(SFRA) Liverpool City Council Strategic Flood Risk Assessment - January 2008
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Liverpool City Council
Strategic Flood Risk Assessment
(SFRA)
January 2008Contents
Section 1 – Introduction
Section 2 – Liverpool context
Section 3 – Policy context
Section 4 – Roles and responsibilities
Section 5 – Flood Risk Assessment
- Background
- Risk of flooding
- Flood Defences
- Residual Risk
- Extreme Events and Climate Change
Section 6 - Spatial Development and Flood Risk
Section 7 - Summary and conclusions
Appendices
Appendix A – Methodology and sources of information
Appendix B – Guidance for Developers and Development Control
Appendix C – RSS and Core Strategy Issues and Options Appraisal
List of Figures
Figure 1: Location map
Figure 2: Flood Risk Vulnerability and Flood Zone ‘Compatibility’ (Table D.3 –
PPS25)
Figure 3: Liverpool Bay Shoreline Management Plan (SMP) - Sub Cell 11a - Great
Ormes Head to Formby Point
Figure 4: CFMP Boundaries
Figure 5: Future boundary of SMP
Figure 6: Roles and Responsibilities in flood risk - Liverpool
Figure 7: Location of Low-Water in the Inner Mersey Estuary between 1956 and
1967
Figure 8: Flood Risk Zones for Mersey Estuary Catchment
Figure 9: External DG5 for Mersey Estuary Catchment
Liverpool City Council – Strategic Flood Risk Assessment January 2008
-1-List of Tables
Table 1: Key features and actions proposed within Draft Mersey Estuary CFMP
for Liverpool
Table 2: River Alt and Crossens - assessment of flood risk to people and
economic damages
Table 3: Rivers and Ordinary watercourses within each catchment
Table 4a: Summary of Culverts – information from 1989 study that matches with
1999 study
Table 4b: Summary of Culverts – information from 1989 study that does not
match with 1999 study
Table 5: Tidal levels in Liverpool (Gladstone Dock)
Table 6: Historical information for the Environment Agency Flood Risk Zones
Table 7: Historical areas of flooding
Table 8: Flood locations supplied by Highways
Table 9: Condition of Culverts
Table 10: Incidences of sewer flooding
Table 11: Risk of flooding to and from adjoining authorities
List of Maps
Map 1: Natural features – topography and watercourses
Map 2a: Watercourses – main rivers, canal and catchments
Map 2b: Watercourses – main rivers and ordinary watercourses from 1989
Watercourse Flood Alleviation Study and catchments
Map 2c: Watercourses – main rivers and ordinary watercourses from 1999
Culverted Watercourse Study
Map 3: Culverts
Map 4a: Environment Agency flood risk zones – tidal flood risk
Map 4b: Environment Agency flood risk zones – tidal and river flood risk
Map 5: Flood Risk Zone 3: Estimated functional floodplain (3b) and High
Probability Area (3a)
Map 6: Historical flooding areas
Map 7: Condition of culverts – where information is available, the areas of
poorest condition are identified
Map 8: Historical sewer flooding
Map 9: Summary of identified floodrisk
Map 10: Risk of flooding in and from adjoining authorities
Map 11: Flood Defences – e.g. river wall, Greenfield sites and open spaces, levees
Map 12: Strategic development areas, UDP Allocations and Flood risk
Map 13: Predicted Extreme Tide Levels in 2115
Map 14: Predicted Extreme River Levels (Flood Risk Zone 2)
Liverpool City Council – Strategic Flood Risk Assessment January 2008
-2-1 Introduction
1.1 This SFRA (Strategic Flood Risk Assessment) has been carried out by Liverpool
City Council Planning Policy Department in order to fulfil the requirement set
out in Planning Policy Statement (PPS) 251. This document has been undertaken
between June 2006 and January 2008.
1.2 The SFRA is a tool that plays an important role in delivering sustainable
development for the City of Liverpool, taking account of flood risk issues and
climate change. The main objectives of this SFRA are to:
• Identify land at risk of flooding in Liverpool and the degree of risk from
river, sea and other sources
• Reduce flood risk from and to new development through location, design
and mitigation measures
• Inform policy formulation and the Sustainability Appraisal for the emerging
Local Development Framework concerning land use in flood risk areas
• Provide a framework for development control officers and developers for
dealing with the flood risk in development proposals
1.3 It is an important distinction that the function of the SFRA is to minimise the
risk of flood to new developments and to reduce existing flood risks where
possible. The risk of flooding to existing buildings is not within the remit of
this assessment.
1.4 It is also important to note that this document is a strategic assessment.
Detailed site specific flood risk assessments will still be required in line with
PPS25. This assessment also highlights areas where further investigation may
be required.
1.5 The role and responsibilities of different agencies concerning floodrisk is
complex. This document has been undertaken by Liverpool City Council, but
with the assistance of key partners including the Environment Agency,
Liverpool 2020, United Utilities and Enterprise-Liverpool.
1.6 The structure of this SFRA builds up the picture of flood risk within Liverpool,
starting with the Liverpool context, highlighting for example the need for
urban renewal balanced with the need to address any identified flood risks.
The policy context (section 3) sets out the main documents which influence the
preparation of this SFRA and provides important background information. Due
to the complexities of roles and responsibilities, there is also a summary flow
chart which is designed to aid the development process, ensuring different
agencies are aware of other agencies responsibilities.
1
Planning Policy Statement (PPS) 25 – Development and Floodrisk (2006) - DCLG
Liverpool City Council – Strategic Flood Risk Assessment January 2008
-3-1.7 The key section of the document is section 5, the flood risk assessment. This
provides basic background information, e.g. the locations of watercourses and
culverts and then identifies where the key areas of flood risk are e.g.
Environment Agency indicative flood risk maps and historical areas of flooding.
This provides the basis in which to identify the level of flood risk in strategic
areas (discussed in section 6) but also provides the background information for
more detailed site specific flood risk assessments.
Liverpool City Council – Strategic Flood Risk Assessment January 2008
-4-Figure 1: Location Map
2 Liverpool Context
2.1 Liverpool is located on the River
Mersey in the North West of
England. It covers an area of 112
square kilometres.
