Royal Borough of Kingston upon Thames Strategic Flood Risk ... · 5.3 Assessment of Localised Flood Risk 72. The risk of flooding from other (non fluvial) sources is an important

Royal Borough of Kingston upon Thames Strategic Flood Risk Assessment (SFRA)

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Forward Guidance to Readers

1. This Strategic Flood Risk Assessment document will assist in the identification and

design of sites for future development (from a flood risk perspective), informing both forward planning and development control decision making. It:

a. maps the fluvial flood zones, defined in accordance with PPS25; b. identifies where flooding from other sources has occurred in the past; c. forecasts the potential impact of climate change; d. sets out how to undertake the sequential and exception tests to identify if the

site is appropriate for future development; e. provides clear design recommendations for future development within ‘at risk’

areas; and f. identifies the Council’s expectations for information that is to be supplied in

detailed site based Flood Risk Assessments. 2. This report (and the supporting mapping) represents the Level 1 SFRA1, and

should be used by the Council to inform the application of the Sequential Test. Following the application of the Sequential Test, it may be necessary to develop a Level 2 SFRA2 should it be shown that proposed allocations fall within a flood affected area of the Borough. The Level 2 SFRA should consider the risk of flooding in greater detail within a local context to ensure that the site can be developed in a safe and sustainable manner

3. This SFRA is borough-wide with the exception of Kingston town centre, which was

considered in a separate 2007 Kingston town centre SFRA in support of the K+20 Area Action Plan. The Kingston town centre SFRA can be accessed via: http://www.kingston.gov.uk/browse/environment/planning/kplus20/aap_background_documents.htm.

Use this Document to:

4. Determine which PPS25 flood zone(s) the site falls into. The likelihood of fluvial flooding is least in Zone 1 Low Probability (less than a 0.1% (1 in 1000) chance of flooding in any year), and greatest in Zone 3b Functional Floodplain (greater than a 5% (1 in 20) chance of flooding in any year) - refer to Appendix C Figures 1 to 7. If the site spans more than one PPS25 flood zone, consider the highest probability in the initial instance for planning purposes.

5. Apply the Sequential Test (refer to Section 7.4.1 for further details). It is necessary to

demonstrate that there are no suitable and available alternative sites situated within an area of lower risk. All of the site allocations in the Council’s adopted UDP, with the exception of PS29b (the Territorial Army Depot, Portsmouth Road) are situated within Zone 1 Low Probability. In due course when the UDP site allocations are superseded by allocations in the Local Development Framework, all allocated sites will have been sequentially tested by the Council.

6. Following the application of the Sequential Test, if it is demonstrated that the site is

appropriate for further consideration, make reference to Section 7.4i3 to determine which land use is permissible within the identified PPS25 flood zone, and whether it is necessary to apply the Exception Test.

7. If the Exception Test is to be applied (refer (3) above), then reference should be

made to Section 7.4.1. For all applications, specific design requirements are set out in Section 7.4. These are the minimum requirements that must be incorporated into the site design to ensure Council and Environment Agency approval.

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8. If the site is situated within:

� Zone 3b Functional Floodplain; � Zone 3a High Probability; � Zone 2 Medium Probability; or � Zone 1 Low Probability and is greater than 1ha in area;

then a site based Flood Risk Assessment (FRA) is required. Refer to Section 7.6 for specific requirements of the detailed FRA. Information provided within the SFRA may be used to support the development of the FRA, including (but not limited to):

� Incidents of historical localised flooding are provided in Appendix C Figures 1 to 7;

� An overview of the topography of the Borough is provided in Section 6.6 and Appendix D Figure B (informing the assessment of localised flood risk);

� An overview of the geology of the Borough is provided in Section 6.6 and Appendix D Figure C (informing the design of SuDS);

� An overview of the risk of flooding throughout the Borough is provided in Section 7.5;

� Reference should also be made to the River Hogsmill IUD Pilot Study and the Flood Risk Tool (refer Section 7.3.5) for specific advice regarding localised flood risks in the River Hogsmill catchment.

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Table of Contents 1 Introduction ....................................................................................................................... 1 2 SFRA Approach ................................................................................................................ 2 3 Policy Framework ............................................................................................................. 4

3.1 Introduction............................................................................................................... 4 3.2 National Policy.......................................................................................................... 4

3.2.1 Planning Policy Statement 25: Development and Flood Risk ......................... 4 3.2.2 Planning Policy Statement 1 Supplement: Planning and Climate Change ..... 5

3.3 Regional Planning Policy ......................................................................................... 5 3.3.1 The London Plan ............................................................................................. 5 3.3.2 Sub-Regional Development Framework South London.................................. 6

3.4 Local Planning Policy ............................................................................................... 6 3.4.1 Royal Borough of Kingston upon Thames UPD (Adopted August 2005)........ 6 3.4.2 Royal Borough of Kingston upon Thames Local Development Framework (LDF) 7

4 Data Collection.................................................................................................................. 8 4.1 Overview .................................................................................................................. 8 4.2 Consultation ............................................................................................................. 8 4.3 Environment Agency Flood Zone Maps................................................................... 9 4.4 Historical Flooding.................................................................................................... 9 4.5 Detailed Hydraulic Modelling.................................................................................... 1 4.6 Flood Defences ........................................................................................................ 1 4.7 Topography & Geology ............................................................................................ 1

5 Data Interpretation ............................................................................................................ 2 5.1 Delineation of the PPS25 Flood Zones (Fluvial Flood Risk).................................... 2 5.2 Assessment of Flood Hazard ................................................................................... 4 5.3 Assessment of Localised Flood Risk ....................................................................... 4 5.4 Potential Impacts of Climate Change....................................................................... 5

6 Flood Risk in the Royal Borough of Kingston ................................................................... 7 6.1 Overview .................................................................................................................. 7 6.2 Historical River Flooding .......................................................................................... 7 6.3 Fluvial Flood Risk ..................................................................................................... 7 6.4 Risk to Life from Flooding (Flood Hazard) ............................................................... 8 6.5 Localised Flood Risk ................................................................................................ 9 6.6 Topography & Geology .......................................................................................... 11 6.7 Impacts of Climate Change upon Flood Risk......................................................... 12 6.8 Residual Risk of Flooding ...................................................................................... 12

7 Sustainable Management of Flood Risk ......................................................................... 14 7.1 Overview ................................................................................................................ 14 7.2 Responsibility for Flood Risk Management............................................................ 14 7.3 Strategic Flood Risk Management - The Environment Agency ............................. 15

7.3.1 Overview........................................................................................................ 15 7.3.2 Thames Catchment Flood Management Plan (CFMP) ................................. 15 7.3.3 Lower Thames Strategy ................................................................................ 17 7.3.4 Hogsmill Flood Risk Management Delivery Plan .......................................... 17 7.3.5 River Hogsmill Integrated Urban Drainage (IUD) Pilot Study........................ 17 7.3.6 Beverley Brook Flood Risk Management Strategy ....................................... 18

7.4 Application of PPS25 Within Kingston Borough – The Council ............................. 19 7.4.1 Planning Solutions to Flood Risk Management ............................................ 19 7.4.2 A Proactive Approach – Positive Reduction of Flood Risk through Development................................................................................................................... 20 7.4.3 Localised Flood Risk within the Planning Process........................................ 21 7.4.4 Spatial Planning & Development Control Recommendations ....................... 22 7.4.5 Domestic and Non-Domestic Building Extensions ........................................ 23

7.5 Overview of Flood Risk & SFRA Map Interpretation.............................................. 23 7.5.1 Interpretation of the Kingston Borough SFRA (Maps)................................... 23 7.5.2 Character Area KB1 – Coombe (refer to Figure 001) ................................... 24 7.5.3 ................................................................................................................................ 24 7.5.4 Character Area KB2 – Norbiton & New Malden (refer to Figure 002) ........... 25 7.5.5 Character Area KB3 – Old Malden & Motspur Park (refer to Figure 003)..... 25

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7.5.6 Character Area KB4 – Tolworth, Hook & Riverhill (refer to Figure 004) ....... 26 7.5.7 Character Area KB5 – Chessington (refer to Figure 005) ............................. 27 7.5.8 Character Area KB6 – North Kingston (refer to Figure 006) ......................... 27 7.5.9 Character Area KB7 – Surbiton & Berrylands (refer to Figure 007) .............. 28 7.5.10 Proposal Sites (Adopted UDP August 2005)................................................. 28

7.6 Detailed Flood Risk Assessment (FRA) – The Developer ..................................... 29 7.6.1 Scope of the Detailed Flood Risk Assessment ............................................. 29 7.6.2 Raised Floor Levels & Basements (Freeboard) ............................................ 31 7.6.3 Sustainable Drainage Systems (SUDS)........................................................ 32

7.7 Local Community Actions to Reduce Flood Damage ............................................ 33 7.7.1 Flood Proofing ............................................................................................... 34

7.8 Emergency Planning .............................................................................................. 34 7.9 Insurance................................................................................................................ 35

8 Conclusion & Recommendations.................................................................................... 37 Appendix A PPS25 Constraints – Proposal Sites Appendix B Environment Agency Flood Warning Service (Royal Borough of Kingston) Appendix C Beverley Brook – Delineation of Zone 3b Functional Floodplain Figure 1 Coombe Figure 2 New Malden & Norbiton Figure 3 Old Malden & Motspur Park Figure 4 Tolworth, Hook & Riverhill Figure 5 Chessington Figure 6 North Kingston Figure 7 Surbiton & Berrylands Figure A Overview Map Figure B Topography Figure C Geology

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Glossary

AEP Annual Exceedance Probability e.g. 1% AEP is equivalent to 1% probability of occurring in any one year (or, on average, once in every 100 years)

Core Strategy

The Development Plan Document within the Council’s Local Development Framework which sets the long-term 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.

CLG Communities and Local Government

CFMP Catchment Flood Management Plan

Defra Department of Environment, Food and Rural Affairs

Development The carrying out of building, engineering, mining or other operations, in, on, over or under land, or the making of any material change in the use of a building or other land.

Development Plan Document (DPD)

A spatial planning document 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.

EA Environment Agency

Flood Zone Map Nationally consistent delineation of ‘high’ and ‘medium’ flood risk, published on a quarterly basis by the Environment Agency.

Formal Flood Defence A structure built and maintained specifically for flood defence purposes.

FRA Flood Risk Assessment

Habitable Room

The rooms within a dwelling that are used as living accommodation. Includes living rooms, bedrooms, dining rooms, studies. Kitchens larger than 13 square metres are also included. Bathrooms, toilets and kitchens smaller than 13 square metres are not included. Living rooms greater than 19 square metres and capable of sub-division count as two habitable rooms.

Informal Flood Defence

A structure that provides a flood defence function, however has not been built and/or maintained for this purpose (e.g. boundary wall)

Living on the Edge

A guide to the rights and responsibilities of riverside occupation http://publications.environment-agency.gov.uk/pdf/GEHO0407BMFL-e-e.pdf?lang=_e

LiDAR Light Detection and Ranging - This is a term used for a method of distance measurement using laser light. (Just as RADAR is 'Radio Detection and Ranging' ).

Local Development Framework (LDF)

Will comprise of a portfolio of local development documents which will provide the framework for delivering the spatial strategy for the area.

LPA Local Planning Authority

Planning Policy Guidance (PPG)

A series of notes issued by the Government, setting out policy guidance on different aspects of planning. They will be replaced by Planning Policy Statements.

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Planning Policy Statement (PPS)

A series of statements issues by the Government, setting out policy guidance on different aspects of planning. They will replace Planning Policy Guidance Notes

PPS25 Planning Policy Statement 25: Development and Flood Risk Department of Communities & Local Government, 2006 http://www.communities.gov.uk/publications/planningandbuilding/pps25floodrisk

PPS25 Practice Guide

The Practice Guide supports Planning Policy Statement 25: Development and Flood Risk. It offers guidance and good practice case studies of how to implement PPS25. http://www.communities.gov.uk/publications/planningandbuilding/developmentflood

PPS1 Planning Policy Statement: Planning and Climate Change Supplement to Planning Policy Statement 1 http://www.communities.gov.uk/documents/planningandbuilding/pdf/153119

Previously Developed (Brownfield) Land

Land which is or was occupied by a building (excluding those used for agriculture and forestry). It also includes land within the curtilage of the building, for example a house and its garden would be considered to be previously developed land.

Proposal Sites An area identified in the Council’s UDP that may offer future development potential. The adopted UDP includes a total of 55 Proposal Sites.

Residual Risk A measure of the outstanding flood risks and uncertainties that have not been explicitly quantified and/or accounted for as part of the review process

River Hogsmill Integrated Urban Drainage (IUD) Pilot Study

A partnership study undertaken to better understand the level of flood risk from all sources in the Hogsmill catchment, identify their causes and potential ways of reducing the risk. http://www.defra.gov.uk/environ/fcd/policy/strategy/ha2hogs.htm

SA Sustainability Appraisal (SA) is an appraisal of plans, strategies and proposals to test them against the four broad objectives set out in the Government’s sustainable development strategy.

SEA

Strategic Environmental Assessment (SEA) is a generic term used internationally to describe environmental assessment as applied to policies, plans and programmes. The European ‘SEA Directive’ (2001/42/EC) does not in fact use the term strategic environmental assessment. It requires a formal ‘environmental assessment’ of certain plans and programmes, including those in the field of planning and land use.

SUDS Sustainable Drainage System http://www.ciria.org/downloads.htm

Supplementary Planning Document (SPD)

Provides supplementary guidance to policies and proposals contained within Development Plan Documents. They do not form part of the development plan, nor are they subject to independent examination.

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).

The Lower Thames Strategy

Flood Risk Management Strategy being developed by the Environment Agency to consider the long term mitigation of flood risk within the lower reaches of the River Thames catchment. http://www.environment-agency.gov.uk/commondata/acrobat/geth0107bluseplr_1688514.pdf

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The London Plan Spatial Development Strategy for Greater London http://www.london.gov.uk/thelondonplan/docs/londonplan08.pdf

UDP Royal Borough of Kingston upon Thames Unitary Development Plan (2005) http://www.kingston.gov.uk/browse/environment/planning/planningpolicy/udp_review.htm

Zone 3b Functional Floodplain4

This zone comprises land where water has to flow or be stored in times of flood. Defined as areas at risk of flooding in the 5% AEP ( 1 in 20 chance) design event

Zone 3a High Probability

This zone comprises land assessed as having a 1 in 100 or greater annual probability of river flooding (>1%) or a 1 in 200 or greater annual probability of flooding from the sea (>0.5%) in any year

Zone 2 Medium Probability

This zone comprises land assessed as having between a 1 in 100 and 1 in 1000 annual probability of river flooding (1% – 0.1%) or between a 1 in 200 and 1 in 1000 annual probability of sea flooding (0.5% – 0.1%) in any year

Zone 1 Low Probability

This zone comprises land assessed as having a less than 1 in 1000 annual probability of river or sea flooding in any year (<0.1%)

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1 Introduction 1. Flooding represents a significant risk to both property and life and it is essential that

planning decisions are informed, and take due consideration of the risk posed to (and by) future development by flooding.

2. Planning Policy Statement (PPS) 25: Development and Flood Risk requires that local

planning authorities prepare a SFRA in consultation with the Environment Agency. The purpose of the SFRA is to:

a. determine the variations in flood risk across the Borough taking account of all

forms of flooding, and the impacts of climate change; b. inform and support the preparation of revised flood risk management policies in

the Council’s emerging Local Development Framework (LDF); c. inform the Sustainability Appraisal of Local Development Documents; d. provide the basis to apply the Sequential and Exception Tests in the site

allocation and development control processes; and e. assist emergency planning.

This SFRA will be developed and refined over time.

3. Jacobs was commissioned by the Royal Borough of Kingston upon Thames in July 2006

to develop a Borough-wide Strategic Flood Risk Assessment (SFRA). The initial phase of the investigation was completed in October 2006. However given the pending release of the policy guidance in December 2006, the SFRA process was delayed to enable the study report to reflect fully the final requirements and recommendations of PPS25.

4. This report (and the supporting mapping) represents the Level 1 SFRA5, and

should be used by the Council to inform the application of the Sequential Test. Following the application of the Sequential Test, it may be necessary to develop a Level 2 SFRA6 should it be shown that proposed allocations fall within a flood affected area of the Borough. The Level 2 SFRA should consider the risk of flooding in greater detail within a local context to ensure that the site can be developed in a safe and sustainable manner.

5. This SFRA is Borough-wide except in respect of Kingston town centre. A separate

document, the Kingston Town Centre SFRA was developed as an independent investigation in April 2006 to inform the Kingston Town Centre Area Action Plan, and updated in May 2007 to reflect revisions to PPS25 and the subsequent release of the PPS25 Companion (Practice) Guide. The Kingston Town Centre SFRA is fully consistent with this document, and can be accessed via http://www.kingston.gov.uk/browse/environment/planning/kplus20/aap_background_documents.htm

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2 SFRA Approach 6. The primary objectives of the Kingston Borough SFRA are to inform the revision of

flooding policies and the allocation of land for future development within the emerging Local Development Framework (LDF). The SFRA has a broader purpose however, and in providing a robust depiction of flood risk across the Borough, it can:

� Assist the development control process by providing a more informed response to

development proposals, influencing the design of future development7; � Help to identify and implement strategic solutions to flood risk, providing the basis

for possible future flood attenuation works; � Support and inform the Council’s emergency planning response to flooding.

7. The Government does not provide a specific methodology for the SFRA process.

Therefore, to meet these broader objectives, the SFRA has been developed in a pragmatic manner in close consultation with both the Council and the Environment Agency.

