4.1. Overview

As stated within the NPPF and PPG, developers and local authority planners need to consider flood risk to and from the development as part of planning proposals. To assess and demonstrate that the proposed development will not be at risk of flooding or increase flood risk elsewhere for all flood sources, a site-specific FRA and/or drainage strategy may be required. Development proposals should also aim to reduce local flood risk where possible through the implementation of SuDS and other water management measures. These key principles need to be applied at the strategic level for borough wide planning and at the site level for development proposals and site allocations.

Planning applications are required for development proposals to be considered. The relevant LPA will undertake a period of consultation to review the proposal, referring to internal and external consultees as required. Flood risk to and from the development must be considered as part of the planning proposals. If a site-specific FRA and/or drainage strategy is required, and is either not submitted or is deemed unsatisfactory, the LPA will refuse the application as providing satisfactory documentation is a national policy requirement.

Tables 4-1, 4-2, 4-3 and 4-4 provide requirements and considerations that must be addressed in flood risk and drainage strategy documents to demonstrate that a proposed development is appropriately flood resilient and resistant. Tables 4-1, 4-2, and 4-3 cover planning application and development requirements for Major, Minor and Change of Use developments (including changes to prior approvals), respectively. Table 4-4 provides the requirements for the assessment and management of flood risk from other sources where applicable. FRA Submission and Drainage Strategy Submission Checklists have been developed as part of this SFRA and have been designed to accompany the guidance presented in this section. Further guidance is available via the PPG Site-specific FRA Checklist, the EA’s Standing Advice, and by contacting the relevant LPA or EA where required.

Further developer (Section 4.2), developer management (Section 4.3) and planning policy (Section 4.4) specific guidance regarding flood risk assessment is available in this section. Information regarding the Sequential Test, Exception Test, SuDS, site-specific FRAs and drainage strategies is covered, accompanying the information presented in the tables below.

Download Table 4-1 – Planning Application and Development Requirements for Major Developments (Flood Zones 1, 2, 3a and 3b)

Download Table 4-2 – Planning Application and Development Requirements for Minor Developments (Flood Zones 1, 2, 3a and 3b)

Download Table 4-3  Planning Application and Development Requirements for Change of Use Developments and changes to Prior Approvals (Major and Minor – Flood Zones 1, 2, 3a and 3b)

Download Table 4‑4 – Planning Application and Development Requirements for Individual Sites (Other Flood Risk Sources)

The information presented in Tables 4-1, 4-2, 4-3 and 4-4 are a mixture of legislative and best-practice requirements from various sources, including the NPPF, PPG , and London Plan. The requirements presented in this table may change over time. Please consult the relevant LPA if you are unsure on matters relating to any of the requirement areas outlined in this table.

4.2. Developer Guidance

This sub-section provides developer specific guidance on a range of key requirements to ensure that development proposals are compliant. The guidance accompanies the information presented in the tables in Section 4.1.

4.2.1. Application of the Sequential and Exception Tests

Implementation of a sequential, risk-based approach is vital in determining the suitability of a site for development with regards to flood risk. For proposed development sites that require the application of the Sequential Test, and in some instances, the Exception Test, this document, and the Web Maps, provide the basis for applying these tests at a site-specific level.

Proposed development sites within multiple flood risk zones are classed under the highest Flood Zone present on site. For example, a site that partly falls under Flood Zone 1 and Flood Zone 2 is formally classified as a site in Flood Zone 2. The Flood Zone that each proposed site falls under helps inform the approach needed for the site and the information required for the planning application. The Sequential Test will need to be applied to steer the entire proposed site to the areas with the lowest risk of flooding. If the Exception Test is required, application is based on the highest flood risk zone the site is in and will need to be passed for the planning application.

Sequential Test

The Sequential Test ensures that a sequential approach is followed to steer new development to areas with the lowest probability of flooding. For sites that require it, but have not undergone Sequential Testing as part of the site allocations identified in the Borough’s Local Plan, a site-specific Sequential Test is required. The search area and definition of reasonable available alternative sites must be determined in line with the guidance below in consultation with the relevant LPA. The Scope is not limited to, but should include the following, and any scope should be shared with the LPA for review and agreement prior to the Test being undertaken.