2.2 Liverpool is a predominantly Knowsley
urban area, with a population of
444,500 (2004 population Sefton
estimate). The City has seen St. Helens
significant change over the past
Liverpool
century including a population
decline from its peak in 1931 of
846,101 to the present day. Wirral
Halton
2.3 The city has a history strongly
linked with its river, the Mersey,
providing an international seaport and maritime trade, between the 18th and
20th Century. However, the 1980s industrial crisis led to a severe economic
decline within Liverpool, the legacy of which is still a major issue today.
2.4 Over the years, the City has mounted a succession of major housing
regeneration and redevelopment programmes to address these problems,
dealing variously with slum clearance and housing stock rehabilitation. Areas
of the city are now designated as priorities for action under the government’s
Housing Market Renewal Initiative (HMRI), which is a long-term programme to
transform those inner city neighbourhoods dominated by unpopular housing
through a comprehensive regeneration process, including housing
redevelopment and refurbishment on a major scale.
2.5 Despite these issues, Liverpool is a regional centre for financial and
professional services, retail provision, tourism, higher education, hi-tech
industries, manufacturing and transportation. The Mersey Ports and Liverpool
John Lennon Airport are key transport hubs and perform a central role in the
City’s economy.
2.6 The City Council’s aim for the City is:
"We aim to build and safeguard a fair, prosperous and open city where no-one
is in poverty; where our citizens are well educated and take part in the
decisions that affect them and where the cultural and religious differences
between people are valued and celebrated." (2006)
2.7 This context demonstrates some of the key assets within Liverpool and the
different pressures and issues that the City faces. Without an appropriate
assessment of the potential risks of flooding, there is a danger that the success
of the City and future developments will be jeopardized by flooding, causing
far reaching damage to buildings, economy, image and people though loss of
belongings and personal injury. Further detailed consideration of the level of
flood risk in key development areas is provided in section 6.
Liverpool City Council – Strategic Flood Risk Assessment January 2008
-5-3 Policy Context
3.1 There are a variety of planning documents that provide a broad context to
planning and floodrisk, as it is a key cross-cutting issue. Planning Policy
Statement 1: Delivering Sustainable Development2, provides the overarching
principles for the planning system refers to the need to avoid new
developments in areas at risk of flooding and sea-level rise. In addition, other
guidance relating to different types of development such as PPS3: Housing,
PPS6: Planning for Town Centres and PPG4: Industrial, Commercial
Development and Small Firms need to be taken into account. The Supplement
to PPS1 on Climate Change3 also needs to be considered, particularly with
regard to mitigation and adaptation.
3.2 A brief overview of the key policy documents that provide specific guidance
relating to planning and floodrisk from a national through to local level are as
follows:
National:
Making Space for Water – DEFRA (2005)4
3.3 Making Space for Water is the Government’s strategy for flood and coastal
erosion risk management in England. The key issues within this document are:
• To assess flood risk in the planning process
• To involve people in the decision making process as well as in the
prevention of and protection against risk
• To have a holistic and global approach to the risk and to collect better data
• To test and provide new tools to manage the risk
• To be ready to change land use in order to manage the risk
Planning Policy Statement (PPS) 25 (2006): Development and Floodrisk
3.4 PPS25 was adopted in December 2006. It provides the guidance to ensure that
floodrisk is taken into account at all stages of the planning process to avoid
inappropriate development in areas at risk of flooding, and to direct
development away from areas of highest risk.
3.5 PPS25 expects local authorities to apply a risk-based approach to the
preparation of development plans and their decisions on development control
through a sequential test.
3.6 The detailed provisions of the sequential test are essential to the consideration
of planning applications and in determining allocations within the Local
Development Framework and direct reference should be made to PPS 25 (Annex
D, Table D.1).
2
Planning Policy Statement 1: Delivering Sustainable Development (ODPM) - 2005
3
Planning Policy Statement: Planning and Climate Change - Supplement to Planning Policy
Statement 1 (DCLG) - 2007
4
Making Space for Water – DEFRA 2004/2005
http://www.defra.gov.uk/environ/fcd/policy/strategy/1stres.pdf
Liverpool City Council – Strategic Flood Risk Assessment January 2008
-6-3.7 In brief, the flood risk zones range from zones 1 to 3. They refer to the
probability of flooding from rivers, the sea and tidal sources and ignore the
presence of existing defences because these can be breached, overtopped and
may not be in existence in the lifetime of the development. The basic
principles are that development should be steered towards flood risk zone 1.
Where no reasonably available sites exist in Flood Zone 1, Flood Zone 2 can be
considered and finally if no available sites are located in flood risk zone 1 and
2, should flood zone 3 be considered.
3.8 PPS25 also implements an ‘exception test’ approach to certain types of
development within flood risk zones 2 and 3. The key principles of which are
that:
• The development provides wider sustainability benefits to the community
that outweigh floodrisk
• The development is on developable previously developed land or where
there are no reasonable alternatives on developable previously developed
land
• A flood risk assessment demonstrates that the development will be safe,
without increasing flood risk elsewhere and, where possible, will reduce
flood risk overall
3.9 The Exception Test is only appropriate for use when there are large areas in
Flood Zones 2 and 3, where the Sequential Test alone cannot deliver
acceptable sites.
3.10 Different land uses are considered to be more appropriate in different flood
risk areas. The types of development, their suitability and the need to apply
the exception test is summarised within table D.3 of PPS25 and shown in figure
2 below:
Figure 2: Flood Risk Vulnerability and Flood Zone ‘Compatibility’ (Table D.3
– PPS25)
Flood Risk Essential Water Highly More Less
Land Use Infrastructure Compatible Vulnerable Vulnerable Vulnerable
Vulnerability
classification
Zone 1 ! ! ! ! !
Zone 2 ! ! Exception ! !
Test
Flood Zones
Required
Zone 3a Exception Test ! " Exception !
Required Test
Required
Zone 3b Exception Test ! " " "
Required
Key:
! Development is appropriate
" Development should not be permitted
Liverpool City Council – Strategic Flood Risk Assessment January 2008
-7-3.11 PPS 25 (Annex E) sets out the minimum requirements for flood risk
assessments:
• Consider risk of flooding both from and to a development
• Consider the effects of parts of the flood risk management infrastructure
including raised defences, flow channels, flood storage areas and other
artificial features together with the consequences of their failure
• Consider the vulnerability of those that could occupy the development,
taking account of the sequential and exception tests and the vulnerability
classification including safe access
• Consider and quantify the different types of flooding and identify flood risk
reduction measures so that assessments are fit for the purpose of the
decisions being made.
