Seawater Intrusion in Layered Aquifers

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Abstract
Seawater intrusion beneath a semipervious layer in a two‐layer coastal aquifer system is described. Freshwater can occur beneath the aquitard because of the head losses induced by upward flow through the semipervious layer. A steady state Dupuit model is formulated to predict the piezometric head variation landward of and above the intruding seawater. Exact solutions are given for the landward head variation, but a numerical solution is necessary for the zone above the intruding seawater. The mathematical model is compared to experimental results of a Hele‐Shaw model study of Long Island, New York. The analysis provides reasonable predictions of the shape of the interface between freshwater and seawater, but the location of the toe of the seawater wedge is inadequately described, apparently because of regional flow conditions on the island that are not simulated in the analysis.