8. A considerable amount of knowledge exists with respect to flood risk within the Borough,

including information relating both to historical flooding, and the predicted extent of flooding under extreme weather conditions (i.e. as an outcome of detailed flood risk modelling carried out by the Environment Agency). The Kingston Borough SFRA has used this existing knowledge, underpinning the delineation of zones of ‘high’, ‘medium’ and ‘low’ probability of flooding, in accordance with PPS25. These zones constitute a robust and transparent evidence base for the development of flood risk management policy, and the allocation of sites for future development.

9. A summary of the adopted SFRA process is provided in the figure below, outlining the

specific tasks undertaken and the corresponding structure of the SFRA report.

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10. It is important to recognise that all of the rivers that affect the Borough flow into, or

from, adjoining authorities within the Thames Valley. Future development within the Borough, if not carefully managed, can influence the risk of flooding posed to residents within neighbouring areas. Conversely, inappropriate planning decisions within adjacent districts can also impact adversely upon flooding within the Borough.

11. A number of authorities within the Thames Valley are carrying out similar strategic flood

risk investigations at the current time. Whilst the delivery teams and programmes underpinning these studies vary from one district to the next, all are being developed in close liaison with the Environment Agency. Consistency in adopted approach and decision making with respect to the effective management of flood risk throughout the Thames system is imperative. Regular discussions with the Environment Agency have been carried out throughout the SFRA process to this end, seeking clarity and consistency where needed.

12. It is also noted that a key recommendation of the River Hogsmill Integrated Urban

Drainage (IUD) Pilot Study (refer Section 7.3.5) is that a working group is established to discuss cross boundary issues relating to flood risk. The IUD study was carried out at a catchment scale, developing a Flood Risk Tool that reflects how changes in the upper Hogsmill catchment (e.g. Reigate & Banstead) may affect downstream areas (including Epsom & Ewell and the Royal Borough of Kingston).

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3 Policy Framework

3.1 Introduction 13. This section provides a brief overview of the strategy and policy context relevant to flood

risk in the Royal Borough of Kingston upon Thames. 14. A framework of national and regional policy directive is in place, providing guidance and

direction to local planning authorities. Ultimately however, it is the responsibility of the Council to establish robust policies to address flood risk.

3.2 National Policy

3.2.1 Planning Policy Statement 25: Development and Flood Risk8 15. Planning Policy Statement 25 (PPS25) was published in December 2006 and sets out the

planning objectives for flood risk management. It states that all forms of flooding and their impacts are material planning considerations. The aim of PPS25 is to ensure that flood risk is taken into account at all stages of the planning process in order to prevent inappropriate development in ‘at risk’ areas.

16. The key objectives for planning are appraising, managing and reducing flood risk. To

appraise the risk it is stated that flood risk areas need to be identified, and that the level of risk needs to be defined. To facilitate this, PPS25 indicates that Regional Flood Risk Appraisals and Strategic Flood Risk Assessments should be prepared.

17. To manage the risk, Local Planning Authorities (LPAs) need to develop policies which

“avoid flood risk to people and property where possible, and manage any residual risk, taking account of the impacts of climate change”. LPAs should also only permit development in flood risk areas if there are no feasible alternatives located in areas of lower flood risk.

18. To reduce the risk, PPS25 indicates that land needed for current or future flood

management should be safeguarded; new development should have an appropriate location, layout and design and incorporate sustainable drainage systems (SUDS); and that new development should be seen as an opportunity to reduce the causes and impacts of flooding by measures such as provision of flood storage, use of SUDS, and re-creating the functional flood plain.

19. A partnership approach is stressed in PPS25 to ensure that LPAs work with partners

such as the Environment Agency. The Environment Agency can provide both information and advice relating to flood risk, and should always be consulted when preparing policy or making decisions which will have an impact on flood risk.

20. The future impacts of climate change are highlighted, as climate change will lead to

increased flood risk in many places in the years ahead. When developing planning policy, LPAs need to consider if it is necessary to encourage the relocation of existing development to locations at less of a risk from flooding in order to prevent future impacts of flooding.

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21. PPS25 also gives specific advice for determining planning applications, which needs to be considered when developing policy. LPAs should ensure that flood risk assessments (FRAs) are submitted with planning applications where this is appropriate; they should apply the sequential approach, (defined in the PPS) which ensures that lower risk areas are considered preferable to higher risk areas; priority should be given to the use of SUDS; and new development should be designed to be resilient to flooding as appropriate.

22. The PPS25 Practice Guide was published by Communities and Local Government in

June 2008, providing additional guidance on the principles set out in PPS25.

3.2.2 Planning Policy Statement 1 Supplement: Planning and Climate Change9

23. The statement supplements the existing PPS1: Delivering Sustainable Development.

The document highlights the issue of climate change, and sets out ways planning should prepare for its effects, which includes managing flood risk.

3.3 Regional Planning Policy

3.3.1 The London Plan10 24. The London Plan is the adopted regional spatial strategy relevant to the Royal Borough of

Kingston. This document includes a number of policies relevant to flood risk. The three key policies relate to flood plains; flood risk management; and sustainable drainage.

25. Policy 4A.12 “Flood Plains” states that boroughs should identify areas at risk from

flooding and highlights the need to refer to PPS25. This SFRA document identifies areas at risk from flooding and covers many of the issues highlighted in PPS25. The policy also indicates that boroughs should avoid permitting built development in functional flood plains.

26. Policy 4A.13 “Flood Risk Management” states “Where development in areas at risk from

flooding is permitted, (taking into account the provisions of PPS25), the Mayor will, and boroughs and other agencies should, manage the existing risk of flooding, and the future increased risk and consequences of flooding as a result of climate change, by

• protecting the integrity of existing flood defences; • setting permanent built development back from existing flood defences to allow for the management, maintenance and upgrading of those defences to be undertaken in a sustainable and cost effective way; • incorporating flood resilient design; • establishing flood warning and emergency procedures.

Opportunities should also be taken to identify and utilise areas for flood risk management, including the creation of new floodplain or the restoration of all or part of the natural floodplain to its original function, as well as using open space in the flood plain for the attenuation of flood water. The Mayor will, and boroughs and other agencies should, take fully into account the emerging findings of the Thames Estuary 2100 Study, the Regional Flood Risk Appraisal and the Thames Catchment Flood Management Plan.”

27. Policy 4A.14 “Sustainable Drainage” seeks to ensure that surface water run-off is

managed as close to its source as possible in line with the drainage hierarchy: • store rainwater for later use; • use infiltration techniques, such as porous surfaces in non-clay areas; • attenuate rainwater in ponds or open water features for gradual releaseto a

watercourse;

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• attenuate rainwater by storing in tanks or sealed water features for gradual release to a watercourse;

• discharge rainwater direct to a watercourse; • discharge rainwater to a surface water drain; • discharge rainwater to the combined sewer.

Developers are encouraged to achieve greenfield run off from their sites through incorporating rainwater harvesting and sustainable drainage. Boroughs should encourage the retention of soft landscaping in front gardens and other means of reducing, or at least not increasing, the amount of hard standing associated with existing homes.

28. The London Plan 2008 also includes the revised Borough level housing targets, which in

Kingston’s case are to provide an additional 3,850 homes over the period 2007/8 to 2016/17.

29. The policies mentioned above will need to be considered when the Royal Borough of

Kingston upon Thames is considering how to allocate land to meet housing targets and other land use requirements.

3.3.2 Sub-Regional Development Framework South London11 30. The Sub-Regional Development Framework South London provides guidance relating to

flood risk. However, this document (finalised in May 2006) is non-statutory. The document states that new development proposals within the indicated flood risk area will need to be supported by a flood risk assessment, and notes the importance of carrying out an SFRA for areas along the River Thames and its tributaries.

31. Surface water run-off is mentioned in guidance on restoration of rivers. The document

highlights that the areas around tributary rivers should be sustainably managed to ensure that the overall water management of these rivers more closely reflects natural patterns. The document also states that provision should be made for the storage of surface water during storms within the flood plain. The guidance on SuDS is sound and the Royal Borough of Kingston upon Thames will consider these points when preparing their policies.

32. The recently consolidated London Plan proposes a revision of the Sub-regional

Development Frameworks in 2008.

3.4 Local Planning Policy

3.4.1 Royal Borough of Kingston upon Thames UPD (Adopted August 2005) 33. The Royal Borough of Kingston upon Thames UDP was adopted in August 2005, and

contains policies that address flooding: 34. Policy STR7b (Water Resource Management) states:

“The Council places importance on sustainable and positive management of the Borough’s water resources, through:

� protecting watercourses and riverside areas from inappropriate development and seeking enhancements, including riverside access, and promotion of natural riverside vegetation where practicable

� promoting good riverside design of development, especially alongside the River Thames;

� promoting recreational and transportation uses of watercourses and water features which do not adversely affect local amenity or nature conservation value;

� prioritising flood protection and taking due account of water conservation, water quality and drainage issues.”

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35. The supporting guidance (Paragraph 7.14) states:

“Government advice in PPG25 (Development and Flood Risk) sets out a sequential test to be used for allocating land and development control decisions. The sequential test uses a risk-based search sequence to locate developments in areas which avoid flood risk or, otherwise, manage the risk effectively, whilst recognizing the uncertainties that are inherent in the prediction of flooding. The Council considers that, based on current information, its land-use allocations are consistent with the sequential approach in PPG25. There are no major built development allocations proposed on functional flood plain land or undeveloped/sparsely developed areas of high flood risk. Where proposals come forward for new development in existing developed areas of high flood risk, the Council will use Policy OL18 to refuse development which increases the risk of flooding, and require appropriate mitigation measures to ensure new development does not exacerbate existing risks. At the same time, the Council will, in partnership with the Environment Agency, continue working towards reducing the risk of flooding in all parts of the Borough. “

36. Policy OL18 (Flooding) states:

“In areas at risk from flooding, the Council will resist development which will increase the risk of flooding. Where any development is permitted, the Council may require appropriate flood protection measures in conjunction with the Environment Agency.”

37. The adopted policy is based upon PPG25, the predecessor to the current policy

guidance. It broadly encapsulates the key underlying principles set out in PPS25, however it is recommended that future revisions to the policy are sought, providing specific reference to the sequential approach set out in PPS25 (mirroring the policy established for the Kingston Town Centre AAP).

38. Finally, a suite of development control recommendations have been identified and agreed

in close consultation with the Environment Agency and the Council (refer Section 7.4). They represent the minimum design measures that will be expected by the Environment Agency should development be permitted to proceed. It is essential to ensure that the development control recommendations can be imposed consistently at the planning application stage. Therefore it is recommended that the development control recommendations presented in the SFRA are incorporated into a Development Control DPD.

3.4.2 Royal Borough of Kingston upon Thames Local Development Framework (LDF) 39. Work has commenced on the preparation of the Local Development Framework (LDF),

which will eventually replace the policies and Proposal Sites in the Unitary Development Plan. The SFRA will inform policy development and the Sustainability Appraisal of LDF documents.

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4 Data Collection

4.1 Overview 40. A considerable amount of knowledge exists with respect to flood risk within the Royal

Borough of Kingston, including (but not limited to):

� Historical river flooding information; � Information relating to localised flooding issues (surface water, groundwater

and/or sewer related), collated in consultation with the Council and the Environment Agency;

� Detailed flood risk mapping; � Environment Agency Flood Zone Maps; � Topography (LiDAR12).

41. This data has been sourced from key stakeholders, as highlighted below. The data has

been used to inform the delineation of zones of ‘high’, ‘medium’ and ‘low’ probability of flooding as explained in Section 5, and the findings of this interpretation is outlined in Section 6. The formulation of planning and development control recommendations to manage and reduce the risk is provided in Section 7.

4.2 Consultation 42. Consultation has formed a key part of the data collation phase for the Kingston Borough

SFRA. Data has been sourced from the following key stakeholders Royal Borough of Kingston upon Thames

Planning Consulted to identify existing development Proposal Sites Drainage Consulted to identify areas potentially at risk from river flooding and/or areas with urban drainage issues Emergency Planning Consulted to discuss issues of specific relevance to the Borough’s emergency response to flooding

Environment Agency The Environment Agency has been consulted to source specific flood risk information to inform the development of the SFRA. In addition, the Environment Agency is a statutory consultee under PPS25 and therefore must be satisfied with the findings and recommendations for sustainable flood risk management into the future. For this reason, the Environment Agency has been consulted during the development of the SFRA to discuss potential flood risk mitigation measures and planning recommendations.

Thames Water Thames Water is responsible for the management of urban drainage (surface water) and sewerage within the Borough. Thames Water was consulted to discuss the risk of localised flooding associated with the existing drainage/sewer system.

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Communities and Local Government (CLG)

PPS25 was released in final form in December 2006, mid way through the development of the Kingston Borough SFRA. Similarly, the Practice Guide Companion to PPS25 was released in draft form in February 2007. Whilst the underlying principles of the policy guidance did not change, some subtle modifications were made to the document, resulting in a need to seek clarity from Communities and Local Government's (CLG) (authors of PPS25) by both the Council and the Environment Agency. CLG were consulted on a number of specific issues throughout the SFRA process, including the definition of Zone 3b Functional Floodplain, and the incorporation (or otherwise) of climate change impacts within the delineation of the PPS25 flood zones.

4.3 Environment Agency Flood Zone Maps 43. The Environment Agency’s Flood Map shows the natural floodplain, ignoring the

presence of defences, and therefore areas potentially at risk of flooding from rivers or the sea. The Flood Map shows the area that is susceptible to a 1 in 100 (1% annual exceedance probability (AEP)) chance of flooding from rivers in any one year, and/or an area with a 1 in 200 (0.5% AEP) chance of flooding in any given year from the sea. It also indicates the area that has a 1 in 1000 (0.1% AEP) chance of flooding from rivers in any given year. This is also known as the Extreme Flood Outline. The Royal Borough of Kingston upon Thames is situated immediately upstream of the formal tidal limit of the River Thames (i.e. Teddington Weir). Whilst extreme tides may indeed extend upstream of this location, the effects are relatively small. Consequently, it is fluvial flooding that dominates the prediction of the Environment Agency (and hence PPS25) flood zone extents.

44. The Flood Map outlines have been produced from a combination of a national

generalised computer model, more detailed local modelling (if available), and some historic flood event outlines. The availability of detailed modelling for the Borough is further discussed in Section 4.5. The Environment Agency’s Flood Map provides a consistent picture of flood risk for England and Wales.

45. The Environment Agency’s knowledge of the floodplain is continuously being improved by

a variety of studies, detailed models, data from river flow and level monitoring stations, and actual flooding information. They have an ongoing programme of improvement, and updates are made on a quarterly basis.

4.4 Historical Flooding 46. Flooding has been observed within the Royal Borough of Kingston a number of times

within living memory, affecting homes and businesses. Whilst prescriptive information relating to the precise location, depth and cause of flooding is not always available, anecdotal information highlights the importance of careful and informed decision making when locating future development within a Borough.

47. Detailed historical flood mapping is not available within Kingston (with the exception of

the River Thames), however where observations have been provided, these have been recorded in the flood zone maps accompanying this document. Many of these are incidents of a ‘localised nature’, however it is important to recognise that often the cause of observed flooding is difficult to ascertain, particularly after the floodwaters have passed.

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4.5 Detailed Hydraulic Modelling

48. A number of detailed flooding investigations have been carried out by the Environment Agency throughout the Royal Borough of Kingston. These detailed modelling investigations generally incorporate the development of a detailed hydraulic model, providing a more robust understanding of the localised fluvial flooding regime in line with Section 105 (2) of the Water Resources Act

49. Detailed hydraulic modelling (and mapping of predicted flood extents) for rivers within the

Royal Borough of Kingston include the lower reaches of the River Thames (Jacobs, 2006) and the River Hogsmill (Jacobs, 2007).

50. It is noted that detailed modelling of Beverley Brook has also been carried out in previous

years, however a number of reviews have been carried out which have highlighted errors and uncertainties in the outputs. Consequently, improvements to the model are needed. It is understood that the Environment Agency has commissioned detailed 2D modelling of Beverley Brook, and it is currently expected that the outputs of this investigation will be available by the summer of 2009.

51. It should be noted that the detailed hydraulic models developed on behalf of the

Environment Agency assume ‘typical’ conditions within the respective river systems that are being analysed. The predicted water levels may change if the operating regimes of the rivers involved are altered (e.g. engineering works which may be implemented in the future), or the condition of the river channel is allowed to deteriorate.

4.6 Flood Defences 52. A formal flood defence is a structure constructed specifically to redirect the flow of

floodwater, and maintained for this purpose by its respective owner (regardless of ownership). An ‘informal flood defence is a structure that is not specifically built to redirect floodwater and is not maintained for this specific purpose, but may afford some protection against flooding. These can include boundary walls, industrial buildings, railway embankments and road embankments situated immediately adjacent to rivers.

53. The location of formal and information flood defences throughout the Borough has been

identified (and mapped) in consultation with the Environment Agency.

4.7 Topography & Geology 54. Topographic information has been provided by the Environment Agency (2005) for the

Borough in the form of LiDAR (Light Detection and Ranging). LiDAR enables a detailed Digital Elevation Model (DEM) to be developed that, in simple terms, provides a three dimensional representation of the terrain.

55. Geological information has been retrieved from the British Geological Society (BGS),

providing an overview of soils and substrate.

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5 Data Interpretation The data captured from key sources to inform the development of the Kingston Borough SFRA is outlined in Section 4 above. This section provides an overview of how this data was interpreted to meet the requirements of PPS25. The findings of these analyses are presented in Section 6 below.

