The confluence phenomenon is fairly common in the natural river[1-2]. In the confluence regions, two
mutual mixing streams lead to unique hydraulic behavior such as flow field changing, spiral flow, convex
water surface, local flow stagnation, and so on. In the confluence region the flows mutual mix so
violently as to lose energy very greatly, so the original equilibrium state of mainstream and tributary is
broken, which weaken highly sediments and pollutants transport, impact water ecological environment
and seriously reduce river flood discharge capacity. Therefore the confluence problem has been a focus of
attention of water conservancy, shipping, flood control and environmental protection department.