Simulations of evolution of salt-water distribution in young dunes near the French-Belgian border
Van Meir, N.; Lebbe, L. (1999). Simulations of evolution of salt-water distribution in young dunes near the French-Belgian border. Natuurwet. Tijdschr. 79(1-4): 105-113
In: Natuurwetenschappelijk Tijdschrift. L. Walschot/Natuur- en Geneeskundige Vennootschap: Gent. ISSN 0770-1748, more
Also appears in:
De Breuck, W.; Walschot, L. (Ed.) (1999). Proceedings of the 15th Salt-Water Intrusion Meeting Ghent (Belgium), 25-29 May 1998. Natuurwetenschappelijk Tijdschrift, 79(1-4). Natuurwetenschappelijk Tijdschrift: Gent. 307 pp., more
A part of the Holocene evolution of the groundwater flow and distribution in the young dunes near the French-Belgian border is simulated in a cross-section perpendicular to the coastline by the model of Konikow and Bredehoeft. This model was adapted so that the groundwater flow is density dependent. The schematization of the groundwater reservoir is based on a detailed lithostratigraphical study. In the phreatic aquifer a number of discontinuous semi-pervious layers occur. The presence of these layers along with the geomorphologic history of the dunes and the surrounding areas result in a rather complex evolution of the treshening of the unconfined aquifer The simulation starts after the formation of the old dunes some 3000 years ago. Under a 900 m-wide dune ridge a fresh-water lens grows until it reaches the impervious substratum. After five hundred years the fresh-water lens almost reaches a dynamic equilibrium. Under the shore a fresh-water tongue is formed between the salt-water lens in the upper part of the aquifer and the salt-water foot in the lower part of the aquifer under the backshore. Under the tidal-flat area situated north of the old dunes there is seepage of fresh and salt water. Between A.D. 700 and 1280 the dune ridge enlarged gradually landward due to sand transport over the adjacent tidal-flat area. At the same time the remaining tidal-flat area was reclaimed as polders. So, the area where fresh water infiltrates gradually enlarged while the drainage level in the polder area gradually lowered. During this time the pervious layers under the dune area rapidly freshened. The freshening of the semi-previous layers under the dunes is considerably slower. Finally, the flow of salt water trom the polder area towards the dune area due to an overexploitation of the unconfined aquifer in the dune area is simulated.
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