Using a subsurface barrier to control seawater intrusion and enhance groundwater extraction in coastal aquifers: An analytical study

Abstract

Previous 3D studies on the effectiveness of subsurface barriers against seawater intrusion in coastal aquifers have been largely limited to numerical models, lacking analytical methods that are easy to implement and computationally efficient. This study presents an analytical methodology, based on the Schwartz-Christoffel conformal mapping method and the potential theory, for predicting the extent of seawater intrusion and the maximum safe extraction rate of a single well in a head-controlled, rectangular coastal aquifer with the addition of a subsurface physical barrier. The barrier is assumed to fully penetrate the aquifer depth and has a finite length in the shore-parallel direction. Consistency between analytical and numerical results highlights the capability of the proposed method to predict the steady-state toe position and the maximum safe extraction rate. The sensitivity analysis indicates that, for a given barrier length, the optimal barrier location (i.e., distance to the coastline) depends on the aquifer conditions (i.e., dispersivity, hydraulic gradient, and the thickness of the aquifer), in terms of the effectiveness of fully penetrating barriers in reducing the extent of seawater intrusion. Whereas the fully penetrating barriers that are longer and closer to the extraction well are always more effective in enhancing the maximum safe extraction rate, independent of aquifer conditions. The presented methodology provides a simple analytical tool for first-order assessment of seawater wedge extents and safe extraction rates in response to engineered barriers in coastal aquifers, serving as an alternative to 3D numerical modeling.