Modelling the effects of the Pleistocene glaciations on the Northwest European geohydrological system
Modelstudie naar het effect van Pleistocene ijstijden op het geohydrologische systeem in Noordwest Europa
Weert FHA van , Leijnse A
RIVM Report 715401001
A large-scale 2-dimensional vertically integrated groundwater model has been constructed to investigate the geohydrological responses to glacial climate conditions. The groundwater model is based on the hydrogeological model of the Cenozoic and Mesozoic sediments in the subsurface of Northwest Europe constructed by the Dutch Geological Survey. Three different layers are distinguished above the relatively impervious base of Palaeozoic and Precambrian rocks. Boundary conditions to simulate groundwater flow related to various stages of the Pleistocene glaciations in the Northwest European lowlands have been inferred from palaeo-environmental reconstructions for the last three glacial cycles. Testing of the model concepts was carried out using a strongly simplified model. Effects of subglacial meltwater infiltration, excess meltwater redistribution and proglacial drainage of the highly pressurized groundwater system were examined. Sensitivity analyses with both the simplified and the large-scale model were carried out to identify important processes and system parameters. The effect of glaciation on the NW European groundwater system was investigated with the large-scale model. First, groundwater heads and velocities during an extreme cold climatic situation were compared with the present situation. Second, the geohydrology during the complete Saalian glacial cycle was studied by means of a sequence of steady-state simulations. This was followed by a final study on the effects of glaciations in the last 480,000 years. Results of the simulations indicate relatively high groundwater velocities and pressures, both in the subglacial areas and ice-marginal permafrost areas during cold periods. Extreme high velocities may develop when the ice sheet advances to the southern margins of the Upper Plio/Pleistocene aquifer in Northwest Europe. Areas with reduced meltwater infiltration which are assumed to be favourable areas for subglacial erosion processes coincide with areas where eskers, tunnel valleys and glacial basins are found. During relatively short periods in the Pleistocene glaciations high groundwater velocities were observed in areas containing the salt formations to be seen as potential repositories for radioactive waste.