Strategic flood risk assessment report

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JBA Project Manager

Ben Gibson BSc MSc MCIWEM C.WEM
JBA Consulting
35 Perrymount Road
Haywards Heath
West Sussex
RH16 3BW

Revision History

Contract

This report describes work commissioned by New Forest District Council and New Forest National Park Authority, on behalf of David Illsley, by a letter dated 20 September 2016. New Forest District Council’s representative for the contract was Andrew Herring and New Forest National Park Authority's representative for the contract was David Illsley. Kristie Darling, Georgina Latus, Aaron Barber, Ffion Wilson and Ben Gibson of JBA Consulting carried out this work.

Prepared by

..................................................Kristie Darling BSc
Technical Assistant

.......................................................................Georgina Latus BSc
Technical Assistant

.......................................................................Aaron Barber BSc
Technical Assistant

.......................................................................Ffion Wilson BSc MSc PIEMA
Analyst

.......................................................................Ben Gibson BSc MSc MCIWEM C.WEM
Chartered Senior Analyst

Reviewed by

.................................................Alastair Dale BSc PGDip MIAHR
Director

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Purpose

This document has been prepared as a Final Report for New Forest District Council and the New Forest National Park Authority. JBA Consulting accepts no responsibility or liability for any use that is made of this document other than by the Client for the purposes for which it was originally commissioned and prepared.

JBA Consulting has no liability regarding the use of this report except to New Forest District Council and New Forest National Park Authority.

Acknowledgements

We would like to acknowledge the assistance of:

• New Forest District Council and New Forest National Park Authority
• The Lead Local Flood Authorities (Hampshire County Council and Wiltshire Council)
• The Environment Agency
• Southern Water
• Wessex Water

Copyright

© Jeremy Benn Associates Limited 2017

Carbon Footprint

A printed copy of the main text in this document will result in a carbon footprint of 470g if 100% post-consumer recycled paper is used and 598g if primary-source paper is used. These figures assume the report is printed in black and white on A4 paper and in duplex.

JBA is aiming to reduce its per capita carbon emissions.

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Executive Summary

Introduction

New Forest District Council and New Forest National Park Authority have commissioned a Level 1 Strategic Flood Risk Assessment (SFRA) to provide a comprehensive evidence base to support the production of their respective Local Plans. This updated SFRA replaces the Level 1 SFRA published by New Forest District Council and New Forest National Park Authority in 2007. This report includes appropriate information contained in the PUSH SFRA covering the 'Solent' area and the Isle of Wight.

The SFRA has been prepared in a series of phases and this report is prepared under Phase 4 and draws on outputs prepared during Phases 1-3.

SFRA objectives

The updated SFRA update (2017 SFRA) will be used within decision making and to inform decisions on the location of future development and the preparation of sustainable policies for the long-term management of flood risk.

The key objectives of the review performed during the preparation of the 2017 SFRA are:

1. To take into account the latest flood risk policy
2. Take into account the latest flood risk information and available data
3. To provide individual flood risk analysis for sites identified by the Council and the National Park Authority as part of their respective Local Plan preparation.
4. To provide a comprehensive set of maps displaying flood risk information

SFRA Outputs

There are two levels of SFRA, described as follows:

• Level 1 – performed where flooding is not a major issue and where development pressures are low.
• Level 2 – Where it is not possible to find enough land for Plan allocations at locations outside of flood risk and so more detailed information is required to understand how the safety of the allocations might be affected (the Exception Test).

This report fulfils Level One SFRA requirements.

To meet the objectives, the following outputs have been prepared:

• Assessment of all potential sources of flooding
• Mapping of location and extent of functional floodplain
• Assessment of standard of protection provided by existing flood risk management infrastructure
• Assessment of the potential impact of climate change on flood risk
• Assessment of locations where additional development may increase flood risk elsewhere
• Identification of critical drainage areas and recommendations on potential need for Surface Water Management Plans
• Recommendations of the criteria that should be used to assess future development proposals and the development of a Sequential Test and sequential approach to flood risk.
• Guidance for developers including requirements for site specific flood risk assessments and the process for flood map challenges.

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Summary of Level 1 Assessment

Appraisal of flood risk

• There have been several recorded flood incidents across the study area, from a combination of sources. The prominent source of flooding is fluvial with a significant influence from tidal conditions. More recent events, investigated by the Lead Local Flood Authorities (LLFAs) under Section 19 of the Flood and Water Management Act, indicates that flood events have been associated with exceedance of the capacity of the sewer network.
• There are several watercourses in the study area which are identified to contribute to fluvial flood risk. Flooding may not be from one watercourse alone. Often the combination of watercourses and the interaction of two or more sources of out of bank flow across the floodplain can have profound implications for the extent of the risk (e.g. Dockens Water and the River Avon).
• The study area is bound by the Solent and Christchurch Bay to the south and Southampton Water and the Tidal River Test to the east and as such there is a tidal flood risk. In addition, many river networks discharge into the sea. The combination of high tides and high river levels, can result in the tidal locking as the rivers are unable to discharge. There is also the possibility that tidal defences can fail or be overtopped. The assessment of the ‘residual’ risk of defence failure should be considered on a site by site basis.
• Coastal erosion is a prominent process along much of the study area’s coast. Defences form a very important aspect of the control of the physical coastline.
• The Risk of Flooding from Surface Water (RoFSW) dataset shows that surface water predominantly follows topographical flow paths of existing watercourses or dry valleys with some isolated ponding located in low lying areas.
• Groundwater flooding is an issue in the Hampshire Avon Catchment at times of high water level in the watercourses.
• Historical incidents of flooding are detailed by Southern Water and Wessex Water. This database records incidents of flooding relating to public foul, combined or surface water sewers and identifies which properties suffered flooding. A total of 266 recorded flood incidents have been identified in the study area.
• There are no records of flooding from reservoirs impacting properties inside the study area.
• There are currently 13 Flood Alert Areas and 16 Flood Warning Areas in the study area.

Flood defences

There are a number of EA fluvial flood defences located throughout the study area. The standard of protection provided by these assets varies as does the condition. There are also tidal flood defences and coastal protection measures.

Development and flood risk

The Sequential and Exception Test procedures for both Local Plans and Flood Risk Assessments (FRAs) have been documented, along with guidance for planners and developers. Links have been provided for various guidance documents and policies published by other Risk Management Authorities such as the (LLFAs) and the Environment Agency (EA).

Relevant studies

There are many relevant regional and local key studies which complement the SFRA and have been considered, such as the Shoreline Management Plans, the Catchment Flood Management Plan, River Basin Management Plan, the Preliminary Flood Risk Assessment, Flood Risk Management Plan and Local Flood Risk Management Strategies. Other policy considerations have also been incorporated, such as sustainable development principles, climate change and flood risk management

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Policy Recommendations

The following policy recommendations are to be considered by New Forest District Council and New Forest National Park Authority in the development of the Local Plan.

Development and planning considerations

Sequential approach to development

It is recommended that the sequential approach is adopted for all future developments within the study area.

New development and re-development of land should wherever possible seek opportunities to reduce overall level of flood risk at the site.

Sequential and Exception tests

The SFRA has identified that areas of New Forest District and National Park that are at high risk of flooding from tidal, fluvial and surface water sources. Therefore, proposed development sites at such locations will be required to satisfy the Sequential and, where necessary, Exception Tests in accordance with the NPPF. New Forest District Council and New Forest National Park Authority will use the information in this SFRA when deciding which development sites to take forward in their respective Local Plans.

Site-specific Flood Risk Assessments

Developers should, where required, undertake more detailed hydrological and hydraulic assessments of the watercourses to verify flood extent (including latest climate change allowances), to inform development zoning within the site and prove, if required, whether the Sequential and Exception Tests are satisfied (for windfall sites not included in the plan, evidence on the Sequential Test must be submitted in FRAs). Where a site-specific FRA has produced modelling outlines which differ from the Flood Map for Planning then a full evidence based review would be required. Where the watercourses are embanked, the effect of overtopping and breach must be considered and appropriately assessed.

All new development within the 1% AEP flood extent including an allowance for climate change (for the lifetime of the development) must not normally result in a net loss of flood storage capacity. Where possible, opportunities should be sought to achieve an increase in the provision of floodplain storage. Where proposed development results in a change in building footprint, the developer should ensure that it does not impact upon the ability of the floodplain to store or convey water, and seek opportunities to provide floodplain betterment. Similarly, where ground levels are elevated to raise the development out of the floodplain, compensatory floodplain storage within areas that currently lie outside the floodplain should normally be provided so the total volume of the floodplain storage is not reduced.

