Hull City Council
Strategic Flood Risk Assessment
November 2007 Hull City Council Strategic Flood Risk Assessment
Contents Amendment Record This report has been issued and amended as follows:
Issue Revision Description Date Signed
1 1 Draft June 07 JHG
2 1 Final Nov 07 JHG
Halcrow Group Limited
Arndale House Otley Road Headingley Leeds LS6 2UL Tel +44 (0)113 220 8220 Fax +44 (0)113 274 2924 www.halcrow.com
Halcrow Group Limited has prepared this report in accordance with the instructions of their client, for their sole and specific use. Any other persons who use any information contained herein do so at their own risk.
© Halcrow Group Limited 2007
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Strategic Flood Risk Assessment Hull City Council
Contents
Glossary of Terms
Executive Summary
Level 1 SFRA
Level 2 SFRA
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Strategic Flood Risk Assessment Hull City Council
Glossary of Terms
Annual Monitoring Report (AMR) - Assesses the implementation of the local development scheme and the extent to which policies in local development documents are being successfully implemented.
Area Action Plans - Development plan documents that provide a planning framework for areas of change and areas of conservation.
Core Strategy - Development plan document which sets the long-term spatial planning vision and objectives for the area. It contains a set of strategic policies that are required to deliver the vision including the broad approach to development.
DEFRA - Department of Environment, Food and Rural Affairs Development.
Development Plan - As set out in Section 38(6) of the Planning and Compulsory Purchase Act (2004), an authority’s development plan consists of the relevant regional spatial strategy (or the spatial development strategy in London) and the development plan documents contained within its local development framework.
Development Plan Documents (DPDs) - Spatial planning documents within the council’s local development framework which set out policies for development and the use of land. Together with the regional spatial strategy they form the development plan for the area. They are subject to independent examination. They are required to include a core strategy and a site allocations document, and may include area action plans if required; other DPDs may also be included, e.g. development control policies.
Emergency Planning - Planning for and response to emergencies such as flooding, including consideration of the resilience of emergency infrastructure that will need to operate during flooding.
Environment Agency - Leading public body for protecting and improving the environment in England and Wales.
Environment Agency Flood Zones - Nationally consistent delineation of ‘high’ and ‘medium’ flood risk, published on a quarterly basis by the Environment Agency.
Flood Risk Vulnerability - PPS25 provides a vulnerability classification to assess which uses of land maybe appropriate in each flood risk zone.
Flood Zone 1 – Low Risk - This zone comprises land assessed as having a less than 1 in 1000 annual probability of river or sea flooding in any year (<0.1%).
Flood Zone 2 – Medium Risk - This zone comprises land assessed as having between a 1 in 100 and 1 in 1000 annual probability of river flooding (1% - 0.1%) or between a 1 in 200 and 1 in 1000 annual probability of sea flooding (0.5% - 0.1%) in any year.
Flood Zone 3 – High Risk - This comprises land assess as having a 1 in 100 or greater annual probability of river flooding (>1%) or a 1 in 200 or greater annual probability of flooding from the sea (0.5%) in any year.
Fluvial Flooding - Flooding caused by the river.
Formal Flood Defence - A structure built and maintained specifically for flood defence purposes.
Strategic Flood Risk Assessment Hull City Council
Habitable Room - A room used as living accommodation within a dwelling but excludes bathrooms, toilets, halls, landings or rooms that are only capable of being used for storage. All other rooms, such as kitchens, living rooms, bedrooms, utility rooms and studies are counted.
Informal Flood Defence - A structure that provides a flood defence function, but has not been built or maintained for this specific purpose (e.g. boundary wall).
Integrated Urban Drainage (IUD) - A holistic approach to managing urban drainage flooding, so that towns and cities across the country are better prepared for the impacts of climate change.
LiDAR - ‘Light Detection and Ranging’ is an airborne terrain mapping technique which uses a laser to measure the distance between the aircraft and the ground.
Local Development Documents - The collective term for development plan documents and supplementary planning documents.
Local Development Framework (LDF) - The name for the portfolio of local development documents. It consists of the local development scheme, a statement of community involvement, development plan documents, supplementary planning documents, and the annual monitoring report. Within Hull this document is referred to as the Hull development framework.
Local Development Scheme (LDS) - Sets out the programme for preparing local development documents. All authorities must submit a scheme to the secretary of state for approval within six months of commencement of the act.
‘Making Space for Water’ (DEFRA 2004) - The government’s new evolving strategy to manage the risks from flooding and coastal erosion by employing an integrated portfolio of approaches, so as: a) to reduce the threat to people and their property; b) to deliver the greatest environmental, social and economic benefit, consistent with the government's sustainable development principles, c) to secure efficient and reliable funding mechanisms that deliver the levels of investment required.
Planning Policy Statements - The government has updated its planning advice contained within planning policy guidance notes (PPGs) with the publication of new style planning policy statements (PPSs).
Pluvial Flooding - Flooding caused by rainfall.
Regional Spatial Strategy - Sets out the region’s policies in relation to the development and use of land and forms part of the development plan for local planning authorities.
Residual Risk - The risk which remains after all risk avoidance, reduction and mitigation measures have been implemented.
SAR - ‘Synthetic Aperture Radar’ is an airborne terrain mapping technique which uses microwaves to measure the distance between the aircraft/satellite and the ground.
Statement of Community Involvement (SCI) - Sets out the standards which authorities will achieve with regard to involving local communities in the preparation of local development documents and development control decisions. It is subject to independent examination.
Strategic Environmental Assessment (SEA) - A generic term used to describe environmental assessment as applied to policies, plans and programmes. The European ‘SEA Directive’
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(2001/42/EC) requires a formal ‘environmental assessment of certain plans and programmes, including those in the field of planning and land use’.
Strategic Flood Risk Assessment (SFRA) - Should be carried out by the local planning authority to inform the preparation of its LDDs, having regard to catchment-wide flooding issues which affect the area.
Sustainability Appraisal (SA) - Tool for appraising policies to ensure they reflect sustainable development objectives (i.e. social, environmental and economic factors) and required in the act to be undertaken for all local development documents. It incorporates strategic environmental assessment.
Sustainable Development - Development that meets the needs of the present without compromising the ability of future generations to meet their own needs (The World Commission on Environment and Development, 1987).
Sustainable Drainage Systems (SUDS) – A range of sustainable approaches to surface water drainage management including, source control measures including rainwater recycling and drainage, infiltration devices to allow water to soak into the ground, filter strips and swales, filter drains and porous paving and basin and ponds to hold excess water after rain and allow controlled discharge that avoids flooding.
Supplementary Plan Documents (SPDs) - Provide supplementary information in respect of the policies in development plan documents. They do not form part of the development plan and are not subject to independent examination.
The Exception Test - If, following application of the Sequential Test, it is not possible (consistent with wider sustainability objectives) to demonstrate that there are no reasonably available sites in areas with less risk of flooding that would be appropriate to the type of development or land use proposed, the Exception Test may apply. PPS25 sets out strict requirements for the application of the test.
The Sequential Test - Informed by a Strategic Flood Risk Assessment, a planning authority applies the Sequential Test to demonstrate that there are no reasonably available sites in areas with less risk of flooding that would be appropriate to the type of development or land use proposed.
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Executive Summary
This Strategic Flood Risk Assessment (SFRA) has been produced in accordance with Planning Policy Statement 25 (PPS25) Development and Flood Risk and the Development and Flood Risk: Practice Guide Companion to PPS25 Lliving Draft’, to provide the necessary information for undertaking the Sequential Test and Exception Test. As part of the Level 1 SFRA, new Flood Zones have been produced, using the latest outputs from the River Hull Flood Risk Management (FRM) Strategy that has been made available for use in this study. The Hull Flood Zones (August 2007) are considered more accurate than the existing Environment Agency Flood Zones as they are produced using recent detailed modelling results where hydraulic effects and time-dependant processes have been considered. This will enable greater confidence in the Flood Zones during the application of the Sequential Test. Detailed modelling has also enabled greater confidence in the impacts of climate change on flooding in the city. The Hull Flood Zones (August 2007) have been combined with information relating to flooding from other sources, such as localised pluvial and sewer flooding, in order to create SFRA maps, which provide a comprehensive representation of all known flood risk areas. The findings from this SFRA show that the majority of land within Hull City Council currently has a high risk of flooding and therefore the Sequential Test alone cannot identify sufficient development sites within Hull. The Exception Test will need to be applied where development is proposed within high risk land. Hence, the Level 1 SFRA was followed by a Level 2 SFRA to provide the necessary information to enable the application of the Sequential Test and Exception Test within Flood Zone 3.
The Level 2 SFRA corresponds to the ‘increased scope’ SFRA referred to in Planning Policy Statement 25 (PPS25) Development and Flood Risk. The Level 2 study provides the necessary information for undertaking the Sequential Test and the Exception Test within Flood Zone 3 and builds upon the Level 1 study, which involved the production of new Flood Zones. The more detailed Level 2 study considers the detailed nature of the flood hazard taking account of the presence of flood risk management measures such as flood defences. This allows a Sequential Approach to site allocation to be adopted within Flood Zone 3.
Simplified surface water modelling to identify flood risk areas associated with pluvial flooding has been undertaken. This enables the latest Level 2 Hull SFRA maps to incorporate flood hazard from fluvial, tidal and pluvial flooding.
The findings of the SFRA include recommendations which are to be developed into policy in the future. The recommendations cover how flood risk should be considered within planning, development and implementation.
Hull City Council, Environment Agency and Yorkshire Water all agree with the methodology, maps and recommendations of the SFRA and will be guided by the document when developing planning policy, allocating sites and dealing with planning applications.
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Level 1 SFRA Level 1 SFRA Strategic Flood Risk Assessment Hull City Council
Level 1 SFRA
1 Background Information 1
1.1 Terms of Reference ...... 1 1.2 The Study Area ...... 1 1.3 Constraints on Development...... 1
2 Planning Context 3
2.1 Introduction ...... 3 2.2 National Planning Policy ...... 4 2.3 Regional Planning Policy ...... 6 2.4 Local Planning Policy...... 7 2.5 Environment Agency Policy ...... 8
3 Flood Zones and SFRA Flood Maps 11
3.1 Introduction ...... 11 3.2 The PPS25 Flood Zones...... 11 3.3 Environment Agency Flood Zones...... 12 3.4 SFRA Flood Maps...... 12
4 PPS25 and its Practice Guide Companion 15
4.1 PPS25 - Key Aims...... 15 4.2 Outcomes of the SFRA Process ...... 16 4.3 The Sequential Test of PPS25...... 16 4.4 The Exception Test of PPS25...... 16 4.5 The Practice Guide Companion to PPS25...... 17 4.6 SFRA Levels 1 and 2 ...... 18
5 Study Methodology 19
5.1 Specific Project Outputs...... 19 5.2 Approach to Data Gathering ...... 19 5.3 Flooding Data Collected...... 20 5.4 Production of SFRA Flood Maps ...... 21
6 Flood Risk in the Study Area 25
6.1 Geology and Hydrology...... 25
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6.2 Predicted Flooding (Flood Zones)...... 25 6.3 Historical Flooding...... 26 6.4 Flood Defence Standard ...... 31 6.5 Areas Where Development May Increase Flood Risk Elsewhere ...... 31
7 Flood Risk Management Measures 33
7.1 Flood Defences ...... 33 7.2 Flood Forecasting and Flood Warning Systems...... 34
8 Guidance on the Application of the Sequential Test 37
8.1 Introduction ...... 37 8.2 First Step – Strategic Overview of Flood Risk for all Potential Areas...... 37 8.3 Second Step – Flood Risk Issues in Zone 1...... 37 8.4 Third Step – Sequential Test in Zones 2 and 3 ...... 37 8.5 Relevance to Hull...... 38
9 Guidance for the preparation of Flood Risk Assessments 39
9.1 Introduction ...... 39 9.2 Proposed Development within Flood Zone 1...... 39 9.3 Proposed Development within Flood Zone 2...... 39 9.4 Proposed Developments within Flood Zone 3a ...... 39 9.5 Integrated Urban Drainage (IUD)...... 40 9.6 Raised Floor Levels and Basements ...... 41
10 Guidance for the Application of Sustainable Drainage Systems 43
10.1 Introduction ...... 43 10.2 Types of SUDS Systems...... 43 10.3 Application of SUDS for the Proposed Allocation Sites ...... 44 10.4 Effective application of SUDS techniques...... 44
Separate Figures 47
Appendix A: Project Data Register 49
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Tables
Table 2.1. Proposed timetable for the production of LDF documents ...... 8
Table 3.1. PPS25 Flood Zone definitions ...... 12
Table 5.1. Recommended national precautionary sensitivity ranges...... 23
Table 5.2. Recommended contingency allowances for net sea level rise...... 23
Table 6.1. Historical tidal and fluvial flooding...... 26
Table 6.2. Records of localised flooding and sewer flood risk locations ...... 27
Table 7.1. Descriptions of defence condition...... 33
Figures within text
Figure 3.1. PPS25 Flood Zones
Figure 6.8. Flooding on Chanterlands Avenue (June 2007)
Figure 6.9. Flooding on Park Avenue (June 2007)
Figure 6.10. Flooding of properties (June 2007)
Figure 6.11. Flooding of amenities (June 2007)
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Separate Figures
Figure 1.1. Study Area
Figure 5.1. Modelled Watercourses
Figure 5.2. Ground Elevation Data Coverage
Figure 6.1. Soil Data
Figure 6.2. Existing Flood Zones
Figure 6.3. PPS25 Flood Zones
Figure 6.4. PPS25 Flood Zones with Climate Change
Figure 6.5. Historic River Flooding
Figure 6.6. Local Flooding
Figure 6.7. SFRA Flood Map
Figure 7.1. Flood Defence Condition
Figure 7.2. Flood Warning Areas
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Strategic Flood Risk Assessment Hull City Council
1 Background Information
1.1 Terms of Reference
In May 2007, Hull City Council commissioned Halcrow to produce a Strategic Flood Risk Assessment in accordance with Planning Policy Statement 25 (PPS25) Development and Flood Risk.
Advice on flood risk within the administrative boundary of the planning authority is required to support the preparation of the Hull Development Framework and, in particular, the submission draft of the City Centre Area Action Plan, in accordance with government guidance and the advice from the Environment Agency.
1.2 The Study Area
Hull City lies on the north of the Humber estuary. The main watercourses within the city boundary are the River Hull, Beverley and Barmston Drain, and Holderness Drain (figure 1.1). The Beverley and Barmston Drain outfalls to the River Hull approximately 1.5 kilometres upstream of the Humber while the River Hull and Holderness Drain discharge to the Humber. The city comprises an area of some 7,150 hectares (71.5 kilometres squared) with a population of 250,000. The majority of the study area is urban with residential and commercial properties.
1.3 Constraints on Development
The whole of the Humber Estuary, which abuts the southern boundary of Hull City Council, is designated at an international and national level (possible Special Area of Conservation; Special Protection Area; Ramsar site; and Site of Special Scientific Interest (SSSI)) in recognition of its nature conservation importance.
The existing Environment Agency Flood Zone map indicates that the majority of the city has a high risk of flooding and consequently, having regard to PP25, there is limited space within lower risk areas for future development.
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2 Planning Context
2.1 Introduction
A Strategic Flood Risk Assessment (SFRA) is a living document which is used as a tool by a planning authority to assess all types of flood risk for spatial planning, producing development briefs, setting constraints, informing sustainability appraisals, identifying locations of Emergency Planning measures and requirements for flood risk assessment, and making planning decisions.
The success of the SFRA is heavily dependant upon a planning authority’s ability to implement the recommendations put forward for future sustainable flood risk management. It is ultimately their responsibility to establish robust policies that will ensure future sustainability with respect to flood risk.
A SFRA provides sufficient data and information to enable a planning authority to apply the Sequential Test to land use allocations and the determination of planning applications, and where necessary, the Exception Test. In addition, it allows a planning authority to:
• Prepare appropriate policies for the management of flood risk;
• Inform the Sustainability Appraisal so that flood risk is taken account of, when considering options and in the preparation of strategic land use policies;
• Identify the level of detail required for site specific Flood Risk Assessments (FRAs) in particular locations; and
• Determine the acceptability of flood risk in relation to Emergency Planning capability.
A staged approach is recommended in PPS25 to allow flexibility in the level of assessment (and detail) required. A Level 1 SFRA is defined in the Practice Guide Companion to PPS25, as the level that provides the necessary information for undertaking the Sequential Test. Figure 3.1 of the Practice Guide Companion shows the process by which the Sequential Test as advocated in PPS25 is applied.
Where the need to apply the Exception Test is identified, due to there being an insufficient number of suitably available sites for development within Zones of lower flood risk or due to possible increases in flood risk arising from climate change, the scope of the SFRA could be widened to a Level 2 assessment.
The increased scope involves a more detailed review of the flood hazard (flood probability, flood depth, flood velocity, rate of onset of flooding) taking into account the presence of flood risk management measures such as flood defences. This could include 2-D modelling and full breach analysis for certain locations.
Level 2 outputs would include:
• An appraisal of the condition of flood defence infrastructure and likely future policy;
• An appraisal of the probability and consequence of breach or overtopping of flood defence infrastructure;
• Maps showing distribution of flood risk across Zones;
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• Guidance on appropriate policies for making sites which satisfy parts (a) and (b) of the Exception Test safe, and the requirements for satisfying part (c) of the Exception Test; and
• Guidance on the preparation of FRAs for sites with varying flood risk across the Flood Zone.
This part consists of the Level 1 SFRA, as agreed with the client and Environment Agency. This will primarily be based on the use of existing data and available information. This study conforms with the national and regional planning policy.
Further comment on the scope of the Level 2 SFRA report is included below.
2.2 National Planning Policy
The government issues its planning advice through national Planning Policy Statements (PPSs).
In December 2006 the government published PPS25: Development and Flood Risk. It reflected the general direction set out in ‘Making Space for Water’ (Defra, 2004), the evolving new strategy to shape flood and coastal erosion risk over the next 10-20 years (see glossary of terms).
PPS25 states that flooding, in all its forms, is a material planning consideration in the determination of planning applications and the formulation of planning policy. PPS25 states that flood risk should be considered alongside other spatial planning concerns such as transport, housing, economic growth, natural resources, regeneration and the management of other hazards.
There is a close correlation between climate change and flood risk. A draft PPS, Planning and Climate Change, was published in December 2006 for consultation until March 2007. It sets out how planning, in providing for new homes, jobs and infrastructure, should help shape places that are resilient to climate change. When finalised, the PPS will supplement PPS1, Delivering Sustainable Development.
There will also be a need to tie in with Defra’s Integrated Urban Drainage (IUD) pilot studies, launched in January 2007. These pilot studies will test new approaches to reducing the impact of urban drainage flooding, so that towns and cities across the country are better prepared for the impacts of climate change.
The following subsections provide an overview of the relevant national planning policy documents and a brief explanation of their relevance for the SFRA.
2.2.1 Planning Policy Statement 1 (PPS1): Creating Sustainable Communities (2005)
PPS1 sets out the government’s objectives for the planning system. It confirms that good planning should deliver the right development in the right place and time, and protect the environment. It
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identifies Sustainable Development as the core principle underpinning planning and requires that Development Plans ensure it is pursued in an integrated manner.
2.2.2 Planning Policy Statement 3 (PPS3): Housing (2006)
PPS3 has been developed in response to recommendations in the Barker Review of Housing Supply (March 2004). Its principal aim is to underpin the necessary step change in housing delivery, improving supply and affordability of housing in all communities including rural areas.
PPS3 states that the government’s key housing policy goal is to ensure that everyone has the opportunity of living in a decent home, which they can afford, in a community where they want to live. The specific outcomes that the planning systems should deliver are:
• Well designed, high quality housing that is built to a high standard;
• A mix of market and affordable housing for all households in all areas;
• A sufficient quantity of housing, taking into account need and demand and seeking to improve choice;
• Housing developments in suitable locations offering a good range of community facilities and with good access to jobs, key services and infrastructure;
• A flexible, responsive supply of land, which is used efficiently and effectively, including the use of previously developed land.
Housing policies should help deliver Sustainable Development objectives, in particular seeking to minimise environmental impact taking account of climate change and flood risk, and take into account market information, in particular housing need and demand.
2.2.3 Planning Policy Guidance 15 (PPG15): Planning and the Historic Environment (1994)
PPG15 sets out policies on the protection of the historic environment and recognises that planning plays an important role in preserving built and natural heritage.
2.2.4 Planning Policy Guidance 17 (PPG17): Planning for Open Space and Recreation (2002)
PPG17 recognises the importance that public open spaces, green areas and recreational rights of way can play in supporting regeneration and contributing to local quality of life.
2.2.5 Planning Policy Statement 25 (PPS25): Development and Flood Risk (2006)
PPS25 sets out a plan led approach to flood risk. It confirms that all forms of flooding and their impact on the natural and built environment are material planning considerations. It clarifies the Sequential Test that matches type of development to degrees of flood risk and strengthens the requirement to include flood risk assessments at all levels of the planning process. Regional planning bodies and local planning authorities (LPA) should, inter alia, reduce flood risk by safeguarding land from development that is required for current and future flood management e.g. conveyance and storage of flood water and flood defences.
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Amendments to the Town and Country Planning (General Development Procedure) Order 1995 came into force on 1 October 2006 introducing further requirements for LPA to consult the Environment Agency before determining applications for development in flood risk areas.
The Town and Country Planning (Flooding) (England) Direction 2007 was published in December 2006. To safeguard against inappropriate development in flood risk areas, it introduces a requirement for LPA to notify the secretary of state of any application for major development (e.g. ten houses or more) in flood risk area which it proposes to approve against Environment Agency advice. The direction came into force on 1 January 2007.
2.3 Regional Planning Policy
2.3.1 Regional Spatial Strategy for Yorkshire and Humber (RSS12) (based on a selective review of Regional Planning Guidance note 12(RPG12))
Regional planning policies provide the overarching framework for the preparation of the Local Development Framework (LDF) following the enactment of the Planning and Compulsory Purchase Act 2004, and forms part of the statutory Development Plan. A key function of the Regional Spatial Strategy (RSS) is to ensure that development is sustainable. The document will shortly be superseded by a revised RSS (see below).
Policy R2 in the RSS requires that local authorities undertake SFRAs for their areas, and that Development Plans should adopt a risk-based approach to flooding in line with PPG25 (now superseded by PPS25).
2.3.2 The Yorkshire and Humber Plan – The Regional Spatial Strategy (draft December 2005)
The replacement RSS is based on a comprehensive review of the current RSS12. It will guide development to 2021 and beyond, and provides a regional, spatial planning policy framework. It forms part of the Development Plan for the purpose of determining planning applications, and the development of LDF documents must be in general conformity with the RSS.
The consultation draft was published in December 2005, and an independent examination in public was held between September and October 2006. The panel report was published in May 2007, and the Secretary of State’s ‘proposed changes’ were published for public consultation in October 2007. Publication of the final revised RSS is expected early 2008.
One of the main aims of the revised RSS for Yorkshire and Humber is to manage growth and change to ensure a sustainable approach to spatial planning. It is a requirement that the LDF’s Core Strategy is in general conformity with regional planning policy.
Hull is designated as one of the Yorkshire and Humber region’s ‘Regional Cities’, as recommended in the Panel Report, subject of Policy YH5. This states that the regional cities should be the prime focus for housing, employment, shopping, leisure, education, health and cultural development. Such cities should be attractive, cohesive and safe places to live, work, invest and spend time in.
Within the Humber Sub Area, the draft RSS seeks to transform the role of Hull as a Regional City, through remodelling of the city centre to provide more and better jobs, shops, services, public spaces and homes, and transforming residential areas to create a better mix of housing and quality environments. The policy context aims to diversify and develop the sub area’s economy, maximising
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the opportunities offered by the ports complex, which will provide nationally strategic facilities. The development strategy seeks to focus development within urban areas, securing rapid urban renaissance, with development restrained in rural areas and smaller settlements – particularly north and west of Hull.
The plan states that the environment of housing and employment areas in Hull should be reviewed, and notes that the risk of flooding from the Humber and associated river and drainage systems to Hull is a regionally significant investment priority. In respect of housing requirements, draft Policy H4 states that plans, strategies and investment decisions should ensure the provision of homes for a mix of housing that reflects the need of the area, including family homes, to create sustainable communities. Table 13.1 notes that provision should be made for 880 average net annual additions to the housing stock for the period 2008-26, representing a significant change from the past levels of provision. The RSS states that a high level of housing clearance and replacement should occur during the plan period, with reduced vacancy also contributing to the area’s housing provision.
In terms of the economic strategy, the plan states that the Humber area should capitalise on opportunities from the ports and ports logistics cluster, with a specific focus on regeneration and port- related site for the city of Hull. Recognising the role of Rregional Cities, investment should be delivered in locations where it will have maximum benefit and secure competitive advantage.
Draft Policy ENV1 states that flood risk will be proactively managed by reducing causes of flooding to existing and future development, especially in tidal areas, and avoid development in high flood risk areas where possible. The allocation of areas for development will follow a sequential approach and be in the lowest risk sites as identified by Strategic Flood Risk Assessments. Flood management will be required to facilitate development in Hull. The Plan seeks that by 2021, flood risk will have been successfully managed by limiting development and providing suitable defences to existing property in vulnerable areas, and that flood risk has not been a barrier to achieving regeneration and economic regional and sub-regional priorities, provided the development proposals have followed the land allocation process set out in PPS25. Paragraph 15.5 states that RSS does not advocate providing defences to protect new development in flood risk areas unless, following the application of PPS25, there are no alternative lower flood risk sites.
2.4 Local Planning Policy
Hull City Council is preparing its Local Development Framework (LDF), referred to as the Hull Development Framework (HDF). This consists of Development Plan Documents (DPDs), consisting of a Core Strategy, Site Specific Allocations and Adopted Proposals Map, a city policies DPD, Area Action Plan(s), a joint minerals DPD and a joint waste DPD both produced jointly with the East Riding of Yorkshire Council, and other DPD documents as required; Supplementary Planning Documents, a Statement of Community Involvement, the Local Development Scheme and Annual Monitoring Reports, supported by SEA/SA (see glossary of terms).
On adoption, the HDF will replace the existing Hull Local Plan (2000) and Joint Structure Plan for Hull and the East Riding of Yorkshire (2005).
The Local Development Scheme for Hull was updated in March 2007. The proposed timetable for the production of LDF documents is outlined in table 2.1 below.
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Table 2.1. Proposed timetable for the production of LDF documents
Submission Issues and Preferred Document to Secretary Adoption Options Options of State Core Strategy Q1 2008 Q1 2009 Q2 2010 Q4 2011
City Policies DPD and Site Q1 2009 Q2 2010 Q1 2012 Q4 2013 Allocations City Centre Area Action Plan - - Q1 2008 Q1 2009
Joint Waste DPD (with ERYC) Q1 2008 Q4 2008 Q3 2009 Q4 2010
Joint Minerals DPD (with ERYC) Q1 2008 Q1 2009 Q3 2009 Q4 2010
To date, the council have produced a draft City Centre Area Action Plan (CCAAP), which was consulted on as a preferred options draft in June 2006. To support the Strategic Development Area identified in the CCAAP, five Supplementary Planning Documents (SPDs) have been produced which were consulted on in tandem with the draft CCAAP. The next step in the finalisation of the CCAAP and associated SPDs will be the preparation of a submission draft CCAAP for submission to the Secretary of State. The CCAAP and SPDs are expected to be adopted in 2009.