• Consider the effects of a range of flooding events including extreme events
• Include an assessment of the remaining risk (residual) after risk reduction
measures have been taken into account
• Consider how the ability of water to soak into the ground may change with
development, along with how the proposed layout of development may
affect drainage systems
• Consider the affects of climate change
Development and Floodrisk: A Practice Guide Companion to PPS25 ‘Living
Draft’ - A Consultation Draft (February 2007)
3.12 A draft Practice Guide to the adopted PPS25 was published in February 2007
providing more detailed guidance for the implementation of PPS25.
3.13 The document focuses on the following aspects:
• Further guidance for what PPS25 means for those responsible for preparing
Regional Spatial Strategy, Local Development Documents and Sustainability
Appraisal and for developers
• Further guidance on undertaking Regional Flood Risk Appraisals (RFRA’s),
Strategic Flood Risk Assessments (SFRA’s) such as this document and site-
specific Flood Risk Assessments (FRA’s)
• Further guidance on the application of the sequential approach and
Exception Test
• Further guidance on the planning implications of a range of measures for
mitigating the adverse impacts of conventional drainage systems and
provides an overview of the principles of sustainable drainage
• Detailed guidance for risk management by design which looks at the
individual site level and measures that can be implemented
• Further guidance on some of the key residual risk issues
3.14 It should be noted that this SFRA was at a stage close to adoption on the
publication on this practice guidance. This document has been used to check
that this SFRA complies with the requirements set out within it. However it
was not used as the starting point to the process.
Liverpool City Council – Strategic Flood Risk Assessment January 2008
-8-Water Framework Directive
3.15 The WFD entered into force in December 2000 and was transposed into English
and Welsh law in December 2003 as the Water Environment (Water Framework
Directive) (England and Wales) Regulations 2003.
3.16 The main objectives of the Water Framework Directive are considered to be:
• Enhance the status and prevent further deterioration of aquatic ecosystems
and associated wetlands - there is a requirement for nearly all inland and
coastal waters to achieve ‘good status’ by 2015
• Promote the sustainable use of water
• Reduce pollution of water, especially by ‘priority’ and ‘priority hazardous’
substances
• Lessen the effects of floods and droughts;
• Rationalise and update existing water legislation and introduce a co-
ordinated approach to water management based on the concept of river
basin planning.
3.17 WFD demands that headline water issues such as the availability of water
supplies, maintaining the quality of water in rivers and managing flood risk are
considered as a whole rather than in isolation. Increased flood risk can have a
significant impact on water quality with increased run-off reaching the
watercourses.
3.18 There is also a need to have regard to the River Basin Management Plan (RBMP)
for the North West, which is due to be adopted in 2009.
Regional:
Adopted Regional Spatial Strategy (RSS) for the North West (2003)
Draft Regional Spatial Strategy (RSS) for the North West (2006)
3.19 Adopted RSS for the North West sets out the regional approach within Policy
ER8. It requires that the precautionary principle and sequential approach be
applied, that inappropriate development in areas of floodrisk should be avoided
and encourages the promotion of SuDS in all developments. It highlights the
River Mersey network (i.e. the entire river system from the Mersey Estuary to
confluence of Goyt and Tame Rivers at Stockport) as one of the areas at
greatest risk within the region.
3.20 Guidance is provided within policy EM5 in the Draft RSS for the North West.
This policy requires;
• The implementation of “Meeting the Sequential Flood Risk Test – Guidelines
5
for the North West Region ”,
• Exceptional development that is allowed in flood risk zones be resilient to
flooding,
• New developments to incorporate SuDS; and
• Awareness raising of flood issues.
5
Meeting the Sequential Flood Risk Test – Guidelines for the North West Region (2004) – EA and
NWRA
Liverpool City Council – Strategic Flood Risk Assessment January 2008
-9-3.21 Policy CZ2B in the Adopted RSS relates to Coastal Defences and the need for
plans and policies to contain flood risk assessments in line with the Shoreline
Management Plan, direct development away from areas of flood risk, coastal
erosion and land instability and avoid development that prejudices existing
coastal defences. The Draft RSS, policy EM6 relates to Managing the North
West’s Coastline, which supports the Adopted RSS but also includes the need to
consider the impacts of climate change.
3.22 An analysis of strategic policies and their impact on floodrisk is provided in
Appendix C.
Sub Regional
Liverpool Bay Shoreline Management Plan (1999): Sub Cell 11a – Great
Ormes Head to Formby Point
3.23 The Liverpool Bay Shoreline Management Figure 3: Sub cell for Liverpool (11a)
Plan is split into sub cells. The map in
figure 3 shows the sub cell which relates
to Liverpool (sub cell 11a).
3.24 The main objectives of the Shoreline
Management Plan include enhancing and
protecting the rural economy and the
fishery industry, monitoring, enhancing
the landscape quality and the
management and maintenance of coastal
defences. Where possible, these should
be natural defences and should not have
adverse impacts on industries, nature
conservation and the historic
environment.
3.25 The Shoreline Management Plan does not include any specific details that
relate to Liverpool and that need to form the basis for any recommendations or
further investigation within this SFRA. This SFRA should however be in line
with the overall aims and objectives of
the Plan. Work on a revised SMP is due Figure 4: CFMP Boundaries
to commence in 2007.
Catchment Flood Management Plans
3.26 There are two catchment flood Alt and
Crossens
management plans (CFMPs) which are
within the Liverpool City Council
authority area. These are the Mersey
catchments of the River Mersey and the Estuary
River Alt. The following map (figure 4)
provides an overview of these
boundaries:
3.27 The Mersey Estuary Catchment Flood
Management Plan is at the draft stage Reproduced from Mersey Estuary Draft
Catchment Flood Management Plan (© Crown
Copyright All rights reserved 100026380
Liverpool City Council – Strategic Flood Risk Assessment January 2008
- 10 -(March 2007) and the River Alt and Crossens Catchment Flood Management Plan
is at the scoping report stage (April 2007). These documents are key reference
points for the Liverpool Strategic Flood Risk Assessment and it is important this
SFRA is in conformity with these documents. Reference should also be made
directly to these documents.