There are several guidance documents which provide information on the requirements for site-specific FRAs:

• Standing Advice on Flood Risk (Environment Agency)
• Flood Risk Assessment for Planning Applications (Environment Agency)
• Site-specific Flood Risk Assessment: CHECKLIST (NPPG, Defra)

Developers should consult with New Forest District Council, New Forest District Council, New Forest National Park, the relevant LLFA, the Environment Agency and Wessex Water or Southern Water at an early stage to discuss flood risk including requirements for site-specific FRAs, detailed hydraulic modelling, and drainage assessment and design.

Surface water management and SuDS

• Planners should be aware of the conditions and local requirements set by Hampshire County Council or Wilshire County (the LLFAs), for surface water management for major and minor developments and ensure development proposals and applications are compliant with the LLFAs policy.
• Hampshire County Council provide a check list for developers to assist in providing the correct information for planning applications.

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• Hampshire County Council’s Surface Water and Sustainable Drainage: Guidance for Developers, Designers and Planners and Wiltshire Council’s Developers Guidance Note: Flood Drainage and SuDS details the LLFAs expectation on the SuDS disposal destination and state that the drainage hierarchy is to be followed.
• All new development should aim to minimise areas of impermeable ground to reduce surface water runoff and SuDS should be used on all new development, unless it is proved unfeasible
• It should be demonstrated through a Surface Water Drainage Strategy, that the proposed drainage scheme, and site layout and design, will reduce the risk of flooding to properties from surface water, so development is safe. A detailed site-specific assessment of SuDS would be needed to incorporate SuDS successfully into the development proposals. All development should adopt source control SuDS techniques to reduce the risk of frequent low impact flooding due to post-development runoff
• At some locations a site-specific infiltration test should be conducted early on as part of the design of the development, to confirm whether the water table is low enough to allow for SuDS techniques that are designed to encourage infiltration.
• Where sites lie within or close to Groundwater Source Protection Zones or aquifers, treatment steps may be required ahead of discharge to the ground, sewers etc. Development proposals at sites across the area should assess the pollution risk to receiving water-bodies, and include appropriate treatment steps ahead of any discharge to surface or groundwaters. The CIRIA SuDS manual provides further guidance on this issue. The LLFA have published information relating to infiltration tests within their guidance document
• Consideration must also be given to residual risk (exceedance flows) and maintenance of sustainable drainage and surface water systems

Review of planning applications

New Forest District Council and New Forest National Park Authority should consult the Environment Agency’s ‘Flood Risk Assessment: Local Planning Authorities’, last updated 28 February 2017, when reviewing planning applications for proposed developments at risk of flooding. The Council and National Park Authority will consult the relevant statutory consultees as part of the planning application assessment and they may, in some cases, also contact non-statutory consultees (e.g. Wessex Water or Southern Water) that have an interest in the planning application

Infrastructure and safe access

Finished floor levels and safe access

Minimum finished floor levels for development should be above whichever is higher of the following:

• a minimum of 600mm above the 1% AEP fluvial event plus an allowance for climate change and an appropriate allowance for freeboard
• a minimum of 600mm above the 0.5% AEP tidal event plus an allowance for climate change and an appropriate allowance for freeboard
• 300mm above the general ground level of the site.

If it is not practical to raise floor levels to those specified above, consultation with the Environment Agency will be required to determine alternative approaches.

Safe access and egress will need to be demonstrated at all development sites. Emergency vehicular access should be possible during times of flood.

Where development is located behind, or in an area benefitting from, defences, consideration should be given to the potential safety of the development, finished floor levels and the potential for safe access and egress in the event of rapid inundation of water due to a defence breach with little warning.

Resilience measures will be required if buildings are situated in the flood risk area, and opportunities to enhance green infrastructure and reduce flood risk by making space for water should be sought.

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Residual risk

Residual risk is the risk that remains after mitigation measures are considered. The residual risk includes the consideration of flood events that exceed the design thresholds of the flood defences or circumstances where there is a failure of the defences, e.g. flood banks collapse. Residual risks should be considered as part of site-specific Flood Risk Assessments

Further, any developments located within an area protected by flood risk management measures, where the condition of those defences is ‘fair’ or ‘poor’, where the standard of protection is not of the required standard or where the failure of the intended level of service gives rise to unsafe conditions should be identified.

Future flood management

Developments should demonstrate opportunities to create, enhance and link green assets. This can provide multiple benefits across several disciplines including flood risk and biodiversity/ ecology and may provide opportunities to use the land for an amenity and recreational purposes.

Development that may adversely affect green infrastructure assets should not be permitted.

The information provided in the SFRA should be used as a basis for investigating potential strategic flood risk solutions within the study area. Opportunities could consist of the following:

• Catchment and floodplain restoration;
• Flood storage areas;
• Opening up culverts, weir removal, and river restoration; and
• Green infrastructure

For successful future flood risk management, it is recommended that local planning authorities adopt a catchment partnership working approach in tackling flood risk and environmental management.

Potential modelling improvements

The Environment Agency regularly reviews its flood risk mapping, and it is important that they are approached to determine whether updated (more accurate) information is available prior to commencing a site-specific FRA.

Use of Strategic Flood Risk Assessment data

SFRAs are high level strategic documents and, as such, do not go into detail on an individual site-specific basis. This SFRA has been developed using the best available information, supplied at the time of preparation. This relates both to the current risk of flooding from rivers, and the potential impacts of future climate change.

The Environment Agency regularly reviews its hydrology, hydraulic modelling and flood risk mapping, and it is important that they are approached to determine whether updated (more accurate) information is available prior to commencing a site-specific FRA. It should be noted that the Environment Agency’s Flood Zones, on their Flood Map for Planning website, may differ to the maps in the SFRA for a short period of time, whilst new modelling is incorporated into the Environment Agency’s flood maps.

Other datasets used to inform this SFRA may also be periodically updated and following the publication of this SFRA, new information on flood risk may be provided by Risk Management Authorities.

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List of Figures

• Figure 2-1: Flood Risk Regulation Requirements .............................................................. 6
• Figure 2-2: Flood risk and the preparation of Local Plans†................................................ 9
• Figure 3-1: Applying the Sequential Test in the preparation of a Local Plan ..................... 16
• Figure 3-2: Applying the Exception Test in the preparation of a Local Plan ...................... 17
• Figure 4-1: River Basin Districts in New Forest District and National Park ........................ 21
• Figure 6-1: New Forest District and National Park topography.......................................... 35
• Figure 6-2: Bedrock aquifer designation in New Forest District and National Park ........... 36
• Figure 6-3: Superficial aquifer designation in New Forest District and National Park........ 37
• Figure 9-1: Four principles of SuDS design........................................................................ 60
• Figure 9-2: Groundwater Source Protection Zones in New Forest District and National Park ........................................................................................................................... 64

List of Tables

• Table 2-1: When to consult authorities in New Forest District and National Park.............. 14
• Table 3-1: Flood Zone descriptions .................................................................................... 15
• Table 4-1: Peak river flow allowances for the South East river basin district..................... 21
• Table 4-2: Peak river flow allowances for the South West river basin district.................... 21
• Table 4-3: Peak rainfall intensity allowance in small and urban catchments ..................... 23
• Table 5-1: Fluvial flood risk models used in this SFRA ...................................................... 26
• Table 5-2: RoFSW risk categories...................................................................................... 29
• Table 6-1: Southern Water Sewer Incident Report Form data........................................... 41
• Table 6-2: Wessex Water Inadequate Capacity Incidents data ......................................... 42
• Table 6-3: Summary of flood risk to the key towns and villages in the study area............. 44
• Table 7-1: Flood defence condition rating .......................................................................... 48
• Table 7-2: Flood defence mapping..................................................................................... 49
• Table 9-1: Examples of SuDS techniques and potential benefits ...................................... 61
• Table 9-2: Example SuDS constraints and possible solutions ........................................... 62
• Table 10-1: Environment Agency Warnings explained ...................................................... 68
• Table 12-1: Overview flood risk information for the Level 1 SFRA sites ............................ 79

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Using this document

Abbreviations and Glossary of Terms

Hyperlinks

Hyperlinks have been provided where there are useful reference points. These are shown as green bold text.

