Flood risk mapping - Example United Kingdom

In the UK only one organisation is responsible for mapping inundation  probabilities. Two kinds of maps contain information on the probability of inundation:

  • the Flood zone map and
  • the Flood map.

The Flood zone map presents zones of fluvial and tidal flood extent. The Flood Map is based upon the Flood Zones Map, but also includes the extent of areas defended by raised flood defences. The Flood Zone and Flood Map outlines take no account of climate change. They represent the situation now and show the potential (or theoretical) area, which is at risk to flooding assuming that no flood defences or structures (sluices/weirs/bridges/roads and railways embankments) are in place. The different zones are specified as shown in the table below:

In UK inundation maps are published on the Internet. But, experiences with Internet publication of flood maps in the UK were less positive, because after publication real-estate prices dropped in flood-sensitive areas and some insurance companies refused to insure properties in these areas unless they were defended to a 1 in 75 year standard or above.

The appropriate scale of maps in UK

Areas of relative flood risk can be illustrated on a series of maps.

The scales of the maps should be selected according to the area to be covered and the degree of detail which is required. Typical scales are:

  • District wide Flood Risk Maps rural areas - 1/ 25,000
  • District wide Flood Risk Maps urban areas - 1/10,000
  • Action Area or Development Area Plans - 1/ 2,500 or 1/5,000.

The Environment Agency has a Flood Mapping Strategy which has three key outputs:

  • A 1/50,000 scale Flood Map, which will be developed over the 5-year period of the Strategy to illustrate the probability of flooding, taking into account the presence and effect of flood defence systems. This map shows areas of land that could be flooded, and the map is published on the Internet for public reference. Currently the map does not allow for the presence of defences, but when interrogated for further information, high, moderate or low likelihoods of flooding are indicated.
  • A Historic Flood Map will be developed which will illustrate the maximum extent of any recorded flooding from rivers, the sea and groundwater springs. This will show areas of land that have flooded
  • The production of 1/10,000 scale Flood Zone Maps for England and Wales which have been provided to the LPAs for planning consultations to support the implementation of PPG25. These maps are not available to the general public, but they are being up-dated regularly by the Environment Agency.

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Flood risk mapping






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