5.1. Overview

Future developments and climate change are some of the key factors that are increasing the risk of flooding events across the UK and globally. Several key drivers, including urban development expansion, could see an increase in flood risk from various sources. For example, increased foul drainage from an increased local population places a greater pressure on the local sewer system. This has the potential to increase the risk of sewer flooding, especially in areas with combined sewers which drain foul and surface water. A decrease in permeable ground cover due to urban development may increase the risk of surface water and ordinary watercourse flooding.

The pressure of accommodating more developments may mean a larger number of developments being proposed for sites within higher risk Flood Zone areas, placing them at greater risk of flooding. The impact of development and projected future population growth may not only have an impact on the flood risk presented by different flood sources, but present a greater overall flood risk to people and properties due to the accumulative risk from each source. To meet flood risk mitigation requirements whilst facilitating housing development needs, local policy targeting the impact of future growth on flood risk is required.

The NPPF and accompanying PPG state that a sequential, risk-based approach to the location of development should be applied. This would enable possible flood risk to people and property to be avoided whilst taking impacts of climate change into account. This underpins the strategic recommendations for the borough and supports the site-specific recommendations. For further information, see Section 5.3.

5.2. The Impact of Future Growth on Flood Risk

To meet the demands presented by future growth, the London Plan provides a minimum housing development target for each London Borough. These targets are based on the requirements of accommodating a growing population whilst meeting a range of social needs. The current London Plan approach is shown below.  Increasing development is an identified driver of increased flood risk.

Takes account of London’s locally distinct circumstances of pressing housing need and limited land availability and aims to deliver sustainable development.

London’s development requirements are rapidly increasing over time. The current London Plan provides a ten-year housing target for each borough, spanning 2015 to 2025. These targets require a minimum of 71,456 housing properties to be constructed by 2025 across the West London sub-region (see Table 5-1).

Table 5-1. Current London Plan Ten Year Annual Average Housing Supply Monitoring Targets 2015 - 2025

Planning AuthorityMinimum Ten-Year TargetAnnual Monitoring Target
Total71,4567,145
Barnet23,4892,349
Brent15,2531,525
Ealing12,9721,297
Harrow5,927593
Hillingdon5,593559
Hounslow8,222822

The projected housing targets presented in the 2017 Draft London Plan require a minimum of 139,830 housing properties to be supplied between the 2019/20 – 2028/29 ten year period (see Table 5-2). Each Boroughs annual target is higher compared to the figures presented in the current London Plan, providing an insight into the potential future growth of developments in the West London sub-region. Many of the housing developments created to meet these numbers are expected through small sites. Policy H2 ‘Small Sites’ of the Draft London Plan highlights that small sites should play a greater role in delivering new houses, stating that boroughs should:

“Pro-actively support well-designed new homes on small sites through both planning decisions and plan-making.”

Opportunity Areas are major sources of brownfield land which have a significant capacity for development, and are also seen as a way of meeting London’s housing development targets. The Draft London Plan highlights Opportunity Area Planning Frameworks as the means to develop policies and supporting documentation required to develop a plan-led approach and provide the required infrastructure.

Table 5-2. 2017 Draft London Plan Ten Year Targets for Net Housing Completions (2019/20 - 2028/29)

Planning AuthorityTen-year Housing TargetAnnualised Average
Total139,83013,983
Barnet31,3403,134
Brent29,1502,915
Ealing28,0702,807
Harrow13,9201,392
Hillingdon15,5301,553
Hounslow21,8202,182

The requirements of the NPPF and PPG state that all developments need to demonstrate that they will remain safe for the entirety of their lifetime in terms of flood risk and coastal change. The PPG defines the lifetime of residential developments as a minimum of 100 years unless reasons are stated for otherwise. The lifetime of non-residential developments are defined by their individual characteristics, and require the planners and developers to assess the lifetime of the development. Developments need to ensure that flood risk is not increased elsewhere, and where possible, flood risk is reduced overall. This should be achieved through the inclusion of flood risk and drainage at all developments’ master planning stage to reduce local flood risks to and from development sites. Achieving these objectives, and those listed in Section 2 and Section 4, is vital in ensuring that the impact of future growth on flood risk is mitigated as much as possible. The safeguarding of land used for flood mitigation purposes can help to free-up other land for development that might not otherwise have been suitable under the PPG’s vulnerability table. This provides opportunities for strategic flood risk management approaches which the boroughs’ LLFAs, in partnerships with other RMAs, are actively taking to safeguard future land. Partnership working such as this further demonstrates the benefit of having a joint SFRA for the sub-region. The following flood alleviation schemes provide examples of partnership projects:

The Brent Catchment Partnership are undertaking a series of projects to improve and enhance watercourses within the River Brent catchment. Amongst the potential projects are the Silk Stream, Tokyngton Park, and Greenford Flood Alleviation Schemes that will be delivered by Barnet, Brent, and Ealing respectively. These projects will all be delivered alongside EA with the objective to transform “up to 10 kilometres of heavily modified river to a more natural condition by 2021”. These projects provide opportunities to safeguard land to achieve this objective.
The River Pinn and Cannon Brook Flood Alleviation Scheme is a partnership between Harrow, Hillingdon and the EA. As part of the scheme objectives, the partnership aims to obtain a better understanding of flood risk in the River Pinn catchment, and to deliver a viable scheme that could reduce future flood risk. Flood storage areas have been identified as a possible measure, which could provide opportunities to safeguard land for flood mitigation purposes.

