Groundwater flooding can cause significant social and economic disruption and is a threat in many areas of North West Europe, including the UK.
For example, it is estimated that 380 000 properties located on the exposed Chalk of southern England are vulnerable to this form of flooding.
Flooding legislation recently introduced in Europe and transposed into UK law has recognised the importance of groundwater flooding by incorporating a requirement to assess the risk and undertake measures to reduce this where significant.
The characteristic feature of groundwater flooding events is the relatively long duration compared with fluvial flooding.
Groundwater flooding is defined here as the emergence of groundwater at the ground surface away from perennial river channels or the rising of groundwater into man-made ground, under conditions where the 'normal' ranges of groundwater level and groundwater flow are exceeded.
The impact of groundwater flooding can occur before water levels reach the ground surface where there is inundation of building basements and buried services or other assets below ground level.
Groundwater levels that rise above ground have the potential to reach low-lying areas protected from fluvial flooding.
Exceptionally large flows from perennial springs or large flows from intermittent or dormant springs, which also come under the above definition of groundwater flooding, can cause both localised flooding in the vicinity of the springs and down gradient where surface water drainage channels may not be adequate.
Three main settings have been identified in the UK where significant groundwater flooding can occur:
The first two of these settings encompass the majority of sites affected by groundwater flooding in the UK. The BGS is currently undertaking research in these settings to improve the understanding of the flooding mechanisms involved.
Current and recent completed research projects being undertaken are identified in the associated pages. The understanding gained from this research has been the basis for the production of susceptibility to groundwater flooding maps, which cover England, Wales and Scotland.
Contact David Macdonald for further information