Study On The Development Law And Risk Assessment Of Debris Flow In The High And Cold Mountainous Areas Of The Middle And Lower Reaches Of Niyang River

The Niyang River Basin is located in the southeast of the Qinghai-Tibet Plateau and is one of the most serious debris flow disasters in China.The middle and lower reaches of the Niyang River are close to the northern boundary of the Yarlung Zangbo River suture zone,which is strongly influenced by the regional tectonic and tectonic movements and widely developed granite and metamorphic rocks,forming a large amount of loose solid deposits in the tributaries of the Niyang River.It provides abundant solid source for the formation of debris flow,combined with sufficient rainfall in summer and ice and snow melt water to provide favorable hydrodynamic conditions for the development of debris flow,which makes debris flow particularly developed in this area.In the study area,the most developed and densely populated section of the Niyang River Basin,Gengzhang ~ Estuary,is selected,which is 77.5 km long and has 36 debris flow geological hazards.The Niyang River basin is a typical alpine mountain area,and the large and medium-sized tributarine gully sources are widely distributed in modern oceanic glaciers.Because of its high altitude and difficult traffic,it is difficult to monitor debris flow in this area,which makes debris flow in this area have the randomness of the time and place of outbreak and great harm.Hard to control.With the development of the western development of our country,the basic construction of Niyang River Basin and the migration of poverty alleviation continue to advance.These engineering activities are inevitably in contact with debris flow,but the project can not blindly take measures to avoid it.Based on the field investigation and remote sensing data of the slime flow,the distribution law of debris flow and the typical debris flow analysis,the main control factor and the formation mechanism of the debris flow are analyzed,and the regional geographic data are collected,collated,spatially analyzed and divided by GIS technology to analyze the mud in the middle and lower reaches of the river.Rock flow hazard zoning map.The advantages of "3S" technology are deeply applied to the risk assessment and analysis of the middle and lower reaches of the river,and the spatial data such as geological data,DEM data,remote sensing data and rainfall data are synthetically analyzed and studied,and the main contents and results are as follows:(1)there are 36 debris flows in the main area of human activities in the middle and lower reaches of the river basin,which can be divided into two types,namely,rainfall type debris flow and glacial rainfall type debris flow,of which rainfall type debris flow is more common,and the glacial debris flow peculiar to the snow and snow areas in the mountains is also more developed in this area,accounting for 38.89% of the total debris flow.Because of the complex topography,strong structure and more glacier distribution in the high mountain areas,the material source of the debris flow is rich,most of which are gathered in the valley and developed into more destructive viscous debris flow.(2)taking into account the applicability and accuracy of the watershed characteristics of debris flow disaster and the hazard assessment map,the study area is refined to 119 sub basin units by 15000 threshold,and the risk assessment of debris flow is carried out as an evaluation unit.Based on the formation conditions,controlling factors and formation mechanism of debris flow,and referring to the previous evaluation methods of debris flow in high and cold mountainous areas,the geological conditions(formation lithology,distance from structural belts,peak acceleration of ground motion),topography and landforms(slope,slope direction,relative elevation of river basin and watershed system geomorphic information entropy)are selected.Value),meteorological conditions(monthly rainfall,temperature in 5-9 months),surface vegetation cover(vegetation normalization index)of the 4 kinds of factors,a total of 10 representative factors involved in the risk analysis of debris flow.(3)when evaluating the debris flow in the high and cold mountainous areas,two unconventional evaluation factors are added to the geomorphic entropy and the temperature of the basin system.The residual quality of the basin is judged by the geomorphic information entropy of the basin system and the development stage of the basin.The calculated entropy value of the watershed geomorphic information is between 0.065 and 1.588,and the statistical discovery is found.In the 119 sub basin units of the study area,there are 19 basins in the young years,36 in the early stage of the Zhuang,24 in the form year period,26 in the late stage of the Zhuang,and 14 in the old age.The temperature factor,through the knowledge of thermodynamics,the empirical formula,the relation between air pressure and altitude,and the Clausius equation of the karabalon,spread the measured temperature data on the elevation.The average temperature of 5-10 months is 13.88,and the average temperature of 11-4 months is 4.3.As the basic data,the temperature index is finally divided into space.The distribution of perennial seasonal snow melting area,perennial snow and glacier area,no ice and snow area.(4)based on the AHP-entropy weight evaluation model,the risk assessment results of debris flow geological hazards in the middle and lower reaches of the Yangyang River Basin are obtained.The study is divided into four areas: extremely dangerous area,high risk area,middle danger area and low risk area.The most dangerous areas are mainly located in the lower reaches of the nyanghe River,and the main distribution in the right bank of the nyanghe river is located in the right bank of niangnangba,nimi village,and the lower reaches of the kimu gully,respectively.The region is distributed in the middle and lower reaches of the big gully in the study area,and the low risk areas are mainly distributed in the flat and wide valley and the U trough valley formed by the ancient glaciation.