Our Local Plan

Strategic Flood T Risk Assessment 1 r ._,and � Update September 2015

Revision Schedule

Date Details Prepared by Reviewed by Approved by

September Draft SFRA update Matthew Marie Surtees Sarah 2015 Chapman Thompson December SFRA update Matthew Marie Surtees Planning Policy 2015 Chapman Committee

Planning Policy Tandridge District Council The Council Offices 8 Station Road East Oxted, Surrey RH8 0BT

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Executive Summary

This Tandridge District Council Strategic Flood Risk Assessment (SFRA) 2015 Update report updates the Tandridge District Strategic Flood Risk Assessment 2007. This report has been prepared to update the work that was included in the previous SFRA and provide appropriate supporting evidence for Tandridge District Local Plan. Since the previous SFRA there have been a number of changes to the planning system, including the Localism Act (2011) and the 2012 National Planning Policy Framework (NPPF) with accompanying Planning Practice Guidance (March 2014). In addition, the provisions of the Flood and Water Management Act (2010) have been substantially commenced under a programme that was initiated by Defra in April 2010 and the Flood Risk Regulations came into force in December 2009 (these regulations transposed the EU Floods Directive into UK law). SFRA objectives There are two levels of SFRAs . Level One: where flooding is not a major issue and where development pressures are low. The Assessment should be sufficiently detailed to allow application of the Sequential Test.

. Level Two: where land outside flood risk areas cannot appropriately accommodate all the necessary development and the NPPF’s Exception Test needs to be applied. The Assessment should consider the detailed nature of the flood characteristics within a flood zone. An SFRA was completed in 2007 that formed part of the evidence base for the examination into the Tandridge District Core Strategy. The report comprised of a level one desk-based study that used existing information to carry out an assessment that was proportionate to the risk and appropriate to the scale, nature and location of development. The objectives of this SFRA is to update and review the 2007 SFRA which covers the whole of the District and if required a more detailed assessment of potential employment and housing allocations emerging through the Local Plan process. SFRA outputs This report is a level one Strategic Flood Risk Assessment and as set out in the Planning Practice Guidance it “should be sufficiently detailed to allow application of the Sequential Test to the location of development and to identify whether development can be allocated outside high and medium flood risk areas, based on all sources of flooding, without application of the Exception Test” (Paragraph: 012 Reference ID: 7-012-20140306).

Summary The findings of this updated SFRA have fed into the Housing and Economic Land Availability Assessment and assisted in the development of the strategic policies options within the Regulation 18 consultation paper. If site allocations are necessary at the regulation 19 stage to deliver the amount of housing that is required within the Local Plan, the SFRA, along with the Caterham Bourne Flood Alleviation Project, the Burstow Flood Alleviation Project, and the modelling of the River Eden will provide the necessary information required to undertake the site specific assessments. This will ensure that any allocation of sites will take account of the long term solutions to flooding within the district, particularly if the acquisition of land is required to deliver a flood alleviation scheme. The SFRA presents Flood Zone Maps that outline the Environment Agency flood zones as Flood Zone 1, low probability, Flood Zone 2, medium probability and Flood Zone 3a, high probability. In addition, the map from the Environment Agency showing the risk of flooding from surface water and ground water have played a key role within this SFRA. The application of the Sequential Test (and where appropriate, the Exception Test) in order to steer vulnerable development away from

2 areas of flood risk, remains a fundamental part of the planning process and these maps have been used in the assessment and will be used in the future for the assessment of the site allocations.

Recommendations This Level 1 SFRA report has been developed by building heavily upon existing knowledge with respect to flood risk within the district. The report has not been prepared to consider site-specific allocations, instead, it has informed the development of the Strategic Options (Regulation 18) consultation. As mentioned above there are three key pieces of modelling that are being carried out: . Caterham Bourne Flood Alleviation Project; . Burstow Flood Alleviation Project; and . Environment Agency modelling of the flood zones 2 and 3 in the River Eden catchment. Once these projects are completed the SFRA will be updated so that the information contained within them will assist in the flood risk assessment for the site allocations. In summary, the SFRA is a ‘living’ document and will be reviewed regularly in light of emerging policy directives and an improving understanding of flood risk within the district. Proceeding with the SFRA in the production of the Local Plan: . The Council will apply the Sequential Test to the potential development sites and identify those sites they consider will be necessary to apply the Exception Test; . The layout of buildings and access routes should adopt a sequential approach, steering buildings (and hence people) towards areas of lowest risk within the boundaries of the site. This will also ensure that the risk of flooding is not worsened by, for example, blocked flood flow routes. . Consultation with Surrey County Council as the Local Lead Flood Authority and the Environment Agency following completion of the Exception Test will be carried out to ensure that they accept the justification for progressing with sites that require the Exception Test; and . The SFRA outputs will be used by the district to assess flood risk to windfall sites which become available for redevelopment. If such sites require the Exception Test a site-specific flood risk assessment will be needed to be considered sound.

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Contents

Executive Summary ...... 2

Introduction ...... 5

The Planning Framework, Flood Risk Policy and catchment studies ...... 12

Roles and responsibilities in the management of flood risk ...... 16

Overview of Geology and Topography in Tandridge District ...... 21

Flood defences ...... 23

Flooding from artificial sources ...... 25

Overview of types of flooding ...... 27

Historic flood events and sources of flooding by area...... 31

Overview of all development options ...... 45

Flood risk management in the Local Plan ...... 48

Conclusions and recommendations ...... 51

Appendix 1 Advice Note on contents of a Sustainable Drainage Statement ...... 52

Appendix 2: Flood event records from the three catchments ...... 62

Appendix 3 Topographic map ...... 63

Appendix 4 Map showing areas at risk from river flooding ...... 64

Appendix 5 Map showing areas at risk from surface water flooding ...... 65

Appendix 6 Map showing areas at risk of groundwater flooding ...... 66

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Introduction Purpose of the Strategic Flood Risk Assessment This Tandridge District Council Strategic Flood Risk Assessment (SFRA) 2015 Update report updates the Tandridge District Strategic Flood Risk Assessment 2007. This report has been prepared to update the work that was included in the previous SFRA and provide appropriate supporting evidence for Tandridge District Local Plan. Since the previous SFRA there have been a number of changes to the planning system, including the Localism Act (2011) and the 2012 National Planning Policy Framework (NPPF) with accompanying Planning Practice Guidance (March 2014). In addition, the provisions of the Flood and Water Management Act (2010) have been substantially commenced under a programme that was initiated by Defra in April 2010 and the Flood Risk Regulations came into force in December 2009 (these regulations transposed the EU Floods Directive into UK law). The planning practice guidance provides a summary diagram of how flood risk should be taken into account in the preparation of Local plans, this is set out below.

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Figure 1 Taking flood risk into account in the preparation of a Local Plan

Local planning authority undertakes a level 1 strategic flood risk assessment

The authority uses the strategic flood risk assessment to: - Inform the scope of the sustainability appraisal for consultation; and - Identify where development can be located in areas with a low probability of flooding

The authority assesses alternative development options using the sustainability appraisal, considering flood risk (including potential impact of development on surface water run-off) and other planning objectives.

Can sustainable development be achieved through new development located entirely within areas with a low probability of flooding? Yes No

Use the Strategic Flood Risk Assessment to apply the Sequential Test and identify appropriate allocation sites and development. If the Exception Test needs to be applied, consider the need for a Level 2 Strategic Flood Risk Assessment.

Assess alternative development options using Sustainability Appraisal, balancing flood risk against other planning objectives.

Use the sustainability appraisal to inform the allocation of land in accordance with the Sequential Test. Include a policy on flood risk considerations and guidance for each site allocation. Where appropriate, allocate land to be used for flood risk management purposes.

Include the results of the application of the Sequential Test (and Exception Test where appropriate) in the Sustainability Appraisal Report. Use flood risk indicators and Core Output Indicators to measure the Plan’s success.

The SFRA will form an integral part of the Council’s evidence base in terms of identifying locations for development and preparation of flood risk policies in the Local Development Framework. The primary objective of the SFRA is to be part of the evidence base supporting the Local Plan so that it is in accordance with the NPPF.

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The Strategic Flood Risk Assessment will be used to refine information on river flooding risk shown on the Environment Agency’s Flood Map for Panning (Rivers and Seas). In order to achieve this, the Planning Practice Guidance states that SFRAs need to provide sufficient detail on all types of flood risk to enable the Local Planning Authority (LPA) to:

. determine the variations in risk from all sources of flooding across their areas, and also the risks to and from surrounding areas in the same flood catchment;

. inform the sustainability appraisal of the Local Plan, so that flood risk is fully taken into account when considering allocation options and in the preparation of plan policies, including policies for flood risk management to ensure that flood risk is not increased;

. apply the Sequential Test and, where necessary, the Exception Test when determining land use allocations;

. identify the requirements for site-specific flood risk assessments in particular locations, including those at risk from sources other than river and sea flooding;

. determine the acceptability of flood risk in relation to emergency planning capability;

. consider opportunities to reduce flood risk to existing communities and developments through better management of surface water, provision for conveyance and of storage for flood water. This document has been prepared under the requirements of the National Planning Policy Framework (NPPF) and accompanying Flood Risk and Coast Change Planning Practice Guidance to the National Planning Policy Framework published in March 2014, as well as the Environment Agency’s Strategic Flood Risk Assessments guidance. The extent of the study area is shown in figure 2.

SFRA Objectives There are two levels of SFRAs

Level One: where flooding is not a major issue and where development pressures are low. The Assessment should be sufficiently detailed to allow application of the Sequential Test.

Level Two: where land outside flood risk areas cannot appropriately accommodate all the necessary development and the NPPF’s Exception Test needs to be applied. The Assessment should consider the detailed nature of the flood characteristics within a flood zone.

An SFRA was completed in 2007 that formed part of the evidence base for the examination into the Tandridge District Core Strategy. The report comprised of a level one desk-based study that used existing information to carry out an assessment that was proportionate to the risk and appropriate to the scale, nature and location of development. The objectives of this SFRA is to update and review the 2007 SFRA which covers the whole of the District and if required a more detailed assessment of potential employment and housing allocations emerging through the Local Plan process.

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The information gathered for this study has enabled the Council to refine information on river flooding risk shown on the Environment Agency’s Flood Map for planning. The assessment will be used to:

 determine the variations in risk from all sources of flooding across their areas, and also the risks to and from surrounding areas in the same flood catchment;

 inform the sustainability appraisal of the Local Plan, so that flood risk is fully taken into account when considering allocation options and in the preparation of plan policies, including policies for flood risk management to ensure that flood risk is not increased;

 apply the Sequential Test and, where necessary, the Exception Test when determining land use allocations;

 identify the requirements for site-specific flood risk assessments in particular locations, including those at risk from sources other than river and sea flooding;

 determine the acceptability of flood risk in relation to emergency planning capability;

 consider opportunities to reduce flood risk to existing communities and developments through better management of surface water, provision for conveyance and of storage for flood water.

