Risk Assessment Of Geological Hazards In The Lower Reaches Of The Zagunao River Based On GIS

The study area is located in the east of Lixian County of Aba Tibetan and Qiang Autonomous Prefecture, located in the southeast of Qinghai-Tibet Plateau, which belongs to the typical river erosion, alpine Canyon landscape.The study area has strong new tectonic movement, frequent earthquake activity, deep valleys, complex geological conditions, the environmental problem is very prominent, especially the landslide, collapse, debris flow and other geological disasters, which is one of the most typical regions of “museum of geological hazards” in Sichuan Province. Therefore, it has a very important significance to reduce losses caused by geological disasters in the study area by assessing risk of geological hazards in the lower reaches of Zagunao River, Xuecheng area. At the same time, it also has guilding significance for environmental protection, urban planning, the siting of the key project construction and disaster prevention and mitigation of the study area.Through field investigation and indoor data processing, establish an analysis and evaluation model that uses the method of analytic hierarchy process and information quantity method, combined with ARCGIS software's powerful data processing, analysis and statistical functions, this paper assesses the susceptibility and risk of 91 geological disasters in study area, and draw susceptibility zoning map and risk zoning map. The concrete results of the study are as follows:(1)Summarize the basic development rule of geological disasters in the study area. Based on the study of 38 landslide, 32 rockfall, and 21 debris flow in the study area, it is concluded the following rules:(1)In terms of time, geological disasters in the study area occurred from May to September each year, particularly in June and July.(2)From space, the landslide disaster in the area are mainly distributed along the Zagunao River and its tributaries, and the landslide tend to appear on the right bank of Zagunao River than left bank. The rockfall appeared at steep slopes below the height 2200 meters, and distributed on the left bank of Zagunao River than right bank. Debris flow appeared in more than 1500 meters above sea level, and distributed on the left bank of Zagunao River than right bank. The scales of debris flows are medium and large.(2)Select the most favorable assessement factors combination of rockfall, landslide and debris flow. The statistical analysis function of ARCGIS shows that:(1)the landslide disaster is most likely to happen at the slope of 20-50 gradient, north and northwest to the Weiguanqun group and the fourth and the fifth of Maoxian group.(2)the rockfall is most likely to happen at the slope of 40-60 gradient, south and southwest to the upper and lower Weiguanqun group.(3)the debris flow is most likely to happen at the slope of 30-50 gradient, 3-4 debris point density per square kilometers, and 450-500 mm of rainfall per year.(3)Construct the assessment model of geological disasters in the study area. this paper establish four level indicators of the analytic hierarchy process method to determine the weight of each evaluation factor, according to the information quantity method to determine the information value of internal level classification of each evaluation factors, then information quantity of each factor calculated by information quantity method and the weight calculated by analytic hierarchy process are multiplied to get a weighted amount of information, finally import the weighted information value of each calculated evaluation factor to each layer of ARCGIS, and provide the stack basis for the zoning of the risk assessment and susceptibility assessment.(4) Using GIS to carry out the susceptibility assessment and risk assessment zoning of the study area :Select information quantity method and analytic hierarchy process method to construct evaluation model, using digital elevation model, combined with the powerful calculation function of ARCGIS to carry out raster overlay calculation of each factors affecting the susceptibility assessment and risk assessment of geological hazards, obtain the comprehensive influence value of all the factors, and according the result of numerical value, the susceptibility and risk zoning were carried out.