Flow Nonuniformity and Energy Dissipation in Moderate-Sloped Stepped Chutes with a Labyrinth Crest

Abstract

In recent years, the rehabilitation of spillways and design of new dam constructions have considered the combination of a stepped chute with a labyrinth weir crest, highlighting the need for hydraulic information for this specific spillway type. To address currently missing design guidance, a novel study was conducted on a 10.7° round-crested labyrinth weir with a 3H:1V sloped chute with multiple step heights. The results include guidance for estimating flow depths along the chute and selecting a chute wall height; the role of the labyrinth weir on aeration, streamwise and transverse flow uniformity, and general flow patterns; and energy dissipation by the labyrinth crest and by individual steps. It was found that stepped chutes with a labyrinth crest are aerated from the impact of the nappes in the labyrinth outlet cycles, which continued to the chute entrance where the maximum air concentrations and flow depths occurred. The labyrinth crest also generates nonuniform flow patterns and air-water flow properties that have a significant effect on energy dissipation as the nonuniformity and potential drag reduction (due to the stronger aeration) results in less energy dissipated compared with published literature of stepped spillways with linear crests. The present findings provide first guidance for practitioners to combine labyrinth weirs with stepped chutes.