  • Search Area: The default area should be the whole of the LPA area in question. This can be reduced where justified by the functional requirements of the development or relevant objectives of the Local Plan. Examples of these include:
    • Functional requirements – Industrial or infrastructure developments that may service an area wider than the LPA.
    • Local plan objectives – Regeneration of a specific area may be targeted and the proposed development type may meet the needs of the specified regeneration area.
  • Reasonable available sites: These generally include sites that are suitable (can accommodate the requirements of the proposed development), developable and deliverable. Sources of where these could be selected from include the following:
    • List of sites prepared as part of the evidence base or background documents produced to inform the Local Plan.
    • Sites listed under a Local Authority’s brownfield land register, which contains information on previously developed sites that are considered to be appropriate for residential development. This includes sites with and without planning permission.

Exception Test

Following the application of the Sequential Test, if it is determined that the proposed development cannot be located in an area with a lower probability of flooding, the Exception Test should be applied. The Exception Test is designed to help ensure that flood risk to both people and property will be managed across the lifetime of the proposed development. To pass the Exception Test, the PPG sets out two considerations that need to be achieved. Both considerations will need to be satisfactorily demonstrated to the LPA for development to be allocated or permitted. These considerations are:

  • The development provides wider sustainability benefits to the community that outweigh flood risk, informed by a SFRA where one has been prepared; and
  • A site-specific FRA 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.

To satisfy the Exception Test, a sustainability appraisal or evidence demonstrating the development proposal’s sustainability benefits should be provided. A sustainability appraisal should demonstrate the evidence of the wider sustainability benefits that the development would bring at that specific site. This may include evidence demonstrating how the proposed development meets the objectives set out in the sustainability appraisal of the Local Plan, or evidence demonstrating policy compliance regarding affordable housing or defined housing needs for the area. In addition, the planning and design of the development needs to demonstrate that the site will remain safe and operational during a flood event. This may involve:

  • Designing buildings to avoid flooding by, for example, raising floor levels.
  • Implementing resilient and / or resistant features to reduce the impact of a flood. For example, resilient features, such as installing electrical equipment above flood level, are designed to ensure the internal elements of a property to be recovered as quickly and as cost effectively as possible. Flood resistant features, such as installing flood doors and barriers, are designed to ensure water stays out of a property up to a given height.
  • Utilising SuDS as a priority.
  • Mitigating the potential impacts of flooding through design (for example ensuring more vulnerable development lies in less at-risk parts of a site) and flood resilient and resistant construction.
  • Developing emergency evacuation procedures. Flood warnings and / or flood alerts (these are included in the Web Map) need to be considered along with the emergency evacuation procedures in the design and layout of the proposed development.
  • Leaving space in developments for flood risk management infrastructure to be maintained and enhanced.
  • Providing adequate flood risk management infrastructure which will be maintained for the lifetime of the development.

The PPG Flood Risk Vulnerability and Flood Zone Compatibility table sets out some circumstances where the Exception Test will need to be applied following the Sequential Test.

4.2.2. Sustainable Drainage Systems (SuDS)

Sustainable Drainage Systems (SuDS) incorporate a range of measures and management techniques designed to manage surface water runoff. All new developments should incorporate SuDS in line with the Non-statutory technical standards for sustainable drainage systems, unless there are practical and justifiable reasons for why they are not appropriate. The PPG highlights that the final decision on whether SuDS are truly inappropriate for a particular development proposal is a matter of judgement for the LPA.

The SuDS measures should aim to achieve greenfield runoff rates, providing management and attenuation features that ensure that surface water runoff is managed as close to the source as possible. Greenfield runoff conditions must be achieved for any greenfield sites. Development on current brownfield sites should also aim to achieve greenfield runoff rates where practical. To assist, several policy and guidance documents provide information to assist with the implementation of sustainable drainage. In addition to the London Plan, the London Sustainable Drainage Action Plan, and CIRIA guidance documents The SuDS Manual and Guidance on the Construction of SuDS provide important information.

