沙波运动对冲积河流悬移质冲刷不平衡输沙的影响

Influence of sand wave migration on non-saturated suspended load transport in alluvial rivers

基于冲积河流河床活动交换层动力学基本方程和悬移质不平衡输沙方程,利用数值方法计算了冲积河流冲刷不平衡输沙过程。结果表明,冲积河流床面沙波准周期性运动的动力学特征影响了河床中泥沙暴露至河床表面的速度,延缓了河床冲刷时由河床表面补充到水体中的速度,从而对悬移质不平衡输沙产生显著影响。分析结果同时表明,悬移质冲刷不平衡输沙恢复饱和系数的理论值是在不考虑沙波运动对河床内部泥沙暴露到河床表面的速度的制约条件下得到,使得理论值大于经验统计值。

The transport equation of suspended sediment is solved numerically to investigate the process of sediment-starved flow recovered to saturated flow by erosion. An equation describing the dynamic procedure of the mixing of bed material due to migration of bed forms such as ripples and dunes in the mixing layer is introduced. The equation reveals that before the armoring layer is formed during river degradation, the sediment grains being eroded by flow at bed surface coming from inner part of the mixed layer are exposed to fiver bed surface by mixing produced by migration of sand waves. The numerical results shows that the erosion rate can be significantly slow down by the quasi-periodic movement of sand waves. This research also indicates that the theoretical expression for recovery coefficient of non-saturated suspended load transport during river degradation that the theoretical value is much larger than the is obtained by assuming no limitation on the rate, so empirical value.