Crag aquifer characteristics and water balance for the Thurne catchment, northeast Norfolk

A study of the hydrogeological controls on the Pleistocene Crag aquifer in northeast Norfolk is reported. Geophysical methods, in particular multichan nel seismic reflection profiling, have provided useful information on the i nternal structure of the aquifer. The Crag represents a layered aquifer, wi th horizons of clay and silt strata able to limit the overall vertical perm eability of the aquifer. A laterally continuous clay horizon is identified at around - 25 mOD and is mapped as far as the coast. Shallow wells and bor eholes in the Crag are prone to contamination. Nitrate is widely recorded, with concentrations of typically up to 150 mg l(-1) in shallow wells, deriv ed from mainly agricultural sources, although deeper boreholes are less aff ected given the restricted downward movement of groundwater. The land drain age systems within this lowland area dominate the hydrology and hydrogeolog y of the catchment. Surface flows into the River Thurne are controlled by t he operation of drainage pumps and a catchment water balance demonstrates t hat groundwater principally discharges to the drainage ditches within the e xtensive arable and grazing marshes in the catchment.