Liverpool City Council Strategic Flood Risk Assessment (SFRA) January 2008

Contents 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

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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 Culverts Map 3: 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) Historical flooding areas Map 6: Map 7: Condition of culverts – where information is available, the areas of poorest condition are identified Map 8: Historical sewer flooding Summary of identified floodrisk Map 9: 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)

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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

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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.

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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 urban area, with a population of 444,500 (2004 population estimate). The City has seen significant change over the past century including a population decline from its peak in 1931 of 846,101 to the present day.

Figure 1: Location Map

Knowsley Sefton St. Helens Liverpool 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.

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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:

3.3

National: Making Space for Water – DEFRA (2005)4 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: • • • • •

3.4

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 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 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 3

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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 Land Use Vulnerability classification Zone 1

Water Compatible

Highly Vulnerable

! !

! !

Zone 3a

Exception Test Required

!

"

Zone 3b

Exception Test Required

!

"

Zone 2 Flood Zones

Essential Infrastructure

!

Exception Test Required

More Vulnerable

! ! Exception Test Required

"

Less Vulnerable

! ! ! "

Key: ! Development is appropriate " Development should not be permitted

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3.11

3.12

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) 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 sitespecific 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.

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3.15

Water Framework Directive 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 coordinated 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.

3.19

3.20

Regional: Adopted Regional Spatial Strategy (RSS) for the North West (2003) Draft Regional Spatial Strategy (RSS) for the North West (2006) 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. 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 -9-

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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.

3.23

Sub Regional Liverpool Bay Shoreline Management Plan (1999): Sub Cell 11a – Great Ormes Head to Formby Point Figure 3: Sub cell for Liverpool (11a) The Liverpool Bay Shoreline Management 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 Figure 4: CFMP Boundaries the Plan. Work on a revised SMP is due to commence in 2007.

3.26

3.27

Catchment Flood Management Plans There are two catchment flood management plans (CFMPs) which are within the Liverpool City Council authority area. These are the catchments of the River Mersey and the River Alt. The following map (figure 4) provides an overview of these boundaries: The Mersey Estuary Catchment Flood Management Plan is at the draft stage

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Alt and Crossens

Mersey Estuary

Reproduced from Mersey Estuary Draft Catchment Flood Management Plan (© Crown Copyright All rights reserved 100026380

January 2008

(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. 3.28

Mersey Estuary Draft Catchment Flood Management Plan (March 2007)6 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.

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):

Figure 5: Future boundary of SMP

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.environmentagency.gov.uk/regions/northwest/1072087/1697828/?version=1&lang=_e

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Table 1: Key features and actions proposed within the Draft Mersey Estuary CFMP for Liverpool Policy Unit 11 Problem/risk

Policy

Justification

Actions

Risks, uncertainties and dependencies

Liverpool: Covers the north Mersey Estuary component and includes the city of Liverpool 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 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). 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 longterm 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. 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 Future flooding risks (including climate change etc.) are an uncertainty. SMP and CFMP need to be consistent to ensure no overlap or gaps in policy

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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.environmentagency.gov.uk/regions/northwest/1072087/1697392/?version=1&lang=_e

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• 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 urban conurbations)

No. of people at risk* (1% a.p. event)

Maximum water depth (m) (1% 1.p. event)

Ranked risk to people

Current economic damages (£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: 3.39

3.40

3.41

Liverpool City Council – Contaminated Land Inspection Strategy (2002) 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. 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) 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.

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3.45

10. Adoption

9. Examination

8. Consultation on submission DPD

7. Drafting of Submission DPD

6. Consultation on Preferred Options Report

Preparation of the Core Strategy (Development Plan Document – DPD) is underway. The key milestones in the production of a DPD is: 5. Drafting of Preferred Options Report

3.44

4. Consultation on Issues and Options Paper

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. Drafting of Issues and Options Paper

3.43

2. Consultation on scoping report

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).

1. Preproduction/ scoping

3.42

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 Option A Option B

The Core Strategy should control development in identified areas of flood risk The Core Strategy should include a prudent avoid all development in areas of flood risk 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 - 15 -

January 2008

Issue Option A Option B

The Core Strategy should encourage drainage techniques that reduce the risk of flooding The Core Strategy should encourage the use of Sustainable Urban Drainage Systems (SuDS) in all new development 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

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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.

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Figure 6: Roles and Responsibilities in flood risk - Liverpool ENVIRONMENT AGENCY DCLG

- Overall Responsibility for land use planning policy (PPS 25)

DEFRA - Overall policy responsibility for flood and coastal erosion risk

- Flood management and funding flood defence works on main rivers - Power to maintain and improve main rivers - Statutory consultee for planning - Information and advice to local authorities - Warning system for flood risk

LIVERPOOL CITY COUNCIL (LCC)

UNITED UTILITIES

- Sewers and water supply - Surface water drainage where via adopted sewers

- Development control (planning) – ensure new development is not at risk of flooding or exacerbates existing issues - Emergency planning - Highways Maintenance - Policy planning – LDF – provide framework for development control decisions - Where appropriate, to reduce flood risk from "ordinary watercourses" and from land drainage problems

HIGHWAYS AGENCY

- Managing road drainage from trunk roads

GOVERNMENT OFFICE FOR THE NORTH WEST

- Scrutinise planning policies including flood risk policies - Consider whether applications should be called in (to Secretary of State) when EA have objected

LANDOWNERS (riparian)

- Landowners have the primary responsibility for draining their land and managing the flood risk issues associated with their property (including the City Council where they own the land)

LIVERPOOL ENTERPRISE - Drainage of non-main roads, ditches 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

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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.

