Effect of jet air content on 3D plunge pool scour

Plunge pool scour is a widely studied phenomenon in dam engineering because of its damaging effect that can cause structure collapse. High velocity airwater jet originates from a trajectory spillway and causes a plunge pool scour downstream of the structure which has to be evaluated. Presence of air in the jet significantly affects the geometry of the scour hole. The effect of air content in 3D plunge pool scour is investigated in this study. For different jet angles, tailwater levels and discharges, experiments were carried out at the hydraulic laboratory of University of Pisa, Pisa, Italy. A simple experimental setup was prepared where air water mixture was delivered using a circular pipe to a stilling basin comprising of a uniform granular material. Various geometrical parameters and the scour profile of the scour hole were studied. The experimental results in terms of scour geometry and length were compared with those of the respective tests conducted with black water condition. Some useful design deductions were proposed.