5.1 Delineation of the PPS25 Flood Zones (Fluvial Flood Risk)

56. It is emphasised that the risk of an event (in this instance a flood event) is a function of both the probability that the flood will occur, and the consequence to the community as a direct result of the flood. PPS25 endeavours to assess the likelihood (or probability) of flooding, categorising the Borough into zones of low, medium and high probability. PPS25 then provides recommendations to assist the Council to manage the consequence of flooding in a sustainable manner, for example through the restriction of vulnerable development in areas of highest flood risk.

57. To this end, a key outcome of the SFRA process is the establishment of flood maps that

will inform the application of the Sequential Test in accordance with Appendix D (Table D1) of PPS25. To inform the planning process, it is necessary to review flood risk across the area, categorising the area in terms of the likelihood (or probability) that flooding will occur.

58. The Borough has been delineated into the PPS25 fluvial flood zones summarised below,

and presented in the Flood Risk Maps (Appendix C, Figures 1 to 7). Zone 3b Functional Floodplain

Land assessed as having a 1 in 20 or greater annual probability of flooding in any year (i.e. 5% AEP); and/or Areas susceptible to flooding within which “water has to flow or be stored in times of flood” (PPS25).


Land assessed as having a 1 in 100 or greater annual probability of flooding in any year (i.e. 1% AEP)13.


Land assessed as having between a 1 in 100 (i.e. 1% AEP) and 1 in 1000 (i.e. 0.1% AEP) annual probability of river flooding in any year.

Zone 1 Low Probability

Land assessed as having a less than 1 in 1000 annual probability of river flooding in any year (i.e. 0.1% AEP).

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Delineation of Zone 3b Functional Floodplain 59. Zone 3b Functional Floodplain is defined as those areas in which “water has to flow or be

stored in times of flood”. The definition of functional floodplain remains somewhat open to subjective interpretation. PPS25 states that “SFRAs should identify this Flood Zone (land which would flood with an annual probability of 1 in 20 (5%) or greater in any year or is designed to flood in an extreme (0.1%) flood, or at another probability to be agreed between the LPA and the Environment Agency, including water conveyance routes).” For the purposes of the Kingston Borough SFRA, Zone 3b has been defined in the following manner:

� land where the flow of flood water is not prevented by flood defences or by

permanent buildings or other solid barriers from inundation during times of flood; � land which provides a function of flood conveyance (i.e. free flow) or flood

storage, either through natural processes, or by design (e.g. washlands and flood storage areas);

� land subject to flooding in the 5% AEP (1 in 20) flood event (i.e. relatively frequent inundation expected, on average once every 20 years).

60. Detailed modelled flood extents for the 1 in 20 year design event (where available) were

adopted for the basis of Zone 3b Functional Floodplain delineation for the River Thames and the River Hogsmill.

61. No detailed modelling information was provided for Beverley Brook. For planning

purposes therefore, a simple hydrological and hydraulic assessment was made of the system to estimate the anticipated 1 in 20 year (5%) flood outline. The adopted methodology is outlined in Appendix C.

62. There is clearly a degree of uncertainty surrounding the predicted Zone 3b extent within

the Beverley Brook catchment, however this is intended to reinforce the potential risk that river flooding may pose to property within close proximity of the Brook. Should the Council consider future development within this area following the successful application of the Sequential Test, it will be essential for a more rigorous assessment of flood risk to be carried out (as part of the detailed site based Flood Risk Assessment) to ensure that the adopted design is sustainable over the lifetime of the proposed development.

Delineation of Zone 3a High Probability

63. Zone 3a High Probability is defined as those areas of the Borough with a 1% AEP (100

year) or greater chance of flooding. 64. For planning purposes, the Environment Agency has issued a series of Flood Zone Maps

as depicted on the Environment Agency’s website (www.environment-agency.gov.uk). Only in those areas within which detailed flood mapping is not available and/or fit for purpose, the Environment Agency’s Flood Zone Maps have been adopted to underpin the SFRA process. This includes primarily the Beverly Brook corridor, and tributaries of the River Hogsmill. At these locations, detailed topography has been used to carry out a ‘sensibility check’ of the flood zone maps. This check has sought to ensure that the flood extents mirror sensibly the surrounding topography, and that indicative flood levels on the left and right overbanks are equal. No changes to the predicted flood zone extents were deemed necessary in this instance as an outcome of this sensibility check.

65. The detailed modelling outputs developed by the Environment Agency, where available

(i.e. the River Thames and River Hogsmill), have been adopted for the delineation of Zone 3a High Probability. In some instances, this may differ from the published EA flood zone map. The EA updates the Flood Zone Map on a quarterly basis, and therefore revisions to the EA FZM will incorporate emerging detailed flood risk mapping in due course. To avoid potential confusion, developers should use the published FZM to determine whether or not a detailed FRA will be required. They should then approach the EA at an early stage for the most up to date information for outline design (and FRA preparation) purposes.

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Delineation of Zone 2 Medium Probability

66. Zone 2 Medium Probability is defined as those areas of the Borough that are situated

between the 0.1% AEP (1 in 1000 year) and the 1% AEP (1 in 100 year) flood extents. In this instance, Zone 2 Medium Probability is defined in accordance with the Environment Agency Flood Zone Map.

Delineation of Zone 1 Low Probability

67. Zone 1 Low Probability is defined as those areas of the Borough that are situated above

(or outside of) the 0.1% AEP (1000 year) flood extent. For SFRA purposes, this incorporates all land that is outside of the shaded Zone 2 and Zone 3 flood risk areas (as defined above).

5.2 Assessment of Flood Hazard

68. The assessment of flood risk has thus far considered the maximum extent to which flooding will occur during a particular fluvial flood event. This provides the basis for assessing broadly the areas potentially impacted by flooding. Of equal importance however is the speed with which flooding occurs as river levels rise. The inundation of floodwaters into low lying areas can pose a considerable risk to life.

69. Substantial research has been carried out internationally into the risk posed to

pedestrians during flash flooding. This research has concluded that the likelihood of a person being knocked over by floodwaters is related directly to the depth of flow, and the speed with which the water is flowing. This is referred to as ‘Flood Hazard’.

70. For example, if a flood flow is relatively deep but is low energy (i.e. slow moving), then an

average adult will be able to remain standing. Similarly, if the flow of water is moving rapidly but is very shallow, then once again an average adult should not be put off balance. If however the flow is both relatively deep and fast flowing, then a person will be washed off their feet, placing them at considerable risk. The risk to health and safety as a result of submerged hazards during flooding conditions (given the often murky nature of floodwaters) is also a consideration.

71. The risk to life (as a result of flooding) within the Royal Borough of Kingston upon

Thames has been assessed and delineated in accordance with emerging Defra guidance provided in the form of ‘Flood Risk to People’ (FD2320 and FD2321, refer www.defra.gov.uk). This is discussed further in Section 6.4 below.

5.3 Assessment of Localised Flood Risk 72. The risk of flooding from other (non fluvial) sources is an important consideration. The

recent flooding that affected England, and particularly the South East, in the summer of 2007 highlighted the potential risk that groundwater, surface water runoff and sewer flooding can have upon an area. Newbury (West Berkshire), Sheffield and Hull all suffered severe flooding from non fluvial sources. Indeed reports of localised flooding resulting in severe disruption to road and rail networks were widespread throughout the Kingston upon Thames area following particularly heavy rainfall on 20 July 2007.

73. Information has been provided by the Council relating to anecdotal observations of

localised flooding problems. These typically result from blocked culverts and gullies, surface water runoff, and failures of the underground sewer system during particularly intense rainfall. Some very general information has also been provided by Thames Water, providing a simple overview (per post code area) of the number of properties that have been affected by sewer flooding over the past decade.

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74. This information only identifies localised problems once they have occurred. PPS25 strongly advocates the prediction (where possible) of potential flood risk, seeking an avoidance strategy that guides development away from these areas wherever possible. It is very difficult to predict the potential risk of localised flooding in the future, particularly given that many of these incidents will be as a result of (for example) the collection of leaves over a gully during a rainfall event.

75. The topography and geology of the Borough however provides a means of identifying

those areas within which surface water runoff is likely to cause the most disruption, and potentially damage to property. Areas in which the soils are highly impermeable (reducing the capacity of infiltration into the ground during periods of wet weather) and localised ‘sags’ in the topography (where ponding is likely to occur) can be considered at risk of localised flooding, which should be taken into account early in the planning process.

76. In an endeavour to address this high degree of uncertainty, and building upon the general

principles set out above, Defra and the Environment Agency has commissioned a series of pilot “Integrated Urban Drainage” (IUD) studies. These studies are focussed specifically upon assessing (and managing) the potential risk of flooding within urbanised area from localised sources. The River Hogsmill Integrated Urban Drainage Pilot Study was completed in 2008, providing an overview of the potential risk of flooding to properties within the Royal Borough of Kingston from sewers, surface water (flash) flooding, fluvial flooding and groundwater. The findings of the Hogsmill IUD study have been used to inform the development of the Kingston Borough SFRA, and is discussed further in Section 7.3.5 below.

77. It is important to recognise that development can fundamentally alter drainage patterns,

obstructing overland flow routes, and altering the volume and speed of runoff. The SFRA has therefore captured all readily available information relating to historical localised flooding (and the anticipated susceptibility to future flooding from localised sources) to inform future detailed FRAs. It is essential to highlight however that this should not be considered a comprehensive representation of all localised flood risks as indeed not all observed incidents may have been reported, and the blockage of culverts and gullies can happen anywhere.

5.4 Potential Impacts of Climate Change 78. A considerable amount of research is being carried out worldwide in an endeavour to

quantify the impacts that climate change is likely to have on flooding in future years. Climate change is perceived to represent an increasing risk to low lying areas of England, and it is anticipated that the frequency and severity of flooding will change measurably within our lifetime. PPS25 (Annex B) states that a 10% increase in the 1% AEP (100 year) river flow can be expected within the next 20 years, increasing to 20% within the next 100 years.

79. Consideration must be given to the probable change in flood risk over the lifetime of

development as a result of climate change. The likely increase in flow over the lifetime of the development should be assessed proportionally to the guidance provided by the EA as outlined above.

80. Detailed modelling of the impact of climate change throughout the Borough is available

only for the River Thames and River Hogsmill. For consistency therefore, and in the absence of a definitive flood outline elsewhere within the Borough, for planning purposes the anticipated extent of the 1% AEP (100 year, ie Flood Zone 3a) flood affected area in 2106 can be approximated by the current 0.1% AEP (1000 year) flood outline, i.e. Zone 2 Medium Probability.

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81. It is important to remember however that the potential impacts of climate change will

affect not only the risk of flooding posed to property as a result of river flooding, but it will also potentially increase the frequency and intensity of localised storms over the Borough. This may exacerbate localised drainage problems, and it is essential therefore that the detailed FRA considers the potential impacts of climate change upon localised flood risks, as well as the risks of fluvial flooding. The River Hogsmill IUD Pilot Study (Jacobs, 2007) has reviewed the potential impact that climate change may have upon the risk of flooding from other (non fluvial) sources. The results of that study will feed into the review of this document.

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6 Flood Risk in the Royal Borough of Kingston

6.1 Overview

82. The northern and eastern boundaries of the Royal Borough of Kingston upon Thames are delineated by the River Thames and Beverley Brook respectively, and the River Hogsmill flows through the heart of the Borough (refer Appendix D, Figure A). A review of potential flood risk (from all sources) has been carried out, and this is outlined below.

6.2 Historical River Flooding

83. Flooding has occurred within the Royal Borough of Kingston as recently as July 2007, during which a number of roads and rail connections were severely disrupted following a prolonged period of particularly heavy rain. Numerous incidents of localised flooding have been identified in consultation with the Environment Agency and the Council throughout the Borough, and these are outlined below (and presented in the adjoining maps). These are predominantly issues of a localised nature however, and are not associated with flooding from rivers.

84. Flooding from rivers within the Royal Borough of Kingston has historically been largely

contained to Kingston upon Thames town centre, within which both the River Thames and the River Hogsmill have broken their banks, inundating property and disrupting livelihood. Kingston upon Thames is the subject of the Kingston Town Centre SFRA (Jacobs, 2007) and falls outside the scope of current investigation, however it is important to once again emphasise that development within the upper reaches of the River Hogsmill catchment can increase in the risk of flooding downstream if not carefully managed.

6.3 Fluvial Flood Risk

85. The risk of flooding to property from rivers within the wider Borough of Kingston is relatively low. The river valleys are relatively well defined, and effective planning controls have prevented development from encroaching heavily upon the waterway corridors of the River Hogsmill and Beverley Brook. Consequently, a large proportion of the delineated PPS25 flood zones (depicting the areas potentially at risk of flooding from rivers in a 1 in 100 year, and 1 in 1000 year design event) are currently open space.

86. There are some exceptions, and a very small number of properties immediately adjoining

the River Hogsmill (Surbiton Stream) and Beverley Brook corridors may experience flooding of back gardens during a 1 in 100 year design event. The Kingston upon Thames town centre is indeed at risk of relatively frequent flooding not only from the River Hogsmill, but also from the River Thames. Once again however, it is reiterated that Kingston upon Thames has been explicitly considered as part of the Kingston Town Centre SFRA, and therefore does not form part of the current investigation.

87. Not surprisingly, the predicted extent of flooding in the 1 in 1000 year event markedly

increases the number of properties potentially at risk of flooding from rivers within the Borough. This is particularly evident within New Malden (adjoining Beverley Brook), Southborough & Hook (adjoining the upper reaches of Surbiton Stream) and the Sewage Works upstream of Kingston upon Thames (adjoining the River Hogsmill).

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88. It is highlighted that an event of this magnitude (i.e. 0.1% chance of occurring in any year,

or 1 in 1000) is difficult to model accurately, and uncertainty in the predicted flood extent is inevitable. This does however provide a good depiction of areas that may be at risk in the future. Development may increase runoff from the catchment if not managed carefully through the design process. Climate change is also expected to increase the intensity of rainfall, and collectively these contributing factors may result in a measurable increase the frequency and magnitude of flood flows within the local rivers, increasing the risk of river flooding to these properties.

6.4 Risk to Life from Flooding (Flood Hazard)

Flood Hazard due to Overbank Flooding

89. The speed and depth with which the River Thames and its tributaries flood into developed areas of the Royal Borough of Kingston is an important consideration. Deep, fast flowing water may potentially pose risk to life. This must be considered when planning future development.

River Thames

90. Detailed modelling indicates that the likelihood of a rapid river level rise within the River

Thames system, resulting in the rapid inundation of urban areas that may pose a risk to life, is considered to be very small. This is primarily due to relatively large catchment area, resulting in a generally extended response time. In simple terms, the time between a rainfall event occurring and river levels rising to the point at which flooding occurs generally exceeds 18 hours14 at Kingston upon Thames. Furthermore, the depth of flooding within overbank (developed) areas is typically relatively low, and is unlikely to pose a risk to life.

River Hogsmill & Beverley Brook

91. The River Hogsmill and Beverley Brook catchments are relatively small (in comparison to the River Thames) and will respond far more quickly, with river levels rising typically within 1 to 6 hours of a rainfall event. Within the Royal Borough of Kingston, outside of the town centre15 relatively few properties and/or roads are at risk of fluvial flooding. Furthermore, the extent, depth and velocity of the flow overland are generally low. For this reason, overbank flooding from the River Hogsmill and/or Beverley Brook is considered unlikely to pose an immediate risk to life.

Flood Hazard due to Reservoir Failure

92. There are no known water storage facilities within (or adjacent to) the Royal Borough of

Kingston upon Thames that may pose a potential risk of flooding to properties within the Borough.

Flood Hazard due to Flood Defence Failure

93. Two formal flood defence structures have been identified within the Environment

Agency’s National Flood & Coastal Defence Database (NFCDD), situated at the Sewage Treatment Works (River Hogsmill) and Motspur Park (Beverley Brook) respectively. These appear to be situated at the periphery of the natural floodplain, and therefore during a flooding event, the depth of water behind the embankment will be very minimal. Consequently, the likelihood of these defences suffering a catastrophic collapse and potentially posing a risk to life is considered negligible.

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94. Notwithstanding this however, there are a number of embankments situated throughout the Borough that alter the natural progression of floodwater as it flows overland (i.e. once breaking out of the river). These embankments are typically raised road or rail structures that clearly have not been constructed to hold water. As water levels rise however, these embankments will provide a barrier to the flow, altering the flooding regime. Ponding may occur behind the embankments, increasing the depth and width of the floodplain. Conversely however, areas on the ‘dry side’ of the embankments may be offered a degree of protection against flooding that they would not otherwise receive if the floodwaters were permitted to take their natural course.

95. The structures within the Borough that are recognised as ‘informal flood defences’ include

(for example) Robin Hood Way at Kingston Vale, and the railway embankment at Motspur Park.

96. These structures are typically substantial engineered embankments that are extremely

unlikely to suffer catastrophic failure as a result of flooding. For this reason, the risk of catastrophic failure resulting in a direct risk to life at these locations is considered negligible, and therefore the flood hazard associated with these structures has not been considered further in this instance.

6.5 Localised Flood Risk

Local Drainage Issues

97. A number of observed incidents of flooding throughout the Royal Borough of Kingston have been collated through discussions with the EA and the Council as part of this investigation, and these are captured (and described) in the adjoining flood maps. Not surprisingly, many of these incidents are within relatively densely urbanised parts of the Borough, in particular Berrylands (adjoining Surbiton Stream). The date and cause of flooding has been listed on the maps wherever possible, however it is important to recognise that this can often be somewhat subjective.

