Do I Need a Flood Risk Assessment?


A Flood Risk Assessment (FRA) is a report that evaluates the impact of flood risks to a site. Flooding can occur from different sources such as rivers, the sea, sewers, groundwater, reservoirs, and as a result of surface water run-off.

An FRA should evaluate the risks to a site from all of these sources and, where feasible, provide recommendations for mitigation measures to alleviate the impact of flooding on a site and its surrounding area.

An FRA is generally required to be submitted as part of a planning application for all potential site developments proposed in designated flood zones. It is critical for developers to understand the potential flood risks to a new development, not only to determine the safety of the new development in relation to its flood risk but also to understand the impacts the development may have on the surrounding area in terms of increasing flood risk.


What Are the Main Objectives for an FRA?

The aim of an FRA is to find out:

  • Whether the proposed development is likely to be affected by current or future flooding from a range of sources.
  • Whether the development will increase flood risk elsewhere.
  • Whether the mitigation measures proposed to deal with the potential flood risk are appropriate.
  • Whether the development will be safe over its lifetime.


Do I Need a Flood Risk Assessment?

Requirements for an FRA differ between Scotland, England, and Wales where planning matters are devolved. A Flood Risk Assessment in England is required when:

  • The proposed development is located within Flood Zone 2 or Flood Zone 3; or,
  • The site is located within Flood Zone 1 but is greater than 1 hectare in size; or,
  • The site is located within Flood Zone 1 and is less than 1 hectare, but is affected by other sources of flooding such as surface water, groundwater, fluvial, and sewers.

What Are Flood Zones?

There are 3 flood zones as defined by the Environment Agency; Flood Zone 1, 2, and 3.

The flood zones are based on the likelihood of an area flooding from rivers or the sea, and for catchments greater than 3km²; with Flood Zone 1 areas least likely to flood and Flood Zone 3 areas more likely to flood.

However, these flood zones do not always consider every single river in an area, and don’t consider blocked drains; nor do they currently take the effects of climate change into consideration. Therefore, sites shown to be in Flood Zone 1 can still experience flooding.

Flood Zone 1:

Areas within Flood Zone 1 are deemed to have less than a 1 in 1000 (0.1%) annual probability of flooding in any given year. Flood Zone 1 is the lowest risk flood zone.

There are typically very few restrictions in terms of flood risk to development in Flood Zone 1 areas, the exception is for development over 1ha in size which must have a flood risk assessment undertaken as part of a planning application; and areas deemed to be at high risk of flooding from surface water, known as Critical Drainage Areas.

Flood Zone 2:

Areas within Flood Zone 2 have between a 1 in 1000 (0.1%) and 1 in 100 (1%) annual probability of flooding in any given year. Flood Zone 2 is considered a medium risk.

Developments situated within Flood Zone 2 require an FRA to be submitted as part of any planning application, showing the risks of flooding to the site.

Flood Zone 3:

Flood Zone 3 is split into 2 separate zones, 3a and 3b by the local planning authorities. However, Flood Zone 3 areas appear as a general Flood Zone 3 area on maps, due to the EA not splitting these zones. Areas within Flood Zone 3a have a 1 in 100 (1%) or greater annual probability of flooding in any given year.

Flood Zone 3b:

Flood Zone 3b’s are areas classified as functional floodplain and are deemed to be the areas most at risk land of flooding from rivers or the sea. Areas located within Flood Zone 3b typically have a 1 in 20 (5%) chance of flooding in any given year.

There are significant restrictions as to what can be developed on Flood Zone 3b land.


Standing Advice:

There is standing advice available for certain types of development which can help simplify the level off assessment required. You should follow the Environment Agency’s standing advice if your proposed development is classed as the following:

  • A minor extension (Household or non-domestic extensions less than 250 square metres) in Flood Zone 2 or 3;
  • A ‘more vulnerable’ development in Flood Zone 2;
  • A ‘less vulnerable’ development in Flood Zone 2; and
  • A ‘water compatible’ development in Flood Zone 2.

You should also follow standing advice for developments concerning a change of use into one of these vulnerable categories, or into the water compatible category.

It is extremely important to know whether you require an FRA to accompany a proposed development, for both safety and legal purposes. The last thing you want is your proposed development displacing water and someone using this to make a claim against you.

How Can We Help?

At FPS Environmental we have an extensive background and experience undertaking flood risk assessments to support planning applications across a range of properties, flood zones, and development proposals.

Our flood risk assessments use the most up-to-date and high-tech data available, combined with working collaboratively with a range of sectors such as the Environment Agency, Architects, Lead Local Flood Authorities, and with the client themselves.

Our highly qualified engineers and consultants will work closely with you to understand the risk and develop solutions to mitigate flood risk for your development.

If you’re unsure and need advice, then get in touch with our team of specialists who can help and advise at or call 020 8050 3194.

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