Modeling Coastal Ground-Water Response to Beach Dewatering

Abstract
There has been renewed interest in the use of beach dewatering as a technique to combat beach erosion. Although several test and prototype installations have been undertaken worldwide, no guidelines are available to aid the engineering design of such projects. In this paper, we present a numerical model that simulates two-dimensional ground water flow in a coastal aquifer under beach drainage, including water table lowering and seepage face reduction. The boundary element method is applied to solve the Laplace equation for the velocity potential. An internal boundary is used to simulate drainage. We conducted simulations for two different types of drainage systems, i.e., artificial and gravity drainage. The behavior of the water table from the simulations was found to be consistent with field observations. The results also showed that the location and size of the drain affect the efficiency of the drainage system. The system efficiency slightly increases with the size and vertical elevation of the drain. As the drain is shifted landward, the system becomes considerably less efficient. Although they do not represent design criteria, these results indicate considerations which affect the performance of beach dewatering system.