| Yuanyang County,Honghe Prefecture,Yunnan Province is located in the southern section of the Ailao Mountains,and is located on the south bank of the Red River.The terrain is undulating,the neotectonic movement is strong,and the unique geographical location and geological environment create favorable geological conditions for geological hazards such as landslides.Therefore,it is necessary to further study the mechanism of geological hazards(especially landslides)in Yuanyang County and the evaluation of geological hazard zoning in Yuanyang County.The selection of evaluation unit in geological hazard evaluation system is the key to affect the evaluation results.In the evaluation system,the relevant geological evaluation factors are selected,and the study area is divided into multiple regular or irregular independent units,similar to grids,slopes,watersheds,etc.,with each evaluation factor attribute and hazard distribution data.The evaluation unit is put into the corresponding evaluation model as an independent individual to participate in the calculation,and finally the susceptibility index of the entire study area is obtained.On this basis,in order to compare the influence of the grid unit and the slope unit frequently used in the study on the accuracy of the evaluation results in the geological hazard evaluation system,this paper takes Yuanyang County as the research area,closely follows the research theme of " comparative study of evaluation unit in landslide geological hazard evaluation system," and comprehensively applies the relevant theories and methods of geology,mathematical statistics,computer science and spatial geographic information.This paper systematically studies the development types and characteristics of geological disasters such as landslides in Yuanyang County,the distribution of time and space,the analysis of landslide hazard conditions,the acquisition of evaluation index factors,the division of evaluation units,the establishment of susceptibility and risk assessment models,and the following results have been achieved:(1)Based on the study of the natural geological environment characteristics of Yuanyang County,the geological hazards such as landslides in Yuanyang County were investigated in detail,and the development and spatial and temporal distribution characteristics of geological hazards were mastered.(2)The GIS technology is used to classify the influencing factors,and the spatial superposition analysis is carried out with the slope geological hazards and debris flow hazards.The correlation between them is counted and analyzed,and the basic index system of geological susceptibility and risk assessment is established,which lays the foundation for the subsequent evaluation work.(3)Through a comprehensive analysis of the control relationship between geological hazards and evaluation factors and a large number of literature references,elevation,engineering geological rock group,land use type,landform type,slope direction,distance from fault,distance from river and slope are selected to participate in the calculation of landslide geological hazard evaluation system.The random forest model is used to analyze and calculate the weight of each factor,so as to ensure the rationality of the selection of 9 evaluation indexes.In addition,based on the annual average maximum daily rainfall(1948-2020)in Yuanyang County,it is divided into four rainfall conditions : heavy rain,rainstorm,heavy rainstorm and extremely heavy rainstorm as the inducing factors of landslide geological hazard risk assessment in Yuanyang County.(4)According to the watershed method,Yuanyang County is divided into 7851 slope units and the most suitable grid unit algorithm is divided into 12985257 grid units.(5)In order to ensure the objective comparison of the susceptibility evaluation results of landslide geological hazards under the grid unit and the slope unit,the weighted information model combining the subjectively weighted analytic hierarchy process(AHP)and the objective statistical information model(ICM)is used to evaluate the susceptibility of the two evaluation units.On this basis,this paper improves the disadvantages of using rainfall as a single inducing factor to participate in the evaluation system in the risk assessment of geological hazards.Taking the average annual maximum daily rainfall as the inducing factor,based on the extreme value hypothesis under different rainfall conditions,the risk assessment results of landslide geological hazards under four conditions of heavy rain(25-50mm),rainstorm(50-100mm),heavy rainstorm(150-250mm)and extremely heavy rainstorm(>250mm)are obtained respectively.(6)The mathematical statistics and ROC(Receiver Operating Characteristic curves)curve accuracy test were carried out on the distribution of 228 geological hazard landslide points in different susceptibility levels and different working conditions.The results show that the two evaluation units are in the susceptibility and risk.In the comparison of the evaluation results,the zoning results under the slope unit system are superior to the zoning results under the grid unit system in the distribution relationship between hazard points and risk levels.In addition,ROC(receiver operating characteristic curves)curve was used to test the results of susceptibility and risk assessment.The AUC(Area Under Curve)value of the evaluation results under the slope unit system was higher than that of the grid unit.Finally,the evaluation results of the slope unit were more reasonable and accurate.Compared with the actual geological hazard susceptibility and risk survey results,the evaluation results of landslide geological hazards under the slope unit are highly consistent with the actual survey results. |
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