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Figure 2 SFRA study area

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Approach General assessment of flood risk The NPPF Planning Practice Guidance retains key elements of Planning Policy Statement 25. The SFRA adopts the flood risk management hierarchy originally laid out in the PPS25 Practice Guide summarised in figure 3.

Step one - Assess Appropriate flood risk assessment

Step two - Avoid Apply the sequential approach

Step three - Assess Apply the sequential test at site

Step four - Control e.g. SUDS, design, flood defences

Step five - Mitigate e.g. flood resilient construction Figure 3 Flood risk management hierarchy

This hierarchy underpins the risk based approach that is the basis for making all decisions that involve development and potential flood risk.

Technical assessment of flood hazards Flood risk within the Tandridge District has been assessed by using existing Environment Agency Flood Zone mapping, information from the Local Lead Flood Authority and additional modelling that is currently being carried out along the course of the Caterham Bourne.

Consultation

 The following parties (external to Tandridge District Council) will be consulted during the preparation of this SFRA:  Environment Agency  Surrey County Council – Local Lead Flood Authority  Thames Water

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 Southern Water  Sutton and East Surrey Water  Neighbouring authorities: o Croydon Borough Council o Bromley Borough Council o Sevenoaks District Council o Wealdon District Council o Mid Sussex District Council o Crawley Borough Council o Reigate and Banstead Borough Council

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The Planning Framework, Flood Risk Policy and catchment studies

Introduction The over arching aim of planning policy on development and flood risk is to ensure that flood risk is taken into account at all stages of the planning process. The purpose of this section of the report is to highlight the main changes to the planning framework and flood risk responsibilities since the 2007 SFRA was published. These changes have been taken into account in preparing this SFRA update. Flood Risk Regulations (2009) and Flood and Water Management Act (2010) Flood Risk Regulations (2009) and Flood and Water Management Act (2010)

The Flood Risk Regualtions transpose the EU “Floods Directive” into UK law and place responsibility upon all Lead Local Flood Authorities (LLFAs) to manage local flood risk. Under the Regulations the Environment Agency is responsible for flooding from rivers, the sea and reservoirs with Lead Local Flood Authorities (in this instance Surrey County Council) being responsible for local and all other sources of flooding.

Figure 4 Flood Risk Regulation timetable

Task Organisation Completion

Preliminary Flood Risk Assessment Report SCC June 2011 Review Preliminary Flood Risk Assessment Report December EA and publish 2011 Produce Flood Risk and Flood Hazard Maps SCC June 2013 Review Flood Risk and Flood Hazard Maps and December EA publish 2013 Flood Risk Management Plans SCC June 2015 December Review Flood Risk Management plans and publish EA 2015

Figure 4 sets out the requirements and timescale for implementing the requirements of the Directive. As the Lead Local Flood Authority Surrey County Council has prepared a Preliminary Flood Risk Assessment in accordance with the regulations, this covers the local authority area.

The Government has strengthened planning policy on the provision of sustainable drainage and new consultation arrangements for ‘major’ planning applications (10 or more dwelling houses and buildings 1,000m2 or more) were introduced on 15 April 2015.

Decisions about the suitability of sustainable drainage provision are made by the local planning authority. However, under the new consultation arrangements Surrey County Council, in its role as Lead Local Flood Authority, is a statutory consultee for all major applications. Previously the Environment Agency had that statutory responsibility.

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Therefore all ‘major’ planning applications submitted to the Council are now required to include a Surface Water Drainage Statement. Appendix 1 is the advice note setting out what information should be included in such statements.

Surrey Preliminary Flood Risk Assessment Surrey Preliminary Flood Risk Assessment In the first instance, the regulations required Surrey County Council (as the LLFA) to prepare and publish a Preliminary Flood Risk Assessment (PFRA) on past and future flood risk from local sources of flooding. The Regulations also require the LLFA to identify significant Flood Risk Areas. The PFRA reports on significant past and future flooding from all sources except Main River and Reservoir (covered by Environment Agency). It should be noted that the assessment was carried out prior to the flood event that occurred in the winter of 2013/2014. The main findings of the report include an analysis of the national surface water modelling maps which indicates there is considerable risk of flooding from surface water across Surrey, particularly in the North, where the London IFRA extends. Based on figures from the Environment Agency, approximately 46,500 properties are estimated to be at risk from flooding to a depth of 0.3m during a rainfall event with a 1 in 200 annual chance of occurring.

The report states that the Tandridge section of London IFRA covers an area roughly 15km2 (5.8 square miles). The area covers the section of Caterham and the west and centre section of Warlingham. This area contains 17 recorded locations that have experienced flooding in the past, with 4 known property floods, one of which is affected by foul water sewer flooding.

Localism Act (2011) Localism Act (2011)

The Localism Act was given Royal Assent on 15 November 2011 with the purpose of moving the balance of decision making from central government back to councils, communities and individuals.

Additionally Provision 110 of the Act places a duty to cooperate on local authorities in relation to planning of sustainable development. This duty to cooperate requires local authorities to “engage constructively, actively and on an ongoing basis in any process by means of which development plan documents are prepared so far as relating to a strategic matter”.

The Localism Act also provides new rights to allow local communities to shape new development by coming together to prepare neighbourhood plans. This means local people can decide where new homes and businesses should go and what they should look like. Local planning authorities will be required to provide technical advice and support as neighbourhoods draw up their proposals. National Planning Policy Framework The National Planning Policy Framework The National Planning Policy Framework (NPPF) was issued on 27 March 2012 to replace the previous documentation, as part of reforms to make the planning system less complex and more accessible, to protect the environment and to promote sustainable growth. It replaces most of the Planning Policy Guidance Notes (PPGs) and Planning Policy Statements (PPSs).

The NPPF is guidance for local planning authorities to help them prepare Local Plans. Paragraph 100 of the NPPF states “Local Plans should be supported by a strategic flood risk assessment and

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

Planning Practice Guidance on flood risk has been published alongside the NPPF and sets out how the policy should be implemented. Surface Water Management Plans Surface Water Management Plan Technical Guidance Surface Water Management Plans (SWMPs) outline the preferred surface water management strategy in a given location and are undertaken, when required, by LLFAs in consultation with key local partners who are responsible for surface water management and drainage in their area. SWMPs establish a long-term action plan to manage surface water in an area and should influence future capital investment, drainage maintenance, public engagement and understanding, land-use planning, emergency planning and future developments. At the time of the publication of this SFRA update, no SWMP has been published that covers the Tandridge District area. Association of British Insurers Guidance on Insurance and Planning in Flood Risk Areas for Local Planning Authorities in England entertainment Guidance on Insurance The Association of British Insurers (ABI) and the National Flood Forum have published guidance for local authorities on planning in flood risk areas. The guidance aims to help local authorities in England when producing local plans and dealing with planning applications in flood risk areas. The guidance complements the National Planning Policy Framework. The key recommendations from the guidance are:

. Ensure strong relationships with technical experts on flood risk . Consider flooding from all sources, taking account of climate change . Take potential impacts on drainage infrastructure seriously . Ensure that flood risk is mitigated to acceptable levels for proposed developments . Make sure Local Plans take account of all relevant costs and are regularly reviewed

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Catchment studies The following documents and significant planning applications that include a flood risk assessment have assisted in gathering the necessary information for the SFRA:

Area 1 Caterham Bourne

Work in progress . Caterham Bourne Flood Alleviation Scheme Existing studies . Croydon Flood Investigations into Caterham Bourne (2014) . Protocol for Flooding of the Caterham Bourne (2015) . Arup Caterham Bourne Study (2002) Significant planning applications . Planning application 2008/423 for the construction of 167 flats at Whyteleafe House, 439 Godstone Road, Whyteleafe.

Area 2 Upper River Mole

Work in progress . Burstow Flood Alleviation Scheme Existing studies . Burstow Flooding Inspection Report | SCC Highways Operations | July 2014 . Burstow flood modelling work in 2010 has been incorporated into the EA FZ 2+3 Significant planning applications . Land at Coopers Close, Smallfield 2014/1809 for the erection of 51 units was refused and now at appeal, there is also another application that is currently being considered by the Council, 2015/1581 for 48 dwellings.

Area 3 Upper River Eden

Work in progress . The Environment Agency are updating their mapping and modelling for the River Eden. Existing studies . River Eden (Medway) Catchment Action Plan (2014) Significant planning applications

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Roles and responsibilities in the management of flood risk

Introduction This section examines the roles and responsibilities of the various authorities and agencies involved in the management of flood risk, relevant to Tandridge District. It will also consider local community actions to reduce flood risk. This summary takes into account the changes to legislation that have come into effect since the publication of the original SFRA, including the Flood Risk Regulations 2009 and the Flood and Water Management Act 2010, which introduced new flood risk management responsibilities.

Figure 5 Authorities roles and responsibilities in Tandridge District Risk Management Authority Responsibility (RMA) Main rivers and reservoirs . Preliminary Flood Risk Assessments (per river basin district)1 . Identify Significant Flood Risk Areas Environment Agency . Flood Risk and Hazard Maps . Flood Risk Management Plan . Enforcement authority for Reservoirs Act 1975 Surface water, groundwater, ordinary watercourse, other sources of flooding . Prepare and publish a PFRA Local Lead Flood Authority . Identify Flood Risk Areas (Surrey County Council) . Prepare Flood Hazard and Flood Risk Maps . Prepare Flood Risk Management Plans . SuDS Approval Body Internal Drainage Board Maintain the integrity of the waterways and land (Upper Medway Internal Drainage drainage of the surrounding areas Board) Ordinary watercourses Local Authority . Prepare a Local Plan (Tandridge District Council) . Tandridge Multi Agency Flood Plan

Figure 5 shows the key strategic planning links for flood risk and associated documents. It shows how the how the Flood Risk Regulations and Flood and Water Management Act, in conjunction with the Localism Act’s ‘duty to cooperate’, introduce a wider requirement for the exchange of information and the preparation of strategies and management plans.

The Environment Agency The Environment Agency has statutory responsibility for flood management and flood defence. The recent Flood and Water Management Act 2010 introduced a requirement for the Environment Agency to develop a national strategy for the management of coastal erosion and all sources of flood risk for England. One of the main functions of the Environment Agency is the provision of advice on flooding issues to support the planning system, acting as a statutory consultation body on the preparation of Preliminary Flood Risk Assessments and Strategic Flood Risk Assessments and as a statutory consultee on all planning applications for development in flood risk areas. It also provides advice to developers on flooding matters. In addition to its advisory function, the

1 Environment Agency did not prepare a PFRA; instead they submitted an exception under the Regulations

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Environment Agency is responsible for flood forecasting and the operation of flood warning systems.