This SFRA will inform the submission draft of the CCAAP.
In line with PPS25 and the living draft practice guide companion, this SFRA will enable Hull City Council to prepare appropriate policies for the management of flood risk within its DPDs and inform the Sustainability Appraisal process in order that flood risk is taken into account when considering options and the preparation of strategic land use policies. We are mindful of the suggestion in the documents in taking a joint approach to the SFRA process, where a catchment based approach to flood management may be desirable. On that basis, and in the spirit of the guidance, we will identify any development locations within Hull City Council’s administrative area where additional or allocated development could increase flood risk in an area outside the City Council’s control.
2.5 Environment Agency Policy
The Environment Agency is in the process of producing the Hull and Coastal Streams Catchment Flood Management Plan (CFMP). The CFMP is a high level planning tool that will develop and set policies for sustainable flood risk management for the whole catchment are in the long term.
The subsequent strategy should then identify preferred management measures to deliver CFMP policies for specific areas within the catchment. The River Hull Flood Risk Management Strategy is being developed ahead of the CFMP due to the condition of the defences throughout the catchment.
The Environment Agency is in the process of producing the Humber Flood Risk Management Strategy and River Hull Flood Risk Management Strategy. These strategies consider how flood risk is to be managed across the catchment over the next 100 years. Both of these strategies are key to effective long term flood risk management and informed planning decisions are made.
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The River Hull Flood Risk Management Strategy which is due to be consulted on throughout 2008 indicates that taking account of climate change Hull will be protected against a 1% (1 in 100 years) probability flood event for the next 100 years.
The Humber Flood Risk Management Strategy which is nearing completion indicates that Hull will be protected against a 0.5% (1 in 200 years) probability flood event for the next 100 years.
Since December 2002 the Environment Agency has developed ‘Local Standing Advice’ to assist the Council with determining planning applications and consultation with the Environment Agency. The Local Standing advice sub-divides Flood Zone 3 into three areas of different risk. Where development is proposed within the highest risk area the Environment Agency are consulted, within the medium risk area a condition is attached to the planning permission to ensure floor levels are raised by 600 millimetres and within the least risk area of Flood Zone 3 floor levels are raised by 300 millimetres.
The SFRA should be reviewed once the CFMP and Flood Risk Management Strategies have been completed and high level policies are set.
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3 Flood Zones and SFRA Flood Maps
3.1 Introduction
A good understanding of the PPS25 Flood Zones, the Environment Agency Flood Zones and SFRA Flood Maps is of fundamental importance for SFRAs. Flood Maps are the key elements in a SFRA as they provide a visual understanding of flood risk at strategic level.
3.2 The PPS25 Flood Zones
The PPS25 Flood Zones are adjacent areas that subdivide the spatial variation of flood probability from rivers and the sea. These are the functional floodplain (3b) and the high (3a), medium (2) and low (1) probability Flood Zones (figure 3.1).
It is important to note that within each Flood Zone there is a spatial variation of flood probabilities and the range is clearly defined. The “functional floodplain” for example, comprises land where water has to flow or Figure 3.1. PPS25 Flood Zones be stored in times of flood. The functional floodplain can be drawn therefore on a map by combining the flood extents of many frequent floods, with high probability of occurrence.
There are many methods that estimate the probability of occurrence of a flood, based on historical events, measurements of flows, modelling studies, etc. The term average means for example that a flood that has a 100% (or 1 in 1 chance) probability of occurrence in a given year, will flood fairly regularly every year however it may not flood all years.
The PPS25 definition of the Flood Zones is given in table 3.1 overleaf.
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Table 3.1. PPS25 Flood Zone definitions
Zone Definition
This Zone comprises land assessed as having a less than 1 in Zone 1 - Low Probability 1000 annual probability of river or sea flooding in any year (<0.1%).
This Zone comprises land assessed as having between a 1 in 100 and 1 in 1000 annual probability of river flooding (1%– Zone 2 - Medium Probability 0.1%) or between a 1 in 200 and 1 in 1000 annual probability of sea flooding (0.5% – 0.1%) in any year.
This Zone comprises land assessed as having a 1 in 100 or greater annual probability of river flooding (>1%) or a 1 in 200 Zone 3a - High Probability or greater annual probability of flooding from the sea (>0.5%) in any year.
This Zone comprises land where water has to flow or be stored in times of flood. SFRAs should identify this Flood Zone (land which would flood with an annual probability of 1 in Zone 3b - The Functional 20 (5%) or greater in any year or is designed to flood in an Floodplain extreme (0.1%) flood, or at another probability to be agreed between the local planning authority (LPA) and the Environment Agency, including water conveyance routes).
Zone 3 Zone 3 = Zone 3a + Zone 3b
3.3 Environment Agency Flood Zones
The existing Environment Agency Flood Zones are published and updated quarterly to their website at http://www.environment-agency.gov.uk/subjects/flood/?lang=_e).
The only difference in the definition of the PPS25 Flood Zones and the Environment Agency Flood Zones is that the latter exclude the functional floodplain. Both definitions do not rely on the presence of defences (formal or informal, see glossary of terms at the end of this report) as these could fail during a flood as a result of poor maintenance. They also relate to flooding from rivers and the sea however this is not exactly the case for the Environment Agency Flood Zones.
Historically the Environment Agency and its predecessors have kept formal maps of tidal and fluvial flooding to the standards required by legislation. Originally this mapping recorded historical flood events. In 2001, PPG25 (the predecessor of PPS25) imposed a duty on the Environment Agency to produce Flood Zone Maps. These maps needed to show the predicted extent of tidal and fluvial flooding for the high, medium and low Flood Zones, but not the functional floodplain as this is a recent PPS25 requirement. The probabilities of flooding associated with these Flood Zones are the same as those for the PPS25 Flood Zones, shown in table 3.1.
3.4 SFRA Flood Maps
SFRA Flood Maps in general reproduce the Environment Agency high, medium and low probability Flood Zones where no other more up-to-date information is available. However, in the case of Hull
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City Council, the SFRA maps are based on hydrodynamic modelling results from the River Hull Flood Risk Management (FRM) Strategy that have been made available for use in this study. These SFRA maps are considered more accurate than the existing Environment Agency Flood Zones as they are produced using recent detailed modelling results where hydraulic effects and time-dependant processes have been considered. The SFRA Flood Maps also include assessments of the functional floodplain.
SFRA Flood Maps do not only show updated Flood Zones, they also show ‘localised flooding areas’ from other sources/forms of flooding, such as pluvial flooding, sewer flooding and groundwater flooding where appropriate. These maps also indicate the areas flooded in June 2007. SFRA Flood Maps produced as part of this SFRA are discussed further in section 5.4.
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4 PPS25 and its Practice Guide Companion
4.1 PPS25 - Key Aims
The key aims of PPS25 are reproduced below:
The aims of planning policy on development and flood risk are to ensure that flood risk is taken into account at all stages in the planning process to avoid inappropriate development in areas at risk of flooding, and to direct development away from areas at highest risk. Where new development is, exceptionally, necessary in such areas, policy aims to make it safe without increasing flood risk elsewhere and where possible, reducing flood risk overall.
Regional planning bodies and local planning authorities (LPAs) should prepare and implement planning strategies that help to deliver Sustainable Development by:
Appraising risk
• Identifying land at risk and the degree of risk of flooding from river, sea and other sources in their areas;
• Preparing Regional Flood Risk Appraisals (RFRAs) or Strategic Flood Risk Assessments (SFRAs) as appropriate, as freestanding assessments that contribute to the sustainability appraisal, policy and allocations of their plans.
Managing risk
• Framing policies for the location of development which avoid flood risk to people and property where possible, and manage any residual risk, taking account of the impacts of climate change;
• Only permitting development in areas of flood risk when there are no reasonably available sites in areas of lower flood risk and benefits of the development outweigh the risks from flooding.
Reducing risk
• Safeguarding land from development that is required for current and future flood management e.g. conveyance and storage of flood water, and flood defences;
• Reducing flood risk to and from new development through location, layout and design, incorporating SUstainable Drainage Systems (SUDS);
• Using opportunities offered by new development to reduce the causes and impacts of flooding e.g. surface water management plans; making the most of the benefits of green infrastructure for flood storage, conveyance and SUDS; recreating functional floodplain; and setting back defences.
A partnership approach
• Working effectively with the Environment Agency, water companies, other operating authorities and other stakeholders to ensure that best use is made of their expertise and information so that plans are effective and decisions on planning applications can be
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delivered expeditiously (this is currently being implemented by a series of pilot projects for DEFRA);
• Ensuring spatial planning supports flood risk management policies and plans, River Basin Management Plans and Emergency Planning, and
• Building effective partnerships between the various drainage authorities such as water companies, local authorities, Environment Agency, internal drainage boards and improving partnership working to find solutions to urban flooding problems to enable IUD.
4.2 Outcomes of the SFRA Process
The broad planning objectives of PPS25, described above, effectively set the scope for the specific outcomes of the SFRA process. The SFRA in turn then informs planning and development control decisions that ensure the objectives set out above can be achieved.
It is important to reiterate that PPS25 is not applied in isolation as part of the planning process. The formulation of flood risk policy and the allocation of land for future development must also meet the requirements of other planning policy. Clearly a careful balance must be sought in these instances, and the SFRA aims to assist in this process through the provision of a clear and robust evidence base upon which informed decisions can be made.
4.3 The Sequential Test of PPS25
A planning authority applies the Sequential Test to demonstrate that there are no reasonably available sites in areas with less risk of flooding that would be appropriate to the type of development or land use proposed.
Preference should be given to locating new development in Flood Zone 1, as defined in section 3.2. If there is no reasonably available site in Flood Zone 1, the flood vulnerability (or level of resilience to damages from flooding) of the proposed development can be taken into account in locating development in Flood Zone 2 and then Flood Zone 3.
Within each Flood Zone new development should be directed to sites with lower flood risk (towards the adjacent Zone of lower probability of flooding) from all sources, such as fluvial, tidal, groundwater and surface water, as indicated by the SFRA.
Following application of the Sequential Test, it may not be possible for the development to be located in Zones of lower probability of flooding consistent with wider sustainability objectives. In these cases, the Sequential Test should be applied within Flood Zone 3 to ensure development is located within the areas of lowest risk within Flood Zone 3.
This approach has been undertaken in line with Environment Agency local standing advice in Hull.
4.4 The Exception Test of PPS25
The Exception Test is only applied after application of the Sequential Test. This test provides a method of managing flood risk while still allowing necessary development to occur.
PPS25 states that 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, but where some continuing development is necessary for wider sustainable development reasons, taking into account
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the need to avoid social or economic blight and the need for essential civil infrastructure to remain operational during floods. It may also be appropriate to use it where restrictive national designations such as landscape, heritage and nature conservation designations, e.g. Areas of Outstanding Natural Beauty (AONBs), Sites of Special Scientific Interest (SSSIs) and World Heritage Sites (WHS), prevent the availability of unconstrained sites in lower risk areas.
For the Exception Test to be passed:
(a) It must be demonstrated that the development provides wider sustainability benefits to the community that outweigh flood risk, informed by a SFRA where one has been prepared. If the Development Plan Document has reached the ‘submission’ stage (see figure 4 of PPS 12: Local Development Frameworks) the benefits of the development should contribute to the Core Strategy’s Sustainability Appraisal;
(b) The development should be on developable, previously-developed land or, if it is not on previously developed land, that there are no reasonable alternative sites on developable previously-developed land; and
(c) A flood risk assessment (FRA) must demonstrate that the development will be safe, without increasing flood risk elsewhere, and, where possible, will reduce flood risk overall.
4.5 The Practice Guide Companion to PPS25
A practice guide companion to PPS25 was published for consultation in February 2007. It is a ‘living draft’ web-based consultation paper (see http://www.communities.gov.uk/index.asp?id=1504639). It is comprehensive and incorporates many recommendations from previous guidance documents.
The guide reaffirms the adoption of a risk-based approach to flooding by following stepped hierarchical measures at all stages in the planning process. Avoidance/prevention is always the first measure, followed by substitution, control and finally mitigation. This is summarised in table 1.2 of the practice guide companion to PPS25 and it is reproduced in the table below).
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Table 1.2. Overview of the flood risk management hierarchy.
The above table has been taken from “Development and Flood Risk: A Practice Guide Companion to PPS25 ‘Living Draft’”.
The Sequential Test of PPS25 is the most important flood risk management tool for spatial planning, as it implements the high level measures of avoidance/prevention and substitution (see section 4.3).
4.6 SFRA Levels 1 and 2
A Level 1 SFRA is defined in the practice guide companion to PPS25, as the level that provides the necessary information for undertaking the Sequential Test.
Where the need to apply the Exception Test is identified, due to there being an insufficient number of suitably available sites for development within Zones of lower flood risk, the scope of the SFRA is widened to a more detailed Level 2 study.
The scope of this section of the report is a Level 1 SFRA to inform the plan-making process of the Core Strategy (see section 2.4). The planning authorities will use this information to undertake Sequential Testing in identifying general locations for development, formulate strategic policies and inform the city council’s emergency plan. The study covers the area within the administrative boundaries of the city council.
For the allocations, DPD and AAPs, more detail will be required, in particular for the existing built-up areas where development is likely to continue. This will be included in the following section of this report which covers the Level 2 SFRA.
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5 Study Methodology
5.1 Specific Project Outputs
The specific outputs are based on the required outputs for a Level 1 SFRA, as follows:
i. Map existing Flood Zones 1, 2 and 3 across the plan area.
ii. Map Flood Zones 1, 2 and 3 across the plan area in accordance with PPS25. This includes identification of Flood Zone 3b: the functional floodplain.
iii. Map Flood Zones 1, 2 and 3 for the future climate change scenario as set out in PPS25 annex B, taking account of recommended contingency levels for sea level rise, and recommended national precautionary sensitivity ranges for peak rainfall intensities, peak river flows, off-shore wind speeds and wave heights.
iv. Identify areas at risk from flooding from sources other than rivers and the sea (section 6.3.3).
v. Identify and take into account flood risk management measures including flood defences and emergency warning systems (see section 7).
vi. Guidance on the application of the Sequential Test (see section 8).
vii. Guidance for the preparation of flood risk assessments (see section 9).
viii. Guidance on possible mitigation measures, including the likely applicability of different Sustainable Drainage Systems (SUDS) techniques for managing surface water runoff at key Level 1 SFRA development sites (see section 10).
ix. Identify locations where development would significantly increase the risk of flooding elsewhere (see section 6.5).
5.2 Approach to Data Gathering
The main sources of data for this study have been the Environment Agency, previous studies undertaken by Halcrow, a number of relevant websites, Hull City Council and Yorkshire Water.
Priority has been given to the collection of geo-referenced information in electronic format, to ensure the effective management of the data within a GIS environment. All incoming data has been recorded on a comprehensive project data register (appendix A).
The quality review of the information has been carried out by an experienced core team. The team has been able to review the collected data, assess its significance and quality, and advise on which part of the collected data needed to be used for the SFRA.
The main approach has been to build on the large number of strategic studies and relevant available data. Although the Hull and Coastal Streams Catchment Flood Management Plan (the Hull CFMP) is not yet complete the Scoping stage is completed and this has provided a good foundation for catchment understanding and flood risk assessment. The Humber and River Hull Flood Risk Management (FRM) strategies, which are ongoing, have provided a large quantity of detailed information.
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Valuable flood risk information for localised flooding areas (as opposed to the ‘non-localised’ Flood Zones) was obtained from the engineers working for Hull City Council. The collected information complemented information provided by the Environment Agency, Yorkshire Water and the local planning authorities.
5.3 Flooding Data Collected
5.3.1 Introduction
For the purpose of this assessment, forms of flooding (also defined as sources of flooding) are divided into three categories:
1. tidal and river flooding
2. groundwater flooding
3. flooding from other sources
The reason for adopting this classification is to provide an understanding of data limitations and assumptions as there are different standards for the collection of each of these types of data.
The various sources of flooding within the study area are described and shown in section 6.
5.3.2 Tidal and Fluvial Flooding
Information relating to tidal and fluvial flooding has been obtained from:
1. River Hull FRM Strategy outputs, including hydrodynamic model and results (Halcrow, 2007): Provides theoretical predictions of flood water levels and flood extents for a range of annual probability floods for both with and without defences. The modelled watercourses and floodplain are shown in figure 5.1.
2. Old Fleet Drain outputs, including report and flood maps (JBA, 2003): Provides theoretical predictions of flood water levels and flood extents for a range of annual probability floods on Old Fleet Drain. The modelled watercourses are shown in figure 5.1.
3. Ground elevation data (Environment Agency, 2006): Data is used in the hydrodynamic model to provide floodplain ground levels as well as defence crest levels in some locations. Data is also used to convert the model results (water levels) into a flood map/Flood Zone. A range of different ground elevation data has been used in the River Hull FRM Strategy including SAR, high level LiDAR, low level LiDAR. The coverage of these datasets is shown (figure 5.2).
4. Autumn 2000 Floods; Performance Review and Action Plan (Environment Agency, 2001): Provides description and locations of observed river flooding, the cause and the mitigation measures employed, where appropriate.
5. Flood extent GIS layers (Environment Agency, 2005): Includes 1969 and 1997 flood extents. Provides approximate locations of observed flooding.
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6. Existing Flood Zones (Environment Agency, 2007): Provides theoretical predictions of flood extents without defences for the 1% annual probability flood (river) and 0.5% annual probability flood (sea) and 0.1% annual probability flood (river and sea).
7. Photographs (various): Includes 1969 RAF aerial photography. Provides locations of observed flooding.
5.3.3 Groundwater Flooding
General information relating to groundwater flooding in the area has been obtained from the Hull CFMP (scoping stage) report as well as the CAMS (Catchment Abstraction Management) report. The Environment Agency is not aware of any formal records of groundwater flooding in the area.
5.3.4 Flooding from Other Sources
Information relating to flooding from other sources has been obtained from:
1. Autumn 2000 Floods; Performance Review and Action Plan (Environment Agency, 2001): Provides description and locations of observed localised flooding, the cause and the mitigation measures employed, where appropriate.
2. DG5 register information of sewer flooding risk (Yorkshire Water, 2006): Provides locations at risk of external sewer flooding. At the time of writing, no further data, such as information we requested on capacity studies and recent/planned improvements, had been received from Yorkshire Water.
3. Localised flooding experience (Hull City Council, June 2007): Provided description and locations of observed flooding and the cause of the flooding. Hull City Council has provided a hard copy map highlighting areas affected by the June 2007 flooding, which has been digitised for inclusion on the SFRA flood maps.
4. News reports on the recent (June 2007) flooding (www.thisishullandeastriding.co.uk, 2007 and www.bbc.co.uk/humber, 2007): Provides description and locations of observed localised flooding as well as a number of photographs taken by the public.
5.4 Production of SFRA Flood Maps
5.4.1 PPS25 Flood Zones
The River Hull FRM Strategy model and model results have been used as the primary source of information for the production of flood maps throughout the study area. The Flood Zones produced are based on model results for flooding from the River Hull and flooding from the Humber, these being modelled separately.
For Flood Zones 2 and 3a, the “do nothing” strategy option was used to model flooding from the River Hull as this option effectively removes the River Hull flood defences and the Hull Tidal Surge Barrier. This is in line with PPS25, which states that these Flood Zones ignore the presence of flood defences.
For Flood Zone 3b (the functional flood plain), the “maintain” strategy option, which includes flood defences, was used to model floods with an annual probability of 4% (1 in 25 years). This is in line with the practice guide companion to PPS25, which states that the functional floodplain (Zone 3b) is determined considering the effects of defences and other flood risk management infrastructure.
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Although the modelled 4% (1 in 25 years) flood is larger flood than the recommended 5% (1 in 20 years) flood, the increase in flood extent (and therefore area of functional floodplain) is small. As PPS25 defines a functional floodplain as land where water has to flow or be stored in times of flood, it was agreed between Hull City Council and the Environment Agency that the functional floodplain should not include urban areas as water does not have to flow or be stored here. Consequently, Flood Zone 3b was later post-processed to exclude urban areas and isolated properties.
As part of this SFRA, the River Hull FRM Strategy model was adapted to enable flooding from the Humber to be modelled. In order to model the “without defences” situation, typical ground levels behind the defences were obtained from LiDAR data and used in the model to approximate the ground profile along the Humber frontage. The resulting flood extent was later post-processed to include the flow path from tidal flooding from the Humber.
It should be noted that the PPS25 Flood Zones are based on results from 1-D hydrodynamic modelling and may not accurately represent flow paths in some locations, though they are still considered more accurate than the existing Environment Agency Flood Zone maps.
5.4.2 Localised Flooding
Valuable information regarding localised flooding, particularly from the recent (June 2007) flooding, was obtained from the engineers working for Hull City Council. This information in most cases complements the non-localised information provided by the Flood Zones and the information provided by Yorkshire Water (highlighted on the Flood Maps).
In some cases the Flood Zones and the localised flooding areas overlap, particularly at locations where there is a combination of forms of flooding (for example fluvial flooding combined with high intensity surface runoff). In limited cases there is also an overlap due to a dual interpretation of a form of flooding which may considered to be both localised as well as part of a Flood Zone. This is one of the key issues of Integrated Urban Drainage (IUD).
5.4.3 Climate Change
In October 2006, DEFRA published a document identifying the climate change impacts to be considered in undertaking flood risk appraisals in the United Kingdom. In addition to sea level rise of approximately 1 metre in north east England over the next 100 years, the document also sets out how short duration rainfall could increase by 30 percent and flows by 20 percent, and suggests winters will become generally wetter. These effects will tend to increase both the size of Flood Zones associated with the sea and rivers, and the amount of flooding experienced from “other sources”.
The main climate change tables B.1 and B.2 from PPS25 are reproduced below in table 5.1 and table 5.2.
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Table 5.1. Recommended national precautionary sensitivity ranges.
1990 to 2025 to 2055 to 2085 to Parameter 2025 2055 2085 2115 Peak rainfall intensity +5% +10% +20% +30%
Peak river flow +10% +20%
Offshore wind speed +5% +10%
Extreme wave height +5% +10%
Table 5.2. Recommended contingency allowances for net sea level rise.
Net Sea Level Rise (mm/yr) relative to 1990
Administrative Region 1990 to 2025 to 2055 to 2085 to 2025 2055 2085 2115
East of England, East Midlands, London, South East England (south of 4.0 8.5 12.0 15.0 Flamborough Head)
South West 3.5 8.0 11.5 14.5
North West England, North East 2.5 7.0 10.0 13.0 England (north of Flamborough Head)
From the above predictions, the increase in river flow and total sea level rise between now and 2105 has been derived as:
• increase in river flow to 2105: 20 percent
• total sea level rise to 2105: 0.995 meters
These climate change impacts were then input into the model and used to produce model results and Flood Zones that include an allowance for climate change i.e. are representative of 2105.
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6 Flood Risk in the Study Area
6.1 Geology and Hydrology
6.1.1 Hydrology
The River Hull catchment includes large areas of the Yorkshire Wolds in its Headwaters as well as flat, artificially drained agricultural land in its middle and lower reaches. Holderness Drain catchment includes flat artificially drained agricultural land to the east of the River Hull as well as a large area of slightly higher land to the east of Monk Dyke in Eastern Holderness.
The River Hull is fed by a number of springs and becks within the Yorkshire Wolds, which join together south of Driffield in the East Riding of Yorkshire. The river flows through open countryside before it skirts past the eastern edge of the town of Beverley and reaches Kingston upon Hull. It flows through the centre of the heavily populated and industrial area of the City of Kingston upon Hull, before joining the Humber estuary at Victoria Pier, near to The Deep and the Tidal Surge Barrier.
The upland part of the catchment is made up of highly permeable chalk which means that there is very little runoff from these catchments but there is a large baseflow component. This baseflow component varies significantly throughout the year and during large storm events.
The low level drains which drain much of the flat, low lying land adjacent to the middle and lower reaches of the Hull and the Holderness Drain are almost entirely made up of artificial channels. These channels form a complex network where flow direction and sub-catchment boundaries are not clearly defined.
6.1.2 Geology and Soils
The impact of geology on flood risk is determined by the permeability of rocks and overlying soils. Geological data shows that chalk underlies the city. As chalk is permeable, a greater proportion of rainfall could infiltrate into the ground depending on overlying soil or the presence of infiltration devices. Maximising infiltration would reduce the amount of surface runoff which reaches rivers, which in turn reduces peak flows by delaying the transport of water from the catchment into the watercourses. The permeable chalk underlying the city should enable infiltration devices, such as soakaways and other SUstainable Drainage Systems (SUDS) to be successfully applied; this is discussed in more detail in section 10.
Soils affect a number of factors relating to the time it takes rainfall to enter river channel. The permeability of a soil affects the amount of rainfall which will infiltrate into the soil rather than run off the surface of it. It also affects the speed at which water will percolate through the soil into the underlying geology. Within Hull City the chalk bedrock is overlain by tills composed of loam, clays, sands and gravels which are a product of glacial deposition from the ice sheets of the ice age (figure 6.1). The predominant soil type in the city is seasonally wet deep clay, which typically has a low permeability, which naturally would cause much of the rainfall to run off the surface as opposed to infiltrate into the soil. The implications of this are discussed in more detail in section 10.
6.2 Predicted Flooding (Flood Zones)
The existing Environment Agency Flood Zones and the PPS25 Flood Zones, derived from the latest modelling results from the River Hull FRM Strategy (see section 5.4.1), are shown in figures 6.2 and 6.3 respectively. In the case of the latter, allocation/development areas have been overlaid to help
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enable the application of the Sequential Test. A full definition of the Flood Zones can be found in section 3.
As can be seen in both versions of the Flood Zones, the majority of the city is within Flood Zone 3, clearly showing the reliance on defences within the city. This is because the ground levels in the city are generally lower than the high tide level of the Humber, which influences levels on the floodplain when defences are removed from the model.
The PPS25 Flood Zones are considered more accurate than the existing Environment Agency Flood Zones as they are produced using detailed modelling results where hydraulic effects and time- dependant processes have been considered. The PPS25 Flood Zone extents are smaller because they account for a full tidal cycle and not just a peak tidal level, as used in the existing Flood Zones.
The PPS25 Flood Zones with an allowance for 100 years of climate change are shown in figure 6.4. By comparing this with figure 6.3, it is clear that potentially climate change will cause a significant increase in the extent of Flood Zone 3, potentially placing many more properties (over 10,000) within the high probability of flooding category.
6.3 Historical Flooding
6.3.1 Tidal and Fluvial Flooding
A list of historical tidal and fluvial flood events that have been recorded for Hull is given in table 6.1 below. Approximate flood extents for the 1969 and 1997 floods are shown in figure 6.5. The River Hull water levels through the city are dominated by the tidal Humber levels and are not significantly affected by fluvial flooding, which is dominant in the headwaters and middle reaches of the River Hull. Since the installation of the Hull Tidal Surge Barrier in 1980, which protects the city from tidal surges, there have been no major floods from tidal surges.
Table 6.1. Historical tidal and fluvial flooding
Source Date Location Cause River Hull 1969 Kingston upon Hull - areas adjacent Tidal surge. to River Hull and Holderness Drain. Widespread flooding (855 houses).
Beverley and Feb 1997 North Hull. Overtopping of bank tops. Barmston Drain
River Hull various Isolated areas adjacent to River Hull, Overtopping of defences mainly through industrial area. during storm tides which where not high enough to trigger operation of the Hull tidal surge barrier. This is due to the poor condition of some of the defences.