98. On 20 July 2007, widespread localised flooding was experienced throughout the Greater

London area, including within the Royal Borough of Kingston. An incident report prepared by the Council during the midst of the flooding has been provided, highlighting the following observations:

� Kingston Bypass (A3) has been closed due to flooding in the Hook and New

Malden underpasses; � All traffic is being diverted out of the Town Centre due to severe flooding; � Wood Street, Richmond Road and London Road underpasses (Town Centre)

have been flooded; � Cambridge Road (A240) has been closed due to flooding; � No trains are stopping at Kingston.

99. The capturing of historical incidents of flooding within the Borough as part of the SFRA is

an important trigger to prospective developers to consider what has happened in the past, developing a design that will seek to ensure that similar problems do not reoccur in the future. It is important to recognise however that historical flooding is not necessarily a measure of the potential risk of flooding in the future. Indeed, localised flooding (including surface water (flash) flooding, groundwater flooding, and/or surcharging of the sewer system) may occur anywhere within the Borough.

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100. The River Hogsmill Integrated Urban Drainage Pilot Study (Jacobs, 2008) has considered

the potential risk posed by flooding from other (non-river) sources, including surface water flooding (or overland flow), and exceedance of the surface & foul sewer networks. Modelling has been undertaken, and it is estimated that approximately 80 properties within the Borough are potentially at risk from surface water (flash) flooding in a 1 in 100 year storm event. This is flooding from runoff that is conveyed overland before reaching a drain or gully. A further 200 properties are potentially at risk from surcharging of the sewer network in the 1 in 100 year event. This is flooding from clean and/or foul water that exceeds the capacity of the underground sewer system, and is therefore surcharged back onto the surface.

101. It is important to highlight that, throughout much of England, the drainage (sewer) network

is typically designed to cater for no greater than a 1 in 30 year design storm. For this reason, any event that exceeds this probability can be expected to result in overland flow that may pose a risk of flooding to local properties. The modelling carried out as part of the Hogsmill IUD Pilot Study has highlighted that the densely populated areas of Berrylands and Southborough (adjoining the lower reaches of Surbiton Stream) are most susceptible to flooding of this nature16. This is supported to a large degree by the density of observed incidents of flooding within this area (refer flood maps).

102. The risk of flooding from surface water and/or the sewer network is difficult to predict

accurately, and is heavily dependant upon local conditions during the passing of a storm. For example, leaves and/or a parked car may be blocking a gully, water levels within the receiving watercourse may be elevated preventing free drainage from (or backing up of) the sewers. It is important therefore to ensure that the potential risk of localised flooding to a property is considered within a local context. This is most appropriate at the development application stage (i.e. as part of the detailed Flood Risk Assessment).

103. A Flood Risk Tool has been developed as part of the River Hogsmill IUD Pilot Study

(refer Section 7.3.5) that holds up-to-date information relating to flooding within the catchment including (for example) overland flow paths. This is a useful source of data to inform the planning process, and further information is available at www.defra.gov.uk/environ/fcd/policy/strategy/ha2.htm. Developers should seek localised flooding related information from the Environment Agency at an early stage in the development of the detailed FRA.

104. It is anticipated that a Surface Water Management Plan (SWMP) will be commenced

within the coming year. This will be a borough wide investigation, and will identify areas that may potentially be at risk from surface water and groundwater flooding. It is recommended that the Council seeks a detailed Flood Risk Assessment (FRA) for all proposed development within areas that are considered to be susceptible to flooding from surface water and/or groundwater, irrespective of the land area (i.e. including sites that are less than 1ha in area).

105. Until such time as the SWMP is in place however, incidents of observed localised flooding

should be adopted as the trigger for a FRA (refer adjoining flood risk maps). The purpose of the FRA is to ensure both that the potential risk of flooding to the proposed development is understood and mitigated, and that the proposed development does not worsen the risk posed to surrounding properties, as explained in Section 7.6.1.

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Groundwater Flooding

106. A large proportion of the Royal Borough of Kingston overlay London Clay (refer below) and consequently the risk of groundwater flooding will typically be very low. Areas adjoining the River Thames corridor however are often characterised by deposits of gravel above the clay layer. These are referred to as ‘Thames Gravels’ and there is evidence within adjoining Boroughs of groundwater flooding occurring some distance from the river as a result of water finding a pathway through the gravels during high river levels.

107. Evidence of historical groundwater flooding within the Royal Borough of Kingston is

relatively limited, but it is important to recognise that the risk of groundwater flooding is highly variable and heavily dependent upon local conditions at any particular time. It is not possible to sensibly develop a strategic map of ‘groundwater risk’ as part of the SFRA process. The risk of groundwater flooding was considered as an integral part of the River Hogsmill IUD Pilot Study, and ‘groundwater envelopes’ have been established on the basis of observed incidents of groundwater related flooding within the Borough. It is important to recognise however that historical flooding is not a robust measure of the risk of flooding in future years.

108. Due to the high degree of variability when considering groundwater flooding, it is

important to ensure that the potential risk of groundwater flooding to a property is considered within a local context. This is most appropriate at the development application stage (i.e. as part of the detailed Flood Risk Assessment).

6.6 Topography & Geology

Topography

109. The Royal Borough of Kingston is situated immediately adjacent to the River Thames, and a relatively large proportion of the Borough is contained within the River Hogsmill catchment. Only a small proportion of the Borough (including Surbiton and New Malden) fall outside of the River Hogsmill catchment, draining to the River Thames and Beverley Brook respectively. An overview of the topography of the Borough is provided in Appendix D, Figure B.

110. The topography of Kingston Borough is characterised to a large degree by its rivers.

Whilst a large proportion of the Borough could be described as gently undulating, the escarpment that forms the western boundary of the Hogsmill catchment is a noticeable area of high ground separating the town centres of Kingston upon Thames and Surbiton. The river corridors throughout the Borough are generally well defined, however it is clear from the flood maps accompanying this report that there are areas adjoining the waterways that are susceptible to river flooding. A large proportion of these areas have not been developed, and indeed it is important that the planning process continues to protect these areas as natural floodplain corridors.

Geology

111. The geology of the Royal Borough of Kingston is characterised to a very large degree by

London Clay, as outlined in Appendix D, Figure C. The impermeable nature of the soils can increase the susceptibility of the area to surface water (or flash) flooding following periods of heavy rainfall. Immediately adjoining the River Thames, deposits of gravel overlay the London Clay, and this can lead to localised incidents of groundwater flooding. The geology of the Borough will heavily influence the functionality of Sustainable Drainage (SuDS) techniques, and should be carefully considered as part of the design process. This is discussed further in Section 7.6.3.

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6.7 Impacts of Climate Change upon Flood Risk

112. Detailed modelling of the potential impacts of climate change upon fluvial flood risk within the Royal Borough of Kingston has been carried out by the Environment Agency for the River Thames and River Hogsmill only (as reflected in the adjoining maps). Within other areas of the Borough that have not been modelled, including Beverley Brook and the tributaries of the River Hogsmill, Zone 2 Medium Probability is considered a reasonable approximation of the likely extent of the High Probability flood zone in 100 years as a result of climate change for planning purposes.

113. It is clear that climate change will not markedly increase the extent of river flooding

within most areas of the Borough. Consequently, few areas that are currently situated outside of Zone 3 High Probability will be at substantial risk of flooding in the forseeable future. This is an important conclusion from a spatial planning perspective.

114. It is important to recognise that those properties (and areas) that are currently at risk

of flooding may be susceptible to more frequent, more severe flooding in future years. It is essential therefore that the development control process (influencing the design of future development within the Borough) carefully mitigates against the potential impact that climate change may have upon the risk of flooding to the property.

115. For this reason, all of the development control recommendations set out below require all

floor levels, access routes, drainage systems and flood mitigation measures to be designed with an allowance for climate change. This provides a robust and sustainable approach to the potential impacts that climate change may have upon the Borough over the next 100 years, ensuring that future development is considered in light of the possible increases in flood risk over time.

116. Once again, it is emphasised that the potential impacts of climate change will affect not

only the risk of flooding posed to property as a result of river flooding, but it will also potentially increase the frequency and intensity of localised storms over the Borough. This may exacerbate localised drainage problems. The potential impact that climate change may have upon localised flood risks within the Borough is assessed by the River Hogsmill IUD Pilot Study.

6.8 Residual Risk of Flooding

117. It is essential that the risk of flooding is minimised over the lifetime of the development in all instances. It is important to recognise however that flood risk can never be fully mitigated, and there will always be a residual risk of flooding.

118. This residual risk is associated with a number of potential risk factors including:

� a flooding event that exceeds that for which the local drainage system has

been designed; � the residual danger posed to property and life as a result of flood defence

failure; � general uncertainties inherent in the prediction of flooding.

119. The modelling of flood flows and flood levels is not an exact science, therefore there are

inherent uncertainties in the prediction of flood levels used in the assessment of flood risk. The adopted flood zones underpinning the Royal Borough of Kingston are largely based upon the detailed flood mapping within the area. Whilst these provide a robust depiction of flood risk for specific modelled conditions, all detailed modelling requires the making of core assumptions and the use of empirical estimations relating to (for example) rainfall distribution and catchment response.

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120. Taking a conservative approach for planning purposes, the Environment Agency advises that finished floor levels are raised to 300mm above the peak design flood level (including climate change) when advising developers.

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7 Sustainable Management of Flood Risk

7.1 Overview

121. An ability to demonstrate ‘sustainability’ is a primary government objective for future development within the UK. The definition of ‘sustainability’ encompasses a number of important issues ranging broadly from the environment (i.e. minimising the impact upon the natural environment) to energy consumption (i.e. seeking alternative sources of energy to avoid the depletion of natural resources). Of particular importance however is sustainable development within flood affected areas.

122. Recent history has shown the devastating impacts that flooding can have on lives, homes

and businesses. A considerable number of people live and work within areas that are susceptible to flooding, and ideally development should be moved away from these areas over time. It is recognised however that this is often not a practicable solution. For this reason, careful consideration must be taken of the measures that can be put into place to minimise the risk to property and life posed by flooding. These should address the flood risk not only in the short term, but throughout the lifetime of the proposed development. This is a requirement of PPS25.

123. The primary purpose of the SFRA is to inform decision making as part of the

planning and development control process, taking due consideration of the scale and nature of flood risk affecting the Borough (as discussed in the previous chapters of this report). Responsibility for flood risk management resides with all tiers of government, and indeed individual landowners, as outlined below.

7.2 Responsibility for Flood Risk Management

124. There is no statutory requirement for the Government to protect property against the risk of flooding. Notwithstanding this however, the Government recognise the importance of safeguarding the wider community, and in doing so the economic and social well being of the nation. An overview of key responsibilities with respect to flood risk management is provided below.

125. The Regional Assembly should consider flood risk when reviewing strategic planning

decisions including (for example) the provision of future housing and transport infrastructure.

126. The Environment Agency has a statutory responsibility for flood management and

defence in England. It assists the planning and development control process through the provision of information and advice regarding flood risk and flooding related issues.

127. The Local Planning Authority is responsible for carrying out a Strategic Flood Risk

Assessment. The SFRA should consider the risk of flooding throughout the district and should inform the allocation of land for future development, development control policies and sustainability appraisals. Local Planning Authorities have a responsibility to consult with the Environment Agency when making planning decisions.

128. Landowners & Developers17 have the primary responsibility for protecting their land

against the risk of flooding. They are also responsible for managing the drainage of their land such that they do not adversely impact upon adjoining properties.

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129. The Environment Agency has developed a guide entitled “Living on the Edge” that provides specific advice regarding the rights and responsibilities of riparian owners, the Environment Agency and other bodies. The guide is targeted at owners of land situated alongside rivers or other watercourses, and is a useful reference point outlining who is responsible for flood defence, and what this means in practical terms. It also discusses how stakeholders can work collaboratively to protect and enhance the natural environment of our rivers and streams. This guide can be found on the Environment Agency’s website at www.environment-agency.gov.uk.

7.3 Strategic Flood Risk Management - The Environment Agency

7.3.1 Overview

130. With the progressive development of urban areas along river corridors, particularly during the industrial era, a reactive approach to flood risk management evolved. As flooding occurred, walls or embankments were built to prevent inundation to developing areas. Needless to say, construction of such walls should be carefully assessed so that it does not result in the redistribution of floodwater, inadvertently increasing the risk of flooding elsewhere.

131. The Environment Agency (EA) in more recent years has taken a strategic approach to

flood risk management. The assessment and management of flood risk is carried out on a ‘whole of catchment’ basis. This enables the Environment Agency to review the impact that proposed defence works at a particular location may have upon flooding at other locations throughout the catchment.

132. A number of flood risk management strategies are underway within the region,

encompassing many of the large river systems that influence flood risk within the Royal Borough of Kingston upon Thames. A brief overview of these investigations is provided below.

7.3.2 Thames Catchment Flood Management Plan (CFMP)

133. “One of the Environment Agency ’s main goals is to reduce flood risk from rivers and the sea to people, property and the natural environment by supporting and implementing government policies.

134. Flooding is a natural process – we can never stop it happening altogether. So tackling

flooding is more than just defending against floods. It means understanding the complex causes of flooding and taking co-ordinated action on every front in partnership with others to reduce flood risk by:

� Understanding current and future flood risk; � Planning for the likely impacts of climate change; � Preventing inappropriate development in flood risk areas; � Delivering more sustainable measures to reduce flood risk; � Exploring the wider opportunities to reduce the sources of flood risk, including

changes in land use and land management practices and the use of sustainable drainage systems.

135. Catchment Flood Management Plans (CFMPs) are a planning tool through which the

Agency aims to work in partnership with other key decision-makers within a river catchment to explore and define long term sustainable policies for flood risk management. CFMPs are a learning process to support an integrated approach to land use planning and management, and also River Basin Management Plans under the Water Framework Directive.”18

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136. The flood risk regime within the Royal Borough of Kingston upon Thames is heavily

influenced by the River Thames and its tributaries. The Thames system is under careful consideration by the Environment Agency, and resources are currently being targeted at a strategic level to ensuring that the nature and severity of flood risk throughout the wider greater London area is broadly understood. This will enable the Environment Agency, responsible for the future management of flood risk within the area, to target future activities in a cost effective and sustainable manner. The River Thames CFMP was completed in July 2008, and the published Executive Summary can be located at http://www.environment-agency.gov.uk/commondata/acrobat/thames_cfmp_2103822.pdf.

137. The following key messages have been extracted from the published CFMP, of direct

relevance to the Kingston Borough SFRA:

Lower Thames Policy Unit (areas in close proximity to the River Thames) It will be important to identify which aspects of PPS25 (location, layout or design) will be the focus for managing flood risk when considered alongside the finalised option for the Lower Thames Flood Risk Management Strategy.

� Where we can, we will progress options to reduce flood risk that are most

effective and sustainable in the long-term. � It is vital that there is a shared vision for land use so that we can focus on the

most effective way of managing flood risk. In some places it will be through adaptation of the urban environment to make it more resilient to flooding and in others it will be about locating new development in areas of lowest risk

� These areas are located on large rivers where it is not generally possible to increase the capacity of the river to convey more flow. Within the urban floodplains we are seeking long-term adaptation to increase the resilience of what is at risk. In some cases re-locating areas of development may become an option

� Managing the consequences of flooding will be very important, particularly those areas where redevelopment rates are low and flood defences are not viable

It will be important to identify which aspects of PPS25 (location, layout or design) will be the focus for managing flood risk when considered alongside the finalised option for the Lower Thames Flood Risk Management Strategy.

Hogsmill Policy Unit and Beverly Brook Policy Unit

� We need long-term adaptation of the urban environment. There are massive opportunities to reduce flood risk through redevelopment. In most areas we need to change the character of the urban area in the floodplain through re-development. It must be resilient and resistant to flooding and result in a layout that re-creates river corridors

� We are seeking to re-create river corridors through redevelopment so that there is space for the river to flow more naturally and space in the floodplain where water can be attenuated

� We will be seeking to build flood defences as redevelopment occurs and as part of an overall catchment plan. This is because more attenuation and more space in the river corridors are needed for defences to be sustainable. This is more complex but represents better value for society in the long-run even if it is more costly for the Environment Agency today

� These areas are very susceptible to rapid flooding from thunderstorms. Emergency response and flood awareness are particularly important

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7.3.3 Lower Thames Strategy

138. The Lower Thames Strategy is being carried out by Halcrow and Jacobs on behalf of the EA, triggered as an outcome of the widespread flooding experienced within the catchment in 2003. The initial phase of the investigation was completed in 2005, considering the management of flood risk from the River Thames between Datchet and Walton Bridge. A subsequent phase has since been considered, reviewing the reach extending from Walton Bridge to Teddington.

139. The Strategy has investigated a number of large-scale engineering solutions, community

based measures and non-structural options to mitigate the risk to urban areas as a result of flooding from the River Thames. The engineering solutions considered included flood walls, flood storage, channel improvements (i.e. widening and/or deepening of the river channel), and the construction of new flood relief channels.

140. It has been concluded that there are a number of technical, environmental and economic

constraints that will dictate the viability of these engineering works for the reach of the Thames d/s of Walton Bridge, and these remain under investigation. In the short term, the Lower Thames Strategy is endeavouring to support the planning ‘impetus’ provided by the Thames CFMP, encouraging the local planning authorities to reduce risk through the implementation of effective and sustainable planning decisions and encouraging the adoption of individual property protection measures.

141. It is important to emphasise that the intention of the study is not to reduce flood risk in

order to make way for future development. It is also unlikely that the physical management measures identified will be in operation within foreseeable planning timeframes.

142. For this reason, the SFRA has not taken the potential flood risk reduction measures into

account. Within future planning horizons however, the revision of the SFRA should review the status of schemes recommended as an outcome of the Lower Thames Strategy, and consider the potential impact that these may have had upon flood risk within the Borough.

