Hazard Assessment Of Landslide Geological Disaster In Baishui River Basin

Baishui River basin is located in binding site of Songpan Garze fold system,Qinling fold system and upper Yangtze platform.Poor physical geology phenomena developed widely,the terrain landform is complex and structure activities are intensive.There are 129 large-giant scale landslides.These geologic hazards threaten the safety and property of the residents all the time.Therefore,carrying out the hazard assessment of landslide disaster in Baishui River basin can render some reference value to landslide disaster prevention and has very important practical significance to decrease casualties and property losses caused by landslide effectively.This paper is based on the project of” Large Scale Deposits Development and Environmental Effects Study in Northwest Sichuan Province”.According to field investigation and combined with previous research results,we analyze and study landslides' engineering geological conditions,distribution regularities,development characteristics,influencing factors and formation mechanisms in the basin.Based on ARCGIS software,we evaluate the risk of landslide hazards of this area by means of AHP-CF method.In this paper,the following main results are achieved:(1)Baishui River basin which is located at the juncture of Sichuan Province and Gansu Province gradually reduced from northwest to southeast.In the basin,the territory is full of mountainous mountains and rivers.Geological structures like faults,folds and so on are well developed in the basin.Neotectonic movement is intense and earthquake occurred frequently.In the area,a majority of soft and hard rocks which are slate,phyllite,limestone and metasandstone alternate each other.(2)The 129 large-giant scale landslides mainly distribute in belts,lying along middle reaches of Baishui River,middle and lower reaches of Hei River,middle reaches of Bai River,Malian River and upper reaches of Zhonglu River.These landslides show clump distribution in Buziba country area of Malian River,Shijiba country area of Baishui River and Shuanghe country area of Baishui River.At the same time,a part of landslides have a certain degree of selectivity to two sides of rivers.Most landslides distribute in deeply cut valley which is between 1000 m and 2500 m and there are 46 ancient landslides,47 old landslides,36 new landslides.(3)Among the landslides in Baishui River basin,24 landslide plane shape are strip,43 are tongue shape,22 are semicircle,40 are irregular shape.There are 24 soil landslides and 105 rock landslides.These soil landslides are all loess landslides.For a portion of rock landslides,the landslide mass is covered thick loess or contains non-disintegrated bedrock.There are 41 medium thickness landslides,79 deep seated landslides and 9 superdeep seated landslides.There are 75 large scale landslides,52 ultra-large scale landslides and 2 giant scale landslides.The development characteristics of landslides which are along with different rivers are distinguishing.(4)The landslide geological disasters in Baishui River basin are affected by internal and external factors,including: topography and geomorphology,engineering geology rock groups,embankment structure,geological structure,river system,rainfall condition,human engineering activity and earthquake.Statistical analysis shows:(1)Most landslides distribute at a slope of 30~40°,at an elevation of 200~600m and in soft and hard alternating rocks.They are sensitive to west and southwest direction,consequent and reverse slope.(2)Geological structure and river system control the development of landslides to some extent.(3)All landslides occurred in the range of average annual rainfall 400~600mm in the basin.(4)There is a close relationship between human engineering activity and the distribution of landslides.The formation mechanisms of landslides mainly have 3 types,including bending-sliding type,sliding-shearing type and shearing-shattering-sliding type.(5)Based on the analysis of landslide distribution regularities,development characteristics and influencing factors,we select 9 evaluating factors that include slope gradient,slope aspect,slope elevation,engineering geology rock groups,embankment structure,geological structure,river system,rainfall condition,human engineering activity and assessment units which are 300*300m blocks to establish a landslide hazard assessment indicator system.Combined with the certainty factor(CF)and analytic hierarchy process(AHP)evaluation model,we obtain landslide hazard assessment results in Baishui River basin meanwhile the results are verified by mathematical statistics method and ROC curve analysis method.The results are divided into four levels:(1)High risk zone.The area is 1557.22km2 and has 74 landslides.(2)Medium risk zone.The area is 3327.18km2 and has 39 landslides.(3)Low risk zone.The area is 2584.64km2 and has 15 landslides.(4)Extreme low risk zone.The area is 788.11km2 and has 1 landslide.