The dynamic response of a drainage system of a concrete lined plunge pool due to loading by spillway water jet impact is investigated by use of a numerical model. Despite the primary assumption of a complete impervious concrete liner for the plunge pool, it is consid-ered, that due to presence of cracks and joints in the liner, dynamic pressure of the water jet is propagated within the drainage system which, in turn, may result to further pressure amplification in the drainage pipes. A finite element formulation is used to simulate this phenomenon. Loading of system is generally defined as pressure time-history produced by the water jet, however, regarding to random nature of this loading, a stochastic analysis is employed taking a Power Spectral Density (PSD) function as the input loading. In this way, response of the sys-tem is evaluated in a probabilistic sense. The analysis revealed, that in some regions of the drainage network, amplification of significant order may occur. These high local pressure val-ues can result to high dynamic uplift pressures which may cause local failure of the anchorage system and the concrete slab.