The Environment Agency is responsible for the assessment and management of flood risk at the local level on a 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. Catchment Flood Management Plans (CFMPs) are a planning tool through which the Environment 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. Surrey County Council Under the Flood Risk Regulations 2009 and the Flood & Water Management Act 2010 Surrey County Council has been given a new role as Lead Local Flood Authority (LLFA) in the management of flood risk. The Act requires the LLFA to produce a Preliminary Flood Risk Assessment highlighting areas of potential significant flood risk. The Preliminary Flood Risk Assessment for Surrey was published in June 2011. The LLFA must also develop, maintain, apply and monitor a strategy for local flood risk management in its area and co-operate with other authorities in the discharge of these functions.

The LLFA must investigate flooding incidents in its area and publish the investigation results. It must also maintain a register of structures or features considered to have a significant effect on flood risk in the area. The Act confers powers to LLFAs, together with district councils, internal drainage boards and the Environment Agency to designate structures and features that affect flooding or coastal erosion. Once a feature is designated, the owner must seek consent from the authority to alter, remove or replace it.

The Act also introduces a requirement for a SuDS Approving Body (SAB) at county level. As of the 15 April 2015, Surrey County Council, as the SAB have responsibility for the approval of proposed drainage systems in new ‘major’ developments. Approval must be given before the developer can commence construction. The SAB is also responsible for adopting and maintaining SuDS which serve more than one property.

In addition to the above new responsibilities the County Council also retains its existing responsibilities in relation to highways drainage in its capacity as Highways Authority.

Upper Medway Internal Drainage Board Internal Drainage Boards (IDB) are responsible for water level management in low lying areas. Not all areas require an IDB, and they currently cover approximately 10% of England. They work in partnership with other authorities and land owners to actively manage and reduce the risk of flooding. Within Tandridge the Upper Medway is covered by the Medway Internal Drainage Board, they work alongside the Environment Agency to maintain the integrity of the waterways and land drainage of the surrounding areas.

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Tandridge District Council

- Spatial Planning

In accordance with the guidance set out in the NPPF the Council is required to formulate policies for the allocation of sites and management of development which seek to avoid flood risk to people and property, and where possible, the management of flood risk elsewhere. This Strategic Flood Risk Assessment will be used to inform the sustainability appraisals of future Development Plan Documents to ensure that flood risk is adequately addressed in future policies and site allocations.

The Council will need to apply a sequential approach to the allocation of land for development in the district to ensure areas that are at low risk of flooding are given priority for development and areas subject to flooding are only considered once all sites at low risk have been exhausted.

- Development Management

Flood risk is a material consideration in the determination of planning applications. In exercising its duties as Local Planning Authority the Council is required to consult the Environment Agency on planning applications in areas of flood risk. The Council also needs to ensure that the Sequential and Exception Tests set out in the NPPF are applied to all applications for development in areas at risk of flooding. The information contained in this Strategic Flood Risk Assessment will be used as the basis for carrying out the Sequential Test for specific developments. The Council also has a role in promoting the use of SuDS in new developments through the development management process.

- Emergency Planning

Emergency planning is a critical element of any sustainable flood risk management solution. 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 a major flooding event. The Council’s primary responsibilities under the Act are:

. assess the risk of an emergency occurring; . assess the risk of an emergency making it necessary or expedient for the person or body to perform any of his or its functions; . 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; . 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 . In accordance with the above responsibilities the Council has developed a Multi- Agency Flood Plan which sets out the actions to be taken by the Council and other organisations as part of a multi-agency response to a significant flood in the district.

- Riparian Owners Riparian owners are those that own land or property adjacent to a watercourse (this can include home owners and organisations such as Surrey County Council as the highways authority). Riparian owners have a responsibility to maintain the bed and banks of the watercourse; this includes maintenance of any owned structures, such as trash screens or culverts.

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Section 25 of the Land Drainage Act (1991) outlines that where the flow of a watercourse is obstructed; the riparian owner is responsible to resolve the condition. Section 28 of the Land Drainage Act (1991) outlines the responsibility of the riparian owner to undertake maintenance of their watercourse if it is impeding the flow of water. Riparian owners must let water flow through their land without obstruction and must accept flood flows through their land. Riparian owners have no duty in common law to improve the drainage capacity of a watercourse. Further information can be found in the EA’s document Living on the Edge (2012) .

- Local Residents

It is essential to ensure a broad awareness with respect to flood risk, providing members of the community with the knowledge and tools that will enable them to help themselves should a flood event occur. The following measures are cost effective solutions that property owners may introduce to minimise the damage sustained to their own homes in the case of flooding:

Environment Agency Flood Warning System The Environment Agency offers a service whereby residents can sign up for free flooding alerts by a variety of means e.g. phone, text, e-mail. Residents of areas affected by flooding are advised to make use of this service. Further information about this can be found on the Environment Agency’s website www.environment-agency.gov.uk

Community Flood Plans Local communities can create their own flood plans to enable them to be better prepared for flooding. The Environment Agency has produced a guidance document which gives practical advice for communities and groups on how to create a flood plan. In addition to this the National Flood Forum offers support to communities and individuals at risk of flooding. The Forum is currently working with the Whyteleafe community, where they are supporting the flood group in organising their own multi-agency meeting and to develop their rolling flood action plan. This group is made up from representatives of the local community that have been affected by flooding.

Flood Proofing & Flood Resilience There are a variety of flood proofing measures that may be undertaken, both in new properties and existing properties. In new properties 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. However, plumbing may still be impacted as a result of mains sewer failure. 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 damage. Materials for the construction of the building, the fitments (e.g. kitchen cupboards) and the furniture should be chosen to ensure that are likely to suffer minimal damage should they be submerged in floodwater. In existing properties the placement of a temporary watertight seal across doors, windows and air bricks can prevent flooding 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. The government has provided advice on being prepared for flooding.

Insurance Many residents and business owners perceive insurance to be a final safeguard should damage 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 was rigorously reviewing its approach to providing insurance protection to homes and businesses situated within flood affected areas. The widespread flooding that has occurred in recent years has

19 further exacerbated the discussion surrounding the future of insurance for householders and business owners situated within flood affected areas. The government has published information in relation to Flood Risk and Insurance which sets out the most up to date information on insurance in areas at risk of flooding. This can be found on the government website.

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Overview of Geology and Topography in Tandridge District

Tandridge is a predominantly rural district. There are three main built up areas: Caterham; Warlingham/Whyteleafe in the north and Oxted/Hurst Green/Limpsfield just south of the M25 motorway. There are two larger rural settlements (that is excluded from the Green Belt) Lingfield in the south-east and Smallfield in the south-west. There are also a number of villages and some other smaller settlements and areas of sporadic development in the Green Belt. The central part of Woldingham is also excluded from the Green Belt and forms a “detached” built up area. About 94% of the area is Green Belt.

Geology Tandridge District has a varied geology. The line of the North Downs forms the most distinctive geological feature in the District. To the south lies the Weald, an area mainly of fine sands, sandstones and clays. The North Downs escarpment itself runs right across the District. The northward dip of the Chalk Group gives rise to the characteristic south facing escarpment of the North Downs. The chalk is subdivided into three formations: Upper, Middle and Lower, most of the chalk downland consists of the Upper Chalk. The Middle and Lower Chalk is only exposed along the scarpe face or in some of the valleys of the dip slope. The chalk is highly permeable, however, much of the Downs is capped with clay and clay with- flints and it is therefore highly impermeable. Figure 6 Geological map of Tandridge

The British Geological Survey provides an online map showing the geology of the Country - http://mapapps.bgs.ac.uk/geologyofbritain/home.html Topography Topographical data is important in assessing flood risk areas as they identify lowlying areas and potential areas that could be subject to overland flow.

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The topography of Tandridge District is characterised by the ridge of the top of the North Downs (just north of the route of the M25) that represents the boundary between the River Wandle which flows north out of the District and the two catchments to the south, the Mole which flows west out of the district and the Upper Medway which flows east.

The topographic map uses LiDAR (Light Detection And Ranging) from the Environment Agency and shows three distinctive dry valleys, all leading into Whyteleafe valley which contains the Bourne, appendix 3 also provides a topographic map of the district using Ordnance Survey contour lines. Whyteleafe valley is dry unless the groundwater level reaches a certain height causing the Bourne to flow, figure 15 later in this document shows the groundwater emerging in the Woldingham Valley.

Figure 7 The topography of Tandridge

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Flood defences

Flood defences are designed to reduce the risk to people, development and the natural environment from flooding. There are two types of flood defences: formal defences, typically raised defences which are specifically designed and maintained for the purposes of flood defence; and informal defences, such as structures which are not specifically designed and maintained for flood defence but may afford some protection, e.g. railway and road embankments near rivers.

The Council is not aware of any informal defences that have a significant impact on the urban areas, however, the Environment Agency have identified 23 formal defences within Tandridge(these are listed of the EA assets NFCDD). The defences cover a 7.4km stretch along the banks of the Ray Brook, there is a further 0.8km of defences along the River Eden, the location of the defences are shown in figure 3. As stated in the previous section the EA flood map shows the natural fluvial floodplain and ignores the presence of defences, therefore the flood zone along this length of the River Eden and Ray Brook may have been reduced.

Figure 8 The formal flood defences within Tandridge

Following the flooding of the Caterham Bourne in the winter of 2013/2014 a major projects review was completed to identify opportunities to mitigate future impact and reduce flooding risk. One of the opportunities for improvement was the retention of water upstream from the urban area of Whyteleafe. Resulting from this three upstream flood areas adjacent to Woldingham Road were constructed by Surrey Council who are now responsible for maintaining and inspecting them.

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Figure 9 Flood storage reservoirs along Woldingham Road

Location of storage reservoirs along Woldingham Road

3 Bug 1

A22 Woldingham 2

Railway

Temporary storage during the flood period at area 1

27 February 1 March

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Sluice gate at reservoir 3

Figure 10 flood storage areas

Storage Area Capacity Gate control

1. Primary storage area 10,000m3 Sluice gate 2. Secondary storage area 10,000m3 Sluice gate 3. Emergency storage area 2,000m3 Sluice gate

Figure 11 SCC inspection routine for the storage areas

Date Frequency

Summer (1st April to 30th September) Quarterly Winter (1st October to 30th March) Monthly Amber flood warning issued for catchment area Daily Red flood warning issued for catchment area Hourly

The inspections will be completed by a trained structural inspector and will be responsible for assessing: water levels; condition of sluice gate; activating Woldingham Emergency Flood Plan if there is any risk to overall containment and dangerous water levels.

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Flooding from artificial sources

Within Tandridge there are no canals, lakes where the water is retained above natural ground level or large reservoirs, however, Sutton and East Surrey Water do manage three small reservoirs that are within or near to the urban areas, these are listed below:

. Westhall Road, Warlingham (Grid 535383 157946) Area 13,055m2 . Stanstead Road, Caterham (Grid 533112 154565) Area 2,288m2 . Tillingdown Hill, Caterham (Grid 534440 155691) Area 4,003m2 Bay Pond in Godstone is a historic reservoir retained by a bank on the south side, there is a remote risk that this could fail resulting in rapidly flowing deep water. The predicted area that would be affected is woodland, consequently the threat to life and property damage would be minimal. The fact that the area is located within flood zone 3 will ensure that future development is not located in this vulnerable area.

