The Vulnerability Assessment Method Research Of Small Watershed Debris Flow

Guizhou is the only mountain provinces without plain in china,the land with more than 40 degrees slope accounted for nearly 60% of the province's land.The study area,named Ertanghe basin,is located in the Bijie-Anshun area,where debris flow is prone to outbreak,and it is a quite active area of debris flow in Guizhou Province.Due to the dense distribution of debris flow,the high mountains terrain with steep gradient,the intensive concentration of population and economic at the foot of mountain in debris flow catchment basin,the local residents' lives and property are heavily threatened,and this will undoubtedly greatly interfere with the social development,construction and resident's normal life in the Ertanghe Basin,which seriously restricts the development of local economy.For a long time,the research on the hazard of debris flow disaster is devoted to the study of the susceptibility and danger of disaster,and as an important part of hazard assessment,vulnerability assessment is rarely involved.So it is necessary to carry out the debris flow disaster region and single gully vulnerability assessment research and summarize the methods,to provide theoretical support for the realization of small watershed the debris flow risk quantification and prevention plan.This paper relies on the special project of Guizhou Provincial Department of land and resources,"Guizhou Province geological disaster hazard assessment and control model of a typical small watershed ",typical and representative Ertanghe basin was selected.By the analysis of the vulnerability assessment methods of debris flow in small basin,a method system for evaluating the vulnerability of debris flow for different scales in small watershed was proposed based on different hazard zone and threat object.Firstily,based on the analysis of data collection,the interpretation of high resolution remote sensing image and the field investigation,we divided the types of debris flow hazard-affected body,and made a number statistics,and their value was caculated.Then the attribute information is assigned in ARCGIS software,and the database of hazard-affected body in Ertanghe basin is established.And through reading and analysing a large number of papers,vulnerability assessment indicators,models and methods are discussed and demonstrated,taking into account the specific situation and the quick and accurate balance of vulnerability assessment in the study area,four kinds of social vulnerability evaluation factors,including economy,environment,substance and society,were selected,the vulnerability evaluation formula of small watershed for single debris flow was set up by using mathematical model method,and the vulnerability of 17 debris flows in the study area were caculated.On the basis of vulnerability classification standard,making debris flow basin study area vulnerability zoning map.Considering the debris flow hazard pattern,and debris flow accumulation fan in mountain area,where there are the most frequent human activities,the most concentrated industrial and agricultural production and the most densely distribution of urban villages,is the most serious casualties and property economic zone caused by debris flow.We took the actual debris flow fan for the evaluation units of debris flow vulnerability in small watershed,the method of hazard-affected body value and the actual affected population number were used to determine the vulnerability of debris flow in the study area.At last,typical debris flow gullies were selected and use FLO-2D numerical simulation software to simulate the run-out range and movement patterns of debris flow.According to the numerical simulation of the run-out range and the characteristic parameters,the physical vulnerability index of debris flow hazard-affected body in accumulation fan was caculated and used to make vulnerability assessment.The evaluation principle of three kinds of evaluation mode is simple and clear.They are easy to be popularised and applicable to debris flow vulnerability assessment of different scale for small watershed,which can provide theoretical support for the future development of small watershed debris flow hazard quantification and disaster mitigation plan.