Study On The Characteristics And Risk Assessment Of Debris Flow In The Nanke River Basin, Jinping County, Yunnan Province

Debris flow is a kind of natural disaster which mainly occurs in mountain area or valley,but the research of debris flow has never stopped,because the sudden occurrence of debris flow often brings peoples life and property safety problems.At about 2:10 on June 24,2019,the Nanke Village Committee of Jinping County encountered an extremely heavy rain.According to statistics from the State Hydrological Bureau at 10 o'clock on the 24 th,the rain at the Nanke Rainfall Station exceeded 378 mm in the past 24 hours,resulting in the occurrence of mountain torrents and mudslides,causing serious casualties and economic property losses.Since the original geological environment balance has been broken,the three rivers in the Nanke River Basin have been transformed into highly prone debris flow ditches.Based on the results of field surveys,this article takes the three debris flow ditches in the Nanke River debris flow basin as the research object.Based on the analysis of the basic characteristics of the debris flow in the Nanke River Basin,including the formation characteristics and the flow characteristics,an evaluation model is constructed.In this paper,two commonly used evaluation models(Liu Xilin model and analytic hierarchy process)are adopted.By constructing these two models and selecting various evaluation factors,the respective risk degree is obtained,based on the comparison results,the risk assessment of debris flow gully is carried out and relevant prevention and control suggestions are put forward.The main findings of this paper are as follows:(1)Through field investigation and collection of a large number of data,this paper analyzes the general situation of physical geography and regional geological features such as traffic position,meteorology,hydrology,stratigraphic lithology,geological structure,neotectonic movement and human engineering activities,etc.,it also provides the basic data for the study of development characteristics and risk assessment of debris flow disasters in Nanke River.(2)Through a combination of field test and laboratory analysis,the formation conditions of Nanke River debris flow are studied.There are three debris flow ditches that threaten the safety of people's lives and properties,namely Nanke River Debris Flow Main Ditch,Longshu River and Nanke River.The two branch ditch of the Xihe River have a large vertical drop,and most of the landslides provide a source of debris flow.Through investigation,it is found that the Nanke River Basin is prone to debris flow disasters when encountering strong rainfall conditions.(3)The paper analyzes the flow characteristics of the Nanke River debris flow,and concludes that the debris flow in the Nanke River Basin is a valley-type,heavy rain,low-viscosity,large-scale,and moderately dangerous water-rock(sand)-type debris flow.A single-ditch debris flow risk assessment method was used to quantitatively evaluate the risks of the three ditches in Nanke River.It is concluded that the Longshu River and Nanxi River debris flow ditches are both moderately dangerous,and the main Nanke River ditch is of medium-high risk.,And compared with the on-site investigation results for analysis and verification,it can objectively and accurately evaluate the debris flow risk in the study area.