River Flooding

Normally, any type of development work on a site greater than 1 ha in size requires a flood risk assessment. A flood risk assessment covers both river (fluvial) and surface water (pluvial) flooding.

Map

Normally, any type of development work on a site greater than 1 ha in size requires a flood risk assessment. A flood risk assessment covers both river (fluvial) and surface water (pluvial) flooding. A flood risk assessment will use information gathered from the national Environment Agency (EA) and includes the use of the national EA's Flood Map for Planning. This map shows data including the flood zone an area is in and how this relates to the likelihood of fluvial flooding. The flood zones are as follows:

Zone 1 (Low Probability) - Land having a less than 1 in 1,000 annual probability of river or sea flooding.
Zone 2 (Medium Probability) - Land having between a 1 in 100 and a 1 in 1,000 annual probability or river flooding; or land having between a 1 in 200 and 1 in 1,000 annual probability of sea flooding.
Zone 3a (High Probability) - Land having a 1 in 100 or greater annual probability or river flooding; or land having a 1 in 200 or greater annual probability of sea flooding.
Zone 3b (Functional Floodplain) - This zone comprises land where water has to flow or be stored in times of flood. Local planning authorities, in agreement with the local Environment Agency, should identify in their Strategic Flood Risk Assessments areas of functional floodplain and their boundaries.

The EA Flood Map for Planning does not consider the possible impacts of climate change and consequent changes in the future probability of flooding. For the future risk, the EA provides a service to check the long-term flood risk for an area in England, with similar services for areas in Wales, Scotland and Northern Ireland. The National Planning Policy Framework in England (NPPF) classifies the vulnerability of developments to flooding into five categories. These categories are detailed in Table 2.

Table 2: Flood Risk Vulnerability Classification

Similar classifications exist for Wales, Scotland and Northern Ireland. Based on the vulnerability of a development, the NPPF identifies within what Flood Zone(s) a development is appropriate. The flood risk vulnerability and Flood Zone 'compatibility' of developments is summarised in Table 3.

Table 3: Development Compatability