When Do You Need a Flood Risk Assessment? | FPS Environmental

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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 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 – and surface water should not be ignored.
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.