Other historic reservoirs are Hedgecourt Lake at Felbridge and Wire Mill Lake at Newchapel. The downstream areas of both lakes are sparsely populated and all fall within flood zone 3 which will restrict future development.

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Overview of types of flooding

Flooding is a natural hazard that can happen in a wide variety of locations at any time. There are a number of forms of flooding which present a range of different risks. The speed of inundation and the duration of different forms of flooding varies greatly. With climate change, the frequency, patterns and severity of flooding are forecast to change and become more damaging. Flooding can occur directly from rainfall on the ground surface as well as rising groundwater, or overwhelmed sewers and drainage systems. Every flood event has the potential to impact on people, property and the environment. Within Tandridge there have been a number of different types of flooding in the District, these include river flooding, groundwater flooding and overland flooding, there have also been a number of sewer flooding incidents.

Fluvial Flood Risk During heavy or prolonged rainfall events, rivers can experience large flows which cause them to exceed their capacity. In the natural environment open spaces near the river act as storage areas or ‘flood plains' for out-of-channel flow, alleviating downstream flood risk. Urbanisation can severely affect this natural process. Faster run-off rates from upstream urban areas can result in an increase in flow in the rivers downstream, and building on the flood plain can significantly increase the risk of flooding both directly to the development concerned and on a wider basis by removing capacity from the flood plain. The Environment Agency has produced maps of the Country showing the ‘flood zones’. The table below sets out the probability of each zone flooding.

Flood Definition Zone Zone1 Land having a less than 1 in 1,000 annual probability of river or sea flooding. Low (all land outside Zones 2 and 3) Probability

Zone 2 Land having between a 1 in 100 and 1 in 1,000 annual probability of river Medium flooding; or Probability Land having between a 1 in 200 and 1 in 1,000 annual probability of sea flooding.

Zone 3a Land having a 1 in 100 or greater annual probability of river flooding; or High Land having a 1 in 200 or greater annual probability of sea flooding. Probability

Zone 3b This zone comprises land where water has to flow or be stored in times of flood. The Local planning authorities should identify in their Strategic Flood Risk Functional Assessments areas of functional floodplain and its boundaries accordingly, in Floodplain agreement with the Environment Agency. (Not separately distinguished from Zone 3a on the Flood Map)

See appendix 4 for a map of the district showing areas that are susceptible fluvial flooding. Surface water flooding Flooding from surface water runoff is usually caused by intense rainfall that may only last a few hours and usually occurs in lower lying areas, often where the drainage system is unable to cope with the volume of water.

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The updated Flood Map for Surface Water (uFMfSW) predominantly follows topographical flow paths of existing watercourses or dry valleys with some isolated ponding located in low lying areas. If the uFMfSW indicates a risk to a site allocation then this will be considered in further detail as the plan progresses. It should be noted that, because of its broad-scale nature, wherever possible these mapped outlines should be used in conjunction with other sources of local flooding information to confirm the presence of a surface water risk. The uFMfSW assesses a flooding scenario as a result of rainfall with the following chance of occurring in any given year: . 1 in 30 . 1 in 100 . 1 in 1000 See appendix 5 for a map of the district showing areas that are susceptible to surface water flooding.

Groundwater flooding In comparison to fluvial flooding, current understanding of the risks posed by groundwater flooding is limited and mapping of flood risk from groundwater sources is in its infancy. There is currently no one organisation with responsibility to respond to groundwater flooding, therefore the risks and mechanisms of groundwater flooding are poorly reported. However, under the Flood and Water management Act (2010), LLFAs have powers to undertake risk management functions in relation to groundwater flood risk. Groundwater level monitoring records are available for areas on Major Aquifers. However, for lower lying valley areas, which can be susceptible to groundwater flooding caused by a high water table in mudstones, clays and superficial alluvial deposits, very few records are available. The Environment Agency have produced Areas Susceptible to Groundwater Flooding (AStGWF) which is a strategic scale map showing groundwater flood areas on a 1km square grid. The map has been developed by using the top two susceptibility bands of the British Geological Society (BGS) 1:50,000 Groundwater Flood Susceptibility Map and thus covers consolidated aquifers (chalk, sandstone etc., termed 'clearwater' in the data attributes) and superficial deposits. It shows the proportion of each 1km grid square where geological and hydrogeological conditions show that groundwater might emerge. The susceptible areas are represented by one of four area categories (listed below) showing the proportion of each 1km square that is susceptible to groundwater emergence. It does not show the likelihood of groundwater flooding occurring. In common with the majority of datasets showing areas which may experience groundwater emergence, this dataset covers a large area of land, and only isolated locations within the overall susceptible area are actually likely to suffer the consequences of groundwater flooding. Whilst the EA clearly state that the data should not be interpreted as identifying areas where groundwater is actually likely to flow or pond, thus causing flooding, it may be of use for identifying where, for example, further studies may be useful.

FLOODTYPE Flood susceptibility type:

Clearwater; Clearwater and superficial deposits; or Superficial deposits flooding.

CLASS Area classification (proportion of each 1km square that is susceptible to groundwater flood emergence):

< 25%; >= 25% <50% >= 50% <75% >= 75%.

See appendix 6 for a map of the district showing areas that are susceptible to groundwater flooding.

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Flooding from sewers Sewer flooding occurs when intense rainfall overloads the sewer system capacity (surface water, foul or combined), and/or when sewers cannot discharge properly to watercourses due to high water levels. Sewer flooding can also be caused when problems such as blockages, collapses or equipment failure occur in the sewerage system. Infiltration, entry of soil or groundwater into the sewer system via faults within the fabric of the sewerage system, is another cause of sewer flooding. Infiltration is often related to shallow groundwater, and may cause high flows for prolonged periods of time.

Since 1980, the Sewers for Adoption guidelines have meant that most new surface water sewers have been designed to have capacity for a rainfall event with a 1 in 30 chance of occurring in any given year, although until recently this did not apply to smaller private systems. This means that, even where sewers are built to current specification, they are likely to be overwhelmed by larger events of the magnitude often considered when looking at river or surface water flooding (e.g. a 1 in 100 chance of occurring in a given year). Existing sewers can also become overloaded as new development adds to their catchment, or due to incremental increases in roofed and paved surfaces at the individual property scale (urban creep). Sewer flooding is therefore a problem that could occur in many locations across the district.

The impact of climate change Lead by the Environment Agency, a considerable amount of research is being carried out to quantify the impacts that climate change is likely to have on flooding in future years. According to Investing in the Future: Flood and Coastal Risk Management in England a Long Term Strategy (Environment Agency) it is predicted that climate change will result in sea level rises, an increase in the frequency and severity of storms. The Environment Agency have produced an advice note to assist in the consideration of climate change when preparing development plans, Adapting to Climate Change. The report uses UK Climate Projections 09 (UKCP09) for rainfall and temperature to develop river flood flows projections through the century, these are set out in the table below for the south east of England. The information provided in the table is derived for change to river flow likelihood of a 1 in 50 (2%) chance of occurring in any year. The change factor corresponds to the central estimate of change from the research. The upper and lower estimates are provided to represent the full range of potential changes in river flow for use in most circumstances. The projections are percentage changes to a 1961-90 baseline. Figure 12 Changes to river flood flows compared to a 1961-90 baseline

South East England Total potential Total potential Total potential change change change anticipated for anticipated for anticipated for the 2020s the 2050s the 2080s Upper end estimate 30% 55% 100% Change factor 10% 20% 30% Lower end estimate -15% -5% 0%

The report also uses the UKCP09 to set out the change to extreme rainfall intensity compared to a 1961-90 baseline.

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Figure 13 Change to extreme rainfall intensity compared to a 1961-90 baseline Applies across all of Total potential Total potential Total potential England change change change anticipated for anticipated for anticipated for the 2020s the 2050s the 2080s Upper end estimate 10% 20% 40% Change factor 5% 10% 20% Lower end estimate 0% 5% 10%

The NPPF requires that the impacts of climate change be taken into account in the preparation of Local Plans. It is therefore necessary to consider the impacts of climate change upon flood risk in the district as part of this Strategic Flood Risk Assessment. No detailed modelling of the potential impacts of climate change upon fluvial flood risk within the district has been carried out. Therefore, for planning purposes, the Environment Agency’s 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. Although this is considered a conservative estimate, in planning terms it is essential to the potential impact that climate change may have upon the district. It is considered that the Caterham Bourne Flood Alleviation Project, the Burstow Stream Flood Alleviation Project and the modelling being undertaken by the Environment Agency in the River Eden Catchment will take account of the effects of climate change. The SFRA will be updated to take account of the new data. Adopting the pragmatic comparison between Zone 3 and Zone 2 above, it is clear that climate change will not markedly increase the extent of river flooding within most areas of the district. Consequently, few areas that are currently situated outside of Zone 3 High Probability will be at substantial risk of flooding in the foreseeable future. This is an important conclusion from a spatial planning perspective. 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 district. This may exacerbate localised drainage problems, and it is essential therefore that detailed FRAs for developments consider the potential impacts of climate change upon localised flood risks, as well as the risks of fluvial flooding. The peak rainfall intensity is relevant to the design of the proposed surface water drainage systems, including SuDS for any development. It is also important to recognise that those properties and areas that are currently at risk of flooding may be susceptible to more frequent, and more severe flooding in future years. It is essential therefore that the development management process mitigates against the potential impact that climate change may have upon the risk of flooding both to and from properties and that developers consider the possible change in flood risk over the lifetime of the development. In the case of residential development the lifetime of the development should be 100 years unless there is a specific justification for considering a shorter period.

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Historic flood events and sources of flooding by area

The previous Tandridge SFRA published in 2007 included an assessment of historic flooding in the district. To summarise, it describes how Tandridge has suffered from flood events in the past, including several events in recent history which saw a number of properties across the district flooding with the Caterham Bourne and Burstow Stream causing the majority of the problems. Since the publication of the 2007 SFRA there have been two notable flood events within the District which took place in the summer of 2007 and the winter of 2013/2014. The assessment of past flood events and sources of flooding within the district looks at the three catchment areas: Area 1 . Caterham Bourne Area 2 . Upper River Mole Area 3 . Upper River Eden

Appendix 2 provides a record of past flood events from the three areas, however, this section will focus on the floods that occurred in the winter of 2013/14 as there is a large amount of detailed information available that enables us to better analyse the flooding. Weather conditions for the 2013/14 winter flood event Storm events hit the UK in late December 2013, followed again in January and February 2014.These storms came from the Atlantic and were characterised by unusually large and deep areas of low pressure, which brought rainfall and very strong winds. The rainfall is reflected by the spikes in daily rainfall totals, representing major rainfall events, shown in Figure 14 below.