Mersey Estuary Draft Catchment Flood Management Plan (March 2007)6
3.28 The Draft Catchment Flood Management Plan provides an overview of the flood
risk in the Mersey Estuary catchment and sets out the preferred plan for
sustainable flood risk management over the next 50 – 100 years.
3.29 The aims of the Mersey Estuary Catchment Flood Management Plan are:
• To reduce the risk of flooding and harm caused by floods to people, the
natural, historic and built environment;
• To maximise opportunities to work with nature and to bring about a range
of benefits from flood risk management, and make an effective
contribution to sustainable development;
• To support the implementation of EU directives (Water Framework
Directive and the forthcoming Floods Directive), meeting Government and
other policies and targets, and our corporate vision;
• To promote sustainable flood risk management;
• To inform and support planning policies, statutory land use plans and
implementation of the Water Framework Directive so that future
development in the Mersey Estuary CFMP catchment is sustainable in terms
of flood risk.
3.30 Within the revised Shoreline Management Plan (work on the revised document
is expected to commence in 2007), the boundary is due to be amended. This
will take the boundary of the Shoreline Management Plan further into the
Mersey Estuary. This is demonstrated in figure 5.
Figure 5: Future boundary of SMP
3.31 The draft report provides important
background information about the
catchment, such as topography, geology,
hydrology and land use and land
management (see summary in section 5,
paragraph 5.10). The draft report also
provides an overview of flood risk issues
which are included within each relevant
sub-section of section 5: Risk of Flooding.
3.32 The following table summarises the key
features and actions proposed within the
Draft Mersey Estuary Catchment Flood
Management Plan for the Liverpool area
(known as policy unit 11): Reproduced from Mersey Estuary Draft
Catchment Flood Management Plan (© Crown
Copyright. All rights reserved. 100026380, 2007)
6
Mersey Estuary Catchment Flood Management Plan (CFMP) – Consultation Draft, Environment Agency
(March 2007) http://www.environment-
agency.gov.uk/regions/northwest/1072087/1697828/?version=1&lang=_e
Liverpool City Council – Strategic Flood Risk Assessment January 2008
- 11 -Table 1: Key features and actions proposed within the Draft Mersey Estuary CFMP
for Liverpool
Policy Unit 11 Liverpool:
Covers the north Mersey Estuary component and includes the city of Liverpool
Problem/risk There are approximately 373 properties and 28 commercial properties at risk of
flooding with flood risk areas lying in the north of the unit and also near the
waterfront. However, there is little history of flooding in this policy unit, and
current flood risk management is thought to be appropriate in this heavily
urbanised and industrialised unit.
Policy Policy number 4
Take further action to sustain the current scale of flood risk into the future
(responding to the potential increases in flood risk from urban development, land
use change, and climate change).
Justification There is a population of approximately 319,000 (approx. 22% of the whole
catchment) in this policy unit. The current number of properties at risk for a
baseline 100:1 (1%) chance event is approximately 500 (approx. 2% of the total
number of properties at risk in the catchment for the same event).
Currently, the estimated damages to residential properties in this policy unit are
approximately £117M for a 10:1 (10%) chance event, 50:1 (2%) chance event and
100:1 (1%) chance event. Estimated damages for the latter event could increase by
18% and 77% by 2055 and 2105 respectively as a result of the impacts of climate
change and any further development planned within the catchment. The current
expected annual damages in this policy unit are approximately £12M /yr and
amount to 5% of the total damages within the catchment.
This policy is selected as flood defence assets are currently more than adequate
for current flood risk, although flood risk at these locations may rise in the long-
term due to climate change and any possible further development. Although there
is a World Heritage Site within the unit, it is subject to a low risk of flooding with
tidal issues covered by the SMP. Planned future developments within this policy
unit are not extensive and involve development on existing brownfield sites. If
development is necessary, flood risk areas should be avoided.
There are no environmental designations within flood risk areas although it does
border with a number of Mersey Estuary designations. No pollution inventory sites
lie within flood risk areas. Maintaining current flood risk means an appropriate
level of management is sufficient enough for the unit and adequate enough for
tidal levels taking into account aforementioned features.
Actions All identified actions in the action plan are considered to be ‘high’ priority –
essential to achieve policy aim and has a large effect
11.1: Carry out existing level of maintenance in the short term. Undertaking
detailed study to deliver plans such as System Asset Management Plans, Asset
Replacement Programmes. Potential schemes will be identified through this
process and will be implemented on a priority basis. All plans should seek to
address gaps in knowledge. Completed set of System Asset Management Plans.
11.2: Development Control advice to ensure no increase in run-off from new
developments and seek opportunities to reduce current run-off rates where
possible. Develop integrated urban drainage strategy, implementation of SuDs
where feasible.
11.3: Develop integrated urban drainage strategy, with review of receiving
watercourses/ catchments, foul and surface water, and consider the effects of
climate change. Develop integrated urban drainage strategy
Risks, Future flooding risks (including climate change etc.) are an uncertainty.
uncertainties SMP and CFMP need to be consistent to ensure no overlap or gaps in policy
and
dependencies
Liverpool City Council – Strategic Flood Risk Assessment January 2008
- 12 -River Alt and Crossens Catchment Flood Management Plan – Scoping Report
(April 2007)7
3.33 The Alt-Crossens catchment lies within the administrative local authority areas
of:
• Liverpool City Council
• Sefton Metropolitan Borough Council
• Knowsley Borough Council
• West Lancashire District Council
• St. Helens Borough Council (only a minor part in the south-east)
3.34 The Draft report is due to be published in early 2008.
3.35 The main tributaries entering the River Alt within its upper reaches are:
• Hall Brook in Croxteth Park
• Sugar Brook, servicing a heavily urbanised area
• Fazakerly Brook which serves the densely populated Tue Brook and Anfield
areas of Liverpool
• Tue Brook - substantially culverted
• Deys Brook - substantially culverted
• Thornhead Brook - substantially culverted
• Knowsley Brook, primarily draining a largely rural area
• Kirkby Brook, largely rural but provides drainage for the urban area of
Kirkby.
