Stepped spillways, as highly effective energy dissipation facilities, have been widely applied in hydraulic engineering. By introducing an inclination angle to the horizontal step surface, either energy dissipation efficiency or sediment transport capacity can be enhanced. The manner and size of vortices within the steps vary with changes in the inclination angle and spillway slope, enhancing energy dissipation through momentum exchange between the main flow and these vortices. This study, drawing upon data in the literature and numerical simulations, investigates the influence of a spillway slope and step inclination angle on the energy dissipation characteristics of inclined stepped spillways. Results indicate that the energy dissipation rate decreases with an increasing spillway slope while increasing with a greater upward inclination of the step’s horizontal surface. However, changes in both parameters show a limiting effect on vortex development. As the spillway slope decreases and the step inclination angle increases, the rate of vortex size expansion diminishes. Finally, an inclination/slope ratio is proposed to characterize the energy dissipation effect of inclined steps, and an empirical formula relating the energy dissipation rate to the relative critical depth, relative spillway height, and inclination/slope ratio is established, with errors controlled within 10%.

Aiming to increase energy dissipation and prevent the cavitation potential of a traditional stepped spillway (TSS) at large unit discharges, a kind of pre-aeration stepped spillway, called a hydraulic-jump-stepped spillway (HJSS), is introduced in this paper. Unlike a TSS, a basin added upstream of the stepped chute in the HJSS plays a vital role in the hydraulic performance owing to the formation of a hydraulic jump in the basin. This paper presents experimental research on the hydraulic performance of the HJSS in comparison to a TSS with the same chute slope (θ = 39.3°) for a wide range of unit discharges, including the flow pattern, energy dissipation, pre-aeration effect, and maximum splash height. The results showed that the HJSS corresponded to a large energy dissipation rate, the air was effectively entrained at the inlet of the stepped chute, and there was an observation of splash formation in the foregoing and downstream steps. Under large unit discharges, the HJSS maintained an energy dissipation rate exceeding 80%. Additionally, at the inlet, the air concentrations reached 4.5% on the bottom and 11.2% on the sidewall. The findings of this research could be used as a general guideline for stepped spillway design with large unit discharges.