Groundwater flooding occurs when the water table, the level of water below the ground, rises above the ground surface or into cellars and basements.
Over an average year, the water table naturally rises and falls depending on the seasonal rainfall. Where wet weather is prolonged, for example one or more seasons of above average rainfall, the water table can rise to a point where it rises above the ground surface in certain locations, usually low lying locations with underlying permeable rocks, known as aquifers. To find out if your property or workplace is located on an aquifer, the Environment Agency’s online maps may be useful.
Identifying groundwater flooding
Groundwater can be identified by one or more of the following key characteristics:
- persistent presence of flood water for long periods of time (weeks to months)
- flood water responds very slowly to rainfall events and water levels continue to rise hours or days after a rainfall event
- water levels take days or weeks to fall following a rainfall event
- water is clear and clean looking compared to muddy river flood water.
Unfortunately, unlike fluvial (river) flooding and surface water flooding, there are no freely available groundwater flood risk maps. However, the British Geological Survey (BGS) has recently produced the first national hazard data set for groundwater flooding which is available at a cost directly from the BGS.
As the Lead Local Flood Authority (LLFA), we have the responsibility of managing the risk of flooding from groundwater. Whilst groundwater is practically very difficult to manage and prevent, if you have any concerns or would like to report groundwater flooding, please visit the Report flooding or request advice page.