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1 Introduction

1.1 Purpose of the Strategic Flood Risk Assessment

This Strategic Flood Risk Assessment (SFRA) document replaces the Level 1 SFRA published by New Forest District Council and New Forest National Park Authority in 2007 and includes, as appropriate information contained in the PUSH SFRA covering the 'Solent' area and the Isle of Wight. The SFRA study area is shown in Figure 1-1. This report replaces the content that was included in the previous SFRA, integrates as appropriate information contained in the PUSH SFRA and provides a comprehensive evidence base to support the production of Local Plans being prepared for the administrative areas of the New Forest District Council and New Forest National Park Authority.

The updated SFRA (2017 SFRA) will be used within decision making and to inform decisions on the location of future development and the preparation of sustainable policies for the long-term management of flood risk.

The key objectives of the review performed during the preparation of the 2017 SFRA are:

1. To take into account the latest flood risk policy
2. Take into account the latest flood risk information and available data
3. To provide individual flood risk analysis for sites identified by the two local planning authorities as part of their respective Local Plan preparation.
4. To provide a comprehensive set of maps displaying flood risk information

Updated information is available to inform the SFRA, including changes to each of the datasets which inform flood risk and guidance and policy documents.

1.2 SFRA structure

This Phase 4 report is a compilation of previous work carried out in the preceding phases of the Level 1 SFRA, described as follows:

• Phase 1: Data review and method statement
• Phase 2: Flood risk mapping
• Phase 3: Site summary sheets

1.3 Levels of SFRA

The Planning Practice Guidance advocates a tiered approach to risk assessment and identifies the following two levels of SFRA:

1. Level One: where flooding is not a major issue and where development pressures are low. The assessment should be sufficiently detailed to allow application of the Sequential Test.
2. Level Two: where land outside Flood Zones 2 and 3 cannot appropriately accommodate all the necessary development creating the need to apply the NPPF’s Exception Test. In these circumstances, the assessment should consider the detailed nature of the flood characteristics within a Flood Zone and assessment of other sources of flooding.

This report fulfils Level One SFRA requirements.

“Local Plans should be supported by a strategic flood risk assessment and develop policies to manage flood risk from all sources, taking account of advice from the Environment Agency and other relevant flood risk management bodies, such as Lead Local Flood Authorities and Internal Drainage Boards. Local Plans should apply a sequential, risk-based approach to the location of development to avoid, where possible, flood risk to people and property and manage any residual risk, taking account of the impacts of climate change”.

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1.4 SFRA outputs

To meet the objectives, the following outputs have been prepared:

• Assessment of all potential sources of flooding
• Mapping of location and extent of functional floodplain
• Assessment of standard of protection provided by existing flood risk management infrastructure
• Assessment of the potential impact of climate change on flood risk
• Assessment of locations where additional development may increase flood risk elsewhere
• Identification of critical drainage areas and recommendations on potential need for Surface Water Management Plans
• Recommendations of the criteria that should be used to assess future development proposals and the development of a Sequential Test and sequential approach to flood risk.
• Guidance for developers including requirements for site specific flood risk assessments and the process for flood map challenges.

1.5 SFRA user guide

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1.6 Consultation

The following parties (external to New Forest District Council and the New Forest National Park Authority) have assisted with the provision of information to inform the SFRA Environment Agency:

• Hampshire County Council
• Wiltshire Council
• Southern Water
• Wessex Water

Information from other parties (e.g. the Partnership for Urban South Hampshire [PUSH]) was obtained where available online. As shown on Figure 1-1 the New Forest National Park includes land within New Forest District, Wiltshire and Test Valley; and that for planning purposes the National Park Authority is the sole planning authority for the whole of the designated National Park area.

1.7 Use of SFRA data

It is important to recognise that SFRAs are high level strategic documents and, as such, do not go into detail on an individual site-specific basis. The SFRA has been developed using the best available information at the time of preparation. This relates both to the current risk of flooding from rivers, and the potential impacts of future climate change.

SFRAs should be a ‘living document’, and as a result should be updated when new information on flood risk, new planning guidance or legislation becomes available. New information on flood risk may be provided by New Forest District Council, New Forest National Park Authority, the Partnership for Urban South Hampshire (PUSH), the Environment Agency, Hampshire County Council, Wiltshire Council, Southern Water and Wessex Water. In addition, it is possible that information available from Southampton Water Harbour Authority (Associated British Ports Southampton [ABPS]) could be influential with respect to flood risk. Such information may be in the form of:

• New hydraulic modelling (flood risk) results
• Flood event information following a flood event
• Policy/ legislation updates

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• Environment Agency flood map updates
• New flood defence schemes, works, dredging regimes etc.

The Environment Agency regularly reviews its flood risk mapping, and it is important that they are approached to determine whether updated (more accurate) information is available prior to commencing a detailed Flood Risk Assessment.

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Figure 1-1: Study area

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2 The Planning Framework and Flood Risk Policy

2.1 Introduction

The overarching aim of development and flood risk planning policy in the UK is to ensure that the potential risk of flooding is taken into account at every stage of the planning process. This section of the SFRA provides an overview of the planning framework, flood risk policy and flood risk responsibilities.

2.2 Flood Risk Regulations (2009) and Flood and Water Management Act (2010)

2.2.1 Flood Risk Regulations, 2009

The Flood Risk Regulations (2009) translate the current EU Floods Directive into UK law and place responsibility upon all Lead Local Flood Authorities (LLFAs) to manage localised flood risk. Under the Regulations, the responsibility for flooding from rivers, the sea and reservoirs lies with the Environment Agency. However, responsibility for local and all other sources of flooding rests with LLFAs. In the instance of this SFRA, the LLFAs are Wiltshire Council and Hampshire County Council. Detail on the responsibilities of LLFAs is provided in Section 2.11.2.

Figure 2-1 illustrates the steps that were initially taken to implement the requirements of the EU Directive in the UK in accordance with the Flood Risk Regulations. The Regulations established a process that is repeated on a 6-year cycle.

Figure 2-1: Flood Risk Regulation Requirements

2.2.2 Preliminary Flood Risk Assessments (PFRAs)

Under this action plan and in accordance with the Regulations, LLFAs initially had the task of preparing a Preliminary Flood Risk Assessment (PFRA) report.

The documents that cover the study area are the Hampshire County Council's PFRA (2011) and Wiltshire Council's Draft PFRA (2011). The threshold for designating significant Flood Risk Areas is defined by Defra and the PFRA is the process by which these locations can be identified.

Of the ten national indicative Flood Risk Areas that were identified by the Defra/Environment Agency, none encroach on the New Forest District Council or the New Forest National Park.

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A review of preliminary flood risk assessments was required to be completed by the LLFAs by the 22 June 2017. The LLFAs should be contacted to understand any changes to the previous recommendations or outputs made as part of the latest process.

2.2.3 Flood Risk Management Plans (FRMPs)

Under the Regulations the Environment Agency exercised an ‘Exception’ and did not prepare a PFRA for risk from rivers, reservoirs and the sea. Instead they had to prepare and publish hazard and risk mapping and an FRMP.

The study area is covered by the South East River Basin District Flood Risk Management Plan (FRMP) (2016) and the South West River Basin District FRMP (2016). The two FRMPs cover the period of 2015 to 2021. The FRMP draws on policies and actions identified in Catchment Flood Management Plans (Section 2.6) and also incorporates information from Local Flood Risk Management Strategies (Section 2.2.5).

2.2.4 Flood and Water Management Act (FWMA), 2010

Following the 2007 floods, Sir Michael Pitt was appointed to chair an independent review into the floods. The final report was published in June 2008. The Flood and Water Management Act (2010)¹ implements some of Sir Michael Pitt’s recommendations and aims to create a simpler and more effective means of managing both flood risk and coastal erosion.

The FWMA established Lead Local Flood Authorities (LLFAs). Hampshire County Council and Wiltshire Council are the LLFAs for the study area. Further information on the LLFA role and responsibilities are provided in Section 2.11.2.

2.2.5 Local Flood Risk Management Strategies

Hampshire County Council and Wiltshire Council are responsible for developing, maintaining, applying and monitoring a LFRMS’s for Hampshire and Wiltshire respectively. The Hampshire Local Flood Risk Management Strategy (2013) and the Wiltshire Local Flood Risk Strategy (2014) are used as a means by which the LLFAs co-ordinate Flood Risk Management on a day to day basis. The Strategies also set measures to manage local flood risk i.e. flood risk from surface water, groundwater and Ordinary Watercourses.

2.2.6 The National Flood and Coastal Erosion Risk Management Strategy for England (2011)

The National Flood and Coastal Erosion Risk Management Strategy for England provides the overarching framework for future action by all risk management authorities to tackle flooding and coastal erosion in England. It was prepared by the Environment Agency with input from Defra.