Figure 14 Daily Rainfall totals at Charlwood, Surrey for Winter 2013-14 The major storm event occurring on the 23rd to 25th December resulted in 50-70mm of rainfall within 24 hours over an area from Dorset to Kent. This is indicated by the peak in rainfall of nearly 60mm in Figure 14. This daily rainfall represents approximately two-thirds of the monthly average rainfall for December. Combined with high groundwater levels and saturated soil from the high levels of rainfall leading up to the event, the rainfall gave rise to local pluvial flooding and also subsequent fluvial flooding from the Caterham Bourne, the river Eden, the Redhill Brook and the Burstow Stream. The persistent high levels of rainfall for this period lead to a sharp rise in river flows leading to fluvial flood warnings across the south east of England.

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Area 1 Caterham Bourne

The northern part of Tandridge, including Caterham, Warlingham and Whyteleafe, lies within the upper catchment of the Caterham Bourne. The Caterham Bourne is an ephemeral watercourse, meaning it flows intermittently usually after periods of heavy or prolonged rainfall, and is predominantly dry at other times. Historically, it is recorded to flow heavily approximately every 7 years, although smaller flows can be observed more frequently. When the level of groundwater rises and reaches ground level, water starts emerging on the surface. Water from these springs find its way into existing ditches and drainages. The source location is reported to vary with three valley flow paths leading towards the Wapses Lodge roundabout on the A22 at the southern tip of Whyteleafe. The Environment Agency map the start of the designated main river at Wapses lodge2, where the three flow paths combine. The route of the Bourne then flows in a North West direction through Whyteleafe and into Croydon, roughly following the course of the A22. Groundwater can also rise above underground structures such as existing culverts and sewers, and break surface at permeable points. Due to urban development, many parts of the Bourne have been culverted over the years with varying size pipes while some sections of the Bourne remain as open ditches. Not all culverts and ditches have the capacity to cope with large flow events such as the one experienced in the winter of 2013/2014.

2Environment Agency. Flood Map for Planning (Rivers and Sea) http://maps.environment- agency.gov.uk/wiyby/wiybyController?topic=floodmap&layerGroups=default&lang=_e&ep=map&scale=7&x= 534523.8854166673&y=158842.2708333329

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Figure 15 Groundwater emergence paths in Woldingham (February 2014)

Source: Croydon Flood

Figure 16 Rainfall records within the Caterham Bourne catchment

Source Sutton and East Surrey Water

The graph shows that the catchment experienced significantly higher than average rainfall for a number of months which lead to the flooding of both properties and essential infrastructure. Records from the flood show the impact of the Caterham Bourne flooding:

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. A number of residential properties were affected by: internal; basement; front and rear garden flooding; sewage backing up in the WC; and sewage in the garden. During the flooding the Council was aware of four properties having to be evacuated and another eight properties were without WC facilities for over six weeks; . 13 businesses either reported flooding or were impacted by the flooding, of these 3 commercial premises were vacated during the flooding; . Along the course of the Caterham Bourne 1,086 homes suffered from power cuts; . A temporary pedestrian bridge was constructed along the A22, this helped children in getting to school; . Located just outside of the District in the London Borough of Croydon is Kenley Water Works which supplies water to more than 46,000 properties, a large number of these are located in Tandridge. The site was at risk of being overwhelmed by contaminated flood water, however, large scale pumps ran constantly to reduce the level of flood water. . The A22 which is the main access into Croydon was shut for four weeks. . Flooding of the railway line into Caterham also occurred. Figure 17 Photos of flooding at various points along the Caterham Bourne

Closure of the Pedestrian bridge along

7 February 13 February

Railway line into Businesses affected

8 February 12 February

Topography and Land Use The topography of the Bourne catchment is characterised by steep slopes and valleys. The route of the A22 through Caterham, Whyteleafe and on to Purley is located in a natural valley, which has the potential to exacerbate flooding due to rapid runoff rates from the steep slopes and accumulation of runoff on the road. To the south of Wapses Lodge roundabout the catchment is largely green open space on the lower slopes that are used for agricultural and wooded on the higher slopes. To the north of Wapses Lodge roundabout the landuse change dramatically as there is a large amount of development focused alongside the A22, in the valley.

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Geology and Soils The bedrock geology in the catchment is made up of undifferentiated chalk formations, including the Lewes Chalk Formation, Seaford Chalk Formation, Newhaven Chalk Formation and Culver Chalk Formation3. The Holywell Chalk and New Pitt Chalk formations are located at the bottom of the valley in Whyteleafe, along the A22. Chalk is highly permeable and the EA Aquifer Designation maps4 indicate that the Bourne catchment overlies a ‘Principal Bedrock’ aquifer. The superficial deposits of Clay with Flint are located on top of the A22 valley and Head deposits of gravel, sand, silt and clay are located in the valley itself. The permeability of the soils in the catchment area is very high, with free draining shallow lime-rich soil in the valleys and slightly acid loamy soils on the top of slopes5.

Sources of Flooding As noted above, exceptionally high rainfall in December 2013 and January 2014 caused groundwater to rise rapidly and this is the predominant source of flooding during this event. However the catchment is complex particularly as the Bourne flows through Whyteleafe, where further sources contribute to flooding. The table below breaks down some of the sources identified in the 2014 floods. Gr ou ndw at er

- The main source of flooding during the flood event following record rainfall in October and December 2013 and January 2014, led to the emergence of springs and flooding of gardens and basements. This then influenced fluvial, sewer and surface water flooding. - The exceptionally high groundwater levels in the underlying chalk led to: . The Bourne rising, leading to high flows downstream in through Whyteleafe (flows of 1m3 a second through the sluice gate at Wapses lodge were record), . The ingress of rising groundwater into the foul sewer network (sewer).

3 http://www.bgs.ac.uk/data/mapViewers/home.html 4 Environment Agency. 2014. What’s in Your Backyard? ‘Aquifer Designation’ maps. Available at www.environment-agency.gov.uk/wiyby 5 National Soil Resources Institute. 2014. Soilscapes. Cranfield University. Available at www.landis.orguk/soilscapes/

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Figure 18 shows the level of water within the bore hole during the flood period compared to historic records Source Sutton and East Surrey Water

Surface water

Heavy and prolonged periods of rainfall led to surface water runoff which exceeded the immediate capacity of the surface water drainage network in a number of locations. This was further exacerbated by the lack of infiltration due to already saturated soil caused by high groundwater levels.

Fluvial

Although this flood is largely considered a groundwater flood by the EA, the Bourne is a designated main river from Wapses Lodge roundabout to Kenley. Structural assets such as trash screens caused water to back up as the high flows brought new debris combined with household waste items to block them up. Some culverts along the Bourne did not have sufficient capacity to convey the large volumes of flow, causing manholes to surcharge or water to back up and overflow upstream.

Sewer flooding

Heavy and prolonged periods of rainfall led to surface water runoff which exceeded the capacity of the drainage network. Significant pumping was required to prevent closure of the Kenley Water Treatment Works and to avoid property flooding. This led to greater volumes of water entering the sewer system as routes were sought to get water away from the risk area.

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Rising groundwater entered the foul sewer network, causing manholes to overflow and surcharge raw sewage internally and externally.

It should be noted that Tandridge District is working in partnership with: Surrey County Council; London Borough of Croydon; Environment Agency; Sutton and East Surrey Water; and Thames Water on the Caterham Bourne Flood Alleviation Project. The group has secured £4.9million of Local Enterprise Partnership funding to deliver flood alleviation measures along the course of the Caterham Bourne. Atkins plc have been commissioned to carry out a study that will recommend the preferred flood management approach. This will be achieved by: ­ Developing a robust understanding of flooding mechanisms and impacts in the study area; ­ A computer model of Caterham Bourne watercourse, water sewers, groundwater and surface water flood risk plus highway and other drainage systems in the area will be built and tested to better understand flow routes, flood depths and flood extents across the study area; ­ The outputs will include likely impacts from other factors such as climate change and urbanisation; and ­ ‘Options’ (ways of tackling the problem) will be tested against the model to identify those most likely to deliver benefits. A study was carried out by ArupWater following the flooding of the Caterham Bourne in the winter of 2001/2002. The map below shows (in red) that there are a number of pinch points in the channel that would be prone to flooding if a 1 in a 100 year event was to occur. To reduce the risk of flooding in these areas the report recommends replacing the pipes shown in the table below with pipes of larger capacity. The pipe sizes are shown in the table below.

Recommended u/s node to d/s Existing pipe Location pipe diameter node diameter (mm) (mm) Railway culvert near Ch021 to 021a 675 900 sports field From railway culvert to Ch034 to 034 650 900 Godstone Road Source Caterham Bourne Study ArupWater p.21

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Disused Gasholder

Railway Culvert Ch034 to 034

Railway Culvert Ch021 to 021a

Figure 19 Caterham Bourne showing areas prone to 1 in 100 year flood event Source ArupWater

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Area 2 Upper River Mole

The western part of Tandridge lies within the Upper Mole catchment with the Burstow Stream, Nutfield Brook, Salfords Stream, and associated tributaries flowing generally in the westerly and northerly direction towards the River Mole. Historical flood Burstow rain gauge is located in the Upper River Mole catchment. The records from this gauge during the 2013/14 winter flood event have been analysed by the Environment Agency to calculate indicative rainfall event return periods (EA Technical Report Winter Floods 2013/14 West Thames Area Flood and 2013-2014 Post flood Event Analysis Kent and South London Area May 2015). The available data suggests rainfall was reasonably consistent over the Mole headwater region. Over 23rd and 24th December, the Upper Mole catchment received up to 76mm of rain on land that was already saturated. During the Christmas Eve event almost 70mm of rainfall was recorded at the Burstow gauge. Data from this rain gauge suggests that the maximum return period observed for any single event during winter 2013/14 was 31 years. In contrast, the maximum accumulated rainfall totals for durations of 30, 60 and 90 days gives return period estimates of 61, 103 and 52 years respectively. The 30 and 60 day accumulations are the greatest in the 35 year rainfall AMAX series, with 314mm and 546mm respectively. The upper catchment overlies Wealden Group geology which is typically very impermeable in nature, giving rise to a rapid river response to the rainfall events. The flashy nature of the individual events was witnessed in the River Mole with water levels reported to have risen by approximately 0.3m per hour, and following its peak, returning to its regular level 10 hours later (Ref: Mole Valley notes 2/6/14). This rapid (or flashy) response can be seen in the figure below with the sharp peaks on the 24th December 2013, 17th January and the 1st February 2014.

