Relative contributions of longitudinal and transverse shear dispersion to solute mixing in meandering channels

River bends induce complex three-dimensional (3D) flows that govern solute residence time distributions (RTDs) through turbulent diffusion, longitudinal shear dispersion, and transverse shear dispersion. However, their individual contributions to solute mixing across varying channel sinuosity remain insufficiently quantified. This study simulates solute transport by employing a quasi-3D Lagrangian particle-tracking model to quantify the relative importance of longitudinal and transverse shear dispersion across a wide range of channel sinuosity. We find that solute residence times increase with channel sinuosity because enhanced velocity shear and secondary flow promote dispersion. Although longitudinal shear dispersion dominates solute transport at sinuosity below 2.0, its dominance shifts to transverse shear dispersion at higher sinuosity. At a sinuosity of 3.7, the relative contribution of transverse shear dispersion to RTDs is twice the value from longitudinal shear dispersion. These results elucidate that curvature-driven flow exerts significant control on river mixing.