For further information on strategic projects in the sub-region, refer to the EA’s FCERM Investment Programme, contact the local Environment Agency Partnership and Strategic Overview Officer or the LLFA Officer for details.

Although the above-mentioned flood alleviation schemes are led by the Boroughs or the EA, their potential progression to implementation heavily relies on the need for matched funding. Rules on the use of grant money from DEFRA’s Flood and Coastal Erosion Risk Management Grant in Aid and TRFCC’s Local Levy funding streams requires a certain amount of partnership funding to have been secured before schemes may become viable to implement.

Opportunities for the progression of these and similar strategic flood risk infrastructure schemes should be taken through the use of funding contributions. Examples of such contributions include planning obligations under Section 106 (S106) of the Town and Country Planning Act 1990 and the Community Infrastructure Levy (CIL) under Part 11 of the Planning Act 2008. S106 funding allows for developers to enter into agreements with an LPA to make proposed development sites acceptable in planning terms. Similarly, CIL funding agreements allow potential for LPAs to provide contributions towards the costs of implementing infrastructure improvements required for the development of the area.

Natural Flood Management is an example of a strategic flood risk management approach that benefits from the safeguarding of land. These management techniques utilise natural processes to reduce flood risk and coastal erosion. Natural flood management often takes a hydrological catchment based approach by managing water along the length of a watercourse’s catchment area. In addition to flood risk mitigation benefits they can provide, they can also benefit people and wildlife through habitat restoration and water quality improvement. Natural Flood Management projects provide opportunities for partnership working and provide boroughs’ LLFAs and RMAs with the opportunity to implement an approach as identified by the EA and the draft London Plan. The following flood alleviation schemes provide examples of Natural Flood Management projects:

The Park Woods, Ruislip Natural Flood Management Scheme is a partnership between Hillingdon Council, Thames 21, Natural England and the EA. The Natural Flood Management Scheme aims to slow the velocity of the water in the catchment area by replicating the characteristics of natural rivers. Implementing large woody debris along various points of the watercourse to attenuate water has been identified as a means of achieving this. The floodplain will also facilitate water attenuation.

5.3. Recommended Policies

This section builds on the findings presented throughout the SFRA and provides recommendations that each Borough can adopt as part of their flood risk planning policies within their developing Local Plans. The recommended policies set out strategic and site-specific principles to guide flood risk management for prospective development within each borough and the sub-region as a whole. They provide part of the solution to the general growth trends and associate strategic flood risk management issues identified in Sections 5.1 and 5.2. Recommendations have been suggested instead of model policies given the Borough Local Plans are at different stages of being updated. These policies acknowledge that a lot of developments will be based on small and windfall sites and have been developed to support this.