Figure 20 Instantaneous Flow in the River Mole at Horley, Winter 2013-14 (ref EA 2014) Due to its responsive catchment type, the River Mole experienced its maximum peak flow in excess of 60m3/sec at Horley (just outside the District) on December 23rd to 24th. However, it was the duration and repetition of high flow events that contributed to the scale of the flooding encountered during winter 2013/14. While the mean flow recorded at the Horley gauge is 1.4m3/sec, a flow of 10m3/sec was exceeded 26 times over this winter period, indicating that the river was almost continually flooded. Smallfield is the main settlement within this area and the ‘main river’ Burstow Stream flows through the middle of the village inline with Weatherhill Road. The events set out above meant that Smallfield suffered extensive flooding during the Christmas period of 2013 that has continued through January and into February 2014. The flooding resulted in: . A number of residential properties were affected by: internal; basement; front and rear garden flooding; sewage backing up in the WC; and sewage in the garden; . Many of the roads being impassable; . The primary school has suffered from sewage surcharging onto the playground, although this occurred during the Christmas holidays it has happened in the past resulting in the school having to be closed;

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. The Smallfield GP surgery suffered with internal flooding which caused a huge amount of disruption for the patients and the day to day running of the surgery.

Smallfield surgery car Wheelers

5 December 3 January

Topography and land use The topography of the Upper Mole catchment is largely characterised by low lying rural and agricultural flood plains. The Smallfield settlement is located within the catchement along the Burstow Stream. The M23 motorway was constructed between 1972 and 1975 and runs north to south just to the west of Smallfield. The motorway is elevated, however, there are a number of large culverts running through the embankment to ensure that the flow of water is not impeded. Geology and soils The underlying bedrock geology of the sub area is the impermeable Weald Clay (mudstone) formation. To the east of Smallfield’s centre, surrounding the Burstow Stream are superficial River Terrace Deposits which have the potential to allow groundwater flooding at the surface. Due to the low permeability rainfall is unable to sink into the rocks, instead it quickly runs-off into streams causing the river network to respond rapidly to rainfall events. This rapid response to rainfall is known as ‘flashy’.

Sources of flooding As noted above, the catchment experienced exceptionally high levels of rainfall in December 2013 and January 2014. The rainfall during the 24 hours 23-24 Dec was the wettest for 35 years, yielding over 71mm in parts of the Mole catchment. Each millimeter of rainfall equals 1litre of rainfall per square meter. Extremely intense rainfall events cause water to flow overland into rivers very rapidly, exacerbated by the ground being saturated. The table below breaks down some of the sources identified in the 2014 floods.

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Surface water

Over winter 2013/14 the periods of prolonged rainfall led to the ground quickly becoming saturated, increasing rates of surface water runoff during subsequent rainfall events. This runoff regularly exceeded the capacity of drainage systems, both road-side ditches and pipes, leading to surface water ponding and overland flow and the flooding of roads and property. The open fields to the north east of Smallfield dip down towards the urban area which causes overland flow. A ditch along the eastern boundary of the settlement protects the properties and channels the water south, however, this has caused highway flooding along Plough Road.

Fluvial

The Burstow Stream flows in a generally westerly direction and is typical of an urban watercourse with a mixture of culverted sections and open stretches. The 2013/14 flood event and the EA modelling shows that parts of Smallfield village are at significant risk of fluvial flooding as the culvert sections of the river exceed capacity and the open sections bursting their banks.

Groundwater

Groundwater flooding is most likely to occur in low lying areas underlain by permeable rock (aquifers), however, with a largely impermeable bedrock it is considered that the southern part of area 2 is at low risk from groundwater flooding.

Sewer flooding

The heavy and prolonged periods of rainfall led to surface water runoff which exceeded the capacity of the drainage network, this lead to surcharging of the fowl water system and affected the primary school and a number of properties within Smallfield.

Tandridge District is working in partnership with: Surrey County Council; Reigate and Banstead Borough Council; and Environment Agency; on an initial assessment into the Smallfield and Burstow Flood Alleviation Scheme. The group has secured £55,000 of Environment Agency Local Levy funding and has commissioned Atkins plc to carry out the work. This will develop a robust understanding of flooding mechanisms and impacts in the study area and identify the preferred option to alleviate flood risk within the catchment. The study will also consider the development options for the Local Plan to ensure that any future development within the catchment is correctly located and where possible provides flood alleviation measures.

Area 3 Upper River Eden

The eastern and central part of Tandridge lies within the upper catchment of the River Eden, with the Eden Brook and associated tributaries flowing south from Oxted, and east from Horne and Lingfield, over the Surrey border and into Kent at Edenbridge.

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Historical floods There are several rain gauges located in the upper River Eden catchment. Two site records have been analysed as part of the Surrey County Council Section 19 Flood Investigation Report for Eastbourne Road, South Godstone to calculate indicative rainfall event return periods. 5- day Rainfall 8- day Rainfall Rain Gauge Rainfall Depth Estimated Rainfall Depth Estimated (mm) Return Period (mm) Return Period Felbridge 100.2 1 in 10 131 1 in 27 Godstone 78 1 in 3 102.8 1 in 7 Figure 21 Indicative Return Periods for the Winter 2013-14 rainfall in the Upper River Eden catchment (ref: Eastbourne Road, South Godstone Section 19 Flood Investigation Report) In common with the upper catchment of the River Mole, much of the upper catchment of the River Eden overlies geology belonging to the Wealden Group which is typically very impermeable in nature, giving rise to a rapid river response to the rainfall events. The two main settlements within this area are Oxted and Lingfield. The former is located in the upper catchment of the River Eden and the river flows through the urban area, Lingfield is located to the south where the Eden Brook flows to the south of the settlement and then flows under the railway line and up the western side where it is joined by the Ray Brook. The Met Office reported that the Winter of 2013/14 was the wettest ever recorded, this resulted in large areas of land being flooded within the catchment that caused: . A small number of residential properties to be affected by: internal; basement; front and rear garden flooding; and . Many of the roads surrounding Lingfield to be impassable with the only access in and out of the village being Newchapel Road.

Haxted

1 February

Topography and land use There are a number of settlements within the catchment, however, it is largely characterised by low lying, slightly undulating operational agricultural land.

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Geology and soils

Oxted is underlain by various sandstone formations and the area to the south of the town is underlain by Weald Clay. Lingfield is underlain by Upper Tunbridge Wells Sand formation (sandstones and siltstones) and superficial deposits of River Terrace Deposits and Alluvium broadly follow the path of the Eden Brook. To the north of Lingfield is Wealden Group (clay).

Sources of flooding

As noted above, the catchment experienced exceptionally high levels of rainfall in December 2013 and January 2014. The rainfall during the 24 hours 23-24 Dec was the wettest for 35 years, yielding over 71mm in parts of the Mole catchment. Each millimeter of rainfall equals 1litre of rainfall per square meter. Extremely intense rainfall events cause water to flow overland into rivers very rapidly, exacerbated by the ground being saturated.

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The table below breaks down some of the sources identified in the 2014 floods.

Surface water

The periods of prolonged rainfall led to the ground quickly becoming saturated, increasing rates of surface water runoff during subsequent rainfall events and due to the low lying topography meant that large expanses of agricultural land and roads were flooded.

Fluvial

The flood defences along the course of the Ray Brook and the Eden were built to protect the area against a 1 in 20 year flood event, however, these breached during the course of the flooding resulting in the surrounding flood plain being underwater for a significant amount of time.

Groundwater

Within the upper catchment of the River Eden the sub area is underlain by the Weald Clay Formation mudstones in the south and various sandstone formations in the north. There is limited potential for groundwater flooding to occur across the sub area.

Sewer flooding

The Council is not aware of any sewer flooding incidents that have occurred within the catchment.

Following the 2013/14 flood, the Environment Agency is using the information collated during the event to update the flood model for the catchment. Need more information about the modelling work being carried out on the River Eden.

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Overview of all development options

Tandridge District Council (TDC) is preparing a Local Plan to guide development in the district to 2033. The Local Plan will include housing and employment targets and will seek to allocate sites to ensure such targets can be delivered, while also containing a set of policies to manage development in a sustainable manner. The timetable for the Plans production is set out below:

At the time of writing the amount of development proposed by the Local Plan and its distribution is unknown. The Strategic Housing Market Assessment is due for publication in December 2015 and this will set out the ‘objectively assessed housing need’ which will help in establishing the amount of development that will be delivered through the Local Plan. The Regulation 18 consultation will be carried out in December 2015 and the following ways for delivering development in the future will be considered. It should be noted that the different scenarios will deliver varying degrees of development.

Figure 22 Proposed development scenarios as set out in the Local Plan Regulation 18 consultation

Scenario Description of development scenario

Continue to focus all future development into the existing urban areas (no change 2a to current policy) and make best use of existing employment sites.

Continue to focus all future development into the existing urban areas but build at 2b a higher density and make best use of existing employment sites.

Focus development into the existing urban areas and sites in the Green Belt around the main urban settlements and large rural service settlements (these 3 settlements are Oxted, Caterham, Warlingham, Whyteleafe, Smallfield, Lingfield and Godstone). Commercial development will seek to maximise existing employment areas.

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Focus development into the existing urban areas and sites in the Green Belt around the rural service settlements and limited service settlements (these settlements are Bletchingley, Woldingham, South Nutfield, Dormansland, South 4 Godstone, Tatsfield, Blindley Heath, Limpsfield Chart, Nutfield, Felbridge and Old Oxted). Commercial development will seek to maximise existing employment areas. This combines scenarios two, three and four (this scenario is based on maximum 5 capacity).

A large extension of 4,000 homes and 33,500m2 of commercial floorspace to an 6 existing settlement.

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Figure 23 Location of settlements listed within the development scenarios

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Flood risk management in the Local Plan

This section will look at the practices and policy measures needed to the manage flood risk in the borough as outlined in the preceding sections. This will include the use of the Sequential Test and Exception Test in the allocation of sites and in the assessment of planning applications, as well as policies to address specific aspects of the identified flood risk.

The Sequential Test The Sequential Test is part of the risk based approach to flood management and is required by the NPPF. It seeks to ensure that Local Planning Authorities steer development to areas of lowest flood risk, requiring them to establish that there are no reasonably available development sites within the areas of lowest flood risk before considering development in areas of higher flood risk.

The Sequential Test is used by Local Planning Authorities at the site allocation stage when preparing development plan documents, however it is also carried out at the application stage in the case of windfall sites or where the allocations in the current development plan have not been subjected to such testing.

Figure 24 Application of the Sequential Test for Local Plan preparation

Source Planning Practice Guidance Paragraph: 020 Reference ID: 7-020-20140306 Links can be found here to Table 1, Table 2 and Table 3

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Table 3 that is referred to in the diagram stipulates permissible development types for different Flood Zones. This considers the degree of flood risk posed to the site in terms of the likely vulnerability of the proposed development to damage and the risk to the lives of the site occupants should a flood occur. Wherever possible, development should be restricted to the suitable land uses summarised in Table 1 and Table 2. 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.

The Exception Test If the Sequential Test concludes that it is not possible for development to be located exclusively within the areas of lowest risk the Exception Test must be applied.

