Inside a beach drainage system: A tridimensional modeling

The capabilities of Computational Fluid Dynamics (CFD) to investigate detailed aspects of a physical phenomenon are here used to study the drainage efficiency of a Beach Drainage System (BDS), namely a low-environmental impact tool for shoreline stabilization. Since its controversial performances, a specific and detailed analysis is needed to investigate the performances of BDS. In this regard, the CFD could be an ally to physical modeling with its flexibility. Furthermore, perhaps the most notable of the advantages is its capability to investigate aspects that otherwise it would have been more difficult to measure experimentally. In order to focus the attention on what happens during the percolation inside the drain, a simplified domain is taken into account in order to achieve the tridimensional modeling of filtering phenomenon inside a perforated pipe by means of the OpenFOAM® solver IHFOAM. It solves the volume-averaged Reynolds-averaged Navier–Stokes (VARANS) equations to simulate flow through fine porous media such as the one in a sandy beach. A parametric study has been carried out, with respect to the porous medium and the draining surface characteristics as well as the flow regime inside the BDS. Different solutions on the draining surface are considered, namely different arrangements of the holes within the water flows through. This work aims at investigating the influence on the drainage performances when an oscillating groundwater level (simulating the swash infiltration) is considered. A comparative analysis shows that the finer the sand (lower permeability), the less the draining pattern (i.e. the extent of the perforated surface over the whole surface of the pipe) counts. Results show a good efficiency of the drainage system, that can be addressed, for a given permeability, not only to the conveyed discharge, but also to the hydraulic regime inside the pipe, resulting in a more spread draining surface.