Author(s): Youichi Yasuda; Keito Masui
Linked Author(s): Youichi Yasuda
Keywords: Energy dissipator; Stacked Boulders; Surface jet flow; Drop structure; Mainstream position
Abstract: For the jump formation just below low drop structures during flood stages, a main flow is located near the bottom, and it might be easy to form local scouring at the downstream of the apron with protection blocks. This might be caused by the curvature of streamline due to the impingement of main flow, and the maximum velocity with high turbulence near the bottom continues far downstream. The protection of river bed against the main flow with high turbulence is not secured by the jump formation. In this study, a sloping energy dissipator installed below low drop structure was proposed. The dissipator has gentle slope (i.e., 1/10 to 1/20 slopes) with stacked boulders. The function may help for both lifting a main flow and preventing local scouring. It is possible to form a surface jet flow without a plunging even if the tailwater level is lower. Also, the formation of the surface jet flow has a high turbulence in the main flow. The flow velocity at water side is lower than that at center part. The velocity measurement yields that the maximum velocity at each vertical section decays in a short distance. For different discharges, tailwater levels, relative drop heights, and inflow conditions, hydraulic conditions required to form a surface jet flow have been made clear. For the formation of surface jet flow, distribution of turbulent intensity at the end of the slope has been discussed from the view point of protection of riverbed.
Year: 2020