Paragraph 102 of the NPPF sets out the requirements of 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 Strategic Flood Risk Assessment where one has been prepared; and . a site-specific flood risk assessment must demonstrate that the development will be safe for its lifetime taking account of the vulnerability of its users, without increasing flood risk elsewhere, and, where possible, will reduce flood risk overall Both elements of the test will have to be passed for development to be allocated or permitted.”

Use of the Sequential and Exception Tests in Site Allocations Local Plan | Strategic Policies consultation (Regulation 18)

The report sets out an overview of flood risk, this information fed into the assessment of the Housing and Economic Land Availability Assessment sites and assisted in the formulation of the options that will be consulted on in the Regulation 18 consultation of the Local Plan.

Local Plan | Strategic Policies consultation (Regulation 19)

If additional housing sites are submitted to the Council during the Regulation 18 consultation they will need to be tested in the Housing and Economic Land Availability Assessment (HELAA) along with any potential new employment sites or other major land allocations. If site allocations are required site-specific assessments will need to be undertaken to ensure all forms of flood risk at a site are fully addressed. In addition, following the Sequential Test, some sites may be put forward for the Exception Test. These will require further work in a detailed FRA. Any site that does not pass the Exception Test should not be allocated for development. It is normally the responsibility of the developer to provide a FRA with an application. However, a LPA can decide to commission a detailed, site-specific FRA to help them decide upon allocations in the high risk zone. The SFRA cannot provide this level of site-specific information.

It is recognised that, whilst only a relatively small proportion of the district is situated within flood affected areas, some of these areas affected correspond to some of the areas being considered for future growth. Limiting future residential development in these areas may impact upon the economic and social welfare of the existing community, and consequently there may be pressing planning needs that may warrant further consideration of these areas. This being the case, the Council will need to consider site allocations in areas of higher flood risk and apply the Exception Test accordingly.

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When allocating land for development, the potential cumulative impact of the loss of floodplain storage at the development site, and elsewhere within the catchment, needs to be considered and, if required, mitigation should be provided. Whilst individual developments may only have a minimal impact on flood risk, multiple developments may have a significant effect, however, there may be the opportunity for development to provide flood risk benefits downstream.

Requirements for flood risk assessments The aim of a FRA is to demonstrate that the development is protected to the 1% annual probability event and is safe during the design flood event, including an allowance for climate change. This includes assessment of mitigation measures required to safely manage flood risk. Development sites that are being considered for allocation that require a FRA should: . Apply the Sequential and, when necessary, Exception Tests . Not increase flood risk, either upstream or downstream, of the site, taking into account the impacts of climate change . Not increase surface water volumes or peak flow rates, which would result in increased flood risk to the receiving catchments . Use opportunities provided by new development to, where practicable, reduce flood risk within the site and elsewhere . Ensure that where development is necessary in areas of flood risk (after application of Sequential and Exception Tests), it is made safe from flooding for the lifetime of the development, taking into account the impact of climate change . All sources of flood risk, including fluvial, surface water and drainage need to be considered.

FRAs being submitted as part of the site allocations should follow the approach recommended by the NPPF and associated guidance, in consultation and using guidance provided by the Environment Agency and the Local Lead Flood Authority (Surrey County Council).

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Conclusions and recommendations

Conclusions The findings of this updated SFRA have fed into the Housing and Economic Land Availability Assessment and assisted in the development of the strategic policies options within the Regulation 18 consultation paper. If site allocations are necessary at the regulation 19 stage to deliver the amount of housing that is required within the Local Plan, the SFRA, along with the Caterham Bourne Flood Alleviation Project, the Burstow Flood Alleviation Project, and the modelling of the River Eden will provide the necessary information required to undertake the site specific assessments. This will ensure that any allocation of sites will take account of any long term solutions to flooding within the district, particularly if the acquisition of land is required to deliver a flood alleviation scheme. The SFRA presents Flood Zone Maps that outline the Environment Agency flood zones as Flood Zone 1, low probability, Flood Zone 2, medium probability and Flood Zone 3a, high probability. In addition, the map from the Environment Agency showing the risk of flooding from surface water and ground water have played a key role within this SFRA. The application of the Sequential Test (and where appropriate, the Exception Test) in order to steer vulnerable development away from areas of flood risk, remains a fundamental part of the planning process and these maps will be used in the assessment and used in the future for the assessment of the site allocations.

Recommendations This Level 1 SFRA report has been developed by building heavily upon existing knowledge with respect to flood risk within the district. The report has not been prepared to consider site-specific allocations, instead, it has informed the development of the Strategic Options (Regulation 18) consultation. As mentioned above there are three key pieces of modelling that are being carried out: . Caterham Bourne Flood Alleviation Project; . Burstow Flood Alleviation Project; and . Environment Agency modelling of the flood zones 2 and 3 in the River Eden catchment. Once these projects are completed the SFRA will be updated so that the information contained within them will assist in the flood risk assessment for the site allocations. In summary, the SFRA is a ‘living’ document and will be reviewed regularly in light of emerging policy directives and an improving understanding of flood risk within the district. Proceeding with the SFRA in the production of the Local Plan: . The Council will apply the Sequential Test to the potential development sites and identify those sites they consider will be necessary to apply the Exception Test; . The layout of buildings and access routes should adopt a sequential approach, steering buildings (and hence people) towards areas of lowest risk within the boundaries of the site. This will also ensure that the risk of flooding is not worsened by, for example, blocked flood flow routes. . Consultation with Surrey County Council as the Local Lead Flood Authority and the Environment Agency following completion of the Exception Test will be carried out to ensure that they accept the justification for progressing with sites that require the Exception Test; and . The SFRA outputs will be used by the district to assess flood risk to windfall sites which become available for redevelopment. If such sites require the Exception Test a site-specific flood risk assessment will be needed to be considered sound.

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Appendix 1 Advice Note on contents of a Sustainable Drainage Statement

TANDRIDGE DISTRICT COUNCIL

1. Introduction 1.1 The Government has strengthened planning policy on the provision of sustainable drainage and new consultation arrangements for ‘major’ planning applications are being introduced from 15 April 2015. 1.2 Decisions about the suitability of sustainable drainage provision are made by the local planning authority. However, under the new consultation arrangements Surrey County Council, in its role as Lead Local Flood Authority, is a statutory consultee for all major applications. Previously the Environment Agency had that statutory responsibility. 1.3 Therefore all ‘major’ planning applications submitted from 15 April 2015 are required to include a Surface Water Drainage Statement. 1.4 The purpose of this advice note is to set out what information should be included in such statements. This advice note forms part of the Council’s ‘local validation list’ and major applications that are not submitted with a Surface Water Drainage Statement will not be regarded as a ‘valid’ application. 2. Requirements 2.1 It will be essential that the type of sustainable drainage system (SuD) for a site, along with details of its extent/position, is identified at the design stage of the whole scheme. This information will be required for both outline and full applications so it is clearly demonstrated that the SuD can be accommodated within the development that is proposed. 2.2 It will no longer be acceptable to leave the design of SuDs to a later stage to be dealt with by planning conditions. 2.3 The Government has introduced non-statutory technical standards (https://www.gov.uk/government/publications/sustainable-drainage-systems-non-statutory- technical-standards) for the design, maintenance and operation of SuD. The SuD must adhere to the principles of these standards. 2.4 Surface water run-off should be controlled as near to its source as possible through a sustainable drainage approach to surface water management. SuDs seek to mimic natural drainage systems and retain water on or near to the site, when rain falls, in contrast to traditional drainage approaches, which tend to pipe water off-site as quickly as possible. SuDs therefore offer significant advantages over conventional piped drainage systems. 2.5 Approved Document Part H of the Building Regulations 2010 also establishes a hierarchy for surface water disposal, which encourages a SuDS approach beginning with infiltration where possible e.g. soakaways or infiltration trenches. Where SuDS are used, it must be established that these options are feasible, can be adopted and properly maintained and would not lead to any other environmental problems. 2.6 Where the intention is to dispose to soakaway, these should be shown to work through an appropriate assessment carried out under Building Research Establishment Digest 365. 2.7 Before disposal of surface water to the public sewer is considered all other options set out in Approved Document Part H of the Building Regulations 2010 should be exhausted. When no other practicable alternative exists to dispose of surface water other than the public sewer, the Water Company or its agents should confirm that there is adequate spare capacity in the existing system taking future development requirements into account.

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2.8 Where an application is part of a larger site which already has planning permission it is essential that the new proposal does not compromise the drainage scheme already approved. 2.9 Development which involves a culvert or an obstruction to flow on an Ordinary Watercourse will require consent under the Land Drainage Act 1991 and the Floods and Water Management Act 2010. In the case of an Ordinary Watercourse the responsibility for Consenting lies with the Lead Local Flood Authority (LLFA). An Ordinary Watercourse is defined as any watercourse not identified as a Main River on maps held by the Environment Agency and DEFRA. For further information on Ordinary Watercourses contact the LLFA. The Environment Agency would still wish to be consulted on any proposed culverting or an obstruction to flow on a Main River 3. Further information and guidance 3.1 Applicants are strongly advised to discuss their proposals with Lead Local Flood Authority (Surrey County Council) at the pre-application stage to ensure that an acceptable SuDS scheme is submitted.

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Tandridge District Council Surface Water Drainage Statement

In order to provide the required information on surface water drainage from the proposed development this pro-forma must be completed in full and be submitted with any planning application which seeks permission for ‘major’ development. This information contained in this form will be used by Surrey County Council in its role as Lead Local Flood Authority and ‘statutory consultee’ on SuDs for all ‘major’ planning applications. The pro- forma is supported by the Defra/EA guidance on Rainfall Runoff Management and uses the storage calculator on www.UKsuds.com. The pro-forma should be considered alongside other supporting SuDS Guidance, but focuses on ensuring flood risk is not made worse elsewhere. The SuDs solution must operate effectively for as long as the development exists. This pro-forma is based upon current industry standard practice. Evidence paragraph 1. Site Details

Site Address & post code or LPA reference Grid reference Is the existing site developed or Greenfield? Total Site Area served by drainage system (excluding open space) (Ha)* Topographical survey plan showing existing site layout, site levels and drainage system

* The Greenfield runoff off rate from the development which is to be used for assessing the requirements for limiting discharge flow rates and attenuation storage from a site should be calculated for the area that forms the drainage network for the site (whatever size of site and type of drainage technique). Please refer to the Rainfall Runoff Management document or CIRIA manual for detail on this.

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2. Impermeable Area

Existing Proposed Difference Notes for developers & Local Authorities (Proposed-Existing) Impermeable area (ha) If the proposed amount of impermeable surface is greater, then runoff rates and volumes will increase. Section 6 must be filled in. If proposed impermeability is equal or less than existing, then (areas to be shown on a plan) section 6 can be skipped & section 7 filled in. Drainage Method N/A If different from the existing, please fill in section 3. If existing drainage is by infiltration and the (infiltration/sewer/watercourse) proposed is not, discharge volumes may increase. Fill in section 6.

