The Development Characteristics And Risk Assessment Of Ronglang Debris Flow In Rangtang County,sichuan

Debris flow is a natural disaster mostly occurs in mountain area of China.Especially the southwest part of our country,where the mountain area has special topography,abundant precipitation and material resources,debris flow disasters are particularly common.In the flood season of 2015,a debris flow disaster broke out in Ronglang gully,Rongmuda Township,Rangtang County,Sichuan Province,which caused some damage to Rongmuda Township,located at the mouth of the gully.At present,the debris flow is still likely to break out.In order to ensure the safety of local residents and property,systematic study on the development characteristics and risk assessment of Ronglang debris flow is of great significance to the selection and design of comprehensive control measures.On the basis of field investigation,this paper explores the regional background information of debris flow formation,analyses and summarizes the characteristics of topographic and geomorphological,materials resources and water source of Ronglang gully,and clarifies the formation and development conditions of debris flow.According to the characteristic parameters of debris flow dynamics,using Liu Xilin evaluation model and Fuzzy Analytic Hierarchy Process(FAHP)to determine the risk degree of Ronglang debris flow.The results are compared and analyzed,and the risk grades are synthetically obtained.At the same time,the ANSYS CFX numerical simulation software is used to simulate the dynamics process and the harzard zone of debris flow with a frequency of 20 years and 50years return period,which reflects the danger to residential areas.The main research results are as follows.(1)Based on field survey and data collection,the development characteristics and formation mechanism of Ronglang debris flow are summarized.Ronglang gully basin area is45.59 km~2,with valley landform,steep slope on both sides of the bank,and the developmental branch ditches,abundant loose materials and geological phenomena,which provides favorable topographic and material conditions for the formation of debris flow.The debris flow belongs to rainstorm valley type for the main triggering factor of the debris flow is rainstorm.Under rainstorm or continuous rainfall conditions,water converges and carries loose deposits in the channel and the foot of the bank slope downward to form debris flow disaster.(2)Liu Xilin's evaluation model and Fuzzy Analytic Hierarchy Process(FAHP)are used to calculate and grade the risk degree of debris flow at different frequencies.Choosing the appropriate evaluation index and weight assignment method of debris flow,this paper establishes the evaluation model of Ronglang debris flow,obtains the results of risk assessment of the two methods,and provides a reference basis for the design of prevention and control engineering after analysis and comparison.(3)Using computational fluid dynamics software ANSYS CFX to simulate the three-dimensional flow field of debris flow with a frequency of 20 years and 50 years return period,obtaining the process of debris flow overflow,siltation,velocity field distribution and maximum overflow range,as the range of harzard zone,which can directly reflect the impact of debris flow on Rongmuda Township.Based on this,the design of prevention and control project is put forward.