不同含沙量水流对河床形态调整影响的实验研究

Experimental study on influences of sediment-laden flow with wide sediment concentration range on channel metamorphosis

水沙条件变化后河床形态的调整是河流地貌学中一个极为重要的问题。但国内外学者基于不同的含沙量变化范围得出的结论刚好相反。采用过程响应模型实验方法,研究和验证了河床形态调整对于不同含沙量水流过程的复杂响应现象,从实验的角度部分地修正了Schumm关于水沙条件变化后河床形态调整方向的定性预测关系。

River metamorphosis caused by river regime is one of the most important issues in fluvial geomorphology. In this issue, Schumm has proposed a famous qualitative relation. But the relation is quite different in China when it is applied to hyper-concentrated flows. To resolve this controversy, a process-response model experiment using secondary deposited loess with the median diameter of about 0.042 mm as well as with a wide sediment concentration range conducted in an 11 m × 3 m flume. The experimental results show that sediment-laden flows with the different sediment concentrations have different behaviors in fill-scour and the ways of channel adjustment. Because of the existence of the hyper-concentrated flow, the sediment-laden flow needs less energy dissipation to transport sediment. Therefore, the variations of the channel form exhibit complex relations with those of the sediment concentration. When the sediment concentration is low, the ratio of the width to the depth of the channel will increase and when it increases to a certain degree to the field of hyper-concentrated flow, the width-to-depth ratio will decrease with the increase of sediment concentration. So does the sinuosity. Thus, according to the experimental results and some case studies about the range of non-hyper-concentrated flow in China, Schumm's relation is correct and available, but to hyper-concentrated flow, Schumm's relation should be modified.