Self‐Aeration of Supercritical Water Flow Rushing Down Artificial Vegetated Stepped Chutes

Abstract

AbstractVegetation flow is commonly studied for subcritical flow motions, while in supercritical flow, the presence of vegetation often leads to enhancement of flow self‐aeration, which would in turn alter the flow hydraulics and water‐plant interaction. This paper presents an experimental investigation of aerated water flow cascading down a vegetated stepped chute. The 21.8° sloping chute is equipped with a 12‐m‐long uniformly stepped invert section. The 0.12‐m‐high steps have grate‐shaped rough top surface covered by 0.07‐m‐high flexible artificial plants, and three vegetation densities are tested in skimming flows, in addition to the reference cases of smooth steps and rough steps covered by bare grate only. The air‐water flow properties and free‐surface fluctuations are systematically measured from the upstream clear‐water region to the downstream fully developed aerated region. The experiment results demonstrate that, compared to a man‐made concrete stepped chute, the presence of vegetation cover on the steps reduces the overall self‐aeration and unsteady fluctuating motions of the flow, while it enhances the dissipation of the flow kinetic energy. The present finding also suggests that the modification to flow aeration and energy loss in the vegetated flow over macrostep‐shaped roughness is dependent on the flow regime which is primarily determined by the flow rate for a given slope and step‐induced macroroughness height.