Introduction

In FloodScreen, we make use of a number of datasets made available under the Open Government License:

This page aims to give a brief introduction to each dataset, what they mean, and are used for.

Flood Map for Planning

The Flood Map for Planning (Rivers and Sea) dataset is the Environment Agency’s best estimate of the areas of land at risk of flooding, when the presence of flood defences are ignored.

This dataset is designed to support flood risk assessments in line with Planning Practice Guidance; and raise awareness of the likelihood of flooding to encourage people living and working in areas prone to flooding to find out more and take appropriate action.

The information provided is largely based on modelled data and is therefore indicative rather than specific.

Areas may also be at risk from other sources of flooding, such as high groundwater levels, overland run off from heavy rain, or failure of infrastructure such as sewers and storm drains which does not form part of this dataset.

The information indicates the flood risk to areas of land and is not sufficiently detailed to show whether an individual property is at risk of flooding, therefore properties may not always face the same chance of flooding as the areas that surround them. This is because the Environment Agency do not hold details about properties and their floor levels. Information on flood depth, speed or volume of flow is not included

Definition of English Flood Zones

The definitions of flood zones for England below are taken from the government’s Planning Practice Guidance.

Flood Zones

Flood Zone 1 – Low Probability

Definition

This zone comprises land assessed as having a less than 1 in 1,000 annual probability of river or sea flooding (<0.1%).

Appropriate uses

All uses of land are appropriate in this zone.

Flood Risk Assessment requirements

For development proposals on sites comprising one hectare or above the vulnerability to flooding from other sources as well as from river and sea flooding, and the potential to increase flood risk elsewhere through the addition of hard surfaces and the effect of the new development on surface water run-off, should be incorporated in a flood risk assessment. This need only be brief unless the factors above or other local considerations require particular attention.

Policy aims

In this zone, developers and local authorities should seek opportunities to reduce the overall level of flood risk in the area and beyond through the layout and form of the development, and the appropriate application of sustainable drainage systems.

Flood Zone 2 – Medium Probability

Definition

This zone comprises land assessed as having between a 1 in 100 and 1 in 1,000 annual probability of river flooding (1% – 0.1%), or between a 1 in 200 and 1 in 1,000 annual probability of sea flooding (0.5% – 0.1%) in any year.

Appropriate uses

Essential infrastructure and the water-compatible, less vulnerable and more vulnerable uses, are appropriate in this zone. The highly vulnerable uses are only appropriate in this zone if the Exception Test is passed.

Flood Risk Assessment requirements

All development proposals in this zone should be accompanied by a flood risk assessment.

Policy aims

In this zone, developers and local authorities should seek opportunities to reduce the overall level of flood risk in the area through the layout and form of the development, and the appropriate application of sustainable drainage systems.

Flood Zone 3a – High Probability

Definition

This zone comprises land assessed as having a 1 in 100 or greater annual probability of river flooding (>1%), or a 1 in 200 or greater annual probability of flooding from the sea (>0.5%) in any year.

Appropriate uses

The water-compatible and less vulnerable uses of land are appropriate in this zone. The highly vulnerable uses should not be permitted in this zone. The more vulnerable uses and essential infrastructure should only be permitted in this zone if the Exception Test is passed. Essential infrastructure permitted in this zone should be designed and constructed to remain operational and safe for users in times of flood.

Flood Risk Assessment requirements

All development proposals in this zone should be accompanied by a flood risk assessment.

Policy aims

In this zone, developers and local authorities should seek opportunities to:

  • reduce the overall level of flood risk in the area through the layout and form of the development and the appropriate application of sustainable drainage systems;
  • relocate existing development to land in zones with a lower probability of flooding; and
  • create space for flooding to occur by restoring functional floodplain and flood flow pathways and by identifying, allocating and safeguarding open space for flood storage.

Flood Zone 3b – The Functional Floodplain

Definition

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.

The identification of functional floodplain should take account of local circumstances and not be defined solely on rigid probability parameters. But land which would flood with an annual probability of 1 in 20 (5%) or greater in any year, or is designed to flood in an extreme (0.1%) flood, should provide a starting point for consideration and discussions to identify the functional floodplain.

This layer is not shown in FloodScreen and the local Strategic Flood Risk Assessment for the area should be consulted.

Appropriate uses

Only the water-compatible uses and the essential infrastructure listed in table 2 that has to be there should be permitted in this zone. It 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.

Essential infrastructure in this zone should pass the Exception Test.

Flood Risk Assessment requirements

All development proposals in this zone should be accompanied by a flood risk assessment.

