Development Characteristics And Risk Assessment Of Debris Flow In The Upper Reaches Of Xihan River In Longnan

The upper reaches of the Xihan River Basin is located at the intersection of the Qinghai-Tibet Plateau and the Loess Plateau,with strong tectonic activities,fragile ecological environment and serious debris flow disasters.Therefore,the risk assessment of debris flow is of great significance to local disaster prevention and mitigation.This paper takes the upper reaches of the Xihan River in Longnan City as the object,based on field geological surveys and combined with the regional natural environment background,summarizes the development and distribution characteristics and types of debris flows,and analyzes the formation conditions,influencing factors and typical debris flows of debris flow disasters in this area.The mechanism of formation.On this basis,using the method of deterministic coefficient,starting from the basin unit,carry out the risk assessment of the debris flow disasters in the upper reaches of the Xihan River Basin,and obtain the following conclusions and understandings.1.Field surveys show that there are 144 debris flows in the study area,mainly small and medium-sized debris flows.According to its fluid properties,it can be divided into two categories: viscous debris flow and sparse debris flow.Among them,there are 18 viscous debris flows and 126 sparse debris flows.2.Debris flows are mostly distributed along rivers and rivers.In terms of lithology,they are concentrated in weak rock areas and intensive human activities.In terms of time,the mudslides over the years mostly occurred in the rainy years;from the point of view of the year,the mudslide disasters mostly occurred in the flood season from May to September,and reached the peak in July to August during the main flood season,and accounted for the total amount of the whole year from July to August.More than 60%.3.Different types of debris flow have different formation conditions and cause mechanisms.Among them,the viscous debris flow belongs to the transport-slip debris flow,and its formation process is the process of continuous replenishment through branch ditches and along the way.The thin debris flow belongs to the blockage-break type debris flow,and its formation process is the same as that of mining waste slag.It is closely related to collapse and landslide deposits.These deposits accumulate in the gully and block the river course.Under the influence of heavy rainfall and the strong erosion of water,they lead to the formation of mudslides.4.The risk assessment results show that the debris flow in the study area can be divided into 5 hazard levels: extremely high,high,medium,low,and extremely low.High-risk areas are concentrated in Lixian-Jiangkou-Taoping Town,Yacheng Town and Mahe Township;high-risk areas are concentrated in the north of Mahe Township,Longlin Town,Yacheng Town,Shibao Town,Yongping Town Surrounding;the middle-risk zone is located north of Luoba Town,near Zhongba Township,Honghe Town,Qishan Town and other places;low-risk zone and extremely low-risk zone are mainly distributed in other areas of the study area.