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INTRODUCTION
One-third of the world's drinking water is provided by groundwater. Groundwater is considered the main water source in many coastal regions. Population growth increases water requirements, which increases pumping from aquifers. Saltwater is common in coastal aquifers where the aquifers are in direct contact with the sea (Bear et al. 1999). Saltwater intrusion affects groundwater resources, soil salinity, agricultural productivity and quality in the coastal zone. This may lead to mass migration of farmers looking for jobs somewhere else (El Raey 2009).
Climate change has already increased the mean sea level during the last century by 10-20 mm/yr (IPCC 1996). Future sea-level rise due to climate change is expected to be between 20 and 88 mm/yr (IPCC 2001). The long-term effect of climate change and sea-level rise on saltwater intrusion should be considered. Population growth and continuous development require larger quantities of water, which increases the net abstraction from aquifers to secure the water demand. It is necessary to protect limited resources from saltwater intrusion and other pollutants. The concentration of people in coastal regions and increased related activities has increased the abstraction of groundwater, and this has led to the movement of saltwater toward aquifers and increased the salinity of groundwater. Higher salinity of groundwater limits its usage for irrigation and drinking purposes unless desalinated or mixed with lower salinity water (Abd-Elhamid 2010).
Analytical and numerical models have been used to predict the location and movement of the saltwater/freshwater interface. The numerical models can be categorized as sharp interface models or diffusive (dispersive) interface models. The first attempt at simulating seawater intrusion was introduced by Ghyben (1889) and Herzberg (1901). This model is known as the Ghyben-Herzberg model, which assumes that saltwater and freshwater are immiscible and separated by a sharp interface. Henry (1959) presented a numerical solution of steady saltwater intrusion into a coastal aquifer based on a sharp interface assumption. Henry (1964) developed the first analytical solution including the effect of dispersion in a confined aquifer under steady-state conditions. Henry's problem was later solved by Lee & Cheng (1974) in terms of stream functions. Segol et al. (1975) developed the first transient solution based on a velocity-dependent dispersion coefficient. Numerous other researchers, such as Pinder & Cooper (1970), Frind (1982) and...