Landslide Geological Disaster Hazard Assessment In Minjiang River From Wenchuan To Diexi Based On GIS

Located in the basis of the "triangle block area in northwest Sichuan",which isdeveloped on the Bayan kala–Songpan and Indo-fold belt tectonic zone,the upperreaches of Minjiang River is the transitional terrain of abrupt change fromQinghai-Tibet Plateau to Sichuan basin. Because of the developed fold and faultstructure, Strong neotectonic activity, high mountain and deep valley, stronggravitational effect like the landslide and collapse, and abundant rainfall, all thesefactors make landslide、collaps and debris flow in this area common. Study area ofthis paper is locate in the Wenchuan-Diexi reach of the upper reaches of MinjiangRiver, where developed large-scale and oversize of landslides triggered by earthquake or heavy rain, and impact strongly, endanger the national road No.213, townsand villages near the river. Evaluation of the risk of landslide geological hazardsresearch in line with the need of the geological disasters prevention and control ofWenchuan-Diexi reach, and it has significant practical means to reduce the casualtiesand property loss effectively cause by landslide geohazard in the study area.Study area of this paper is located in the Wenchuan-Diexi reach of the upperreaches of Minjiang River. By large amounts of surveys, analysising the developmentcharacteristics and influencing factor of landslide geological hazards deeply,combining with GIS, informational method and APH, the paper evaluate the risk oflandslide geological hazards of this area further, and draw the conclusion as follow:(1) Many factors affect the distribution of landslides in this area. First,tectostratigraphic effects are obvious. Density of landslides alone the Minjiang fault,Songpinggou fault, and Maoxian-Wenchuan fault is largest; Second, structure of bankslope effects. The bedding slopes are more obvious than the inverse slopes betweenMaoxian and Wenchuan; landslides mainly appear in the place where Minjiang faultand Songpinggou fault are confluent, thus transverse valleys are common betweenMaoxian and Jiaochang; Third, lithological characters effect the distribution oflandslides. Landslides on schist of belonging to Weiguan group of Devonianappearing symmetrically, like the Yejiping landslide and the Zhongfanglandslide.Maoxian group mainly contain sericite-schist, and landslides happen more seriously.(2) Most of these large-scale landslides have obvious perniciousness. There are22super-huge landslides,22huge–sized landslides and6middle-sized landslidesamong all these50landslides, which distribute alone both banks of Minjiang River.These landslides threaten many important utilities like housing estates, the nationalroads and hydropower equipments.(3) On the basis of ArcGIS software, a landslide geological disaster geographicaldatabase in the study area is established. It’s includes physical geographycondition,geological environment,Geological hazard factors and risk assessmentresults, four feature datasets, and recording themselves respectively. It is moreconvenient to browse, query, statistics, management and updates by doing this andcan lay a good foundation for the latter part of landslides statistical analysis and riskassessment.(4) Using the spatial analysis function of ArcGIS to the spatial and timedistribution of landslide geohazard and to compile the control factors of landslidegeohazard. The statistics shows:①The landslide geohazard mainly distribute in theboth side of Minjiang river and it’s branches in the study area;②Slope degree oflandslides in the study area are sensitive to15°-30°m,and the slope upward to thesouth, southeast is the most sensitive;③Landslides in the study area is mainlydeveloped in phyllite metamorphic rock region;④The development of landslide ismore controlled by tectonic and stratum system than other factors.(5)According to the analysis of the formation condition and induced factor of thelandslide in the study area, established risk evaluation index system of landslides instudy area by seven evaluation factors as follows: slope degree, slope direction,formation lithology, geological structure, river system, rainfall and human engineeringactivities. Determine the information amount of evaluation factor within each gradeby using information method, using the AHP to determine the weight of eachevaluation factor, finally completed the assignment of evaluation information right inthe ArcGIS.(6) Using the Raster Calculator tool of ArcGIS to grid compute each evaluationfactor’s information right; Completing risk assessment and regionalization tolandslide geohazard in the study area; Using statistic analysis function of ArcGIS tostatistically analyze hazard zone, and divided the analysis result into four levels:extreme danger zone (23.23%), high danger zone (35.94%), medium risk zone (30.96%) and low risk zone (9.87%).