Aeration, Flow Instabilities, and Residual Energy on Pooled Stepped Spillways of Embankment Dams

Air-water flow experiments were conducted on some flat and pooled stepped spillways with slopes of 8.9 degrees and 26.6 degrees in transition and skimming flows. The study comprised the observations of the flow patterns, characteristic air-water flow properties, and energy dissipation performances. The air-water flow properties showed some differences in terms of interfacial velocity, bubble count rate, and turbulence intensity between the stepped chutes for the two channel slopes. These differences were also reflected in the residual energy data, highlighting a better energy dissipation rate for the pooled stepped spillway with slope of 8.9 degrees. However, the aerated flows on the pooled stepped spillways exhibited some hydrodynamic instabilities, and a safe operation must be tested in physical models. The flat stepped spillway appeared to be the preferable design in terms of energy dissipation and flow stability.