This part of the Alt catchment is historically termed the Upper Alt catchment,
with its notional boundary at the Kirkby Gauging Station, the only flow
monitoring location in the catchment.
3.36 The watercourses of the Alt and Crossens catchments have been modified
considerably. The upper Alt catchment has been extensively urbanised, and
many sections of the channel have been canalised or culverted. The lower Alt
(downstream of Maghull) has been straightened and confined within flood
embankments, significantly changing its character and disconnecting the
channel from its natural floodplain. The changes to the River Alt have resulted
in very flashy, rapid flows from the urban upper catchment but conveyance
problems through the shallow-sloped lower reaches, where pumps are required
to maintain flow movement through the channels.
3.37 The main areas identified to be at risk within the Alt catchment include:
• Acre Lane Brook and Wham ditch, Formby
• Kirkby Brook, Kirkby
• Simonswood Brook, Kirkby
• Whinney Brook, Maghull
• Dovers Brook, Maghull
• Breach of flood banks of Cheshire Lines, Lydiate
7
River Alt and Crossens Catchment Flood Management Plan (CFMP) – Scoping Report, Environment
Agency (April 2007) http://www.environment-
agency.gov.uk/regions/northwest/1072087/1697392/?version=1&lang=_e
Liverpool City Council – Strategic Flood Risk Assessment January 2008
- 13 -• Aintree
• Deys Brook and Tue Brook, Liverpool
The majority of flood risk within the urban areas is as a result of insufficient
culvert or channel capacity and channel obstruction.
3.38 There is limited information regarding surface water flooding in the catchment.
Based on the information available, the risk of flooding from surface water in
individual flood risk areas within the catchment can be considered to be
relatively high in frequency (i.e. approximately on an annual basis) but low
consequence. The following table demonstrates the assessment of flood risk to
people and economic damages:
Table 2: River Alt and Crossens assessment of flood risk to people and economic
damages
Location (main No. of people Maximum Ranked risk to Current
urban at risk* (1% water depth people economic
conurbations) a.p. event) (m) (1% 1.p. damages
event) (£000’s)
Liverpool – West 358 0.63 Low 5,948
Derby
Maghull 1165 1.45 High 35,122
Formby 10 0.75 Medium 56
Mere Brow 3 0.24 Unknown 200
* Assuming 2.5 people on average per property (UK Government Statistics)
Local:
Liverpool City Council – Contaminated Land Inspection Strategy (2002)
3.39 This document sets out the manner in which Liverpool City Council proposes to
implement its inspection duties under Part IIA of the Environmental Protection
Act 1990. It describes the framework within which potentially contaminated
land will be identified and dealt with in a rational, ordered and efficient
manner.
3.40 The links to flood risk are that areas of flooding are highlighted as potentially
contaminated land. In addition increased levels of flooding can lead to
increased contamination, through transporting pollutants during times of flood
and generating the overflow of sewer systems.
Adopted Liverpool Unitary Development Plan (2002)
Emerging Liverpool Local Development Framework (LDF) (ongoing)
3.41 The Adopted Unitary Development Plan (UDP) for Liverpool (2002) sets out the
Council’s approach to flood prevention in Policy EP13. The policy states that
unless appropriate alleviation or mitigation measures are carried out, planning
permission will not be granted for development. This includes developments
that would be at a direct unacceptable risk from flooding, be likely to increase
the risk of flooding elsewhere and those that would result in an adverse impact
on the water environment due to additional surface water runoff.
Liverpool City Council – Strategic Flood Risk Assessment January 2008
- 14 -3.42 The Adopted UDP also includes allocations of land for different types of
development. A number of these have already been developed, but a large
number remain unimplemented and may be brought forward under the UDP in
the future. Each unimplemented site has been assessed for the level of
identified flood risk and the approach that should be taken (see section 6 –
paragraph 6.33 onwards).
3.43 Under the current planning system, Liverpool City Council is producing a Local
Development Framework to replace the existing UDP. A Local Development
Scheme8 (LDS) has been produced and is regularly updated. This contains
details of the documents that are to be produced under the Local Development
Framework and a timetable for their completion. Reference should be made to
the LDS to determine what documents are to be produced when. This SFRA will
inform the production of these documents.
3.44 Preparation of the Core Strategy (Development Plan Document – DPD) is
underway. The key milestones in the production of a DPD is:
Submission DPD
4. Consultation
2. Consultation
6. Consultation
8. Consultation
9. Examination
Options Report
Options Report
Options Paper
Options Paper
on submission
3. Drafting of
5. Drafting of
7. Drafting of
on Issues and
10. Adoption
on Preferred
production/
on scoping
Issues and
Preferred
scoping
1. Pre-
report
DPD
3.45 An Issues and Options Paper9 for the Core Strategy has been published. The
two issues and associated options for an appropriate policy approach to flood
risk are:
Issue The Core Strategy should control development in identified areas of
flood risk
Option A The Core Strategy should include a prudent avoid all development in
areas of flood risk
Option B Development in areas of flood risk will be permitted providing
measures are included that reduce the risk of flooding including
consequential risks elsewhere
8
Local Development Scheme – Liverpool City Council:
http://www.liverpool.gov.uk/Environment/Planning/Local_Development_Framework/adopted_
documents/Local_development_scheme/index.asp
9
Core Strategy Issues and Options Paper – Liverpool City Council (2006)
http://www.liverpool.gov.uk/Environment/Planning/Local_Development_Framework/work_in_
progress/core_strategy_dpd/index.asp
Liverpool City Council – Strategic Flood Risk Assessment January 2008
- 15 -Issue The Core Strategy should encourage drainage techniques that
reduce the risk of flooding
Option A The Core Strategy should encourage the use of Sustainable Urban
Drainage Systems (SuDS) in all new development
Option B Targets for new development incorporating SuDS, either by use (e.g.
residential, commercial) or within particular parts of Liverpool,
should be included within the Core Strategy
3.46 The next stage in the process is to publish a Preferred Options Report which
provides more detail on the policy options. This stage also highlights a
‘preferred option’ based on the consultation responses to the Issues and
Options Report, the findings from the Initial Sustainability Appraisal, national
and regional guidance and any relevant evidence, such as this Strategic Flood
Risk Assessment. An assessment of the findings of this SFRA against these
issues and options is undertaken in Appendix C.
