Numerical analysis of infiltration in a drained beach

The beach drainage system (BDS) is a 'soft' engineering solution for coastal protection and management. It artificially increases beach permeability by inducing the groundwater table lowering and, consequently, it favours the infiltration of sea water inside the beach. The new hydrodynamic condition would produce a reduction of the offshore sediment transport and the settlement of the suspended load. The present work focuses on a numerical simulation of infiltration processes in drained conditions by using the HYDRUS-2D code. The groundwater flow through a partially saturated porous media is described by using the well-known Richard's equation. Numerical results are then compared with experimental ones obtained during an intensive experimental program performed at the Grosser Wellen-Kanal in Hannover on a BDS prototype. Moreover, different beach permeabilities (ranging from silt to coarse sand) and different drain altimetric positions are numerically simulated. These analyses allow to draw some first considerations about BDS design criteria. In particular, a 'limit drain depth', strictly related to beach permeability, is defined as the maximum depth that produces the maximum water table lowering and, as a consequence, the best system efficacy in drying the porous medium