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6.3.2 Groundwater Flooding
Groundwater flooding occurs as a result of water rising up from the underlying rocks or from water flowing from abnormal springs. This tends to occur after much longer periods of sustained high rainfall. Generally groundwater flooding occurs during the winter and spring when groundwater levels reach their peak and start to come above ground in low lying areas. Groundwater flooding takes longer to dissipate because groundwater moves much more slowly than surface water and will take time to flow away underground.
Groundwater flooding most commonly occurs in the areas which lie on the edge of the Wolds, to the west of Hull City Council, as these are the locations where the major aquifers come to the surface. Occasional and sporadic elevated groundwater levels in the Cottingham area have caused flooding in the past, though this is just outside of Hull City Council. The Environment Agency is not aware of any recent examples of groundwater flooding within Hull City Council.
6.3.3 Flooding from Other Sources
Although records of flooding from other sources have been obtained as part of the research for this report, these records (summarised in table 6.2 below) should not be considered a complete record of such flooding.
Table 6.2. Records of localised flooding and sewer flood risk locations
Source Date Location Cause
Sutton Cross unknown Bransholme, around Noddle Hill Way/ This area apparently Drain Biggin Avenue/ Castlehill Road adjacent used to flood because the to Sutton Cross Drain. YWA pumps couldn't cope. Setting Dyke unknown Willerby Road/Wymersley Road area and Lack of maintenance of around the education centre, Coronation the trash screens and Road North near Setting Dyke. pumps. Setting Dyke Oct 2000 Localised flooding at Coronation Road. Blocked trash screens. Western Drain Oct 2000 Localised flooding at Astral Close. Blocked trash screens. Acre Heads Oct 2000 The Ridings (flooding contained by sand Rising levels in the drain. Drain bags). Holderness Oct 2000 Flooding of land around Carlam Hill. Overtopping at low points Drain in bank. Sutton Cross Oct 2000 Lapwing and Curlew Close on the High water levels in the Drain Brandsholme Estate (flooding contained flood locked Sutton Cross by sand bags). Drain.
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Source Date Location Cause
Pluvial/Drains 15 June WEST HULL: Boothferry Road, Beverley Heavy and sustained 2007 Road, Anlaby Road, The Paddock, rainfall overloading Meadowbank, Priory Road, Willerby drainage system. Road, Newland Avenue, Cleveland Street, Normanton Rise, Westborough Way, Anlaby Common, Springhead Avenue, Chanterlands Avenue, Nunburnholme Park, Willerby Road (near Yorkshire Water Museum). Pluvial/Drains 15 June EAST HULL: Holderness Road, John Heavy and sustained 2007 Newton Way, Mount Pleasant, Hedon rainfall overloading Road, Howdale Road. drainage system. Pluvial/Drains 15 June NORTH HULL: Kingswood. Heavy and sustained 2007 rainfall overloading drainage system. Pluvial/Drains 25 June WEST HULL: Wymersley Road, Heavy and sustained 2007 Moorhouse Road, Hotham Road South, rainfall overloading Hotham Drive, Wold Road, Coronation drainage system. Road South, Coronation Road North, Meltonby Avenue, Birdsall Avenue, Brantingham Walk, Priory Road, Fern Hill Road, Appleton Road, Sorrel Drive, Celandine Close, Springhead Avenue, Kendal Way, Hawkshead Green, Legarde Avenue, Malham Avenue, Ingleton Avenue, The Paddock, Hessle Road, Belgrave Drive, Calvert Lane, Dunston Road, Boothferry Road, Analby Road, Kirklands Road, St George’s Road, Bricknell Avenue, Northern Cemetery, Cottingham Road, Allotment and school playing field in Newland, Newland Avenue, Alexandra Road, Grafton Street, Lambert Street, De Grey Street, Pearson Park, Goddard Avenue, Ella Street, Victoria Street, Park Avenue, Westbourne Avenue, Prince’s Road, Chesnut Avenue, Bricknell Avenue, Chanterlands Avenue. Pluvial/Drains 25 June EAST HULL: Swan Street, Chapman Heavy and sustained 2007 Street, Lincoln Street, Holderness Road, rainfall overloading Hedon Road (at A1033 roundabout), The drainage system. Oval and Elm Avenue, Laburnam Avenue, Westcott Street and School, Marlowe Street, East Park sports centre,
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Source Date Location Cause
Stockholme Road, West Carr Lane, Peppleton Close, Corona Drive, Dorchester Road, Holwell Road, Southcoates Avenue, Exeter Grove, Biggin Avenue, Kestrel Avenue, Church Street, Robson Way, Howdale Road, Mallyan Close, Ramsgate Close, Dunvegan Road, Gleneagles Park, Frome Road, Waveney Road, Western Gailes Way, Shannon Road (south), Salthouse Road and Holderness Road (near Holderness Drain), Jervis Road, School off Barham Road, Bradford Avenue, Ecclesfield Avenue. Pluvial/Drains 25 June NORTH HULL: Courtway Road, Hall Heavy and sustained 2007 Road, Orchard Park Road, Thorpepark rainfall overloading Road, Ilthorpe, Homethorpe, Gorthorpe, drainage system. Easethorpe, Dodthorpe, 14th and 8th Avenue, Princess Elizabeth Playing Fields, Parkstone Road, Welwyn Park Drive, Knightly Way, Chevening Park, Runnymede Way, Bushey Park, Rouundabouts on Wawne Road, Hemble Way, Parcevall Drive, John Newton Way, Ashworthy Close, Cookbury Close, Bude Road, School off Bude Road, Bodmin Road, Tiverton Road, Blisland Close, Soffham Close, Hartland Close, Whitstone Close, Davidstow Close, Langtree Close, Cheltenham Avenue, Newtondale, Littondale, Stonesdale. Sewer Flooding Known Bankside, Hull. Overloaded sewer Risk system. Sewer Flooding Known Cleeve Road, Hedon. Overloaded sewer Risk system. Sewer Flooding Known Dane Park Road. Overloaded sewer Risk system. Sewer Flooding Known Downhill Drive, Bransholme. Overloaded sewer Risk system. Sewer Flooding Known Eppleworth Road, Cottingham. Overloaded sewer Risk system. Sewer Flooding Known Leadhills Way, Bransholme. Overloaded sewer Risk system.
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Source Date Location Cause
Sewer Flooding Known Middle Dike Lane, Cottingham. Overloaded sewer Risk system. Sewer Flooding Known Northumberland Avenue. Overloaded sewer Risk system. Sewer Flooding Known Peckforten Close, Bransholme. Overloaded sewer Risk system. Sewer Flooding Known Snuff Mill Lane, Cottingham. Overloaded sewer Risk system. Sewer Flooding Known Analby Road, Analby. Overloaded sewer Risk system. Sewer Flooding Known Noddle Hill Way, Bransholme. Overloaded sewer Risk system. Sewer Flooding Known Sancton Close, Cottingham. Overloaded sewer Risk system.
The above records of localised flooding and sewer flood risk locations have been digitised and are shown in figure 6.6. The specific locations along roads affected by the June 2007 flooding were provided by Hull City Council. However, flood depths for this flood event have yet to be ascertained.
The SFRA flood map (figure 6.7) shows the areas of localised flooding and sewer flooding overlaid on the PPS25 Flood Zones, so as to provide a comprehensive representation of all known flood risk areas.
Photos taken by Hull City Council of the 25th June 2007 flood event give an idea of the severity of the event and its impacts on properties and infrastructure (figures 6.8 to 6.11).
Figure 6.8. Flooding on roads (June 2007) Figure 6.9. Flooding on roads (June 2007)
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Figure 6.10. Flooding of properties (June 2007) Figure 6.11. Flooding of amenities (June 2007)
6.4 Flood Defence Standard
A review of the River Hull and Humber Strategies, which were made available for use on this SFRA by the Environment Agency, was carried out. The River Hull Strategy findings indicate that the current standard of protection of the River Hull defences through Kingston upon Hull is generally 200 years, assuming the Hull Barrier operates as intended. However, there are a small number of isolated low points in the flood defence where the standard of protection is below 25 years. The condition of the River Hull defences is summarised in section 7.1.
The Humber Strategy findings indicate that the current standard of protection of the Humber defences adjacent to Kingston upon Hull is generally 200 years, with the exceptions of Albert Dock East and St Andrews Quay West, where the standard of protection falls at some locations to five and 20 years respectively. The condition of the Humber defences is summarised in section 7.1.
6.5 Areas Where Development May Increase Flood Risk Elsewhere
Careful investigation of local flood risk is required at most locations in the SFRA area before development is allocated. It is not sufficient to assume that allocating development away from Flood Zones 2 and 3 and localised flooding areas and the use of Sustainable Drainage Systems (SUDS) techniques will automatically render flood risk to third parties adequately low irrespective of location (see section 10.4).
The Byelaw states that in areas immediately adjacent to the Humber frontage, i.e. within 8 metres of the Humber, no land should be allocated for any change in use irrespective of flood risk until sufficient land is reserved for necessary improvements to tidal defences, as proposed in Humber strategy. If this is not done, development of this land could increase flood risk elsewhere by compromising construction of essential tidal defence improvements.
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7 Flood Risk Management Measures
7.1 Flood Defences
7.1.1 River Hull
Existing defences on the River Hull consist of steel piling, timber wharfs, concrete walls and masonry walls within the city. The flood defence infrastructure on the River Hull is in a very variable condition; in some parts of the city the hard defences are in a poor condition (figure 7.1). It should be noted that defences in poor condition may not necessarily have a low standard of protection and vice versa.
A description and the implications of each defence condition are given in the National Sea and River Defence Surveys Condition Assessment Manual (Environment Agency, 2004) and is summarised in table 7.1 below.
Table 7.1. Descriptions of defence condition.
Condition Description Very Good In good condition, fully serviceable, no remedial work required. Maintenance to continue as present. No significant defect. Good Minor defects, non-urgent. Minor routine maintenance work required. In reasonable condition, some increase in maintenance needed, probably not more than 5% affected with slight defect. Fair Some cause for concern, requires careful monitoring. Significant maintenance works required. Average condition, some minor repairs needed and moderate 5% – 20% affected. Poor Structurally unsound now or in the near future. Major remedial works required or replacement (one to five years). Extensive repair required in short term. Extensive defect 20% – 50% affected. Very Poor Completely failed or derelict requires complete reconstruction. Major urgent repairs or replacement needed without delay to avoid failure probably beyond repair. Extensive defect >50%.
Responsibility for maintenance of the defences within the city is not clearly defined. The Kingston upon Hull Act 1984 provides Hull City Council with the power to enforce landowners to maintain flood defences to the statutory level. However, it is not easy to enforce owners to maintain the quality of the defences if they do not meet the required crest level. There have been incidences of overtopping within the city due to the poor repair of landowner maintained defences. The Environment Agency also has powers and responsibilities as the River Hull is a Main River.
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7.1.2 Humber
Within the city the defences consist of a mixture of vertical sea walls and concrete revetments. Some of the defences have been raised by the construction of new wave return walls along the length of the crest of the existing structure. To the west, the defences abruptly change from sea walls to natural marshland. Along this length Clive Sullivan Way is on a raised embankment and effectively forms the defence. This embankment extends to Hessle Haven, where it affords protection to Waterside Business Park. The defences here consist of an unprotected earth embankment. The defences are varied in age, with the original dock structures dating mainly from the late 19th Century and the early 20th. The area along the east side of St Andrews Quay was improved between 1997 and 1999. Whilst the new defences are in good condition, the original defences are generally in a poor condition. The area immediately to the west of the Hull Barrier consists of a mixture of different defences in poor condition. Part of the defence along this frontage is formed by the walls of various buildings and abandoned warehouses. The condition of the Humber defences shown in figure 7.1 is based on the latest NFCDD asset data held by the Environment Agency, which may not reflect the current condition of the defences as reported in the Humber Strategy (June 2005).
7.1.3 Hull Tidal Surge Barrier
The Hull Tidal Surge Barrier has been in operation since 1980 to prevent high sea levels caused by surge tides overwhelming river defences. It is approximately 30 metres wide and takes roughly 30 minutes to open or close. The Barrier is closed when a tidal level greater than 4.6 metres AOD is forecast. The reliability of the Barrier is reducing with age and a refurbishment of drive and control mechanisms is planned to be implemented by Environment Agency in 2008/9 to improve this. The highest tide in Hull since the Barrier was built was in late February 1990 when a level of 5.18 metres AOD was reached. There were two other tides around the 5.00 metres AOD mark in the same week. More recently, a North Sea tidal surge of approximately 1 metre occurred on the evening of 12 January 2005 resulting in a level at Hull of 4.85 metres AOD. The tidal event passed without significant flooding because of the Hull Tidal Surge Barrier.
7.2 Flood Forecasting and Flood Warning Systems
Weather systems and tidal events are forecast by Regional Flood Forecasting teams as well as by the Met Office and storm tidal warning service and passed on to local operatives who are on call 24 hours a day and monitor river and sea levels using telemetry. They use this information to operate pumping stations and the Hull Tidal Surge Barrier, as well as to issue flood warnings.
The Environment Agency operates an effective flood warning service within the study area in respect to main river flooding and tidal flooding from the sea. The flood warning system consists of the following codes, with the following meanings:
• Flood Watch - Flooding of low lying land and roads is expected. Be aware, be prepared, watch out!
• Flood Warning - Flooding of homes and businesses is expected. Act now!
• Severe Flood Warning - Severe flooding is expected. There is extreme danger to life and property. Act now!
• All Clear - Flood watches or warnings are no longer in force for this area.
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The Environment Agency operates a total of 24 overlapping flood warning areas within and immediately adjacent to Hull City Council. The principle warning areas are shown in figure 7.2. Within each of these areas a warning is disseminated by loudhailer, automated voice messaging (AVM) or media broadcast as well as on the Environment Agency web site and flood information telephone service ‘Floodline’ (08459 881188) in the event of a flood risk being identified. The warnings within the different flood warning areas are triggered by various different events including high river or sea levels, pumping station failure or the failure of the Hull Tidal Surge Barrier to close.
Currently none of the potential land allocations are being considered for other possible uses, such as flood risk management schemes (storage areas, raised walls, etc) by the Environment Agency or others.
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8 Guidance on the Application of the Sequential Test
8.1 Introduction
This chapter provides guidance on the application of the Sequential Test based on the advice provided by the Environment Agency.
8.2 First Step – Strategic Overview of Flood Risk for all Potential Areas
The recommended initial step is to determine the extents of potential land allocations in large scale maps showing the most up-to-date Flood Zones, in accordance with PPS25 (areas to be drawn in the SFRA Flood Maps). Summary tables of flood risk issues are then prepared for each location, indicating if the potential areas overlap Zones 2 or 3 or if there are records of previous flood incidents (based on the information provided by Hull City Council and discussions with the Environment Agency).
The localised flooding areas of the flood maps provide information on the main areas where flooding has occurred.
8.3 Second Step – Flood Risk Issues in Zone 1
The next step is to use the Flood Maps to analyse all potential sites within Zone 1 by identifying those that have any flood risk issues (for example those affected by other sources of flooding or those that do not have dry access/evacuation routes during flood events).
For the sites with flood risk issues, an assessment of likely significance of flood risk is then carried out in terms of likely probability of flooding and potential consequences/flood damages (advice from a drainage specialist may be required, such as the SFRA consultant, the Environment Agency, a highways drainage engineer and/or the planning authority drainage specialist). The purpose is to identify sites with significant flood risk - high probability of flooding and significant flood damages with deep flooding and high velocities, which could result in loss of property and potentially loss of life, and sites without dry access/evacuation routes during flood events.
If a site with significant flood risk is identified within Zone 1, this would be considered as if it was in the high probability Zone 3a, for further application of the Sequential Test in Zone 3a.
It is important to note that most potential sites that pass the Sequential Test in Zone 1 will still require FRAs. For development proposals on sites comprising one hectare or greater, the vulnerability to flooding from other sources (as well as from river and sea flooding) and the potential to increase flood risk elsewhere through the addition of hard surfaces and the effect of the new development on surface water runoff, should be incorporated in a FRA. This need only be brief unless the factors above or other local considerations require particular attention.
8.4 Third Step – Sequential Test in Zones 2 and 3
The third step is to sequentially allocate sites as described in section 4.3 and as part of a Sustainability Appraisal (SA). It is recommended that prior to incorporating the Sequential Test within the SA, the following actions take place:
• Apply the measure of avoidance/prevention (see section 4.5) by moving the boundaries of the potential sites away from Zones 2, 3a and 3b, for those cases where the loss of site
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area is acceptable. This is generally the case at locations where the loss in area is of the order of ten percent.
• Adopting provisionally land uses that are fully compatible with the vulnerability classification of PPS25, to try to avoid the need to apply the Exception Test where possible.
8.5 Relevance to Hull
The majority of Hull lies in Flood Zone 3 and therefore the Sequential Test, when applied between Flood Zones, is unlikely to identify sufficient development sites within Hull. The Sequential Test within Flood Zone 3 and the Exception Test will need to be applied where development is proposed within Flood Zone 3. The Level 1 SFRA will need to be followed by a Level 2 SFRA to provide the necessary information to enable the application of the Sequential Test within Flood Zone 3 and the Exception Test.
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9 Guidance for the preparation of Flood Risk Assessments
9.1 Introduction
A SFRA is a strategic document that provides an overview of flood risk throughout a study area. Flood Risk Assessments will be required for most proposed developments and the level of detail will depend on the existing level of flood risk in the site (see general FRA requirements for each Flood Zone in table D.1, PPS25 and further guidance in the Practice Guide Companion to PPS25).
It is imperative that site-based Flood Risk Assessments (FRAs) should be discussed early in the planning process and submitted as an integral part of the planning application. Planning applications seeking approval for development within flood affected areas can be regarded as invalid if not supported by a Flood Risk Assessment. The following section reflects best practice on what should be addressed within a FRA.
9.2 Proposed Development within Flood Zone 1
Within all areas, the risk of alternative sources of flooding (surface water, sewage, groundwater, etc) must be considered, and SUDS must be employed to ensure no worsening to existing flooding problems elsewhere within the area. Consideration should also be given to the retention of green space for infiltration.
The SFRA provides specific recommendations with respect to the provision of sustainable flood risk mitigation opportunities that will address both the risk to life and the residual risk of flooding to development within particular ‘Zones’ of the area. These recommendations should form the basis for the site-based FRA.
9.3 Proposed Development within Flood Zone 2
For all sites within medium probability Zone 2, a high level FRA should be prepared based upon readily available existing flooding information, sourced from the Environment Agency and information contained in this SFRA. It will be necessary to demonstrate that the residual risk of flooding to the property is effectively managed through, for example, the provision of raised floor levels and the provision of planned evacuation routes. Consideration should also be given to SUDS and the retention of green space for infiltration.
9.4 Proposed Developments within Flood Zone 3a
All FRAs supporting proposed development within high probability Zone 3a should include an assessment of the following:
• Provision of evidence to enable the local authority to apply the Sequential Test. This will require information outlining the sustainability reasons why the site should be developed over sites at lower risk of flooding. An indication whether other sites are reasonably available for this land use in lower risk Flood Zones is also required.
• Consideration of the vulnerability of use and the potential application of the Exception Test.
• The vulnerability of the development to flooding from other sources (for example surface water drainage, groundwater, etc) as well as from river/tidal flooding, which should be considered together under Integrated Urban Drainage (IUD). This will involve discussion
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with the planning authority, water company and the Environment Agency to confirm whether a localised risk of flooding exists at the proposed site.
• The vulnerability of the development to flooding over the lifetime of the development (including the potential impacts of climate change), for example maximum water levels, flow paths and flood extents within the property and surrounding area. The Environment Agency may have carried out detailed flood risk mapping within localised areas that could be used to underpin this assessment. Where available, this will be provided at a cost to the developer. Where detailed modelling is not available, hydraulic modelling using appropriate methods by suitably qualified specialists will be required to determine the risk of flooding to the site.
• The potential of the development to increase flood risk elsewhere through the addition of hard surfaces, the effect of the new development on surface water runoff, and the effect of the new development on depth and speed of flooding to adjacent and surrounding property. This will require a detailed assessment, to be carried out by suitably qualified specialists. Consideration should also be given to SUDS and the retention of green space for infiltration.
• A demonstration that residual risks of flooding (after existing and proposed flood management and mitigation measures are taken into account) are acceptable. Measures may include flood defences, flood resistant and resilient design, escape/evacuation, effective flood warning and Emergency Planning.
• Details of existing site levels, proposed site levels and proposed ground floor levels. All levels should be stated relevant to Ordnance Datum.
It is highlighted that all forms of flooding need to be considered as localised flooding may also occur, typically associated with local catchment runoff following intense rainfall. A localised risk of flooding must be considered as an integral part of the detailed Flood Risk Assessment.
It is essential that developers thoroughly review the existing and future structural integrity of formal and informal defences, if present, upon which the development will rely (over the lifetime of the development), and ensure that Emergency Planning measures are in place to minimise risk to life in the unlikely event of overtopping or defence failure.
9.5 Integrated Urban Drainage (IUD)
Integrated Urban Drainage should be considered by:
• Identifying causes of flooding in urban areas and considering the best ways of managing urban drainage to reduce flooding.
• Building effective partnerships between the various drainage authorities such as water companies, local authorities, Environment Agency, internal drainage boards and improving partnership working to find solutions to urban flooding problems.
• Using new approaches to reduce the future impact of urban flooding on people and the environment, including: use of models to identify where the water is coming from, surface water management plans, and effective management of stormwater through Sustainable Drainage Systems and above-ground flood routing.
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9.6 Raised Floor Levels and Basements
It is highlighted that many of those areas currently situated within low and medium probability Zones 1 and 2 could become part of the high probability Zone 3. This is important as it means that properties that are currently at relatively low risk will, in 20 to 100 years, assuming precautionary climate change impacts, be within high probability Zone 3a. It is imperative therefore that planning and development control decisions take due consideration of the potential risk of flooding in future years.
It is recommended that wherever possible, floor levels should be situated a minimum of 300 millimetres above the average ground level or adjacent road level, whichever is higher, or determined as an outcome of the site based FRA. Ground levels shall not be increased elsewhere on the site. The height that the floor level is raised above flood level is referred to as the ‘freeboard’, and is determined as a measure of the residual risks. Traditionally, fluvial flood defences have been designed on the basis of best estimates of design water level, with the final level of the flood defences incorporating a freeboard allowance of 300 millimetres for hard defences (flood walls), The developer, however, should always be aware of the sensitivity of design flood levels to inaccuracies in the estimation process and of the potential implications of any physical processes such as settlement and waves.
The use of basements within flood affected areas should be discouraged and habitable uses should not be permitted. Where basement use is permitted however, it is necessary to ensure that the basement access points are situated 300 millimetres above average ground level or adjacent road level, whichever is higher. The basement must have unimpeded access and be of waterproof construction to avoid seepage during flooding conditions. Habitable uses of basements within flood affected areas should not be permitted due to the potential dangers to life during a flood event.
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10 Guidance for the Application of Sustainable Drainage Systems
10.1 Introduction
PPS 1 “delivering Sustainable Development” and PPS25 require that LPAs should promote SUDS. LPAs should ensure policies encourage sustainable drainage practices in their Local Development Documents. SUDS is a term used to describe the various approaches that can be used to manage surface water drainage in a way that mimics the natural environment. The management of rainfall (surface water) is considered an essential element for reducing future flood risk to both the site and its surroundings. Indeed reducing the rate of discharge from urban sites to greenfield (undeveloped) runoff rates is one of the most effective ways of reducing and managing flood risk.
10.2 Types of SUDS Systems
SUDS may improve the sustainable management of water for a site by:
• Reducing peak flows to watercourses or sewers and potentially reducing the risk of flooding downstream;
• Reducing volumes of water flowing directly to watercourses or sewers from developed sites;
• Improving water quality, compared with conventional surface water sewers, by removing pollutants from diffuse pollutant sources;
• Reducing potable water demand through rainwater harvesting;
• Improving amenity through the provision of public open space and wildlife habitat; and
• Replicating natural drainage patterns, including the recharge of groundwater so that base flows are maintained.
Any reduction in the amount of water that originates from a given site is likely to be small. However, if applied across a catchment, the cumulative affect from a number of sites could be significant.
There are numerous different ways that SUDS can be incorporated into a development. The appropriate application of a SUDS scheme to a specific development is heavily dependent upon the topography and geology of the site and the surrounding areas. Careful consideration of the site characteristics is necessary to ensure the future sustainability of the adopted drainage system. The most commonly found components of a SUDS system are described below:
Pervious surfaces - Surfaces that allow inflow of rainwater into the underlying construction or soil.
Green roofs - Vegetated roofs that reduce the volume and rate of runoff and remove pollution.
Filter drains - Linear drains consisting of trenches filled with a permeable material, often with a perforated pipe in the base of the trench to assist drainage, to store and conduct water; they may also permit infiltration.
Filter strips - Vegetated areas of gently sloping ground designed to drain water evenly off impermeable areas and to filter out silt and other particulates.
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Swales - Shallow vegetated channels that conduct and retain water, and may also permit infiltration; the vegetation filters particulate matter.
Basins - Ponds and wetlands areas that may be utilised for surface runoff storage.
Infiltration devices - Sub-surface structures to promote the infiltration of surface water to ground. They can be trenches, basins or soakaways.
Bio-retention areas - Vegetated areas designed to collect and treat water before discharge via a piped system or infiltration to the ground.
Pipes and accessories - A series of conduits and their accessories, normally laid underground, that convey surface water to a suitable location for treatment and/or disposal (although sustainable, these techniques should be considered only where other SUDS techniques are not practicable).
For more guidance on SUDS, the following documents and websites are recommended as a starting point:
• PPS25
• Practice Guide Companion to PPS25
• Interim Code of Practice for Sustainable Drainage Systems, national SUDS working group, 2004
• Best practice guidance for Sustainable Drainage Systems from the Thames Region, providing a clear hierarchy for SUDS requirements at the planning application stage (available from the Environment Agency development control teams).
• www.ciria.org.uk/suds/
In addition to formal SUDS a number of other measures can be designed into new development to provide the same benefits as SUDS. These include the re-contouring of land levels to enable green spaces to hold rainwater thus reducing volumes of water flowing directly to watercourses or sewers. In addition the installation of water butts reduces the rainfall landing on roofs being conveyed directly to the sewers. The capacity of water butts is limited and their success in managing surface water is dependent on their use and maintenance by individuals.
10.3 Application of SUDS for the Proposed Allocation Sites
It is recommended that priority is given to the use of infiltration drainage techniques as opposed to discharging surface water to watercourses. Where infiltration techniques are not viable (due to a high water table, local impermeable soils, source protection Zones etc), discharging attenuated site runoff to watercourses is preferable to the use of sewers. The soil hydrological properties, based on the estimate of the standard percentage runoff from the Flood Estimation Handbook, suggest that the soils within the city are, in principle, are sufficiently permeable to allow the infiltration of surface runoff.
10.4 Effective application of SUDS techniques
Large increases in impermeable areas contribute to significant increases in surface runoff volumes and peak flows and could increase flood risk elsewhere unless adequate SUDS techniques are implemented.
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A critical situation could be that of building a new large development just upstream of an existing development which already suffers from frequent flooding. The correct SUDS technique could in this case, be to build large areas of pervious surfaces (pervious paving, etc) combined with infiltration and rainfall harvesting techniques. The use of large attenuation areas may not be the appropriate SUDS technique, as these attenuate peak flows but do not reduce flood volumes.
