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Debris content plays an important role in controlling erosion capacity and sedimentation characteristics during outburst floods. Numerical models should incorporate sediments in hazard analyses to obtain more accurate assessments of outburst flood magnitudes and downstream behaviors. In this paper, we propose a novel water–sediment mixture flow model to reconstruct the ancient outburst floods at Xuelongnang and demonstrate the performance of this model through comparisons with field evidence. The simulated outburst flood reaches a maximum breach discharge of 10,697.35 m3/s and a peak sediment discharge of 65.29 m3/s, traveling downstream for 87 km within 5.43 h. Based on simulations of riverbed changes, inundation depth, velocity, shear stress, and Froude number, our findings suggest that topographic controls influence hydraulic patterns, which subsequently affect erosional and depositional processes and contribute to landscape evolution. During the downstream propagation of the outburst flood in narrowed valley sections, simulated sediment-simulated deposition occurs downstream while erosion occurs upstream, coinciding with the maximum inundation depths attributed to hydraulic jump phenomena. We also discuss the formation processes of the outburst deposits, identifying areas of greatest channel aggradation. Calculated bed shear stress suggests that sediment transport by the flood deposits on the riverbed decreases as the flood stage wanes, forming the rhythmite-interbedded structures observed in field investigations. This work provides a viable and promising approach to understanding hydro-sediment-morphodynamic processes in flood pathways and the erosional and depositional features left by outburst floods, supporting modern outburst flood hazard prevention and mitigation. [ABSTRACT FROM AUTHOR]

To investigate the effects of internal shear fragmentation on dry granular flow, in this study a series of ring shear tests were performed on quartz sand samples under different normal stresses (100 kPa, 200 kPa, and 300 kPa), shear displacements (3 m, 5 m, 10m, 15 m, and 20 m), and shear rates (30 deg min−1, 60 deg min−1, and 90 deg min−1). Next, the grain-size distributions, fractal dimensions, and microcharacteristics of the quartz sand before and after the experiments were compared and analyzed. The study results show that grain breakage under shearing preferentially occurs at the edges of the particles and forms a bimodal distribution in frequency grain-size distribution curves, which is consistent with observations of rock avalanches. The fine particles prevent the coarse particles from breaking, in turn leading to the ultimate grain-size distribution and stable fractal dimension (2.61) of quartz sand at relatively small shear displacements compared with the travel distance of rock avalanches. The results of this study suggest that the fragmentation of rock avalanches during the shear spread stage may be far less significant than previously believed. Therefore, the fragmentation effect is not considered to be a major factor of the hypermobility in the late stage of rock avalanches. [ABSTRACT FROM AUTHOR]