No abstract

Confluences are critical nodes in a river network and affect flow, sediment transport, water quality, and ecological patterns. Significant changes in hydrodynamics, bed morphology as well as environmental and ecological features occur at the confluence, where the flows from two tributaries combine and adjust to the postconfluence planform geometry. Confluence of two flows with different momentum and velocity ratios (the ratio of the variable of one channel to that of the other) often results in a downstream shear layer driven by the Kelvin-Helmholtz (KH) instability. It enhances turbulent mixing and exchange of momentum and other matter (e.g., sediment and pollutants;

City channels often have a smaller width-to-depth ratio in comparison to natural rivers due to the limited land availability. The penetration of the tributary into the main channel can cause the distortion of the shear layer. The main purpose of the present study is to investigate the mean and turbulent flow structure in the distorted shear layer in a discharge-adjustable plexiglass circulating flume. Three-dimensional velocities were collected and hydrodynamics and turbulence characteristics such as mean velocity field, turbulent kinetic energy, Reynolds shear stress, turbulence spectrum, and occurrence probabilities of quadrant events were analyzed. The results showed that a stronger helical cell was formed and extended for a longer distance