The investigation needs to demonstrate the SuDS measures that the development will include and demonstrate how they connect with any piped drainage system required if infiltration is not possible. The submitted evidence needs to demonstrate that the London Plan drainage hierarchy has been followed, with surface water management features higher up the drainage hierarchy preferably incorporated:

  1. Store rainwater for later use
  2. Use infiltration techniques, such as porous surfaces in non-clay areas
  3. Attenuate rainwater in ponds or open water features for gradual release
  4. Attenuate rainwater by storing in tanks or sealed water features for gradual release
  5. Discharge rainwater direct to a watercourse
  6. Discharge rainwater to a surface water sewer/drain
  7. Discharge rainwater to the combined sewer

To assist the application of the above hierarchy, reference should be made to the SuDS Suitability Mapping available in each borough’s SWMP to determine the potential of implementing infiltration-based SuDS. Where information is available, the SWMP indicates where infiltration based SuDS may be potentially suitable for use, where uncertainties exist and where they are unlikely to be suitable. Where infiltration SuDS are potentially suitable or uncertain, the applicant must provide site-specific infiltration testing or bore hole data to justify use of non-infiltration based surface water management techniques within their drainage strategy.

Not all developments that require a planning application have a bearing on a site’s existing drainage regime, or the potential impact of surface water flooding locally. This may include certain Minor developments that do not increase the built footprint of a site or do not introduce new building structures. Some of these cases may not present an opportunity to improve on-site water management. However, efforts should be made to improve the site’s drainage systems as the current regime may have wider flood risk implications for the area. For further information, contact the relevant LPA.

Further details on SuDS is provided in the tables in Section 4.1 and a West London-specific checklist for drainage strategies is accessible through the Checklist section.

4.2.3. Site-Specific Flood Risk Assessment (FRA)

Site-specific FRAs should be proportionate to the degree of flood risk, making the best use of available information. They should also be appropriate to the scale, nature and location of the development. For example, developments such as single house extensions would generally require a less detailed assessment as they tend not to significantly increase the number of people present in an area at risk of flooding. Conversely, new developments comprising of multiple houses in a similar location would generally require FRAs with greater detail. For further information, see the ‘Site-specific FRA’ key requirement section in Tables 4-1 (Major Developments), 4-2 (Minor Developments), and 4-3 (Change of Use), and the EA produced guidance on FRAs for Planning Applications.

The site-specific FRA requires potential flood depths to be addressed as part of flood risk management and emergency planning where there is a probability of flooding from any flood risk source. Depending on the circumstances, certain mitigation measures will need to be employed to demonstrate that the potential impacts of flood depth will be adequately addressed. The most appropriate measure depends on a range of different factors including flood risk source, the potential impact of the flood risk, and the vulnerability classification of the development amongst others. Where developments are proposed within Flood Zone 3a (surface water), flood plain compensation must account for predicted flood depths for the 1 in 30yr and 1 in 100yr RoFSW mapping or depths predicted by site specific modelling. Further details on the requirements of emergency planning can be found in Tables 4-1, 4-2, and 4-3.

For further guidance on the preparation and development of a site-specific FRA, the PPG has a checklist to provide guidance through the process. A West London-specific FRA checklist has also been developed as part of this SFRA and is accessible through the Checklist section.

4.2.4. Drainage Strategy

As part of, or separate to, site-specific FRAs, information demonstrating how surface water runoff generated by the development site may need to be presented. As FRAs are not required for all developments, producing a separate drainage strategy may be advisable. A drainage strategy is a report that demonstrates how surface water could affect a site of interest and the surrounding areas. A strategy is required for all Major developments not categorised as ‘Change of Use’. This includes sites identified as being at risk of surface water flooding, and those that have a history of surface water flooding. All Minor developments and developments categorised as ‘Change of Use’ which modify existing surface water drainage will also require a Drainage Strategy. The report needs to demonstrate how water is expected to behave on a site, determine the site’s infiltration potential, runoff rates, and flow pathways, both before and after the proposed development is in place.

A Drainage Strategy Submission Checklist has been created alongside this SFRA (accessible through the Checklist section) and aligns with the standards and key policy requirements highlighted throughout Section 4. This template should be completed and included with any drainage strategy submissions to the relevant LPA. All six of the boroughs already have guidance forms that should also be completed and included with drainage strategy submissions where required:

Further details on the SuDS requirements and SuDS implementation to address the impact of future growth are contained in Section 4.1 (Tables 4-1, 4-2, and 4-3) and Section 5.1 respectively.

4.2.5. Flood Risk Management Structures and Features

As described in Section 3.3 and 3.4, a complex system of flood defences exists along the River Thames and its tributaries within the study area. The impact of these defences is shown on the Flood Management Infrastructure Web Map in the ‘Areas Benefitting from Defence’ layer and the location of the defences is shown in the ‘EA Flood Defences’ layer. To be classified as an Area Benefitting from Defence, the defence must provide a minimum standard of protection of 1 in 100yrs. This is why there can be areas with defences shown, but no associated Area Benefitting from Defence, as the defence in question likely provides a standard of protection less than 1 in 100yrs.

