The subterranean flow of fresh and salt water underneath the western Belgian beach

On the gently sloping sandy runnel and ridge beach thirty holes were drilled through the unconfined aquifer. The unconfined aquifer consists of a complex of permeable and semi-permeable layers with a thickness of about 30 m. In each of the boreholes a resistivity logging was performed. The resistivity logging thus obtained provide a fairly good idea of the fresh, brackish and salt water distribution underneath the beach. Five resistivity profiles perpendicular to the shore line were drawn. At one of these profiles the hydraulic head pattern has b pen measured continuously inthe upper and the lower part of the aquifer. From these piezometers groundwater has been sampled for determining the mean anion- and kation concentrations. Based on these data a mathematical model, which describes the flow of fresh and salt water has been developed

Density dependent groundwater flow model of the shore and dune area of the Westhoek nature reserve (Belgium)

The Westhoek nature reserve is a dune area situated along the French-Belgian border. Below the dunes a fresh-water lens is found. A particular distribution of salt-water occurring above fresh-water is found under the adjacent shore. This less known water quality distribution is in dynamic equilibrium. A 2D density dependent groundwater flow model was made using the MOCDENS3D code. First, the groundwater flow and water quality evolution under the shore and in the dunes are modeled. Then the possible impact of sea level rise is simulated for a number of different scenarios. These scenarios reflect different reactions of coastal morphology and human intervention on the sea level rise. Depending on the scenario, the extent of the shore's salt-water lens can increase, decrease or even completely disappear. Simultaneously, the extent of the dune's fresh-water lens can significantly be altered. The simulations illustrate also, besides the effects of sea level rise, that changes in boundary conditions (drainage levels, shore morphology, sea water level), either natural or human induced, can importantly alter the water quality distribution. Because of the high ecological value of the area and the dune's importance for drinking water production, these changes should be well studied beforehand