Fluctuanting pressure at the bottom of a plunge pool

The paper describes the results of a laboratory set of experiments made to investigate the pressure fluctuation field on beneath of a plunge pool subjected to jet impingement. As an example this phenomenon takes commonly place in the case of the drop structure, where the elevation reduces with a take off and impinging portion. When the downstream bottom is nearly horizontal and made of concrete or rock, there is no significant scour, and the drop is followed by a stilling basin where the hydraulic jump takes place. The relevance of the topic is related to the structural design of the linings of the dissipation basin downstream barrages or check dams. Nevertheless the knowledge of the stresses at the basis of plunge pool dissipation basins can be useful to predict a localized erosion process. With reference to the specific case of the prototype of a dam spillway and downstream energy dissipation basin, we discuss the effect of a variable water cushion depth on the reduction of the severe pressure fluctuations that take place at the bottom of the stilling basin. The experiments are made on a 1:40 laboratory model, recording the dynamic behavior of pressure fluctuations in a set of different positions on beneath the plunge pool. The experimental results presented in dimensionless form, give a better understanding of the fluctuating pressure reduction that can be obtained increasing the cushion depth.