For a traditional stepped spillway, low energy dissipation and cavitation damage may occur when the unit discharge is larger than a limit due to reduced air entrainment in the flow. In the present work, a new type of stepped spillway called hydraulic-jump-stepped spillway (HJSS) was developed, and the air was efficiently entrained into the flow by means of a hydraulic jump in the aeration basin, which was an aeration element of this stepped spillway. Compared with the traditional stepped spillway, various aspects of the hydraulic performance of the HJSS were experimentally investigated, including the flow pattern, energy dissipation, air entrainment characteristics and time-averaged pressure. Physical model results demonstrated that the HJSS achieved a higher energy dissipation, a more favorable air entrainment performance, and a more reasonable pressure distribution. The HJSS successfully increased the unit discharge from 50–60m²/s for a traditional stepped spillway to 101.47 m²/s.

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%.

A hydraulic-stepped spillway was designed using an aeration basin to provide aerated flow to the stepped spillway utilizing a hydraulic jump. However, the flow through the entrance of the stepped spillway might separate from the first step top and impact the downstream steps at a large unit discharge, causing a so-called jet flow. A new experimental study was conducted to better understand the jet flow in the hydraulic-jump-stepped spillway with comparisons with conventional stepped spillways. The results showed that the critical condition required for the formation of the jet flow was close to the geometric parameters of the upstream aeration basin. Among these parameters, the height of the reverse step had a more significant effect on the local flow pattern, thus lowering the risk of jet flow. The relationships between the critical condition and the geometry of the aeration basin suggested that the Froude number at the entrance of the stepped spillway was the key parameter forming the jet flow. Compared with conventional stepped spillways, the hydraulic-jump-stepped spillway could effectively extend the practical application for large unit discharges by providing a better understanding of jet flow conditions.

Spillway chutes are critical in dam flood control, particularly in high dams where high water heads and large discharge in narrow canyons amplify the demand for safe discharging. For large unit discharges in spillways, aeration protection is essential to prevent cavitation erosion, but challenges arise from air duct choking in the traditional spillway and nonaerated regions in the stepped spillway. This paper introduces a novel spillway called the pre-aerated stilling basin spillway (PSBS). The primary distinction between PSBS and conventional spillways lies in the placement of aeration facilities. Conventional spillways feature a curved transition section that directly connects to the spillway. In contrast, the PSBS is equipped with a WES crest weir and a vertical sill of the same width, which converts supercritical to subcritical flow. This process strongly entrains air through hydraulic jumps at spillway entrances, thereby preventing cavitation damage. The study aims to experimentally investigate the flow regime, energy dissipation within the PSB, and the near-wall air concentration to ensure effective mitigation of cavitation damage downstream. The findings highlight the impact of the PSB on changing the jump type and relative local energy loss, influenced by the incoming Froude number, sill height, and sill length. Influenced by these factors, the variation in air concentration is crucial for reducing cavitation damage, necessitating potential adjustments in prototype applications to account for scale effects. Under such a pre-aeration approach, the air concentration along the downstream spillway warrants further investigation for the continuous optimization of the PSB’s design and its integration with spillways.

Downstream of the sluice gate or weir, wave-type flows inevitably occur in stilling basins with no tailwater. This paper aims to investigate the hydraulic performance of wave-type flows at a sill-controlled stilling basin through experimental research. The flow pattern, bottom pressure profiles along the stilling basin, and the air concentrations on the bottom and the sidewall were examined in five sill-controlled stilling basins by altering the sill position and the height. The results show that wave-type flow patterns contain submerged and non-submerged jumps, which are relevant to ambient pressure head and air entrainment. The bottom pressure profiles are related to larger pressure fluctuations at large unit discharges and two peak pressure values in the vicinity of the sill. The air concentrations on the bottom and the sidewall decrease with the increasing unit discharge. The flow zone in the vicinity of the sill should be focused upon concerning protection against cavitation damage because of the slight air entrainment and significant pressure fluctuations. These findings advance our understanding of wave-type flows, and their ambient pressure heads and air entrainment are useful for designing the sill-controlled stilling basin in hydraulic engineering.