Research On The Characteristics And Early Warning Analysis Of Lishuba Debris Flow

Lishubagou is a typical rainstorm debris flow valley,which is located in the northwest of Wen County of Longnan City and on the right bank of the Zhonglu River-the first branch of the Baishui River.It has a certain degree of representation in the entire Baishuijiang basin and Southern Gansu area to research the basin's geological environment and precipitation characteristics.In this paper,the characteristics and early warning methods of Lishubagou debris flow were systematically studied through field surveys,indoor experiments,numerical simulations,and theoretical analysis.The following main conclusions were obtained:?1?Based on the comprehensive analysis of the geological environment and rainfall characteristics of the Lishubagou basin,Lishubagou debris flow is characterized as:Large-scale,heavy rainstorm type,diluted debris flow.Analyzing the six-phase development history of debris flow valley and it shows that its scale and power increase from old to new.In case of heavy rain,the start-up mechanism was both slope-surface erosion transport type and channel bed lift type.?2?Using a reasonable method,the bulk density of the debris flow is calculated to be1.76 t/m³,the average flow velocity is 8.047m/s,the peak flow rate is 221?±10?m³/s,the primary solid material volume is 0.693×10⁴ m³,and the overall impinging pressure is15.47 kP_a.The software PFC was used to simulate the complete movement process of debris flow accumulation—migration—release in Lishuabagou,and predict the disaster scale of this debris flow in the future.?3?The comprehensive analysis shows that the daily rainfall threshold(I₂₄)of Lishubagou debris flow ranges from 55 to 85 mm,and the hourly rainfall threshold(I₆₀)ranges from 24.23 to 31.48 mm,by quantifying the environmental index fitting method,frequency method,Critical force method,observation statistics method.And these four methods overcome the disadvantages of single threshold early warning.?4?We Select 90%of the critical rainfall upper and lower limit values as the orange and red warning scale criteria,select 70%of the lower limit of critical rainfall as the yellow warning scale value.Then provide the disaster early warning intensity and corresponding emergency measures of four different levels of red,orange,and yellow.