82.54
82.55
82.47
82.47
82.37
82.29
82.29
82.1
82.16
81.77
81.31
81.3
80.52
79.49
80.07
80.08
79.72
79.72
79.72
79.69
79.47
79.47
79.42
79.32
79.26
79.25
79.18
79.19
79.09
79.09
79.08
79.05
78.81
78.82
Model
Node
100 year
Sensitivity
1
Sensitivity
2
Sensitivity
3
Sensitivity
4
Sensitivity
5
51
50
49
48
47
46
45
44
43
42
41
40
39
38
37
36
35
34
28
27
26
25
24
23
22
21
20
19
18
17
16
15
14
13
12
11
10
9
8
7
5
4
3
2
1
78.83
78.82
78.81
78.76
78.63
78.66
78.66
78.45
78.18
78.07
78
77.97
77.92
77.93
77.86
77.74
77.74
77.39
77.32
77.12
77.04
76.98
76.81
76.53
76.38
76.29
76.15
76.07
76.06
76.03
76.03
75.95
75.89
75.87
75.88
75.81
75.79
75.79
75.78
75.77
75.76
75.76
75.76
75.05
74.51
78.79
78.79
78.77
78.72
78.58
78.6
78.61
78.39
78.13
78.03
77.97
77.93
77.88
77.89
77.82
77.68
77.69
77.32
77.26
77.07
77
76.94
76.76
76.5
76.34
76.24
76.12
76.02
76.02
75.96
75.97
75.88
75.82
75.8
75.81
75.74
75.72
75.72
75.7
75.63
75.63
75.64
75.63
75.05
74.49
78.87
78.86
78.84
78.79
78.69
78.71
78.71
78.51
78.24
78.11
78.05
78.01
77.97
77.97
77.9
77.79
77.79
77.46
77.37
77.16
77.08
77.02
76.86
76.58
76.41
76.33
76.19
76.11
76.1
76.07
76.08
75.99
75.92
75.91
75.91
75.83
75.81
75.81
75.8
75.78
75.78
75.78
75.77
75.07
74.54
78.83
78.82
78.81
78.76
78.63
78.66
78.66
78.45
78.18
78.07
78
77.97
77.92
77.93
77.86
77.74
77.74
77.39
77.32
77.12
77.04
76.98
76.81
76.53
76.38
76.29
76.15
76.07
76.06
76.03
76.03
75.95
75.89
75.87
75.88
75.81
75.79
75.79
75.78
75.77
75.76
75.76
75.76
75.05
74.51
78.96
78.96
78.94
78.88
78.73
78.76
78.76
78.56
78.32
78.22
78.16
78.08
78.05
78.06
77.97
77.82
77.83
77.48
77.4
77.19
77.11
77.04
76.88
76.61
76.45
76.36
76.23
76.14
76.13
76.1
76.11
76.03
75.96
75.95
75.95
75.87
75.86
75.86
75.85
75.84
75.83
75.84
75.83
75.08
74.55
78.84
78.83
78.82
78.77
78.65
78.67
78.67
78.49
78.28
78.21
78.16
77.97
77.92
77.93
77.86
77.74
77.74
77.39
77.32
77.12
77.04
76.98
76.81
76.53
76.38
76.29
76.15
76.07
76.06
76.03
76.03
75.95
75.89
75.87
75.88
75.81
75.79
75.79
75.78
75.77
75.76
75.76
75.76
75.05
74.51
3
Conclusions
A 1-D hydraulic model was constructed for the Westwood Brook. The Westwood Brook was
modelled using the HEC-RAS v3.1.3 software developed by the US Army Corps of Engineers.
Water levels and flows were obtained for the 20%, 10%, 4%, 2% and 1% annual exceedance
probability AEP flood events (5, 10, 25, 50, and 100-year return periods) and have been
tabulated.
The hydraulic model for the Westwood Brook was not calibrated due to the absence of any
gauging station on the watercourses. Sensitivity analyses relating to channel roughness, to
downstream boundary and to climate change have been undertaken and results are shown in
Table -3. A sensitivity analysis to consider climate change was undertaken by increasing the
100 year design flow by 20%.
The model results indicate that for the 1 in 100 year event flows can be expected to remain
within bank for the conditions tested. However, when the flow is increased by 20% to allow for
climate change water begins to overtop the banks. This occurs in the vicinity of the junction
between University Road and Library Road. The flow will be out of bank on the left tributaries
and may affect the Existing Academic Square.
The fluvial flood outline, for the 1 in 100 year flood events and for the climate change effect
were produced for the Westwood Brook catchment as the flooding occurs for the flow calculated
for the 1 in 100-year plus 20% increase in flow.