These defences are owned and maintained by a range of entities depending on their location and history. Most defences are owned and maintained by the EA, but others may be owned and maintained by riparian owners, Local Authorities or other entities. As defined in Table 4-1, any development within the stated buffer zones will need to contact the EA to determine the ownership and condition of any adjacent flood defences. Depending on the nature of the development, a Flood Risk Activity Permit may be required. An assessment of the condition of the defence and the associated impact on the Flood Evacuation Plan should also be considered.

Under section 21 of the FWMA, LLFAs are required to maintain a register of features and structures that are likely to have a significant impact on local flood risk. LLFAs have the power to ‘designate’ these structures and features on this register, which means that an application needs to be submitted to the relevant Borough to alter or remove one. For further information on asset registers and designated structures, contact the Borough directly. As defined in Tables 4-1, 4-2 and 4-3, any development within the stated buffer zones of an Ordinary Watercourse will need to contact the relevant LLFA to determine if any Ordinary Watercourse consents are required. The local of all mapped Ordinary Watercourses is shown on Flood Management Infrastructure Web Map.

4.2.6. Borough-Specific Requirements

In addition to the national, regional and local guidance available for flood risk management, LPAs provide supplementary guidance in the forms of Supplementary Planning Documents (SPD) and/or Supplementary Planning Guidance (SPG). These documents often supplement and operate in conjunction with Local Plans, providing guidance which goes over and above existing policies. Table 4-5 below highlights relevant SPD/SPG documents for each Borough which contains specific requirements on the information presented in Section 4.1. A complete list of SPG/SPD documents for each Borough can be found on their respective websites. It should also be noted that Boroughs may choose to adopt some or all of the Policy Recommendations made in Section 5 and developers should ensure they are applying the most recently published policies.

Table 4-5. Borough Specific Guidance for Planning Applications and Developments

BARNET

Supplementary Planning Guidance/ DocumentsOther Sources
The Local Plan Supplementary Planning Document (SPD): Sustainable Design and Construction document
contains sections on Flood Risk, SuDS and Water Quality Design/Construction Principles which sets out requirements and considerations in certain flood risk related areas. This includes guidance on basements, which provides the following:
  • The council may require a Hydrology report to be submitted which determines the surface flow of water, the subterranean flow of water and land stability where this requires further consideration.
  • Areas with geology more prone to increased groundwater flows such as a non-clay based geology combined with a basement development in a previously vegetated area [a garden] or basement development proximate to surface water flows or basement development on a sloping site over 8 degrees may all require further technical verification.
  • Developers may be required to provide independent verification of further technical evidence and all technical reports should be prepared by a suitably qualified chartered engineer or chartered geologist who is a member of the relevant professional body.
  • The Local Requirements Validation Guidance Notes 2017 contains a list of planning application requirements. For each requirement, the document provides a description, guidance and the legislation or policy that drives the planning application requirement. Requirements addressed include FRAs and drainage statements/ strategies.

    BRENT

    Supplementary Planning Guidance/ DocumentsOther Sources
    The Basement Supplementary Planning Document provides information and guidance on planning matters related to basement development. Each section also features relevant national and local policies which helps guide matters relating to basements. The document features a flood risk specific section. Amongst the information included in this section is a requirement adopted from Brent's SFRA and SWMP, which states that "all basement developments should be fitted with resilience measures." Certain building regulations require resilience measures for basements, which include waterproofing of walls and floors. They also require the inclusion of a positive pumped device to protect from risk of sewer flooding in line with Thames Water recommendations.None

    EALING

    Supplementary Planning Guidance/ DocumentsOther Sources
    None currently available.None

    HARROW

    Supplementary Planning Guidance/ DocumentsOther Sources
    The Supplementary Planning Document: Planning Obligations and Affordable Housing guidance contains a section on flood risk which sets out obligations for proposed developments. As part of these obligations, the SPD states "the Council where applicable will require a commuted sum which would go towards the long-term maintenance of the SUDS." In addition, the document highlights the requirement of a Section 106 agreements to secure offsite attenuation and storage. The Information Requirements for Validation of Planning Applications document contains a list of planning application requirements. Amongst the addressed requirements, the document provides information on when FRAs are required and an overview of what should be included in them.

