Abstract
Movable weirs have been developed to address the weaknesses of conventional fixed weirs. However, the structures for riverbed protection downstream of movable weirs are designed using the criteria of fixed weirs in most cases, and these applications cause problems, such as scour and deformation of structures, due to misunderstanding the difference between different types of structures. In this study, a hydraulic experiment was conducted to examine weir type-specific hydraulic phenomena, compare hydraulic jumps and downstream flow characteristics according to different weir types, and analyze hydraulic characteristics, such as changes in water levels, velocities and energy. Additionally, to control the flow generated by a sluice gate, energy dissipators were examined herein for their effectiveness in relation to different installation locations and heights. As a result, it was found that although sluice gates generated hydraulic jumps similar to those of fixed weirs, their downstream supercritical flow increased to eventually elongate the overall hydraulic jumps. In energy dissipator installation, installation heights were found to be sensitive to energy dissipation. The most effective energy dissipator height was 10% of the downstream free surface water depth in this experiment. Based on these findings, it seems desirable to use energy dissipators to reduce energy, as such dissipators were found to be effective in reducing hydraulic jumps and protecting the riverbed under sluice gates.
Highlights
Weirs are structures installed across rivers in order to raise water levels and prevent backward water flow for efficient water intake and waterway use
This study examined the flow characteristics variation according to sluice gate-type movable weir operation and downstream water level conditions as well as hydraulic jump, changes in their lengths and energy variation
The hydraulic jump lengths were divided by the water depth h1 in the supercritical flow region before the hydraulic jump phenomenon occurred to generalize the hydraulic jump lengths
Summary
Weirs are structures installed across rivers in order to raise water levels and prevent backward water flow for efficient water intake and waterway use. The concrete gravity dam (CGD) was a frequently utilied weir type for water overflow weirs. The CGD slows water inflow from upstream before reaching a weir and allows it to flow over the weir. The flow velocity falls and inflowing silt is deposited. In this manner, the water storage capacity decreases and weirs lose their initial effectiveness. Efforts have been made to develop various movable weirs to reduce such sedimentation processes and fulfil their original purposes for the long term. Concerning movable weirs, there is a turning gate-type movable weir, which turns a weir to discharge silt sedimentation, and a sluice gate-type weir, which lifts a weir to do so [1,2,3]
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