A geohydrologic study of east Gelderland (Netherlands)

Abstract

This paper deals with the results of a geohydrological investigation carried out in the eastern part of The Netherlands (province Gelderland). In this region the demand for water for domestic and industrial use is rapidly increasing. The present demand of 34 million m3 per year is entirely met by extraction of groundwater. With a view on the agricultural interests the problem arises what effect a further increase of the groundwater extraction may have on the productivity of the drought-sensitive soils. This study was made to provide basic data for the solution of this problem. The geological investigations have given a much better insight in the suitability of the aquifers for groundwater exploitation than existed. The transmissivity of the aquifers according to field pumping tests and well logs, varies from about 300 to 10,000 m2/day. This variation is chiefly due to fluvioglacial erosion and aggradation during the Saale Ice Age (buried glacial channels). Utilizing a finite differences equation, in which the available transmissivity values and water table gradients had to be substituted, a map has been prepared showing the intensity of the net subsurface inflow. This flow rate is of practical importance because adding to it the mean precipitation and evaporation values immediately yields the mean drainage intensity. Transmissivity values and values of the drainage resistance were used for the calculation of the drawdown of the water table by extraction of groundwater from deep wells. In general, the groundwater is fresh but remarkable differences in electrical conductivity, sulphate-chloride ratio, hardness and iron content were found in the region. At some places the groundwater temperature was also measured. The differences in chemical composition and in temperature of the groundwater were found to be in fairly good agreement with the occurrence of positive and negative net subsurface inflow.