The Strategy builds on existing approaches to flood and coastal risk management and promotes the use of a wide range of measures to manage risk. It describes how risk should be managed in a co-ordinated way within catchments and along the coast and balance the needs of communities, the economy and the environment.

2.3 National Planning Policy and Guidance

The National Planning Policy Framework (NPPF) was issued in 2012 to replace the previous documentation as part of reforms to make the planning system less complex and more accessible, and to protect the environment and promote sustainable growth. It replaces most of the Planning Policy Guidance Notes (PPGs) and Planning Policy Statements (PPSs) that were referred to in the previous version of the SFRA. The NPPF sets out the Government’s requirements for the planning system and provides a framework within which local people and councils can produce distinctive local and neighbourhood plans to reflect the needs and properties of their communities. The NPPF must be taken into account by local planning authorities when preparing Local Plans and for applicants preparing planning submissions.

National Planning Practice Guidance (NPPG) was published in 2014 and sets out how the NPPF should be implemented. NPPG: Flood Risk and Coastal Change advises on how planning can account for the risks associated with flooding and coastal change in plan making and the application process. It sets out Flood Zones, the appropriate land uses for each zone, flood risk assessment requirements, including the Sequential and Exception Tests and the policy aims for developers and authorities regarding each Flood Zone. Further details on Flood Zones and associated policy is provided in Table 3-1 and throughout this report. The Sequential and Exception tests are covered in greater detail in Sections 3.2 to 3.4.

A description of how flood risk should be taken into account in the preparation of Local Plans is outlined in Diagram 1 contained within the Planning Practice Guidance (Figure 2-2).

The Sequential Test

“The Sequential Test ensures that a sequential approach is followed to steer new development to areas with the lowest probability of flooding. The flood zones, as refined in the Strategic Flood Risk Assessment for the area, provide the basis for applying the Test. The aim is to steer new development to Flood Zone 1 (areas with a low probability of river or sea flooding). Where there are no reasonably available sites in Flood Zone 1, local planning authorities in their decision making should take into account the flood risk vulnerability of land uses and consider reasonably available sites in Flood Zone 2 (areas with a medium probability of river or sea flooding), applying the Exception Test if required. Only where there are no reasonably available sites in Flood Zones 1 or 2 should the suitability of sites in Flood Zone 3 (areas with a high probability of river or sea flooding) be considered, taking into account the flood risk vulnerability of land uses and applying the Exception Test if required”.

The Exception Test

“The Exception Test, as set out in paragraph 102 of the NPPF, is a method to demonstrate and help ensure that flood risk to people and property will be managed satisfactorily, while allowing necessary development to go ahead in situations where suitable sites at lower risk of flooding are not available.

Essentially, the two parts to the Test require proposed development to show that it will provide wider sustainability benefits to the community that outweigh flood risk, and that it will be safe for its lifetime, without increasing flood risk elsewhere and where possible reduce flood risk overall.”.

¹ Flood and Water Management Act (2010): http://www.legislation.gov.uk/ukpga/2010/29/pdfs/ukpga_20100029_en.pdf

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Figure 2-2: Flood risk and the preparation of Local Plans†

† Diagram 1 of NPPG: Flood Risk and Coastal Change (paragraph 004, Reference ID: 7-005-20140306) March 2014

2.4 LLFAs, surface water and SuDS

On 18 December 2014 a Written Ministerial Statement laid by the Secretary of State for Communities and Local Government set out changes to the planning process that would apply for major development from 6 April 2015.

Major developments are defined as

• Residential development: 10 dwellings or more, or residential development with a site area of 0.5 hectares or more where the number of dwellings is not yet known; and
• Non-residential development: provision of a building or buildings where the total floor space to be created is 1,000 square metres or more or, where the floor area is not yet known, a site area of 1 hectare or more.

When considering planning applications, Local Planning Authorities should consult the LLFA on the management of surface water so that:

• the proposed minimum standards of operation are appropriate
• there are clear arrangements for on-going maintenance over the development’s lifetime, through the use of planning conditions or planning obligations.

2.4.1 Defra Non-Statutory Technical Standards for SuDS

On March 23 2015, the Department for Environment, Food and Rural Affairs (Defra) published the Non-Statutory Technical Standards for SuDS. The standards should be used in conjunction with the NPPF and NPPG. These standards cover the following

• Flood risk outside the development
• Peak flow control
• Volume control
• Flood risk within the development
• Structural integrity
• Designing for maintenance considerations
• Construction

2.4.2 C753 CIRIA SuDS Manual (2015)

The C753 CIRIA SuDS Manual (2015) replaces and updates the previous version (C697) providing up to date guidance on planning, design, construction and maintenance of SuDS. The document is designed to help the implementation of these features into new and existing developments, whilst maximising the key benefits regarding flood risk and water quality. The manual is divided into five sections ranging from a high level overview of SuDS, progressing to more detailed guidance with progression through the document. It is recommended that developers and the LPA utilise the information within the manual to help design SuDS which are appropriate for a development.

2.5 Surface Water Management Plans

Surface Water Management Plans (SWMPs) outline the preferred surface water management strategy in a given location and establish a long-term action plan.

In Hampshire, in order to carry out appropriate SWMPs, a strategic level SWMP has been carried out for the entire county in the form of the Preliminary Flood Risk Assessment (PFRA). As there are 11 District, Borough or City Authorities within Hampshire, it has been decided that intermediate SWMPs for each district will be carried out followed by detailed SWMPs where required for specific sites. No SWMPs have currently been carried out by Hampshire County Council for the study area. Further information can be found on the Hampshire County Council website.

Wiltshire Council has not produced any SWMPs for the study area.

2.6 Catchment Flood Management Plans

Catchment Flood Management Plans (CFMPs) are a high-level strategic plan providing an overview of flood risk across each river catchment. The Environment Agency use CFMPs to work with other key-decision makers to identify and agree long-term policies for sustainable flood risk management.

There are six pre-defined national policies provided in the CFMP guidance and these are applied to specific locations through the identification of ‘Policy Units’. These policies are intended to cover the full range of long-term flood risk management options that can be applied to different locations in the catchment.

2.6.1 New Forest CFMP (2009)

The policies for the study area within the New Forest CFMP are:

• Policy 3 – Lyndhurst. Areas of low to moderate flood risk where we (the Environment Agency) are generally managing existing flood risk effectively
• Policy 4 – Milton/Milford, Brockenhurst, Lymington, Hythe/Fawley, Totton. Areas of low, moderate or high flood risk where we (the Environment Agency) are already managing the flood risk effectively but where we may need to take further actions to keep pace with climate change.
• Policy 6 – New Forest. Areas of low to moderate flood risk where we (the Environment Agency) will take action with others to store water or manage run-off in locations that provide overall flood risk reduction or environmental benefits.

2.6.2 Hampshire Avon CFMP (2012)

The policies for the study area within the Hampshire Avon CFMP are:

• Policy 2 – New Forest Streams. Areas of low to moderate flood risk where we (the Environment Agency) can generally reduce existing flood risk management actions
• Policy 4 – Lower Avon. Areas of low, moderate or high flood risk where we (the Environment Agency) are already managing the flood risk effectively but where we may need to take further actions to keep pace with climate change
• Policy 5 – Christchurch. Areas of moderate to high flood risk where we (the Environment Agency) can generally take further action to reduce flood risk

2.6.3 Test and Itchen CFMP (2009)

The policies for the study area within the Test and Itchen CFMP are:

• Policy 2 – Clay Catchment. Areas of low to moderate flood risk where we (the Environment Agency) can generally reduce existing flood risk management actions
• Policy 3 – Rural Chalk/Upper/Middle & Lower Test. Areas of low to moderate flood risk where we (the Environment Agency) are generally managing existing flood risk effectively

2.6.4 Dorset Stour CFMP (2012)

The policy for the study area within the Dorset Stour CFMP is:

• Policy 6 – St Leonards, Verwood and West Moors. Areas of low to moderate flood risk where we (the Environment Agency) will take action with others to store water or manage run-off in locations that provide overall flood risk reduction or environmental benefits.

The CFMPs provide specific ‘actions’ for flood risk management for each sub area.

