IMPROVEMENT OF SEDIMENT-CONTROL FUNCTION OF SLIT DAM

本研究的目的是提高垂直开缝挡沙坝的效率。首先，通过实验澄清了在开缝两侧产生的一对孤立涡的特性，这些涡对水和泥沙通过开缝的溢出行为产生了负面影响。孤立涡不仅减少了溢出流的有效面积，而且使泥沙逆流而上。考虑了一些类型的附加结构来减少孤立涡的负面影响，并选择在狭缝开口的上游口增加一到两对叶片型结构作为改进的基本思路。通过改变结构的数量和几何尺寸，验证了该方法的有效性。结果表明，这些结构在中小洪水事件中显著促进了沟流的发育，从而增加了对大洪水大沙径流的截留能力。最后，在三维流速测量的基础上，研究了叶片式结构对水流和泥沙的影响，以期从水力学角度理解上述试验结果。

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.