Policy aims
  • In this zone, developers and local authorities should seek opportunities to:
  • reduce the overall level of flood risk in the area through the layout and form of the development and the appropriate application of sustainable drainage systems;
  • relocate existing development to land with a lower probability of flooding.

Development Advice Map (DAM)

The Development Advice Map is to be used alongside Planning Policy Wales and Technical Advice Note 15 (TAN 15) to direct new development in respect to flood risk. Together, they form a precautionary framework to guide planning decisions.

The maps are based on Natural Resources Wales' extreme flood outlines (Zone C) and the British Geological Survey drift data (Zone B).

The information provided is largely based on modelled data and is therefore indicative rather than specific.

Areas may also be at risk from other sources of flooding, such as high groundwater levels, overland run off from heavy rain, or failure of infrastructure such as sewers and storm drains which does not form part of this dataset.

Further information on TAN 15 can be found here.

Definition of Flood Zones

The definitions of flood zones for Wales below are taken from the Planning Policy Wales TAN15.

DAM Zone A

Description

Considered to be at little or no risk of fluvial or tidal/coastal flooding.

Use within the precautionary framework

Used to indicate that justification test is not applicable and no need to consider flood risk further.

DAM Zone B

Description

Areas known to have been flooded in the past evidenced by sedimentary deposits.

Use within the precautionary framework

Used as part of a precautionary approach to indicate where site levels should be checked against the extreme (0.1%) flood level. If site levels are greater than the flood levels used to define adjacent extreme flood outline there is no need to consider flood risk further.

DAM Zone C1

Description

Based on Environment Agency extreme flood outline, equal to or greater than 0.1% (river, tidal or coastal).

Areas of the floodplain which are developed and served by significant infrastructure, including flood defences.

Use within the precautionary framework

Used to indicate that flooding issues should be considered as an integral part of decision making by the application of the justification test including assessment of consequences.

Also that development can take place subject to application of justification test, including acceptability of consequences.

DAM Zone C2

Description

Based on Environment Agency extreme flood outline, equal to or greater than 0.1% (river, tidal or coastal).

Areas of the floodplain without significant flood defence infrastructure.

Use within the precautionary framework

Used to indicate that flooding issues should be considered as an integral part of decision making by the application of the justification test including assessment of consequences.

Also that only less vulnerable development should be considered subject to application of justification test, including acceptability of consequences. Emergency services and highly vulnerable development should not be considered.

Risk of Flooding from Rivers and Seas

This is a national scale assessment of flood risk for England and Wales produced using local expertise. The dataset shows the chance of flooding from rivers and/or the sea, based on cells of 50m. Each cell is allocated one of four flood risk categories, taking into account flood defences and their condition. No more detailed resolution is provided.

The map shows an assessment of the likelihood of flooding from rivers and the sea at any location is based on the presence and effect of all flood defences, predicted flood levels, and ground levels.

The chance of flooding can be categorised into one of four categories:

  •   High - greater than or equal to 1 in 30 (3.3%) chance in any given year
  •   Medium - less than 1 in 30 (3.3%) but greater than or equal to 1 in 100 (1%) chance in any given year
  •   Low - less than 1 in 100 (1%) but greater than or equal to 1 in 1,000 (0.1%) chance in any given year
  •   Very Low - less than 1 in 1,000 (0.1%) chance in any given year

This information is not suitable for use in land-use planning. If you are planning a development, you need to use the Flood Map for Planning for England and the Development Advice Map for Wales. This is because for planning purposes you need to use information based on flooding without defences.

Recorded Flood Outlines

Recorded Flood Outlines are datasets which show all of the Environment Agency and Natural Resources Wales records of historic flooding from rivers, the sea, groundwater and surface water. Each individual Recorded Flood Outline contains a consistent list of information about the recorded flood.

Records began in 1946 when predecessor bodies to the Environment Agency and Natural Resources Wales started collecting detailed information about flooding incidents, although the EA and NRW may hold limited details about flooding incidents prior to this date. The absence of coverage by Recorded Flood Outlines for an area does not mean that the area has never flooded, only that we do not currently have records of flooding in this area. It is also possible that the pattern of flooding in this area has changed and that this area would now flood or not flood under different circumstances.

The Recorded Flood Outlines take into account the presence of defences, structures, and other infrastructure where they existed at the time of flooding. It includes flood extents that may have been affected by overtopping, breaches or blockages. Any flood extents shown do not necessarily indicate that properties were flooded internally.