Appendix D
Record of Consultation
Record of Telephone Communication
Page 1 of 1
Job title
University of Warwick Development Plan - Drainage Strategy
Job number
116181-00
Communication from
Andy Williams
File reference
Organisation
Arup
6-02-01
Telephone no
(0)121 213 3233
Communication to
Mr Paul Leaman
Date of communication
Organisation
Warwick District Council
5 August 2004
Telephone no
01926 450000
Copy to
Record of communication
•
AW explained Arup had been commissioned by the University to undertake a
drainage strategy scoping report and as part of this report Arup where trying to
determine if Warwick District Council had any issues or concerns regarding
drainage and land drainage within the University Campus situated within the
Warwick District Council Boundary.
•
PL responded that WDC had no issues with regard to drainage etc at this site.
J:\116000\116181-00\6 REGULATORY BODIES\6-02 LOCAL BODIES\6-02-01 WARKS DISTRICT COUNCIL\0001DRAINAGE ISSUES
AW 2004-08-05.DOC
Action
©Arup F0.7
QA Rev 9.3, 17 November 2003
Record of Telephone Communication
Page 1 of 1
Job title
University of Warwick Development Plan - Drainage Strategy
Job number
116181-00
Communication from
Andy Williams
File reference
Organisation
Arup
6-02-03
Telephone no
(0)121 213 3233
Communication to
David Chiles
Date of communication
Organisation
Coventry City Council
10 August 2004
Telephone no
07771 938809
Copy to
Record of communication
•
AW explained Arup had been commissioned by the University to undertake a
drainage strategy scoping report and as part of this report Arup where trying to
determine if Coventry City Council had any issues or concerns regarding drainage
and land drainage within the University Campus situated within their Boundary.
•
DC explained that CCC had powers under the Land Drainage Act to ensure
landowners drained their sites responsibly. He said that the council would not want
any further increases in runoff entering watercourses policed by the City Council,
and therefore would like to see the use of SUDS and attenuation devices within any
new developments.
•
DC also explained that they had been liaising with the John Fouldes of the EA to
identify critical ordinary watercourses within this area and none had been identified.
•
Based on the above, CCC has no issues with the future development at this time.
J:\116000\116181-00\6 REGULATORY BODIES\6-02 LOCAL BODIES\6-02-03 COVENTRY CITY COUNCIL\0001TELECOM
DRAINAGE ISSUES AW - DC 2004-08-10.DOC
Action
©Arup F0.7
QA Rev 9.3, 17 November 2003
Notes of Meeting
Page 1 of 4
Job title
Meeting name & number
University of Warwick Development Plan Drainage Scoping Study
Job number
EA Liaison Meeting
File reference
116181-00
9.0
Location
EA Offices at Tewksbury
Time & date
10:30
Purpose of meeting
Identify Key Issues for Future Surface Water Management
Present
Andy Williams
John Foulds (EA)
12 August 2004
David Schofield
Giles Matthews (EA)
Apologies
Circulation
Those present
Prepared by
Andy Williams
Date of circulation
12 August 2004
Date of next meeting
C:\DOCUMENTS AND SETTINGS\ANDY.WILLIAMS\LOCAL SETTINGS\TEMPORARY INTERNET FILES\OLK49\0001MINUTES OF EA
LIASON MEETING AW 2004-08-11.DOC
©Arup F0.5
QA Rev 9.3, 17 November 2003
Notes of Meeting
Page 2 of 4
Job title
Job number
University of Warwick Development Plan - Drainage 116181-00
Strategy
1.
Date of Meeting
Action
12 August 2004
DS explained Arup had been commissioned by the University of Warwick to
produce a surface water drainage scoping study to identify what work was
required to be undertaken to produce a drainage strategy for the possible future
development of the University. The purpose of the meeting was to identify the
key EA issues for the university site.
The key points are briefly detailed below:
•
In accordance with Planning Policy Guidance Note 25 (PPG 25), Flood Risk
Assessments (FRA) will be required for future development on the site;
•
Detailed hydraulic analysis of the Westwood Brook will be required as part of
an FRA;
•
The existing EA flood data pertaining to the Canley Brook will suffice an
FRA;
•
No development should take place in the fluvial floodplain;
•
Any additional impermeable area from future development must be attenuated
to the equivalent greenfield rate of runoff;
•
Future surface water design must be carried out for no system flooding on a 1
in 100 year return period storm event;
•
Contemporary sustainable surface water drainage techniques (SUDS) are
encouraged;
•
Culverting of watercourses should be avoided and the re-opening of existing
culverted section would be welcomed;
•
Surface water quality issues should also be considered and addressed;
•
There are ecological issues to be considered and addressed;
•
There are no details of any surface water discharge consents available at this
time.
The strategic way forward for all surface water issues associated with future
development at the University,