The West London Boroughs of Barnet, Brent, Ealing, Harrow, Hillingdon and Hounslow (hereinafter ‘the Boroughs’) have commissioned the production of a joint Level 1 Strategic Flood Risk Assessment (SFRA). The combined area features several cross-boundary Environment Agency-designated Main Rivers, including the Dollis Brook, Duke of Northumberland’s River, River Brent, River Crane, River Colne, River Lee, River Pinn, River Thames and Yeading Brook. These rivers cross boroughs that make up six of the seven local authorities that form the West London Alliance (WLA). Due to these established associations, groupings, and shared borough boundaries, a joint SFRA is beneficial for all Boroughs.

This document and mapping provides consistency and clarity, and sign-posting to common policies and requirements. A joint SFRA also enables the identification of potential improvements which the Boroughs are recommended to adopt and enforce through their future Local Plans to improve local flood risk whilst promoting sustainable development. The Boroughs have delivered the SFRA in an innovative format as a website (for the text content) and a web map (for the supporting flood risk information). This format allows for efficient update of content in the future and ensures that the best available information is presented in a dynamic format.

The overarching aim of this SFRA is to provide the evidence base for ensuring development is steered away from areas identified most at risk from all sources of flood risk, reducing the risk of flooding to residents and buildings. This is required to provide an update to existing borough specific SFRAs, which were predominantly completed in 2008.

The website is broken down into six sections:

  • Section 1 (Introduction) provides an overview of the purpose and objectives of the SFRA.
  • Section 2 (Planning and Policy Framework) provides an overview of the relevant national, regional, sub-regional and local policies relating to flood risk and associated requirements.
  • Section 3 (Sources and Assessment of Flood Risk) provides an overview of the flood risk from all sources across the study area, including climate change implications where this information is available. This is supported by a series of web maps to present the flood risk information.
  • Section 4 (Flood Risk Assessment Guidance) provides guidance for undertaking Flood Risk Assessments (FRA) at the site specific and strategic levels. Borough-specific guidance is included where any key differences exist. This is supported by checklists to assist applicants in completing compliant submissions for Flood Risk Assessments and Drainage Strategies.
  • Section 5 (Policy Recommendations) provides a set of recommended site-specific and strategic policies. These recommendations are based on the findings of this SFRA, which the Boroughs are advised to incorporate into future versions of their Local Plans and/or associated guidance documents. Any opportunities for improved strategic flood risk management methods, including possible funding mechanisms, to assist with Boroughs growth delivery requirements are also highlighted.
  • Section 6 (Review and Next Step) provides a summary of the proposed update schedule for the SFRA (the technical content and the mapping). Recommendations for the need to conduct a Level 2 SFRA are also included based upon the findings of flood risk screening assessments of current borough site allocations.

Key differences within this SFRA compared to the previous SFRAs for all the Boroughs include:

  • Definition of the Flood Zone 3a: Fluvial, tidal and surface water flood risks have been included within the Flood Zone 3a definition to reflect the significant nature of local flood risks within the heavily urbanised boroughs.
  • Application of the Sequential Test and Exception Test: These two approaches include assessment of risk from all sources of flooding (not just fluvial and tidal as previously generally applied).
  • Site-Specific Flood Risk Assessments: The will be required for all development proposals in Flood Zones 2, 3a and 3b – noting the definition of Flood Zone 3a in this SFRA includes surface water flood risk.
  • Drainage Strategies: These are required for all Major developments not categorised as ‘Change of Use’. All Minor developments and developments categorised as ‘Change of Use’ or proposed changes to Previous Approvals which modify existing surface water drainage will also require a Drainage Strategy.


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. 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 at all scales, strategic policy targeting the impact of future growth and climate change on flood risk is required. It is recommended that LPAs develop and implement policy that encourages opportunities for strategic flood risk management approaches which the boroughs’, in partnerships with other organisations (including other boroughs, developers and water companies), can deliver to facilitate development. These should include actively delivering strategic flood risk management projects that can be funded through the following sources and in partnership with relevant organisations:

  • DEFRA’s Flood and Coastal Erosion Risk Management Grant in Aid
  • Thames Regional Flood and Coastal Committee Local Levy funding
  • Planning obligations under Section 106 of the Town and Country Planning Act 1990
  • Community Infrastructure Levy under Part 11 of the Planning Act 2008