Flood Risk Assessment (FRA)

Site Investigation



FRAs are prepared in accordance with good practice guidance as outlined in Development and Flood Risk: A practice guide companion to PPS25.  It requires the FRA to be commensurate with the scope and size of the proposed development, namely;

For developments of less that 1ha (10,000m2) the level of detail required in an acceptable FRA will depend on the size and density of build.  This will range from a brief report for small, low density developments, to a more detailed assessment for a high density development, 2000-10,000m2 in size.  For example: for very small developments (2000m2 and less) an acceptable FRA could be a brief report done by the contractor’s engineer, including information obtained from; the Environment Agency, water company/sewerage undertaker, other relevant authorities, site investigation and local knowledge.

Planning Policy Statement PPS25 Practice Guide identifies the need for reference to the following typical sources of information 

  • Strategic Flood Risk Assessment
  • Environment Agency Flood Map
  • Environment Agency Standing Advice
  • Surface Water Management Plan (SWMP) and Water Cycle Study


Planning Policy Statement 25: Development and Flood Risk (PPS25) sets out the Government’s policy for managing development and flood risk.  It provides guidance to Local Authorities for determining planning applications in areas prone to flooding to ensure that new development is safe and not unnecessarily exposed to flooding.

The policies are based on the Environment Agency’s maps of flood risk zones.  These cover all of England and Wales and map areas prone to flooding in terms of the following.

Zone 1  - Low Probability (Little or No Risk)  

This zone comprises land assessed as having a less than 1 in 1000 annual probability of river or sea flooding in any year.  There are no development constraints.

Zone 2  - Medium Probability (Low to Medium Risk)

This zone comprises land assessed as having between a 1 in 100 (1%) and 1 in 1000 (0.1%) annual probability of river flooding or between a 1 in 200 and 1 in 1000 annual probability of sea flooding in any year.

Zone 3a - High Probability (High Risk)

This zone comprises land assessed as having a 1 in 100 or greater annual probability of river flooding or a 1 in 200 or greater annual probability of flooding from sea in any year. 

Zone 3b - Functional Floodplain

This zone comprises land where water has to flow or be stored in times of flood.  The annual probability that such land will flood will be 1 in 20 or greater.

Flood Risk Zones 3a and 3b are not separately mapped by the Environment Agency (EA).  The advice of the EA is that it is the responsibility of the applicant to determine whether a site is in Zone 3a or 3b in the course of preparing a flood risk assessment. 

PPS25 defines proposed land use by its vulnerability to flooding and relates it to these flood risk categories.  Appropriate developments for each flood zone are given.  The proposed residential development at the site falls under the ‘more vulnerable’ PPS25 classification for a residential usage.  As such more vulnerable development is appropriate in Zone 1.

The aim of this assessment has been to ensure that the development is sustainable in respect of the following key aims.

- the development should not be at a significant risk of flooding, and should not be susceptible to damage due to flooding;

- the development should not be exposed to flood risk such that the health, safety and welfare of the users of the development, or the population elsewhere, is threatened;

- normal operation of the development should not be susceptible to disruption as a result of flooding;

- safe access to and from the development should be possible during flood events;

- the development should not increase flood risk elsewhere;

- the development should not prevent safe maintenance of watercourses or maintenance and operation of flood defences by the FDA;

- the development should not be associated with an onerous or difficult operation and maintenance regime to manage flood risk; the responsibility for any operation and maintenance required should be clearly defined;

- future users of the development should be made aware of any flood risk issues relating to the development;

- the development design should be such that future users will not have difficultly obtaining insurance or mortgage finance, or in selling all or part of the development, as a result of flood risk issues;

- the development should not lead to degradation of the environment.

- the development should meet all of the above criteria for its entire lifetime, including consideration of the potential effects of climate change.

Assessment  adopted the principles set out in Planning Policy Guidance PPG 25 "Development and Flood Risk", Planning Policy Statement PPS 25, and CIRIA report C624 "Development and Flood Risk - Guidance for the Construction Industry".