The Modeling of Salt Water Intrusion
What is Salt Water Intrusion?
Salt water intrusion, or encroachment, is defined by Freeze and Cherry (1979) as the migration of salt water into fresh water aquifers under the influence of groundwater development. Salt water intrusion becomes a problem in coastal areas where fresh water aquifers are hydraulically connected with seawater. When large amounts of fresh water are withdrawn from these aquifers, hydraulic gradients encourage the flow of seawater toward the pumped well or wells. Salt water intrusion is a problem that affects coastal areas around the world. Groundwater Problems in Coastal Areas (Custodio, 1987) is an excellent reference for more information on global salt water intrusion problems, while Atkinson (1986) details salt water intrusion problems for the coastal areas of the United States.
Why is it a Problem?
The encroachment of salt water into fresh water supplies has become cause for concern within the last century as populations in coastal areas have risen sharply and placed greater demands on fresh groundwater reserves. Salt water intrusion causes many problems in these areas, perhaps the most severe being the limitation of potable drinking water. Drinking water standards established by the EPA in 1962 require that drinking water contain no more than 500 mg/L of total suspended solids (TSS), a common measure of salinity (Atkinson, 1986). Seawater contains approximately 30000 mg/L of TSS. Therefore, it is evident that even a small amount of seawater can cause drinking water problems when mixed with fresh water reserves. Also, salinity in irrigation water can be detrimental to agriculture, reducing yields and killing crops with low tolerances to salt. In some cases, conditions may necessitate a change to crops that are more salt tolerant. Salt water has also been shown by Jenki! ns and Moore (1984) to reduce soil erodibility and decrease soil structure and tilth.
How Can it Be Controlled?
The first step in correcting problems with salt water intrusion is to evaluate the size and extent of the problems. This is commonly accomplished by the installation of monitoring wells, which are used to determine the boundaries of the salt/fresh water interface and the rate at which salinity levels are increasing. Using this data and information on the hydrologic and geologic properties of the contaminated aquifer, modeling is often incorporated into problem analysis in order to predict future conditions and to evaluate remediation alternatives.
The Need for Modeling
In the past few decades, modeling has become an important and powerful tool in many branches of science. Models allow engineers and scientists a way to test hypotheses in a manner that is removed and nondestructive to the actual problem at hand. In studies involving salt water intrusion, modeling has been used for many purposes. One common goal of these models is to predict and characterize the movement of...