Abstract: The confluence area of rivers, as a key component of river systems, features complicated hydrodynamics and three-dimensional changes in bed morphology. This study conducts a laboratory water tank experiment of a river confluence and examines the distribution characteristics of its water flow under the condition of low sediment concentration. Four concentration conditions are tested, flow velocity is measured using an Acoustic Doppler Velocimeter (ADV), and the data is denoised. Results show that with an increasing concentration, velocity zoning characteristics in the confluence vary significantly, and the ranges of the flow velocity gradient and the maximum-velocity-covered area are both expanded. This means the dynamic behaviors of fluid and the interactions between fluid layers are enhanced. We also found that in the concentration range of 4.2 to 7.4 kg/m3, the inhibitory effect of sediment on turbulence is insignificant. The results lay an important basis for a deeper understanding of the hydrodynamic process and sediment transport in a river confluence.

Key words: confluence of open channels, sediment concentration, water flow characteristics, ADV, flume experiment