| Fuyang District is a city with a lot of mountains and a little farmland and rivers.There are ups and downs in the territory,overlapping peaks,large and small streams and reservoirs dotted around.Tianmu Mountains in the northwest and Xianxialing in the southeast,Fuchun River runs through the middle of the city,Presenting a topography of"two mountains sandwiched by a river".The frequent occurrence of geological hazards in this area is closely related to the fragile geological environment.Based on"1:50000 Geological Hazard Risk Survey in Fuyang District,Hangzhou",this paper analyzes the temporal and spatial distribution of geological hazards and their pregnancy conditions in Fuyang District based on 368 historical geological hazards and the collected multi-source data sets.With the help of GIS,Matlab,SPSS and other softwares,the risk assessment of geological hazards in Fuyang District was carried out by using IM(information model),BPNN(BP neural network model)and cluster analysis,and the following work was done:(1)Ten factors,such as elevation,slope,aspect,curvature,engineering geological rock group,NDVI(normalized vegetation index),distance from faults,distance from roads,river system and average annual rainfall,are selected to construct the geological hazard risk assessment system in Fuyang District.IM and BPNN are used to count and analyze the distribution of geological hazards in each evaluation factor,and then GIS grid calculation and reclassification are used to divide the study area into four areas:extremely high,high,medium and low geological hazards.In order to evaluate the accuracy and feasibility of the above two methods,ROC curve and its corresponding AUC value are used to further compare and test the two models.The AUC values of the two models are 0.811 and 0.862,respectively,and the accuracy of BPNN is 5.1%higher than that of IM model,which shows that BPNN is more advantageous and reliable in risk assessment in this area.(2)The vulnerability evaluation system of geological hazards is established by selecting four indicators:population density,cultivated land density,road density and GDP density.Taking villages and towns as evaluation units,the vulnerability of geological hazards in the study area is divided into four regions:extremely high,high,medium and low by using the system cluster analysis method.There are 4 low vulnerability in 24 towns,accounting for 16.15%of the total area of the whole region;There are 2 towns with medium vulnerability,accounting for 5.02%of the total area of the county;There are 9 townships with high vulnerability,accounting for 21.53%of the total area of the county;There are 9 towns with extremely high vulnerability,accounting for 57.29%of the total area of the county.Generally speaking,the vulnerability of geological hazards in Fuyang District is medium to high.(3)The function of risk grade judgment matrix and GIS grid calculator is adopted:the results of geological disaster risk and vulnerability zoning in Fuyang city are multiplied by matrix,and then divided into four areas with high,high,medium and low geological disaster risk in turn.The risk areas from high to low are 448.33km~2(24.81%),600.13km~2(33.21%),646.25km~2(35.76%)and 112.57km~2(6.23%),respectively.The overall risk of the study area is high,and the high-risk areas are concentrated in the streets in the middle of the study area and the towns in the east and west.Figuer[49]Table[18]Reference[84]... |
