The Effects of Uncertainty on a Ground Water Management Problem Involving Saltwater Intrusion

摘要

Ground water is an important water supply source for many coastal communities. Significant ground water extraction can lead to landward migration of the saltwater-freshwater interface, which can contaminate the water supply. It is therefore important to consider the potential for saltwater intrusion when developing a ground water management plan in coastal regions. An important tool in analyzing such problems is the numerical model which can predict water levels, ground water flow, and the location of the salt-water interface given a particular pumping regime. Such models require knowledge of hydraulic parameters for each aquifer. Imprecise specification of these parameters can lead to inaccurate results and it is therefore important to evaluate the effect of uncertainty in model parameters. Because the hydraulic conductivity of an aquifer is critically important for predicting the location of the saltwater- freshwater interface, it is a major source of uncertainty in ground water analysis.Here we investigate two types of uncertainty in the context of ground water management problems: (1) modeler's uncertainty reflects inaccurate estimation of mean hydraulic conductivity, and (2) spatial variability reflects our inability to adequately characterize the spatially heterogeneous distribution of hydraulic conductivity at an appropriate scale for precise modeling. Both types of uncertainty are investigated by developing a ground water management problem based on a coastal aquifer on Cape Cod, Massachusetts. The management problem seeks to minimize the threat of saltwater intrusion while meeting the water supply demands of the community. The two types of uncertainty are shown to have different and substantial effects on optimal management designs. These results illustrate the importance of considering uncertainty in determining ground water management solutions in a coastal aquifer environment.