2.7 Shoreline Management Plans

Shoreline Management Plans (SMP) form part of Defra’s strategy for flood and coastal defence. They provide a large-scale assessment of risks associated with coastal evolution and present the policy framework to address these risks in a sustainable manner. The SMP policies defined by Defra are:

• Hold the line – maintain or upgrade the level of protection provided by defences.
• Advance the line – build new defences seaward of the existing defence line.
• Managed realignment – allowing retreat of the shoreline, with management to control or limit the movement.
• No active intervention – a decision not to invest in providing or maintaining defences.

2.7.1 Poole and Christchurch Bays (2011)

The Poole and Christchurch Bays SMP covers the study area from Naish Cliff to Hurst Spit. The following policies are outlined for the study area:

• Hurst Spit and Milford-on-Sea – Hold the line policies are associated with Hurst Spit and Rook Cliff in the short, medium and long term. At Milford seafront, the plan is to hold the line in the short term, with managed retreat in the medium and long term. At Cliff Road, the plan is for managed retreat in the short, medium and long term.
• Hordle Cliff to Chewton Bunny – From Hordle Cliff to Barton the plan is for no active intervention in the short, medium and long term to allow natural rollback. From Barton-on-Sea to Naish Cliff the plan is managed realignment.

2.7.2 North Solent Shoreline Management Plan (2010)

The North Solent SMP covers the study area from Hurst Spit to Lower Test Valley. The following policies are outlined for the study area:

• Hurst Spit to Elmer’s Court – The policy in the short, medium and long term is to hold the line.
• Elmer’s Court to Sowley – The policy is for no active intervention in the short, medium and long term.
• Sowley to Slaternshill – Hold the line is the policy for the short, medium and long term.
• Salternshill to Calshot Spit – The policy is no active intervention in the short, medium and long term.
• Calshot Spit – Hold the line is the policy in the short and medium term, with no active intervention in the long term.

2.8 River Basin Management Plans

River Basin Management Plans (RBMPs) are prepared under the Water Framework Directive (WFD) and assess the pressure facing the water environment in River Basin Districts. New Forest District and New Forest National Park fall with the South East river basin district RBMP and the South West river basin district RBMP.

2.9 Water Cycle Studies

Water Cycle Studies assist Local Authorities to select and develop sustainable development allocations so that there is minimal impact on the environment, water quality, water resources, and infrastructure and flood risk. This can be achieved in areas where there may be conflict between any proposed development and the requirements of the environment through the recommendation of potential sustainable solutions.

No Water Cycle Study has been carried out by New Forest District Council or the New Forest National Park Authority. Future investigations may wish to understand if such studies have since been commissioned.

2.10 Riparian ownership

A riparian owner is a person who owns land on, or adjacent to, a watercourse. The law presumes, in the absence of any other evidence, that the land adjoining the watercourse includes the watercourse to its mid-point; therefore, there may be more than one riparian owner of a watercourse.

Anyone with a watercourse in or adjacent to their land has rights and responsibilities as a riparian owner. The Environment Agency, LLFA and other risk management authorities have permissive powers to work on watercourses under their jurisdiction, however, they are not required to do so.

Under land drainage law, watercourses cannot be obstructed and the riparian owner must accept water flowing onto their land.

Hampshire County Council have prepared Flood Risk Management Guidance for Landowners (2016) which provides further information on the rights and responsibilities of riparian owners.

2.11 Roles and responsibilities of Risk Management Authorities

The roles and responsibilities of Risk Management Authorities (RMAs) in the New Forest District and New Forest National Park are summarised as follows.

2.11.1 New Forest District Council and New Forest National Park Authority

As a Local Planning Authority, New Forest District Council and New Forest National Park Authority assess, consult on and determine whether or not development proposals are acceptable, so that flooding and other, similar, risks are effectively managed.

The Council and the National Park Authority will consult relevant statutory consultees as part of planning application assessments and may, in some cases, also contact non-statutory consultees, such as Wessex Water and Southern Water, that have an interest in the planning application.

2.11.2 Hampshire County Council and Wiltshire Council

As LLFAs, Hampshire County Council and Wiltshire Council’s duties include:

• Local Flood Risk Management Strategy (LFRMS): LLFAs must develop, maintain, apply and monitor a LFRMS to outline how they will manage flood risk, identify areas vulnerable to flooding and target resources where they are needed most.
• Flood Investigations: When appropriate and necessary LLFAs must investigate and report on flooding incidents (Section 19 investigations).
• Register of Flood Risk Features: LLFAs must establish and maintain a register of structures or features which, in their opinion, are likely to have a significant effect on flood risk in the LLFA area.
• Designation of Features: LLFAs may exercise powers to designate structures and features that affect flood risk, requiring the owner to seek consent from the authority to alter, remove or replace it.
• Consenting: When appropriate, LLFAs will perform consenting of works on ordinary watercourses.
• Preparing and issuing information to satisfy the requirements of the Flood Risk Regulations

Hampshire County Council and Wiltshire Council are also the Local Highway Authority and manage highway drainage, carrying out maintenance and improvement works on an on-going basis, as necessary, maintain existing standards of flood protection for highways, making appropriate allowances for climate change. It also has the responsibility to ensure road projects to no increase flood risk.

2.11.3 Environment Agency

The Environment Agency is responsible for protecting and enhancing the environment as a whole and contributing to the government’s aim of achieving sustainable development in England and Wales. The Environment Agency has powers to work on Main Rivers to manage flood risk. These powers are permissive, which means they are not a duty, and they allow the Environment Agency to carry out flood and coastal risk management work and to regulate the actions of other flood risk management authorities on main rivers and the coast.

The EA also has powers to regulate and consent works to Main Rivers. Prior written consent is required from the Environment Agency for any work in, under, over or within nine metres of a Main River or between the high-water line and the secondary line of defence e.g. earth embankment.

The Environment Agency also has a strategic overview role across all types of flooding as well as other types of water management matters. Additionally, the Environment Agency prepares and issues mapping and plan to meet the requirements of the Flood Risk Regulations.

2.11.4 Water and wastewater providers

Southern Water and Wessex Water are the sewerage undertaker for the study area. They have the responsibility to maintain surface, foul and combined public sewers to ensure the area is effectively drained. When flows (foul or surface water) are proposed to enter public sewers, Southern Water or Wessex Water will assess whether the public system has the capacity to accept these flows as part of their pre-application service. If there is not available capacity, they will provide a solution that identifies the necessary mitigation. Southern Water or Wessex Water will also comment on the available capacity of foul and surface water sewers as part of the planning application process. Further information can be found on the respective Southern Water and Wessex Water websites.

Southern Water and Wessex Water also supply potable water, along with Bournemouth Water, to the study area. Consent, prior to commencing work, is required from the relevant provider if installing water systems, or altering existing systems, is intended.

2.12 When to consult authorities

The new and emerging responsibilities under the Flood and Water Management Act 2010 and the Flood Risk Regulations 2009 are summarised in Table 2-1.

3 The Sequential, risk based approach

3.1 The sequential, risk-based approach

This approach is designed to ensure areas with little or no risk of flooding (from any source) are developed in preference to areas at higher risk, with the aim of keeping development outside of medium and high flood risk areas (Flood Zones 2 and 3) and other sources of flooding, where possible. The sequential approach can be applied both between and within Flood Zones.

When drawing up a local plan, it is often the case that it is not possible for all new development to be allocated on land that is not at risk from flooding. In these circumstances, the Flood Zone maps (that show the extent of inundation assuming that there are no defences) do not contain enough information and a greater understanding of the scale and nature of the flood risks is required, as described in a Level 2 SFRA.

3.1.1 Flood Zones

Table 1 of NPPG Flood Risk and Coastal Change identifies the following Flood Zones. These apply to both Main River and Ordinary Watercourses. Flood risk vulnerability and flood zone compatibility is set out in Table 3 of the NPPG. Table 3-1 summarises this information and also provides information on when an FRA would be required.

3.2 Applying the Sequential Test and Exception Test in the preparation for a local plan

When preparing a Local Plan, the Local Planning Authorities should demonstrate that a range of site allocations has been considered, using an SFRA to apply the Sequential and Exception Tests where necessary.

The Sequential Test should be applied to the whole Local Planning Authority area to increase the likelihood of allocating development in areas not at risk of flooding. The Sequential Test can be undertaken as part of a Local Plan Sustainability Appraisal. Alternatively, it can be demonstrated through a free-standing document, or as part of strategic housing land or employment land availability assessments. NPPG for Flood Risk and Coastal Change describes how the Sequential Test should be applied in the preparation of a Local Plan (Figure 3-1).