SUDS techniques will be required for most, if not all, proposed land allocations and planning applications must include due consideration of appropriate SUDS techniques. The attenuation to ‘greenfield’ (undeveloped condition) discharge should be the norm and the method adopted will depend on the individual circumstances. Developers should consult with the Environment Agency and Yorkshire Water at an early stage about their SUDS proposals, to ensure that they are adopting the most affective methods for their site.
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Separate Figures
Figure 1.1. Study Area
Figure 5.1. Modelled Watercourses
Figure 5.2. Ground Elevation Data Coverage
Figure 6.1. Soil Data
Figure 6.2. Existing Flood Zones
Figure 6.3. PPS25 Flood Zones
Figure 6.4. PPS25 Flood Zones with Climate Change
Figure 6.5. Historic River Flooding
Figure 6.6. Local Flooding
Figure 6.7. SFRA Flood Map
Figure 7.1. Flood Defence Condition
Figure 7.2. Flood Warning Areas
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Appendix A: Project Data Register
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50 Hull City Council SFRA Appendix A: Project data register Page 1 of 5
Type of Hard / Data_ID Category Name Notes / Description Version / date Data Author Data Owner File format File name / Drawing No. data Digital
1 Actual flood event data Recorded levels/flows 01/01/06 Environment Agency Environment Agency Tabular Digital Excel various
2 Actual flood event data Flood extents 25/10/05 Environment Agency Environment Agency GIS Digital SHP various
3 Actual flood event data Photographs 01/10/05 Various Various Photo Digital JPEG various
Agency have no data for 4 Actual flood event data Questionnaire responses Public Environment Agency Document Hull
Autumn 2000 Floods: Performance Review and Word 5 Actual flood event data 22/01/01 Environment Agency Environment Agency Document Digital Autumn2000Floods_EA_2001.doc Action Plan document
Agency have no data for 6 Actual flood event data Flooding History database Environment Agency Environment Agency Hull
7 Development info Planning applications See data items 82 to 91 01/03/07 Hull City Council Hull City Council GIS Digital SHP various
8 Development info Land bids See data items 82 to 91 01/03/07 Hull City Council Hull City Council GIS Digital SHP various
9 Development info Allocations See data items 82 to 91 01/03/07 Hull City Council Hull City Council GIS Digital SHP various
10 Development info Current Hull City Council Local Plans 01/05/00 Hull City Council Hull City Council Document Hard
11 Development info Hull city centre action plan sites 12/05/06 Hull City Council Hull City Council GIS Digital GIS SDAs2005.shp
City Centre Area Action Plan: Pre-submission Draft 12 Development info 01/06/06 Hull City Council Hull City Council Document Digital PDF various and Final Draft Supplementary Planning Documents
Environment Agency Consultation comments on the 13 Development info Environment Agency Hull City Council Document Digital PDF various City Centre Area Action Plan: Pre-submission Draft
14 Development info Hull Standing Advice spreadsheet 15/05/07 Environment Agency Hull City Council Tabular Digital Excel HullStandingAdvice_EA_2007
Have hard copy and GIS 15 Development info Hull Standing Advice planning maps 15/04/07 Environment Agency Hull City Council Drawing Hard Kingston upon Hull Planning Maps layers
The Town and Country Planning (Local TheTownAndCountryPlanningRegulations_TSO_ 16 Development info 01/01/04 Parliament The Stationary Office Document Digital HTML Development) (England) Regulations 2004 2004.htm
17 Flood defence Asset condition (fluvial) 01/08/06 Halcrow Environment Agency Document Digital SHP asset-condition.shp
Need to calculate this for 18 Flood defence Standard of Protection (fluvial) the Final Model with and 01/04/07 Halcrow Environment Agency Drawing Digital PDF various without freeboard.
19 Flood defence NFCDD (fluvial) 06/06/07 Environment Agency Environment Agency GIS Digital SHP various
See Humber Strategy 20 Flood defence Asset condition (tidal) 01/06/06 Halcrow Environment Agency Tabular Digital PDF various outputs
See Humber Strategy 21 Flood defence Standard of Protection (tidal) 01/06/06 Halcrow Environment Agency Tabular Digital PDF various outputs Hull City Council SFRA Appendix A: Project data register Page 2 of 5
Type of Hard / Data_ID Category Name Notes / Description Version / date Data Author Data Owner File format File name / Drawing No. data Digital
22 Flood defence NFCDD (tidal) 06/06/07 Environment Agency Environment Agency GIS Digital SHP various
flood_warning_areas_010k_Hull_cfmp_500m_pa 23 Flood defence Flood warning areas 01/10/05 Environment Agency Environment Agency GIS Digital SHP rt_in.shp
Consultation Document: Managing the Backbone of ManagingTheBackboneOfTheCity- 24 Flood defence 01/01/04 Environment Agency Environment Agency Document Digital PDF the City: River Hull Flood Defences in the City of Hull consultation_EA_2004.pdf
25 Flood Zone data Flood Zone 2 01/01/06 Environment Agency Environment Agency GIS Digital SHP NE_floodzone2_v3_3.shp
26 Flood Zone data Flood Zone 3 01/01/06 Environment Agency Environment Agency GIS Digital SHP NE_floodzone3_v3_3.shp
27 Flood Zone data Areas benefitting from defences 01/01/06 Environment Agency Environment Agency GIS Digital SHP NE_areasbenefit_v1_8.shp
NFCDD data (data items 28 Flood Zone data Defences 19 and 22) provides more 01/01/06 Environment Agency Environment Agency GIS Digital SHP NE_defences_v2_1.shp detail There are no flood storage 29 Flood Zone data Flood storage areas 01/01/06 Environment Agency Environment Agency GIS Digital SHP NE_fsa_v1_8.shp areas in Hull City Council
Geological and soil 30 Geological GIS data 01/10/05 Environment Agency Environment Agency GIS Digital SHP various information
Coverage for whole of Hull 31 Ground elevation data LiDAR 01/10/06 Environment Agency Environment Agency GIS Digital ESRI Grid various City Council
Coverage for whole of Hull 32 Ground elevation data SAR 01/10/05 Environment Agency Environment Agency GIS Digital ESRI Grid various City Council
Julie Dracup, 33 Ground water Hull and East Ridings CAMS Document 01/09/05 Environment Agency Document Digital PDF various Environment Agency
Hull Strategy data item 34 Ground water Groundwater Aspects: YORKMOD Review 01/05/97 Andrew Taylor, Halcrow Environment Agency Document Hard 404
SHP and 35 Ground water Groundwater GIS map 01/01/06 Environment Agency GIS Digital various JPEG
36 Hydrometric data Location of gauges 01/10/05 Environment Agency Environment Agency GIS Digital SHP various
37 Mapping OS 10,000 raster 07/06/07 Ordnance Survey Environment Agency GIS Digital TIF various
38 Mapping OS 25,000 raster 01/10/05 Ordnance Survey Environment Agency GIS Digital
39 Mapping OS 50,000 raster 07/06/07 Ordnance Survey Environment Agency GIS Digital TIF various
40 Mapping Ordinary watercourses 06/06/07 Environment Agency Environment Agency GIS Digital TAB / SHP Hull_SFRA_Reaches.shp
41 Mapping Main rivers 25/10/05 Environment Agency Environment Agency GIS Digital SHP NE_centrelines_v3_0.shp
42 Mapping Hull City Council boundary 12/03/07 Hull City Council Hull City Council GIS Digital SHP CITYBOUNDARY.shp Hull City Council SFRA Appendix A: Project data register Page 3 of 5
Type of Hard / Data_ID Category Name Notes / Description Version / date Data Author Data Owner File format File name / Drawing No. data Digital
Department for Department for Planning Policy Statement 25 - Development and 43 Policy 01/12/06 communities and local communities and local Document Digital PDF PlanningPolicyStatement25.pdf Flood Risk government government Department for Department for Development and Flood Risk: A Practice Guide 44 Policy 19/02/07 communities and local communities and local Document Digital PDF PPS25PracticeGuideCompanion_2007.pdf Companion to PPS25 'Living Draft' government government
Consultation Document: Planning Policy Statement: Department for Department for PlanningAndClimateChangeSupplementToPPS1- 45 Policy Planning and Climate Change: Supplement to 01/12/06 communities and local communities and local Document Digital PDF consultation_2006.pdf Planning Policy Statement 1 government government
Flood and Coastal Defence Appraisal Guidance: FCDPAG3_ClimateChangeImpactsNote_Defra_ 46 Policy FCDPAG3 Economic Appraisal: Supplementary note 01/10/06 DEFRA DEFRA Document Digital PDF 2006.pdf to Operating Authorities – Climate Change Impacts
47 Relevant Studies Humber FRM strategy report and relevant outputs 01/06/06 Halcrow Environment Agency Document Digital various various
48 Relevant Studies Hull FRM strategy report and relevant outputs 01/08/06 Halcrow Environment Agency Document Digital various various
Hull CFMP scoping stage report and relevant 49 Relevant Studies 01/08/06 Halcrow Environment Agency Document Digital various various outputs
Have both digital and an Word 50 Relevant Studies Hull Strategic Flood Risk Assessment (Draft) 01/08/04 Scott Wilson Hull City Council Document Digital Hull SFRA FINAL 31_08_04.doc original hard copy document Government Office for Regional Spatial Strategy for Yorkshire and the 51 Relevant Studies 01/12/04 Yorkshire and the The Stationary Office Document Digital PDF RegionalSpatialStrategy_TSO_2004.pdf Humber to 2016 Humber Strategic Flood Risk Assessment for East Riding of Hull Strategy data item East Riding of Yorkshire 52 Relevant Studies 01/01/02 Document Hard Yorkshire 181 Council
East Riding Integrated Coastal Zone Management East Riding of Yorkshire IntegratedCoastalZoneManagementPlan_ERYC 53 Relevant Studies 01/06/02 Document Digital PDF Plan: Towards a Sustainable Coast Council _2005.pdf
At Risk: Planning for Flood Risk in Yorkshire and the Yorkshire and Humber 54 Relevant Studies 01/01/04 Environment Agency Document Hard Humber Assembly Hull City Council and Joint Structure Plan for Kingston upon Hull and East 55 Relevant Studies 01/06/05 East Riding of Yorkshire Document Digital PDF JointStructurePlan_ERYC_2005.pdf Riding of Yorkshire Council Humber Estuary Shoreline Management Plan: 56 Relevant Studies 01/09/00 Environment Agency Document Digital PDF HumberEstuarySMP_EA_2000.pdf Planning for the Rising Tides
Coastal Flood Risk - Thinking for Tomorrow, Acting Association of British 57 Relevant Studies 01/11/06 Document Digital PDF CoastalFloodRisk_ABI_2006.pdf Today: Summary Report Insurers
Consultation Document: Humber Flood Risk 58 Relevant Studies 01/08/05 Environment Agency Document Digital PDF HumberFRMStrategy-consultation_EA_2005.pdf Management Strategy: Planning for the Rising Tides
59 Relevant Studies Inspectors Report on the Yorkshire and Humber Plan Not yet published due March 2007
60 Surface water Improvement scheme info Yorkshire Water Yorkshire Water
61 Surface water Capacity studies Yorkshire Water Yorkshire Water
62 Surface water Model / model results Yorkshire Water Yorkshire Water Hull City Council SFRA Appendix A: Project data register Page 4 of 5
Type of Hard / Data_ID Category Name Notes / Description Version / date Data Author Data Owner File format File name / Drawing No. data Digital
GIS shapefiles showing flooding locations 63 Surface water DG5 Flooding information 01/08/06 Yorkshire Water Yorkshire Water Document Digital SHP various generated by Halcrow 2006 using address data.
Obtained low level LiDAR 64 Topographic survey Road levels (A63) Carillion Highways Agency instead
Up to 300 year return 65 Water levels Extreme water levels for Humber Estuary 01/07/99 ABP ABP Tabular Digital Excel Time-varying-surge.xls period
SFRA Brief for Halcrow Consultancy Hull City Council's brief for Word 66 Project documents 15/03/07 Hull City Council Hull City Council Document Digital SFRA Brief Hull (Draftv2).doc this SFRA document Department for Improving The Flood Performance Of New Buildings - ImprovingTheFloodPerformanceOfNewBuildings 67 Flood defence 15/03/07 EA, DEFRA communities and local Document Digital PDF Flood Resilient Construction _2007.pdf government Halcrow proposal for this 68 Project documents Hull SFRA Proposal 01/05/07 Halcrow Halcrow Document Digital PDF various SFRA
source_protection_zones_50k.shp 69 Environmental Source protection zones 06/01/05 Environment Agency Environment Agency GIS Digital SHP source_protection_zones_indiv_50k.shp
70 Environmental Source protection locations 15/08/03 Environment Agency Environment Agency GIS Digital SHP source_protection_locations_50k.shp
71 Environmental Rigs 06/12/04 Environment Agency Environment Agency GIS Digital SHP rigs.shp
72 Environmental Authorised Landfill Sites 25/10/06 Environment Agency Environment Agency GIS Digital SHP Authorised_Landfill_Sites_010k.shp
73 Environmental Bathing waters 30/10/06 Environment Agency Environment Agency GIS Digital SHP bathing_waters_shp.shp
74 Environmental Consent Discharges 30/10/06 Environment Agency Environment Agency GIS Digital SHP Consent_Discharges_WIMS_ne.shp
75 Environmental GQA biology points 30/10/06 Environment Agency Environment Agency GIS Digital SHP gqa_biology_points_ne.shp
76 Environmental GQA chemistry points 30/10/06 Environment Agency Environment Agency GIS Digital SHP gqa_chemistry_points_ne.shp
77 Environmental GWV 30/10/06 Environment Agency Environment Agency GIS Digital SHP gwv_100k.shp
78 Environmental Licence Abstractions 30/10/06 Environment Agency Environment Agency GIS Digital SHP Licence_Abstractions_NaldPoint_ne.shp
79 Environmental OSPAR 30/10/06 Environment Agency Environment Agency GIS Digital SHP ospar.shp
80 Environmental Sampling sites 30/10/06 Environment Agency Environment Agency GIS Digital SHP Sampling_Sites_WIMS_ne.shp
81 Environmental Source protection zones 30/10/06 Environment Agency Environment Agency GIS Digital SHP souce_protection_zones_50k.shp
82 Development info Sites allocated for business and science park 12/03/07 Hull City Council Hull City Council GIS Digital SHP Allocated_for_business_and_science_park.shp
Allocated_for_employment_use_E3aii_E4_E12.s 83 Development info Allocated for employment use E3aii (E4 E12) 12/03/07 Hull City Council Hull City Council GIS Digital SHP hp Hull City Council SFRA Appendix A: Project data register Page 5 of 5
Type of Hard / Data_ID Category Name Notes / Description Version / date Data Author Data Owner File format File name / Drawing No. data Digital
84 Development info Area Development Framework 060504 04/05/07 Hull City Council Hull City Council GIS Digital SHP Area Development Framework 060504.shp
Committed_for_employment_use_E3ai_E4_E12. 85 Development info Sites committed for employment use E3ai (E4 E12) 12/03/07 Hull City Council Hull City Council GIS Digital SHP shp
86 Development info Employment sites 12/03/07 Hull City Council Hull City Council GIS Digital SHP employment.shp
Existing_areas_of_predominantly_employment_ 87 Development info Existing areas of predominantly employment uses 12/03/07 Hull City Council Hull City Council GIS Digital SHP uses.shp
88 Development info Existing port area E6 12/03/07 Hull City Council Hull City Council GIS Digital SHP Existing_port_area_E6.shp
89 Development info Housing Land 2007 Q3 12/03/07 Hull City Council Hull City Council GIS Digital SHP HousingLand2007Q3.shp
90 Development info SDAs 2005 12/05/06 Hull City Council Hull City Council GIS Digital SHP SDAs2005.shp
91 Development info Strategic employment location (E3b E12i) 12/03/07 Hull City Council Hull City Council GIS Digital SHP Strategic_employment_location_E3b_E12i.shp
North East Assembly Safe and dry: Towards a regional flood risk North East Assembly and 92 Policy 01/01/00 and Environment Document Digital PDF SafeAndDry_EAandNEA_2000.pdf assessment for the north east Environment Agency Agency Contains report, floodmap 93 Relevant Studies Old Fleet Drain flood mapping study 01/03/03 JBA Environment Agency Document Digital PDF various and photos
Coverage of Humber 94 Ground elevation data Low level LiDAR data for Humber 01/03/05 Environment Agency Environment Agency GIS Digital ascii grid various frontage
Coverage of river/channel 95 Ground elevation data Low level LiDAR data for Hull 01/02/06 Environment Agency Environment Agency GIS Digital ascii grid various cooridor Level 2 SFRA Level 2 SFRA Strategic Flood Risk Assessment Hull City Council
Level 2 SFRA
1 Background Information 1
1.1 Terms of Reference ...... 1 1.2 Planning Context...... 1 1.3 The Study Area ...... 1 1.4 Constraints on Development...... 2
2 Summary of Level 1 SFRA 3
3 Scope and Outputs 5
3.1 Scope of the Level 2 SFRA...... 5 3.2 Outputs from the Level 2 SFRA ...... 5
4 Existing Flood Defences 7
4.1 Condition ...... 7 4.2 Standard of Protection ...... 7 4.3 Tidal Surge Barrier...... 8 4.4 Likely Future Policy...... 8 4.5 Extent and Cost of Works ...... 8
5 Flooding With and Without Defences 13
5.1 Flooding Without Defences...... 13 5.2 Flooding With Defences (Overtopping)...... 13 5.3 Impacts of Climate Change...... 16 5.4 Areas Benefiting from Defences ...... 16 5.5 Failure of Hull Tidal Surge Barrier...... 16
6 Flooding with Defences (Breaches) 19
6.1 Breaches ...... 19 6.2 Breach Model and Locations ...... 19 6.3 Flood Hazard...... 20 6.4 Results ...... 20 6.5 Impacts of Climate Change...... 21
7 Surface Water Flood Risk 23
7.1 Introduction ...... 23
Strategic Flood Risk Assessment Hull City Council
7.2 Data Collection...... 23 7.3 Surface Water Modelling...... 23 7.4 Model Results ...... 24 7.5 Surface Water and Climate Change ...... 24 7.6 June 2007 Flood Event ...... 24 7.7 Surface Water Flood Risk Zones ...... 25 7.8 Recommendations ...... 25
8 Distribution of Flood Hazard 27
8.1 Introduction ...... 27 8.2 Development of Flood Hazard Zones ...... 27 8.3 Flood Hazard Zones...... 28 8.4 Climate Change ...... 29
9 Planning Guidance 31
9.1 Introduction ...... 31 9.2 Application of the Sequential and Exception Tests...... 31 9.3 Local Standing Advice...... 31
10 Recommendations 33
10.1 Introduction ...... 33 10.2 Policy Recommendations ...... 33 10.3 Development Control Recommendations ...... 42 10.4 Technical Recommendations...... 44
Separate Figures 47
Appendix A: Breach Modelling Detail 49
A.1 Breach Dimensions and Durations ...... 51 A.2 Breach Flows ...... 51 A.3 Flood Inundation Modelling (2d) ...... 51
Appendix B: Surface Water Modelling Detail 53
B.1 Deriving Inflows...... 55 B.2 Deriving Drainage Capacity ...... 55 B.3 Setting Up 2d Model...... 56 B.4 Setting Up Model Simulations...... 57
Strategic Flood Risk Assessment Hull City Council
B.5 Sensitivity Analyses ...... 58 B.6 Model Results ...... 59
Appendix C: Sequential Test and Exception Test Approach 61
Appendix D: Local Standing Advice Table 63
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Tables
Table 6.1. Flood hazard classification...... 20
Table 7.1. Classification of surface water flood risk...... 25
Table A.1 Environment Agency floodbank breach criteria (Environment Agency)...... 51
Table A.2. 2d cell sizes used for modelling breaches...... 52
Table B.1. Key model simulation parameters ...... 57
Figures within text
Figure 1.2 River Hull frontage
Figure 4.1 Poor condition defences
Figure 4.2 Good condition defences
Figure 4.4 Hull Tidal Surge Barrier
Figure 5.3 Flood extent and depth from overtopping of River Hull defences
Figure 7.1 Deriving surface water flow component
Figure 7.20 Surface water flooding in June 2007
Figure 10.1 River Hull frontage though the city
Figure 10.2 River Hull frontage adjacent to residential property
Figure 10.4 Narrow high street in Old Town
Figure 10.5 Aerial of flood storage park
Figure 10.6 View within flood storage park
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Separate Figures
Figure 1.1. Study Area
Figure 4.3. Standard of protection
Figure 5.1. SFRA Level 1 Flood Zones
Figure 5.2. SFRA Level 1 Flood Zones with climate change
Figure 5.4. PPS25 Flood Zones with defences
Figure 5.5. Flood depths with defences
Figure 5.6. PPS25 Flood Zones with defences with climate change
Figure 5.7. Flood depths with defences with climate change
Figure 5.8. Flood Zone 3a with and without defences
Figure 5.9. Impact of Hull Barrier failure
Figure 6.1. Flood depth for modelled breaches
Figure 6.2. Flood velocity for modelled breaches
Figure 6.3. Flood hazard for modelled breaches
Figure 7.2. Surface water model extent
Figure 7.3. Surface water model geometry
Figure 7.4. Sensitivity to roughness – 20% decrease
Figure 7.5. Sensitivity to roughness – 20% increase
Figure 7.6. Sensitivity to storm duration - 3hr storm
Figure 7.7. Sensitivity to storm duration - 12hr storm
Figure 7.8. Sensitivity to drainage capacity - no drainage capacity
Figure 7.9. Sensitivity to drainage capacity – 100% increase in drainage capacity
Figures 7.10 to 7.16. Surface water flood depth (theoretical flood events)
Figure 7.17 Surface water flood depth – 1% flood event with climate change
Figure 7.18 Surface water flood depth – 25th June 2007 event
Figure 7.19 Surface water flood risk zones
Figure 8.1 Flood Zones without surface water
Strategic Flood Risk Assessment Hull City Council
Figure 8.2 Flood Zones including surface water risk
Figure 10.3 Flood Zones including surface water risk with strategic development areas
Strategic Flood Risk Assessment Hull City Council
1 Background Information
1.1 Terms of Reference
In May 2007, Hull City Council commissioned Halcrow to produce a Strategic Flood Risk Assessment (SFRA) in accordance with Planning Policy Statement 25 (PPS25) Development and Flood Risk.
Advice on flood risk within the administrative boundary of the planning authority is required to support the preparation of the, Hull Development Framework and, in particular, the submission draft of the City Centre Area Action Plan, Core Strategy and other DPDs, in accordance with government guidance and the advice from the Environment Agency.
As the majority of the city of Kingston Upon Hull is at high risk of flooding, it was agreed that a Level 2 SFRA would be undertaken in addition to a Level 1 SFRA to provide the necessary information to enable a sequential approach to site allocation and the determination of planning applications to be adopted within the high risk area (Flood Zone 3).
1.2 Planning Context
This Level 2 SFRA, together with the Level 1 study conforms to National and Regional Planning Policy.
A SFRA is a living document which is used as a tool by a planning authority to assess all types of flood risk for spatial planning, producing development briefs, setting constraints, informing sustainability appraisals, identifying locations for emergency planning measures and requirements for flood risk assessment, and making planning decisions.
The success of the Strategic Flood Risk Assessment is heavily dependant upon a planning authority’s ability to implement the recommendations put forward for future sustainable flood risk management. It is ultimately their responsibility to establish robust policies that will ensure future sustainability with respect to flood risk.
A summary of National, Regional and Local Planning Policy in the context of flood risk is given in the Level 1 report.
1.3 The Study Area
Hull City lies on the north of the Humber estuary. The main watercourses within the city boundary include the River Hull, Beverley and Barmston Drain, and Holderness Drain (figure 1.1). The Beverley and Barmston Drain outfalls to the River Hull approximately 1.5 kilometres upstream of the Humber while the River Hull and Holderness Drain discharge to the Humber. The city comprises an area of some 7,150 hectares (71.5 kilometres squared) with a population of 250,000. The majority of the study area is urban with residential and commercial properties.
1 Strategic Flood Risk Assessment Hull City Council
Figure 1.2. River Hull frontage
1.4 Constraints on Development
The whole of the Humber Estuary, which abuts the southern boundary of Hull City Council, is designated at an international and national level (possible Special Area of Conservation; Special Protection Area; Ramsar site; and Site of Special Scientific Interest, SSSI) in recognition of its nature conservation importance.
Both the existing Environment Agency Flood Zone map and the new Flood Zones, produced as part of the Level 1 SFRA, indicate that the majority of the city has a high risk of fluvial and/or tidal flooding and consequently there is limited space within lower risk areas for future development.
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2 Summary of Level 1 SFRA
A Level 1 SFRA is defined in the Practice Guide Companion to PPS25 as the level that provides the necessary information for undertaking the Sequential Test, which is used to determine land uses that are compatible with the level of flood risk at each allocated development site within a Local Authority area.
Where the need to apply the Exception Test is identified, due to there being an insufficient number of suitably available sites for development within zones of lower flood risk, the scope of the SFRA is widened to a more detailed Level 2 study (this report).
The scope of the Level 1 study was to inform the plan-making process of the Core Strategy. The planning authorities will use this information to undertake the Sequential Test to identify general locations for development, formulate strategic policies and inform the City Council’s Emergency Plan. The study covers the area within the administrative boundaries of the City Council, shown in figure 1.1.
As part of the Level 1 study, new Flood Zones were produced, using the latest outputs from the River Hull Flood Risk Management (FRM) Strategy that were made available for use in this study. The new Flood Zones are considered more accurate than the existing Environment Agency Flood Zones as they are produced from recent detailed modelling results using more accurate ground level data and considering hydraulic effects and time-dependant processes. This enables greater confidence to be given to the Flood Zones during the application of the Sequential Test. Detailed modelling has also enabled greater confidence in the impacts of climate change on flooding in the city. The revision to the Flood Zones (not including surface water flood risk) will need to be reflected in the Environment Agency’s Flood Map and website updated accordingly.
The new Flood Zones were combined with information relating to flooding from other sources, such as localised pluvial and sewer flooding in order to create SFRA maps, which provide a comprehensive representation of all known flood risk areas. This SFRA map includes the roads that were confirmed as having flooded during the June 2007 event.
The Level 1 SFRA also provided guidance on the application of the Sequential Test, guidance on the preparation of Flood Risk Assessments (FRAs) and guidance on the application of Sustainable Drainage Systems (SUDS).
The findings from the Level 1 study show that the majority of land within Hull City Council currently has a high risk of flooding and therefore it is not possible to locate all development in Flood Zone 1 and 2. As a consequence, a Sequential Approach within Flood Zone 3 is required and where appropriate the Exception Test will need to be applied where development is proposed within high risk areas. The Level 1 study has therefore been followed by a Level 2 SFRA (this report) to provide the necessary information to enable the application of the Sequential Test and Exception Test within Flood Zones 3 for the allocations, DPD (Development Plan Documents) and AAPs (Area Action Plans). More detail on flood risk has been developed in this Level 2 study, in particular for the existing built-up areas where development will continue.
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3 Scope and Outputs
3.1 Scope of the Level 2 SFRA
The Level 2 SFRA must provide the necessary information to enable the application of the Sequential Test and Exception Test within Flood Zones 3 for the allocations, DPD (Development Plan Documents) and AAPs (Area Action Plans). This more detailed study should consider the detailed nature of the flood hazard taking account of the presence of flood risk management measures such as flood defences.
