Study On The Characteristics And Formation Mechanism Of Slpoe Debris Flow Along The Yarlung Tsangpo River Section Of Sino-nepal Highway

The Sino-Nepal Highway is the only international through-road in Tibet from China to Nepal and South Asia.It is also an important bridge for the Chinese and Nepalese people to maintain traditional friendship.Along the Yarlung Tsangpo river section,it starts from Qushui County of Lhasa City in the east,and ends in Shigatse City in the west.Affected by the strong neotectonic movement,the debris flow on the slope is densely developed in the region.Based on the second comprehensive scientific investigation of the Qinghai-Tibet Plateau as a subproject “Research on Geological Structure Background and Risk of Geological Hazards of the South Asian Passage”,this paper makes a preliminary study on the development characteristics and formation mechanism of debris flow disasters based on the statistical analysis of geomorphology and the principle of soil erosion,and draws the following conclusions:(1)About 118 slope debris flows have been developed along the river section of the Sino-Nepal Highway,65 on the left side of the river bank,accounting for 55%,and the right side of the river bank 53,accounting for 45%.According to the geomorphologic morphology and stratigraphic lithologic characteristics,the study region is divided into three sections: Qushui County-Kare Township wide valley,Kare Township-Dazhuka canyon valley and DazhukaShigatse wide valley.Debris flow development in the Kare Township-Dazhuka canyon section is the most serious,followed by the Dazhuka-Shigatse wide valley section,and the Qushui county-Kare Township wide valley section is the least.According to the different slope erosion patterns of the debris flow,the slope debris flow in the study region is mainly divided into three types,which are named "Branches" slope debris flow,"Combs" slope debris flow and "Skirts" slope debris flow accounted for 55.9%,35.6%,and 8.5%,respectively.(2)Combined with the principle of soil erosion,the formation process of slope debris flow is mainly hydraulic erosion under the action of rainfall.The main processes include: raindrop splashing under rainfall ? sheet erosion under surface runoff erosion ? surface runoff drop under water gully erosion.The reason for showing different types of erosion landforms is mainly the result of the combination of different debris flow source types and different gully shapes;the " Branches " slope debris flow is caused by landslide soil erosion and scattered slope type soil erosion landforms are formed under the action of concave valleys;while " Combs " slope debris flow is formed by scattered land erosion forms under the action of linear valleys.(3)According to the change of geomorphological information entropy in the debris flow basin,it is concluded that the slope debris flow in the Qushui-Kare section and the DazhukaShigatse section gradually declines,and the slope debris flow in the Kare-Dazhuka canyon section gradually becomes vigorous.It is suggested that the Qushui-Kare section and the Dazhuka-Shigatse section can adopt the debris flow prevention measures combined with biological and the construction of the barrage dam project;Kare-Dazhuka section can be combined with biological control measures and the construction of aqueducts.In particular,the aqueduct shape should preferentially choose the V-shaped groove rate structure that can promote the debris flow movement.