Abstract:The complex water and sediment conditions and river form in mountainous rivers result in abundant vegetation covering the beach, which significantly changes the water and sediment movement and bed deformation characteristics. The experiments were conducted in a physical model with natural vegetation for studying the effects of vegetation and sediment supply on the river deformation and flow structure in the channel. According to the experimental results, it can be concluded that vegetation leaves increase the disturbance of water flow and reduce the flow velocity. When the upstream supply sediment occurs, the sediment is wavily transport in the vegetated beach, and form some small sand dunes around the vegetation zone, and most of the sediment is deposited at the head and tail of the beach. When the submerged vegetation withered, the stems and leaves are washed away, the flow washes the foot bases of the beach more intensely. Vegetation and sediment supply can adjust the flow division ratio of the branch. Sediment supply and vegetation reduce the diversion ratio of left branch. As a summary, vegetation and sediment supply significantly reduce velocity and thus have an important influence on the water-sediment movement, which accelerates the beach development and adjusts the flow division of branch.