The paper deals with the analysis of the groundwater flow in a drained beach. Infiltration processes in static conditions (without running waves) are numerically simulated by using the \textit{HYDRUS-2D} software.\\ Nevertheless field and laboratory experiences give the possibility to study the influence of the system on both nearshore hydrodynamics and morphodynamics, a numerical model, able to reproduce the drainage main physical processes, is fundamental in order to define the main 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 Beach Drainage System (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.