Study On Waterway Regulation Of Typical Rocky Rapids In A Branching Channel By Hydrodynamic Model

The main problems in waterway regulation on branching rapids of mountain rivers are choosing navigation paths and improving flow condition. The main measures are: damming improving flow condition riverbed excavation etc. Riverbed excavation is always used in reducing velocity of a channel with bad flow condition. In singularity channel, velocity can be reduced with the increase of crossing area by excavating riverbeds. It is different in branching rapids. Excavating riverbeds in one channel may not only reduce the velocity area in some areas but also increase the velocity in other areas by increasing flow rate in this channel without correspondent changes in riverbeds of rocky rapids. In result, the velocity in waterway may be increased instead of be reduced, the flow condition may also be deteriorated. Thus, which branch should be excavated and how to excavate in improving the flow condition of the branch should be further explored.A 2-D hydrodynamic-numerical model was applied to typical rocky rapids called Jiyutan by comparing different computational models. Based on the comparison of different schemes, the change of the discharge and the flow current in a branch were analyzed, and the relationship between the flow condition and excavation area, scope as well as mode was discussed, the conclusions show:(1) In a branching rocky rapids, the velocity may be reduced and flow condition can be improved by excavating one channel partly. On the other hand, the velocity may also be increased by excavating another channel, which should be treated cautiously.(2) The change of flow rate in a typical branching rocky channel is related to excavation area scope and mode. More excavation area scope and width, more increase in flow rate.(3) In excavation channel, the velocity in engineering area may be reduced, but the velocity in other areas of this channel may be increased and the flow condition may be deteriorated as a result of the increase of flow rate in this channel. Thus, it should be discussed and studied before engineering practice.