Sustainable Drainage Systems (SuDS): guidance for developers

Last updated: 12 December 2022

Flood risk assessments

The following section explains when a site-specific flood risk assessment (FRA) is required to support a planning application and what information needs to be included in an FRA.

When a flood risk assessment is required

The requirement for an FRA to be submitted to support a planning application is set out Footnote 55 of the National Planning Policy Framework (2021) which states that ‘a site-specific flood risk assessment should be provided for:

  • all development in Flood Zones 2 and 3
  • In Flood Zone 1, an assessment should accompany all proposals involving: sites of 1 hectare or more
  • land which has been identified by the Environment Agency as having critical drainage problems; land identified in a strategic flood risk assessment as being at increased flood risk in future
  • or land that may be subject to other sources of flooding, where its development would introduce a more vulnerable use

Information to include in a flood risk assessment

If your site meets the criteria as set out in Footnote 55 of the NPPF then a site-specific FRA must be submitted to support your planning application.

An FRA must assess the risk of all sources of flood risk to your site including surface water, groundwater and fluvial and demonstrate that the proposed development will not increase flood risk.

Sources of flooding

This section provides an explanation of the sources of flooding that Buckinghamshire may be at risk of, who is responsible for managing flooding from different sources and where information for some sources of flooding can be found.

Riparian responsibilities

A landowner with a watercourse flowing through their land or along their boundary has riparian responsibilities to maintain the watercourse within their land ownership, this includes ensuring that water continues to flow in the watercourse without obstruction.

Find out more about riparian responsibilities.

Why flood risk needs to be considered in a planning submission

When investigating sites for development, managing flood risk from all sources must be considered at an early stage to inform layout and design. This section discusses the wider planning policy context for considering flood risk, explains the different sources of flood risk and introduces requirements of planning applications.

A flood risk assessment (FRA) must demonstrate to the Local Planning Authority how flood risk will be managed now and over the development’s lifetime, taking climate change into account.

Policy – National Planning Policy Framework (2021) – Paragraph 167

‘When determining any planning applications, local planning authorities should ensure that flood risk is not increased elsewhere. Where appropriate, applications should be supported by a site-specific flood-risk assessment. Development should only be allowed in areas at risk of flooding where, in the light of this assessment (and the sequential and exception tests, as applicable) it can be demonstrated that:

a) within the site, the most vulnerable development is located in areas of lowest flood risk, unless there are overriding reasons to prefer a different location;

b) the development is appropriately flood resistant and resilient such that, in the event of a flood, it could be quickly brought back into use without significant refurbishment;

c) it incorporates sustainable drainage systems, unless there is clear evidence that this would be inappropriate;

d) any residual risk can be safely managed; and

e) safe access and escape routes are included where appropriate, as part of an agreed emergency plan.’

Sequential approach to locating development

If a site is at risk of any source of flooding a sequential approach must be taken when locating development, this means proposing development in areas shown to be at no or low risk of flooding opposed to areas at higher risk of flooding.

Taking a sequential approach is required by both paragraph 159 of the National Planning Policy Framework (NPPF) (2021) and paragraph 018 (Ref ID 7-018-20140306) of the Planning Practice Guidance (2014).

This is to ensure that development can be safely and sustainably delivered, and developers do not propose development which is inappropriate on flood risk grounds.

Policy – National Planning Policy Framework (2021) – Paragraph 159

‘Inappropriate development in areas at risk of flooding should be avoided by directing development away from areas at highest risk (whether existing or future). Where development is necessary in such areas, the development should be made safe for its lifetime without increasing flood risk elsewhere.’