Reduction of the channel junction scour using a bed sill: a 3D numerical study

Open-channel junctions are distinguished by prominent scour zones, where bed scouring modifies river morphology, potentially affecting hydraulic structures and undermining the stability of channel banks and beds. Despite investigations into the causes of channel junction scour, studies on mitigation measures remain limited. This study aims to assess the effectiveness of a bed sill in mitigating scour at a right-angled open-channel junction, utilizing three-dimensional (3D) computational fluid dynamics (CFD) modeling and simulating sediment transport in both bed-load and suspended-load forms. The predictive accuracy of the model is validated through comparison with laboratory data reported in the literature. To address junction scour, a bed sill is installed at various downstream locations from the junction. Comparative analyses indicate that the efficacy of scour reduction is heavily dependent on the bed sill’s placement. Specifically, placing the bed sill downstream of the flow contraction region significantly reduces the near-bed secondary currents from the channel centerline towards the outer bank, leading to decreased bed shear stress and consequently less scouring. Conversely, positioning the bed sill within the flow contraction region proves ineffective in reducing scour. These findings contribute to a better understanding of junction scour mitigation strategies.