Mountain torrents often induce active sediment movements. There is a substantial interaction between the sediment movement and the mountain torrents. The existing research involves the prototype observation and analysis of the process of water and sediment and the study of the basic transport law of the sediment. The main theory and formula of sediment motion mechanics are generally established for the constant uniform flow on the gentle slope, but the mountain torrents are usually unsteady and non-uniform flows on the steep slope. The sediment model is different from the actual observation result, and the main reason may be to calculate the motion of the sediment in the unsteady flow by the formula obtained under the condition of constant flow.
At present, the study of resistance to overland flow has already been quite extensive at home and abroad, but there are still the following problems.
The slope is limited to the gentle slope, which is generally less than 10 degrees.
Although the research about resistance to overland flow begins to carry on the experimental study of the rough moving bed, the data is limited, which affects the comprehensive analysis of its influencing factors and the further quantitative relationship.
Due to the lack of quantitative relation of resistance to overland flow with power process, overland flow and hydrodynamics models of watershed inviariably use the empirical parameters of open-channel flow (such as Manning coefficient), which causes the great uncertainty of the confluence of overland flows and the prediction of floods in mountain areas. So far, some progress has been made in the study of sediment transport under the action of weak unsteady flow, but it is still far from clear understanding of the law of sediment movement in mountain rivers under the action of strong unsteady and rapid flow. It is necessary to carry out systematic and in-depth study, which is of great value for understanding and forecasting the process of mountain torrents evolution.
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