Flood Zones

You may have discovered this page when trying to answer the question ‘Which flood zone is my property in?’.  We will aim to help you find out. Plus we will explain why they even exist.

We are all aware that flooding exists. This could be from the sea, rivers, reservoirs or from surface water.  The Environment Agency created the various flood zones as a method to aid planning.

Flood zones are divided into four – Flood Zones 1, 2 and 3 – yes, that is only three! That is because the Environment Agency only maps three, but local authorities split Zone 3 into 3a and 3b.

You can establish which flood zone you are in by visiting this Environment Agency website.

Further Guidance can be found on the Government pages here.

Flood Zone 1

Low Probability

Areas deemed to be in flood zone 1 have been shown to be at less than 0.1% chance of flooding in any year. Land having a less than 1 in 1,000 annual probability of river or sea flooding. (Shown as ‘clear’ on the Flood Map – all land outside Zones 2 and 3)

There are very few restrictions in terms of flood risk to development on flood zone 1 areas, the exception is for development over 1 hectare 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 rainfall known as Critical Drainage Areas.

Flood Zone 2

Medium Probability

Areas deemed to be in flood zone 2 have been shown to have between 0.1% – 1% chance of flooding from rivers in any year or between 0.1% – 0.5% chance of flooding from the sea in any year.

Land having between a 1 in 100 and 1 in 1,000 annual probability of river flooding; or land having between a 1 in 200 and 1 in 1,000 annual probability of sea flooding. (Land shown in light blue on the Flood Map).

Flood zone 2 development needs to submit a flood risk assessment as part of its planning application which shows the risk of flooding to the site.

Flood Zone 3a

High Probability

Areas within flood zone 3 have been shown to be at a 1% or greater probability of flooding from rivers or 0.5% or greater probability of flooding from the sea.

Land having a 1 in 100 or greater annual probability of river flooding; or Land having a 1 in 200 or greater annual probability of sea flooding.(Land shown in dark blue on the Flood Map).

Flood zone 3 development needs to submit a flood risk assessment as part of its planning application which determines if the site is classified as flood zone 3a or 3b as well as reviewing flood risk on the site and proposing suitable mitigation.

Flood Zone 3b

The Functional Floodplain

Flood zone 3b is classified as functional floodplain, and is deemed to be the most at risk land of flooding from rivers or the sea. Local planning authorities have classified areas at significant risk of flooding to be within flood zone 3b. This classification is usually classified as land which had a 5% probability of flooding also known as a 1:20 chance.

This zone comprises land where water has to flow or be stored in times of flood. Local planning authorities should identify in their Strategic Flood Risk Assessments areas of functional floodplain and its boundaries accordingly, in agreement with the Environment Agency. (Not separately distinguished from Zone 3a on the Flood Map)

What can be built and where?

Essential infrastructure

• Essential transport infrastructure (including mass evacuation routes) which has to cross the area at risk.
• Essential utility infrastructure which has to be located in a flood risk area for operational reasons, including electricity generating power stations and grid and primary substations; and water treatment works that need to remain operational in times of flood.
• Wind turbines.

These can be constructed in Zones 1 and 2. In Zones 3a and 3b an Exception test is required. In Flood Zone 3a essential infrastructure should be designed and constructed to remain operational and safe in times of flood.

Highly vulnerable (including basement flats)

• Police and ambulance stations; fire stations and command centres; telecommunications installations required to be operational during flooding.
• Emergency dispersal points.
• Basement dwellings.
• Caravans, mobile homes and park homes intended for permanent residential use.
• Installations requiring hazardous substances consent. (Where there is a demonstrable need to locate such installations for bulk storage of materials with port or other similar facilities, or such installations with energy infrastructure or carbon capture and storage installations, that require coastal or water-side locations, or need to be located in other high flood risk areas, in these instances the facilities should be classified as ‘Essential Infrastructure’).

These can be constructed in Zone 1 but in Zone 2 an exception test is required. They cannot be built in Zone 3a or 3b.

More vulnerable (including houses and flats)

• Hospitals.
• Residential institutions such as residential care homes, children’s homes, social services homes, prisons and hostels.
• Buildings used for dwelling houses, student halls of residence, drinking establishments, nightclubs and hotels.
• Non–residential uses for health services, nurseries and educational establishments.
• Landfill and sites used for waste management facilities for hazardous waste.
• Sites used for holiday or short-let caravans and camping, subject to a specific warning and evacuation plan.

These can be constructed in Zones 1 and 2 but in Zone 3a an exception test is required. They cannot be built in Zone 3b.

Less vulnerable

• Police, ambulance and fire stations which are not required to be operational during flooding.
• Buildings used for shops; financial, professional and other services; restaurants, cafes and hot food takeaways; offices; general industry, storage and distribution; non-residential institutions not included in the ‘more vulnerable’ class; and assembly and leisure.
• Land and buildings used for agriculture and forestry.
• Waste treatment (except landfill and hazardous waste facilities).
• Minerals working and processing (except for sand and gravel working).
• Water treatment works which do not need to remain operational during times of flood.
• Sewage treatment works, if adequate measures to control pollution and manage sewage during flooding events are in place.

These can be constructed in Zone 1, 2 and 3a. They cannot be built in Zone 3b.

Water-compatible development

• Flood control infrastructure.
• Water transmission infrastructure and pumping stations.
• Sewage transmission infrastructure and pumping stations.
• Sand and gravel working.
• Docks, marinas and wharves.
• Navigation facilities.
• Ministry of Defence defence installations.
• Ship building, repairing and dismantling, dockside fish processing and refrigeration and compatible activities requiring a waterside location.
• Water-based recreation (excluding sleeping accommodation).
• Lifeguard and coastguard stations.
• Amenity open space, nature conservation and biodiversity, outdoor sports and recreation and essential facilities such as changing rooms.
• Essential ancillary sleeping or residential accommodation for staff required by uses in this category, subject to a specific warning and evacuation plan.

These can be constructed in Zone 1, 2 and 3a. In Zone 3b water-compatible uses, should be designed and constructed to:

• remain operational and safe for users in times of flood;
• result in no net loss of floodplain storage;
• not impede water flows and not increase flood risk elsewhere.

 

Page Updated: 21st November 2020