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1. Introduction
Groundwater constitutes an important water resource, supplying water for domestic, industrial and agricultural uses. One-third of the world’s drinking water is provided by groundwater. Groundwater is not always available when and where needed, especially in water-short areas where heavy use has depleted underground reserves. Groundwater quality is also an important issue. In fact, with the increasing demand for water in most parts of the world and with the intensification of water utilization, the quality problem becomes the limiting factor in the development and management of water resources in many parts of the world. High salinity of groundwater limits its usage for irrigation and drinking purposes unless desalinated or mixed with lower salinity water. The protection of groundwater resources becomes an essential matter under the conditions of increasing demand and decreasing the available resources. The sources of groundwater salinization include: infiltration of saline wastes, return flow from agriculture, evapotranspiration and saltwater intrusion.
Saltwater intrusion is one of the most wide-spread and important processes that degrades groundwater quality by raising the salinity to levels exceeding acceptable drinking water and irrigation standards, and endangers future exploitation of coastal aquifers. Salinization of groundwater is considered one of the main sources of pollution. About 70 percent of the earth’s population lives in coastal areas and 95 percent of the earth’s water lies in the oceans and seas at high levels of salinity (Freeze and Cherry, 1979). These coastal regions face serious hydrological problems such as scarcity of freshwater, contamination of groundwater and seawater intrusion. Excessive pumping has led to a dramatic increase in saltwater intrusion problems.
Freshwater and saltwater are actually miscible fluids and therefore the zone of contact between them takes the form of a transition zone caused by hydrodynamic dispersion. Across this zone, the density of the mixed water varies between that of freshwater to that of seawater. Under certain conditions the width of this zone is relatively small, when compared with the thickness of the aquifer, so that the boundary can be considered as a sharp interface that separates the two regions occupied by the two fluids. In this case the two fluids are assumed to be immiscible. But, if the transition zone is wide this assumption becomes invalid (Bear, 1979). Saltwater intrusion can be...