Figure 3-1: Applying the Sequential Test in the preparation of a Local Plan

The Exception Test should only be applied following the application of the Sequential Test and as set out in Table 3 of the NPPG Flood Risk and Coastal Change. The NPPG describes how the Exception Test should be applied in the preparation of a Local Plan (Figure 3-2)

Figure 3-2: Applying the Exception Test in the preparation of a Local Plan

It is understood that New Forest District Council and New Forest National Park Authority will each prepare a stand-alone Sequential Test for the respective portions of the study area.

3.2.1 Sequential Test

Local circumstances must be used to define the area of application of the Sequential Test (within which it is appropriate to identify reasonably available alternatives). The criteria used to determine the appropriate search area relate to the catchment area for the type of development being proposed. For some sites this may be clear, in other cases it may be identified by other Local Plan policies. A pragmatic approach should be taken when applying the Sequential Test.

New Forest District Council and New Forest National Park Authority, with advice from the Environment Agency, are responsible for considering the extent to which Sequential Test considerations have been satisfied, and will need to be satisfied that the proposed development would be safe and not lead to increased flood risk elsewhere.

The Sequential Test does not need to be applied for individual developments under the following circumstances:

• The site has already been identified in development plans through the application of the Sequential Test.
• Applications for minor development or change of use (except for a change of use to a caravan, camping or chalet site, or to a mobile home or park home site).

It is normally reasonable to presume and state that individual sites that lie in Zone 1 satisfy the requirements of the Sequential Test; however, consideration should be given to risks from all sources, areas with critical drainage problems and critical drainage areas.

3.2.2 Exception Test

If, following application of the Sequential Test it is not possible for the development to be located in areas with a lower probability of flooding the Exception Test must then be applied if deemed appropriate. The aim of the Exception Test is to ensure that more vulnerable uses, such as residential development can be implemented safely and are not located in areas where the hazards and consequences of flooding are inappropriate. For the Test to be satisfied, the following two elements have to be accepted for development to be allocated or permitted:

1. 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.

   Local Planning Authorities will need to consider what criteria they will use to assess whether this part of the Exception Test has been satisfied, and give advice to enable applicants to provide evidence to demonstrate that it has been passed. If the application fails to prove this, the Local Planning Authority should consider whether the use of planning conditions and / or planning obligations could allow it to pass. If this is not possible, this part of the Exception Test has not been passed and planning permission should be refused.

2. A site-specific Flood Risk Assessment must demonstrate that the development will be safe for its lifetime, taking account of the vulnerability of its users, without increasing flood risk elsewhere, and, where possible, will reduce flood risk overall.

   The site-specific Flood Risk Assessment should demonstrate that the site will be safe and the people will not be exposed to hazardous flooding from any source. The following should be considered:

   • The design of any flood defence infrastructure.
   • Access and egress.
   • Operation and maintenance.
   • Design of the development to manage and reduce flood risk wherever possible
   • Resident awareness.
   • Flood warning and evacuation procedures.
   • Any funding arrangements required for implementing measures.

The NPPG provides detailed information on how the Test can be applied. For the purpose of supporting land use allocation with respect to satisfying appropriate levels of safety and hazards, the evidence in the Level 2 SFRA is used to provide strategic information so the nature and scope of the flood risk management or mitigation responses is identified.

3.3 Actual flood risk

If it has not been possible for all future development to be situated in Zone 1 then a more detailed assessment is needed to understand the implications of locating proposed development in Zones 2 or 3. This is accomplished by considering information on the “actual risk” of flooding. The assessment of actual risk takes account of the presence of flood defences and provides a picture of the safety of existing and proposed development. It should be understood that the standard of protection afforded by flood defences is not constant and it is presumed that the required minimum standards for new development are:

• residential development should be protected against flooding with an annual probability of river flooding of 1% (1 in 100 chance of flooding) in any year; and
• residential development should be protected against flooding with an annual probability of tidal (sea) flooding of 0.5% (1 in 200 chance of flooding) in any year.

The assessment of the actual risk should take the following issues into account:

• The level of protection afforded by existing defences might be less than the appropriate standards and hence may need to be improved if further growth is contemplated.
• The flood risk management policy for the defences will provide information on the level of future commitment to maintain existing standards of protection. If there is a conflict between the proposed level of commitment and the future needs to support growth, then it will be a priority for the Flood Risk Management Strategy to be reviewed.
• The standard of safety must be maintained for the intended lifetime of the development. Over time the effects of climate change may reduce the standard of protection afforded by defences, due to increased river flows and levels, and so commitment is needed to invest in the maintenance and upgrade of defences if the present-day levels of protection are to be maintained and where necessary land secured that is required for affordable future flood risk management measures.
• The assessment of actual risk can include consideration of the magnitude of the hazard posed by flooding. By understanding the depth, velocity, speed of onset, rate of rise and duration of floodwater it is possible to assess the level of hazard posed by flood events from the respective sources. This assessment will be needed in circumstances where a) the consequences of flooding need to be mitigated or b) where it is proposed to place lower vulnerability development in areas of flood risk.

3.4 Impact of additional development on flood risk

When allocating land for development, consideration must be given to the potential cumulative impact of development on flood risk. The increase in impermeable surfaces and resulting increase in runoff increases the chances of surface water flooding if suitable mitigation measures, such as SuDS, are not put in place. Additionally, the increase in runoff may result in more flow entering watercourses, increasing the risk of fluvial flooding downstream.

Consideration must also be given to the potential cumulative impact of the loss of floodplain as a result of development. The effect of the loss of floodplain storage should be assessed, at both the development and elsewhere within the catchment and, if required, the scale and scope of appropriate mitigation should be identified. Further information on flood plain compensation is provided in Section 8.3.4.

Whilst the increase in runoff, or loss in floodplain storage, from individual developments may only have a minimal impact on flood risk, the cumulative effect of multiple developments may be more severe without appropriate mitigation measures.

The cumulative impact of development should be considered at the planning application and development design stages and the appropriate mitigation measures undertaken, within an appropriate FRA, to ensure flood risk is not exacerbated, and in many cases the development should be used to improve the flood risk. It is possible that it might be more appropriate to consider strategic measures, but additional studies would be required to provide evidence that the provisions supported the principle of development and were deliverable.

Maintenance and upkeep of SuDS have been neglected in the past as a result of lack of clarity over where responsibility rests. Therefore, is it important that maintenance and upkeep for mitigation measures, such as SuDS, has been set out as part of a drainage strategy and that management funding for the lifetime of the development is agreed.

4 Climate change

4.1 Climate change and the NPPF

The NPPF sets out how the planning system should help minimise vulnerability and provide resilience to the impacts of climate change. NPPF and NPPG describe how FRAs should demonstrate how flood risk will be managed over the lifetime of the development, taking climate change into account.

4.2 Revised climate change guidance

The Environment Agency published updated climate change guidance on 19 February 2016, which supports the NPPF and must now be considered in all new developments and planning applications. The document contains guidance on how climate change should be taken into account when considering development, specifically how allowances for climate change should be included with FRAs. The Environment Agency can give a free preliminary opinion to applicants on their proposals at pre-application stage. There is a charge for more detailed pre-application planning advice

4.3 Climate change allowances

By making an allowance for climate change it will help reduce the vulnerability of the development and provide resilience to flooding in the future. The 2016 climate change guidance includes climate change predictions of anticipated change for peak river flow and peak rainfall intensity. The guidance also covers sea level rise and water height. These allowances are based on climate change projections and difference scenarios of carbon dioxide emissions to the atmosphere. Due to the complexity of projecting climate change effects, there are uncertainties attributed to climate change allowances related to the confidence in the prediction. As a result, the guidance presents a range of possibilities to reflect the potential variation in climate change impacts over the three periods as a consequence of differing levels of confidence in the predictions.

4.4 Peak river flows

Climate change is expected to increase the frequency, extent and impact of flooding, reflected in peak river flows. Wetter winters and more intense rainfall may increase fluvial flooding and surface water runoff and there may be increased storm intensity in summer. Rising river levels may also increase flood risk.

The peak river flow allowances provided in the guidance show the anticipated changes to peak flow for the river basin district within which the subject watercourse is located. Once the river basin district has been identified, guidance on uplift in peak flows are provided for three allowance categories, Central, Higher Central and Upper End which are based on the 50th (Central), 70th (Higher Central) and 90th (Upper End) percentiles respectively. The ‘percentile’ is a measure of the confidence in the magnitude of the allowance, i.e. lower uplift values (50th percentile – ‘Central) are statistically more likely and thus attributed with greater confidence compared with higher uplift values (e.g. 90th percentile – ‘Upper End’). The allowance category to be used is based on the vulnerability classification of the proposed development and the flood zones within which it is to be located.

