Energy dissipation and air entrainment on stepped spillways with non-uniform cavity sizes

An experimental study was conducted on a large size stepped spillway model with a moderate slope (26.6o) for a range of discharges between 0.020 and 0.237 m/s. In some experiments, the stepped chute was equipped with uniform steps of 5 and 10 cm heights respectively. In addition several non-uniform configurations with combinations of 5 and 10 cm high steps were investigated. For each configuration, the air-water flow properties were measured for several discharges. The study yielded some challenging outcomes in terms of energy dissipation and aeration on stepped spillways with non-uniform cavity sizes. A comparative analysis with the stepped spillways with uniform step heights showed that the energy dissipation rate, the residual head, the flow resistance and the mean air concentration were close for all geometries. This might be used for the design of prototype spillways with non-uniform step heights, but the flow pattern of the non-uniform step configurations showed some instabilities. A stepped spillway design with uniform step heights is the preferable design option.