WEKU - A GIS-SUPPORTED STOCHASTIC-MODEL OF GROUNDWATER RESIDENCE TIMES IN UPPER AQUIFERS FOR THE SUPRAREGIONAL GROUNDWATER-MANAGEMENT

The supraregional GIS-supported stochastical model, WEKU, for the dete rmination of groundwater residence times in the upper aquifers of larg e groundwater provinces is presented. Using a two-dimensional analytic al model of groundwater flow, groundwater residence times are determin ed within two extreme cases. In the first case, maximal groundwater re sidence times are calculated, representing the part of groundwater, th at is drained by the main surface water of a groundwater catchment are a. In the second case, minimal groundwater residence times for drainag e into the nearest surface water are determined. Using explicit distri bution functions of the input parameters, mean values as well as poten tial ranges of variations of the groundwater residence times are deriv ed. The WEKU model has been used for the determination of groundwater residence times throughout Germany. The model results - mean values an d deviations of the groundwater velocity and the maximal and minimal g roundwater residence times in the upper aquifers - are presented by ge neral maps and discussed in detail. It is shown that the groundwater r esidence times in the upper aquifer vary regionally, differentiated be tween less than 1 year and more than 2000 years. Using this informatio n, the time scales can be specified, until measures to remediate pollu ted groundwater resources may lead to a substantial groundwater qualit y improvement in the different groundwater provinces of Germany. With respect to its supraregional scale of application, the WEKU model may serve as a useful tool for the supraregional groundwater management on a state, federal or international level.