推移质翻越低坝输移特性的试验研究

Experimental study on characteristics of bed load transport over low-head, run-of-river dams

对于山区河流低坝而言,平时淤积在坝前的推移质粗沙可能会在洪水期集中翻越坝顶,形成高强度输沙。本文开展水槽试验,研究推移质粗沙自上游起动、推进、再翻越坝顶后向下游输移的过程,分析了输沙参数的变化特性及数理规律,描述了翻坝输沙模式及运动特征,揭示了输沙规律与河床形态之间的自然联系。取得如下认识:①输沙量随时间大致以幂函数规律增长。②低坝附近区域河床形态终将趋于稳定,上游和下游均形成相对稳定的曲面斜坡淤积体。③在不同的水流强度下推移质翻坝输移模式存在差异。对于一般水流强度工况,上游淤积体曲面斜坡表面泥沙颗粒以滚动或滑动模式起动,推移至接近坝顶位置时再跃移翻坝,后向下游输移;对于更高水流强度工况,后期的翻坝输沙模式可能发生显著转变,周期性边壁漩涡成为翻坝输沙的主要动力来源。

During flood period,the bed load deposited behind a run-of-river dam on a mountain river could be carried over the dam crest by the flow which would intensify sediment transport. In this study,flume experiments are conducted to reveal the transport process of bed load from upstream to downstream after starting,advancing,and then over the top of a dam. This study analyzes the variation and mathematics of sediment transport parameters;describes the over-dam sediment transport model and its movement characteristics;and clarifies the natural relationship between sediment transport rule and riverbed morphology. In general,the findings of this study are:(1) The relationship between the volume of sediment transport and time can be expressed using a power function;(2) The morphology of riverbed around the dam will stabilize,and form stable curved slope deposits in the upstream and downstream;(3) The over-dam transport modes of bed load are distinct under different flow intensities. For general flow intensities,sediment particles roll or slide on the curved slope surface of the upstream sediment body at the beginning. When they are close to the dam,they are carried over the dam crest by the flow and transported to the downstream. For higher flow intensities,the later over-dam transport mode could change significantly. Specifically,the periodic edge-wall vortex is the key driver of over-dam sediment transport.