3.47 The Core Strategy should set out the key elements of the planning framework
for the area and although this Strategic Flood Risk Assessment will feed into
the Core Strategy, it may be of greater importance to the more detailed
policies that are produced for example, through the Technical Policies
Development Plan Document where sites will be allocated. When allocating
sites, the level of flood risk in that area will be an important consideration.
3.48 More detailed policies will follow the Core Strategy through the production of:
Land Allocations DPD, Technical Policies DPD, Joint Merseyside Waste DPD and
a series of Area Action Plans. Work has commenced on the Joint Merseyside
Waste DPD and the North Liverpool Area Action Plan. A series of
Supplementary Planning Documents (SPD’s) have also been produced/ will be
produced for which again, this SFRA will inform. Information regarding the
documents published under the Local Development Framework can be found on
the City Council website: www.liverpool.gov.uk/ldf
Liverpool City Council – Strategic Flood Risk Assessment January 2008
- 16 -4 Roles and Responsibilities
4.1 There are a number of different individuals, bodies and agencies involved in
flood risk and flood management, ranging from the individual property owner
that is located in an area of flood risk to national government agencies that
take a strategic role in flood risk management.
4.2 It is important in the context of this SFRA to determine the different roles and
responsibilities to aid the development process with regards flood risk. The
flow chart in figure 6 below summarises the different roles and responsibilities
within Liverpool.
4.3 Annex H of PPS25 sets out in more detail these roles and responsibilities at a
more general level.
Liverpool City Council – Strategic Flood Risk Assessment January 2008
- 17 -Figure 6: Roles and Responsibilities in flood risk - Liverpool
ENVIRONMENT AGENCY
- Flood management and funding
HIGHWAYS
DCLG DEFRA flood defence works on main
- Overall rivers AGENCY
- Overall policy - Managing road
Responsibility for land - Power to maintain and improve
responsibility for drainage from trunk
use planning policy main rivers
flood and coastal roads
(PPS 25) - Statutory consultee for planning
erosion risk
- Information and advice to local
authorities
- Warning system for flood risk
GOVERNMENT
OFFICE FOR
LIVERPOOL CITY COUNCIL (LCC) THE NORTH WEST
- Development control (planning) – ensure new development is not at - Scrutinise planning
risk of flooding or exacerbates existing issues policies including flood
- Emergency planning risk policies
- Highways Maintenance - Consider whether
UNITED - Policy planning – LDF – provide framework for development control decisions applications should be
UTILITIES - Where appropriate, to reduce flood risk from "ordinary watercourses" and called in (to Secretary
- Sewers and water supply from land drainage problems of State) when EA have
- Surface water drainage objected
where via adopted sewers
LANDOWNERS (riparian)
- Landowners have the primary responsibility for draining their LIVERPOOL ENTERPRISE
land and managing the flood risk issues associated with their - Drainage of non-main roads, ditches
property (including the City Council where they own the land) and drains
LIVERPOOL 20/20 – Advisory role to Liverpool City Council - culverts on ordinary watercourses and flood defences (where applicable)
on a contractual basis
DEVELOPERS – Implement requirements to: - prevent risk of flooding to development, - prevent increased risk of flooding to other areas,
- ensure water and sewer supply are adequate, - manage surface water run-off, - implement SuDs etc.
INSURANCE COMPANIES – Development in areas at a significant risk of flooding may create problems with getting insurance which in turn
creates problems with property buyers obtaining a mortgage. Responsibility for this can fall to the above agencies. The Association of British
Insurers and the Council of Mortgage Lenders will comment on individual proposals on which the Environment Agency object and where there
appears to be a high risk. The insurance industry may also make representations about proposals for the location of new development during plan
preparation.
Liverpool City Council – Strategic Flood Risk Assessment January 2008
- 18 -5 Flood Risk Assessment
5.1 This section sets out the main body of the flood risk assessment, drawing
together data from a variety of sources, illustrated by maps and associated
descriptions. This information should form the starting point for a detailed
flood risk assessment for site specific proposals and is the basis for the
assessment provided in section 6, identifying specific risks within strategic
sites.
5.2 The Practice Guidance to PPS25 states that:
“In local authority areas where flooding is not a major issue and where
development pressures are low, a less detailed approach will be required
relative to that necessary in areas where there is high development pressure
and flooding is a significant issue.”
5.3 This section relies on a desk-top analysis of information previously collected
and reported in a variety of different documents and through consultations
with different agencies and officers involved in the floodrisk process. The
information used therefore varies in level of detail, accuracy and date and as
such the source of data is shown where possible.
5.4 In considering the information available, the main point to remember is
everywhere is potentially subject to flood risk. Nowhere is free of risk, but
some areas are potentially at greater risk. The quality of data does not alter
actual risk, but could affect the judgement about whether an area is at high
risk or not. For that reason the SFRA takes a cautious approach to the use of
data.
5.5 The section builds up the picture of floodrisk within Liverpool, starting with
background information and then considering different factors such as culverts,
the condition of culverts, historical flooding and flood defences.
Liverpool City Council – Strategic Flood Risk Assessment January 2008
- 19 -5.6 Background information
5.7 This section is split into the following sub-sections and maps, which should be
viewed as part of this section:
• Natural Features
o Map 1A and Map 1B: Natural features – topography and watercourses
• Watercourses
o Map 2a: watercourses – main rivers and canal
o Map 2b: watercourses – main rivers and ordinary watercourses from 1989
Watercourse Flood Alleviation Study and catchments
o Map 2c: watercourses – main rivers and ordinary watercourses from 1999
Culverted Watercourse Study
• Culverts
o Map 3: Culverts
Natural Features
(Refer to Map 1A and Map 1B: Natural Features – topography and watercourses)
5.8 The open watercourses within Liverpool are predominantly on low-lying land.
The city could be considered to be ‘divided’ between the waterfront which is a
flat area lying between 7 and 11m of altitude and the area to the north-east,
lying between 16 and 32 m of altitude. This is split by an inner area of land
which has higher altitudes, reaching 63m in places. In simplistic terms, water
should drain towards each of the watercourse catchments (see paragraph 5.20
below). However, the topography and hydrology of Liverpool is complex and
their consequences on flood should be given further consideration.
