A Practical Guide to Flood Risk


Today we’re going to take a look at Flood Risk and the Town Planning Process, covering the basic considerations you need to keep in mind if you’re looking to progress a development.

Whilst there is much more to know about flooding, for a developer, there are a few key things you should be aware of.  Including when a Flood Risk Assessment is required and what the sequence of assessing a site is.

So, what exactly is Flood Risk?

This may sound a simple question.  Essentially it means that some locations are susceptible to flooding from all sources, climate change is anticipated to make the situation worse.  To know what the flood risk is for your site, take a look at the Environment Agency Flood Risk Map.

What are Flood Zones?

Flood Zones are defined by the Environment Agency, all land/property lies within a flood zone.  Zones are set on the likelihood of an area flooding.

Flood zone 1 area are least likely to flood, flood zone 2 has a great chance of flooding and flood zone 3 is most likely to flood.

You can check what Flood Zone your site is within via the Flood  Risk Map for Planning.

How do I know when a Flood Risk Assessment is required?

When submitting a planning application (for any type of development) 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.

Who carries out a Flood Risk Assessments?

You’ll usually need a flood risk consultant to carry out a Flood Risk Assessment (FRA). If it’s for a simple, low risk development like a house extension you may be able to do it yourself.

A FRA should be proportionate to the development and site.  So for instance a householder extension is not likely to increase the number of people in an area of flooding whereas a development in a similar flood zone could attract significant numbers.  The level of detail would clearly be different.

What is a Flood Risk Assessment?

A Flood Risk Assessment (FRA) should establish the risks of flooding from all sources, the potential to increase flooding elsewhere, measures to deal with these effects and risks, evidence to allow the Local Planning Authority to apply the Sequential Test, if necessary and in relation to the Exception Test, if applicable.

What is a Sequential Test?

The National Planning Policy Framework sets out that a risk based approach to development is required as part of this process.  This is in the form of a sequential test so to avoid, where possible flood risk to people and property.  Development should not be allocated or permitted if there are reasonably available sites appropriate for the proposed development in areas with a lower risk of flooding.

The Environment Agency has published Guidance for developers carrying out sequential testing as part of FRA. This includes advice on searching for alternative sites, and the provision of information about potential alternative sites. There is often disagreement over the area of the test. However, the test should not be constrained by landownership and realistically will often extend across a town or district area.

A Sequential Test does not need to be applied for development on sites allocated in development plans as they will have already been through this process.  Nor should it be necessary to apply a sequential test to a site in Flood Zone 1.

What is the Exceptions Test?

If it is not possible to locate development in areas of lower risk of flooding (the sequential test has been passed) an exceptions test may be required, depending on the flood zone and flood risk vulnerability classification of the development.  See table below:

What are the Flood Risk Vulnerability Classifications?

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.

Highly vulnerable

  • 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’).

More vulnerable

  • 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.

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.

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.

The 2 parts to the exceptions test requires proposed development to show that it will provide wider sustainability benefits to the community that outweigh flood risk (evidence is required to demonstrate this).  And that it will be safe for its lifetime, without increasing flood risk elsewhere and where possible reduce flood risk overall (for example evacuation plans, warnings and layout of a development).

Applications for some minor development (i.e. householder, small non-residential extensions) and changes of use would not be subject to the sequential or exception tests but would still require a site-specific flood risk assessment.

What’s the Process for assessing Flooding on a Site?

A Flood Risk Assessment (FRA), when required should be submitted along with your planning application to your Local Planning Authority (LPA).

The LPA will review your FRA and tell you if it’s satisfactory. Local Planning Authorities take advice from the Lead Local Flood Authorities (LLFA) who are responsible for managing local flood risk and the Environment Agency to ensure development does not adversely affect flood risk.

Planning applications that do not have a satisfactory Flood Risk Assessment may be refused.

How can Planning House Help?

A town planner can provide you with the guidance you need for a smooth transition please feel free to CONTACT US to discuss your situation.  We’re not experts in flood risk however we work with some great consultants who are!

If you’re not sure we’re the right fit for you then take a look at our blog on When to Hire a Town Planner and our download on choosing a Town Planner to help you find a town planner that’s right for you.