Groundwater Levels in a Drained Beach in Long and Short Waves Conditions

Drainage of beaches is thought to be a soft engineering solution to counteract erosion. The present work aims to show the response of the groundwater table level when it is influenced by a drain inside the sand, in the vicinity of the shoreline. The knowledge of the water table dynamics helps to identify the role played by the drain, and consequently it is useful to address its function on the overall BDS functioning. The water table dynamics has been mathematically investigated, in presence of both long and short waves. An analytical solution for the Boussinesq equation with long waves and a drainage boundary condition within the porous medium is presented. A VOF numerical tool has been used to study the groundwater table fluctuations driven by the short waves swash. A comparison between the analytical solution and the numerical results in terms of groundwater level has been carried out. The numerical model reproduces the drain-induced dynamics inside the beach. The analytical model, on the other hand, although it is developed under the long wave hypothesis, seems to catch, at least qualitatively, the water table evolution in case of short period regular waves. It enables to think of it as a preliminary evaluation tool for the BDS design.