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Density-dependent 3-D groundwater model “Uitkerkse Polder”

This study aims to predict the effect of surface water level management on the groundwater system with a groundwater model in the “Uitkerkse Polder”, a low-lying area on the coast between Blankenberge and Wenduine (Belgium).  The groundwater system in the Polder consists of a semi-confined sandy aquifer below a top layer of clay and peat.  The groundwater is divided into a superficial freshwater lens on top of a saline groundwater body. The simulation of the salt transport as a result of a surface water level change is part of the study objectives.

A groundwater model was made from the Uitkerkse Polder and the surrounding, topographically higher areas. The model is both a flow model and a transport model to simulate the transport of salts. The higher density of salt against fresh water affects the groundwater head. Therefore, the flow model was made dependent on groundwater density, and thus indirectly of the salt concentration.  The model was calibrated with measured hydraulic head time series and validated with vegetation and discharge data.  Finally, three different scenarios were calculated with the model, where the levels of the surface water system were changed.