Study on the Surge Wave Field Characteristics of Granular Landslide-Induced Waves in the Confluence Zone of Reservoir Main and Tributary Channels

Landslide surges are characterized by their sudden onset, extensive propagation range, and destructive force. During propagation, these surges are influenced by the complex topography of the Three Gorges Reservoir area. To investigate the wave field characteristics of landslide-induced waves propagating at the confluence of main and tributary rivers in the Three Gorges Reservoir area, a three-dimensional physical model experiment was designed and conducted for granular landslide-induced waves at the confluence section. This study examined the landslide motion process and wave height variation characteristics across different regions. Results indicate that the maximum wave height of the leading wave in the opposite bank propagation zone exhibits a negative correlation with water depth, a positive correlation with landslide volume, and a positive correlation with landslide inclination angle. Regarding the propagation of the leading wave along the river direction, observations in the near-field zone reveal that the attenuation of the leading wave along the river direction follows a trend from slow to fast, with the attenuation rate gradually decreasing as the propagation distance increases. At equivalent propagation distances, the decay rate of the first wave height in the downstream direction was greater than that in the upstream direction. In tributary areas, the maximum wave height often occurs in subsequent waves. As surges triggered by landslides at different upstream and downstream locations propagate to tributaries, both the first-wave height and maximum wave height of upstream landslide surges in tributary areas are smaller than those of downstream landslide surges. Furthermore, the spatial distribution of their maximum wave heights differs due to variations in the topography of the confluence points on both sides. Using multivariate nonlinear regression methods, empirical formulas for the first-wave height decay of both downstream and upstream landslide-induced waves were derived. This provides theoretical support for refined research and prediction of surge waves in river-type reservoirs.