These allowances are provided, in the form of figures for the total potential change anticipated, for three climate change periods:

• The ‘2020s’ (2015 to 2039)
• The ‘2050s’ (2040 to 2069)
• The ‘2080s’ (2070 to 2115)

The time period used in the assessment depends upon the expected lifetime of the proposed development. Residential development should be considered for a minimum of 100 years, whilst the lifetime of a non-residential development depends upon the characteristics of that development. Further information on what is considered to be the lifetime of development is provided in the NPPG.

New Forest District and New Forest National Park lie within the South East and the South West River Basin Districts as illustrated in Figure 4-1. The allowances for the two river basin districts are provided in Table 4-1 and Table 4-2.

Figure 4-1: River Basin Districts in New Forest District and National Park

4.4.1 High++ allowances

High++ allowances only apply in assessments for developments that are very sensitive to flood risk, for example large scale energy generating infrastructure, and that have lifetimes beyond the end of the century. H++ estimates represent the upper limit of plausible climate projections and would not normally be expected for schemes or plans to be designed to or incorporate resilience for the H++ estimate. Further information is provided in the Environment Agency publication, Adapting to Climate Change: Advice for Flood and Coastal Erosion Risk Management Authorities

4.4.2 Which peak river flow allowance to use?

The flood zone and flood risk vulnerability classification should be considered when deciding which allowances apply to the development or the plan. Vulnerability classifications are found in the NPPG. The guidance states the following

Flood Zone 2

Flood Zone 3a

Flood Zone 3b

4.5 Peak rainfall intensity allowance

Climate change is predicted to result in wetter winters and increased summer storm intensity in the future. This increased rainfall intensity will affect land and urban drainage systems, resulting in surface water flooding, due to the increased volume of water entering the systems. The table below shows anticipated changes in extreme rainfall intensity in small and urban catchments. These allowances should be used for small catchments and urban drainage sites. For catchments, larger than 5km², the guidance suggests the peak river flow allowances should be used.

For Flood Risk Assessments, both the central and upper end allowances should be assessed to understand the range of impact.

4.6 Tidal/coastal change

Sea level allowances have been used in the preparation of this report and should be considered for use in FRAs. Additionally, offshore wind speed and extreme wave height allowances should be considered as part of tidal/coast climate change assessment. The EA guidance and allowances can be found on their website

4.7 Using climate change allowances

To help decide which allowances to use to inform the flood levels that flood risk assessments and management strategies are based on for a development or development plan allocation, the following should be considered:

• likely depth, speed and extent of flooding for each allowance of climate change over time considering the allowances for the relevant epoch (2020s, 2050s and 2080s)
• vulnerability of the proposed development types or land use allocations to flooding
• ‘built in’ resilience measures used, for example, raised floor levels
• capacity or space in the development to include additional resilience measures in the future, using a ‘managed adaptive’ approach

4.8 Groundwater

The effect of climate change on groundwater flooding problems, and those watercourses where groundwater has a large influence on winter flood flows, is more uncertain. Milder wetter winters may increase the frequency of groundwater flooding incidents in areas that are already susceptible, but warmer drier summers may counteract this effect by drawing down groundwater levels to a greater extent during the summer months. The effect of climate change on groundwater levels for sites in areas where groundwater is known to be an issue should be considered at the planning application stage.

4.9 The impact of climate change in New Forest District and New Forest National Park

4.9.1 Previous studies

The UK Climate Projection 2009 (UKCP09) predict the following climatic changes to the study area:

South East England

• Increased summer temperatures of 3.1°C by 2050
• Increased winter temperatures of 2.5°C by 2050
• Reduced summer rainfall of 19% by 2050 making summers much drier
• Increased winter rainfall of 19% by 2050.

South West England

• Increased summer temperatures of 3.1°C by 2050
• Increased winter temperatures of 2.3°C by 2050
• Reduced summer rainfall of 20% by 2050 making summers much drier
• Increased winter rainfall of 18% by 2050.

The New Forest National Park Authority have produced a Conservation in the New Forest National Park – Climate Change factsheet. Within this document, the threats and opportunities of climate change to the national park are shown. The threats include:

• Rising sea levels and possible increased storminess will increase coastal erosion and damage coastal infrastructure.
• Replacement of existing sea defences unlikely to be affordable.
• Historic sites in coastal locations may be lost as sea levels rise.
• Storm and flood damage to caravan sites and other tourist infrastructure.
• Flow rates in streams and rivers will reduce in summer and increase in winter with major temperature, erosion and ecological issues.

The document sets out how the New Forest National Park Authority can help reduce the impacts of climate change.

Wiltshire Council has produced a Climate change Action Plan to consider the impacts and opportunities across all the council services. The plan states that investment in flood and coastal defence assets will need to steadily increase in the future.

The plan states that due to changing rainfall, it is expected that there will be more extreme weather events with an increase in the frequency and intensity of heavy rainfall, leading to flash flooding in summer and saturated soils leading to flooding in winter. More frequent heatwaves are also expected along with continuing sea level rise.

Concerted efforts will also be needed by local authorities and partner organisations to improve the management of catchments, the coast, and urban areas in ways that alleviate the potential for flooding

Wiltshire Council have also prepared an Energy Change and Opportunity Strategy for the period 2011-2020. The strategy suggests the long term/seasonal changes and extreme events that will be observed in Wiltshire in the future. The strategy provides new action plans to tackle climate change, including how water resources will be effected and what the council will do to manage any changes.

New Forest District Council are monitoring coastal changes through a regional monitoring programme. The programme comprises field-based, remote sensing, and environmental surveys to provide detailed baseline digital mapping of marine and terrestrial environments. The programme includes analysis of aerial photography through a series of PDFs to illustrate the changing coastline.

4.9.2 SFRA climate change modelling

Climate change modelling for the watercourses in the study area was undertaken based on the new climate change guidance. Existing Environment Agency hydraulic models were run for the 2080s period for all three allowance categories. Mapping of the climate change modelling outputs are provided in Appendix D.

4.9.3 Adapting to climate change

NPPG Climate Change contains information and guidance for how to identify suitable mitigation and adaptation measure in the planning process to address the impacts of climate change. Examples of adapting to climate change include:

• Considering future climate risks when allocating development sites to ensure risks are understood over the development’s lifetime
• Considering the impact of and promoting design responses to flood risk and coastal change for the lifetime of the development
• Considering availability of water and water infrastructure for the lifetime of the development and design responses to promote water efficiency and protect water quality
• Promoting adaptation approaches in design policies for developments and the public realm for example by building in flexibility to allow future adaptation if needed, such as setting new development back from watercourses
• Identifying no or low cost responses to climate risks that also deliver other benefits, such as green infrastructure that improves adaptation, biodiversity and amenity, for example by leaving areas shown to be at risk of flooding as public open space.

Hampshire County Council has produced a Climate Resilience Toolkit Web App which provides information and advice on how buildings can be designed and adapted to be more resilient to the effects of a changing climate. This toolkit offers a practical resource for those who work on and manage buildings and estates in Hampshire.

Hampshire County Council provides further information about how they are preparing for the impacts of climate change on their website.

5 Sources of information used in preparing the SFRA

5.1 Fluvial flood risk models used in this SFRA

Table 5-1 lists the fluvial flood risk modelling used to inform the SFRA.

Hydraulic models available, but not used as part of the SFRA:

• Generalised JFlow modelling from 2004, 2008, 2009 and 2016.

New generalised modelling of these areas was prepared given discrepancies between inflow locations and latest ground elevations, and to ensure consistency across the full SFRA area.

• Danes Stream (2009) – InfoWorks RS (1D-2D)
• Lymington River (2007) – ISIS-TUFLOW (1D-2D)

The Environment Agency indicated that these models were not fit for informing the Flood Map, so were not considered further.

5.2 Fluvial flooding

Flood Zones 2, 3a and 3b as shown in Appendix C.2 haves been compiled for the study area as part of this SFRA based on the results of the models in Table 5-1. Flood Zones are based on the undefended scenario with the exception of Zone 3b, which includes the presence of defences on the basis that land behind existing defences is not functional flood plain.

