EXPERIMETAL STUDY ON BIFURCATED CHANNEL CHANGES AND SEDIMENT TRANSPORT IN A MOUNTAIN RIVER

Movable bed experiments with large-scale bed forms and bifurcated channels were conducted by using a steep slope channel and heterogeneous bed materials in order to investigate mechanisms of stream channel change and sediment transport in a mountain river. From the experimental results and observation, it was found that a bifurcated channel in a mountain river has unstable mechanism such a mainstream changes alternately from one to another at the nodal point of bifurcated channel, and that bed evolution and sediment discharge in the lower reach are obviously influenced by the mainstream alternations. For interpretation of the mechanism, a simple mathematical model was introduced, which was derived from the sediment continuous equation. Self-excited change of a mainstream due to the change of sediment transport rate at the nodal point was shown by the model without considering influence of alternating bar migration.