河流冲刷过程中表层床沙粗化对不平衡输沙的影响

Effect of Coarsening Surface Bed Material on Non-Equilibrium Sediment Transport Process during River Degradation

在分析前人的不平衡输沙研究成果的基础上 ,针对非均匀沙河床 ,提出了床沙交换速率的新物理概念 ,计算研究了不同床沙交换速率时表层床沙的粗化过程及非均匀沙含沙量恢复饱和过程。研究表明 ,由于较细泥沙的冲刷率总大于较粗泥沙 ,因此在床面薄层内泥沙随冲刷迅速粗化 ,致使挟沙力降低 ,不平衡输沙距离较均匀沙情况大大延长。床沙交换速率愈慢 ,则冲刷距离愈长。

Previous investigations of non equilibrium and equilibrium sediment transport are analyzed and a two dimensional mathematical model of non equilibrium sediment transport in river channels with non uniform bed material is presented. The concept of exchange rate of bed material is introduced, and a very short time step is used in the calculation. The main reason why the sediment recovering equilibrium distance for the non uniform bed material is far longer than that for uniform bed material is discussed. Because the size composition of surface bed material is coarsened, the scouring of finer sand is far less than that for the initial state and the distance of non equilibrium sediment transport becomes much longer. A slower exchange rate of bed material then leads to a longer distance of non equilibrium sediment transport.