Enhancing flow aeration on an embankment sloped stepped spillway using a labyrinth weir

This study presents for the first time a detailed laboratory investigation on the influence of a labyrinth weir as an aerator and corresponding effects on the air-water flow properties in a moderate-sloping (3H:1V) stepped chute. For comparison, an identical study was conducted with a broad-crested weir. All experiments included two near-prototype scale step heights (0.1 m and 0.2 m) and were conducted for a wide range of flow conditions (0.6 <= dc/h <= 3.1) with conductivity probe measurements at half and quarter distances from the side walls. It was observed that the labyrinth significantly modified the flow entering the chute, generated non-uniform flow patterns and enhanced air entrainment immediately downstream of the weir; no clearwater region was present. Air-water flow properties downstream of the labyrinth weir exhibited larger transverse variability that diminished in the streamwise direction. The labyrinth weir produced higher mean air concentrations, increased bubble count rates with smaller bubble sizes, and caused additional bubble property differences, thereby increasing the interfacial area and enhancing air-water mass transfer or re-aeration efficiency relative to the broad-crested weir case.