Lithostratigraphic controls on recharge to the Chalk aquifer of Southern England

Newly developed borehole closed circuit television (CCTV) lighting has shown that films of water can develop on open borehole walls at discrete levels within the deep unsaturated zone of the chalk, the levels being associated with marl horizons. The CCTV images, together with jacking tensiometers, have been used to observe unsaturated zone processes in selected boreholes. Work focused on two catchments in southern England, the Pang in Berkshire and the Brighton ‘block’ in Sussex. Deep jacking tensiometers were used to measure the associated pressure head (matric potential). The data suggest that recharge to the water table occurs through the matrix, throughout the year. The data also suggest that marl seams can influence recharge processes significantly, creating horizons with high matric potential. As a result, fracture flow and storage could be more important in chalk sequences where they are abundant and well developed.