Experiment on the Hydrodynamic Characteristics of Plunging Flows in Bedrock Canyon Bends

Bedrock river incision drives the evolution of the Earth's landscape and is influenced by river hydraulic power. However, the relationship between plunging flows and the curvature of bedrock canyons is poorly understood, which encouraged us to explore how the bend's curvature and undulating beds affect plunging flows. A generalized physical model was built to investigate the hydrodynamic characteristics of plunging flows in a constant curvature flume with plain and undulating beds. Our experimental findings demonstrated that plunging flows were related to secondary circulation, topography, and width-to-depth ratios. Plunging flows occurred when secondary circulation reached its peak, and as secondary circulation vanished, the intensity of plunging flows decreased. The undulating bed topography in the bedrock bends suppressed secondary circulation and the development of plunging flows. Bed topography may be a dominant factor in plunging flows in bedrock bends. The potential erosion area in bedrock bends was related to the intensity of plunging flows, which caused velocity inversion to increase the shear stress near the bed. With higher discharges and undulating beds, the intensity of the transverse shear stress of the riverbed near the center was greater. The potential erosion area in bedrock bends was concentrated at the center of the cross-section around the bend apex upstream. Our experimental results can improve incision models in terms of the distribution of shear stress and flow structure in bedrock bends.