Investigating skimming flow conditions over stepped spillways using particle image velocimetry

Turbulent flow over stepped spillways can be considered the most significant flow that can cause severe problems at the downstream side, near the toe of the structure, such as sediment erosion which normally occurs due to the high amount of water energy. The presence of turbulent flow over the steps can cause cavitation damages due to pressure differences over the steps. The turbulent flow, which is induced at certain times of the year, especially during the flooding seasons, is examined experimentally and numerically in this study. Flow measurements were conducted using Particle Image Velocimetry (PIV) system in a hydraulic flume where the dam break condition is applied in order to achieve the skimming turbulent flow. Two cases of stepped spillways were tested, normal stepped spillways and gabion stepped spillways. For each case, measurements of the instantaneous turbulent velocity field were taken at different locations of the physical models of a slope of (1V:2H). A comparison has been conducted between the gabion and normal steps to assess the required time to attach skimming flow. The results indicated that the presence of the porous media could increase the required time to attach skimming flow.