Risk Zoning Of Debris Flow Disaster In Fengdie District,Zhouqu County Of Gansu Province

Debris flow is one of the most frequent and most dangerous types of geological disasters in nature.Debris flow often destroied and buried civilian houses and infrastructure in an instant,causing casualties and clogging of rivers,causing serious harm to human life and property.Zhouqu County is a high-incidence area and dense area of debris flow disasters.The mudslide disaster has caused great losses to local residents,which seriously restricts the economic development and infrastructure construction of Zhouqu County.Fengdie District is a reconstruction and resettlement area after the Zhouqu 8·8 extra large mudslide,with 5 mudslides distributed around it.Fengdie District,which is located at the mouth of the mudslide,has a large number of residential areas,government offices and schools.It has a large population density and high economic value.Once affected by mudslides,it will bring immeasurable life,property and society economic losses.This paper takes the Fengdie District in Zhouqu County of Gansu Province as the research area.Based on the on-site investigation,combined with local planning,using numerical simulation and GIS-based platform,quantitative analysis of debris flow hazard and debris flow disaster in Fengdie District under different working conditions.In order to bear the vulnerability of the disaster body,the risk zoning of debris flow disasters was carried out.Using FLO-2D numerical simulation software and ARCGIS spatial analysis module,five mudslides such as Yinshangou,Taizigou,Shuiquangou,Guazangou and The Gully on the other side of Guazan Village are simulated in the vicinity of Fengdie District.Under four rainstorm conditions,such as once in 10 years,once in 20 years,once in 50 years,and once in 100 years,the flow velocity,accumulation depth and accumulation range of debris flow are used as indicators to quantitatively evaluate the risk of debris flow in each ditch.The simulation results show that the high-risk area of Fengdie District is concentrated in the mudstone flow of Yinshangou and the debris flow accumulation area of Taizigou,and is mainly distributed in the debris flow fan of Yinshangou.The reason for this result is related to the geographical location of the Yinshangou basin and the development characteristics of the debris flow.Based on the planning data of Fengdie District,the assets and population were selected as indicators of vulnerability assessment.The former includes housing construction,roads and cultivated land.According to the local economic development potential of Zhouqu County,the unit price of different disaster-bearing bodies is determined;the latter’s secondary evaluation index is population density,and its value is determined by the difference in building use,such as residents district,office area,school,etc.Based on the classification and statistical calculation method and ARCGIS tool,the vulnerability model of debris flow hazard in the study area was established.Through this model,the area of asset vulnerability and population vulnerability in the maximum risk range of five debris flow and drainage areas was obtained.The research results show that the high-vulnerability areas of the assets are concentrated in the construction of disaster-bearing bodies such as buildings with high value density.The vulnerable areas in the middle are mainly cultivated land,urban trunk roads,general roads,etc.The asset vulnerability is closely related to the value of the disaster-bearing body.The high-volume and vulnerable areas are mainly concentrated in the densely populated housing buildings such as schools and high-rise residential areas.The medium-risk areas are mainly low-rise residential buildings.The population vulnerability and house building functions and layers are great relationship.Based on the basic principle of Risk = Hazard × Vulnerability,the spatial superposition of risk and vulnerability is completed under the ARCGIS platform,and the risk value of each evaluation unit is obtained according to asset risk and population risk.The natural breakpoint classification method was selected to classify the risk of debris flow disasters in the study area into high,medium and low levels.The results of the zoning show that under different storm conditions,the Yinshangou and Taizigou accumulation areas are the most concentrated areas of high-risk areas of assets and population,and are also the locations of the peaks and new towns with high vulnerability values.Among them,Yinshangou high-risk area accounts for the largest proportion,which is due to the distribution of high-vulnerability and high-hazard value evaluation grids.