Study On Risk Assessment And Early Warning Model Of Debris Flow In Shijiaying Township,Beijing

Debris flow disasters have occurred in many debris flow gullies in Beijing mountainous area,causing serious losses.Taking shijiaying Township,Fangshan District,Beijing as the research area,based on literature and field survey,combined with UAV aerial survey and geophysical exploration,this paper studies the topography,source reserves and distribution,rainfall,classification,development stage and susceptibility of 19 debris flow gullies in the study area.According to the characteristics of debris flow gullies in the study area,the hazard and vulnerability evaluation index system was constructed,and the hazard and vulnerability evaluation was carried out.Based on the hazard and vulnerability assessment,the risk assessment is carried out.Based on the rainfall data of shijiaying meteorological station,the rainfall characteristics of shijiaying township are analyzed,and the debris flow early warning model is established.The following understanding and achievements have been achieved:(1)The topography,material source and rainfall of shijiaying are favorable to the occurrence of debris flow.According to the distribution location and characteristics of material sources,the material sources are divided into four types: channel accumulation material source,slope accumulation material source,collapse accumulation material source and artificial accumulation material source,and the material source reserves of 19 debris flow gullies are evaluated.The average rainfall from 2008 to July 2017 was 170.0 mm,112.1 mm in August,105.8mm in June and 90.7 mm in September.(2)Combined with the selection principle of hazard evaluation index and the characteristics of debris flow gully in the study area,nine indexes including the drainage area are selected to build the hazard evaluation index system.AHP,entropy method and distance function combination weighting method are used to obtain the subjective weight,objective weight and combination weight respectively.On this basis,the hazard assessment of debris flow gully is carried out.The results show that there are 3 debris flow gullies with high hazard,13 gullies with medium hazard and 3 gullies with low hazard in the study area.(3)The vulnerability evaluation model of debris flow gully is improved,and the vulnerability evaluation index system based on disaster loss index and disaster resistance ability index is established.The evaluation index system of disaster resistance ability of 10 secondary items in three aspects of prevention and control engineering,monitoring and early warning,and emergency response is established,and the evaluation of disaster resistance ability of debris flow gully is carried out on this basis.The results show that the anti disaster ability of shijiaying debris flow gully is low as a whole;There are 5,4 and 10 debris flow gullies with high,medium and low resistance to disasters respectively.The results of vulnerability assessment show that five of the19 debris flow gullies are highly vulnerable,six are moderately vulnerable,and eight are low vulnerable.(4)Risk assessment adopts risk = hazard × Vulnerability model,the results show that: 4debris flow gullies are high risk,8 debris flow gullies are medium risk,7 debris flow gullies are low risk.(5)The early warning model of debris flow is constructed.By analyzing the rainfall characteristics of the debris flow event in shijiaying Township,the rainfall to stimulate the debris flow can be divided into two types: the rainfall dominated type,the indirect pre rainfall and the rainfall dominated type.The RTI early warning model of shijiaying debris flow is established,and the single gully early warning model is constructed with the help of monitoring equipment.