Risk Assessment And Zoning Study Of Geological Hazards In The Liuku-Lujiang Section Of The Lower Valley Of The Nujiang River

The Liuku-Lujiang section of the lower Valley of the Nujiang River is located in the northwestern border of Yunnan Province and is under the jurisdiction of Lushui City and Baoshan City.The geological background conditions in the area are relatively complicated.The Nujiang fault runs through the entire area and the tectonic activity is strong.In addition,under the background of the western development,human engineering activities are extremely active,which makes the frequency of geological disasters in the study area increase year by year.The production and life of the people inside have caused varying degrees of influence.Therefore,carrying out geological hazard risk assessment and zoning research on the Liuku-Lujiang section of the lower reaches of the Nujiang River Valley can provide a certain reference for the geological disaster prevention and urban planning site selection in the study area,and at the same time effectively reduce the personnel caused by geological disasters The loss of life and property has important practical significance.This article relies on the "Research on Quaternary River Valley Evolution and Disaster Trends in the Yunnan Section of the Nujiang River Basin",based on field investigations,combined with previous research results,to influence the geological disasters in the Liuku-Lujiang section of the lower Valley of the Nujiang River,Distribution and development characteristics were analyzed and studied.Finally,based on Arc GIS software,the weight of evidence method(Woe)and fuzzy comprehensive evaluation method(Fuzzy)were used to carry out risk assessment and zoning of geological hazards in the study area.The main contents and results of the research are as follows:(1)The Liuku-Lujiang section of the lower valley of the Nujiang River is located in the southern part of the Hengduan Mountains in western Yunnan.The overall terrain is high in the north and low in the south,high in the east and west and low in the valley.A total of 76 collapses,72 landslides and 81 debris flows were developed in the entire study area.(2)Through the investigation of the geological disasters in the Liuku-Lujiang section of the lower Valley of the Nujiang River,the spatial and temporal development rules of geological disasters in the region were revealed:(1)In terms of time distribution,geological disasters such as avalanches,slips,and currents in the study area are prone to occur from May to October of each year,of which mid-July to early August are the high incidence;(2)From the perspective of spatial distribution,the collapse is mainly concentrated in the townships with relatively active human engineering activities such as Luzhang,Liuku and Lujiang,and the scale is mainly small and medium;The landslides and debris flows are mainly distributed in the middle and upper reaches of the study area where structural activity is extremely active.Among them,the scale of landslides is mainly large and medium-sized.The distribution of debris flows is mainly large,large and medium-sized,and small debris flows are not well developed.(3)Performing a statistical analysis on the factors affecting the geological disasters in the Liuku-Lujiang section of the lower valley of the Nujiang River,and based on Arc GIS software,analyze the impact of each influencing factor on the development of geological disasters such as avalanches,slips,and currents in the study area.The best combination of factors conducive to the formation of geological disasters.According to statistical analysis:(1)The collapse disaster has the strongest sensitivity in the slope> 50°,terrain relief> 400 m,NDVI <0.2 and rainfall < 960mm;(2)Landslide disasters are most sensitive in slopes of 20 ? 45°,terrain relief of 320-400 m,NDVI between 0.2 ? 0.35 and rainfall of 960-1000mm;(3)The debris flow disaster has the strongest sensitivity in the slope of 20 ? 40°,terrain relief> 400 m,NDVI between 0.2 ? 0.35 and rainfall of 1000 ? 1040 mm.(4)Using the weight of evidence method and fuzzy comprehensive evaluation method to separate the geological disasters such as avalanches,landslides,and currents in the study area through hazard zoning,and then use Arc GIS software to overlay the hazard zoning layers of the three types of disasters,thus draw the zoning map of geological hazard risk in the whole study area.The obtained comprehensive zoning map of risk(right of evidence method / fuzzy comprehensive evaluation method): the extremely high-risk area accounts for approximately 7.6% / 15.9% of the total area,the high-risk area accounts for approximately 22.3% / 18% of the total area,and mediumrisk The area accounts for 30.9% / 26.3% of the total area,and the low-risk area accounts for 39.2% / 39.8% of the total area.(5)According to the accuracy test results of the two evaluation methods based on the ROC curve,it is known that both the collapse and the landslide have a higher accuracy rate,and the prediction results for the debris flow disaster are lower.By comparison,we can see that the overall evidence-based the evaluation results obtained by the method are more accurate.Therefore,this article finally selects the evaluation results based on the weight of evidence method combined with the actual situation in the study area,and divides the danger degree of the geological disasters in the area into four levels: low,medium,high,and extremely high risk,so as to obtain the results of the comprehensive zoning of geological hazard risk in the Liuku-Lujiang section of the lower Valley of the Nujiang River are obtained.