不同水沙条件下顺直型河道交错边滩演变规律

顺直型河道在自然河流演变中常常形成典型的具有犬牙交错形状的边滩地形,在不同水河条件的河流中,边滩发育演变情况各不相同,为了研究水沙条件对其演变的具体影响,利用室内概化模型试验,研究了顺直型河道交错边滩在不同水沙条件下演变的规律。试验发现:①上游来沙减少后,河段内交错边滩的面积及尺寸相应减小,交错边滩之间的间距也会缩短。②顺直型河段交错边滩的下移速度随上游来沙减少而减缓;其主要原因是大沙组情况下滩尾淤积,压缩附近的主槽主流,继而造成对岸下游的边滩头部冲刷下移,清水组情况下滩尾淤积的泥沙较少,该现象相应减弱。③顺直型河道在大沙条件下表现出冲滩淤槽的趋势,河道逐渐被“抹平”,滩槽差异缩小。④随着上游来沙的减少,河道主槽开始冲刷,在抗冲性较强的边界旁,主河道会顶冲河岸下切出深槽,滩槽更加分明,在交错边滩下移的同时,靠岸的深槽往往不会被填平,形成“倒套”。

Evolution of Alternate Bars in Straight Channel under Different Discharge and Sediment Conditions

The evolution of alternate bars in straight channel under different discharge and sediment conditions was studied in this research via generalized flume model experiment. The conclusions are as follows: (1) The area and size of alternate bars in straight channel declined with the reduction of sediment load from the upstream, and simultaneously the spacing between bars became shorter. (2) The downward movement speed of alternate bars decreased as the sediment load from the upstream decreased. In the case of large sediment load supplied from the upstream, siltation at the end of bars compressed the mainstream nearby, thus causing the beachhead of the opposite bank to move downstream. Such phenomenon was weakened when the sediment supplied from the upstream reduced. (3) In the presence of large sediment load from the upstream, the alternate bars were scoured although the principal channel was in deposition. With the reduction of sediment load supplied from the upstream, the channel was scoured instead. The deep trough which was close to the river bank sometimes would not be filled when alternate bars moved downstream, leading to the formation of inverted watercourse.