7.3.4 Hogsmill Flood Risk Management Delivery Plan

143. The Environment Agency’s approach to flood risk management in the River Hogsmill catchment will be outlined within the Hogsmill Flood Risk Managemetn Delivery Plan. This delivery plan will be developed in accordance with the outcomes and recommendations of the Thames Catchment Flood Risk Management Plan for the Hogsmill Policy Unit. The plan will include the recommendations of the Hogsmill IUD pilot study and previous studies carried out within the catchment. The Hogsmill Delivery Plan is due to be completed early 2009.

7.3.5 River Hogsmill Integrated Urban Drainage (IUD) Pilot Study 144. The Hogsmill Integrated Urban Drainage (IUD) Pilot Study was commissioned and funded

by Defra under project HA2 of the Government’s “Making space for water strategy”, and was completed in June 2008. The findings of the study are presented in the published report provided on the Defra website at http://www.defra.gov.uk/environ/fcd/policy/strategy/ha2/Hogsmill/finalreport.pdf

145. The Hogsmill IUD Pilot covers the whole of the Hogsmill catchment, encompassing the

northern most extents of the Borough of Reigate & Banstead, the Borough of Epsom & Ewell, and a large proportion of the Royal Borough of Kingston upon Thames. The four main partners involved in the delivery of the project included the local authorities of Kingston and Epsom & Ewell, Thames Water and the Environment Agency who are the lead organisation for the study. The technical delivery of the study was carried out by Jacobs.

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146. The primary objective of the Hogsmill IUD Study was “to better understand the level of flood risk from all sources in the catchment, identify its causes, and potential ways of reducing the risk”. The study identified that, across the catchment, over 1300 homes are at risk from surface water flooding. A further 3900 homes are at risk of flooding from rivers. Within the borough of Kingston, the study determined that approximately 4% of the damages sustained by flooding are as a result of surface water flooding19. Rather, the primary risk to property is as a result of river flooding.

147. A summary of the key findings in relation to the mechanisms of flooding within the

catchment is presented below, providing an overview of the critical physical characteristics that should be carefully considered when assessing the risk of flooding locally (i.e. as part of a detailed FRA).

Issue Findings

Impact of river flooding on surface water flooding

Surface water flooding is generally not affected by river flooding, other than within 50m of the river

Impact of transport infrastructure

There are several railway lines across the catchment that represent a barrier or diversion to natural overland flow paths

Importance of geology The upper catchment is chalk, which means there is no need for a pipe drainage system in these upper most reaches (i.e. Reigate & Banstead)

Flooding of low lying ground

The area of low lying ground adjacent to the River Hogsmill is modest, and limited to old quarries. There are no flood defences that would be vulnerable to breach at times of flooding.

Flooding mechanisms due to surface water flooding in 1% (1 in 100) event

Surface water flooding is typically around 0.2m in depth, except where ponding occurs upstream as a result of barriers to the flow. The velocity of overland flow is variable, up to approximately 1.5m/s.

148. A primary outcome of the Hogsmill IUD Study is a GIS based Flood Risk Tool (FRT). The

tool is “intended to provide a means of improving communication between stakeholders as to existing flood risk, developed as a single repository for available data and information on all sources of flood risk within the Hogsmill Catchment”. The FRT:

� Displays all potential flood risk in an integrated way; � Improves the knowledge and flood risk awareness for stakeholders; � Provides a useful tool to inform better planning decisions, and encourage

appropriate mitigation measures. 149. A suite of comprehensive flood risk maps, indicating the risk of flooding from all sources

within the Hogsmill catchment, is provided in Appendix A of the Hogsmill IUD Study. The Council is actively encouraged to reference these maps to provide an appreciation of the nature and severity of the risks posed by flooding within the area that they are considering for future development.

7.3.6 Beverley Brook Flood Risk Management Strategy

150. The Beverley Brook Flood Risk Management (FRM) Strategy is being carried out by the Environment Agency. The Strategy is focussing upon reducing damage to property situated within the Beverley Brook catchment. The Beverley Brook FRM Strategy is ongoing, and it is important that the findings and recommendations of the study are borne in mind to ensure (for example) that planning protection is provided to areas that may be sought for possible flood storage in future years.

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7.4 Application of PPS25 Within Kingston Borough – The Council

7.4.1 Planning Solutions to Flood Risk Management

The Sequential Test

151. Historically, urbanisation has evolved along river corridors due to the rivers providing a critical source of water, food and energy. This leaves many areas of England with a legacy of urban centres that, because of their close proximity to rivers, are at risk of flooding.

152. The ideal solution to effective and sustainable flood risk management is a planning led one, i.e. steer urban development away from areas that are susceptible to flooding. PPS25 advocates a sequential approach that will guide the planning decision making process (i.e. the allocation of sites). In simple terms, this requires planners to seek to allocate sites for future development within areas of lowest flood risk in the initial instance. Only if it can be demonstrated that there are no suitable sites within these areas should alternative sites (i.e. within areas that may potentially be at risk of flooding) be contemplated. This sequential approach is referred to as The Sequential Test, and is summarised in Figure 4.1 of the PPS25 Practice Guide (June 2008).

153. It is important to remember that PPS25 stipulates permissible development types. This considers both the degree of flood risk posed to the site, and the likely vulnerability of the proposed development to damage (and indeed the risk to the lives of the site tenants) should a flood occur. The Council must restrict development to the permissible land uses summarised in PPS25 Appendix D (Table D2). This may involve seeking opportunities to ‘swap’ more vulnerable allocations at risk of flooding with areas of lesser vulnerability that are situated on higher ground.

154. It is important to recognise that the principles of the sequential approach are applicable throughout the planning and development cycle, and refer equally to the forward planning process (delivered by Council as part of the LDF) as they do to the assessment of windfall sites. The Council will assist where possible with supporting information. The detailed FRA will be required to demonstrate the careful and measured consideration of whether indeed there is an alternative site available within an area of lesser flood risk, in accordance with the PPS25 Sequential Test20.

The Exception Test

155. A proportion of Kingston is situated within Zone 3a High Probability, including urban and retail centres. Prohibiting future development within these areas may have a detrimental impact upon the economic and social welfare of the existing community. It is essential that a sequential approach is taken to underpin all planning decisions as stipulated above. It may be however that pressing planning arguments (that outweigh flood risk) remain, putting into place a requirement to investigate further the possibility of regeneration and/or future development within areas at risk of flooding.

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It is absolutely imperative to highlight that the SFRA does not attempt, and indeed cannot, fully address the requirements of the PPS25 Sequential Test. As highlighted in Figure 4.1 of the PPS25 Practice Guide, it is necessary for the Council to demonstrate that sites for future development have been sought within the lowest flood risk zone (i.e. Zone 1 Low Probability). Only if it can be shown that suitable sites are not available within this zone can alternative sites be considered within the areas that are at greater risk of possible flooding (i.e. Zone 2, and finally Zone 3).

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156. Should this be the case, the Council and potential future developers are required to work through the Exception Test (PPS25 Appendix D) where applicable. It is important to remember that the Sequential Test should always be carried out prior to the Exception Test. For the Exception Test to be passed:

� “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 DPD has reached the ‘submission’ stage, the benefits of the development should contribute to the Development Plan Document’s Sustainability Appraisal;

� the development should be on developable, previously development land or if it is not on previously developed land, that there are no reasonable alternative sites on previously developed land; and

The first two points set out in the Exception Test are planning considerations. A planning solution to removing flood risk must be sought at each specific location in the initial instance, seeking to relocate the proposed allocation to an area of lower flood risk (i.e. Zone 1 Low Probability or Zone 2 Medium Probability) wherever feasible.

The Kingston Borough SFRA has been developed to inform the Sequential Test. It will be the responsibility of the Council to carry out the Sequential Test on the basis of this information, allocating potential sites for future development accordingly. Equally developers proposing sites in Zone 3 or Zone 2 will be required to demonstrate within the detailed Flood Risk Assessment that the Sequential Test has been applied, and (where appropriate) that the risk of flooding has been adequately addressed in accordance with PPS25.

� a FRA must demonstrate that the development will be safe, without increasing flood

risk elsewhere, and, where possible, will reduce flood risk overall;

The management of flood risk throughout the district must be assured should development be permitted to proceed, addressing the third critical element of the Exception Test. The SFRA has provided specific recommendations that ultimately should be adopted as design features, with evidence provided of how they will be fulfilled prior to permission being granted for all future development. It is the responsibility of the prospective developer to build upon these recommendations as part of a detailed Flood Risk Assessment to ensure that the specific requirements of PPS25 can be met.

157. An overview of flood risk throughout the borough has been provided in Section 6. Future planning decisions should consider the spatial variation in flood risk across the district, as defined by the delineated flood zone that applies at the specified site location, and apply the recommendations provided below accordingly. It is reiterated that PPS25 applies to allocated sites identified within the emerging LDF and to future windfall sites.

7.4.2 A Proactive Approach – Positive Reduction of Flood Risk through Development

158. PPS25 does not only consider the risk of flooding posed to new development, it also seeks to positively reduce the risk of flooding posed to existing properties within the Borough. This principle should be adopted as the underlying ‘goal’ for all planning and development control decisions.

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159. Developers should be encouraged to demonstrate that their proposal will deliver a positive reduction in flood risk, whether that be by reducing the frequency or severity of flooding (for example, through the introduction of SuDS), or by reducing the impact that flooding may have on the community (for example, through a reduction in the number of people within the site that may be at risk). This should not be seen as an onerous requirement, and indeed if integrated into the design at the conceptual stage, will place no added demands upon the development and/or planning application process. It is highlighted that the principles of flood risk reduction through redevelopment are reinforced by the findings and recommendations of the Thames CFMP (refer Section 7.3.2 above).

160. Possible risk reduction measures for consideration may include the following:

� The integration of SuDS to reduce the runoff rate from the site; � A change in land use to reduce the vulnerability of the proposed development; � A reduction in the building platform area; � The raising of internal floor levels and flood proofing (within existing buildings) to

reduce potential flood damage; � The rearrangement of buildings within the site to remove obstructions to overland

flow paths; � The placement of buildings to higher areas within the site to limit the risk of flood

damage.

161. It is recommended that each FRA summarises how a reduction in flood risk has been achieved within the proposed (re)development. This may be specified as (for example) a reduction in flow from the site, a reduction in water levels within (or adjacent to) the site, or a reduction in the consequences of flooding.

7.4.3 Localised Flood Risk within the Planning Process

162. The PPS25 Practice Guide requires the application of a sequential approach when allocating land, taking into consideration all sources of flooding. The local drainage related problems identified within the Kingston Borough SFRA relate to historical incidents, the source of which is often somewhat uncertain. It is important to recognise therefore that these are not necessarily a measure of ‘risk’, but rather problems that have occurred due to a particular set of local circumstances in the past (for example, the blockage of a local gully inlet). These may or may not reoccur in future years.

163. It is unreasonable to restrict future development within areas that may have suffered a

localised flooding incident in years past that were the result of circumstances unlikely to reoccur. It is essential however not to overlook the potential risk of localised flooding during the design process. The Council when seeking to allocate sites, and developers through FRAs, must consider localised flood risk. Whilst the incidents that have been identified in this SFRA will typically not result in widespread damage or disruption, a proactive approach to risk reduction through design can mitigate the potential for damage, both to the development itself and elsewhere. Specific development control recommendations have been provided accordingly.

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onsid

ere

d in

th

is r

egard

, and it

is

hig

hly

questio

nable

wheth

er

insura

nc

e a

gain

st floodin

g r

ela

ted

dam

age

s w

ill b

e

availa

ble

in the lo

nger

term

. F

utu

re d

eve

lopm

ent

with

in Z

one 3

b F

unctio

na

l Flo

odp

lain

can o

nly

be c

onsid

ere

d f

ollo

win

g a

pplic

atio

n o

f th

e S

equ

entia

l Te

st.

Fu

ture

dev

elo

pm

en

t w

ithin

Zone 3

a H

igh P

robability

can o

nly

be c

ons

idere

d f

ollo

win

g

applic

atio

n o

f th

e S

equen

tial T

est

Futu

re d

evelo

pm

ent w

ithin

Zon

e 2

Med

ium

Pro

bability

ca

n o

nly

be c

onsid

ere

d f

ollo

win

g

app

licatio

n o

f th

e S

equentia

l Test

It is

impo

rtant to

recognis

e that site

s w

ithin

Zone 1

may b

e s

uscep

tible

to f

loodin

g f

rom

oth

er

sourc

es.

Develo

pm

ent m

ay c

ontr

ibute

to a

n in

cre

as

e in

flo

od r

isk

els

ew

here

if

not care

fully

miti

gate

d

Land U

se (

refe

r T

able

D2

of

PP

S2

5)W

ate

r C

om

patib

le D

evelo

pm

ent and/o

r Essen

tial I

nfr

astr

uctu

reL

and u

se

should

be r

estr

icte

d to W

ate

r C

om

patib

le o

r Less V

uln

era

ble

deve

lopm

ent.

M

ore

Vuln

era

ble

de

velo

pm

ent m

ay o

nly

be c

onsid

ere

d if

Exce

ptio

n T

est can b

e p

asse

d

Land u

se

should

be r

estr

icte

d to W

ate

r C

om

patib

le, Less V

uln

era

ble

or

More

V

uln

era

ble

develo

pm

ent. H

ighly

Vuln

era

ble

develo

pm

ent m

ay o

nly

be c

onsid

ere

d if

Ex

ceptio

n T

est can

be p

ass

ed

No r

es

tric

tions

Pe

rmitt

ed D

evelo

pm

ent &

Pro

pert

y

Subdiv

isio

nN

ot A

pplic

able

Build

ing e

xte

nsio

ns (

inclu

din

g o

ut-

build

ings

) should

be d

isc

oura

ged

to a

void

rais

ing

flood

levels

els

ew

here

. P

rope

rty s

ubd

ivis

ion m

ay in

cre

ase the

inte

nsity

of

develo

pm

ent, a

nd

the p

op

ula

tion a

t risk,

an

d s

hould

be d

isc

oura

ged

No

restr

ictio

ns

No r

es

tric

tions

Deta

iled F

lood R

isk

Assess

ment

(FR

A)

Re

quired

Requ

ired

Required

Required

for

all

site

s g

rea

ter

than

1ha in

are

a. R

ecom

men

d that all

site

s c

arr

y o

ut

an

assess

ment of

localis

ed

flo

od r

isks

, in

clu

din

g s

urf

ace w

ate

r flood

ing (

wh

ere

sew

er

syste

m is

exc

eeded)

and g

rou

ndw

ate

r floodin

g, w

here

an in

cid

ent of

localis

ed

flood

ing h

as b

een o

bs

erv

ed.

Flo

or

Le

vel

No m

inim

um

level s

tipula

ted b

y P

PS

25

Site

Access &

Egre

ss

Not A

pplic

able

No m

inim

um

level s

tipula

ted b

y P

PS

25

Basem

ents

Not A

pplic

able

Ba

sem

ent

dw

elling

s (

self c

onta

ined

) are

no

t perm

itte

d w

ithin

Zone 3

a H

igh P

robability

.

No

sle

epin

g a

ccom

odatio

n is

perm

itted a

t ba

sem

ent

level.

All

basem

ents

mus

t have a

n

access p

oin

t fo

r escape

that is

above the

1 in

100

year

riv

er

flood

level,

inclu

din

g

clim

ate

change.

All

basem

en

ts m

ust h

ave a

n a

ccess p

oin

t fo

r escape t

hat is

ab

ove the

1 in

100

year

river

flo

od le

vel,

inclu

din

g c

limate

change

.N

o r

es

tric

tions

Site

Run

off

Buff

er

Zone

SPA

TIA

L P

LA

NN

ING

REC

OM

MEN

DA

TIO

NS

PPS

25 R

equ

irem

ent

Zone 2

Mediu

m P

robability

Zo

ne 1

Lo

w P

roba

bility

Zon

e 3

b F

un

ctio

nal F

loodpla

inZ

on

e 3

a H

igh

Pro

bab

ility

Oth

er

DEV

ELO

PM

EN

T C

ON

TR

OL R

EC

OM

ME

ND

ATIO

NS

To

be s

ituate

d a

min

imum

of

300m

m a

bove t

he 1

in 1

00 y

ear

river

flo

od le

vel,

inclu

din

g c

limate

change

Imple

me

nt S

uD

S to e

nsure

that ru

noff

fro

m the s

ite (

post re

develo

pm

ent)

does n

ot

exceed g

reenfield

runoff

rate

s. A

ny S

uD

S d

esig

n m

ust ta

ke d

ue a

ccount o

f gro

und

wate

r an

d g

eolo

gic

al c

on

diti

ons (

refe

r S

ectio

n 8

.6.3

)

A m

inim

um

8m

buff

er

zone m

us

t be p

rov

ided to ‘t

op o

f ba

nk’

with

in s

ites im

media

tely

adjo

inin

g a

riv

er

corr

idor.

