Fresh water winning and salt water encroachment in the Amsterdam dune water catchment area

Abstract

In the Amsterdam dune-water catchment area, a freshwater lens of some 40 to 90 m thickness is resting on salt water in the lower aquifer, located at a depth of 20 m to 160 m - O.D. Waterextraction from the lower aquifer has disturbed the fresh-water/salt-water interface, extending it into a zone of dispersed, brackish water. For many years, the extraction area has been overdrawn. This article will discuss salinity conditions in the Amsterdam catchment area, and draw up a comparison between its current stock of fresh water and the original volume present before the start of waterwinning in the area. With the introduction, in 1957, of artificial recharge through infiltration of Rhine-water into the upper aquifer above 15 m - O.D., water extraction from the lower aquifer, which had been hampered by increasing salt-water contamination of the wells owing to the upconing of brackish water, was virtually stopped. The lower aquifer, however, still holds a vast stock of fresh water, which, if developed by a system of intermittent extraction, could substantially contribute to the water supply of the greater Amsterdam area.