    HILLINGDON

    Supplementary Planning Guidance/ DocumentsOther Sources
    None currently available.The Development Management Policies document is one of several documents that make up the Local Plan Part 2. It provides detailed policies that helps guide the Boroughs decisions on individual planning applications. Policies DMEI 9 and 10 specifically refers to the management of flood risk and water, whilst Policies DMEI 8 and 11 address flood risk and water management as part of the overall policy. Key local level guidance and requirements include:
  • Developers to engage with relevant water and wastewater infrastructure providers prior to submitting a planning application (Policy DMEI 10).
  • Strict control is to be exercised to manage surface water in CDAs (Policy DMEI 9).
  • HOUNSLOW

    Supplementary Planning Guidance/ DocumentsOther Sources
    The Residential Extension Guidelines: Supplementary Planning Document contains a flood risk section with information aimed to guide developers on building alterations and extensions with regards to flood risk. This includes the following guidance on basements, "all basements, extensions and conversions likely to flood must have internal access to a higher floor and must include flood resistance and resilience in their design techniques. Basements must not include sleeping accommodation."The TE2100 Plan provides guidance and recommendations for developers to ensure the objectives of the Plan are met. Sub-regions within the TE2100 policy area are broken up into 'Action Zones' which highlights different sub-regional characteristics, flood sources and how those could be addressed. Hounslow lies within Action Zone 1 ('West London') of the TE2100 policy area: Recommendations 6, 9, 10 and 12. In addition, Action Zone 0 Recommendations 7 and 11 are applicable for all developers in the TE2100 plan. Further information on the TE2100 Plan can be found in Section 2.2.

    4.3. Developer Management Guidance

    This sub-section provides development management specific guidance to ensure that the key requirements for individual planning applications can be effectively evaluated and assessed. Development should be considered at a strategic level, so it is important to identify how individual development proposals fit within a wider flood risk management strategy for a given area. The guidance accompanies the information presented in the tables in Section 4.1.

    4.3.1. Application of the Sequential and Exception Tests

    Implementation of a sequential, risk-based approach is vital in determining the suitability of a site for development with regards to flood risk. Developers need to apply the Sequential Test, and in some instances, the Exception Test, for any proposed development site that requires them. This document, and the Web Maps, provide the basis for applying these tests at a site-specific level.

    Guidance on development in London, and the types of sites and locations to be considered, has seen a push towards certain considerations. The current London Plan identifies small site developments making an important contribution towards meeting housing objectives. In addition, the need to adopt a sequential approach to guide retail, commercial and leisure developments towards town centres is also of importance. These development objectives are consistent with the guidance and policies laid out in the draft of the new London Plan, making them important considerations for Boroughs when considering new development proposals.

    The PPG contains information on development compatibility within different Flood Zones. This table works in conjunction with the PPG Flood Risk Vulnerability Classifications table to provide guidance on the types of development that may be considered as suitable within Flood Zones.

    Sequential Test

    The Sequential Test ensures that a sequential approach is followed to steer new development to areas with the lowest probability of flooding. This means that certain development proposals should not be permitted in high and medium flood risk areas, where there are reasonably available sites appropriate for the proposed development in areas of lower flood risk. Within each Flood Zone, all sources of flooding need to be considered when applying this risk-based approach to the proposed development site.

    For sites that have not undergone Sequential Testing but require it, developers will need to complete a site-specific Sequential Test and provide evidence that the Test has been undertaken as part of the planning application. For information on the Sequential Test search area and definition of reasonable available sites, see Section 4.2.1.

    Exception Test

    Developers may need to provide evidence that the Exception Test has been applied if the Sequential Test demonstrates that the proposed development cannot be located in a lower flood risk area. Through the Exception Test, the developer needs to demonstrate that flood risk to both people and property will be managed across the lifetime of the proposed development. The PPG sets out two considerations that need to be achieved in order to pass the Exception Test. Both considerations need to be satisfactorily demonstrated by the developer before development can be allocated or permitted. These considerations are:

    • The development provides wider sustainability benefits to the community that outweigh flood risk, informed by a SFRA where one has been prepared; and
    • A site-specific FRA must demonstrate that the development will be safe for its lifetime taking account of the vulnerability of its users, without increasing flood risk elsewhere, and, where possible, will reduce flood risk overall.

