Modeling and analysis of seawater intrusion in the coastal aquifer of eastern Cap-Bon, Tunisia

A numerical model that treats density-dependent variably saturated flow and miscible salt transport is used to investigate the occurrence of seawater intrusion in the 'Korba' aquifer of the eastern coast of Cap-Bon in norther n Tunisia. We examine the interplay between pumping regimes and recharge sc enarios and its effect on the saline water distribution. More localized sim ulations are used to examine, in vertical cross sections, the effects of we ll location and soil type and the role of the vadose zone in possible remed iation actions. The exploratory simulations suggest interesting interaction s between the unsaturated zone and the saltwater-freshwater interface with possible implications for groundwater exploitation from shallow unconfined coastal aquifers, involving in one case feedback between seawater intrusion and the high pressure head gradients around the pumping-induced drawdown c one and in another case threshold-like interface displacement for tight soi ls such as clays. The data processing steps undertaken in this GIS and mode ling study are described in some detail, and a critical assessment is given of the data availability and of the requirements for successful monitoring and modeling of seawater intrusion risks in heavily exploited coastal aqui fers such as those found in the semi-arid regions of the Mediterranean basi n. It is shown how, with the aid of GIS, reasonably reliable information ca n be assembled from maps, surveys, and other sources of geospatial and hydr ogeological data, an approach that is necessary in the many regions of the world with acute water resource problems but with limited means for underta king systematic data acquisition and environmental monitoring actions. None theless the need for more concerted monitoring of relevant parameters and p rocesses and of closer coordination between monitoring and modeling is stre ssed. An idea of the extent of over-exploitation of the Korba aquifer is ob tained by examining the pumping and rainfall/infiltration data, and the sim ulation results support groundwater pumping as the mechanism for and seawat er intrusion as the origin of the salt contamination observed in the soils and subsurface waters of the Korba plain.