An Improved Physical Model for Open Channel Confluences: Bridging the Gap Between Laboratory and Field Observations

Abstract Despite decades of research on hydro‐morphodynamic processes at open‐channel confluences, significant discrepancies persist between flume experiments and field observations. This study investigated the underlying causes by compiling and comparing geometric and hydraulic parameters from both natural confluences and laboratory setups. The analysis suggested that these discrepancies largely stem from unrealistic boundary conditions commonly used in experimental designs. To address this issue, this study developed an improved physical model of concordant confluences that more accurately replicated the morpho‐hydraulic characteristics of natural confluences. Key features included a smooth downstream junction, a large post‐confluence width‐to‐depth ratio, downstream channel widening, representative junction angle and discharge ratio. This experiment avoided the unrealistic large separation zone and scour holes near the downstream junction corner caused by sharp‐angled junction. Large Reynolds stresses and turbulent kinetic energy within the shear layer primarily drove scour hole formation, while streamwise‐oriented vortical cells offered additional contributions. In contrast, flow acceleration along the main channel promoted scour step development through low‐intensity sediment redistribution. This study presented a more realistic and representative physical model for simulating hydro‐morphodynamics at confluences with concordant beds and helped bridge the gap between laboratory findings and field‐scale dynamics.