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Surface water planning

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Developers and flood risk

Developers will need to demonstrate that:

  • the most vulnerable developments (e.g. an electricity substation) are located in areas of lowest flood risk unless there are overriding reasons to use a different location within the site
  • the development is appropriately flood resilient and resistant, including:
    • safe access and escape routes where required
    • any residual risk can be safely managed (including by emergency planning)
    • gives priority to the use of sustainable drainage systems
  • they have considered the availability of water and water infrastructure for the lifetime of the development and designed responses to promote water efficiency and protect water quality.

Flood Risk Assessments

Site-specific Flood Risk Assessments (FRAs) are undertaken by applicants when a planning application is submitted where flood risk is an issue. The National Planning Policy Framework (NPPF) states that FRAs should identify and assess the risks of all forms of flooding to and from the development and demonstrate how these flood risks will be managed so that the development remains safe throughout its lifetime, taking climate change into account.

The following guidance from the NPPF should be applied to all sources of flood risk:

As in most areas of development control, the best outcomes are secured through proactive working and early pre-application discussions between developers and planners.

Do

Don’t

  • Start as early as possible
  • Undertake pre-application discussions
  • Ensure geographical scope suitable for the sequential test
  • Consider all sources of flooding
  • Consider current and future flood risk
  • Assume a standard format and cost for all SFRAs
  • Use an SFRA to justify preconceived land allocations and housing targets
  • Assume that the Environment Agency will produce an SFRA for you or has all the information
  • Assume one is not needed if there’s no history of flooding

Surface Water Drainage Assessments

We have published local guidance intended to inform developers of our expectations relating to the completion of Drainage Assessments. Please ask for our Local Standards and Guidance for Surface Water Drainage in Northamptonshire for more information.

Although site specific Flood Risk Assessments may not be required for sites not identified as being at risk of flooding, there may still be a requirement to provide a Drainage Assessment in order to consider the impact the development may have on surface water management.

Groundwater Flood Risk Assessments

If properties have been affected by groundwater flooding or where the local planning authority has highlighted a potential groundwater flooding issue related to a potential development, this source of flood risk should be included within the site specific flood risk assessment. A conceptual model of the groundwater on site is often required to enable the risk to be assessed and to provide a basis for designing any required mitigation measures. Data on the geology, topography, historical land use and hydrology of the site should also be incorporated into the detailed groundwater flooding assessment.

The former Northamptonshire County Council, supported by ESI Ltd, undertook a study to assess the risk of flooding from ground water across the county. Due to license restrictions, extracts of this map can only be provided to developers at a scale of 1:125,000 with a supporting text summary of the risk for a particular site.

This information is available through the Flood Data and Information Request service or the Technical Flood Advice service.

Standards of protection - Local requirements

Following significant flooding to Northampton town centre in Easter 1998, improvements were made to the defences along the River Nene.

In order to secure the level of protection provided by the new defences, the standard set for new developments goes beyond approved industry standards.

All new development in the Upper Nene catchment must be designed for a flood with a 0.5% probability of occurring in any one year, including an appropriate allowance for climate change.

Residual flood risk

In any development there is a residual flood risk, which is the flood risk after all measures of risk avoidance, reduction and mitigation have been taken. Measures should be in place to manage and plan for the residual risk, such as through evacuation procedures.

Last updated 25 May 2023

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