Risk Analysis Of Geological Hazards In The Shoujiang River Basin Of The Upper Reach Of Minjiang

Shoujiang is in the southern part of Wenchuan,which is situated between Aba Tibetan and Qiang Autonomous Prefecture in the western part of the Sichuan basin.It is a tributarie of Minjiang.With complex geological conditions,strong neotectonic movement,plentiful rain,high frequency hazards which hinder and threaten the economic construction and the safety of lives and property of people occur in the study area,especially large scale and high frequency landslides,collapses and debris flows.So,investigation and risk assessment of geological hazards in study area is in order to provide effective support for disaster prevention and reduction in the future,which is of great importance.Based on collecting date and field investigation,taking the geological hazards in the Shoujiang river basin as the object,this paper which is through GIS analyzed the regularities of distribution,development characteristics and influenced factors of the geologic hazards,completed the risk analysis and hazard zoning by analytic hierarchy process and information quantity method.The concrete results of the study are as follows:(1)The Shoujiang river basin whose terrain is high west and low east is located in the southern Longmenshan tectonic belt.The study area which is in ample precipitation exposes some of Longmen mountain and Sichuan basin division stratigraphy,and lots of Maerkang partition stratigraphy.Under the background of this geological environment,43 landslides,41 collapses,and 8 debris flows were developed in the study area.(2)Based on the investigation and analysis of the geological hazards,some results are:(1)From the time point of view,the geological hazards always happen in May to September month every year,especially June,July,August month;(2)From the spatial distribution,landslides are mainly distributed from the Xuankou~Shuimo~Sanjiang,and the left bank of the river is more than the right bank;whose scale are large and super large,collapses are mainly distributed both sides of Heishijiang,Zhonghe,Xihe in the upper reaches of Sanjiang;debris flows which is caused by heavy rain is mainly distributed from the Xuankou~Shuimo~Sanjiang,and the scale is mainly large and medium-sized.(3)Build a individual geographic database for geological disasters basing on the ArcGIS software.Through ArcGIS,this paper analyzes what are beneficial to the geological hazards,generalizes what is the most powerful group for geological hazards development.Statistical analysis shows that:(1)landslides are most impressible under the backgrounds that are slope which is between 20 to 40°,rocks which is soft and hard clastic rocks,rainfall which is between 1050 to 1075mm;(2)collapses are most impressible under the backgrounds that are slope which is between 0 to 20°,rocks which is hard magmatic rock,rainfall which is between 1000 to 1025mm;(3)debris flows are most impressible under the backgrounds that are slope which is between 20 to 40°,rocks which is soft and hard clastic rocks,rainfall which is over 1025 mm.(4)Definit the weights information of each evaluation factor by information quantity method combined with analytic hierarchy process.Determine the weights of evaluation factors by constructing the hierarchical structure of four indicators,use the information quantity method by calculating the weights information of each evaluation factor,and complete the evaluation of the amount of information in the ArcGIS software.(5)Complete the risk assessment and risk zoning in the Shoujiang basin based on spatial weighted summation overlay function of ArcGIS platform.The danger area is divided into four grades: low risk area(43.02%),medium risk area(21.67%),high risk area(18.47%),extremely dangerous area(16.84%).(6)With ROC curve method,verify risk assessment results of geological hazard by comparison of risk zoning with known geological hazards.The result shows that the outcome of geological hazard assessment based on the information quantity method and ArcGIS is of high accuracy,and the application of risk analysis of geological hazards in the Shoujiang area is reasonable.