    The PPG Flood Risk Vulnerability and Flood Zone Compatibility table sets out some circumstances for Exception Test application following Sequential Testing. Evidence of Exception Testing may need to be applied for particular developments within areas subject to redevelopment or regeneration. For developments that are part of regeneration strategies, it is likely that they will provide the wider sustainability benefits required to pass that aspect of the Exception Test. All submitted planning applications still need to demonstrate that the development will be safe for its lifetime, will not increase flood risk elsewhere and, where possible, will reduce flood risk overall. For information on how the second consideration of the Exception Test could be achieved by the developer, see Section 4.2.1.

    4.3.2. Sustainable Drainage Systems (SuDS)

    Sustainable Drainage Systems (SuDS) incorporate a range of measures and management techniques designed to manage surface water runoff. They are designed to mimic natural drainage as closely as possible, providing an alternative to ‘hard engineered’ traditional drainage. They provide opportunities to:

    • Reduce the causes and impacts of flooding, providing opportunities to reduce the overall local flood risk.
    • Minimise pollution from urban runoff at source.
    • Enable groundwater recharge where infiltration is possible.
    • Combine water management with green space, providing environmental, amenity and recreational benefits.

    As highlighted in Section 2.2.2 of this document, Policy 5.13 of the London Plan is a key policy with regards to flood risk and water resource management. The policy provides the drainage hierarchy to ensure that reasonable measures are taken to sustainably manage and reduce the overall amount of rainfall being discharged from a development site. Developers should take measures to ensure that surface water management features higher up the drainage hierarchy are incorporated. The current London Plan drainage hierarchy is as follows:

    1. Store rainwater for later use
    2. Use infiltration techniques, such as porous surfaces in non-clay areas
    3. Attenuate rainwater in ponds or open water features for gradual release
    4. Attenuate rainwater by storing in tanks or sealed water features for gradual release
    5. Discharge rainwater direct to a watercourse
    6. Discharge rainwater to a surface water sewer/drain
    7. Discharge rainwater to the combined sewer

    Developers should aim to achieve greenfield runoff rates via their proposed SuDS measures and ensure that surface water runoff is managed as close to the source as possible. The proposed measures should be incorporated in line with the Non-statutory technical standards for sustainable drainage systems.

    In December 2014, LLFAs became statutory consultees on major planning applications with surface water drainage implications. The associated Written Ministerial Statement, alongside the London Plan, demonstrate the importance of developers incorporating SuDS into their development proposals. This means that LPAs are required to consult LLFAs for expertise and technical advice on the management of surface water before reaching a decision on Major planning applications under the Town and Country Planning (Development Management Procedure) (England) Order 2015.

    The issues that are analysed by LLFAs and LPAs for planning applications are referred to as ‘material planning considerations’, issues that are relevant to the decision making process. SuDS are a material planning consideration for major applications, and decisions on all planning applications require evidence that SuDS are implemented to ensure surface water is managed safely on site. Further information on material planning considerations, planning applications and the decision making process can be found on the Determining a Planning Application guidance page.

    4.3.3. Site-Specific FRAs

    Submitted site-specific FRAs should demonstrate how flood risk will be managed now and in the future over the proposed development’s lifetime. The FRA needs to take climate change into account, and the vulnerability of land use classification of the development (Refer to Table 2 – Flood Risk Vulnerability of the PPG). An FRA should be provided with a planning application for developments in the following circumstances:

    • New proposals in Flood Zone 2 or 3, including Minor Development and Change of Use. Minor developments include property sub-division (as this is ‘development’ defined by Section 55 of the Town and Country Planning Act 1990) and extensions that exceed the parameters of Permitted Development defined by Planning Portal Guidance.
    • Proposals for development areas that are 1 hectare or greater in Flood Zone 1.
    • New proposals, or a Change of Use in development type to a more vulnerable class, where the proposed development could be affected by sources of flooding other than rivers and the sea.
    • Proposals within areas with critical drainage problems as designated by the EA (note that this does not include Critical Drainage Areas as defined by the Borough SWMPs – there are currently no such areas defined by the EA within the West London sub-region at the time of publication of this SFRA in March 2018).

