ABSTRACT
Mountain rivers usually adopt a “U” or “V” shape valley, and can be simplified as rectangular or trapezoidal cross section The river varies as sediment transport; however, the river banks may be non-erodible if they are covered by rocks or artificial protections, or erodible if the banks are formed by soil. Confluence river is one of the basic types of mountain rivers, and in many flume studies, confluence river was simplified as a junction of open channels with rectangular cross sections. The bottom of the flume were filed with sediments to simulate the erosion process in confluence region, but the banks of the flume usually were made by glasses or steal walls, which was unchangeable during the test. In this paper, we adopted a three dimensional numerical code to simulate sediment transport in the confluence region. In each simulation runs, the banks was erodible and non-erodible, the cross section was rectangular or trapezoidal, the flow rate of main channel was larger or smaller than the rate of branch channel, and the width of the main channel was wider or narrower than that of branch channel. The unique flow structure and sediment transport mode under different combination of the boundary conditions are presented in this paper. The study shows that the cross section shape impacts the flow structure and bed form largely as the width of the main channel is comparable to the branch channel, and when the main channel width increases, the impact decreases.