This

rela

tes t

o b

oth

open w

ate

rways

and c

ulv

ert

ed w

ate

rway

corr

ido

rs. R

efe

rence s

hould

be

made to

the E

nv

ironm

ent

Agency

's "

Liv

ing o

n the E

dge"

gu

ide (

ww

w.e

nvir

onm

ent-

agency.g

ov.u

k) t

hat dis

cusses a

ny d

evelo

pm

ent s

ituate

d in

, over,

under

or

adja

ce

nt to

riv

ers

and/o

r str

eam

s

As a

n in

tegra

l part

of

the g

overn

ment’s

“M

aki

ng S

pace f

or

Wate

r” a

genda

, th

e E

nvironm

en

t A

genc

y is

activ

ely

see

king the r

enatu

ralis

atio

n o

f culv

ert

ed w

ate

rcours

es a

s p

art

of

any f

utu

re d

evelo

pm

ent. R

ea

listic

opp

ort

uniti

es to r

ein

sta

te the

natu

ral o

pen w

ate

rway

with

in e

xis

ting c

ulv

ert

ed

reaches

of

the r

iver(

s)

should

be

pro

mote

d

Ensure

that th

e p

ropose

d d

evelo

pm

ent d

oes n

ot

result

in a

n in

cre

ase in

maxim

um

flo

od le

vels

with

in a

djo

inin

g p

rope

rtie

s. T

his

may b

e a

chie

ved b

y e

nsuring (

for

exa

mple

) th

at th

e e

xis

ting b

uild

ing f

oo

tprint is

not in

cre

ased, th

at overla

nd f

low

route

s a

re n

ot tr

uncate

d b

y b

uild

ings a

nd

/or

infr

astr

uctu

re, or

hyd

raulic

ally

linke

d c

om

pens

ato

ry f

lood s

tora

ge

is p

rovid

ed w

ithin

the s

ite (

or

upstr

eam

)

Fo

r re

sid

entia

l pro

pert

y, dry

acces

s is

to b

e p

rovid

ed in

the 1

in 1

00 y

ear

rive

r flood.

For

com

merc

ial p

ropert

y, access

must be

'safe

' in

accord

ance w

ith D

efr

a "

Flo

od R

isk

to

Peo

ple

" (F

D2

320 &

FD

2321)

7.4.

4 S

pat

ial P

lan

nin

g &

Dev

elo

pm

ent

Co

ntr

ol R

eco

mm

end

atio

ns

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�� 23

7.4.5 Domestic and Non-Domestic Building Extensions

164. As referred to in Table 7.4.4 applications for minor domestic extensions and commercial extensions with a footprint of less than 250sqm, are not required to submit a FRA unless there are concerns about the potential cumulative impact from minor extensions. However, such applicants are encouraged to introduce SUDS and other risk reduction techniques wherever possible. Similarly applicants for development less than 1 hectre in Flood Zone 1 are not required to submit a FRA, but are encouraged to install SUDS and other risk reduction measures as well.

165. The progressive loss of valuable floodplain areas to extensions and/or outbuildings some

of which do not require planning permission is a concern. Whilst each individual extension may not result in a measurable impact upon localised flood levels, the cumulative impact of building extensions can significantly increase the risk of flooding.

166. Householder permitted development rights limit the ability of a local authority to control

some developments that increase flood risk. At the time of writing, and in the interests of modernising the planning system, the Government propose to extend permitted development rights for domestic extensions. However, a potential negative consequence of this modernising will be to further reduce planning controls over development and thereby increase flood risk. However, the Government is introducing a requirement to seek planning permission where a resident seeks to introduce/replace an impermeable front garden (i.e. hard standing area).

167. In addition, Councils do have existing statutory provisions that allow them to take back

control where this is necessary. Councils can use the provisions of Article 4 of the Town and Country Planning General Permitted Development Order 1995 to make a direction to remove specific development rights for property in specific geographical areas. This would require the householder to seek planning permission for development, and allow the Council to assess the possible impacts of the works, and decide whether to grant permission, if necessary subject to conditions (such as ensuring the use of permeable materials), or refuse it. Extending planning controls in this way in Flood Zones 3b, 3a and 2 in particular may be considered appropriate. The Council should be mindful that the loss of PD rights can lead to compensation claims from affected landowners.

7.5 Overview of Flood Risk & SFRA Map Interpretation

7.5.1 Interpretation of the Kingston Borough SFRA (Maps) 168. The spatial variation in flood risk across the Borough is depicted in the adjoining maps,

and described below. The Kingston Borough SFRA should be used by both the Council and prospective developers to meet their obligations under PPS25 throughout the planning cycle. Instructions for use are provided below.

The Council (Forward Planning)

Appendix C, Figures 1 to 7 provide an overview of the spatial variation in fluvial flood risk throughout the Borough (i.e. the risk of flooding from rivers), based upon current climate predictions (i.e. 2008). It is necessary to adopt a sequential approach when considering where land should be allocated for future development, and this is described in Section 7.4. These figures should be used to inform this sequential approach. Furthermore, PPS25 provides clear guidance on permissible land use within areas potentially at risk from flooding, and this too is discussed in Section 7.4.

The potential impact of climate change upon Zone 3a High Probability over the next 100 years is depicted in Figures 1 to 7. It is recognised that there is a relatively high degree of uncertainty surrounding climate change predictions, and it is likely that the predicted Zone 3a plus climate change outlines will change over time. In the interim, a conservative assessment has been undertaken as outlined in Section 6.7 above, informing the planning process at the current point in time.

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�� 24

Whilst there is no particular constraint placed upon land use within areas of Zone 1 Low Probability, it is necessary for the Council in identifying sites for future development to take due consideration of flooding from other sources (i.e. non fluvial). Observed incidents of localised flooding are also depicted in Figures 1 to 7, and these should be used to inform design to ensure that future development does not exacerbate these existing problems, and indeed reduces flood risk. Many of these localised sources of flooding can be effectively managed through the design process. However it is recommended that advice is taken from the Environment Agency to ensure that the severity of any local issue that may affect (or be exacerbated by) the proposed allocation is fully understood.

The Council (Development Control) & Developers

It is important that the potential risk of flooding is considered as an integral part of all proposed development. Appendix C, Figures 1 to 7 provide a measure of the severity of flooding within the proposed development site. These should be used to trigger a more detailed assessment of flood risk related issues within the site, as set out in a Flood Risk Assessment (see Section 7.6).

The assessment of localised flooding related issues is imperative for all proposed development, irrespective of its location and/or scale, and the SFRA provides some helpful tools to assist in this regard:

� Appendix C, Figures 1 to 7 provide an indication of areas that have been susceptible to localised flooding historically. This is not a comprehensive record of flooding, and relies upon community reports of flooding made to the Council(s). It is a good indication of areas that may be susceptible however, and reiterates the importance of considering flood risk related issues in areas that are beyond the designated PPS25 flood zones. Information relating to the wider Borough is also provided in Appendix D (including geology and topography).

169. An overview of the risk of flooding (providing a commentary on the maps) throughout the

Borough is outlined below.

7.5.2 Character Area KB1 – Coombe (refer to Figure 001)

Assessment of Flood Risk

A large proportion of Character Area KB1 is elevated and situated within ZONE 1 LOW PROBABILITY. Character Area KB1 is bounded to the east by Beverley Brook. The Environment Agency flood zone map (duplicated in Figure 001) indicates that open space areas adjoining the brook (i.e. to the east of Robin Hood Way) are subject to flooding, falling within ZONE 3A HIGH PROBABILITY. These have been retained as playing fields, and therefore there is no existing and/or potential future development at risk within current planning horizons. Future planning horizons should ensure that the open space areas adjoining the Beverley Brook waterway corridor, delineated as Zone 3a High Probability, are protected against future development. Localised flooding that has been observed historically is reflected in the adjoining flood maps. PPS25 (Appendix F) states that “Surface water arising from a developed site should, as far as is practicable, be managed in asustainable manner to mimic the surface water flows arising from the site prior to theproposed development, while reducing the flood risk to the site itself and elsewhere, taking climate change into account”. To this end, development should (as far as is practicable) be designed so that flows generated by the development are safely contained within the site up to and including the 1% (1 in 100) design event, including an allowance for climate change. Surface water flows that exceed this event should be managed so that they do not pose an unacceptable risk to people or property.

7.5.3

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�� 25

7.5.4 Character Area KB2 – Norbiton & New Malden (refer to Figure 002)


Character Area KB2 is bounded to the east and west by Beverley Brook and River Hogsmill respectively. A large proportion of the area is unaffected by fluvial (river) flooding, situated within ZONE 1 LOW PROBABILITY. A potential risk of flooding is anticipated within those areas adjoining the river corridors however. A potential risk of flooding associated with River Hogsmill is highlighted by the flood zone map (adjoining Figure 002). Currently no property appears to be at risk of flooding in Norbiton, the flood affected zone limited largely to open space areas adjoining the waterway corridor and the Sewerage Works. It is important to recognise however that River Hogsmill poses a marked risk of flooding to Kingston Town Centre, situated immediately downstream. All future development must be carefully planned to avoid any possible exacerbation of flood risk downstream. A potential risk of flooding has also been identified associated with Beverley Brook, affecting properties within New Malden. Properties situated between Malden Golf Course and Beverley Way are situated within ZONE 3A HIGH PROBABILITY. Coombe Brook is a tributary of Beverley Brook. The coarse nature of the flood mapping at this location (refer Figure 002) indicates that there is a considerable degree of uncertainty in the extent of flooding anticipated in the 1% (100 year) flood event. This affects homes within the housing estate adjoining Malden Golf Course and Coombe Road (i.e. Carlton Road & Belborne Road). Any future proposed redevelopment in this area will need to address the extent and severity of flooding associated with Coombe Brook. In the interim, properties within this area are delineated ZONE 3A HIGH PROBABILITY for planning purposes. Future planning decisions should ensure that the open space areas adjoining the Beverley Brook and River Hogsmill waterway corridors, delineated as Zone 3a High Probability, are protected against future development. Localised flooding that has been observed historically is reflected in the adjoining flood maps. PPS25 (Appendix F) states that “Surface water arising from a developed site should, as far as is practicable, be managed in asustainable manner to mimic the surface water flows arising from the site prior to theproposed development, while reducing the flood risk to the site itself and elsewhere, taking climate change into account”. To this end, development should (as far as is practicable) be designed so that flows generated by the development are safely contained within the site up to and including the 1% (1 in 100) design event, including an allowance for climate change. Surface water flows that exceed this event should be managed so that they do not pose an unacceptable risk to people or property.

7.5.5 Character Area KB3 – Old Malden & Motspur Park (refer to Figure 003)


Character Area KB3 is bounded by River Hogsmill to the west and Beverley Brook to the east. A large proportion of the area falls within LOW RISK AREA 1, however properties immediately adjoining the River Hogsmill and Beverley Brook waterway corridors are identified by the Environment Agency flood zone maps (refer Figure 003) as potentially at risk of flooding. A small number of homes within Motspur Park (Albert Road & Motspur Park) and Malden Green (Kingshill Ave) are delineated as ZONE 3A HIGH PROBABILITY, due to their proximity to Beverley Brook. Properties in Pembury Ave and surrounding the Malden Green railway station are delineated as Zone 2 Medium Probability, however the coarse nature of the flood zone map in this area indicates a high level of uncertainty in the accuracy of the predicted 0.1% (1000 year) flood extent in this vicinity. This may be associated with a localised dip in the surrounding topography within which local runoff may pond during an extreme event. There are no known observations of historical flooding at this location however. This zoning affects only core essential infrastructure, including (for example) hospitals and emergency services. For this reason, further investigation to remove the uncertainty is recommended only if essential infrastructure (i.e. development that should not be permitted in Zone 2 Medium Probability in accordance with PPS25) is being considered at these locations in future planning horizons. A small number of homes adjoining the River Hogsmill (i.e. properties in Southwood Drive) and its tributary (properties in the vicinity of Raeburn Ave) fall within ZONE 3A HIGH PROBABILITY, potentially affected by flooding in the 1% (100 year) event. Localised flooding has also been experienced in the vicinity of the River Hogsmill tributary, highlighting the susceptibility of properties to flooding in this locality. Most of the area affected by flooding in the 1% (100 year) event in the River Hogsmill corridor is currently designated open space. Future planning decisions should seek to protect this area from development. Currently the majority of properties within Character Area KB3 do not appear to be at risk of flooding directly. It is important to recognise however that the River Hogsmill and Beverley Brook pose a marked risk of flooding to Kingston town centre and Richmond (London Borough of Richmond upon Thames) respectively, situated downstream. All future development must be carefully planned to avoid any possible exacerbation of flood risk downstream.

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�� 26

Future planning decisions should ensure that the open space areas adjoining the Beverley Brook and River Hogsmill waterway corridors, delineated as Zone 3a High Probability, are protected against future development. Localised flooding that has been observed historically is reflected in the adjoining flood maps. A cluster of historical incidents are evident within Berrylands, and the interim findings of the River Hogsmill IUD Pilot Study confirms a particular susceptibility to surface water flooding and surcharging of the underground drainage system within this vicinity. Future development should carefully consider the capacity of the local drainage system and how this might influence the risk of localised flooding. PPS25 (Appendix F) states that “Surface water arising from a developed site should, as far as is practicable, be managed in asustainable manner to mimic the surface water flows arising from the site prior to theproposed development, while reducing the flood risk to the site itself and elsewhere, taking climate change into account”. To this end, development should (as far as is practicable) be designed so that flows generated by the development are safely contained within the site up to and including the 1% (1 in 100) design event, including an allowance for climate change. Surface water flows that exceed this event should be managed so that they do not pose an unacceptable risk to people or property.

7.5.6 Character Area KB4 – Tolworth, Hook & Riverhill (refer to Figure 004)


A large proportion of Character Area KB4 is situated within ZONE 1 LOW PROBABILITY. The area is bounded to the south east and north west by the River Hogsmill and its tributary respectively. The land adjoining the River Hogsmill corridor is largely open space. These areas are designated ZONE 3A HIGH PROBABILITY for planning purposes. In contrast, Surbiton Stream (a tributary of Hogsmill Brook) is heavily constrained by urban development, and a number of residential properties adjoining the waterway corridor are affected by the predicted 1% (100 year) flood extent. As a result, these properties are categorised as ZONE 3A HIGH PROBABILITY. A large number of properties situated within the uppermost reaches of the River Hogsmill tributary (i.e. Hook) are included within the ZONE 2 MEDIUM PROBABILITY in the current Environment Agency flood risk map (refer Figure 004). There is no obvious overland flow path at this location, indicating a culverted system. The coarse nature of the flood outline would seem to suggest a relatively high degree of uncertainty surrounding the predicted extent of the 0.1% (1000 year) flood, and may be associated with a localised dip in the surrounding topography within which local runoff may pond during an extreme event. There are no known observations of historical flooding at this location, however. This zoning affects only core essential infrastructure, including (for example) hospitals and emergency services. For this reason, further investigation to remove the uncertainty is recommended only if essential infrastructure (i.e. development that should not be permitted in Zone 2 Medium Probability in accordance with PPS25) is being considered at these locations in future planning horizons. Localised flooding that has been observed historically is reflected in the adjoining flood maps. PPS25 (Appendix F) states that “Surface water arising from a developed site should, as far as is practicable, be managed in asustainable manner to mimic the surface water flows arising from the site prior to theproposed development, while reducing the flood risk to the site itself and elsewhere, taking climate change into account”. To this end, development should (as far as is practicable) be designed so that flows generated by the development are safely contained within the site up to and including the 1% (1 in 100) design event, including an allowance for climate change. Surface water flows that exceed this event should be managed so that they do not pose an unacceptable risk to people or property. The majority of properties within Character Area KB4 are not at risk of flooding at the current time. It is important to recognise however that the River Hogsmill and Beverley Brook pose a marked risk of flooding to Kingston town centre and Richmond (London Borough of Richmond upon Thames) respectively, situated downstream. All future development must be carefully planned to avoid any possible exacerbation of flood risk downstream. Future planning decisions should ensure that the open space areas adjoining the River Hogsmill waterway corridor, delineated as Zone 3a High Probability, are protected against future development.

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�� 27

7.5.7 Character Area KB5 – Chessington (refer to Figure 005)


Character Area KB5 is situated within the upper most reaches of the River Hogsmill. With the exception of a narrow corridor of open space adjoining the waterway corridor, virtually the entire area falls within ZONE 1 LOW PROBABILITY. There are no known localised flooding issues affecting KB5. The village of Malden Rushett is categorised as ZONE 2 MEDIUM PROBABILITY within the current Environment Agency flood zone maps (refer Figure 005). This area is situated within the upper receiving waters of the River Hogsmill system, however is not directly linked to the main waterway corridor that commences some distance downstream. The coarse nature of the flood mapping at this location indicates a degree of uncertainty associated with the 0.1% (1000 year) flood outline, and may be associated with a localised dip in the surrounding topography within which local runoff may pond during an extreme event. Historical flooding has been observed at this location, however the source (and scale) of the flooding is unknown. This zoning affects only core essential infrastructure, including (for example) hospitals and emergency services. For this reason, further investigation to remove the uncertainty is recommended only if essential infrastructure (i.e. development that should not be permitted in Zone 2 Medium Probability in accordance with PPS25) is being considered at these locations in future planning horizons. Currently the majority of properties within Character Area KB3 do not appear to be at risk of flooding directly. It is important to recognise however that the River Hogsmill poses a marked risk of flooding to Kingston town centre downstream. All future development must be carefully planned to avoid any possible exacerbation of flood risk downstream. Future planning decisions should ensure that the open space areas adjoining the River Hogsmill waterway corridor, delineated as Zone 3a High Probability, are protected against future development. Localised flooding that has been observed historically is reflected in the adjoining flood maps. PPS25 (Appendix F) states that “Surface water arising from a developed site should, as far as is practicable, be managed in asustainable manner to mimic the surface water flows arising from the site prior to theproposed development, while reducing the flood risk to the site itself and elsewhere, taking climate change into account”. To this end, development should (as far as is practicable) be designed so that flows generated by the development are safely contained within the site up to and including the 1% (1 in 100) design event, including an allowance for climate change. Surface water flows that exceed this event should be managed so that they do not pose an unacceptable risk to people or property.

