This paper deals with the analysis of the groundwater flow on a drained beach. Infiltration processes in static conditions (without running waves) are numerically simulated by using HYDRUS-2D software. Nevertheless, field and laboratory experiments show the possibility of studying the influence of the system on both nearshore hydrodynamics and morphodynamics using a numerical model able to reproduce the drainage main physical processes. It is fundamental in order to define the main Beach Drainage System (BDS) design criteria which, to date, are not yet defined. The groundwater flow through a partially saturated porous media is described using Richard's equation. Numerical results are then compared with the experimental ones obtained during an intensive experimental program performed on a BDS prototype at the GrosserWellen Kanal (GWK) in Hannover. In particular, the study focuses on the BDS influence on the groundwater table inside the beach and drained flows.