Salt water intrusion in a three-dimensional groundwater system in the Netherlands: A numerical study

Salt water intrusion is investigated in a coastal groundwater system in the northern part of the province Noord-Holland, The Netherlands. Density depe ndent groundwater flow is modeled in three-dimensions with MOCDENS3D. This computer code is a version of MOC3D (Konikow et al., 1996) that has been ad apted to simulate transient density-driven groundwater flow. Results from t he model suggests that in this Dutch hydrogeologic system a severe and irre versible salinisation is already occurring. Within a few tens to hundreds o f years, the salinity of the shallow aquifer is estimated to increase subst antially. This salinisation process is a result of human activities such as the reclamation of the low-lying areas during the past centuries. Without changing the present boundary conditions, seepage into the low-lying areas will decrease slightly because of predicted increases in groundwater salini ty. However, the rate in salt load through the Holocene aquitard into the l ow-lying areas will increase significantly due to an increase in salinity i n the shallow aquifer. In addition, a relative sea level rise of 0.5 m per century will intensify the salinisation process, causing an enormous increa se in salt load in all low-lying areas in this part of The Netherlands.