5.9 Map 1B shows the topography to a much more detailed level than Map 1A as it
uses LIDAR data (airborne mapping technique which uses a laser to measure the
distance between the aircraft and the ground at 2 metre intervals) which was
available specifically for the purposes of this Liverpool SFRA. However, the
data does not cover the whole city and this distorts the data in certain areas.
Map 1A should therefore be referred to for an overview of the topography.
5.10 The Mersey Estuary Catchment Management Plan (CFMP)10 provides an overview
of the natural and physical characteristics of the River Mersey catchment. The
following summarises some of the information provided within this document,
specific to Liverpool:
• Solid Geology – Liverpool is predominantly made up of Permian and Triassic
sandstones (this is supported in the River Alt and Crossens Catchment Flood
Management Plan which shows the majority of the Liverpool area as
Permian and Triassic sandstones, undifferentiated, including Bunter and
Keuper. Along an area of the River Alt within Liverpool there is shown to
be ‘Lower Westphalian’ (mainly productive coal measures)).
• Hydrogeology – the majority of Liverpool is considered to be an aquifer
(underground layer of water-bearing permeable rock or unconsolidated
10
Mersey Estuary Catchment Flood Management Plan – Scoping Report – November (2005) and
Mersey Estuary Catchment Flood Management Plan – Draft – March (2007)
Liverpool City Council – Strategic Flood Risk Assessment January 2008
- 20 -materials), with a series of groundwater contour lines and parts of
Liverpool are considered to be ‘Special/source Protection Zones’
(Environment Agency)
• Geomorphology – Below the Runcorn Gap, the estuary opens into a wide
shallow basin which has extensive inter-tidal banks and large areas of salt
marsh on its southern margin. The position of low water channels and the
shape and height of the inter-tidal banks and flats has been variable. This
is illustrated in figure 7 below.
The long-term accumulation of sediment which has resulted from natural
sediment deposition and the outer estuary channel has caused a reduction
in the fluid volume of the estuary. A reduction in volume of 75 million
cubic metres occurred between 1911 and 1961 despite removal by dredging
of 200 million cubic metres of material. Downstream of the main basin, the
estuary converges to form ‘The Narrows’. The morphology of this section of
the estuary has been determined by the underlying geology forming a
straight, narrow section which reaches depths of 30m and experiences
strong tidal currents, preventing accumulation of sediments.
Figure 7: Location of Low-Water in the Inner Mersey Estuary between 1956
and 1967 (reproduced from the Dee and Mersey Estuaries – Environmental
Background – August 1987 – University of Liverpool and the CFMP7)
Within the estuary, water floods rapidly upstream following the topography
until the banks are covered. Ebb tides are slower and more variable in
direction as water gradually drains off the inter-tidal banks. Current flows
in the estuary and the nearshore region comprise two main components:
tidal currents, which are generally predictable and associated with the tidal
rise and fall, and residual (or non-tidal) currents including those driven by
winds. The dominant currents are caused by the tide but other long-term
water movements are significant in terms of sediment and pollution
transport.
From Speke to Hale there are low cliffs which rise to a height of about 15m.
The river water reaches the cliffs at high tide levels and can suffer damage
during storms.
• Bathymetry (Variation of Estuary Depths) and sediments - the main features
are the extensive inter-tidal sand banks and the deep channels carrying the
main tidal flows of the estuary. Regular surveys are undertaken in the
Liverpool City Council – Strategic Flood Risk Assessment January 2008
- 21 -navigable reaches by the Mersey Docks and Harbour Company with results in
the form of Admiralty Charts available on request.
• Soil – Liverpool is shown to be predominantly diamicton. There are patches
of sand predominantly to the southern tip and south of the city centre
along the Mersey. There is a strip of clay, silt and sand around the River
Mersey to the City Centre. From the River Mersey to the east of the local
authority boundary, south of the city centre, there is a strip of a composite
of several solid rock lithologies.
The whole Mersey Estuary CFMP area is almost entirely covered by small
superficial deposits of glacial till with subordinate sands and gravels. More
localised areas of alluvial and Aeolian (wind blown) deposits exist in
significant thicknesses around the Mersey Estuary. These deposits tend to
have a high porosity and high permeability which means that, apart from
urban areas; runoff will be relatively low and soil infiltration relatively
high. It should be noted that during a tidal flooding event, the soil types
will have a negligible impact on the flooding of the low lying parts of the
catchment.
Watercourses
(Refer to Maps 2a – 2c: watercourses (main and ordinary watercourses, canal
and catchments)
Key sources of information for this section are: Watercourse Flood Alleviation
Study (1989) and Culverted Watercourse Study (1999)
5.11 Main river – Main rivers are usually larger streams and rivers, but also include
smaller watercourses of strategic drainage importance. Main rivers are
designated by the Department for Environment, Food & Rural Affairs in
England. The Environment Agency’s powers to carry out flood defence works
apply to main rivers only.
5.12 The main rivers in Liverpool are (shown in dark blue on map 2a):
• River Mersey/Mersey Estuary
• River Alt
• Deys Brook (partial)
• Sugar Brook
• Fazakerley Brook
• Croxteth Brook
• Knowsley Brook (located on the Liverpool/Knowsley boundary)
• Netherley Brook
• Halewood Brook
• Childwall Brook (partial)
5.13 Ordinary watercourse – Ordinary watercourses refers to all other watercourses
not designated as a main watercourse. They fall within a Local Authorities
responsibility for strategic flood risk management, although private land
owners along the watercourse will be responsible for their land.
5.14 Under the provisions of the Land Drainage Act 1991, the local (Land Drainage)
Authority have exactly the same powers of carrying out and funding
Liverpool City Council – Strategic Flood Risk Assessment January 2008
- 22 -improvement works on ordinary watercourses, that the Agency has toward the
main rivers.
5.15 A large proportion of the ordinary watercourses in Liverpool are culverted and
it is therefore difficult to determine exactly where the watercourses are. The
ordinary watercourses identified in the 1989 Watercourse Flood Alleviation
Study differ from those identified as part of the 1999 Culverted Watercourse
Study. The 1999 study is more up-to-date and considered to be more reliable,
however both sources of information are shown on separate maps.
