| Jin Yuan township is located in the southeast of Tangdian district,Kunming City of Yunnan Province,in the West Branch of the Xiaojiang Fault and the East branch.Under the control of complicated tectonic and topographic conditions,debris flow disaster in the area is very well-developed.There are 11 debris flows near the market town,which brought greater security risks to the market town.Through the analysis of the background of geological environment in the study area,study on debris flow formation conditions,development characteristics and the effect of existing construction projects and the possible influence of market towns are considered,to evaluate the risk of debris flow in market towns.The study can provide scientific basis for the warning and prevention of debris flow in Jin Yuan Township,and has a strong practical significance.At the same time,it can provide reference for the risk assessment method and system of debris flow in mountain towns.Through the above research,the main research results are as follows:(1)The study area has developed 11 debris flow,which are located in the right bank of the river,and two of them are gully-type debris flow(Shawan gully debris flow,Laogan gully debirs flow),the other 9 are slope-type debris flow.The basin area of Shawan gully debris flow and Laogan gully debris flow is large,and its branch channel development.According to the scale of outbreak,Shawan gully debris flow is super large debris flow,Laogan gully debris flow is a large debris flow,the other 9 are small and medium sized debris flows.The debris flow in the study area are located in the right bank of the Sijia river,roughly divided into 3 regions——Shawan gully river basin,Laogan gully river basin and back slope area.Town is located in the right bank of Sijia river,two big gully are located in the upstream and downstream of the town,town surrounded by them;The shallow gully in the slope area of the town is very developed,and the other 9 slope-type debris flow are located in the area.(2)The forming region of Shawan gully headward erosion strongly,landslide development of channel slope,which are active debris flows;The outbreak of large-scale debris flow in Laogan gully history,the trench source good cementation,it is difficult to start again,the possibility of large-scale debris flow small;The slope-type debris flow is very developed in the slope area of the town,their size is small,and it is mainly produced by source erosion,lateral erosion and undercut erosion.(3)Through the development characteristics and genetic mechanism of debris flow,and considering the effect of existing treatment projects,the risk of single ditch debris flow is qualitatively evaluated,and the two main factors of debris flow scale and frequency are selected,including 5 main environmental factors: watershed area,length of main gully,relative elevation of watershed,watershed cutting density and unstable gully bed ratio,a single ditch debris flow risk assessment model was established,and 11 debris flow gullies in the study area were quantitatively evaluated.The results of qualitative and quantitative evaluation: Shawan ravine debris flow is extremely dangerous,old Gangou debris is moderate risk,the remaining 9 of the surface of the slope debris flow risk were all low risk.(4)The population density and land cover type are selected as two indexes of vulnerability assessment,and the vulnerability assessment model of hazard formation is established.Through the spot investigation and the image interpretation method,each index is graded,and according to the high vulnerability to low,they are assigned to 4,3,2 and 1 respectively,the weights of population density and land cover type were 0.6 and 0.4 respectively,the zoning map of vulnerability is obtained by superimposing.The main area of high vulnerability area of 0.68km~2,accounting for 7.62% of the total area;the high vulnerability area of 5.84km~2,accounting for 65.47% of the total area;vulnerable area of secondary zone 2.29km~2,accounting for 25.67% of the total area;vulnerable area of low 0.11km~2,accounting for 1.23% of the total area.Finally,the vulnerability of each debris flow gully is calculated by two major indexes: property index and population index,the Laogan gully vulnerability is medium,Shawan gully,Xiaoyunjing groove,Sanyuesan groove,Hongchunshu groove,Diangang groove and Masang groove for high vulnerability,the other 4 debris flow gullies have high vulnerability.(5)Based on the evaluation of risk and vulnerability of debris flow,a model of "risk = danger * vulnerability" is put forward,using the Arc GIS software,the risk assessment results and vulnerability evaluation results were weighted 0.5,and the spatial overlap was carried out to get the risk zoning.The study area is divided into three regions,the area of high risk for 15212m~2,accounting for about 47% of the total area;in the risk area is 15124m~2,accounting for about 47% of the total area;low risk area is 2048m~2,accounting for about 6% of the total area.Finally,the risk degree and the vulnerability degree of the single ditch debris flow are analyzed by the quantitative analysis,and the risk degree of the single ditch debris flow is calculated.The Shawan gully debris flow risk degree is extremely high,0.69;Laogan gully debris flow risk medium,0.36;On the whole,the back slope area of the market town is of moderate risk.Among them,3 grooves,such as Macaokeng groove,Dazhuanwan1# groove and Daaozi groove,are not located in the Central Township,and the vulnerability is smaller than that of the Central Township,so the risk degree of comprehensive evaluation is low. |
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