| Yunlong county is located in the west of Yunnan province,which lies in the rift valley of Lancang River of western Yunnan.The county's regional geological structure is complex,with strong tectonic movements,high mountains and deep valleys,large topographic changes,strong erosion and cutting,soft rock mass development,and strong human engineering activities.Besides,debris flow geological hazards in the area are well developed,seriously restricting the social and economic development of Yunlong county as well as threatening human life safety and property safety.In recent years,faced with the severe geological disaster threat,Yunlong county has carried out a series of prevention and control projects with obvious effects.However,due to special geological conditions and strong human engineering activities,the problem of geological hazards is still serious.Therefore,the risk assessment of geological hazards in Yunlong county can provide scientific basis for the prevention and control of geological hazards and town planning in Yunlong county.Based on the characteristics of geological hazard in the urban area of Yunlong county,detailed site investigations,geological conditions of geological hazard,development characteristics,formation conditions,genetic mechanisms,and influencing factors of debris flow hazards in the urban areas of Yunlong county,this paper establishes geological disaster risk assessment model and carries out geological disaster risk assessment in Yunlong county combined with the existing status of treatment projects.The main results are as follows:(1)Field investigation shows that debris flow,landslide geological hazard are developed in research area,and there are 3 ravine types of debris flow and two landslides in Yunlong county.The debris flow in the Shiwei River is strong,and the branch ditch is developed.Both the main ditch and the branch ditch are cut deeper,resulting in a large number of landslides,slope slumps and potentially unstable slopes.The sources of solid materials are abundant,and large debris flows are easily prone to occur.The thickness of the fully weathered strata within the mudflat flow in Suo Lichang gully is relatively large.The sources of loose solids are mainly collapsing sloughs on the two banks,old debris flows,and mud-rock flow bed deposits.However,the middle and lower reaches of the channel are relatively gentle and the channel is relatively straight.Therefore,the possibility of large-scale debris flow outbreak is small;Dispersed solid sources of debris flow in Nuodeng River are mainly landslides,avalanches and channel accumulation,in which a large landslide in Song Podi,under the action of relatively large rainstorm,flood and mudslide,has the possibility of slipping to the Nuodeng River,forming a blockage debris flow.The landslides of No.1 and No.2 on the right bank of the Bijiang River are all creep-cracking landslides,which are all developed in the Tertiary Guolang Formation Stratum.Among them,the volume of the No.1 landslide accumulation on the right bank of the Bijiang River is 2.566 million cubic meters.When the landslide occurred,the slippery body blocked the Lancang River.After field visits,no signs of new deformation were found in the near future and the overall stability was basically stable.The landslide volume of the No.2 landslide on the right bank of the Bijiang River reached 1.768 million cubic meters.After field investigation,the landslide was basically stable and there were no signs of deformation.(2)By analyzing the geological environment background,development characteristics,formation conditions,and genesis mechanism of geological hazard in the urban area of Yunlong county,the activity intensity of the three debris flow in the region was studied.Firstly,the risk assessment of landslide and debris flow in Yunlong county was qualitatively evaluated.Then,based on the FLO-2D numerical simulation software,three important parameters such as mud depth,flow velocity,and accumulation range were simulated under different frequencies of rainfall before and after treatment,and the mud depth,the product of mud depth and flow velocity are used as a basis for dividing risk degree.In the Arcgis software,the risk partition map of geological hazards under different rainfall conditions before the treatment of Yunlong county was obtained.When the rainfall frequency is P=5%,the proportion of high-risk,medium-risk,low-risk,and non-hazardous areas accounts for 6.09%,3.14%,2.74%,and 88.03%,respectively;When the rainfall frequency is P=2%,the proportion of high-risk,medium-risk,low-risk and non-hazardous areas is 7.08%,5.44%,2.62%,and 84.86%,respectively;When the rainfall frequency was P=1%,the proportion of high-risk,medium-risk,low-risk and non-hazardous areas accounts for 8.41%,6.89%,4.87%,and 79.83%,respectively.(3)Qualitative and quantitative methods are used to evaluate the risk of post-treatment project.When the rainfall frequency is P=5%,the proportion of high risk,medium-risk,low-risk and non-hazardous areas is 3.41%,3.22%,1.33% and 92.04%,respectively.When the rainfall frequency is P=2%,the proportion of high-risk,medium-risk,low-risk and non-hazardous areas is 4.50%,3.75%,2.12% and 89.63%,respectively.When the rainfall frequency is P=1%,the proportion of high risk,medium-risk,low-risk and non-hazardous areas is 6.46%,4.79%,3.00% and 85.75%,respectively.It shows that the effect of the treatment project is significant,and the risk is reduced at all rainfall frequencies,but there are still some hidden dangers of geological hazards.(4)Based on the two indicators of population density and land cover type,the vulnerability assessment of geological hazards in Yunlong county was conducted.The vulnerability assessment results of the disaster-affected body in research areas were divided into three categories: high vulnerable area,middle vulnerable area,and low vulnerable area,accounting for 21.95%,21.86%,and 56.19%,respectively.(5)Based on the risk assessment of geological hazards after treatment and the vulnerability assessment of geological hazards in Yunlong county,Arcgis was used to superimpose these two evaluation results,and the risk assessment results of geological hazards in Yunlong county were analyzed.Under the condition of rainfall once in 20 years,the proportion of high-risk,medium-risk,low-risk,and no-risk areas accounts for 0.49%,6.09%,1.38%,and 92.04%,respectively.Under the condition of rainfall once in 50 years,the proportion of high-risk,medium-risk,low-risk and no-risk areas accounts for 0.80%,7.66%,1.91%,and 89.63%,respectively.Under the condition of rainfall once in a century,the proportion of high-risk,medium-risk,low-risk,and no-risk areas accounts for 1.34%,10.54%,2.36%,and 85.76%,respectively. |
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