Channel confluences are common in natural rivers and many hydraulic engineering projects.The flow structure at confluences become very complex because of the interaction between tributary and Main River. The experiments were performed in a combined flume with 30° angle between main and tributary flume located at Sichuan University. The velocity was measured using a three component Acoustic Doppler Velocimeter (ADV) over a grid defined throughout the junction region. Based on the analysis of the velocity at confluence, the distinctive characteristics of a channel confluence flow may be divided into several zones including a zone of separation immediately downstream of the junction branch channel, a maximum and minimum velocity region at upstream and downstream in the confluent channel, and a shear plane developed between the two combining flows at downstream of confluent channel. In addition, there are different direction secondary circulations at the high and low velocity zone.
