ABSTRACT
Large parts of the Netherlands are situated several meters below mean sea level. Saline groundwater is attracted from the sea and from deep saline aquifers, and subsequently, intrudes near-surface coastal groundwater systems. The salinization of the subsoil is caused by human-driven processes of land subsidence that have been going on for nearly a millennium. A database from TNO of chloride concentration measurements throughout the Dutch coastal zone documents these salinizing processes in the subsoil, though locally also freshening processes are taking place. Here the results are reported of a variable-density groundwater fl ow and coupled solute transport model in three-dimensions of the coastal groundwater system of the Rijnland Water Board. Computations demonstrate that an anticipated relative sea-level rise accelerates the ongoing salt water intrusion to the aquifers. On average, the aquifer will contain much more saline groundwater. More areas will experience higher rates of upward fl ow of groundwater, because the head difference increases between rising mean sea level and surface water levels of subsiding land. In addition, the amount of salt encroaching the low-lying areas increases signifi cantly. Water management sectors like drinking water supply and agriculture will be affected. It is necessary to anticipate on these threats, already in the near future. Various technical measures to compensate the salinization are considered; extraction of saline groundwater seems to be the most feasible one.
