The influence of density difference, discharge ratio and wind on the mixing at large river confluence

Numerical simulations for a large river confluence were conducted to comprehend the influences of three factors: density difference, discharge ratio, and wind shear on tributary flow dispersion. The present study focused on the confluence channel of the Nakdong River and the Yangsan Stream in South Korea, with simulation conditions selected based on realistic conditions. Numerical results revealed that tributary flow can disperse upstream under high discharge ratio conditions, which becomes stronger with density stratification. In particular, when the tributary flow is denser than the mainstream, bathymetry around the junction determines the flowing direction of the density current. Thus, understanding tributary flow dispersion under varying conditions is vital due to its influence not only downstream but also upstream of the confluence. Additionally, wind shear impact on the mixing between mainstream and tributary flow is notable but less significant than density difference or discharge ratio.