MODELING THE EFFECTS OF SALT-WATER-INTRUSION DYNAMICS FOR A COASTAL KARSTIFIED BLOCK CONNECTED TO A DETRITAL AQUIFER

The contamination by salt-water intrusion affecting the coastal aquifer at Castell de Ferro (Granada, Spain) is especially influenced by the coexistence of two coastline lithological formations with highly differing transmissivity (highly karstified limestones and detrital sediments). Despite not having a very high intrusion volume (0.1-0.2 hm(3)/year), the aquifer does have a high saline content. In order to explain this phenomenon, we first of all modeled the ground-water flow (MODFLOW) in the aquifer. Two models were then used for the fresh-water/salt-water contact: one assuming a sharp interface (BADON2) and the other taking into account density-dependent mass transport (MOCDENSE). Our conclusion is that the high saline content of the aquifer is due to the existence of a preferential route for ground-water now through the karstified materials in contact with the detrital materials and the sea. The detrital materials located beside the karstified massif therefore constitute the route for only 10%-20% of the system's total outlet to the sea, which is not enough water to wash the salts resulting from salt-water intrusion. We also find that in this type of aquifer two-dimensional transport models do not provide the most realistic results, since the effect in a direction transverse to the ground-water flow of very transmissive material cannot be simulated in this type of profile. In this case, and despite its limitations, better results are obtained using the sharp interface model.