Geohydrological investigations with a view to groundwater catchment, a case history

Abstract

With the intention to give an impression of the usually applied geohydrological procedures for the foundation of a pumping station in the Netherlands, the investigations for the well field at Beerschoten (provincie of Utrecht, The Netherlands) are reviewed. The area concerned is located on the western slope of ice pushed hills forming the Utrecht Ridge. The subsoil consists predominantly of Pleistocene sandy deposits of fluviatile origin, with local loam layers. The groundwater has a suitable quality for the preparation of drinking water and requires only a simple treatment. From a pumping test it appeared that the studied area is situated in the transition zone between a recharge and a discharge area and that loam layers delay the propagation of drawdowns from the pumped aquifer to the phreatic surface. The transmissivity of the aquifer from which the water will be withdrawn amounts to 3500 m2/day. On the base of subsequent studies carried out by means of a mathematical method and electrical model tests a prediction of the consequences of the withdrawal for the groundwater table has been given. Several relatively simple statistical methods are described, from which it appears that in spite of a certain lack of appropriate data. The prediction given was reasonably reliable and also that after adjustments for several external influences the actual consequences of the withdrawal could be very well determined. As in many other cases, the practical sustained yield in this area depends merely on the drawdowns due to the withdrawal and on the decrease of underground flow to ditches. From the point of view of water resources management the survey forms an example of a case where a series of multi-purpose investigations should serve to arrive at an optimum exploitation of the groundwater.