Excessive precipitation during extreme weather conditions can readily trigger high-energy flood disasters. These floods often carry substantial amounts of bedload sediment as they propagate, resulting in basal erosion and alterations to riverbed topography. These changes in topography, in turn, influence flood propagation. Consequently, accurately predicting the propagation of high-energy floods and the accompanying morphology changes presents a considerable challenge due to the intricate interactions between water and sediment. The internal structure of the bedload layer, particularly the vertical distribution of velocity and sediment concentration within the bedload layer, plays a crucial role in forecasting sediment transport rates and subsequent morphological evolution. However, limited experimental and numerical studies have investigated this issue, primarily due to the thinness of the bedload layer and the intense water-sediment interactions it entails.

 

In this paper, the propagation of dam-break floods and the internal structure of the corresponding bedload layer are examined using a two-phase Smoothed Particle Hydrodynamics (SPH) mathematical model. The computed granular velocity and sediment concentration distributions within the bedload layer are compared with observed data to validate the accuracy of the mathematical model. Subsequently, a power function is proposed to represent the vertical distribution of granular velocity within the bedload layer, with two power coefficients depending on a dimensionless Shield’s number related to the surface flow velocity. Following this, a new and reliable equation is developed to estimate the bedload sediment transport rate. Utilizing this new equation, the bedload sediment transport rate in open channels can be accurately estimated, further aiding in predicting riverbed topographic changes and corresponding flood propagation, while also facilitating sediment management in practical engineering and field studies.