Development Characteristics And Risk Assessment Of Debris Flow In Dashagou Valley,Tianshui Area

The Tianshui area is located at the transitional junction of the Tianshui Seismic Belt and the Fenwei Seismic Belt,with the frequent geo-disasters of landslide,collapse and debris flows,which seriously restricts the development of national land space planning and urban construction.The Dashagou Valley in Gangu County,Tianshui area,belongs to the first-class tributary of the Weihe River,with large drainage area and poor vegetation coverage.Due to heavy rainfall,earthquakes and human activities,the deterioration of the geological environment in the area is more serious,which lays a foundation for the outbreak of debris flow.Once a debris flow occurs,it will seriously threaten the lives and property of residents in the area and the safety of towns.Based on the long-term field investigation and the related data of geo-hazard in Gangu area,the geological environment background of the research area are analyzed,and the developmental characteristics and forming conditions of the debris flow in Dashagou Valley are studied.Meanwhile,the main motion process and the risk assessment of debris flow in Dashagou Valley are discussed.The main results obtained by the paper are as follows:(1)Through the inductive analysis of the geological tectonic setting of meteorological hydrology,topography and stratum lithology in the study area,the background of the occurrence of debris flow in Dashagou Valley is preliminarily revealed.It mainly includes the seasonal intensive rainfall,the sparse vegetation in the ditch,the fracture of rock mass and soil,the development of surrounding fault zone.and more human engineering activities(2)Using the high-precision remote sensing image,aerial data and geological survey data,the development characteristics,formation conditions and motion characteristics of the debris flow in Dashagou Valley in Gangu County,Tianshui area were analyzed.It shows that the formation area of the debris flow is 23.03km2,accounting for 93.03%of the total area of the basin;the circulation area is about 1.99km2,accounting for 4.87%of the total area of the basin.And the total reserves of loose solid matter in the area is 286.45×104m3;the gravity of debris flow is 16.03 kN/m3;the flow velocity of the debris flow can reach 4.53m/s,and the peak flow rate in a hundred years can reach 267.66 m3/s.(3)Using high-precision remote sensing technology,GIS technology and fluid mechanics,based on the comprehensive analysis of rainfall data and high-precision topographic data in the study area,the movement characteristics of the debris flow in Dashagou Valley was studied with the help of software FLO-2D.The development trend of debris flow under different recurrence periods such as 10 years,20 years,50 years and 100 years was analyzed,and the impact range were predicted.(4)Based on the entropy method and the analytic hierarchy process,and by establishing a combined weighting model and using the comprehensive index method,the risk assessment of each basin unit of the debris flow area in Dashagou Valley was discussed.