The following categories have been used to define each Flood Zone:

• Flood Zone 1: Comprised of land having a less than 1 in 1,000 annual probability of river or sea flooding in any year.
• Flood Zone 2: Comprised of land having between a 1 in 100 and 1 in 1,000 annual probability of river flooding or 1 in 200.
• Flood Zone 3a: This zone comprises land assessed as having a greater than 1 in 100 annual probability of river flooding.
• Flood Zone 3b: This zone comprises land where water has to flow or be stored in times of flood (the functional floodplain). The joint SFRA identifies this Flood Zone as land which would flood with a 5% chance in each and every year (a 1 in 20 annual probability), where modelling exists. The presence of defences are considered when mapping Flood Zone 3b.

If existing or proposed development is shown to be in Flood Zone 3a where no Flood Zone 3b information exists, further work should be undertaken as part of a detailed site specific assessment to understand the extent of Flood Zone 3b.

If existing development or infrastructure is shown in Flood Zone 3b, additional consideration should be given to whether the specific location is appropriate for designation as ‘Functional’ with respect to the storage or flow of water in time of flood.

Where flood risk is dominated by tidal and coastal mechanisms, the flood mechanisms may differ from that of fluvial flooding. In tidal and/or coastal flooding, flood volumes might not necessarily provide the same functionality as for river flooding. Given this potential difference in influence, the functional nature of a floodplain in a tidal/coastal situation may be less evident or not applicable at all and so should be assessed for the specific sites under consideration

5.2.1 Climate change

Hydraulic modelling has been undertaken to provide updated climate change flood mapping for the New Forest District and National Park Authority areas. This modelling follows the latest guidance for climate change in FRAs/SFRAs released by the Environment Agency in February 2016 (and updated in April 2016).

Climate change for fluvial events has been prepared for the Central, Higher Central and Upper End estimates for the 2080s epoch (2070-2115). Present day flood risk information is available for comparison.

New Forest District and the New Forest National Park Area are situated across two River Basin Districts; the South East, and South West River Basin Distracts. Therefore, different allowances have been used in the different River Basin Districts as shown in Table 4-1 and Table 4-2.

5.3 Tidal/Coastal flooding

Tidal and coastal modelling is available for Southampton Water, which was prepared in 2014², but no hydraulic modelling of tidal/coastal flooding is available for the Solent and Christchurch Bay, so alternative methods have been used to prepare outputs along this coastline (refer to section 5.3).

The tidal mapping provides information for present day Flood Zone 3b, 3a and 2 and for the for the climate change Flood Zones 3a to the year 2115.

The existing Southampton Water information used 2012 as the base year for the present-day sea level, so the tidal boundary is 20mm lower than would be the case if the assessment were completed for the 2017 base year. However, in the context of the resolution of modelling and the scale of information presented for a Level 1 SFRA, it is not considered that this would notably alter predictions.

² Environment Agency (May, 2014) Southampton Water Coastal Modelling study, Final Main Assessment Report.

5.3.1 Tidal/coastal flooding along the Solent and Christchurch Bay coastline

The Environment Agency has provided guidance relating to extreme still water levels in the Solent and Christchurch Bay areas (document: Extreme Still Water Levels for Planning: Hampshire & Isle of Wight (2016)³) which draws on information from the Coastal Flood Boundary dataset (2015)⁴ and the Extreme Sea Levels for Southern Estuaries and Harbour Study (2015)⁵.

The information provided is points around the Hampshire and Isle of Wight coast which contains corresponding peak still water levels for the 200-year and 1000-year return period (0.5% and 0.1% AEP) events, which relate to Flood Zones 3a and 2, respectively. Information is provided for the present day (year 2008) and climate change (2070 and 2115) years. No information is provided in the Extreme Still Water Levels for Planning for the 20-year return period (5% AEP) event which would be used to inform Flood Zone 3b, but this information is available within the Extreme Sea Levels for Southern Estuaries and Harbour Study (2015) study report.

To prepare flood extents from this data, points from the water level datasets were extracted and their water levels projected inland to produce a water surface. The elevations from a 5m DTM (prepared from filtered LIDAR data) were then subtracted from the water surface to indicate areas of flooding (where the water level is above ground level). Areas of disconnected flooding were removed (as high ground would prevent ingress of tidal/coastal water). For Flood Zone 3b, where the presence of defences are considered, checks were made against the reported standard of protection for defences. If the standard of protection of the defence was greater than 20-years, then any predicted flooding behind the defences was removed. If standard of protection information wasn’t available, then a.) the crest level in the defence dataset, or b.) the crest level data from LIDAR data (in that order of preference) was used to inform whether flooding should be retained behind the defence line.

In the approach noted above no allowance was made for the influence of waves and potential for overtopping of defences and/or raised ground along the tidal frontage. The influence of waves may be most prominent in the Lymington area, but reducing further east. The need to consider waves is recommended if detailed analysis of sites is conducted where this may be influential. Additionally, no consideration of breach modelling/mapping has been conducted for the Level 1 SFRA. Again, this should be considered if necessary as part of more detailed investigations into sites.

Coastal Flood Zone mapping can be found in Appendix C.1 and coastal climate change mapping can be found in Appendix D.1.

5.4 Surface water

Mapping of surface water flood risk in New Forest District Council and New Forest National Park Authority has been taken from the updated the Risk of Flooding from Surface Water (RoFSW) published online by the Environment Agency. These maps are intended to provide a consistent standard of assessment for surface water flood risk across England and Wales in order to help LLFAs, the Environment Agency and any potential developers to focus their management of surface water flood risk.

The RoFSW is derived primarily from identifying topographical flow paths of existing watercourses or dry valleys that contain some isolated ponding locations in low lying areas. They provide a map which displays different levels of surface water flood risk depending on the annual probability of the land in question being inundated by surface water (Table 5-2).

³ Environment Agency, 2016. Extreme Still Water Levels for Planning: Hampshire & Isle of Wight (March, 2016)
⁴ Environment Agency, 2015. Coastal Design Sea Levels - Coastal Flood Boundary Extreme Sea Levels.
⁵ JBA Consulting for the Environment Agency, 2015. Extreme Sea-Levels for Southern Estuaries and Harbours (April, 2015)

Although the RoFSW offers improvement on previously available datasets, the results should not be used to understand flood risk for individual properties. The results should be used for high level assessments such as SFRAs for local authorities. If a particular site is indicated in the Environment Agency mapping to be at risk from surface water flooding, a more detailed assessment should be considered to more accurately illustrate the flood risk at a site-specific scale. Such an assessment will use the RoFSW in partnership with other sources of local flooding information, such as the modelling undertaken as part of the SWMPs, to confirm the presence of a surface water risk at that particular location.

5.5 Groundwater

Mapping of groundwater flood risk has been based on the Areas Susceptible to Groundwater Flooding (AStGWF) dataset.

The AStGWF dataset is a strategic-scale map showing groundwater flood areas on a 1km square grid. It shows the proportion of each 1km grid square, where geological and hydrogeological conditions indicate that groundwater might emerge. It does not show the likelihood of groundwater flooding occurring, does not take account of the chance of flooding from groundwater rebound and does not define areas of inundation in the same way that fluvial or surface water mapping does. This dataset covers a large area of land, and only isolated locations within the overall susceptible area are actually likely to suffer the consequences of groundwater flooding.

The AStGWF data should be used only in combination with other information, for example local data or historical data. It should not be used as sole evidence for any specific flood risk management, land use planning or other decisions at any scale. However, the data can help to identify areas for assessment at a local scale where finer resolution datasets

5.6 Sewers

Historical incidents of flooding are detailed by Southern Water through their Sewer Incident Report Form (SIRF) Data and by Wessex Water in their Inadequate Capacity Incidents data. These databases records incidents of flooding relating to public foul, combined or surface water sewers and displays which properties suffered flooding.

5.7 Reservoirs

The risk of inundation due reservoir breach or failure of reservoirs within the area has been mapped using the outlines available from the Risk of Flooding from Reservoirs dataset made published by the Environment Agency.

5.8 Suite of maps

All of the mapping can be found in the appendices to this SFRA and is presented in the following structure:

• Appendix A: Grid squares for appendix mapping
• Appendix B: Watercourses
• Appendix C: Flood Zones
  • Appendix C.1: Coastal Flood Zones
  • Appendix C.2: Fluvial Flood Zones
• Appendix D: Climate change flood risk mapping
  • Appendix D.1: Coastal climate change
  • Appendix D.2: Fluvial climate change
• Appendix E: Surface water flood risk mapping
• Appendix F: Areas susceptible to groundwater flooding
• Appendix G: Flood Alert and Flood Warning Areas
• Appendix H: Historic flood risk records
• Appendix I: Flood defence mapping
• Appendix J: