Characteristics of rainstorm and glacial snowmelt-induced debris flow in the paraglacial zone of Yigong Zangbo
To investigate the distinctive characteristics of rainstorm and glacial snowmelt-induced debris flows in fringe regions of glaciers,this study focused on 64 debris flows located in the middle and lower reaches of the Yigong Zangbo Basin.We used field investigations to comprehensively analyze and inform our remote sensing-based interpretations,and established matrix laboratory-based mathematical expressions for them.The objective was to identify variations in the backgrounds of formation of the two types of debris flows as well as the extent of hazard posed by them to downstream areas of accumulation.The findings revealed the following.(1)Glacial snowmelt-and rainstorm-induced debris flows exhibited dissimilar or analogous distributions in terms of key topographical factors,including the relative differences in elevation and indices of the shapes of their longitudinal profiles.(2)The maximum and minimum material reservoirs for glacial snowmelt-induced debris flows within a single gully were 6 740 X 104 m3 and 253 X 104 m3,respectively,while those for rainstorm-induced debris flows were 228 X 104 m3 and 1.5X104 m3,respectively.(3)Glacial snowmelt-induced debris flows had maximum and minimum peak discharges of 1 498.2 m3/s and 105.4 m3/s,respectively,while rainstorm-induced debris flows had those of 126.7 m3/s and 2.0 m3/s,respectively.The noticeable disparity in flow between them arose not only due to differences in the area of the catchment,but also due to the influence of glacial meltwater and snowmelt in case of glacial snowmelt-induced debris flows.Notably,the maximum and minimum peak flows of glacial meltwater during a 100-year period of recurrence were 79.7 m3/s and 0.6 m3/s,respectively,with a snowmelt equivalent of 32.52 mm/d.(4)The distances over which solid loose materials were carried by glacial snowmelt-induced debris flows in the areas of accumulation were significantly greater than those carried by rainstorm-induced debris flows.For instance,the maximum washout distance for a single gully affected by glacial snowmelt-induced debris flows was 414.3 m,while the equivalent distance for rainstorm-induced debris flows was 43.6 m.We examined the mechanisms underlying the differential development of the two forms of debris flows in the region,and our results provided valuable insights for the management and control of debris flows in analogous areas.