Numerical simulation and geomorphic impact of the 2000 Yigong River outburst flood

Abstract Currently, there is a shortage of research on modern outburst floods, which hinders our comprehension of the connection between the hydrological features of these events and their geomorphic and sedimentary characteristics. This lack of research also restricts our understanding of the impact of these extreme disasters on the long-term evolution of human survival and living environments. Nevertheless, the 2000 Yigong River outburst flood provides us an opportunity for studying the typical modern outburst floods. The peak discharge of the dammed lake outburst flood was recorded at 1.26×10 5 m 3 /s, leading to significant changes in the riverbed and valley gradient, ultimately causing the riverbed to shift. Moreover, it formed a large amount of gravel bars and slack water deposits downstream of the breach. These sediments are relatively well preserved and provide us with a complete chain of evidence to study modern outburst floods. The dynamics of the flood were simulated using the HEC-RAS 2D unsteady flow model. The relationship between the lateral migration of the channel and the shear stress of the river bed during peak discharge was determined. This reflected the direct control effect of the hydrodynamic conditions of the outburst flood on the lateral migration of the river bed. The sedimentary morphology, scale, and maximum gravel size of the boulder bar downstream of the breach were found to be closely related to the channel width and local hydrodynamic conditions.The relationship between the hydrological characteristics and sedimentary characteristics of the outburst flood was quantitatively analyzed. The slack water deposit in Jiazhong village was formed during the peak discharge, while the horizontally-bedded laminations containing coarse sand and fine gravel in the tributary valley were mainly formed during the flood decline after the peak discharge.The latest findings in this study provide valuable additions to the research on the devastating floods that have been investigated in the rugged terrain of the Yarlung Tsangpo River basin.