Beijing Fangshan District, Single Ditch Debris Flow Risk Assessment

Debris flow disaster is a natural disaster characterized by its formation and its complexity,sudden outbreak and great damage.In the history of Beijing,there have been many serious mudslide disasters.The Ma'an Xihougou Valley in this study area is located in the low mountainous area in the southwest of Fangshan District,Beijing.In the “7.21” torrential rain in 2012 in Fangshan District of Beijing,a large-scale debris flow disaster occurred in Ma'anxi Taihougou,which caused a serious impact on the life and property safety and industrial and agricultural production activities of the Mizoguchi residents.This paper carried out quantitative risk assessment of debris flow in the Taihougou watershed of Maanxi in the study area.After field investigation of debris flow disasters in the study area,the development characteristics,source distribution,formation mechanism and induced factors of debris flow gullies in this area were analyzed in detail.On this basis,through the combination of remote sensing interpretation and FLO-2D two-dimensional numerical simulation,the quantitative risk assessment of debris flow disasters that may be suffered in the future of Maanxi Taihougou in the study area is carried out.The main research contents include:(1)In the process of risk assessment based on FLO-2D two-dimensional numerical simulation software,obtain high-precision DEM in the basin,accurately determine the number and location of the simulation starting point(inflow point),the debris accumulation range and other requirements for risk assessment.Parameter.The numerical simulation of the post-ditch of Maanxi in the study area was carried out under three different rainfall frequencies.The simulated debris flow depth and flow velocity were combined to obtain the debris flow intensity map.Finally,the intensity of the debris flow is combined with the rainfall cycle to obtain a dangerous map of the risk of debris flow in the study area.(2)In the evaluation of the vulnerability of single-ditch debris flow in this paper,the FLO-2D numerical simulation result processing software Mapper Pro is used to estimate the flood disaster losses of all the disaster-bearing bodies in the risk area of the Ma'antai-Taigou debris flow in the study area.Vulnerability evaluation.The debris flow simulation mud depth(H)and the material property attributes of various types of disaster-bearing bodies are taken as the factors of material vulnerability assessment,and the loss of all types of disaster-bearing bodies within the risk of debris flow is obtained in the software,and finally according to the vulnerability value.The calculation results are divided into three levels: low vulnerability,medium vulnerability and high vulnerability,which results in a vulnerability map within the risk range of the debris flow in the back channel of Maanxi.(3)Using the zoning map of the risk and vulnerability of the debris flow in the Ma'anxi post-cavity in the study area,the risk assessment model of the debris flow in the study area is obtained by using the GIS platform.