Geological Hazard Characteristics And Risk Assessment Of Brahmaputra From Wolong To Zhibai Stream Segment

The Brahmaputra from Wolong to Zhibaihe stream segment is located on the southeastern edge of the Qinghai-Tibet Plateau,the middle and lower reaches of the Brahmaputra.The study area is situated in one of the fastest areas in the Qinghai-Tibet Plateau where the crust is uplifting.In the valley form,the wide valley alternates with the valley.Different valley geomorphic units develop different types of geological hazards.Geological disasters threaten the construction of highways,railways,airports,and hydropower stations seriously.Based on the field investigation and combined with the environmental geological conditions in the study area,This paper studies the characteristics and distribution of geological disasters in landslides,debris flows and collapses in the survey area.At the same time,geological hazard assessment has been carried out.The main achievement as follows:(1)In the study area,there were a total of 20 landslides,53 landslides,and 10 landslides.In the wide valley area,the main is high rocky landslide,And The canyon area is dominated by landslides form by deposits of ice and sediment.Meanwhile,both have differences in scale,predisposing factors,formation time,etc.the debris flow is distributed in the non flowing water branches in the two sides of the main stream.On the left bank of the river,there are mostly rainfall debris flows,and the right bank is dominated by larger glacial debris flows.This is determined by the elevation of the different branch gullies and the shape of the supporting trench.The development of collapse geological disasters is controlled by precipitating factors such as strong earthquakes,artificial slopes,and river erosion.(2)Based on the detailed investigation on the geological background and the material composition of the accumulation body of the Landslide in Longan Village,Four stages of the landslide formation and evolution experience were deduced: structure surface slide along the contact surface,Rock mass ejection from the parent rock stage,Collision and blockage of the river stage,Self stabilization stage.Since the 20 th century,the Zelongnong glacial mudslides have erupted several times and destroyed downstream villages.Through the detailed investigation,analysis of the geomorphic units and provenance characteristics of each area,it has been concluded that the debris flow is induced under the conditions of earthquake or high temperature.The source of the ice-cold bodies in the formation area suddenly starts up,and the ice-mass accumulation body at the bottom and both sides of the scraper valley is transported along the way.The potential energy is converted into kinetic energy,and it is washed down to make up the gully,covers the ancient accumulation fan,and even blocked Brahmaputra.(3)This article selects lithology,geological structure,slope,river system,rainfall,slope direction,the height of tug,seismic intensity and human engineering activity as evaluation factors.The risk assessment of geological hazards in the study area was conducted using a combination of analytic hierarchy process(AHP)and information volume method,And the results are finally divided into extremely high risk areas,high risk areas,middle risk areas,and low risk areas.The evaluation results are basically consistent with the distribution of geological disasters in field surveys and accurately reflect the development of geological disasters.(4)The risk assessment results showed that the extremely high risk areas and high risk areas of geological disasters accounted for 12% and 23%,and they were mainly distributed along the banks of the wide valley or on the canyon sections,Tectonic,rivers erosion and human engineering have a strong influence.The middle-risk area accounts for 33%,which spreads in the middle-alpine landscape between the Wolong and Mirui Townships.The main controlling factors are height of tug and geological structure,which are less affected by human engineering activities.The low-risk areas are mainly distributed in the middle alpine and high mountain areas in the upper reaches of Wolong Town and the high-altitude areas of the ditch-sourced ditch in the left bank of Brahmaputra,accounting for 32% of the study area.In the area,the lithology of the stratum is hard and the degree of natural weathering is weak.The average annual rainfall is below 500 mm,and it is hardly affected by human engineering activities.