    As early as possible, development management should refer this SFRA and the Web Maps to developers, highlighting the key areas that developers should take note of as it could impact their proposals. For development proposals in areas at risk of fluvial or tidal flooding, there is a statutory requirement for LPAs to consult with the EA before planning permission is granted under the Town and Country Planning (Development Management Procedure) (England) Order 2015. For advice on when the EA should be consulted, and guidance for where fluvial / tidal flood risk is an issue, the EA has developed Standing Advice. In addition, the PPG has a checklist which can aid in the process of reviewing a site-specific FRA.

    4.3.4. Drainage Strategy

    Developers may need to demonstrate how surface water runoff generated by the development site will be managed. This may be demonstrated through a drainage strategy, a report that should demonstrate how surface water could affect a site of interest and the surrounding areas. A strategy is required for all Major developments not categorised as ‘Change of Use’. All Minor developments and developments categorised as ‘Change of Use’ which modify existing surface water drainage will also require a Drainage Strategy.

    DEFRA published the Non-statutory technical standards for sustainable drainage systems in March 2015. The document sets out non-statutory technical standards for SuDS relating to:

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

    These standards should be used for the assessment of surface water drainage strategies submitted with planning applications.

    4.3.5. Flood Risk Management Structures and Features

    The impact of flood defences along the River Thames and its tributaries can be seen on the Flood Management Infrastructure Web Map in the ‘Areas Benefitting from Defence’ layer. In addition, the location of the flood defences can also be seen on the map in the ‘EA Flood Defences’ layer. Places classified as Areas Benefitting from Defence provide a minimum standard of protection of 1 in 100yrs.

    Most defences are owned and maintained by the EA, but others may be owned and maintained by riparian owners, Local Authorities or other entities. As highlighted in Tables 4-1, 4-2 and 4-3, developments within the stated buffer zones will need to contact the EA to determine the ownership and condition of any adjacent flood defences. Developers may also need to submit a Flood Risk Activity Permit depending on the nature of the development. Developers should also consider providing an assessment of the condition of the defence and the associated impact on the Flood Evacuation Plan.

    If a development is within the buffer zone of an Ordinary Watercourse (as defined in Tables 4-1, 4-2 and 4-3) developers are required to contact the relevant LLFA to determine if any Ordinary Watercourse consents are required. The local of all mapped Ordinary Watercourses is shown on Flood Management Infrastructure Web Map.

    4.3.6. Borough-Specific Requirements

    Developers are required to follow any borough-specific requirements when addressing flood risk as part of their planning application submission. LPAs may provide guidance through Supplementary Planning Documents (SPD) and/or Supplementary Planning Guidance (SPG) that accompany the Local Plan. These are listed in Table 4-5. Development management should refer to these when reviewing planning applications as they support the borough-wide objectives for flood risk management.

    4.4. Planning Policy Guidance

    This sub-section provides guidance on managing flood risk at a strategic level. The NPPF and PPG highlight that developments should be directed away from the highest areas of risk and that developments should be made safe without increasing flood risk elsewhere. Due to development needs and demands, the NPPF identifies that it may not always be possible to completely avoid flood risk areas. The guidance provided in this sub-section supports borough level strategic planning and supplements information presented in the tables in Section 4.1.

    4.4.1. Application of the Sequential and Exception Tests

    The NPPF highlights the need for a sequential, risk-based approach to be considered for development. This approach aims to keep development out of Flood Zones 2 and 3, and areas at risk from other sources of flooding, where possible. Implementation of the sequential, risk-based approach requires proposed development sites to be reviewed through the application of the Sequential Test, and in some instances, the Exception Test. This document, and the Web Maps, provide the basis for applying these tests, at the site-specific level.

    Strategic application of the Tests for Allocated Sites, if required, are generally completed as part of the Local Plan development process by LPA officers. This process should be informed by the initial screening assessment completed for current Allocated Sites provided in Appendix A. Recommendations for Level 2 SFRAs are made in Section 6 where further flood risk information and assessment may be required to inform the Tests. Guidance is provided in the following sections for application of the Test at the Local Plan / strategic scale.

    Sequential Test

    The Sequential Test ensures that a sequential approach is followed to steer new development to areas with the lowest probability of flooding. This document provides the evidence base for the Sequential Test to be applied at a borough-wide level in preparation for a Borough’s Local Plan and associated Allocated Sites. If the application of the Sequential Test demonstrates that development can be allocated in Flood Zone 1, then the Sequential Test has been passed. However, some lower flood risk areas may not be suitable for development due to various other reasons. In these instances, the Sequential Test should be applied to guide the development to the lowest risk area appropriate for the development type. This increases the possibility of facilitating development which is at the lowest risk of flooding in line with the relevant vulnerability of land use classification. The PPG flowchart demonstrating the ‘Application of the Sequential Test for Local Plan Preparation’ provides guidance.