7.5.8 Character Area KB6 – North Kingston (refer to Figure 006)


The risk of flooding influencing future development within Kingston town centre has been reviewed in detail in the Kingston Town Centre Strategic Flood Risk Assessment (Jacobs, 2006). This is not considered in this SFRA. The vast majority of Character Area KB6 is situated in ZONE 1 LOW PROBABILITY. The largely residential area situated between Richmond Road and the River Thames is affected by fluvial flooding from the Thames, and a small number of properties situated on the eastern side of Skerne Road fall within the 1% (100 year) flood extent, designated ZONE 3A HIGH PROBABILITY. Properties adjoining Albany Views are not currently affected by flooding in the 1% (100 event), however detailed flood risk mapping indicates that climate change may increase the extent of flooding in future years. These properties may be affected by the 1% (100 year) flood extent within 50 years, and therefore for planning purposes it is recommended that this area is designated Zone 2 Medium Probability. Skerne Road is an identified flow path during River Thames flooding for relatively frequent events, including the 5% (20 year) design flood. As such, Skerne Road is considered ZONE 3B FUNCTIONAL FLOODPLAIN. As a road corridor, this will not unduly influence future development within the region. Emergency planning should carefully consider the potential risk to residents during flooding events, ensuring that an alternative evacuation route is available. Localised flooding that has been observed historically is reflected in the adjoining flood maps. PPS25 (Appendix F) states that “Surface water arising from a developed site should, as far as is practicable, be managed in asustainable manner to mimic the surface water flows arising from the site prior to theproposed development, while reducing the flood risk to the site itself and elsewhere, taking climate change into account”. To this end, development should (as far as is practicable) be designed so that flows generated by the development are safely contained within the site up to and including the 1% (1 in 100) design event, including an allowance for climate change. Surface water flows that exceed this event should be managed so that they do not pose an unacceptable risk to people or property.

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7.5.9 Character Area KB7 – Surbiton & Berrylands (refer to Figure 007)


Character Area KB7 is bounded by the River Thames to the west and the River Hogsmill to the east. The majority of the area falls within ZONE 1 LOW PROBABILITY, and therefore future development is generally not restricted under flood risk grounds. Notwithstanding this, detailed modelling indicates that future climate change may result in a small number of properties immediately adjoining the River Thames (i.e. situated to the west of the A307) being at risk of fluvial flooding during the 1% (100 year) design event within the next 50 years. It is recommended therefore that these areas are designated Zone 2 Medium Probability for planning purposes. Kingston town centre has been considered in detailed within the Kingston Town Centre SFRA (Jacobs, 2007) and is not investigated further in this study. The area immediately to the east of the town centre however is affected by flooding associated with the River Hogsmill, impacting upon a number of properties in the vicinity of Mill Street and Villiers Road. This area is designated ZONE 3A HIGH PROBABILITY accordingly, and careful planning is required within this area to minimise the potential risk to property and life. It is noted that this area is situated immediately downstream of the Sewerage Works (also contained within ZONE 3A HIGH PROBABILITY). It is understood that releases from the Sewerage Works results in a rapid increase in water levels within the River Hogsmill downstream. Discussions have been held with Thames Water in this regard, and it was confirmed that releases occur only in accordance with strict licence conditions that are in place to ensure that there is no impact upon flood risk downstream. Localised flooding that has been observed historically is reflected in the adjoining flood maps. PPS25 (Appendix F) states that “Surface water arising from a developed site should, as far as is practicable, be managed in asustainable manner to mimic the surface water flows arising from the site prior to theproposed development, while reducing the flood risk to the site itself and elsewhere, taking climate change into account”. To this end, development should (as far as is practicable) be designed so that flows generated by the development are safely contained within the site up to and including the 1% (1 in 100) design event, including an allowance for climate change. Surface water flows that exceed this event should be managed so that they do not pose an unacceptable risk to people or property.

7.5.10 Proposal Sites (Adopted UDP August 2005) 170. An assessment of flood risk relating to the Proposal Sites identified in the Adopted UDP

has been undertaken, and is presented in adjoining Appendix A. The risk of flooding posed to (and by) the proposed development has been considered. Where possible at this stage, a cross check has been carried out between the proposed land use, and the vulnerability criteria provided by PPS25. This provides an indication of whether or not the sites are likely to meet the requirements of the Exceptions Test. Please note that the Exceptions Test should not be considered until such time as the Sequential Test has been applied.

171. All of the site allocations in the Council’s adopted UDP, with the exception of PS29b (the

Territorial Army Depot, Portsmouth Road) are situated within Zone 1 Low Probability. In due course when the UDP site allocations are superseded by allocations in the Local Development Framework, all allocated sites will have been sequentially tested by the Council

172. It is reiterated that this assessment does not attempt to review the specific proposal sites

situated within Kingston Town Centre (refer Kingston Town Centre Area Action Plan and supporting SFRA).

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7.6 Detailed Flood Risk Assessment (FRA) – The Developer

7.6.1 Scope of the Detailed Flood Risk Assessment 173. The SFRA is a strategic document that provides an overview of flood risk throughout the

district. Once the Sequential Test has been applied in accordance with Section 7.4 to determine the allocation of sites for future development, it is imperative that a site-based Flood Risk Assessment (FRA) is carried out by the developer for all proposed developments. This should be submitted as an integral part of the planning application. It is emphasised that, for windfall sites, it will be necessary for the developer to demonstrate that the Sequential Test has been applied (in accordance with PPS25) within the detailed FRA.

174. The FRA should be commensurate with the risk of flooding to the proposed development.

For example, where the risk of flooding to the site is negligible (e.g. Zone 1 Low Probability), there is little benefit to be gained in assessing the potential risk to life and/or property as a result of flooding. Rather, emphasis should be placed on ensuring that runoff from the site does not exacerbate flooding lower in the catchment. The particular requirements for FRAs within each delineated flood zone are outlined below.

175. Proposed Development within Zone 3a High Probability and Zone 3b Functional

Floodplain

All FRAs supporting proposed development within Zone 3b Functional Floodplain and Zone 3a High Probability should include an assessment of the following.

� The vulnerability of the development to flooding from other sources (e.g. surface water drainage and/or groundwater) as well as from river flooding. In addition to the use of information provided within the SFRA, this will involve discussion with the Council 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 all sources of flooding, i.e. 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 (with respect to fluvial flooding) 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 by suitably qualified engineers may be required to determine the risk of flooding to the site. The propensity of culverted systems to block, increasing the risk of flooding, should be considered.

� The presence of both formal and de-facto (including, for example, local road and/or rail embankments) flood defences within the proximity of the site must be considered. Flood defences may alter the risk of flooding within the site, and it is imperative that any change in the flooding regime as a result of a flood defence is thoroughly understood. The integrity of the defence must be assessed to ensure that the defence will be structurally sound throughout the lifetime of the proposed development. The potential impact of a defence failure must be considered.

The detailed FRA should utilise the background information provided within this Level 1 SFRA, as explained in Section 7.5.1. It is important to reiterate that the SFRA provides the best available information at the time of writing. As highlighted below, the Environment Agency is an excellent source of information to inform the development of the detailed FRA, and they should be contacted as early as possible to source additional (more recent) information as appropriate.

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� 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 a suitably qualified engineer. It is emphasised that the detailed assessment of potential impacts elsewhere should not be limited (in a geographical sense) to within the borough. Future development within the district may adversely affect sites within adjoining Boroughs, and it is essential that this is mitigated.

� 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, provision for 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

� Details of proposed sustainable drainage systems (SUDS) that will be implemented to ensure that runoff from the site (post redevelopment) does not exceed greenfield runoff rates and volumes. Any SUDS design must take due account of topographical, groundwater and geological conditions (refer Section 5);

� The developer must provide a clear and concise statement summarising how the proposed (re)development has contributed to a positive reduction in flood risk within the borough.

176. Proposed Development within Zone 2 Medium Probability

� For all sites within Zone 2 Medium Probability, a high level FRA commensurate with the level of risk posed to the site should be prepared based upon readily available existing flooding information, sourced from the EA. 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 (refer Section 7.6.3) and the provision of a planned evacuation route.

� The risk of alternative sources of flooding (e.g. urban drainage and/or groundwater) must be considered, and sustainable drainage techniques must be employed to ensure no worsening to existing flooding problems elsewhere within the area. Once again, it is reiterated that future development within the district may adversely affect sites within adjoining Boroughs, and it is essential that this is mitigated.

� As part of the high level FRA, the developer must provide a clear and concise statement summarising how the proposed (re)development has contributed to a positive reduction in flood risk within the borough.

� Details of proposed sustainable drainage systems (SUDS) that will be implemented to ensure that runoff from the site (post redevelopment) does not exceed greenfield runoff rates and volumes. Any SUDS design must take due account of topographical, groundwater and geological conditions (refer Section 7.6.3).

177. Proposed Development within Zone 1 Low Probability

For all sites greater than 1 hectare in area, and/or sites within close proximity of an observed localised flooding incident (refer adjoining flood maps), a simple Flood Risk Assessment must be prepared:

� The risk of alternative sources of flooding (e.g. urban drainage and/or groundwater) must be considered, and sustainable drainage techniques must be employed to ensure no worsening to existing flooding problems elsewhere within the area. Once again, it is reiterated that future development within the borough may adversely affect sites within adjoining Boroughs, and it is essential that this is mitigated.

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� As part of the FRA, the developer must provide a clear and concise statement summarising how the proposed (re)development has contributed to a positive reduction in flood risk within the borough.

� Details of proposed sustainable drainage systems (SUDS) that will be implemented to ensure that runoff from the site (post redevelopment) does not exceed greenfield runoff rates and volumes. Any SUDS design must take due account of topographical, groundwater and geological conditions (refer Section 7.6.3).

178. Liaison with the Environment Agency To assist local planning authorities, the Environment Agency has produced standing advice to inform on their requirements regarding the consultation process for planning applications on flood risk matters. Full details of their Flood Risk Standing Advice can be found at http://www.pipernetworking.com/floodrisk/index.html. The Environment Agency is an excellent source of information for the preparation of the detailed FRA. The external relations team should be contacted as early as possible to source information relating to (for example) historical flooding, hydraulic modelling and topography (LiDAR). The information provided within this SFRA is the best available at the time of writing. More up to date information may be available, and contact should be made with the EA at an early stage to ensure that the detailed site based FRA is using the most current datasets, avoiding unnecessary re-work. It is recommended that a draft of the detailed FRA is provided to the EA for review and comment before submission with the Planning Application, thereby reducing potentially costly delays to the planning process. The Council and the EA will liaise on the suitability of the FRA as submitted, with the EA providing technical assistance to the Council.

7.6.2 Raised Floor Levels & Basements (Freeboard)

179. The raising of floor levels above the 1% AEP (100 year) fluvial flood level will ensure that the damage to property is minimised. Given the anticipated increase in flood levels due to climate change, the adopted floor level should be raised above the 1% AEP (100 year) predicted flood level assuming a 20% increase in flow over the next 100 years.

180. Wherever possible, floor levels should be situated a minimum of 300mm above the 1%

AEP (100 year) plus climate change flood level, determined as an outcome of the site based FRA. A minimum of 750mm above the 1% AEP (100 year) flood level should be adopted if no climate change data is available. 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.

181. The use of basements within flood affected areas should be discouraged. Where

basement uses are permitted however, it is necessary to ensure that the basement access points are situated 300mm above the 1% AEP (100 year) flood level plus climate change. The basement must be of a waterproof construction to avoid seepage during flooding conditions. Habitable uses of basements within flood affected areas should not be permitted. It must be demonstrated that any below ground construction does not adversely increase the risk of groundwater flooding to adjoining properties.

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7.6.3 Sustainable Drainage Systems (SUDS)

182. 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 of reducing future flood risk to both the site and its surroundings. Indeed reducing the rate of discharge from urban sites to greenfield runoff rates is one of the most effective ways of reducing and managing flood risk. The integration of sustainable drainage systems into a site design can also provide broader benefits, including an improvement in the quality of runoff discharged from the site, the capture and re-use of site runoff for irrigation and/or non potable uses, and the provision of greenspace areas offering recreation and/or aesthetic benefits.

183. SUDS improve the sustainable management of water for a site by21:

� reducing peak flows to watercourses or sewers and potentially reducing the risk of flooding downstream;

� reducing volumes and the frequency of water flowing directly to watercourses or sewers from developed sites;

� improving water quality over 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; � replicating natural drainage patterns, including the recharge of groundwater so

that base flows are maintained.

184. In catchment terms, any reduction in the amount of water that originates from any given site is likely to be small. But if applied across the catchment in a consistent way, the cumulative affect of a number sites could be significant.

185. There are numerous different ways that SUDS can be incorporated into a development

and the most commonly found components of a SUDS system are described in the following table22. The appropriate application of a SUDS scheme to a specific development is heavily dependent upon the topography and geology of the site (and its surrounds). For example, infiltration techniques are unlikely to function effectively in areas of impermeable soils (including London Clay, as is characteristic of so much of the Borough). Careful consideration of the site characteristics is needed to ensure the future sustainability of the adopted drainage system. On-going maintenance needs to be easy to manage and enforce, and should be secured through a planning condition.

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.

Further EA guidance is provided at http://www.environment-agency.gov.uk/regions/thames/323147/2093788/

Filter drain 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.

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.

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Infiltration Devices Sub-surface structures to promote the infiltration of surface water to ground. They can be trenches, basins or soakaways.

Bioretention areas Vegetated areas designed to collect and treat water before discharge via a piped system or infiltration to the ground

186. For more guidance on SUDS, the following documents and websites are recommended

as a starting point:

� Interim Code of Practice for Sustainable Drainage Systems, National SUDS Working Group, 2004

� Planning Policy Statement 25, Annex F (CLG, December 2006) � www.ciria.org.uk/SUDS/

187. Furthermore, the Environment Agency (Thames Region) has issued best practice guidance for Sustainable Drainage Systems (October 2006), available from the Environment Agency development control teams. This provides a clear hierarchy for SUDS, reflecting the degree of sustainability offered by the SUDS application as captured in the table below. Developers should demonstrate within their Flood Risk Assessment that this hierarchy has been considered as part of the design process.

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7.7 Local Community Actions to Reduce Flood Damage

188. It is estimated that over 2,500 homes within the Borough are at ‘significant’ risk of flooding (i.e. affected by flooding in events up to and including the 1.33% AEP (75 year) event). It is essential therefore to ensure a broad awareness with respect to flood risk, providing the community with the knowledge (and tools) that will enable them to help themselves should a flood event occur.

189. The following ‘community based measures’ are cost effective solutions that local

communities could introduce to minimise the damage sustained to their own homes from flooding. Further guidance is provided by the EA, Defra and CLG23 (refer the National Flood Forum (www. floodforum.gov.uk)).

190. It is recommended that the Borough seek to proactively raise awareness within the

community with respect to flooding (and indeed ‘self help’ flood risk reduction opportunities) through, for example, the circulation of a targeted newsletter to affected residents to coincide with the release of the Kingston Borough SFRA.

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7.7.1 Flood Proofing

191. The ‘flood proofing’ of a property may take a variety of forms:

For new homes and/or during redevelopment � Raising of floor levels

The raising of floor levels above the anticipated maximum flood level ensures that the interior of the property is not directly affected by flooding, avoiding damage to furnishings, wiring and interior walls. Plumbing may still be impacted as a result of mains sewer failure.

� Raising of electrical wiring

The raising of electrical wiring and sockets within flood affected buildings reduces the risks to health and safety, and reduces the time required after a flood to rectify the damages sustained.

For existing homes

� Flood boards The placement of a temporary watertight seal across doors, windows and air bricks to avoid inundation of the building interior. This may be suitable for relatively short periods of flooding, however the porosity of brickwork may result in damage being sustained should water levels remain elevated for an extended period of time. This may lessen the effectiveness of flood proofing to existing properties affected by flooding from larger river systems such as the Thames.

7.8 Emergency Planning

192. The Council is designated as a Category 1 Responder under the Civil Contingencies Act 2004. As such, the Council has defined responsibilities to assess risk, and respond appropriately in case of an emergency, including (for example) a major flooding event. The Council’s primary responsibilities are24:

a. from time to time assess the risk of an emergency occurring; b. from time to time assess the risk of an emergency making it necessary or

expedient for the person or body to perform any of his or its functions; c. maintain plans for the purpose of ensuring, so far as is reasonably practicable,

that if an emergency occurs the person or body is able to continue to perform his or its functions;

d. maintain plans for the purpose of ensuring that if an emergency occurs or is likely to occur the person or body is able to perform his or its functions so far as necessary or desirable for the purpose of:

i. preventing the emergency, ii. reducing, controlling or mitigating its effects, or iii. taking other action in connection with it

193. The Environment Agency monitor river levels within the main rivers affecting the Borough

(including the River Thames and the River Hogsmill), and based upon weather predictions provided by The Met Office, make an assessment of the anticipated maximum water level that is likely to be reached within the proceeding hours (and/or days). Where these predicted water levels are expected to result in the inundation of populated areas25, the Environment Agency will issue a series of flood warnings within defined flood warning areas, encouraging residents to take action to avoid damage to property in the first instance (refer Appendix B).

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194. As water levels rise and begin to pose a risk to life and/or livelihood, it is the responsibility of the emergency services to coordinate the evacuation of residents. This evacuation will be supported by the Council. It is essential that a robust plan is in place that clearly sets out (as a minimum):

� roles and responsibilities; � paths of communication; � evacuation routes; � community centres to house evacuated residents; � contingency plans in case of loss of power and/or communication.

195. Coordination with the emergency services and the Environment Agency is imperative to

ensure the safety of residents in time of flood. A relatively small proportion of the Borough is at risk of river flooding (as indicated by the shaded PPS25 flood risk zones in the adjoining maps). As outlined in Appendix B, forewarning will be provided where possible to encourage preparation in an effort to minimise property damage and risk to life. It is worth highlighting however that the benefits of flood warning are often compromised to a large degree by the lack of ‘take up’ within the local community. This emphasises the extreme importance of raising local awareness with respect to the potential risks of flooding.

