IMPROVEMENT OF SEDIMENT-CONTROL FUNCTION OF SLIT DAM

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The purpose of this reseach is to improve the efficiency of sediment retention dams with vertical slit-openings.First, characteristics of an couple of isolated vortexes, being generated on the both sides of a slit-opening and giving negative effects to the behavior of water and sediment spilling through the slit-opening, were clarified experimentally. The isolated vortexes were found to reduce the efficient area of spilling flow as well as to reversely transport the sediment toward upstream.Some types of additional structure for reducing the negative effects of the isolated vortexes were considered and addition of one or two couples of vane-type structures to the upstream mouth of the slit-opening was selected as a basic idea of improvement.The efficiency of this measure is tested experimntally by changing the number and geometric dimensions of the structures. As the result, it was proved that those stuctures significantluy promote the development of gully streams in medium and minor flood events and thus increase the retention capacity for heavy sediment run-off by big floods.Finally, based on measurements of three dimensional flow velocity, the influence of the vane-type structures to flow and sediment is investigated in order to understand the results of the above-mentioned tests from hydraulic points of view.