3.2 Outputs from the Level 2 SFRA
The specific outputs for this Level 2 SFRA are as follows:
i. Establish the standard of existing flood defences, including information on the likely return period, and any natural or man made barriers to reduce flood flow, including the Hull Tidal Surge Barrier;
ii. Advise on the potential costs of any new flood defence infrastructure that may be needed to raise the flood defence standard to 1% for fluvial and 0.5% for coastal/tidal defences throughout the city;
iii. Assess coastal, fluvial and other flood risk in the defined built-up areas of Hull, taking into account the effect of defences or topography and the likely frequency of such events;
iv. Assess flood risk in these areas having regard to the climate change scenarios in PPS25 annex B;
v. Assess the potential effect of flood defence failure such as bank breaching to establish areas of rapid inundation and the extent of flooding;
vi. Assess the impact of a failure of the River Hull Tidal Surge Barrier not operating during a high tide storm surge;
vii. Produce maps showing the impact of a range of flood events in terms of impact, speed of onset, depth and velocity and variance of flooding;
viii. Detailed map of Flood Zones 1, 2 and 3 across the plan area, with further refinement of Zone 3 to reflect agreed sub-categories;
ix. Develop a matrix/table which enables the application of the Sequential Test and Exception Test, building on the existing Local Standing Advice;
x. Identify the types of development appropriate within individual flood zones, including the measures that will need to be in place to make development acceptable. This will need to have regard to the Sequential Test, vulnerability of the use and the application of the Exception Test;
xi. Provide guidance on appropriate mitigation measures, including the likely applicability of different SUstainable Drainage Systems (SUDS) techniques for managing surface water run-off;
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xii. Provide guidance on the preparation of Flood Risk Assessments for development sites of varying risk across the flood zone; xiii. Provide direction on when the Environment Agency should be consulted in relation to development within the floodplain. This approach will build on the Local Standing Advice maps and will need to be agreed between Hull City Council and the Environment Agency. Reference will be required to table D2 within PPS25; xiv. In the light of this assessment, consider the need to amend/adapt the existing Environment Agency Local and National Standing Advice relating to the determination of planning applications; xv. Produce draft policy statements (for inclusion in the Local Development Framework) dealing with the need to minimise the risk of flooding.
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4 Existing Flood Defences
4.1 Condition
The condition of the existing River Hull and Humber defences is described and illustrated in the Level 1 SFRA report; a summary is given below.
The existing River Hull flood defences are in a very variable condition; in some parts of the city the hard defences are in a poor condition. The Kingston upon Hull Act 1984 provides Hull City Council with the power to enforce landowners to maintain flood defences to the statutory level. However, it is not easy to enforce owners to maintain the quality and/or the standard of protection of the defences. There have been incidences of overtopping within the city due to the poor repair of landowner maintained defences. The Environment Agency also has permissive powers as the River Hull is a Main River.
The existing Humber flood defences are varied in age, with the original dock structures dating mainly from the late 19th Century and the early 20th. The area along the east side of St Andrews Quay was improved between 1997 and 1999. Whilst the new defences are in good condition, the original defences are generally in a poor condition. The area immediately to the west of the Hull Tidal Surge Barrier consists of a mixture of different defences in poor condition. Part of the defence along this frontage is formed by the walls of various buildings and abandoned warehouses. The defences from Victoria Dock eastwards have also been improved and those at the Minerva Pier were improved in the 1980s.
Figure 4.1. Poor condition defences Figure 4.2. Good condition defences
4.2 Standard of Protection
A review of the River Hull and Humber Strategies, which were made available for use on this SFRA by the Environment Agency, was carried out. The River Hull FRM Strategy findings indicate that the current standard of protection of the existing River Hull defences through Kingston upon Hull is generally 0.5% (1 in 200 years), assuming the Hull Tidal Surge Barrier operates as intended. However, there are a small number of isolated low points in the flood defence where the standard of protection is below 50% (1 in 2 years).
The Humber Strategy findings indicate that the current standard of protection of the existing Humber defences adjacent to Kingston upon Hull is generally 1% to 0.5% (1 in 100-200 years), with the
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exceptions of Albert Dock East and St Andrews Quay West, where the standard of protection falls at some locations to 20% (1in 5 years) and 5% (1 in 20 years) respectively. The outer dock wall at Albert Dock East would overtop in an event with a return period of only 20% (1 in 5 years) and water would flow into the dock, which thus provides a greater standard of protection, about 5% (1 in 20 years), to the land behind the dock.
The current standard of protection of the existing River Hull and Humber flood defences is shown in figure 4.3.
4.3 Tidal Surge Barrier
The Hull Tidal Surge Barrier has been in operation since 1980 to prevent high sea levels caused by surge tides overwhelming river defences. It is approximately 30 metres wide and takes roughly 30 minutes to open or close. The Barrier is closed when a tidal level greater than 4.6 metres AOD is forecast. The reliability of the Barrier is reducing with age and a refurbishment of drive and control mechanisms is planned to be implemented in 2008/9 to improve this. The highest tide in Hull since the Barrier was built was in late February 1990 when a level of 5.18 metres AOD was reached. There were two other tides around the 5.00 metres AOD mark in the same week. More recently, a North Sea tidal surge of approximately one metre occurred on the evening of 12 January 2005 resulting in a level at Hull of 4.85 metres AOD. The tidal event passed without significant flooding because of the Hull Tidal Surge Barrier. Figure 4.4 Hull Tidal Surge Barrier
4.4 Likely Future Policy
The likely future policy for the River Hull flood defences through the city, as preliminary advised by the preferred River Hull FRM Strategy solution, is to maintain the flood defence levels to the statutory levels as defined in the Kingston upon Hull Act 1984. Assuming the Hull Tidal Surge Barrier continues to operate, this statutory defence level will provide a standard of protection of 1% (1 in 100 years).
The likely future policy for the Hull Tidal Surge Barrier, as preliminary advised by the River Hull FRM Strategy, is to continue to maintain and refurbish the Barrier, as necessary in order to continue to protect the city from tidal surge levels greater than 4.6 metres AOD.
The likely future policy for the Humber flood defences adjacent to Kingston Upon Hull, as advised by the preferred Humber Strategy option, is to provide a 0.5% (1 in 200 years) standard of protection.
4.5 Extent and Cost of Works
The extent and cost of works required have been obtained from the River Hull and Humber Strategies and are summarised below.
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4.5.1 River Hull (and the Beverley and Barmston and Holderness Drains)
The extent of works recommended in the River Hull FRM Strategy1 is to:
• Continue to maintain and repair flood defences through the city in order to sustain a standard of protection of 1% (1 in 100 years) for the next 100 years.
• Construct a flood defence embankment adjacent to the Bransholme area in the east of the city to provide the Bransholme area with a high standard of protection from flooding from the Holderness Drain.
The present value cost for the above work has been estimated at £60.59 million (not including any work to the Hull Tidal Surge Barrier).
4.5.2 Hull Tidal Surge Barrier
Continue to maintain and refurbish the Barrier, as necessary in order to continue to protect the city from tidal surge levels greater than 4.6 metres AOD. The present value cost for this work has been estimated at £7.8 million
4.5.3 Humber
The Humber defences adjacent to Kingston Upon Hull are included under Management Unit 2 (MU-2) of the Humber Strategy. This unit extends from North Ferriby in the west to Paull Village in the east and is separated into two Flood Cells (2/1 and 2/2). The present value costs over 100 years for MU-2 for the preferred option is approximately £30 million.
The proposed scheme for this frontage is described in the Project Appraisal Report and the Detailed Appraisal Reports that support the Humber Strategy2 and is reproduced below:
Improvement of the defences between the Hull Barrier and Victoria Pier to provide 0.5% (1 in 200 years) standard of protection comprise:
• Construction of a new concrete wall from a point of high land near to the Hull Tidal Surge Barrier along the western edge of an unused dry dock. This new wall runs through an area of derelict land and some of the existing structures will have to be demolished to make space for the new wall.
• Continuation of the new wall by raising the level of the existing seawall, from the derelict area along the existing alignment of the defence which is partially formed by the walls of existing office buildings. The walls of the office buildings will be strengthened to provide adequate protection against extreme storm events and shutters be provided to protect openings such as office windows.
• Refurbishment of the existing defences to improve condition and stability over a 50 year design life.
1 River Hull Flood Risk Management Strategy Phase 2 Report, Environment Agency, September 2007. 2 Flood Cell 2/2 Hull West Detailed Appraisal Report, Humber Estuary Flood Defence Strategy, Environment Agency, June 2005.
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• Replacement of a section of sheet piling to provide an improved condition and a design life of 50 years.
• Raise the level of the engineering brickwork wall along the existing alignment of defence along the southerly section of the frontage.
Improvement of the defences between St Andrews Quay and Albert Dock to provide 0.5% (1 in 200 years) standard of protection comprise:
• Raising of an existing embankment running from the edge of St Andrews Quay to high ground at Clive Sullivan Way. The defences will run along the western end of the retail park on St Andrews Quay, protecting the assets against outflanking of the defences.
• Construction of a new wave return wall along the crest of the existing defences at Albert Dock, running from the eastern end of the scheme completed in 1999 to the newly replaced lock gates at the entrance to Albert Dock.
• Refurbishment of the seaward face of the quay walls from St Andrews Quay to Albert Dock.
No immediate improvements are planned to the defences between Hedon Haven Clough and the east bank of the River Hull. The review of defence standards undertaken for the Key Issue Assessment showed that the standard of protection is satisfactory, and it was decided that works would not be needed on this frontage within the first 15years. However, further analysis of the existing standard of protection should be carried out during the next five years to establish when it may be necessary to improve these defences.
It has been assumed that works designed and implemented as part of the recommendations for the Humber Strategy will have a design life of 50 years, and as such a cost has been allowed for reconstruction/ refurbishment of the works 50 years after the initial implementation date. To account for the need for more robust structures due to climate change and seal level rise, and future increases in material costs, future rebuild costs have been increased by 30%.
Although the locally low standard of the defences and the value of property defended would suggest that the works should be included in the first five years of the strategy, discussions have to be held with Hull City Council to agree the alignment of the defences and the areas to be defended. Once such agreement has been reached, further work will have to be done on assessing the stability and strength of existing structures. Therefore it is considered prudent to assume that construction is undertaken in years six to ten of the strategy but that it could be brought forward if, during the course of those studies, there is found to be an urgent need for improvement. It is also possible that, if redevelopment of areas within the cell proceeds sooner, the flood defences could be improved as part of the redevelopment, possibly with a contribution from the developer.
The proposed scheme has no impact on the estuary processes. There will be no encroachment into the designated pSPA and pSAC areas and there is no opportunity for habitat creation. There should be no impact on the running of the docks or on the business parks. The defence alignment could be moved between the Hull Barrier and Victoria Pier at very little additional cost to provide further space for redevelopment. There would also be scope for redevelopment of the land at the west end of St Andrews Quay. In both these instances, it may be possible to obtain a contribution from the developer for improvement or realignment of the defences.
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4.5.4 Other Flood Defence Assets
In addition to the River Hull and Humber flood defences, the following assets within or adjacent to Hull City Council have a flood risk management aspect:
• Yorkshire Water surface water sewer system: provides drainage of surface water for urban areas within Hull.
• Beverley and North Holderness Internal Drainage Board drains: provides drainage for rural areas to the north of Hull City Council.
• Preston Internal Drainage Board drains: provides drainage for rural areas to the east of Hull City Council.
• Watercourses maintained by Hull City Council: provides drainage for urban and some rural areas within and adjacent to Hull and includes Sutton Cross Drain and Foredyke Stream.
Only limited information on the above assets has been made available for this study. Consequently, the condition, standard of protection and likely future policy for these assets is not included within this study.
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5 Flooding With and Without Defences
5.1 Flooding Without Defences
Flood Zones were produced in accordance with PPS25 as part of the Level 1 study and are based on theoretical predictions of flood extents without defences and without the Hull Tidal Surge Barrier (figure 5.1). For the “without defences” situation, the majority of the city is within Flood Zone 3, clearly showing the reliance of Hull on defences within the city. This is because the ground levels in the city are generally lower than the high tide level of the Humber, which influences levels on the floodplain when defences are removed.
Climate change impacts were modelled and Flood Zones that include an allowance for climate change i.e.are representative of 2105 were produced (figure 5.2). These indicate that flooding will increase in extent across the city, particularly in the south west of the city (Pickering area) and the eastern parts of the city (Summergangs area). Analysis of model results indicates that climate change could increase flood depths by between 0.3 and 1.5 metres across the city for Flood Zone 3, i.e. for the 1% fluvial and 0.5% tidal flood. The largest increases are predicted to occur to the south west of the city in the Anlaby Park area and in the western part of the city centre south of the A1105 road.
5.2 Flooding With Defences (Overtopping)
As specified in PPS25, this Level 2 study takes into account the beneficial effects of flood defences. Consequently, flood extents have been produced for the “with defences” situation.
Flooding behind defences can occur either as a result of:
• water levels rising to exceed the level of the defence (overtopping), or
• constructional failure of the defence, either in whole or in part (breach)
These mechanisms of flooding have been considered separately. Flooding from overtopping is described in section 5.2 (this section), with further detail in appendix A, whereas flooding from breaches is described in a separate main chapter (chapter 6) as it is more involved. The results from the overtopping scenario have been used to create equivalent Flood Zones for the “with defences” situation, while the results from the breach scenario have been used to help assess the distribution of flood risk (chapter 7).
5.2.1 Flood Inundation Modelling (1d)
The River Hull FRM Strategy model and model results have been used as the primary source of information for the production of flood maps throughout the study area. The flood extents produced are based on model results for flooding caused by overtopping of flood defences from the River Hull and from the Humber, these being modelled separately.
The “Preferred” Strategy solution, which is representative of the existing situation and includes current flood defences, was used to model flooding from the River Hull. This option includes the Hull Tidal Surge Barrier operating as intended.
As part of this SFRA, the River Hull FRM Strategy model was adapted to enable flooding from the Humber to be modelled. In order to model the “with defences” situation, defence levels were obtained from the Humber Strategy and used in the model to approximate the defence profile along the
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Humber frontage. The resulting flood extent was later post-processed to include the likely flow paths from tidal flooding from the Humber.
5.2.2 Flood Inundation Modelling (2d)
Flooding from overtopping of the River Hull defences was also simulated using more detailed 2d modelling techniques for three locations along the River Hull in order to better understand the likely flow paths and areas affected. Locations were chosen where the standard of protection was known to be low as follows:
• Right bank near Reservoir Road off Clough Road.
• Left and right bank adjacent to Lime Street and Wincolmlee between Scott Street Bridge and North Bridge.
• Right bank near the Museum just downstream of Drypool Bridge.
The Hull Strategy 1d hydraulic model representing the existing situation was used to model overtopping during a 1% flood. For each of the above locations, the overtopping flow was extracted from the relevant section of the modelled bank top in the 1d River Hull model and applied as a point source inflow within a 2d model. Using a 2d model rather than a 1d model enables flow paths and flood extents to be more accurately modelled, though this usually takes longer to set up and process.
The 2d model, having a cell size/resolution of 10 metres, was developed using TUFLOW 2d hydraulic modelling software (version 2006-06-BF) and is based on LiDAR ground elevation data. TUFLOW is more accurate than other 2d flood routing software, such as raster routing techniques, as it employs the full two-dimensional, depth averaged, momentum and continuity equations for free-surface flow.
The results from the 2d modelling indicate that flooding from overtopping of the Hull defences is only significant for the right bank adjacent to Wincolmlee due to low bank top levels. Predicted flood extent and depth for a 1% flood is shown in figure 5.3.
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Figure 5.3 Flood extent and depth from overtopping of River Hull defences
5.2.3 Flood Zones With Defences
In order to be able to compare flooding with and without defences, equivalent Flood Zones were produced for the “with defences” situation by modelling the same flood events that are used to define the PPS25 Flood Zones. These are the 1% flood (river) and 0.5% flood (sea) for Flood Zone 3a and 0.1% annual probability flood (river and sea) for Flood Zone 2.
The Hull Strategy 1d model representing the existing situation as opposed to the proposed strategy solution was used. The resulting Flood Zones with defences are shown in figure 5.4. These are primarily based on results from 1d hydrodynamic modelling and may not accurately represent flow paths in some locations. Predicted flood depths have also been output from the model for Flood Zone 3, i.e. for the 1% fluvial and 0.5% tidal flood, and are shown in figure 5.5. It should be noted that a nominal flood depth of 150 millimetres has been assumed for manually digitised flow paths, which have been added to supplement the 1d modelling results. It should also be noted that depths adjacent to Old Fleet Drain have been inferred from the Old Fleet Drain flood extents using ground elevation data.
The flooding predicted in the south west of Kingston Upon Hull is from the Humber overtopping the defences at Albert Dock. The flooding predicted in the Neat Marsh area is from Old Fleet Drain, while the flooding immediately to the south of this is from the Humber. The flooding predicted adjacent to the Bransholme area is from Holderness Drain. Flood extents and depths for the “with defences” situation are used to define flood hazard zones as described later in this report (chapter 8).
Considering the likely future policy and works for flood defences outlined in sections 4.4 and 4.5, flooding to urban areas within Hull City Council from overtopping of the River Hull, Holderness Drain and Humber would be prevented (up to the 1% flood) under the proposed strategy solutions.
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5.3 Impacts of Climate Change
Following PPS25 guidance on climate change impacts, which is taken from Defra, 2006 and is described more fully in the Level 1 report, the increase in river flow and total sea level rise between now and 2105 has been derived as:
• Increase in river flow to 2105: 20%
• Total sea level rise to 2105: 0.995 meters
These climate change impacts were then input into the model and used to produce model results and Flood Zones that include an allowance for climate change i.e. are representative of the year 2105 with current defences. The Flood Zones with defences and climate change (figure 5.6) show that extent of flooding will increase significantly across the city with climate change. The result is similar to the “no defences with climate change” scenario. Predicted flood depths have also been output from the model for Flood Zone 3, i.e. for the 1% fluvial and 0.5% tidal flood, and are shown in figure 5.7. It should be noted that a nominal flood depth of 150 millimetres has been assumed for manually digitised flow paths, which have been added to supplement the 1d modelling results.
Analysis of model results indicates that climate change could increase flood depths by between 0.1 and 1.5 metres across the city for Flood Zone 3, i.e. for the 1% fluvial and 0.5% tidal flood, assuming current defence levels. The largest increases are predicted to occur to the south west of the city in the Anlaby Park area and to the west of the city centre adjacent and to the north of the A1033.
However, under the preferred flood risk management options of the River Hull and Humber FRM Strategies, described in sections 4.4 and 4.5, the depths of flooding in the city would be significantly reduced. In this case, only a small area adjacent to Old Fleet Drain is predicted to flood to a depth greater than 0.6 metres. The impact of climate change when assessed alongside defence improvements illustrate the city will be protected for increases in sea level through the improvements in flood defences.
5.4 Areas Benefiting from Defences
Technically speaking, the entire study area benefits from flood defences. This is because areas that flood with defences present, e.g. from overtopping, would flood to a greater extent, experiencing greater flood depths and flood risk if defences were not present. However, for the purposes of this report, areas where 1% fluvial flooding and 0.5%t tidal flooding is completely prevented due to the presence of defences have been termed ‘areas benefiting from defences’. Areas benefiting from defences are therefore equivalent to the difference between Flood Zone 3 with defences and Flood Zone 3 without defences as illustrated by the light blue area in figure 5.8. This shows that most of Hull benefits from defences including areas of land up to 5 kilometres away from watercourses and the sea. It can therefore be concluded that flood defences are vital for protecting large areas of Hull from fluvial and tidal flooding.
5.5 Failure of Hull Tidal Surge Barrier
Although the Flood Zones without defences assume the Hull Tidal Surge Barrier fails to operate, it is necessary to model a Barrier failure for the “with defences” situation in order to understand the effects of a Barrier failure in isolation. As the Barrier only affects water levels on the River Hull, flooding from the Humber is not affected. Consequently, only flooding from the River Hull has been considered in assessing the affects of a Barrier failure.
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The hydraulic model for the “preferred” Hull Strategy solution scenario, which is representative of the existing situation and includes current flood defences, was modified to prevent the Barrier from operating. A 1% (1 in 100 years) tidal surge event as well as a 1% (1 in 100 years) combined tidal surge plus fluvial event were modelled and the results were used to create a flood extent for the barrier failure scenario. Figure 5.9 shows the 1% (1in 100 years) flood extent with and without a barrier failure. As can be seen from the figure, a barrier failure could cause flooding to large areas of Kingston Upon Hull in the City Centre, Riverside Industrial area, West Park, Sculcoates, Wilmington and Hedon Road areas. Initial calculations suggest that currently up to 17,000 properties could be affected in a 1% (1 in 100 years) return period flood. This number could increase to over 60,000 in the year 2105 when including allowances for climate change and no improvements to flood defences.
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6 Flooding with Defences (Breaches)
6.1 Breaches
Breaching of flood embankments is the principal cause of major flooding in lowland areas. An earth embankment may be breached as a direct result of overflowing. Overtopping of a bank, especially when concentrated over a short length of bank, results in a rapid flow of water down the back (landward) slope of the bank, which can easily cause erosion potentially leading to a breach and possible failure of the defence.
Experience shows that when a fluvial floodbank breaches, even if not by overtopping, it does so near the peak of the flood when the flow in the river and hence flood levels are at or near their maxima.
Detailed hydrological and hydraulic modelling of the river channel in question with its variable inflow, outflow, breach flow and water level, is necessary to determine the exact volume flowing through the breach. Even then, assumptions have to be made regarding the location, size and type of the breach itself.
Sea banks, often in exposed coastal locations, may be subject to a tremendous battering from wave action especially if, as is often the case, the tidal surge is accompanied by a severe storm. For this reason their seaward slopes are protected with rock armour or concrete facing. Under normal conditions coastal defences will be protected to some degree by a wide, gently sloping beach on which much wave energy will be dissipated before reaching the sea bank, but this may be completely submerged (and thus ineffective) at high tide. Wave action will therefore be at its most damaging at the peak of the surge tide when the bank is also under greatest hydraulic stress.
Since the shores of the Humber are relatively sheltered and not subject to the full impact of the North Sea, the tidal defences are not subject to the same extreme conditions to which tidal defences on an exposed coast are subject. Furthermore, in many places along the Humber Estuary banks there is a protective apron of saltmarsh on their seaward side though this too can be submerged by extremely high tides.
6.2 Breach Model and Locations
The results from the breach inundation modelling, described in this chapter, with more detail in appendix B, are intended to be used to help assess the distribution of flood risk across Flood Zone 3 (chapter 7). This is intended to enable a Sequential Approach to locating development within Flood Zone 3 and where appropriate the Exception Test. A limited number of breaches have been assessed as part of this Level 2 study. The locations of these have been chosen carefully so as to fulfil as many of the following criteria:
• provide a suitable spread of breach locations throughout the study area
• breaches located on left and right banks of the River Hull as well as the Humber defences
• breaches located where the defences are known to be in poor condition
• breaches located where the defences are known to provide a low standard of protection
• breaches located where a breach could have the largest impact, e.g. where adjacent ground levels are low, maximising the breach flow, volume and extent of flood waters
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Initial breach locations were provided to both Hull City Council and the Environment Agency for comment. The Agency recommended a number of alternative locations, which were then incorporated into the final breach location list. The final breach locations, a total of 14, are shown in figure 6.1.
6.3 Flood Hazard
In addition to flood depths and velocities, flood hazard has been calculated for each breach. The Flood Hazard has been calculated within the TUFLOW software using the UK Flood Hazard formula given in Defra’s ‘Flood Risks to People’ Guidance Document (2006) as follows:
Flood Hazard = flood depth (m) x [velocity (m/s) + 0.5] + DF
Where DF (Debris Factor) is dependent on land use, flood depth and velocity. For predominantly urban land use, DF = 0 for flood depths up to 0.25 metres and DF = 1 for flood depths over 0.25 metres. The flood hazard land use was defined as ‘urban’ for all areas in Hull City Council.
The following classification for flood hazard, as given by Defra, has been applied:
Table 6.1. Flood hazard classification
Indicative Flood Hazard Degree of Flood Description Depth Value Hazard Ranges Caution Up to 0.25 < 0.75 Low “Flood zone with shallow flowing metres water or deep standing water” Dangerous for some (i.e. children) Up to 0.5 0.75 – 1.25 Moderate “Danger: flood zone with deep or metres fast flowing water” Dangerous for most people 0.5 metres to 1.25 – 2.5 Severe “Danger: flood zone with deep 3.00 metres fast flowing water” Dangerous for all 0.5 metres to > 2.5 Extreme “Extreme danger: flood zone over 3.00 with deep fast flowing water” metres
6.4 Results
Grids (in ASCII format) of maximum flood depth, maximum flood velocity and maximum flood hazard were extracted from the TUFLOW results. These are shown in figures 6.1 to 6.3.
The results show that large areas of Hull would experience flood depths of over 0.5 metres and face a significant to extreme flood hazard from a defence breach. Flood velocities over 0.8ms-1 would be experienced close to the breach locations and at a number of isolated locations such as where the breach flow is constricted through a narrow flow path. In terms of flood depth and flood hazard, the worst affected areas are in the North of Hull, particularly the Kingswood and Bransholme areas,
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where the River Hull defences are embanked, producing a higher head of water and hence greater flows through the breaches here.
6.5 Impacts of Climate Change
A detailed 2d analysis of the impacts of climate change has not been carried out as part of this study due to time and budgetary restrictions. The SFRA needed to be completed in a timely manner to facilitate the submission of the CCAAP, to inform the development of the Core Strategy prior to consultation on the Issues and Options paper. In addition the SFRA is required to enable the application of the Sequential Test and Exception Test when determining planning applications. However, a qualitative assessment has been carried, which has indicated the following:
Climate change will significantly increase flood depths, velocities and hazard from breaches of both River Hull and Humber defences. Climate change will have the biggest impact for breaches of the tidal defences along the Humber. This is because peak River Hull water levels through the city will not increase as much as tidal Humber water levels assuming the Hull Barrier continues to operate, i.e. close during tidal surge events. When improvements in defence standards are considered the depths of flooding as a result of climate change are negligible due to the appropriate standard of flood defences across the city.
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7 Surface Water Flood Risk
7.1 Introduction
For the purpose of the SFRA there is a need to better understand the risk from surface water flooding and the performance of the urban drainage system during flood events. This section, with more detail in appendix C, outlines the simplified (conceptual) drainage/surface water modelling study that has been undertaken for Hull City Council SFRA, including data collection, methodology, assumptions, and results.
The impact on the results of the SFRA, in terms of the Flood Zones produced, are also discussed.
7.2 Data Collection
The following data was collected / made available for this study:
• Ordnance Survey 1:10,000 and 1:50,000 mapping data was obtained from Hull City Council.
• Ground elevation data in the form of filtered LiDAR data was obtained from the River Hull FRM Strategy (Environment Agency). The data represents a “bare earth” situation and does not include features such as buildings or tree canopies.
• Observed rainfall data (rain gauge data), which includes the June/July 2007 events was obtained from the Environment Agency.
• Design event rainfall data (theoretical rainfall data) was obtained for Kingston upon Hull from MicroDrainage Pluvius software.