5.16 The ordinary watercourses identified in the 1989 Watercourse Flood Alleviation
Study are (not all watercourses are named): (shown in light blue on map 2b):
• Mab Lane Drain
• Thornhead Brook
• Hall Brook
• Deys Brook (partial)
• Upper and Lower Tue Brook
• Becher’s Brook
• Lower Brook
• Upper Brook
• Jordan River
• Old Garston River
• Oglet Brook
• Childwall Brook (partial)
5.17 The ordinary watercourses identified in the 1999 Culverted Watercourse Study
are: (shown in light blue on map 2c):
• Mab Lane Drain
• Thornhead Brook
• Deys Brook (partial)
• Upper and Lower Tue Brook
• Upper Brook
• Jordan River
• Upper Jordan
• Old Garston River
• Oglet Brook
• Childwall Brook (partial)
• Lee Park
• Allerton Brook
• Forty Pits Drain
• Stamfordham Drive Drain
• Brunswick Street Drain
• Wavertree Culvert
5.18 It should be noted that irrespective of whether it is a main or ordinary
watercourse, the riparian landowner (any watercourse within or adjacent to
the boundaries of your property) is ultimately responsible for the ownership
and therefore maintenance and repair. This applies equally to culverted
watercourses.
Liverpool City Council – Strategic Flood Risk Assessment January 2008
- 23 -5.19 Canal: The Leeds and Liverpool Canal is located to the north of the city and is
shown on map 2a. Plans are underway to provide a link between the canal and
Pier Head.
5.20 Catchment (can also be known as river drainage basin) – the area of land that
drains into a particular watercourse. The 1989 Watercourse Flood Alleviation
Study identifies three main catchments in Liverpool, referred to as North (River
Alt catchment), South and West (Direct to Mersey Estuary) and East (Ditton
Brook Catchment), shown in red on maps 2a to 2c. The rivers and ordinary
watercourses which fall within each catchment are:
Table 3: Rivers and Ordinary watercourses within each catchment
North (River Alt South and West (Direct East (Ditton Brook
catchment) to Mersey Estuary) Catchment)
River Alt Kirkdale Childwall Brook
Mab Lane Drain Beacon’s Gutter Netherley Brook
Thornhead Brook Pool River Halewood Brook
Hall Brook The Mill Stream
Deys Brook Dingle Drain
Sugar Brook Dickinson’s Dingle
Tue Brook Lower Brook
Fazakerley Brook Upper Brook
Croxteth Brook Jordan River
Knowsley Brook Cressington Park Drain
Becher’s Brook Old Garston River
Speke Hall Drain
Oglet Drain
For the remaining maps, the ordinary watercourses identified in the 1999
Culverted watercourse Study are used (as shown in map 2c). Reference should
still however be made to map 2b when considering a development proposal.
Culverts
(Refer to Map 3: Culverts)
5.21 A Culvert is a pipe used to enclose a watercourse, which may be used to allow
water to pass underneath the ground. There are a large number of culverts in
Liverpool.
5.22 A summary of the culverts in Liverpool is shown in table 4a and 4b below and
illustrated on map 3: The 1999 Culverted Watercourse Study provides a table
and map showing where the culverts are – this is illustrated in Map 3 (culverts
are shown in red and open channels as blue). The 1989 Watercourse Flood
Alleviation Study describes where some of the culverts are across the city. This
can be in conflict with the information in the 1999 study. As such the following
tables summarise the information and are split according to whether they
match with the information in the 1999 study or are in conflict with it.
Liverpool City Council – Strategic Flood Risk Assessment January 2008
- 24 -Table 4a: Summary of Culverts – information from 1989 study that matches with
the 1999 study
Those that are completely open channels:
• River Mersey • Croxteth Brook
• Sugar Brook • Knowsley Brook
• Fazakerley Brook • Netherley Brook
• Halewood Brook ((small section
culverted at end)
Upper Tue Culverted over most of its length for many years. There is a
Brook short open section between Green Lane and Gardner Road
Thornhead Culverted over much of its length to facilitate development.
Brook There is still a section of open channel upstream of the Sefton
Rugby Union Football Ground.
Lower Tue From the ‘Walton Triangle’ to Long Lane the watercourse is
Brook culverted except for a short length at Harper Road. From Long
Lane to Higher Lane, the watercourse flows in open channel,
except for a section at Wareing Road that was culverted.
Childwall Watercourse has been culverted from its source down to the
Brook Netherley Brook as development has proceeded. There is a
section of open channel on the upstream ‘ordinary’ river at the
King George’s Memorial Field
Deys Brook There has been extensive urban development within the Brook’s
catchment and substantial culverting has taken place. The only
open channels are thought to be at West Derby Golf Course and
from Croxteth Hall Lane to the River Alt
River Alt Predominantly an open channel. Some major culverts have
been constructed to facilitate development. Located at
Hambleton Close and Hare Croft
Table 4b: Summary of culverts – information from the 1989 study that does not
match with the 1999 study
Upper and Drainage function transferred to sewers. Sections of the
Lower Brook original watercourse have been maintained and incorporated in
the landscaping of Sefton Park, discharging into the boating
lake
Jordan Drainage function transferred to a constructed sewer. There is
a short section immediately downstream of Aigburth Road just
inside the entrance to Otterspool Park, where the entrance to
the old brick culvert, constructed in the 19th century is partially
visible.
Becher’s Located on the border of Liverpool City Council. East to West
Brook section along Aintree Race Course is an open channel. North of
the racecourse to the River Alt is culverted
Liverpool City Council – Strategic Flood Risk Assessment January 2008
- 25 -Oglet Brook Largely culverted as the development of the airport and Speke
Housing Estate has taken place. There is still a section of open
channel that runs east to west along the southern edge of the
playing fields that lie between Hale Road and the airfield
Watercourses that are completely culverted:
Hall Brook
Mab Lane Drain
Old Garston River
Former watercourses that have incorporated into the sewerage system and
can no longer be identified as arterial watercourses:
Kirkdale
Beacon’s Gutter
Pool River
The Mill Stream
Dingle Drain
Dickinson’s Dingle
Cressington Park Drain
Speke Hall Drain
Liverpool City Council – Strategic Flood Risk Assessment January 2008
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