THE IMPACT OF GLACIATION ON THE GROUNDWATER REGIME OF NORTHWEST EUROPE

Growth of mid-latitude ice sheets during the glacial cycles of the Qua ternary repeatedly reorganises the pattern of groundwater flow on a co ntinent-wide scale. Relatively small scale non-glacial catchments are replaced by catchments which are integrated on the scale of continenta l ice sheets. Simulations are presented of the response to glaciation of a large part of the western European groundwater system during the last two (Saalian, Weichselian) glacial cycles. A two-dimensional mode l along an ice sheet flowline from western Sweden to The Netherlands i llustrates the impact of glaciation on flow in the vertical plane, and a vertically integrated model illustrates its impact on areal pattern s of flow. Hydraulics heads, hydraulic gradients and flow velocities a re increased far above their modem values, and relatively shallow aqui fers are completely flushed out during glacial periods. There are sign ificant implications for groundwater chemistry and geological structur es. Large seepage pressures generated near to ice sheet margins and ma jor impacts on the distribution of effective pressures will produce st ructures such as hydrofractures, sediment dykes, sediment volcanoes, l oading structures etc. The model can be readily applied to hydrocarbon reservoirs.