水流对破坏后河床演变的作用

摘要

Riverbed is likely to be damaged in natural conditions or due to human activities.In this paper,the post-damaged river-bed is simplified as a triangular pit and two kinds of flow conditions,clear-water and lived-bed,are considered in flume experi-ments and numerical simulations.Velocity and shear stress at different time around the pit were calculated,demonstrating the causes of evolution combining with experimental results.The result under the clear-water condition shows that the erosion occurs only at the knickpoints of the pit due to shear stress;the phenomenon under the live-bed condition shows that sediments deposit into the pit due to small velocity magnitude,and significant long scour occurs downstream;bed shear stress in local regions is still higher than in uniform flow regions when riverbed reaches an equilibrium state.%河床因自然或人为作用会发生破坏。将破坏后河床地形概化为三角形坑，通过水槽试验和数值模拟研究了清水和动床两种水沙条件下坑形河床的演变。采用垂向二维水流数学模型计算得到了不同时刻下坑周围的流速与河床切应力分布，分析了导致河床演变的原因。研究表明：清水冲刷条件下破坏后河床仅在坑缘口处有冲刷侵蚀，是由于此处强切应力所致；动床冲刷条件下坑内流速很小，坑上游来沙在坑内淤积，同时坑下游边坡长距离冲刷显著；河床演变达到平衡状态时，局部切应力仍大于均匀流切应力。