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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 - 20 -

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•

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

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•

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

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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.

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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.

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Table 4a: Summary of Culverts – information from 1989 study that matches with the 1999 study Those that are completely open channels: • River Mersey • • Sugar Brook • • Fazakerley Brook • • Upper Tue Brook Thornhead Brook Lower Tue Brook Childwall Brook Deys Brook

River Alt

Croxteth Brook Knowsley Brook Netherley Brook Halewood Brook ((small section culverted at end) Culverted over most of its length for many years. There is a short open section between Green Lane and Gardner Road Culverted over much of its length to facilitate development. There is still a section of open channel upstream of the Sefton Rugby Union Football Ground.

From the ‘Walton Triangle’ to Long Lane the watercourse is 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. Watercourse has been culverted from its source down to the 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 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 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

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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

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Risk of flooding 5.23

This section is split into the following sub-sections and maps, which should be viewed as part of this section: • •

•

Tidal flooding: River Mersey o Map 4a: Environment Agency flood risk zones – tidal flood risk River flooding o Map 4b: Environment Agency flood risk zones – tidal and river flood risk o Map 5: Flood Risk Zone 3: Estimated functional floodplain (3b) and High Probability Area (3a) o Map 6: Historical flooding areas

Condition of culverts

Map 7: Condition of culverts – where information is available, the areas of poorest condition are identified Sewer flooding o Map 8: Historical sewer flooding o

•

•

• •

Summary of identified flood sources o Map 9: Identified flood risk – Environment Agency flood risk zones, historical flooding areas, historical sewer flooding and condition of culverts

Risk of flooding in and from adjoining authorities o Map 10: Risk of flooding in and from adjoining authorities Groundwater

Tidal flooding: River Mersey (Refer to Map 4a: Environment Agency flood risk zones – tidal flood risk) 5.24

The River Mersey originates at the confluence of the River Tame and the River Goyt in the town centre of Stockport. It flows west, towards Liverpool, becoming tidal at Howley Weir (Warrington) and this is where the Upper Estuary starts. It widens to form the Inner Estuary at Runcorn. The Mersey Estuary continues through the ‘Narrows’ a straight narrow channel with depths of up to 30 m driven by a change in geology. It forms the Outer Estuary, a large area of inter-tidal sand and mud banks as it flows into Liverpool Bay on the Irish Sea.

5.25

Environment Agency Indicative flood plain map of England is shown for the River Mersey in Liverpool in Map 4a and identifies: • Flood Risk Zones 1 (no shading) - low probability – annual probability of flooding: river or sea flooding 1.0%; flooding from the sea >0.5%

5.26

Although areas of flood risk are identified within the Environment Agency Indicative Flood Risk Maps and are a serious consideration, it is a relatively

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limited inland area affected. This is demonstrated in the Mersey Estuary Catchment Flood Management Plan (draft) which shows the Environment Agency Flood Risk Zones for the whole catchment (see figure 8). 5.27

•

•

Figure 8: Flood Risk Zones for Mersey Estuary Catchment

PPS25 defines a Functional Floodplain as land where water has to flow or be stored in times of flood. Specifically, this land: Would flood with an annual probability of 1 in 20 (5 per cent) or Reproduced from Mersey Estuary Draft greater in any year, or at another Catchment Flood Management Plan (© Crown probability to be agreed between Copyright. All rights reserved. 100026380, 2007) the LPA and the Environment Agency (EA), or Is designed to flood in an extreme (0.1 per cent) flood, or at another probability to be agreed between the LPA and the EA

5.28

The Companion Guide to PPS25 (Draft) takes the definition further, stating that whilst developed areas are not generally considered to comprise Functional Floodplains, the definition within PPS25 does not differentiate between developed and undeveloped areas. The functionality of such areas should be considered when defining Zones 3a and 3b, taking into account strategic flood risk management policies. All areas within Zone 3 should be considered as Zone 3b (Functional Floodplain) unless, or until, an appropriate FRA shows to the satisfaction of the EA that it can be considered as falling within Zone 3A (High Probability). Map 5 provides an estimate of which watercourses are within the functional floodplain (3b) and which are within the high probability (3a) flood zone. It is however expected that developers proposing to develop within any of Flood Risk Zone 3 demonstrate whether the site is within a functional floodplain or high probability zone to the satisfaction of the Environment Agency.