    The following process is recommended to complete the Sequential Test for site allocations during Local Plan development based on the PPG development vulnerability classification:

    1. Complete a screening assessment of all sites to identify flood risk sources and how they might be impacted by Climate Change. The Web Maps should be used to identify flooding from all sources as detailed in Section 3. Climate change guidance is provided in Section 3.10. Note this screening assessment has already been completed for sites allocated at the time writing this SFRA – Refer to Appendix A and the Policy Web Map.
    2. Assess how long it is anticipated each development will be present for (the ‘design life’). A design life of 100yrs for residential development and 60yrs for non-residential development is recommended if no other information is available.
    3. Any ‘Highly Vulnerable’ developments should be located within Flood Zone 1. If this is not possible due to a lack of suitable sites, then locations in Flood Zone 2 can be considered where the Exception Test can be passed. If no suitable sites exist in Flood Zones 1 or 2, then further opportunities for development locations should be sought (this could be within or outside the Borough)
    4. A similar process can then be applied to ‘More Vulnerable’ developments with priority given to locations within Flood Zones 1 and 2. If there are no suitable sites, then Flood Zone 3a can be considered – noting that the Exception Test will need to be passed.
    5. ‘Less Vulnerable’ developments can then be located within remaining sites in Flood Zones 1, 2 and 3a (in that order of preference). This development classification is not appropriate for Flood Zone 3b.
    6. ‘Essential infrastructure’ should also be preferentially located in the lowest risk Flood Zone available for the type of infrastructure. This development can be located in Flood Zone 3a or 3b after passing the Exception Test.
    7. ‘Water compatible’ development should be allocated last as they generally have the fewest constraints with regard to flood risk.

    Where proposed site allocations are at a risk of flooding from one or more sources, Level 2 SFRA recommendations are made in Section 6 for specific Allocated Sites within each Borough. The Level 2 SFRA can provide site-specific flood risk management recommendations and an assessment of whether the site could pass the exception test on this basis.

    Exception Test

    The Exception Test should be applied after the Sequential Test if it has been determined that a proposed development cannot be located in an area with a lower flood risk. To pass the Exception Test and ensure that flood risk to both people and property is effectively managed across the proposed developments lifetime, the PPG sets out two considerations that need to be achieved. These considerations are:

    • The development provides wider sustainability benefits to the community that outweigh flood risk, informed by a SFRA where one has been prepared; and
    • A site-specific FRA must demonstrate that the development will be safe for its lifetime taking account of the vulnerability of its users, without increasing flood risk elsewhere, and, where possible, will reduce flood risk overall.

    The PPG ‘Application of the Exception Test for Local Plan Preparation’ flowchart provides guidance on applying the Exception Test for Local Plans. The flowchart highlights that following the borough-wide level Sequential Test, the Exception Test will need to be applied if certain development sites are not in an appropriate location. Guidance for what is deemed an appropriate location is based on NPPF flood risk policy as highlighted in Section 2.2.1. A Level 2 SFRA may also be used to assess Allocated Sites in more detail to determine if the Exception Test can be passed. Recommendations for Level 2 SFRA assessments are made in Section 6.

    4.4.2. Flood Risk Management Structures and Features

    Under Section 21 of the FWMA, LLFAs are required to maintain a register of features and structures that are likely to have a significant impact on local flood risk. LLFAs have the power to ‘designate’ these structures and features on this register, which means that owners and developers need to submit an application to the relevant Borough to alter or remove one. These registers are available to the public and access can be arranged through the relevant LLFA if the information is not already published on the Local Authority website.

    4.4.3. Local Policy Recommendations

    To ensure that future developments incorporate flood risk management measures in line with the findings of this SFRA, a set of strategic and site-specific policy recommendations are provided in Section 5.3. These recommendations could be adopted as part of the flood risk planning policies within the developing Local Plans. Recommendations supporting the implementation of SuDS, the requirement of site-specific FRAs and drainage strategies, and strategic implementation of the Sequential Test are provided amongst other policies designed to guide flood risk management.