5.3.1. Strategic

  1. Boroughs should adopt a sequential approach for planning and development to identify areas that are not susceptible to flood risk impacts posed by climate change. Development should be encouraged in these identified areas to make properties more resilient to increasing flood risk and reduce the reliance on property level protection methods.
  2. Boroughs should apply the Sequential Test to Allocated Sites within the LPA area at an early stage in the Local Plan development process to help identify any lower flood risk areas that may not be suitable for development. This can be used to inform spatial planning and identify key growth locations, increasing the possibility of facilitating development which is not exposed to flood risk whilst meeting development objectives.
  3. Boroughs should implement measures through their Local Plans to deal with the Sequential Test acceptability of windfall site development proposals at the strategic level. The measure could set out locations and quantities of windfall sites that would or would not be acceptable in Sequential Test terms (to provide input to the process defined in Section 4.2.1). This would help create efficiencies in the process.
  4. If it is determined by evidence that there are insufficient sites within Flood Zone 1 to meet the borough’s housing development targets, then windfall developments in Flood Zone 2 or 3 might be acceptable and should be considered (preferably with support of a Level 2 SFRA). This would inform an approach determining locations where the Sequential Test would be passed. Conversely, if the borough has sufficient land available in Flood Zone 1 to accommodate windfall development sites, then it may not be possible or prudent to consider windfall development in Flood Zone 2 or 3 as acceptable.
  5. Existing and planned flood alleviation schemes should be incorporated into Borough Infrastructure Delivery Plans (IDPs). Where these IDPs, or similar corporate work programmes (e.g. planned highway improvement works or Green Infrastructure Plans), identify predicted or actual flood risks, new potential strategic level flood alleviation schemes should be developed.
  6. Boroughs should make space for water storage by identifying strategic locations that are required for current and future flood risk management. These identified areas of land should be safeguarded via Local Plans to facilitate links between flood risk management and other environmental priorities.
  7. Boroughs should adopt a Catchment Based Approach to ensure recognition of catchment wide flood issues to justify the collection and use of S106 funding to investigate and develop flood alleviation schemes within the catchment the development falls within. CDAs defined by the Borough SWMPs (for surface water flooding) or policy sub-areas defined by EA CFMPs (for fluvial / tidal flooding) provide an established technical basis for this approach.
  8. Boroughs should set up mechanisms to enable the use of CIL charges to be used for flood alleviation schemes across the borough to address the cumulative impact of development on flood risk.
  9. Boroughs should use their Local Plans to ensure developments within CDAs (as defined by SWMPs) provide increased surface water drainage requirements. Examples could include increased storage through the use of SuDS to restrict off-site runoff rates to greenfield (or lower) conditions.
  10. Boroughs should develop standing advice for the assessment of minor development planning applications with surface water implications. This will aid LPAs in making informed and consistent decisions where the EA and / or LLFA has no statutory duty to provide comments as part of an application’s review exercise.
  11. Boroughs should review the benefits of removing Permitted Development rights for sites which fall within Flood Zones 3a and / or 3b, collaborating on Article 4 Directions where justifiable, defendable and beneficial. This could include provisions around sub-divisions, extensions and paving of gardens in specific areas.
  12. Boroughs should use their Local Plans to ensure developments with a high susceptibility to groundwater flooding (as identified in the Sewer, Groundwater & Artificial Flood Risk Interactive Web Map and other available data) demonstrate that increased groundwater mitigation and management measures have been implemented to protect people from groundwater flooding. Any known groundwater and flow routes should be safeguarded to ensure ground water flood risk is not increased on site or elsewhere.
  13. Boroughs should consider implementation of further surface water flood risk mitigation requirements for proposed developments within Flood Zone 3a (surface water) where the development is also within the 1 in 30yr RoFSW mapped extents. These requirements could be similar to those adopted for Flood Zone 3b (fluvial / tidal) Functional Floodplain with modifications as follows:
    1. Development within the 1 in 30yr RoFSW mapped extent will be treated as if it were Flood Zone 3b (Functional Floodplain) as defined in PPG Table 1 (Paragraph 065).
    2. Development may be possible within the 1 in 30yr RoFSW mapped extents outside of existing infrastructure or solid building footprints.
    3. To enable development, the proposals must provide mitigation and resilience against flood risks (taking advice from the LLFA as appropriate) and provide appropriate compensation on existing flood risk levels (addressing the predicted 1 in 30yr and 1 in 100yr RoFSW mapped depths as a minimum), supported by detailed flood risk modelling if appropriate.
    4. The development must not increase flood risk elsewhere and where possible reduce flood risk overall.
    5. Where beneficial to flood risk and/or other planning requirements, it may also be possible for development to occur within the functional floodplain through the relocation (but not increase of footprint size) of an existing building’s footprint within a site.

5.3.2. Site-specific

  1. Ensuring that land within development sites are safeguarded for potential flood mitigation use through the active consideration of predicted flood mapping from all sources at the master planning stage.
  2. Developers must submit completed Flood Risk Assessments and Drainage Strategy (with supporting Checklists) to demonstrate compliance with requirements detailed in Sections 2 and 4 for all Major development proposals.
  3. Drainage Strategies with the supporting checklist must be provided for all Minor developments and for Change of Use proposals if they impact the proposed development’s current drainage regime. Site-specific Flood Risk Assessments with the accompanying checklist must be provided for Minor developments and Change of Use proposals if they:
    1. Are outside of Flood Zone 1.
    2. Are inside an EA defined area with a critical drainage problem.
    3. Change the existing footprint of the building(s).
    4. Are at risk from any other sources of flooding.
  4. As part of a submitted development proposal, developers must provide evidence to the LPA to demonstrate that the Sequential Test has been undertaken. Developers must also provide evidence that an on-site sequential approach has been taken to direct vulnerable uses to the lowest risk parts of the development site.
  5. Where development is proposed for sites within Flood Zones 3a (surface water), evidence must be submitted to demonstrate that:
    1. There will be no increase of flood risk to properties outside of the development boundary.
    2. Consultation has been undertaken with the relevant LLFA to consider potential wider impacts or benefits the development could have on the local surface water catchment.
    3. Relevant strategic documents (such as the Thames CFMP, LFRMS and SWMP) have been reviewed.
    4. The LLFA has been consulted to determine if the development should contribute to any catchment wide flood alleviation schemes being considered by the LLFA (such as a S106 contribution to wider catchment flood risk management infrastructure).
  6. Development should maximise the use of open spaces to ensure spaces for water to flow during times of flood.
  7. Developments that seek to increase impermeable surfaces within a site, including small areas such as front gardens, will be resisted where appropriate.
  8. Developers should aim to incorporate permeable paving in hardstanding areas to provide flood mitigation benefits in new and existing developments. In areas where the geology does not facilitate infiltration (e.g. areas underlain with clay), permeable paving should be underlain with gravel or feature an underground storage system.
  9. Development proposed in ‘dry islands’ should be designed for safe access and egress in a flood event. Dry islands are considered as flood risk areas due to the potential loss of important local services during flood events and lack of safe access routes. They require safe access and egress routes to be developed for the lifetime of the property, factoring in the impacts of climate change.