5.29

There is considerable information available regarding the River Mersey from a number of sources. Two of the key sources are: • Shoreline Management Plan/Catchment Flood Management Plan11 (predominantly at the moment in the CFMP but future revision of the SMP may provide further guidance) and • ‘National Tidal and Sea Level Facility12’/ Proudman Oceanographic Laboratory – Natural Environment Research Council13 which although a national resource is based within Liverpool.

Mersey Estuary Catchment Flood Management Plan – Scoping Report (November 2005) and Mersey Estuary Catchment Flood Management Plan – Draft (March 2007) 12 National Tidal and Sea Level Facility - reflects the importance of national sea level monitoring to the public, academic community and government - http://www.pol.ac.uk/ntslf/ 11

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5.30

Some of the information included within these sources is as follows: • Tidal elevations – measurement locations at Liverpool Gladstone Dock (north of Liverpool local authority boundary) – measured by National Tidal & Sea Level Facility network (NTSLF) and at Gladstone Lock by Mersey Docks & Harbour Company • Tidal predictions – 7 day forecast and highest and local tidal predictions for the years 2005 – 2025 at Gladstone Lock • Sea level trends – from 1850 to 2005 at Gladstone Dock • River flows – measurement point unknown • Various different types of modelling and forecasting.

5.31

Some of the key points from this data are as follows: •

The River Mersey has the second highest tidal range in the UK, varying from 4m at neap tides to 10m at spring tides. The river flow is about 1% of the tidal flow. Tidal levels are as follows in table 5: Table 5: Tidal levels in Liverpool (Gladstone Dock) Highest Astronomical Tide (HAT) Mean High Water Spring (MHWS) Mean High Water Neap (MHWN) Highest 2000 Highest 2001 (Mean Spring Range) MSR

•

•

10.25m 9.31m 7.42m 9.84m 10.08m 8.27m

Lowest Astronomical Tide (LAT) Mean Low Water Spring (MLWS) Mean Low Water Neap (MLWN) Lowest 2000 Lowest 2001 (Mean Neap Range) MNR

-0.02m 1.04m 3.10m 0.27m 0.04m 4.32m

Tidal levels are quoted relative to chart datum (approximately the lowest level due to astronomical effects and excluding meteorological effects). The heights of chart datum (CD) relative to ordnance datum (OD, at Newlyn) in the UK is -4.93m for Liverpool, e.g. if there is a data value for Liverpool of 10.25m relative to CD and the data is required relative to OD, then this would be 5.32m (i.e. 10.25m - 4.93m). A general trend of sea-level rising has been recorded from 1850 to 2005. If this trend continues, this could have dramatic impacts on the frequency and extent of flood risk along the River Mersey. This is due to various factors but includes climate change (see climate change section below (paragraphs 5.73 to 5.84) A storm surge is defined as an increase or decrease in sea level in relation to the predicted tide level. It is usually caused by the action of wind stress on the water surface which may be coupled with a change in level caused by variation in barometric pressure. The shallow north-eastern part of the Irish Sea including Liverpool Bay and the Mersey estuary is particularly

13

Proudman Oceanographic Laboratory - research focuses on oceanography encompassing global sea-levels and geodesy, numerical modelling of continental shelf seas and coastal sediment processes. In addition, they undertake activities of surveying, monitoring, data management and forecasting - http://www.pol.ac.uk/home/ Liverpool City Council – Strategic Flood Risk Assessment - 29 -

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susceptible to storm surges whereas surges have been shown to be less likely in the Irish Sea at spring tides rather than at neap tides. The highest astronomical tide (HAT) for Liverpool is 5.37 m14 above Ordnance Datum Newlyn (ODN). A theoretical maximum value of 6.1 m ODN has been suggested for Liverpool Bay. This height was exceeded in November 1977 when a severe storm coincided with a spring tide. Sea conditions arising from storm surges have caused considerable damage to natural and artificial sea defences. 5.32

The western most boundary of Liverpool, fronting onto the River Mersey includes a variety of land uses. In addition, the boundary itself varies in its structure from mud flats to the south of the city to the river wall, docks, promenades, industrial buildings and apartments towards the north of the city.

5.33

The only recording of flooding along the length of the Mersey within Liverpool is at Pier Head. This is reportedly due to exceptionally high tides backed up by strong winds from the west, causing the river to overtop the river wall at Pier Head. A small amount of water is reported to cover a restricted area of the Pier Head promenade lasting for approximately 1 – 2 hours. Due to the frequency of this occurrence and the location, an emergency plan of sandbagging is in place.

5.34

Additional information indicates that the docks are not designed to fulfill a flood defence role, with any such role being incidental. This information also indicates that in the event of extreme surges, flood waters can enter the port via lock gates at Gladstone so flood defence is ultimately provided by the east quays rather than the river wall.

River Flooding (Refer to Map 4b – Environment Agency Flood Risk Zones – Tidal and River Flooding and Map 6: Historical flooding areas) 5.35

Environment Agency Flood Risk Zones – Environment Agency Indicative flood plain map of England is shown for the rivers in Liverpool in map 4b and identifies: • Flood Risk Zones 1 (no shading) - little or no risk – annual probability of flooding: river, tidal and coastal