Quantitative Risk Assessment Of Debris Flow To Villages

Mountain villages are the areas where debris flow disasters occur most frequently and caused huge fatalities and economic loss due to the complex geographical and geological conditions and weak ability disaster prevention capability.Risk assessment of buildings and population is the basis of risk management of debris flow in mountain villages.At present,China has not yet formed a debris flow risk assessment system in mountain villages on regional and local scale.The risk identification of debris flow in large-scale villages mainly depends on a manual survey,which is inefficient and inaccurate.The quantitative study on the risk of single building and population is rare.It is necessary to carry out quantitative risk assessment of debris flow mountain villages,and to construct a set of scientific and feasible risk assessment system.The risk assessment system could be used to realize the accurate identification of high-risk towns,villages on regional scale and high-risk buildings and population in specific village,which could provide scientific decision-making basis for the prevention and mitigation of debris flow in villages in China.In this paper,the Hengduan Mountainous area was selected as the study area,a thematic disaster risk assessment database was established by means of remote sensing interpretation,historical data collection and on-site investigation.The spatial distribution of debris flow-prone catchments,debris flow events and their relationship with related environmental factors were discussed.The causes and influence factors of fatalities and damage to buildings due to debris flow in villages were discussed.The risk assessment and zoning of debris flow at township scale were carried out,and the method and process of debris flow risk identification based on high-definition remote sensing image and big data analysis were put forward.The quantitative risk assessment of building and indoor personnel risk was carried out,and the processes of quantitative calculation of building and personnel risk were improved.The main research results of this paper are as follows:1.The main control factors of debris flow disaster in Hengduan Mountain area and the characteristics of debris flow disaster in villages have been clarified.The spatial distribution law of debris flow-prone catchments and debris flow disaster in Hengduan Mountain area is revealed.The density of landslides,water system,and fault zones are the main factors that determine the spatial pattern of debris flow disasters.Rainfall characteristics of debris flow disasters in different geographical regions are significantly different.Debris flow occurs most frequently inJune,July and August.Debris flow events and fatalities in the three months accounted for 80.76%and 82.59%,respectively.Dadu River Basin,Min River Basin,Yalong River basin and Jinsha River Basin(the main river below Shigu)are the three river basins where debris flow occurs most frequently with 88.6%of debris flow events.Local villagers,mine workers,construction workers in hydropower station,tourists are the main deaths due to debris flow.Women,children and the elderly are vulnerable to debris flow in mountain village.The population density is an important factor affecting death tolls caused by debris flow.Death tolls in villages and debris flow volume have obvious positive correlation:log(F)=0.3107log(V)-0.2816.The F is debris flow fatalities in village;V is debris flow volume(m³).2.Indicator system of life risk assessment on township scale based on posterior information and micro-socio-economic index was constructed.Indicators of debris flow hazard assessment were constructed based on the posterior information of historical disasters and large data of villages and towns.The number of settlements easily affected by debris flow disasters and the frequency of historical debris flow are selected as indicators;the debris flow hazard in towns was evaluated by using the method of linear function comprehensive evaluation.The indicators of population vulnerability based on micro-economic index were constructed.Population density of each township,the number of non-local people,the number of children under 5 and the number of elderly people over 65,the average disposable income of rural residents,and the average years of schooling were selected as indicators.Population vulnerability on township scale was evaluated by TOPSIS method based on combination weighting method.Finally,the risk assessment of debris flow to population of towns was carried out in Hengduan Mountain area.The results show residents in 166 towns have very high risk.These towns account for10.20%of the total number.These towns are mainly located in Wenchuan County,Xiangcheng County,Derong County,Rangtang County,Daba County,Yanyuan County,Weixi Countyand Dongchuan District.3.A rapid risk identification method based on the dangerous distance and height of buildings was established.Based on the analysis of 272 buildings damaged by debris flow and 26 debris flow events,the dangerous distance and height of buildings threated by debris flow were put forward and a danger level identification matrix for buildings was established.A method of building boundary extraction and process of dangerous buildings identification based on high precision remote sensing images and digital elevation model were proposed.It can overcome the subjective randomness of large-scale manual investigation.Quantitative risk assessment of debris flow to buildings and people in door were proposed by considering the frequency of historical debris flow events and danger level of buildings.The method can rapidly identify the debris flow risk in village in large area and provide a scientific method for the identification of high-risk villages and towns.4.Method and process of quantitative risk assessment of buildings and people indoor in villages have been improved and perfectedA method for calculation of building vulnerability based on debris flow velocity,depth,and building physical characteristics including building structure,number of floors,building row toward torrent,and bounding wall range was established:V_b=I×(1-R_e),R_e=a×CS+b×NF+c×BR+d×BW.A method for calculating indoor rate of residents in villages was presented:P(T)=(_TI^t1+_TI^t2+…+_TI^tn)/n.The quantitative risk assessment of buildings and population was improved and the risk calculation process of indoor personnel was perfected.Quantitative evaluation of effect of engineering project for debris flow was realized.The method fills up the blank of the quantitative risk assessment of population,and provides scientific basis foridentifying high-risk buildings and population in villages.The main innovations are as follows:1.The risk assessment method based on the prior analysis of debris flow causes does not take into account the cause information of debris flow disasters in villages and towns,and can not accurately reflect the threat degree of debris flow disasters in mountain village.In this study,the number of settlements affected by debris flow disasters and the frequency of historical debris flows are taken as indicators,and a hazard assessment index system of debris flows in villages constructed based on the posterior information of historical disasters and large-scale data of villages and towns,it can objectively reflect the danger degree of debris flow in villages and towns.2.A method for rapid risk identification of mountain villages in large area based on dangerous distance of buildings threated by debris flow was established.Based on the analysis of a large number of sample data,this paper puts forward the danger distance and height threated by debris flow;a danger level identification matrix for buildings was established.The process and method of quickly extracting building patches from high-precision remote sensing images and recognizing building danger level based on geographic information technology are explored.The vulnerability of building and population was proposed according to the damage characteristics of buildings with different danger level and the mortality probability of residents.Then,a method of debris flow risk assessment is developed,which takes into account the frequency of debris flow in small watershed.This method is not only easy to be used in practice,but also can meet the requirements of large-scale identification of high-risk villages,which provides the basis for further refinement of debris flow investigation and risk assessment.3.The calculation method of building vulnerability has been improved and calculation method of indoor rate of residents by considering characteristics of human activity based on a single building has been proposed.A method for calculation of building vulnerability based on dynamic strength parameters of debris flow and building physical characteristics was established,which improves the quantitative risk assessment method of buildings,and realizes the quantitative evaluation of effect of engineering project of debris flow.The calculation method of indoor rate of residents was proposed,which fills up the blank of the quantitative risk assessment of population.The paper carried out debris flow risk assessment on towns,villages and building scale in Hengduan Mountainous area,where debris flows occur most frequently.The research is close combination with debris flow mitigation in mountain villages.A theoretical framework and technical system of risk assessment at regional scale and local scale(high-risk towns?high-risk villages?high-risk buildings and population)have been presented.The quantitative risk assessment method of buildings and population has been improved.The framework and methods realized the precise risk identification of debris flow in a large area and a specific village.The research results can provide scientific basis for precision management of debris flow risk,and provide a theoretical reference for the deployment of debris flow disaster prevention and mitigation project in mountain villages.