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

Hydrogeologie van het duingebied tussen Koksijde en Oostduinkerke

The lithology of the unconfined aquifer between Koksijde and Oostduinkerke have been deduced from well logs. From a pumping test a value of 340 m2/d was obtained for the transmissivity and 3.10-3 for the elastic storage coefficient. Analyses of water samples indicated that the groundwater contains more salt near the water catchment than to north of it. Geo-electric well logging has shown the presence of fresh water over the entire thickness of the aquifer at the high-tide line. The groundwater currents have been computed by means of a mathematical model for two cases of a groundwater extraction of 1,5 million m3 per year

The role of hydrogeological research in the realization of a combined pumping and deep infiltration system at the excavation ‘Duinenabdij’

Hydrogeological interventions in ecologically valuable areas must be well studied beforehand. Modelling of these interventions based on field observations and field studies is herein a valuable step. This is illustrated with an example in the western Belgian coastal plain. A new drainage system had to be designed for the preservation of the archaeological excavation site ‘OLV Ten Duinen’. This site is situated in a valuable and protected dune area. A system of pumping and deep infiltration of water was studied to optimise the draining of the site but to minimise the effects in the nearby dunes. A double pumping test was used to derive the relevant parameters. These were then used to simulate and find the optimal configuration of the extraction and deep infiltration wells

Modeling of historical evolution of salt water distribution in the phreatic aquifer in and around the silted up Zwin estuary mouth (Flanders, Belgium)

The evolution of the salt-water distribution around the Zwin estuary mouth is modeled for a period of about five centuries. The modeled area is situated in the Flemisch coastal plain near the border of The Netherlands and Belgium. The Zwin estuary is the former waterway to the medieval seaports of Bruges and Damme. During the considered period this alluvial estuary silted up and the modeled area changes from an area around a tidal channel, over a mud flat to a rather complex polder dune area. The evolution is simulated by the 3D density depended groundwater flow model MOCDENS3D (Lebbe & Oude Essink, 1999). The row direction of the applied finite-difference grid is parallel to the present coast line. The simulation is based on old paintings and a large number of maps which allow a relatively detailed reconstruction of the evolution of the landscape. The results show the historical evolution of a large number of different inverse density problems in this area