196. Areas suffering from localised flooding issues will tend to be at greater risk. These areas

are susceptible to ‘flash’ flooding, associated with storm cells that pass over the Borough resulting in high intensity, often relatively localised, rainfall. It is anticipated that events of this nature will occur more often as a result of possible climate change over the coming decades. Events of this nature are difficult to predict accurately, and the rapid runoff that follows will often result in flooding that cannot be sensibly forewarned.

197. All urbanised areas are potentially at some degree risk of localised flooding due to heavy

rainfall. The blockage of gullies and culverts as a result of litter and/or leaves is commonplace, and this will inevitably lead to localised problems that can only realistically be addressed by reactive maintenance.

198. It is recommended that the Council advises the local Resilience Forum of the risks raised

in light of the Kingston Borough SFRA, ensuring that the planning for future emergency response can be reviewed accordingly.

7.9 Insurance

199. Many residents and business owners perceive insurance to be a final safeguard should damages be sustained as a result of a natural disaster such as flooding. Considerable media interest followed the widespread flooding of 2000 when it became clear that the insurance industry were rigorously reviewing their approach to providing insurance protection to homes and businesses situated within flood affected areas. Not surprisingly, the recent widespread flooding of July 2007 has further exacerbated the discussion surrounding the future of insurance for householders and business owners situated within flood affected areas.

200. The following quotations are an extract from the Association of British Insurers (ABI)

website, dated August 2007: “The UK is unique in offering flood cover as a standard feature of household and most business policies. Unlike much of Europe and worldwide, cover is widely available to the UK’s 23.5 million householders.

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In the long term, this situation could worsen, unless we take action to reduce flood risk to people and property. Climate change will increase winter rainfall, the frequency of heavy rainfall, and sea levels and storm surge heights. With no change in Government policies or spending, climate change could increase the number of properties at risk of flooding to 3.5 million. Furthermore, continued pressure on land could mean even more new developments being situated in floodplains. By spreading the risk across policy holders, insurance enables householders and businesses to minimize the financial cost of damage from flooding. In the modern competitive insurance market, premiums reflect the risks that customers face. This enables insurance to be offered at very competitive prices to customers living in low flood risk areas. In 2003 ABI members agreed to extend their commitment to provide flood insurance to the vast majority of UK customers. The result of discussions between Government and insurers was a Statement of Principles, which aims to provide reassurance to the overwhelming majority of insurance customers living in the floodplain about the continued availability of insurance in future. Individual property owners can do much to increase the resistance and resilience of their properties to flood damage - further information is available. ABI has issued a factsheet for property owners on a range of measures that could be taken by a homeowner to improve the resilience of their property to flood damage.”

201. In summary, for the time being, residents and business owners can be assured that

insurance will be available to assist in recovery following a flood event. It would appear fair to say however that the future availability of flood insurance within the UK will be heavily dependant upon commitment from the government to reduce the risk of flooding over time, particularly given the anticipated impacts of climate change. Investment is required in flood defence and improving the capacity of sewage and drainage infrastructure. By following the Sequential and Exception Tests in PPS 25, and the local advice provided in this SFRA, spatial planning decisions will be informed in relation to flood risk so that they are safe and in the right location’

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8 Conclusion & Recommendations

202. Planning policy needs to be informed regarding the risk posed by flooding. A collation of potential sources of flood risk has been carried out in accordance with PPS25, developed in close consultation with both the Council and the Environment Agency. Zones of ‘high’, ‘medium’ and ‘low’ probability of flooding have been identified in accordance with PPS25, providing the basis for the application of the PPS25 Sequential Test. Other (non river related) sources of flooding have also been identified, and together these should inform the development control process.

203. A planned solution to flood risk management should be sought wherever possible,

steering vulnerable development away from areas affected by flooding in accordance with the PPS25 Sequential Test. It is also vitally important to recognise the significant potential to reduce flood risk through redevelopment, and this should be actively sought as an integral part of the planning process. Specific planning recommendations have been provided to guide decision making and design in relation to both future development and redevelopment within the Borough (refer Section 7.4.4).

204. Where other planning considerations must guide the allocation of sites and the Sequential

Test has been applied, specific recommendations have been provided to assist the Council and the developer to address the requirements of the Exception Test. These should be applied as development control recommendations for all future development (refer Section 7.4.4).

205. Flood risk management policy is essential to ensure that the development control recommendations can be imposed consistently. The development control recommendations presented in the SFRA should be incorporated into a Development Control DPD (refer Section 7.4).

206. Emergency planning is imperative to minimise the risk to life posed by flooding within the

Borough. It is recommended that the Council advises the local Resilience Forum of the risks raised in light of the Kingston Borough SFRA, ensuring that the planning for future emergency response can be reviewed accordingly.

A Living Document

207. The SFRA has been developed building upon existing knowledge with respect to flood risk. A rolling programme of detailed flood risk mapping within the South East region is underway. This, in addition to observed flooding that may occur throughout a year, will improve the current knowledge of flood risk within the Borough and may marginally alter predicted flood extents. Furthermore, Communities and Local Government (CLG) are working to provide further detailed advice with respect to the application of PPS25, and future amendments to the PPS25 Practice Guide are anticipated. Given that this is the case, a periodic review of the Kingston Borough SFRA will be advisable.

208. It is recommended that the Kingston Borough SFRA is reviewed on a regular basis. The

following key questions should be addressed as part of the SFRA review process:

Question 1 Has any flooding been observed within the Borough since the previous review? If so, the following information should be captured as an addendum to the SFRA:

� What was the mapped extent of the flooding? � On what date did the flooding occur? � What was the perceived cause of the flooding? � If possible, what was the indicative statistical probability of the observed

flooding event? (i.e. how often, on average, would an event of that magnitude be observed within the Borough?)

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� If the flooding was caused by overtopping of the riverbanks, are the observed flood extents situated outside of the current Zone 3a? If it is estimated that the frequency of flooding does not exceed, on average, once in every 100 years then the flooded areas (from the river) should be incorporated into Zone 3a to inform future planning decision making.

Question 2

Have any amendments to PPS25 or the Practice Companion Guide been released since the previous review? If so, the following key questions should be tested:

� Does the revision to the policy guidance alter the definition of the PPS25 Flood Zones presented within the SFRA?

� Does the revision to the policy guidance alter the decision making process required to satisfy the Sequential Test? (refer Section 7.4)

� Does the revision to the policy guidance alter the application of the Exception Test? (refer Section 7.4)

� Does the revision to the policy guidance alter the categorisation of land use vulnerability, presented within Table D2 of PPS25 (December 2006)?

If the answer to any of these questions is ‘yes’ then a review of the SFRA recommendations in light of the identified policy change should be carried out.

Question 3

Has the Environment Agency issued any amendments to their flood risk mapping and/or standing guidance since the previous policy review? If so:

� Has any further detailed flood risk mapping been completed within the Borough, resulting in a change to the 20 year, 100 year or 1000 year flood outline? If yes, then the Zone 3b and Zone 3a flood outlines should be updated accordingly.

� Has the assessment of the impacts that climate change may have upon rainfall and/or river flows over time altered? If yes, then a review of the impacts that climate change may have upon the Borough is required.

� Do the development control recommendations provided in Section 7.4 of the SFRA in any way contradict emerging EA advice with respect to (for example) the provision of emergency access, the setting of floor levels and the integration of sustainable drainage techniques? If yes, then a discussion with the EA is required to ensure an agreed suite of development control requirements are in place.

The Environment Agency Flood Zone Map is reviewed on a quarterly basis. If this has been revised within the Borough, the updated Flood Zones will be automatically forwarded to the Council for their reference. It is recommended that only those areas that have been amended by the Environment Agency since the previous SFRA review are reflected in Zone 3 and Zone 2 of the SFRA flood maps. This ensures that the more rigorous analyses carried out as part of the SFRA process are not inadvertently lost by a simple global replacement of the SFRA flood maps with the Flood Zone Maps.

Question 4

Has the implementation of the SFRA within the spatial planning and/or development control functions of the Council raised any particular issues or concerns that need to be reviewed as part of the SFRA process?

7

1

2

3

4

5

6

(c) Crown Copyright 2006. All rights reserved.Royal Borough of Kingston upon Thames.

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Royal Borough of Kingston upon Thames SFRAFIGURE A Overview Map

Zone 2 Medium ProbabilityZone 3a High ProbabilityZone 3b Functional FloodplainClimate Change

Elevation(mAOD)

00 - 55 - 1010 - 1515 - 2020 - 2525 - 3030 - 3535 - 4040 - 4545 - 5050 - 5555 - 6060 - 6565 - 7070 - 7575 - 8080 - 8585 - 9090 - 9595 - 100

Royal Borough of Kingston upon Thames SFRAFIGURE B Topography


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Royal Borough of Kingston upon Thames SFRAFIGURE C Geology

River Terrace Deposits

Sand and Gravel

London Clay

Superficial Deposits

Bedrock Geology

32

31

Gibbon Road

Coombe Ridings

Royal Borough of Kingston upon Thames SFRAFIGURE 001

Coombe


100019285

Localised Drainage Issues:

Coombe Ridings (2000) - Water inbrickwork at back of house

Gibbon Road (2003) - Water inCellar

Raised Flood Defence

Localised Drainage Issue

Proposals Site


Climate Change


Zone 3b Functional Floodplain

29

31

26

33a

29

27

34

6

Gibbon Road

Cranes Park

Darley Drive

Beverley Road

Galsworthy Road

Raeburn Avenue (1) Royal Borough of Kingston upon Thames SFRAFIGURE 002

New Malden and Norbiton


100019285


Darley Drive (2003) - Overflowing manhole inschool grounds, probably due to leaking main, rainfallmakes the situation worse.

Beverley Road (2003) - Water below floorboards

Gibbon Road (2003) - Water in Cellar

Galsworthy Road (2002) - Water entering blockof flats in basement

Raeburn Avenue (1) (2002) - Damp garden



Proposals Site


Climate Change



The Crest

Hazel Bank

Pune Gardens

th

Beverley Road

Purbeck Avenue

Alexandra Drive

Greenfield Avenue

Raeburn Avenue (2)

Raeburn Avenue (1)

s' Road

Raeburn Open Space

40

29

33a

29

42

26


Old Malden and Motspur Park


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Proposals Site


Climate Change




Raeburn Open Space- Lagoon site suffers from flooding from timeto time - cause unknown

Alexandra Drive - combination of ground flows combined with sewersurcharge causes road to "flood" and affects two properties. Therewas also a groundwater issue at the rear of these two properties.

Beverley Road (2003) - Water below floorboards

Hazel Bank (2000) - Groundwater flooding of garden

The Crest (2000) - Basement flooded

Pune Gardens (2001) - Waterlogged Garden

Purbeck Avenue (2001) - Groundwater issues

Raeburn Avenue (1) (2002) - Damp garden

Greenfield Avenue (2002) - Void under house filling up due toheavy rainfall

Raeburn Avenue (2) (2003) - Waterlogged garden

44

45

40

42

41

50a43

47

A243 (2)

A243 (1)

Hazel Bank

Clayton Road

Ellerton Road


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Proposals Site


Climate Change




Hazel Bank (2000) - Groundwaterflooding of garden

Ellerton Road (2000) - Floodedgarden

Clayton Road (2002) - Water infoundations


Tolworth, Hook and Riverhill

A243 (2)

A243 (1)

Filby Road

50

Zoo Development Envelop

47


100019285



Proposals Site


Climate Change




A243 (1) (2005) - Waterloggedgarden for 5 months

Filby Road (2001) - Waterdraining into garden from neighbours

A243 (2) (2003) - Regular flow fromgarden down driveway, otherhouses affected opposite

Royal Borough of Kingston Upon Thames SFRAFIGURE 005Chessington

Gibbon Road

Skerne Road

Coombe Ridings

Galsworthy Road

311

32

22

5

12

17

4

2

11

27

13

6

29a

30

10


100019285


Skerne Road (2000) - Damp Cellar

Coombe Ridings (2000) - Water inbrickwork at back of house

Galsworthy Road (2002) - Waterentering block of flats in basement

Gibbon Road (2003) - Water in Cellar


North Kingston



Proposals Site


Climate Change



29

40

35

26

19

22

29

39b

17

39a

27

34

13

29b

21

36

The Crest

Fishponds

Cranes Park

Pune Gardens

Avenue SouthAlexandra Drive

Greenfield Avenue

Raeburn Avenue (2)

Raeburn Avenue (1)

King Charles' Road

Raeburn Open Space

Browns Road/ King Charles Crescent

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Appendix A

Kingston Borough SFRA PPS25 Constraints – Proposal Sites

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Overview

In accordance with PPS25, it is necessary for a local authority to adopt a sequential approach when allocating sites for future development. This is outlined in Section 7.4.1 of the SFRA, however it must be demonstrated that sites for future development have been sought within the lowest flood risk zone (i.e. Zone 1 Low Probability). Only if it can be shown that suitable sites are not available within this zone can alternative sites be considered within the areas that are at greater risk of possible flooding. The SFRA does not endeavour to address this aspect of the Sequential Test. It can however review emerging allocations, and in light of the delineated PPS25 flood zones, provide clear recommendations for permissible land uses (as defined by PPS25).

The Adopted Approach

A review of the Adopted UDP Proposal Sites has been undertaken as part of the SFRA process. The sites, as identified in the adopted Kingston Borough UDP (August 2005) were overlaid onto the adopted PPS25 flood zones. The attached table summarises:

� the locality of each site; � the flood zone within which that site falls; and � the restrictions that flood risk places upon the future development of the site.

Interpretation of Proposal Sites Review (attached table)

The attached table has adopted a ‘traffic light’ system to mirror the decision matrix provided within PPS25 (Appendix D). The table should be interpreted in accordance with the following legend. In some instances, sites are only partially affected by flooding, and the ‘traffic lights’ within the attached matrix reflect the most significant risk of flooding within the site. At these locations, future development may be permitted to proceed, however this should be restricted to the lowest risk areas of the site if at all possible.

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PPS25 Zone Specific Comments

Appendix AKingston UDP Sites - PPS25 Constraints

December 2008

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Appendix B

Environment Agency Flood Warning Service (Royal Borough of Kingston)

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In England and Wales the Environment Agency operates a flood warning service in areas at risk of flooding from rivers or the sea. Using the latest available technology, Agency staff monitor rainfall, river levels and sea conditions 24 hours a day and use this information to forecast the possibility of flooding. If flooding is forecast, warnings are issued using a set of four easily recognisable codes.

• A Flood Watch would be issued when water levels along the river are forecast to overtop the banks.

• A Flood Warning is issued when the Environment Agency anticipates flooding to property.

• The trigger for issue of a Severe Flood Warning is dependent on a number of factors, but is essentially used when there is thought to be extreme danger to life.

• All Clear is issued when previous flood watches or warnings are no longer in force for the area.

Nationally, the Agency aims to give a two-hour warning in advance of any flooding taking place. However in certain cases this may not always be possible. All warnings are highly dependent on our ability to forecast. There are two basic meteorological systems that concern us. Frontal rain bringing heavy and prolonged rainfall over a catchment or convective storms which produce very high intensity rainfall for shorter periods directly over part of a catchment. Both are regularly experienced in Thames Region and the Kingston Borough. Both types of rainfall event brings risk of severe flooding, however, it is the unpredictable nature of the convective storm cells which present the most significant risk to delivery of an effective warning service. We have a comprehensive rain gauge network and have direct access to Met Office radar products which show rainfall intensities and amounts For the London Catchments (Hogsmill, Beverley Brook, Wandle and Ravensbourne) a 2 hour warning lead-time is impractical in many of the urban areas and upper catchments within Thames Region as low-to-peak flow can occur over just half an hour. Within London, the intensity of rainfall is monitored, and the Thunderstorm Action Plan (TAP) is triggered if a possible risk of localised flooding is anticipated. A Flood Watch will then be issued for the London rivers.

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Appendix C

Beverley Brook Delineation of Zone 3b Functional Floodplain

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Delineation of Zone 3b Functional Floodplain Beverley Brook Catchment In the absence of detailed hydraulic modelling within the Beverley Brook catchment, a simple risk-based assessment was carried out (adopting first principles) to delineate Zone 3b Functional Floodplain for planning purposes. The adopted methodology is set out below:

a. The predicted 1 in 100 year flood outline (defined by the Environment Agency flood zone map) is overlain onto the Borough topography at pre-defined intervals, and a cross section extracted through the river to define the ‘shape’ of the floodplain;

b. Using Manning’s Equation at each identified cross section, an approximation of

the 1 in 100 year flow is derived, equating to the flood level (and extent) defined by the EA Flood Zone Map;

c. For comparison purposes, an estimate of the 1 in 20 year and 1 in 100 year peak

design flows is derived at the cross section using the Flood Estimation Handbook (FEH). The ratio between the 20 and 100 year peak design flows is determined;

d. Applying this design flow ratio at each cross section location to the flow

determined in (2) above, Manning’s Equation is then used once again to assess the approximate 1 in 20 year flood level (and extent) within the floodplain.

It is highlighted that this methodology assumes that Beverley Brook is flowing freely and is not subject to backwater affects from the River Thames. This is considered a reasonable assumption. The simplistic nature of the SFRA modelling in entirely appropriate for planning purposes, but it is important to recognise that a margin of uncertainty in the adopted outlines is inevitable. It must be ensured that the SFRA is used to trigger a more detailed assessment of flood levels at the planning application (i.e. detailed FRA) stage.