• Yorkshire Water drainage/pumping capacity was obtained from table 6.1, the June 2007 floods in Hull (Interim Report by the Independent Review Body, 24th August 2007).
7.3 Surface Water Modelling
A simplified approach to surface water drainage has been assumed, as shown in figure 7.1. Detail on the surface water modelling including, deriving inflows, deriving drainage capacity, setting up the 2d model, model simulations and sensitivity analysis are included in appendix B.
Rainfall = X mm / minute
Surface Water flow = [X – 0.062] mm / minute
Drainage flow = 0.062 mm / minute
Infiltration = 0.000 mm / minute
Figure 7.1. Deriving surface water flow component
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7.4 Model Results
Maximum depth grids were extracted from the model results. Maximum depths are shown for each return period event (figures 7.10 to 7.16). The model results show that the areas at greatest risk, i.e. the areas where surface water flooding depths are greatest and most extensive are as follows:
• Rural area west of Willerby Carr Dike and to the north of Setting Dike, including the Education Centre and the Police Station.
• Residential area in west of city to the north of East Ella, which includes: Allotment Gardens off Calvert Road, Bristol Road, Shropshire and Warwickshire Close, Setting Dike.
• Residential area and college and playing fields to the south of Spring Bank West.
• Hessle in the south west.
• St Andrews Quay.
• Areas adjacent to Hedon Road, particularly near the A1033 and Holderness Drain.
• Schools and playing fields on the eastern edge of Hull City Council adjacent to Neat Marsh.
• Sutton area, particularly between Robson Way and Sutton Cross Drain.
• Rural areas in the north east of Hull adjacent to Wawne Drain and Holderness Drain.
• Kingswood area in the north of Hull.
7.5 Surface Water and Climate Change
A climate change simulation was carried out by applying a 20% increase in rainfall for the 1% flood. The results, shown in figure 7.17 indicate that flood depths would increase with climate change across the whole city, particular in those areas that are currently at greatest risk of surface water flooding, listed above. Comparing model results for the 1% flood shows that surface water flood depths will typically increase by 0.10 to 0.13 metres in these areas, though the increase will be over 0.25 metres in some isolated locations.
7.6 June 2007 Flood Event
In addition to theoretical flood events, the 25 June 2007 flood event was simulated. The maximum depth and flood extents results (figure 7.18) show general agreement with observations of surface water flooding collated by Hull City Council. The results also show that the flood depths and extents are generally greater than those for the 0.5%t theoretical flood. Investigation of observed and theoretical rainfall profiles and volumes indicates that the June 2007 event had Figure 7.20. Surface water flooding in June 2007 a greater total volume and a more rectangular profile than the 0.5%theoretical event. This indicates that either the June 2007 event was larger than the 0.5% theoretical event, i.e. had a return
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period of greater than 200 years, or the theoretical rainfall data from the Pluvius software is under- estimating rainfall for Hull. It is recommended that the Environment Agency’s estimation of return period for the June 2007 event is considered, when available, and used to adjust the theoretical rainfall data if and where appropriate.
7.7 Surface Water Flood Risk Zones
The areas predicted to be most at risk from surface water flooding, i.e. where surface water depths are high, were identified. This was carried out by applying the classification given in table 7.1 to the 0.5% surface water flood results from the model. This classification was agreed with Hull City Council, the Environment Agency and Yorkshire Water and is based on professional judgement and consideration to the mitigation levels for flooding. It was decided that the classification applied should be purely a function of depth as flow velocities for surface water flooding are low and surface water flood risk is primarily from flood depths as opposed to velocities.
Table 7.1. Classification of surface water flood risk
Flood Zone Definition Depth of Surface Water
FZ 3a (i) Flood Zone 3a low risk area 0.15 to 0.30 metres FZ 3a (ii) Flood Zone 3a medium risk area 0.30 to 0.60 metres FZ 3a (iii) Flood Zone 3a high risk area over 0.60 metres
The low, medium and high surface water flood risk areas were post-processed to remove isolated puddles and smooth the flood extent. These are shown in figure 7.19.
7.8 Recommendations
The simplified drainage/surface water modelling study that has been undertaken for this SFRA has enabled a better understanding of the risk from surface water flooding and the performance of the urban drainage system during flood events. The two main limitations of the model are the lack of detail regarding the underlying drainage system and the resolution of the 2d grid, which limits the detail and accuracy of model results.
It is recommended that a more detailed modelling study of surface water flood risk is undertaken for Hull if and when further information relating to the drainage system is collected from Yorkshire Water. Drainage system information that could be incorporated includes:
• Hydraulic model, e.g. InfoWorks CS model, of Yorkshire Water's foul, surface water and combined sewer network. If the full model is not available a comprehensive sewer asset database in GIS format would be adequate.
• Data showing the location of road gullies.
Any information made available by Yorkshire Water should be sourced and reviewed. If necessary, the data should be converted to a more suitable format, such as GIS, so that network capacity can be assessed spatially. An independent surface water sewer model could be developed if adequate data is available.
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Yorkshire Water data could be used to derive a drainage capacity grid that can be applied to the 2d model. This may require a detailed analysis of either a hydraulic model or a GIS asset database, depending on what data is provided.
It is recommended that a finer resolution 2d grid is used to enable greater accuracy and certainty of surface water flood depths and extents. A grid cell size of 10 metres would provide a greater level of detail though would extend model simulation times considerably and may not be practical when applied to the entire study area. Furthermore, it is recommended that any areas sensitive to development, such as strategic development areas, are modelled separately using a local high resolution model. Careful consideration should however be considered to the boundary conditions applied to such local models, specifically the flow entering and leaving the local model from other parts of the city.
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8 Distribution of Flood Hazard
8.1 Introduction
In order to identify areas of lower risk within the high-risk zone (Flood Zone 3), a ‘flood hazard zones’ context has been considered within Flood Zone 3. This builds on the suggested sub-categories for Zone 3 and considers flood depths, velocities and probability. Data provided by hydraulic models, described in previous chapters, has been used in the assessment of ‘hazard zones’ across Hull City Council. This method is based on an adaptation of the ‘consequence assessment’ approach.
Due to approximately 95% of Hull City Council's area being located within Flood Zones 2 and 3 there is a need to further refine the risk associated with land within Flood Zone 3 so that the Sequential and Exception Tests can be applied here. Flood Zone 3 (high risk zone) should be further refined to reflect the following categories:
• Flood Zone 3a (i): Low hazard zone (with appropriate defences and not unacceptable flood risk). Areas protected to the appropriate standard of protection where the consequence of the defences failing is unlikely to be life-threatening.
• Flood Zone 3a (ii): Medium hazard zone (with appropriate defences and not unacceptable flood risk). Areas protected to the appropriate standard of protection where the consequence of the defences failing is unlikely to be life-threatening but damages to properties may be significant.
• Flood Zone 3a (iii): High hazard zone (without appropriate defences or unacceptable flood risk). If a breach was to occur these are areas where there would be a threat of loss of life.
• Flood Zone 3b: Areas of Functional Floodplain are present adjacent to Holderness Drain in the Bransholme area. These are areas where water has to flow or be stored in times of flood.
These suggested sub-categories have been agreed following discussion with the Environment Agency to enable application of the principles of the Sequential and Exception Tests in these areas.
Within Flood Zone 3, further consideration has been given to the detailed nature of the flood hazard including factors such as impact, speed of onset, depth and velocity and variance of flooding, taking account of the presence and likely performance of flood risk management infrastructure.
8.2 Development of Flood Hazard Zones
The PPS25 Flood Zones, which include the above sub-categories of flood hazard have been developed using relevant flood modelling results. The following types of flooding have been considered and incorporated into the PPS25 Flood Zones:
• Tidal and Fluvial flooding without defences.
• Tidal and Fluvial flooding with defences (from overtopping of defences).
• Tidal and Fluvial flooding with defences (from breaching of defences).
• Surface Water Flooding.
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The basic Flood Zones 1, 2, 3a and 3b remain unchanged from the Level 1 SFRA, with the exception of the incorporation of the additional areas of low, medium and high surface water flooding risk that were identified as described in chapter 7. Flood Zone 3a has been split into low, medium and high flood hazard zones as follows:
High Hazard Zone
The high hazard zone (Flood Zone 3a (iii)) has been developed by including those areas that either have a high probability of flooding or have a severe consequence of flooding. The following areas are included:
• Areas within Flood Zone 3a with defences that have a predicted depth of over 0.6 metres.
• Areas that flood during the 4% flood, which are not within the Functional Floodplain, i.e. are developed areas. These areas have a relatively high probability of flooding.
• Areas having either a severe of extreme flood hazard from defence breaches (on both the River Hull and Humber).
• Areas that have a high risk of surface water flooding (depths over 0.6 metres).
Medium Hazard
The medium hazard zone (Flood Zone 3a (ii)) has been developed by including those areas that either have a moderate probability of flooding (1% fluvial; 0.5% tidal for a with defences situation) or have a moderate consequence of flooding (danger to some, e.g. children). The following areas are included:
• All areas within Flood Zone 3a with defences.
• Areas having a moderate flood hazard from defence breaches (on both the River Hull and Humber). A moderate flood hazard is described as having deep or fast flowing water.
• Areas that have a medium risk of surface water flooding (depths between 0.3 and 0.6 metres).
Low Hazard
The low hazard zone (Flood Zone 3a (i)) has been developed simply by including everything outside of the High and Medium hazard zones but within Flood Zone 3a (without defences). Areas that have a low risk of surface water flooding (depths between 0.15 and 0.3 metres) were then added.
8.3 Flood Hazard Zones
The updated PPS25 Flood Zones, produced as part of the Level 2 SFRA are shown for both with and without the surface water flood risk areas (figures 8.1 and 8.2). These show that additional medium (Flood Zone 3a (ii)) and high (Flood Zone 3a (iii)) flood risk areas have been identified due to surface water flood risk in the following areas:
• Rural area west of Willerby Carr Dike and to the north of Setting Dike, including the Education Centre and the Police Station.
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• Residential area in west of city to the north of East Ella, which includes: Allotment Gardens off Calvert Road, Bristol Road, Shropshire and Warwickshire Close, Setting Dike.
• Residential area to the south of Spring Bank West.
• Hessle in the south west.
• St Andrews Quay.
• Areas adjacent to Hedon Road, particularly near the A1033 and Holderness Drain.
• Schools and playing fields on the eastern edge of Hull City Council adjacent to Neat Marsh.
• Bransholme area near Sutton on Hull.
• Rural areas in the north east of Hull adjacent to Wawne Drain.
From the updated PPS25 Flood Zones, in can be seen that in some locations features such as roads and railway embankments define boundaries between Flood Zones 3a (i), (ii) and (iii). This is because these features will act as either partial or complete barriers to flood flows as indicated by hydraulic modelling and inspection of ground level information.
8.4 Climate Change
As a full quantitative assessment of climate change has not been carried out for all the analyses that have been used to develop Flood Zones 3a (ii) and 3a (iii), it is only possible to provide a qualitative assessment of climate change for these zones.
Climate change will increase the size of the high hazard zone so as to include all areas of functional floodplain with climate change (see figure 5.2) and an increased portion of Bransholme near Robson Way and Sutton Cross Drain.
Climate change will also increase flow rates and flood volumes from defence breaches due to increased river water levels. This will therefore increase the flood hazard associated with the defence breach thus increasing the size of both high and medium hazard zone adjacent to the River Hull and Humber. The impact from breaches is likely to be greater along the Humber defences than the River Hull defences because the increase in tidal Humber water levels will be greater than the increase in River Hull water level assuming the Hull Tidal Surge Barrier continues to operate. Consequently, large portions of land adjacent to the Humber, particularly in the west of the city, will likely fall into the high hazard zone.
The medium hazard zone will increase with climate change to cover most areas currently within the low hazard zone. This is primarily due to the increased flooding due to overtopping of the Humber defences as illustrated by the increase in size of Flood Zone 3a with defences (figures 5.4 and 5.6).
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9 Planning Guidance
9.1 Introduction
Guidance on the planning implications of the SFRA has been discussed throughout the SFRA process, between the city council, its consultants, the Environment Agency and Yorkshire Water. This has led to a greater understanding of the planning implications of flooding throughout the study process.
Aspects of the implications with reference to particular case studies were discussed at the SFRA Workshop held in August 2007. This event was attended by key stakeholders with a specific interest in flooding and/or regeneration issues in Hull. The event included a presentation on SFRA work to date and findings of the Level 1 report, and an introduction to associated flood risk strategy within the region (River Hull Flood Risk Management Strategy). Specific case studies (some of which were fictional for the purposes of the workshop) were discussed in groups, in order to begin to formulate practical policy approaches to flood risk in Hull.
The outcomes from these discussions are the Approach to the Sequential and Exception Tests and the Local Standing Advice, which have been provisionally agreed with the Environment Agency.
9.2 Application of the Sequential and Exception Tests
The findings of the SFRA enable the city to be split into flood hazard zones to facilitate the application of the Sequential and Exception Tests. Consideration has been given throughout the SFRA process on how to implement these tests within Hull City Council.
An explanation of the Sequential and Exception Tests and the circumstances in which they apply is contained in the Level 1 report. That document states that further information is required in the form of a Level 2 SFRA to enable the application of the Sequential and Exception Tests in Hull.
The City Council and the Environment Agency have developed an interim approach, pending the adoption of revised planning policy, based on the guidance contained in PPS25 but with a local perspective, to the application of the Sequential and Exception Tests in Hull. This is currently under development, and the latest version is included as appendix C. The agreed interim approach does not seek to deviate from PPS25 in any way - nor would such an approach be endorsed by the Environment Agency – but seeks to provide guidance and certainty to all involved in development in Hull given that the majority of the city is within a high flood risk zone.
It is recommended that the approach in appendix C is implemented, but that it will be continually revised and updated through discussion between the city council, the Environment Agency and Yorkshire Water to reflect the latest situation and current understanding in relation to flood risk and regeneration. The approach will also provide an up to date policy position in Hull, until the adoption of revised planning policy contained in the Hull Development Framework.
9.3 Local Standing Advice
Prior to the undertaking of the SFRA, the Environment Agency and Hull City Council jointly signed up to a Local Standing Advice Agreement, which indicated the level of consultation, FRA or works required to ensure that flood risk is appraised, managed and reduced.
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This agreement ensured a common approach to development in Hull, recognising the constraints of flooding in the city, enabling the City Council to maintain control of development control decisions in the city as per the agreed limitations set by the Environment Agency. The Agency, however, remains a key partner in dealing with flood risk in the city, and will continue to play an advisory role in strategic flood risk issues.
On the basis of the SFRA work, the Standing Advice Table and associated map have been updated to reflect the more precise flood hazard zones identified by the City Council’s consultants. The latest Local Standing Advice table is included in appendix D.
It is recommended that any updates or amendments to the SFRA maps are reflected in the Standing Advice Table, subject to agreement with the Environment Agency and the City Council.
Following on from the technical findings of the Level 1 and Level 2 assessments and the above approaches are the detailed policy findings, outlined in the following section.
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10 Recommendations
10.1 Introduction
Following the technical analysis and appraisal of issues further to the SFRA workshop, this section outlines the recommendations of the SFRA.
The recommendations are split into the following three themes: Policy, Development Control and Technical.
10.2 Policy Recommendations
SFRA01: The findings of the SFRA should be fed into the Hull Core Strategy and other associated Hull Development Framework Documents
In order to ensure a robust approach to flood risk appraisal, management and reduction, the findings of the SFRA need to be incorporated into Hull Development Framework Policy. This will ensure a holistic and robust approach to flood risk management, ensuring that the matter is taken into account at all stages of the planning process.
The findings of the SFRA (specifically the flood hazard maps) clearly demonstrate the level of flood hazard within the city. It will be for the Hull Development Framework to develop planning policy for the city that satisfy spatial/land use requirements whilst also reflecting the level of flood hazard.
Key issues identified by the SFRA include the relatively high level of flood risk that exists within the city, which will be a priority for future spatial planning in Hull. Further, the SFRA highlights the importance of defences to the city. The River Hull FRM Strategy considers the defences and climate change over the next 100 years and recommends (Environment Agency, October 2007) that the defences are maintained to sustain a high standard of protection throughout the city. Future policy should seek to address how defences will be maintained, and address how development can be accommodated. These issues are considered in greater detail in subsequent recommendations.
The City Council should endeavour to ensure that the findings of the SFRA feed into policy preparation and assessment, in consultation with the Government Office, and similarly is incorporated within existing draft planning policy.
Figure 10.1 River Hull frontage though the city Figure 10.2 River Hull frontage adjacent to
residential property
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SFRA02: The Hull Core Strategy should include a clear policy statement on flood risk in the city
Planning for flood risk is a significant issue for the city of Hull. In accordance with PPS12, the Core Strategy should set out the key spatial elements of the planning framework for the area and include core policies. All other development plan documents must be in conformity with it (PPS12, paragraph 2.9).
In setting out a spatial vision for the city, the City Council should incorporate a clear city-wide policy statement on flood risk, drawing on the flood hazard maps, to set a clear policy hierarchy on planning for flood risk. This should reflect the approach of current draft RSS (GOYH Proposed Changes, October 2007) which seeks pro-active management of flood risk through the reduction of causes of flooding to existing and future development, with allocations following a sequential approach in accordance with the findings of the SFRA.
It is recommended that a specific policy on flood risk is included within the Core Strategy. This should focus on ensuring that, where possible:
• Development is located in the lowest risk area;
• New development is flood-proofed to a satisfactory degree and does not increase flood risk elsewhere;
• Surface water is managed effectively on site;
• The City Council applies the sequential approach when determining planning applications;
• Greenspace (including informal greenspace) is utilised for flood storage where practicable.
These issues are considered in greater detail in the following recommendations. Site specific and other detail should then be included in subsequent development plan documents as they are prepared.
SFRA03: Linkages with other Flood Risk Management Strategies
The City Council should ensure that in developing and taking forward the findings of the SFRA it has regard to other developing strategies that consider flood risk management in the Hull and Humber area to ensure that wider concerns are reflected in Hull where appropriate.
The Hull and Coastal Streams Catchment Flood Management Plan (CFMP) is currently under production. On its completion, any relevant recommendations from that study should be incorporated within the SFRA as relevant.
The preferred River Hull Flood Risk Management Strategy (Environment Agency, October 2007) for the city area recommends the defences to be maintained and sustained to 1% (1 in 100 years) standard of protection over a 100 year period, taking into account climate change. An embankment adjacent to Bransholme is proposed enabling the green space to be used for flood water storage.
The study area of this SFRA extends beyond the Hull city limits, for example the Hessle area, and the modelling has considered the impact from this extended area on the city of Hull. However, these areas are not within the control of the City Council, and are marked in grey on the flood risk maps. The City Council should seek to agree an approach to verifying, mapping and managing flood risk
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from the East Riding with the East Riding of Yorkshire Council and ensure that this approach is embedded within the Hull SFRA and East Riding SFRA.
SFRA04: Flood Risk Guidance should be included in the City Centre Area Action Plan
The Hull City Centre Area Action Plan (CCAAP) is at an advanced stage of production, preceding the preparation of the Hull Core Strategy. The SFRA has found the CCAAP area to be predominantly in Flood Zone 3 (a iii) – high hazard.
The CCAAP should be amended as a matter of urgency, in advance of submission to the government office, to ensure that a planned approach to flood risk is embedded within the document, based on the recommendations of this report. This will include reviewing any associated documents, such as the Sustainability Appraisal, to ensure compliance with the SFRA recommendations.
The precise scope of the flood risk policy to be included in the CCAAP is not within the scope of this report. However, initial findings (based on the consultants work and the Strategic Flood Risk Assessment Workshop) have identified the following recommendations for inclusion:
• Highly Vulnerable development should be avoided in the High and Medium Flood Hazard Zones (all of the city centre);
• More Vulnerable development (refer to annex D of PPS25) should not be located on the ground floor (see recommendation R5 below);
• The CCAAP area (as indicated on the Flood Zone Maps figure 10.3) will be considered suitable for development, satisfying the Exception Test, due to the wider sustainability benefits of development in the city centre;
• Flood proofing and flood resilience should be incorporated in the overall design of any development (see SFRA12 below for further details),
• Access/egress points and specified refuge points at 5 metres AOD,
• Any proposals will need to demonstrate that emergency planning measures have been taken into account, secured in perpetuity through legal agreements where appropriate;
• Any particular requirements relating to flood risk and specific designations, such as the historic environment.
It is recognised that the Strategic Development Areas (SDAs) included within the CCAAP have specific design and development issues, which are subject to Supplementary Planning Documents (SPDs) providing detailed design guidance. Further design policy in relation to flood risk, as relevant and sympathetic to each SDA should be included within the SPDs. However, the City Council should be cautious of the approach of adopting the SPDs in order that they may Figure 10.4 Narrow high street in Old Town be used in advance of the formal adoption of the CCAAP, which on adoption will provide statutory guidance on planning for flood risk in the city.
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SFRA05: City centre development – appropriateness of development
As noted in the recommendation above, the SFRA identified the city of Hull as a whole being at a high risk of flooding. The application of the sequential approach alone would simply involve developing in lower risk sites, however due to the specific role of city centres in terms of service provision, jobs and housing development is still required. Particular care should be given to policy development for the city centre, which acts as a social, economic and regeneration hub, and functions as one of the Yorkshire and Humber region’s Regional Cities. National Planning Policy and Regional Planning Policy through the Regional Spatial Strategy (RSS) stipulate development should be focussed to city centre locations. Policy YH5 within the GOYH proposed modifications to the RSS states regional cities should be the prime focus for development. Policy HE1 also states the role of Hull should be transformed through remodelling the city centre to provide more and better jobs, shops, services, public spaces and homes. Given that the city centre meets the criteria of the Exception Test as a suitable area to develop for reasons of wider sustainability (as supported by higher order planning policy), provided development is designed to protect against the risk of flooding there is no requirement to apply the Sequential Approach and Exception Test on a site by site basis within the CCAAP provided the issues below are addressed within development proposals.
In line with other recommendations and the approach adopted in the guidance, the City Council should develop policies which comment on the appropriateness of Vulnerable uses (as defined in PPS25) in the city centre.
In particular, issues for consideration in this context include:
• Guidance on the suitability of land uses on the ground floor, as noted above, More vulnerable development (refer to annex D of PPS25) should not be located on the ground floor;
• Flood proofing and flood resilience should be incorporated in the overall design of any development, particularly so for mixed use and multi storey development;
• Any proposals will need to demonstrate that emergency planning measures have been designed into the scheme;
• The location and appropriateness of uses in terms of specific requirements, such as Disability Discrimination Act compliant access, impact on the historic environment, etc.
SFRA06: Flood Risk and Housing Market Renewal
The SFRA has identified the Housing Market Renewal (HMR) areas to be in a mix of Flood Zones (ranging from Zone 1 to Zone 3 (a iii) – high hazard).
The simple application of the Sequential Approach would involve developing in lower risk sites, however due to the specific role of Housing Market Renewal areas in terms of addressing areas of low housing the demand and the need to regenerate these areas with a variety of uses care should be given to their development. National Planning Policy and Regional Planning Policy through the RSS stipulate development should be focussed to regional cities. Policy YH5 within the GOYH proposed modifications to the RSS states regional cities should be the prime focus for development. Policy HE1 also states the role of Hull should be transformed through the transformation of residential areas to create a better mix of housing and quality environments. Policy HE1e also states housing
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development in the Hull strategic housing market area should be managed to reduce the amount of development in the East Riding and increase development in Hull over the plan period coordinated with the pathfinder programme for renewal. The two Housing Market Renewal Areas are indicated in figure 10.3. Given that the Housing Market Renewal areas meet the criteria of the Exception Test as a suitable area to develop for reasons of wider sustainability (as supported by higher order planning policy), provided development is designed to protect against the risk of flooding, there is no requirement to apply the sequential approach and Exception Test on a site by site basis.
The City Council should ensure that flood risk is considered as part of the spatial planning and regeneration of the Housing Market Renewal areas. The HMR areas should take account of the flood risk and adopt any measures necessary to ensure minimal risk to future communities, not just of the immediate area, but the wider community as a whole. The HMR areas will be subject to other flood management policy, as recommended in this report, and should therefore seek to incorporate flood proofing through design, take advantage of greenspace water storage where possible, and any other measures possible. Further, regeneration should aim to take place on brownfield sites in the first instance in accordance with wider sustainability policies, and where possible new development should seek to reduce run-off rates especially when developing brownfield sites.
The emerging Area Action Plans (AAPs) should include a policy on flood risk reflecting the recommendations of the SFRA to ensure that a planned approach to flood risk is embedded within the document.
SFRA07: The Functional Floodplain as identified in figure 6.2 should be protected from development to provide long term flood risk mitigation for the city
PPS25 defines the Functional Floodplain as the zone to which water will flow, or will store water during times of flood. The guidance states that only Water Compatible Development and/or Essential Infrastructure (refer to table D.2 of PPS25) should be permitted within this zone.
Whilst the fact that an area of Bransholme in Hull is identified as Functional Floodplain ensures its protection to a certain degree, the importance of the area in Bransholme in its capacity as the only flood storage area in Hull should be regarded as being of long-term importance to the city, having an essential role to play in the effective long term flood risk management of Hull.
Areas of Functional Floodplain and other areas of greenspace may also be suitable for tree planting to help draw water from the ground in times of high rainfall and help absorb rainfall. Consideration should be given to tree planting in functional floodplains and greenspace.
It is considered that as a result of the strategic importance of the area in Bransholme, as one of the few significant areas available within the city for flood storage and its location alongside the Holderness Drain, the area should be allocated for flood storage purposes and reserved for that purpose by Hull City Council.
The Functional Floodplain should be identified on the Hull Development Framework Proposals Map, corresponding with the policy statement on flood risk and development in the Core Strategy. The Functional Floodplain should be reviewed annually to ensure that it is still required for that purpose.
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SFRA08: Develop policy on Developer Contributions
Hull City Council should develop a policy on Developer Contributions, potentially based on a tariff or Planning Charge system to cover a variety of planning and infrastructure issues including flood defence and drainage infrastructure. The SFRA demonstrates that the majority of the city benefits from flood defences and drainage infrastructure and therefore a contribution to maintaining and improving existing defences, and the provision of new infrastructure would be justified.
Paragraph G4 of PPS25 states ‘in certain circumstances, to meet the wider aims of sustainable development, it may be necessary to permit development that require provision of flood risk management, including defence and mitigation works. Such provision will generally be funded by the developer, and is only acceptable provided it is consistent with the relevant flood risk management policies, passes the Sequential and Exception tests and does not have a significant adverse impact on flood flows or storage’. Paragraph G5 of PPS25 provides further guidance on the circumstances in which developer contributions should be sought.
Policy ENV1 of RSS for Yorkshire and Humber (GOYH Proposed Changes, October 2007) currently advocates that a region-wide approach to flood risk management reduces the causes of flooding to existing and future development. Development in high flood risk areas should be avoided where appropriate. The outcomes for this policy indicate that flood risk will be successfully managed by limiting development and providing suitable defences to existing property in vulnerable areas. The document cautions that RSS does not advocate providing defences to protect new development in flood risk areas, unless following the application of PPS25, there are no alternative lower flood risk sties (paragraph 15.5).
The Independent Review Body (IRB), which was commissioned to examine the key factors leading to the July flooding in Hull and recommend actions to improve flood prevention in the future, has made initial recommendations on the issue of flood prevention infrastructure. The final recommendations of the IRB which is due by the end of 2007 should be reflected in any policy relating to developer contributions, as relevant.
New developments within areas that have been identified as being at risk from surface water flooding must seek to manage and reduce flood risk. Contributions could be pooled for use on open spaces for use as washlands, general drainage improvements or balance tanks.
Any income received from such contributions should be used to fund any infrastructure identified as being required through the development plan process. Legal agreements should also be sought, where relevant, to secure the provision of any necessary mitigation works and future maintenance commitments.
SFRA09: Develop Flood Risk and Design Policy
Flood risk management, particularly in the highest risk zones, is likely to affect the design of new development. In certain cases, this could be non-invasive such as site layout, landscaped swales or re-profiling of a site to address flood risk management issues. However, in other cases, this could involve invasive design solutions and treatments to ensure that developments are flood resilient and/or resistant, such as the use of particular materials and/or flood exclusion measures (such as barriers to doorways).
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In Hull, the areas at highest risk of flooding, based on the findings of the SFRA, are in some cases also those with greatest design and conservation merit (such as the fruit market), or with the highest patronage on the basis of services, employment and facilities (the city centre).
The City Council will develop policy to address all aspects of flood risk management and design, from the non-invasive measures indicated above on how to minimise flood risk through site design, layout and SUstainable Urban Drainage Systems (SUDS), to the specific design issues relating to design- sensitive areas (including Conservation Areas and Listed Buildings) and disabled access in relation to raised floor levels. On small sites there are difficulties in providing the required length of ramp to meet DDA requirements due to maximum gradient stipulations of one in 12. For example, a 300 millimetres increase in floor level requires a 3.6 metre ramp and a 600 millimetre increase requires a 7.2 metre ramp excluding space for level access and level turning.
SFRA10: Consideration of a variety of development densities and quantities of hardstanding
The SFRA has identified that the majority of Hull is in a high flood hazard zone. In accordance with PPS25, attempts should be made to mitigate against flood risk as much as possible.
The City Council should consider any policy measures that could be incorporated within the Hull Development Framework to amplify flood risk management policy. Such measures should include the adoption of a variety of development densities (in terms of overall development footprint and areas of hardstanding) coupled with higher greenspace requirements to mitigate against flood risk by assisting with flood water storage to prevent unnecessary pressure on drainage infrastructure.
The City Council could adopt a range of housing densities, in accordance with PPS3, which vary across the city and reflect the level of flood risk/flood risk zones as well as the proposed development footprint, levels of hardstanding and proposed greenspace.
SFRA11: Consideration of surface water storage options
A key mitigation measure the City Council should consider is the potential increase of surface water storage.
Surface water storage options, such as the use of green spaces, car parks and school fields, can play a positive role in attenuating flood risk. Such areas should be identified within areas at high risk of surface water flooding. Any surface water storage areas must be at a relatively lower level. Such storage areas can then be used to attenuate the surface flood water, relieving pressure on the drainage network and diverting flood water from residential properties. Figure 10.5 Aerial of flood storage park
As mentioned above, public open space can play an important role in flood risk management by allowing flood water to attenuate in the storage area for slow release, thereby reducing pressure on the drainage system.
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The City Council should consider increasing public open space requirements for new developments to maximise the potential for such sustainable drainage to be incorporated in scheme design. Any policy statements that are developed to this effect should clearly outline the flood risk management benefits that would be derived. Such a requirement could be based on a range, reflecting the various levels of flood risk across the city and the design measures undertaken within the scheme to address flood risk.
Certain types of development can be considered as being particularly suitable for surface water storage, one issue explored during the course of the SFRA was that of school development, which is likely to be a development pressure for the city in the short term. It was generally agreed that such developments (categorised as More Vulnerable in PPS25) should be flood proofed by design. It was recognised that school playing fields allowed an opportunity for flood storage, and that flood waters should be held on site, the capacity of the storage area could be increased through re-profiling of land, to not only manage Figure 10.6 View within flood storage park but enable reduction of flood risk in the adjacent area. Schools could also be designed to be the designated Refuge Area, within the Emergency Plan, with places of safety above 5 metres AOD. Safe access routes to the refuge areas would also need to be identified.
Further study, with partner organisations, will be required to establish the size, type and location of surface water storage areas required. Measures which could be adopted to mitigate against surface water flooding include:
• Compensatory storage;
• Use of old watercourses;
• No increase in the development footprint;
• Reprofiling ground level to redirect flow away from property;
• Surface water run-off must be restricted to existing levels (no increase and reduction if possible);
• Positive alterations to flood paths to direct waters, through measures such as raised kerb heights.
Notwithstanding this, the City Council should seek to protect existing public open space, as well as private greenspace (such as private gardens) on the grounds of flood risk.
Where surface water management options are proposed consideration needs to be given to their adoption and maintenance and it is realised changes at the national level are required to ensure the adoption issue does not hinder the uptake of sustainable urban drainage systems.
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SFRA12: Flood proofing for all new development
The City Council should develop a flood proofing policy for the city, in consultation with key partners, including the Environment Agency, the insurance industry and developers. This should reflect any Local Standing Advice developed with the Environment Agency to date. This should refer to the latest flood proofing measures which could be incorporated in the development of sites – in effect a Hull Flood Standard.
Such flood proofing measures could be based on a zonal approach, reflecting the level of risk and the vulnerability of use, as defined on the Hull Flood Risk Maps and in PPS25. In developing flood proofing policy, the council should consider all sources of flood risk, in terms of external sources and flood risk within the site. Policy should therefore address the surface water drainage management of sites, including site re-profiling, sustainable drainage systems (porous paving, balance tanks, water butts) and specific design measures, such as flood resilience and resistance, including:
• An additional 300 millimetres flood proofing (as required by the Environment Agency) over and above any other requirements agreed through the Standing Advice Agreement;
• Electrical circuits lowered from the ceiling, raised sockets;
• Flood gates to doors;
• Air brick covers;
• Horizontal plaster boards;
• Damp proof membranes.
Any such guidance, or standard, should be the subject of continual review and updating to ensure it reflects the latest techniques and guidance. Further information is contained in ‘Improving the Flood Performance of New Buildings – Flood Resilient Construction’, Department of Communities and Local Government, May 2007 and www.ciria.org.
SFRA13: Minerals and Waste Policy
The City Council should seek to reflect the findings of the SFRA in the Hull and East Riding of Yorkshire Joint Minerals DPD, and Joint Waste DPD, to ensure a holistic approach to flood risk in connection with all land uses. The DPDs should take account of both the Hull SFRA and the East Riding SFRA.
SFRA14: Windfall sites
Windfall sites (i.e. sites which are not the subject of an allocation in an adopted development plan) should be considered against flood risk management policy, as outlined above.
Such sites, dependant on their location within the identified flood zone maps and the use, may need to be subject to the Sequential and Exception Tests, as relevant, and are likely to require site-specific flood risk assessments. See below for SFRA recommendations in respect of the Sequential and Exception Tests.
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10.3 Development Control Recommendations
SFRA15: Guidance on the application of the Sequential and Exception Tests
The Hull SFRA has identified that the majority of Hull has a relatively high risk of flooding. As a result, and in accordance with PPS25, the Sequential Test and Exception Tests will need to be applied to many proposed development schemes.
As mentioned in section 9, the City Council is in the process of developing an approach to the PPS25 requirements regarding the Sequential and Exception Tests, based on the approach identified in PPS25 and linked with the findings of the SFRA, in consultation with the Environment Agency.
It is recommended that a policy statement on the application of the Sequential and Exception Tests is included in the Hull Development Framework, and explicitly requires developers to approach the City Council and other key organisations to discuss issues as outlined above.
Further, the City Council’s Local Standing Advice agreement with the Environment Agency will provide further guidance and a local perspective on the application of flood risk policy.
As a result, it is recommended that the City Council encourage early dialogue and consultation between prospective applicants and key organisations including the City Council, the Environment Agency, Yorkshire Water and other statutory bodies and organisations as relevant, to discuss flood risk issues, including the scope of site-specific Flood Risk Assessments (FRAs), in particular design, flood risk and attenuation issues, along with guidance on the application of the Sequential and Exception Tests.
The interim approach, as contained in appendix C, and should be updated and refined during the development of the Hull Development Framework.
SFRA16: Develop the Local Standing Advice table
The Local Standing Advice table, which reflects the agreement between the City Council and the Environment Agency, should be amended to reflect the findings of this SFRA and PPS25. This should refer to the circumstances in which the Environment Agency will be consulted on applications, in addition also when Yorkshire Water should be consulted on applications, as well as any requirements for flood proofing, floor level requirements and the scope of site specific FRAs.
The Local Standing Advice agreement table provides clarity to prospective applicants and developers to the approach the City Council is adopting in managing flood risk. As a publicly available document its wider circulation should be beneficial in working towards a common approach to development and flood risk.
The Local Standing Advice Agreement table forms part of the SFRA, and should be subject to review and updating on a regular basis.
SFRA17: Removal of permitted development rights in high hazard areas
The findings of the SFRA indicate that the majority of Hull is at relatively high risk of flooding, and PPS25 comments on the vulnerability of land uses (see annex D of PPS25). In light of the potential risk to vulnerable land uses from flooding in the high hazard areas, the City Council should consider whether permitted development rights permitted by the Town and Country Planning (General
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Permitted Development ) Order 1995 for certain types of householder development should be removed.
This would include controlling the loss of urban greenspace (private gardens) and conversions for living accommodation at basement/ground floor level, which would thereby not increase, possibly reduce flood risk to the area and avoid flood risk to people respectively.
This could be achieved through the implementation of an Article 4 Direction, or the application of a local bylaw.
At a minimum, the scope of any such direction or bylaw should apply to those areas at highest risk, as identified on the flood risk maps. However, in view of the fact that adjacent development could increase run-off to areas already at high risk of flooding, the City Council may wish to endorse a wider exclusion area to ensure that risks are minimised.
SFRA18: Location of Development Types
The SFRA shows that the majority of the city is in Flood Zone 3. It will therefore not always be possible to focus More Vulnerable development (as defined in PPS25) outside of Flood Zone 3. The historic development pattern of Hull has led to concentrations of particular types of land use in the city. For example, the River Hull corridor and Humber frontage historically host industrial and commercial land uses. However, as shown on the flood risk maps, these locations – being adjacent to main rivers – are at the highest risk of flooding.
PPS25 categorises such employment uses as Less Vulnerable, suitable in all flood risk zones (see table D.3 of PPS25). Given the likely competition for land between More/Highly Vulnerable development within Hull, Less Vulnerable uses should be directed to higher risk sites, or should at least be required at ground floor level in the high hazard locations. Such an approach would lower risk to the vulnerable uses and would help to safeguard land at lower risks of flooding for more vulnerable development such as housing, hospitals and residential institutions
Similarly, More/Highly Vulnerable development should be steered towards the lowest risk area possible. For example, an ambulance station (Highly Vulnerable) should be located in the lowest risk flood zone, Flood Zone 1, in accordance with PPS25. However, if this is not possible, for overriding reasons such as call/response times, alternative sites in other Flood Zones (in accordance with the sequential approach advocated by PPS25) should be considered. If such a situation occurs, it is likely that increased flood protection (flood resilience and flood resistances) measures will be required to protect strategic infrastructure, such as emergency services command centres, which should be reflected in the standing advice table.
The City Council should therefore seek to steer Highly Vulnerable and More Vulnerable development to the lowest risk locations on the grounds of flood risk where possible. However, flood risk should not stifle regeneration, and the loss of land that currently hosts less vulnerable uses to development of a more vulnerable classification, such as ground floor residential should be avoided where possible. However, where mixed-use regeneration schemes are proposed provided the less vulnerable uses are located on the ground floor and more vulnerable uses are at a first floor level this would be supported.
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This approach should be reflected in the Hull Standing Advice table, which is being developed. The City Council should work with its regeneration and development partners, including Hull Citybuild and Gateway to address the implications of regeneration and flood risk.
SFRA19: Emergency Planning and Evacuation Routes
Hull City Council should incorporate the findings of the SFRA within the Emergency Plan for the City of Hull, in consultation with its key stakeholders. This should specifically identify strategic evacuation routes (‘red routes’) to enable emergency services to continue work during a flood event. The flood risk of key command centres and emergency facilities, and the adequacy of the level of protection which they are afforded, should be assessed using this SFRA.
The Emergency Plan should identify key strategic locations for protection in flooding emergencies, and the locations of refuge areas which are capable of remaining operational during flood events. Based on the findings of this SFRA, there may be some works required, e.g. road raising, to enable the implementation of the Emergency Plan.
Any such approach should consider the findings of the IRB final report. Legal agreements should be sought where necessary to ensure that any maintenance requirements are carried forward in perpetuity.
10.4 Technical Recommendations
SFRA20: Surface Water Management Plan (SWMP) required
The SFRA incorporates flood risk from surface water flooding using a rudimentary 2-D surface water drainage model. This should be developed to more accurately identify areas that are at risk from surface water flooding, and be reflected in the policy approach for those areas.
A SWMP (or similar) should be developed to work towards solutions to urban flooding, developed in partnership with East Riding of Yorkshire Council and other key partners, including Yorkshire Water, and the Environment Agency to ensure integrated working.
SFRA21: Working in Partnership
The SFRA process has involved Hull City Council working in partnership with the Environment Agency, Yorkshire Water, East Riding of Yorkshire Council and Defra. This partnership working must continue, along with sharing of knowledge and information on a continual basis, to ensure the SFRA and any subsequent flood risk management policy is based on the latest and best information available, with mutual agreement with partners in its implementation.
Any partnership working arrangements should reflect the findings of the IRB where relevant.
SFRA22: SFRA Review
The SFRA is a working document and should be subject to rolling review, to ensure that new guidance and data is incorporated within the study. Issues which could trigger a review include the availability of new modelling data, occurrence of a major flood event occurs, revised DCLG advice issued, change to the preferred River Hull FRM Strategy, any significant planning issues arising, etc.
The data the SFRA is based on is detailed in the Level 1 SFRA appendix A, Project Data Register. This should be reviewed regularly to identify any updates or additional data available.
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In any event, review should be undertaken at least every two years or to tie in with the development and review of the Core Strategy, or as required by key stakeholders responsible for flood risk management.
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Separate Figures
Figure 1.1. Study Area
Figure 4.3. Standard of protection
Figure 5.1. SFRA Level 1 Flood Zones
Figure 5.2. SFRA Level 1 Flood Zones with climate change
Figure 5.4. PPS25 Flood Zones with defences
Figure 5.5. Flood depths with defences
Figure 5.6. PPS25 Flood Zones with defences with climate change
Figure 5.7. Flood depths with defences with climate change
Figure 5.8. Flood Zone 3a with and without defences
Figure 5.9. Impact of Hull Barrier failure
Figure 6.1. Flood depth for modelled breaches
Figure 6.2. Flood velocity for modelled breaches
Figure 6.3. Flood hazard for modelled breaches
Figure 7.2. Surface water model extent
Figure 7.3. Surface water model geometry
Figure 7.4. Sensitivity to roughness – 20% decrease
Figure 7.5. Sensitivity to roughness – 20% increase
Figure 7.6. Sensitivity to storm duration - 3hr storm
Figure 7.7. Sensitivity to storm duration - 12hr storm
Figure 7.8. Sensitivity to drainage capacity - no drainage capacity
Figure 7.9. Sensitivity to drainage capacity – 100% increase in drainage capacity
Figures 7.10 to 7.16. Surface water flood depth (theoretical flood events)
Figure 7.17 Surface water flood depth – 1% flood event with climate change
Figure 7.18 Surface water flood depth – 25th June 2007 event
Figure 7.19 Surface water flood risk zones
Figure 8.1 Flood Zones without surface water
47 Strategic Flood Risk Assessment Hull City Council
Figure 8.2 Flood Zones including surface water risk
Figure 10.3 Flood Zones including surface water risk with strategic development areas
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Appendix A: Breach Modelling Detail
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50 Strategic Flood Risk Assessment Hull City Council
A.1 Breach Dimensions and Durations
The length of a breach and the time taken for a breach to be sealed can have a major effect on the extent and depth of flooding. Previous studies were based on standard times to repair breaches in flood defences, which the Environment Agency's Lincoln office considered attainable. These are given in table A.1.
Table A.1 Environment Agency floodbank breach criteria (Environment Agency).
Location of Defence Defence Type Width of Breach (m) Duration of Breach (hrs)
Earth Bank 200 72
Coastal Hard 50 36
Sluice Sluice width 24
Earth Bank 50 36 Tidal River Hard 20 18
Earth Bank 40 30 Fluvial Hard 20 18
The dimensions and duration of a breach depend upon a number of factors:
• ground levels along adjacent land
• defence type
• location of defence
Ground levels along adjacent land determine the ultimate crest level of the breached defence; these have been assessed using LiDAR ground elevation data.
A.2 Breach Flows
Breach flows have been obtained from the 1d River Hull model by modelling separate breaches of the defences during a 100 year flood event. Tidal, fluvial and combined fluvial plus tidal events were simulated and the maximum breach flow/volume was selected. The timing of the breach was set so that the breach is fully formed at maximum river water level.
Breach flow hydrographs from the 1d model are given at the end of this appendix.
A.3 Flood Inundation Modelling (2d)
In order to accurately model flood inundation from breaching of the defences it has been necessary to use 2d modelling techniques as 1d modelling cannot adequately represent the flow paths and
51 Strategic Flood Risk Assessment Hull City Council
velocities arising from breaches. The 14 breaches along the River Hull and Humber flood defences have therefore been modelled using TUFLOW 2d hydraulic modelling software (version 2006-06-BF). TUFLOW is more accurate than other 2d flood routing software, such as raster routing techniques, as it employs the full two-dimensional, depth averaged, momentum and continuity equations for free- surface flow and is therefore better able to represent the rapid inundation that can arise from a breach. Each breach was modelled individually, without consideration of multiple breaches. The location of the breach point source flow was always along a boundary of the 2d domain, as the breached defence was assumed to be a boundary preventing any flow out of the floodplain back into the watercourse.
To model flow across a floodplain, the spatial domain in which the flow occurs needs to be defined. This domain comprises of ground elevation data. A 2d domain was defined for each breach and overtopping scenario. As the extent of the flooding was uncertain, the extent of the 2d domain had to be estimated for initial runs, and modified based on the results. Where flood extents intersected the boundary of the 2d domain, the 2d domain would be extended to ensure that the boundary of the domain would not obstruct flow. However flood defences were used as boundaries to the 2d domains. The defences were therefore assumed not to overtop.
The 2d domain is divided into a regular square grid. Flow and water level in the floodplain is computed at each grid cell. The number of grid cells therefore affects the number of computations that have to be undertaken, the time taken to run the model, and the size of the result files. Furthermore, the grid cell size affects the model timestep required for stability. Smaller grid cells require smaller computational timesteps, which therefore increase the model run time further. For the larger breach scenarios a larger grid cell size was used to allow for practical model run times. The grid cell size used for each breach is given in table A.2 below.
Table A.2. 2d cell sizes used for modelling breaches
Breach location 1 2 3 4 5 6 7 8 9 10 11 12 13 14
2d cell size (m) 25 25 25 25 5 5 5 5 5 10 10 10 10 25
The elevation of each grid cell was extracted from a Digital Terrain Model (DTM), which comprises LiDAR data obtained from the Environment Agency. Additional model geometry features such as ridges and gullies/flow constrictions were then incorporated into the model for breaches one, three and four in order to better define barriers to the flow (such as embankments) and flow paths where these features are not adequately represented on the 25 metres resolution 2d grid.
A Manning’s n roughness value of 0.03 was applied to all the 2d domains. This value was chosen to represent the wide range of roughnesses that can be expected in an urban area. All individual buildings were incorporated into the 2d model by assigning a Manning’s n roughness value of 1.0 to all building areas. This has the effect of representing the major obstruction caused by a building but also enables the flood storage capacity of a building to be modelled. This task was automated by converting the buildings on the OS 1:10,000 map into polygons using GIS software. It should be noted that the impact of individual buildings and flow paths between buildings is not accurately modelled when the 2d cell size is larger than 5 metres.
52 Appendix A1.1: Breach flows (high)
80.0 Breach 1 Breach 2 Breach 3 70.0 Breach 10 Breach 11 Breach 12 Breach 14 60.0
50.0 ) s / 3 m (
w o
l 40.0 f
h c a e r B
30.0
20.0
10.0
0.0 0 10 20 30 40 50 60 70 80 90 100
Time (hours) Appendix A1.2: Breach flows (medium)
20.0 Breach 4
18.0 Breach 9
Breach 13 16.0
14.0
12.0 ) s / 3 m (
w o
l 10.0 f
h c a e r B 8.0
6.0
4.0
2.0
0.0 0 10 20 30 40 50 60 70 80 90 100
Time (hours) Appendix A1.3: Breach flows (low)
1.4 Breach 5
Breach 6
1.2 Breach 7 Breach 8
1.0 ) s /
3 0.8 m (
w o l f
h c a e
r 0.6 B
0.4
0.2
0.0 0 10 20 30 40 50 60 70 80 90 100
Time (hours) Strategic Flood Risk Assessment Hull City Council
Appendix B: Surface Water Modelling Detail
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54 Strategic Flood Risk Assessment Hull City Council
B.1 Deriving Inflows
From discussion with Halcrow drainage specialists, MicroDrainage Pluvius software has been identified as being most appropriate for deriving the design event (theoretical) rainfall data for each return period. This is because the software uses historic Met Office rainfall data for the Kingston upon Hull area and is able to extrapolate large return period events using the Flood Studies Report (FSR) methodology, which is generally more appropriate than Flood Estimation Handbook (FEH) for urban situations. Pluvius rainfall profiles have been generated for a range of storm durations for the 50%, 20%, 10%, 4%, 2%, 1%, and 0.5% floods; these are shown at the end of this appendix.
A critical storm duration of six hours was selected to provide a compromise between the theoretical worst case scenario of very short duration, very high intensity storms (e.g. 30 minute duration; over 200 millimetres/hour peak intensity) and observed storms such as June/July 2007 events, which had durations of approximately 12 and 18 hours. Furthermore, due to the Hull city catchment area being very large and flat, the time of concentration (Tc) is likely to be long:
• Tc = Longest drainage length / Velocity
• = 10,000 m / 0.5m/s
• = 20,000 seconds = 5.6 hours.
The rainfall data output from Pluvius was applied in the TUFLOW model directly as a depth of water per time interval to every cell in the 2d model extent. Separate rainfall boundaries were set up for urban and rural areas so that the urban rainfall boundary could be modified to take into account the underlying drainage capacity of the Yorkshire Water system. Rainfall boundary data was set up for each flood event modelled.
A rainfall boundary was also derived for the June/July 2007 flood event using the raingauge data provided by the Environment Agency. The Great Culvert raingauge was selected as being most appropriate due to it’s proximity to the city.
B.2 Deriving Drainage Capacity
It is assumed that all water falling into Hull’s Yorkshire Water drainage system is pumped into the River Hull or Humber.
Pumping capacity of the Hull catchment (2005 to present) = 62.4 m3/s *
* Source: Table 6.1, The June 2007 floods in Hull (Interim Report by the Independent Review Body, 24th August 2007).
It should be noted that tidal (Humber) water levels have no impact on drainage capacity as drainage waters are over-pumped into the Humber. Consequently, the above pumping capacity is assumed to be constant for all tidal conditions.
In order to be applied to the 2d model effectively, this pumping capacity needs to be converted to equivalent mm/minute so that it can be subtracted from the rainfall falling on the catchment.
As there is currently no evidence available to suggest otherwise, it is assumed that inlets into Hull’s pumped Yorkshire Water drainage system are only present in the urban area of Hull City Council (excluding open watercourses). Consequently, it is assumed that rain falling on urban areas of Hull
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City Council is able to enter the drainage system directly. It is assumed that rain falling on rural areas in or around Hull City Council is not able to enter the drainage system directly but will either pond in the rural areas or flow into an urban area where it can then enter the drainage system.
Total Hull City Council urban area = Hull City Council area - rural areas within Hull City Council.
Total Hull City Council urban area = 7174 Ha - 1109 Ha = 6065 Ha = 60.65 km2
From the above, the equivalent flow of the drainage system can be calculated as follows:
Equivalent flow = 62.4 x 1000 / (60.65 x 1000,000) = 0.00103 mm/sec = 0.062 mm/minute. This value is subtracted from the rainfall falling on the urban areas of the catchment to provide the net Surface Water flow component, i.e. rainfall that does not immediately drain into the Yorkshire Water system (figure 7.1).
The sensitivity of drainage capacity on surface water flood depths has been investigated and is described later on in this report (section B.5).
B.3 Setting Up 2d Model
A suitable model extent was first selected (figure 7.2). In order to model flooding to areas within Hull City Council from rain falling outside Hull City Council, the model extends 1 kilometre beyond the Hull City Council boundary. The model also extends further into the rural area south of Cottingham in order to represent overland flow and to some extent, flow from drains, from the Wolds where the ground starts to rise. Areas of land drained by Cottingham Drain, Setting Dyke and Bilton Drain are included.
A basic 2d model was set up using the ground elevation data using TUFLOW 2d hydraulic modelling software (version 2006-06-BF). This involved setting up an appropriate 2d grid located over the study area having a resolution (or cell spacing) of 25 metres.
Mapping data was then used to identify areas of urban and rural land use in the model extent. These were then digitised and an appropriate Manning’s n roughness value was ascribed to each type of land use as follows:
• Rural areas: n = 0.04
• Urban areas: n = 0.03
All individual buildings were incorporated into the 2d model by assigning a Manning’s n roughness value of 1.0 to all building areas. This has the effect of representing the major obstruction caused by a building but also enables the flood storage capacity of a building to be modelled. This task was automated by converting the buildings on the OS 1:10,000 map into polygons using GIS software.
Additional model geometry features such as ridges and gullies/flow constrictions were then incorporated into the model in order to better define barriers to the flow (such as the River Hull embankments) and flow paths where these features are not adequately represented on the 25 metres resolution DTM. These are shown in figure 7.3. A total of 42 ridges and 50 flow constrictions were incorporated, enabling the following flow paths to be represented:
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• flow under fly-overs
• flow under road and rain bridges
• flow along setting dike
• flow through underpasses and subways and the following flow barriers to be represented:
• roads that are slightly raised above adjacent ground levels
• embankments
B.4 Setting Up Model Simulations
Model control files were set up to run each observed and theoretical flood event to be modelled as well as for the various sensitivity analyses described later on. These control files define the location of model geometry and boundary conditions data as well as specifying model simulation parameters such as start and end times, timestep, initial conditions, output options etc.
The key model simulation parameter values chosen are described and justified in table B.1 below.
Table B.1. Key model simulation parameters
Parameter Value Comment
The rainfall boundary is applied at zero hours; Start time (hours) 0 consequently 2d flow is modelled from zero hours. 24 Flow is simulated for an additional 18 hours after the End time (hours) (35 for the June rainfall event finishes allowing surface water to stop 2007 event) flowing and ponding. Timestep in seconds should be somewhere between ¼ to ½ of the 2d cell size in metres. A timestep of 7.5 Timestep (seconds) 7.5 seconds was found to provide model stability and practical model simulation times. The following results are output: Water depth (m) Map Output Data d h V q F ZUK0 Water level (m AOD) Types ZUK1 Velocity (m/s) Unit flow (m3/s/m) UK Flood Hazard Start Map Output 0 Start outputting results from zero hours. (hours) Results are output (in grid format) every 900 seconds (15 Map Output Interval 900 minutes). In addition to the 15-minute output, maximum values are Store Maximums ON MAXIMUMS output. The maximum values are those of every timestep, and Minimums ONLY not those just at the output data times.
Cell Wet/Dry Depth 0.0003 Direct rainfall models should utilise very small wet/dry depths to minimise mass errors that can arise from cells
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Parameter Value Comment frequently wetting and drying with larger wet/dry depths. Cell Side Wet/Dry The cell side wet/dry depth should be half to two-thirds of 0.0002 Depth the cell wet/dry depth. Sets the default settings to those used in the previous PRE 2007-07- defaults release as these provided greater stability for direct AA rainfall in the Hull model. Required for direct rainfall modelling where very small rainfall depths are added to 2d cells. If four byte reals are Double Precision ON being used, arithmetic errors and large mass errors can occur. This effectively sets the initial water level to ground level. This is required because the default value is 0 metres Set IWL -5.0 AOD and there are significant areas of land near Bransholme where the ground level is below 0 metres AOD. This provides a higher resolution sampling of material values compared with just sampling at the cell centres. Bed Resistance INTERROGATE This higher resolution sampling is particularly useful in Cell Sides modelling urban areas where frequent and large changes in Manning’s n occurs. This offers much faster processing for assigning values Inside Region METHOD B to 2d cells or cell mid-sides that fall within a polygon using commands that process polygons.
B.5 Sensitivity Analyses
In order to understand the impacts of the modelling assumptions used, the sensitivity of flood depths and extents was assessed for the following parameters:
• ground roughness (Manning’s n)
• storm duration
• drainage (pumping) capacity
Model simulations were carried out for ground roughness (Manning’s n) +/- 20%. Model results show that flood depths and extents are largely insensitive to ground roughness (figures 7.4 and 7.5). The most notable exception is the residential area in the west of city to the north of East Ella, where an increased roughness causes water levels to decrease by approximately 0.3 metres in some areas. Increasing ground roughness effectively slows down flow, which can reduce the volume of water ponding in any one place.
Model simulations were carried out for storm durations varying from three to 12 hours (the standard assumed storm duration is six hours) for the same return period flood event. Model results show that flood depths and extents are only slightly sensitive to storm durations (figures 7.6 and 7.7). Longer duration flood events are shown to cause slightly less flooding than shorter, more intense flood events of the same return period. Flood depths for a three hour storm results are up to 0.3 metres greater than the standard six hour storm duration, though this is only observed in very small areas of the city.
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Model simulations were carried out for drainage capacities varying from no drainage capacity to a 100% increase in drainage capacity. As might be expected, model results show that flood depths and extents are moderately sensitive to drainage capacity (figure 7.8 and 7.9) across most of the city and significantly sensitive at a number of locations. The locations that are most affected by drainage capacity are generally in the west of Hull, including East Ella and Pickering Park, but areas of Bransholme, including between Robson Way and Sutton Cross Drain are also affected. The model results show that removing all drainage capacity at these locations could increase surface water flood depths by as much as 0.3 metres, while doubling the current drainage capacity could reduce flood depths by as much as 0.3 metres.
B.6 Model Results
Maximum depth grids (in ASCII format) were extracted from the raw model results using the TUFLOW-to-GIS utility.
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60 Appendix B1: Rainfall profiles (theoretical)
50 50% flood 20% flood 10% flood 45 4.0% flood 2.0% flood 1.0% flood 40 0.5% flood
35 ) r u o 30 h / m m ( y t i s 25 n e t n I l l a f n
i 20 a R
15
10
5
0 0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0 5.5 6.0
Time (hours) Appendix B2: Rainfall profile (25th June 2007)
14.0
25th June 2007
12.0
10.0 ) r u o h /
m 8.0 m ( y t i s n e t n I l l 6.0 a f n i a R
4.0
2.0
0.0 25/06/2007 25/06/2007 25/06/2007 25/06/2007 25/06/2007 25/06/2007 25/06/2007 25/06/2007 25/06/2007 25/06/2007 25/06/2007 00:00 02:00 04:00 06:00 08:00 10:00 12:00 14:00 16:00 18:00 20:00
Date and Time Strategic Flood Risk Assessment Hull City Council
Appendix C: Sequential Test and Exception Test Approach
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62 Assessing Flood Risk – Planning Applications.
PPS25
PPS25 (December 2006) states that the aims of national planning policy on development and flood risk are to ensure that flood risk is taken into account at all stages in the planning process to avoid inappropriate development in areas at risk of flooding, and to direct development away from areas of highest risk.
Local Planning Authorities should prepare and implement planning strategies that help to deliver sustainable development by:
• Appraising risk • Managing risk • Reducing risk
Appraising risk includes identifying land at risk and the degree of risk of flooding from all sources of water including the river, estuary, sea and other sources.
Managing risk requires framing policies for the location of development which avoid flood risk to people and property where possible; manage residual risk; and, only permitting development in areas of flood risk when there are no reasonably available sites in areas of lower flood risk and the benefits of the development outweigh the risks from flooding.
Reducing risk includes the safeguarding of land that is required for current and future flood management from development; the location, layout and design of new development and through design reducing the causes and impacts of flooding by for example surface water management plans.
PPS25 states that Local Planning Authorities should adhere to the following principles:
• Prepare Local Development Documents that set out policies for the allocation of sites • Consider whether there are opportunities to facilitate relocation of development • Consider flood risk alongside other spatial planning issues such as transport, housing, economic growth, natural resources, regeneration, biodiversity, the historic environment and the management of other hazards.
In addition Local Planning Authorities should in determining applications:
• have regard to the national policy in PPS25 and regional policy in the RSS for their region which may be more up to date than policies in their existing development plans • ensure planning application are supported by site specific Flood Risk Assessments as appropriate • apply the sequential approach at a site level to minimise risk by directing the most vulnerable development to areas of lowest flood risk • give priority to Sustainable Urban Drainage Systems; and • ensure that all new development in flood risk areas is appropriately flood resilient and resistant, including safe access and escape routes where required, and that any residual risk can be safely managed.
A risk based approach should be adopted at all levels including, Flood Risk Assessments, The Sequential Approach, The Sequential Test, The Exception Test.
Applying PPS25 to Hull
Spatial planning policy context of Hull
Hull is recognized in the Proposed Modifications of the Regional Spatial Strategy as a Regional City and in the Joint Structure Plan as being a sub-regional centre for development. Table 3.3 in the RSS sets out plan objectives which include: • regenerating areas damaged by past industrial decline; • making full use of urban land and minimising loss of green field land; • protecting and enhancing natural, historic and cultural assets and resources; • seeking wider housing opportunity and choice; • making urban areas attractive high quality safe places where people chose to live; • addressing the causes of and responding to the effects of climate change.
RSS Policy ENV1 ‘Floods and Flood Risk’ states: Development in high flood risk areas will be avoided, where possible, and flood management will be undertaken pro-actively. A - Allocation of areas for development will take place in line with strategic flood risk assessments; B(i) - Flood management will be required to facilitate development in the cities of Leeds, Bradford, Sheffield, Hull and York.
RSS Policy E1- ‘Creating a Successful and Competitive Regional Economy’ states that in order to achieve this investment will be guided to locations where it will have maximum benefit and secure competitive advantage, recognising the role of the Regions cities and urban areas as key drivers of productivity.
RSS policy HE1 – ‘Humber Estuary Sub Area Policy’ states that all plans, strategies, major investment decision and programmes for the Humber Estuary sub area will, where relevant seek to : A – strengthen the role of Hull as a major Sub Regional Centre C – safeguard the area’s main economic assets and settlements from tidal and fluvial flooding. E – Focus most development on main urban area of Hull.
This is reflected in the policies contained in the Joint Structure Plan which identifies Hull as the focus for the majority of future development with the intention of strengthening the sub regional role of Hull whilst managing the risk from flooding.
Flood risk issues in relation to Hull
Hull is almost exclusively flood Zone 3, the highest risk zone. Areas in Flood Zone 1 include Sutton and parts of Bransholme.
Spatial planning policies which direct development towards existing urban areas to maximise use of brown field sites and contribute to more sustainable forms of development and urban regeneration conflict with the advice in PPS25 which states that development should not be encouraged in areas at high risk of flooding.
However PPS25 states that Local Planning Authorities should consider flood risk alongside other spatial planning issues such as transport, housing, economic growth, natural resources, regeneration, biodiversity, the historic environment and the management of other hazards. It does not raise the importance of flood risk above other material planning considerations. It is just one more consideration in the determination of an application.
In determining applications for planning permission regard must be had to the statutory development plan and all other material considerations. Development in Hull has general support in planning policy terms with flood risk being a material consideration.
Applying PPS25 policy, development should be directed to lower flood risk areas wherever possible. This would mean all development in Hull be directed to the limited areas in Zone 1, which are substantially built up with little or no developable land. These areas do not include any areas identified, allocated or reasonably available for employment or retail uses and are predominantly residential. Directing development to these areas would in many cases be contrary to policies in the Hull Local Plan, especially those directing certain types of development to specific areas for example shopping and employment policy that directs such development to existing shopping centres and employment areas, including the City Centre.
In the Hull City Council Relative Flood Risk plan produced by the Environment Agency, Zone 3 has been sub divided into three sub areas within flood Zone 3: Zone 3a(i) low risk; Zone 3a(ii) medium risk; and Zone 3a(iii) high risk.
The City Centre and areas to either side of the River Hull, which include significant areas of employment land uses and established residential areas, comes within the highest flood risk area, Zone 3a(iii). This zone also extends along the River Humber frontage and includes the major docks to the east of the City Centre.
The rest of the City which is made up predominately of residential areas, but includes the main hospital site, university campus on Cottingham Road, shopping centres and supermarkets and the majority of the highway network, are located in Zones 3a(i), (ii) and Zone 1.
Paragraph 16 of PPS25 and paragraph 3.2 of the companion guide state that the Sequential Test should be applied to demonstrate that there are no reasonably available sites in the area with a lower probability of flooding that would be appropriate for the type of development or land use proposed. Paragraph 17 of PPS25 states: ‘in areas at risk of river or sea flooding, preference should be given to locating new development in Flood Zone 1. If there is no reasonably available site in Flood Zone 1 the flood vulnerability of the proposed development can be taken into account in locating development in Flood Zone 2 and then Flood Zone 3. The Sequential Test relates to the proposed land use, not just to the location of the site and whether it is in a particular Zone. Table D2 lists land uses and their Flood Risk Vulnerability. Generally the more vulnerable the land use, the more desirable to locate in a lower risk area. PPS25 refers to reasonably available sites. For a site to be reasonably available it must be available in a reasonable way for the land use proposed by the development.
The suitability of a use on a site would primarily be driven by policies in the statutory development plan which would direct certain types of development/land uses to certain areas in accordance with other national planning policies in PPS1, PPS3, PPS6, PPS13 etc. If the land use would not be appropriate in a particular location because of statutory development plan policies it could be argued that the site is not reasonably available. The starting point is the proposal, the policies of the statutory development plan, and then other material considerations which includes the risk of flooding and other higher order planning policy which has not yet been embedded within the statutory development plan (for example, PPS 25 and PPS 6).
The Environment Agency issued Local Flood Risk Standing Advice for Hull with advice as to when to consult them on planning applications of certain types relative to their development categories and the risk zone they would be located in. This also gives advice of when to consult the EA and in cases where they are not required to be consulted, what the Local Planning Authority should be requiring so they can determine the application.
Suggested Approach in Hull
Flood Zone 3a(i) – low risk
In line with the Hull Local Flood Risk Standing Advice, only consult on highly vulnerable uses and all development over 1ha.
• Finished floor level to be 300mm above ground level and place of safety at 5.0mAOD. (In case of proposals for bungalows, consideration must be given to the practicality of providing a place of safety which in some cases may need to be in the roof space. For this to be beneficial there would have to be a way out of the roof for evacuation. This is not likely to be practical for bungalows for older people or for lifetime homes. Consider the need for an Evacuation Plan?). Bungalows pose particular problems in the event of a flood and their location throughout the city should be strongly influenced by the flood zone map and steered away from high and medium hazard zones. • In cases where the Local Planning Authority are to consider the Sequential Test, they should take the approach that development would be permitted if the proposed land use complies with RSS, JSP and Local Plan policies relating to land use and it passes the Sequential Test. (Paragraph 16 of PPS25 and paragraph 3.2 of the companion guide state that the Sequential Test should be applied to demonstrate that there are no reasonably available sites in the area with a lower probability of flooding that would be appropriate for the type of development or land use proposed). • If the proposed land use (other than householder/minor development and change of use and small scale new residential development) is acceptable in terms of policies in the Development Plan, (eg retail development in a shopping centre) because there are no reasonably available sites in lower risk areas suitable for retail use, the proposal passes the Sequential Test. • Residential development could, subject to detailed planning considerations be accommodated in areas in Zone 1. It may be difficult to demonstrate there were no reasonably available sites in Zone 1 for small scale housing development and also difficult to provide evidence of wider sustainability benefits to the community that outweigh flood risk. As a result it is likely that small scale residential development proposals should be avoided in the high and medium flood hazard zones unless it can be demonstrated there are no alternative sites reasonably available for minor residential schemes, it is unlikely this could be proved. • To pass the Exception Test it is necessary to demonstrate that the development contributes to wider sustainability benefits for the community which outweigh flood risk issues, is on previously developed land and the FRA demonstrates that the development will be safe.
Hospital and University sites –development on these sites to expand either the hospital or the university would be considered as passing the sequential test and exceptions test. The sites are identified in the Local Plan for such uses, extensions would be closely related to the existing use and the wider sustainability benefits to the community outweigh the risk of flooding. However with finished floor levels being set at 300mm above ground level there may be issues with regard to access being DDA compliant. Suggested approach is to require a site specific flood risk assessment to show depth of flood water on the site to inform finished floor levels. If DDA compliant access is required and cannot be achieved with floor levels at 300mm floor level, consult EA with FRA.
Flood Zone 3a(ii)- medium risk
In line with the Hull Local Flood Risk Standing Advice, only consult the Environment Agency on highly vulnerable uses and all development over 1ha.
• Finished floor level to be 600mm above ground level and place of safety at 5.0mAOD. This increase in height of floor levels may have implications for bungalows, accessibility of lifetime homes and on the appearance of a proposal in the street scene. Such cases require a site specific flood risk assessment to determine depth of water on site and then consult the Environment Agency with the FRA. • In cases where the Local Planning Authority are to consider the Sequential test, take the approach that if the proposed land use (with the exception of small scale residential development) complies with RSS, JSP and Local Plan policies relating to land use, it also passes the Sequential Test in line with the reasoning given above for development in Zone3a(i). • To pass the Exception Test it is necessary to demonstrate that the development contributes to wider sustainability benefits which outweigh flood risk issues, is on previously developed land and the FRA demonstrates that the development will be safe.
Case Study – Neighbourhood Integrated Service Centre, Orchard Park.
The site falls within Zone 3a(ii) and was a major development. The land uses were a mix which fell within Less and More Vulnerable as defined by in PPS25. No consultation is required. LPA to consider Sequential and Exception Test and FRA to confirm floor levels of 600mm and place of safety.
Land use considered to be acceptable in this location, exception test considered to be passed because the development provides wider benefits including regeneration of a failing centre and is on previously developed land. A finished floor level of 600mm above site presented accessibility problems, so a FRA was carried out to see if floor levels could be reduced. It concluded that floor levels should be 300mm above average site level.
Need to consult EA if floor level below 600mm.
Applying the 600mm ‘rule’ would in this case create accessibility problems, more desirable to have lower floor level. Therefore we need to know the likely depth of flood water on a development site to determine whether lower floor level achievable. In such cases require a topographical survey of site and FRA to determine depth of flood water on site.
In Zone3a(ii) for applications which include buildings/uses requiring DDA compliant access, require FRA and topographical survey to inform design of building. If DDA compatible access would reasonably be achieved at 600mm floor levels do not consult EA, if not and lower levels required, consult EA.
Flood Zone 3a(iii) – high risk
In line with the Hull Local Flood Risk Standing Advice, consult on all applications except for minor development and some changes of use. In addition to the Sequential Test and Exception Test a Site Specific Flood Risk Assessment will be required. The City Centre, with its Conservation Areas, and major employment areas fall within this area, making almost any development acceptable in terms of policies in the RSS, JSP, Local Plan and emerging City Centre Area Action Plan and Strategic Development Areas.
Policies in the RSS, JSP and the Local Plan collectively will direct development to certain locations, (eg retail development to City Centre or other shopping centres, office development primarily to the City Centre, other employment development to established or strategic employment sites). Residential development to the Housing Market Renewal areas and city centre.
Advice in PPS25 states that flood risk should be considered alongside other spatial planning considerations, including economic growth and regeneration, policies in the development plan direct such development to specific areas and policies in the statutory development plan. If flood risk was given prominence, office, retail, leisure and other employment development would have to be located in a lower flood risk areas than the City Centre. This would be contrary to many policy aims in terms of economic growth, regeneration, transport, and in conflict with predominant land uses in lower flood risk areas. To accord with other policy consideration, in the case of Hull, development will have to be accommodated in the City Centre and have regard to flood risk. Generally, a city centre compatible land use which accords with policies in the statutory development plan will, subject to some detailed considerations, have wider sustainability benefits to the community which outweigh the risk of flooding.
The red area (Flood Zone 3a(iii)) on the flood risk plan is indicative of areas most likely to be at risk from flooding, it does not necessarily mean that flood water would be at such a depth that development is not acceptable. A detailed topographical survey and site specific flood risk assessment, which shows the depth of potential flood water on the site, will be required to inform the design of the development and to assess whether the proposed land use and its wider planning benefits outweigh the risk of flooding. Development in Flood Zone 3a(iii) is likely to be acceptable provided it satisfies the sequential test , exceptions test and is designed to protect adequately against the risk of flooding whilst not increasing the risk elsewhere.
In Zone 3 a (iii) areas where flood water depth is likely to be significant (exceeds a depth of 600m) only in exceptional circumstances (eg City Centre development) should the site be developed for anything other than less vulnerable uses, and where this does occur the more vulnerable development uses should not be located on the ground floor, this is of particular importance for residential use. Most forms of development in the City Centre would not be required to meet the exceptions test due to being of a less vulnerable nature. Howver where more vulnerable uses are proposed they will need to meet the individual requirements of the Exception Test, ie they have wider sustainability benefits to the community that outweigh flood risk issues, (development which complies with RSS, JSP, Local Plan and CCAAP and SDA policies meet this criterion), would be on previously developed land and, subject to design, would be safe in terms of not increasing flood risk elsewhere. All applications for residential new build in Zone 3a(iii) to be referred to the Environment Agency with Sequential Test, Exception Test and Site Specific Flood Risk Assessment.
City Wide Issues
DDA Issues
Development within the City Centre is likely to require DDA compliant access. This is also true of many other developments located outside of the City Centre. The provision of external ramps may not be possible within the site and may not be acceptable to the Local Planning Authority in design terms. Consideration should be given to as near level access as possible and designing in flood protection measures in the building (eg: concrete floors, electrics for the ceilings, damp proof membranes in the walls, air brick covers, flood boards and stop logs in the doors, flood resilient plaster and mortar, horizontal laying of plasterboards, tiled floors, etc.). In many parts of the City Centre it is desirable in urban design terms to have properties ‘at the back edge of pavement’ which limits the ability to provide external access ramps to raised floor levels. Such ramps may in some instances be accommodated inside the building however there will be some instances where due to the size of the property this would be impractical. In such cases, the Local Planning Authority proposes to take a balanced view. There is a requirement for DDA compliant access. A flooding event may be a 1% chance, this level of risk has to be balanced against the day to day needs of a significant minority of the population who require, and deserve, easy and convenient access. Issues of flooding should not be dismissed but other considerations may have a higher importance.
Residential development outside Zone 3a(iii).
Pathfinder Areas
The City is a Pathfinder authority and areas in both West and East Hull have been identified for housing renewal. They are the Newington and St Andrews area in West Hull and Holderness Road in East Hull. These are in Zone 3a(i) and (ii) areas. These areas have been identified as being in need of regeneration and therefore there is likely to be, in the future, a policy presumption in favour of housing development in these areas contained with the Area Action Plans.
Kingswood
Kingswood has the benefit of outline consent for residential development and therefore there is a presumption in favour of such development to be constructed in line with the phasing scheme agreed for the development. Any development proposed which is not subject to the phasing schme should be located in the the lowest risk area of Kingswood. All development will need to be designed to minimise the risk of flooding through raised floor levels as required within the site specific flood risk assessment.
Single Dwellings/Small Scale Residential/Infill and Windfall Sites
A single dwelling house in the garden of an existing dwelling, whilst capable of complying with policies in the statutory development plan, is unlikely to provide any wider sustainability benefits although it would be on previously developed land and it could be designed to be safe from flooding and not increase the risk elsewhere. It would therefore only pass two out of three of the tests in the Exception Test. PPS25 requires that all aspects of the exception Test are passed.
Applications for small scale residential development outside the City Centre would have to demonstrate that the proposal is acceptable in terms of the Sequential Test, which would include reference to the polices in the statutory development plan, and the three elements of the Exception Test, and in many cases would fail when tested against the wider sustainability benefits to the community that outweigh flood risk as there is land available in areas of lower flood risk where residential development would be acceptable.
However, applying this strict approach to all new small scale housing would result in it having to be located within Flood Zone 1. This would result in limiting the total number of new dwellings within the City, and could result in an unacceptable pattern of development across the City as the area of flood zone 1 is less than 5% of the City. Part of Flood Zone 1 is a Conservation Area where consideration must be had to preserving or enhancing the character and appearance of the Conservation Area which may preclude or seriously limit the amount of development in the area.
Allowing small scale residential development in Zone 3a(i) would open up the possibility of a larger proportion of the city being available for such development, contributing to a more acceptable pattern of development across the City without increasing significantly the risk of flood. Sites in Zone 3a(i) would be at higher risk than sites in Zone 1 (and Zone 2) but the risk would not be so significant that housing should not be allowed as safeguards can be built into the design of the building in terms of raised floor levels and other forms of flood proofing.
Strategic Flood Risk Assessment Hull City Council
Appendix D: Local Standing Advice Table
63 Strategic Flood Risk Assessment Hull City Council
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64 Appendix D Hull Local Flood Risk Standing Advice - To be used in conjunction with the Local SFRA Map
A BC D E F G Vulnerability Development within Within Flood Zone 3a Within Flood Zone 3a ii Within Flood Zone 3a i Within Flood Zone 2 Classification 20 metres of the top iii (red) (orange) (yellow) (green) and Flood Development 1 of a bank of a Main Zone 1 (no colour) Category River or Flood Zone 3b
No consultation - floor No consultation - floor No consultation - floor Minor levels of extension to No consultation - No 2 Consult EA with FRA levels of extension to be levels of extension to be Development be no lower than Flood Risk Comments no lower than existing no lower than existing existing Consult EA - Consult EA - Consult EA - Objection Consult EA - Objection No consultation - No 3 Highly Vulnerable Objection in Objection in Principle in Principle in Principle Flood Risk Comments Principle No Consultation - FRA No Consultation - FRA should confirm floor should confirm floor levels of 600mm and levels of 300mm and floodproofing for 300mm floodproofing for 300mm No consultation - No 4 Change of Use More Vulnerable Consult EA with FRA Consult EA with FRA above floor level & place above floor level & place Flood Risk Comments of safety above 5m AOD. of safety above 5m AOD. Consult EA with FRA if Consult EA with FRA if this is not possible. this is not possible.
All other No consultation - No No consultation - No No consultation - No No consultation - No 5 Consult EA with FRA classifications Flood Risk Comments Flood Risk Comments Flood Risk Comments Flood Risk Comments Consult EA - Consult EA - Consult EA - Objection Consult EA - Objection No consultation - No 6 Highly Vulnerable Objection in Objection in Principle in Principle in Principle Flood Risk Comments Principle No Consultation - FRA No Consultation - FRA should confirm floor should confirm floor Non Major levels of 600mm and levels of 300mm and Consult EA with FRA. Consult EA with FRA. Development floodproofing for 300mm floodproofing for 300mm All other LPA to consider LPA to consider No consultation - No 7 above floor level & place above floor level & place classifications Sequential and Sequential and Flood Risk Comments of safety above 5m AOD. of safety above 5m AOD. Exception Tests. Exception Tests. LPA to consider LPA to consider Sequential and Sequential and Exception Tests. Exception Tests. Consult EA - Consult EA - Consult EA - Objection Consult EA - Objection No consultation - No 8 Highly Vulnerable Objection in Objection in Principle in Principle in Principle Flood Risk Comments Principle No Consultation - LPA to No Consultation - LPA to consider Sequential Test consider Sequential Test Consult EA with Consult EA with an Exception Test FRA an Exception Test FRA Sequential Test Sequential Test to confirm floor levels of to confirm floor levels of No consultation - No 9 More Vulnerable evidence & FRA as evidence & FRA as 600mm and 300mm and Flood Risk Comments part of Exception Test part of Exception Test floodproofing for 300mm floodproofing for 300mm above floor level & place above floor level & place of safety above 5m AOD. of safety above 5m AOD.
No Consultation - No Consultation - Sequential Test - FRA to Major Sequential Test - FRA to confirm floor levels of Development confirm floor levels of Consult EA with Consult EA with 600mm and 300mm and floodprooing No consultation - No 10 Less Vulnerable Sequential Test Sequential Test floodproofing for 300mm for 300mm above floor Flood Risk Comments evidence & FRA evidence & FRA above floor level & place level & place of safety of safety above 5m AOD. above 5m AOD. LPA to LPA to consider relevant consider relevant Tests. Tests. Consult EA with Consult EA with No consultation - No No consultation - No No consultation - No 11 Water Compatible Sequential Test & Sequential Test & FRA Flood Risk Comments Flood Risk Comments Flood Risk Comments FRA Consult EA with Consult EA with Essential Sequential Test Sequential Test No consultation - No No consultation - No No consultation - No 12 Infrastructure evidence & FRA as evidence & FRA as Flood Risk Comments Flood Risk Comments Flood Risk Comments part of Exception Test part of Exception Test Consult EA - Consult EA - Consult EA - Objection Consult EA - Objection 13 Highly Vulnerable Objection in Consult EA with FRA Objection in Principle in Principle in Principle Principle Consult EA with Consult EA with Consult EA with Consult EA with Sequential Test Sequential Test Sequential Test evidence Sequential Test evidence 14 More Vulnerable Consult EA with FRA evidence & FRA as evidence & FRA as & FRA as part of & FRA as part of part of Exception Test part of Exception Test Exception Test Exception Test Consult EA with Consult EA with Consult EA with Consult EA with All Development 15 Less Vulnerable Sequential Test Sequential Test Sequential Test evidence Sequential Test evidence Consult EA with FRA over 1 hectare evidence & FRA evidence & FRA & FRA & FRA Consult EA with Consult EA with Consult EA with Consult EA with 16 Water Compatible Sequential Test Sequential Test Sequential Test evidence Sequential Test evidence Consult EA with FRA evidence & FRA evidence & FRA & FRA & FRA Consult EA with Consult EA with Consult EA with Consult EA with Essential Sequential Test Sequential Test Sequential Test evidence Sequential Test evidence 17 Consult EA with FRA Infrastructure evidence & FRA as evidence & FRA as & FRA as part of & FRA as part of part of Exception Test part of Exception Test Exception Test Exception Test
Updated 5th October 2007 Sustaining and improving the quality of people’s lives