What Drives Channel Lateral Migration? Insights from Lab and Numerical Simulations

Understanding the lateral migration of outer banks is critical for meander restoration. Traditional models using near-bank velocity or shear stress as drivers often fall short in explaining observed migration patterns. This study evaluates an alternative factor—the longitudinal gradient of near-bank velocity—alongside conventional drivers. Using observation data from mobile-bed laboratory experiments, a high-resolution Delft3D-Flow model was calibrated to simulate detailed flow structures. The relationships between outer-bank migration rates and near-bank velocity, shear stress, and velocity gradient were then analyzed. Results show that the velocity gradient is a reliable indicator of maximum bank migration at bends, while near-bank velocity or shear stress better predict migration in relatively straight sections where mainstream shifting occurs. These findings enhance our understanding of lateral migration mechanisms and offer improved predictive capacity for river restoration efforts.