| Shimian County is located in the eastern part of the Hengduan Mountains of the Qinghai-Tibet Plateau,with fragile eco-geological environment and high development of debris flow disasters.With the increase of extreme weather in southwest China in recent years,debris flow disasters occur frequently in Shimian County,especially the debris flow disasters caused by “8·11” torrential rain seriously affect the local production and life.therefore,it is necessary to carry out the study on the susceptibility evaluation of debris flow disasters in Shimian County.Based on the project “Emergency investigation of “8·11” extremely heavy Rain Geological disaster in Shimian County,Ya’an City in 2020”,this paper takes Shimian County as the research object,field investigation,participating in the debris flow disaster data cataloguing work,on the basis of detailed analysis of debris flow disasters in the study area and the relationship between the forming conditions,and establishes an index system for evaluating the vulnerability of debris flow disasters in the study area.With the help of GIS technology,the debris flow disaster in the study area is quantitatively analyzed and evaluated by using two kinds of single model(Information model,Certainty Factor model)and 2 kinds of coupling model(Information-Fractal Theory coupling model and Certainty Factor-Fractal Theory coupling model).According to the principles and methods of prevention and control zoning,the study area is divided into three-level prevention and control zones,and some suggestions were put forward.The results are as follows:(1)According to the field investigation,statistics and data collection of geological disasters in Shimian County,the geological and environmental conditions of debris flow in Shimian county are determined,and the development types and distribution characteristics of debris flow in Shimian County are studied and analyzed: 109 debris flows are developed in the study area,mainly small debris flow.The spatial distribution of debris flow disaster is uneven,the development density of debris flow disaster is the highest in Xinmian street where asbestos county seat is located,and the lowest in Yonghe township;the watershed control is obvious,which is mainly concentrated in the valley area in the middle and high mountains of the river valley.mainly distributed in Dadu River,Nanya River and Tianwan River Basin.(2)The combination of topography,geology,vegetation,meteorology,hydrology,human activities and other factors in the study area led to the occurrence of debris flows.Debris flows are concentrated at elevations of 750m～1750m and slopes of 0°～30°;mostly in eroded structural landforms;widely developed in intrusive magmatic rock formations;mostly in areas with an average annual rainfall ranging from 1000 mm to 1200mm;most of them develop on both banks of rivers and along roads with low vegetation coverage and strong human engineering activities.(3)Based on the relationship between debris flow disaster and influence factors,discrete factors and continuity factors are selected and classified,and the evaluation factors are resampled to a grid unit of 32.5m×32.5m in GIS platform.With the help of SPSS software,Pearson correlation coefficient is used to analyze the correlation among factors,and 11 evaluation factors are selected,such as elevation,slope,geomorphology,engineering rock group,distance from fault zone,annual average rainfall,water system density,NDVI,distance from road,human activity density,disaster point density and so on.With the help of GIS hydrological analysis component,the sub-watershed unit of the study area is extracted,and the sub-watershed unit is taken as the regionalization unit,and finally the debris flow disaster susceptibility evaluation system of the study area is constructed.(4)Based on the GIS spatial analysis platform,Information model(I),Certainty Factor model(CF),Information-Fractal Theory coupling model(I-F)and Certainty Factor-Fractal Theory coupling model(CF-F)are constructed respectively.The evaluation results of debris flow disaster susceptibility predicted by the four models have similar spatial distribution characteristics,among which,the debris flow prone areas are mostly on both sides of river and highway with strong human activities and poor vegetation coverage,while the areas prone to debris flow are mostly located in the mountainous areas with high vegetation coverage and sparse population.(5)The historical disaster verification method and the actual disaster incidence rate are used to verify the rationality of the evaluation results of the four models,and the results show that the four models have reliable accuracy.The evaluation accuracy of the four models is compared and analyzed by ROC curve.The results show that the AUC values of I,CF,I-F and CF-F are 0.8099,0.8753,0.8313 and 0.8857 respectively,and the four models have higher accuracy.The evaluation accuracy of the coupling model is higher than that of the single model,the CF-F coupling model is the highest,and the CF-F coupling model is the best evaluation model.(6)According to the principles and methods of geological disaster prevention zoning,combined with the development of debris flow disaster in the study area and the results of the vulnerability zoning of the optimal evaluation model,the prevention and control zoning of debris flow disaster was carried out,and the prevention and control suggestions of debris flow disaster were put forward. |