3. Proposing to Discharge Surface Water via Yes No Evidence that this is possible Notes for developers & Local Authorities Existing and proposed micro- Please provide micro-drainage calculations of existing and proposed run-off rates and volumes in drainage calculations accordance with a recognised methodology or the results of a full infiltration test (see line below) if infiltration is proposed. Infiltration e.g. soakage tests. Section 6 (infiltration) must be filled in if infiltration is proposed. To watercourse e.g. Is there a watercourse nearby? Please provide details of any watercourse to which the site drains including cross-sections of any adjacent water courses for appropriate distance upstream and downstream of the discharge point (as agreed with the LLFA) To surface water sewer Confirmation from sewer provider that sufficient capacity exists for this connection. Combination of above e.g. part infiltration part discharge to sewer or watercourse. Provide evidence above. Has the drainage proposal had Evidence must be provided to demonstrate that the proposed Sustainable Drainage proposal has regard to the SuD hierarchy? had regard to the SUD hierarchy. Layout plan showing where the Please provide plan reference numbers showing the details of the site layout showing where the sustainable drainage sustainable drainage infrastructure will be located on the site. If the development is to be infrastructure will be located on constructed in phases this should be shown on a separate plan and confirmation should be site. provided that the sustainable drainage proposal for each phase can be constructed and can operate independently and is not reliant on any later phase of development.

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4. Peak Discharge Rates – This is the maximum flow rate at which storm water runoff leaves the site during a particular storm event. Existing Rates Proposed Rates Difference (l/s) Notes for developers & Local Authorities (l/s) (l/s) (Proposed-Existing) Greenfield QBAR (mean N/A N/A QBAR is approx. 1 in 2 storm event. Provide this if Section 6 (QBAR) is proposed. annual flood flow rate in a river) 1 in 1 Proposed discharge rates (with mitigation) should be no greater than existing rates for all corresponding storm events. e.g. discharging all flow from site at the existing 1 in 100 event increases 1 in 30 flood risk during smaller events. 1in 100 1 in 100 plus climate N/A To mitigate for climate change the proposed 1 in 100 +CC must be no greater than the existing 1 in change 100 runoff rate. If not, flood risk increases under climate change. 30% should be added to the peak rainfall intensity.

5. Calculate additional volumes for storage –The total volume of water leaving the development site. New hard surfaces potentially restrict the amount of stormwater that can go to the ground, so this needs to be controlled so not to make flood risk worse to properties downstream. Existing Volume Proposed Volume Difference (m3) Notes for developers & Local Authorities (m3) (m3) (Proposed-Existing) 1 in 1 Proposed discharge volumes (without mitigation) should be no greater than existing volumes for all corresponding storm events. Any increase in volume increases flood risk elsewhere. Where volumes 1 in 30 are increased section 6 must be filled in. 1in 100 1 in 100 plus climate To mitigate for climate change the volume discharge from site must be no greater than the existing 1 change in 100 storm event. If not, flood risk increases under climate change.

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6. Calculate attenuation storage – Attenuation storage is provided to enable the rate of runoff from the site into the receiving watercourse to be limited to an acceptable rate to protect against erosion and flooding downstream. The attenuation storage volume is a func tion of the degree of development relative to the greenfield discharge rate. Notes for developers & Local Authorities Storage Attenuation volume (Flow rate control) required to retain Volume of water to attenuate on site if discharging at existing rates; an’t rates as existing (m3) be used where discharge volumes are increasing

7. How is Storm Water stored on site? Storage is required for the additional volume from site but also for holding back water to slow down the rate from the site. This is known as attenuation storage and long term storage. The idea is that the additional volume does not get into the watercourses, or if i t does it is at an exceptionally low rate. You can either infiltrate the stored water back to ground, or if this isn’t possible hold it back with on-site storage. Firstly, can infiltration work on site? Yes No Notes for developers & Local Authorities State the Site’s Geology/drift material overlaying) Avoid infiltrating in made ground. Infiltration Does the site have a high ground water table? Yes/No? If yes, please provide details of the site’s hydrology; Is the site within a known Source Protection Zones (SPZ)? Infiltration rates are highly variable and refer to Environment Agency Yes/No? website to identify and source protection zones (SPZ) Are infiltration rates suitable? Infiltration rates should be no lower than 1x10 -6 m/s. Is the site contaminated? If yes, consider advice from Water should not be infiltrated through land that is contaminated. The others on whether infiltration can happen. Environment Agency may provide bespoke advice in planning consultations for contaminated sites that should be considered. State the distance between a proposed infiltration device Need 1m (min) between the base of the infiltration device & the water table base and the ground water (GW) level to protect Groundwater quality & ensure GW doesn’t enter infiltration devices; !void infiltration where this isn’t possible; Were infiltration rates obtained by desk study or Infiltration rates can be estimated from desk studies at most stages of the infiltration test? planning system if a back-up attenuation scheme is provided.

In light of the Yes/No? If the answer is No, please identify how the storm If infiltration is not feasible how will the additional volume be stored?. The above, is water will be stored prior to release applicant should then consider the following options in the next section. infiltration

feasible? 57

7a. Storage requirements The developer must confirm that either of the two methods for dealing with the amount of water that needs to be stored on sit e. Option 1 Simple – Store both the additional volume and attenuation volume in order to make a final discharge from site at QBAR (Mean annual flow rate). This is preferred if no infiltration can be made on site. This very simply satisfies the runoff rates and volume criteria. Option 2 Complex – If some of the additional volume of water can be infiltrated back into the ground, the remainder can be discharged at a very low rate of 2 l/sec/hectare. A combined storage calculation using the partial permissible rate of 2 l/sec/hectare and the attenuation rate used to slow the runoff from site.

Notes for developers & Local Authorities Please confirm what option has been chosen and how much storage is The developer at this stage should understand the site characteristics and required on site. be able to explain what the storage requirements are on site and how it will be achieved.

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8. Additional Information Notes for developers & Local Authorities Which Drainage Systems measures have been used? SUDS can be adapted for most situations even where infiltration isn’t feasible e.g. impermeable liners beneath some SUDS devices allows treatment but not infiltration. See CIRIA SUDS Manual C697 or equivalent. Drainage system can contain water in a 1 in 30 storm event without This a requirement for sewers for adoption & is good practice even where flooding drainage system is not adopted. Any flooding between the 1 in 30 & 1 in 100 plus climate change storm Safely: not causing property flooding or posing a hazard to site users i.e. events will be safely contained on site. no deeper than 300mm on roads/footpaths. Flood waters must drain away at section 6 rates. Existing rates can be used where runoff volumes are not increased. How are rates being restricted (hydrobrake etc) Hydrobrakes to be used where rates are between 2l/s to 5l/s. Orifices not be used below 5l/s as the pipes may block. Pipes with flows < 2l/s are prone to blockage. Drainage during construction period Provide details of how drainage will be managed during the construction period including any necessary connections, impacts, diversions and erosion control.

9. Management and Maintenance of SuDs Details are required to be provided of the management and maintenance plan for the SUD, including for the individual plots in perpetuity. If open water is involved, a health and safety plan will also be required. How is the entire drainage system to be Clear details of the maintenance proposals of all elements of the proposed maintained in perpetuity? drainage system must be provided to show that all parts of SuDs are effective and robust. Provide a management plan to describe the SUDS scheme and set out the management objectives for the site. It should consider how the SuDs will perform and develop over time anticipating any additional maintenance tasks to ensure the system continues to perform as designed. — Specification notes that describe how work is to be undertaken and the materials to be used. — A maintenance schedule describes what work

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is to be done and when it is to be done using frequency and performance requirements as appropriate. — A site plan showing maintenance areas, control points and outfalls. Responsibility for the management and maintenance of each element of the SUDS scheme will also need to be detailed within the Management Plan .

Where open water is involved please provide a health and safety plan within the management plan. Please confirm the owners/adopters of If these are multiple owners then a drawing illustrating exactly what the entire drainage systems throughout features will be within each owner’s remit must be submitted with this the development. Please list all the Proforma. Please give details of each feature and how it will be managed in owners. accordance with the details in the management plan. Please provide details demonstrating that any third party agreements required using land outside the application site have been secured.

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The above form should be completed using evidence from information which should be appended to this form, the Flood Risk Assessment and site plans. It should serve as a summary of the drainage proposals and should clearly show that the proposed rate and volume as a result of development will not be increasing. If there is an increase in rate or volume, the rate or volume section should be completed to set out how the additional rate/volume is being dealt with.

This form is completed using factual information and can be used as a summary of the surface water drainage strategy on this site.

Form ompleted y<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<;;;;;;;;;;;;;;;;;;;;;;; Qualification of person responsible for signing off this pro-forma ......

ompany<<<<<<<<<<<<<<<<<<<<<<<<<<<<<,;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;; On behalf of (lient’s details) ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;...... Date:<<<<<<<<<<<;;;;;;;;;;;;;;;;;;;;;;;;;;;;

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Appendix 2: Flood event records from the three catchments

The table below lists the flood event records from each of the four areas. Area 1: Caterham Bourne April 2001 Significant amount of flooding occurred along the course of the Caterham Bourne resulting in the A22 being shut for an extensive period of time, and a number of residential and business properties were flooded.

January / February 2014 11 properties flooded, large number of gardens and outbuildings flooded and sewage issues for other properties along the Bourne.

Area 2: Upper River Mole

September 1968 Large number of properties flooded in Crawley, Three Bridges and Horley which affected 401 properties

December 2013 36 properties reported as flooded including Woodside Crescent, Smallfield where over 16 properties were affected.

Area 3: Upper River Eden

1958 September Mainly agricultural land flooding between Lingfield and Edenbridge. There are also EA records of agricultural land being flooded in Limpsfield and possibly 1 property. Some property, including a sewage treatment works flooded in Oxted.

1960 November Extensive catchment wide flooding. Some property flooding was recorded in Oxted and outside of the District in Edenbridge.

1963 November Flooding around Wire Mill Lake area, possibly affecting properties around Woodcock Bridge. Flooding along the Eden Brook towards Jack's Bridge (about one mile south of Lingfield). Widespread flooding along the Eden Brook from upstream of Blindley Heath to the railway line at Lingfield Common.

1968 September Widespread flooding along the Eden Brook and River Eden from upstream of Blindley Heath to Edenbridge. The majority of the properties that were affected were outside of the district in Edenbridge, Hever and Penshurst. Flooding along to Edenbrook in most of the same areas as 1963 and upstream to Hedgecourt Lake.

2013 December Widespread flooding across the catchment resulting in a number of properties being affected and many roads becoming impassable.

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Appendix 3 Topographic map

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Appendix 4 Map showing areas at risk from river flooding

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Appendix 5 Map showing areas at risk from surface water flooding

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Appendix 6 Map showing areas at risk of groundwater flooding

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