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.