Flood risk from groundwater : examples from a Chalk catchment in southern England

Groundwater flooding has moved up the policy-makers' agenda as a result of the United Kingdom experiencing extensive groundwater flooding in winter 2000/2001. However, there is a lack of appropriate methods and data to support groundwater flood risk assessment. The implications for flood risk assessment of groundwater flooding are outlined using a study of the Chalk aquifer underlying the Pang and Lambourn catchments in Berkshire, UK. Groundwater flooding in the Chalk results from the water table reaching the land surface and producing long-duration surface flows (weeks to months), causing significant disruption to transport infrastructure and households. By analyzing existing data with a farmers' survey, it was found that groundwater flooding consists of a combination of intermittent stream discharge and anomalous springflow. This work shows that there is a significant challenge involved in drawing together data and understanding of groundwater flooding, which includes vital local knowledge, reasonable risk assessment procedures and deterministic modelling.