Subsurface Seawater Intrusion Barrier Analysis

Abstract

Seawater intrusion barriers are currently being constructed in the coastal aquifers of Japan based on the results of a computer model employing finite difference numerical techniques. This model provides a practical design and management tool for predicting the likelihood of seawater intrusion through a semipervious subsurface barrier in an unconfined coastal aquifer. The analysis assumes an abrupt interface, the Dupuit approximations, and various simplifying boundary conditions. The movements of both the water table and the freshwater-saltwater interface are numerically simulated in the unsteady state. The computed results are validated with observations obtained from a vertical two-dimensional sand box model. The application of the computer model is illustrated by a site-specific analysis for a proposed subsurface barrier location in a limestone coastal aquifer on Okinawa-jima Island in the Western Pacific Ocean. From this analysis, it is found that the subsurface barrier is able to delay seawater intrusion for about 2 mo under critical conditions of continual pumping of the aquifer without recharge. The subsurface barrier is technically feasible and is a viable solution to the problem of seawater intrusion in coastal aquifers.