The Flood Plain

The Flood Plain.

New Definition by the Environment Agency.

The new EA map of the flood plain shows significant extension to its boundaries. In the Eversley Cross area, for example, it now includes a large number of properties that were not included previously. It is therefore important to understand the meaning of this map which can be seen on

To those interested in the effect of the changes on their properties it should be noted at the outset that the map, in the words of the EA, “is not designed to be accurate at the individual property level”. However, the map will be used by insurance companies and in case of difficulty they should a) be made aware of this statement, and b) they should be told to use it as instructed when checking the level of risk.

This is done electronically by clicking on the required location. This will bring up one of two conditions:

A.      Confirmation that the location is within an area that has a 0.1% (1 in a 1000) or greater chance of a flood happening each year. Note, however, that this is defined as “extreme” a term which could cause confusion. For example, a house in an extreme flood zone is less liable to flooding than a house in a non-extreme zone. The word “extreme” is being applied to the probability not the hazard.

B.      Confirmation that the location is within an area that has a 1% (1 in a 100) or greater chance of a flood happening each year. In this case there are three categories of likelihood; significant, moderate, or low. These categories are not quantified and are said to be for guidance e.g. in insurance assessment. They are said to be subject to annual revision.

It is also said that the map will be updated quarterly (January, April, July, and October). Requests for map modifications will be heard but evidence needs to be factual and not anecdotal.

The new map for the Eversley Cross and Fox Lane areas is attached. It shows a flood plain that extends across the B3272 and up the entire length of Marsh Lane. This is clearly a result of Firgrove Stream being classified as a “main river” and the requirement that all rivers with a catchment area of more than 3km2 need to be assessed. This assessment uses “national geographical modelling” and in our case has nothing to do with the history or likelihood of flooding in Marsh Lane.

When clicking on any location to the south west of Firgrove Stream the result is condition A above. The map is clearly not based on history. North of the stream the new ESA playing field shows as condition B with the cricket square classified as having a “significant” likelihood of flooding. The map is clearly not based on current contours.

Problems for residents who could be affected by the changes in the map can be anticipated.

It is therefore suggested that EPC should apply for an update to the map based on the raised level of the ESA playing field. The higher level undoubtedly takes this area out of the flood plain. Presumably it can also be said that the higher level creates a barrier to flooding in other parts of Eversley Centre.

As we all know it is surface water draining to the river and not the river itself that creates floods in Eversley . Definition of the flood plain should therefore have little relevance. This is not to say, however, that the new definition will not cause problems.

 DB.    08.06.09