Study on stilling basin with step-down floor for energy dissipation of hydraulic jump in high dams

A new type of stilling basin with step-down floor for enhancing the energy dissipation of hydraulic jump in Xiangiaba Project is studied in model test.It is found that the step-down results in remarkable decrease of flow velocity and pulsating pressure acting on the floor,but at the same time,it affects the stabilization of flow regime in stilling basin.Series of model test with various heights of step are carried out to find out the optimal design for the Project.It also found that the energy dissipation efficiency is enhanced when the outlet sections of spillway and mid-level sluice are moderately contracted.