Study on channel variation in mountain rivers

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A large amount of sediment is commonly deposited in the regions with a wide section of mountain streams where sediment yields are very active. Stream channels formed there are braided even in a high flood because the flot width is too wide to form a stable stream. The project of this study is to investigate the processes of channel variation and their associated phenomena such as variation of bed load, sediment sorting and so on. The results obtained from the research are summarized as follows :1. Several streams are commonly produced in a flume bed chosen for the present study. resulting in a braided channel system. The flow direction and width of each stream change in time and space, which brings about varieties of the number of stream as well as of the whole flow width in the braided channel system.2. Such variations of streams in the system are more active in the bed with graded material than with uniform one, because a stream bifurcation occurs more frequently due to a sediment sorting in the former case.3. The sediment discharge rate increases with the decreases of the flow width and the number of stream in the cross section under consideration. In other words, it increases in a converging process of stream and vice versa in a bifurcating phase.4. It is necessary to specify the parameters such as the flow width of each stream and the number of stream formed in the system for the prediction of bed load distribution. A formula of the flow width is developed in terms of a criterion for alternating bar formation. It is very useful for evaluating a temporally averaged sediment rate.