Characteristics of flow and sediment at the confluences of mainstream and tributary of the upper reaches of the Yangtze River

The upper reaches of the Yangtze River is a typical mountain river in the southwest of China, and its tributaries are numerous. This paper deals with the study of the characteristics of flow and sediment accumulation around a confluence of bend-mainstream and tributary of the upper reaches of the Yangtze River. The experiments were carried out in a 180° mobile-bed main channel bend with a by-channel feeding from the top of bend. Uniform sediments having an average diameter of 0.5 mm were used under clear-water scour conditions. Inflow angle and discharge ratios are the main parameters considered in this experiment. The results of this paper indicate that (1) the flow field around the confluence was divided into five zones: banked-up belt I, banked-up belt II, confluence area, collecting area and separating area; (2) A new equation for scour parameters around the confluence was developed; (3) It progressed formula fitting for relationships among the relative length and the relative width of the separating area, discharge ratios, and inflow angles. And it gave formulas for relationships among the relative length and the relative width of the separating area, discharge ratios, and inflow angles in the confluence.