Forecast The Trend Of Large-scale Debris Flows Along Zhouqu-Wudu Section Of Bailong River Basin

The Zhouqu-Wudu section of Bailong River Basin is one of the areas with the most serious debris flow disasters and the highest outbreak frequency in China,and it is also one of the areas with the most intensive debris flow prevention and control projects.In the future,under extreme precipitation conditions,what is the trend of large-scale debris flow activity in this region and whether the blocking project is effective?It is not only a problem of great concern to the government and the public,but also one of the challenging problems in debris flow disaster research.This paper chooses Zhaizi Gully,Sancha Gully,Baicao Gully,Ganjia Gully and Fotang Gully as the research objects in Bailong River Basin.Based on the analysis of the basic characteristics of debris flow gullies,the FLO-2D software which is widely used at home and abroad is used to simulate the activity characteristics of these five debris flows under the conditions of 10,20,50 and 100-year rainstorm with or without blocking works.The simulation results show that:1.Under the condition of no blocking works:(1)The velocity of debris flow in five debris flow gully increases with the intensity of rainstorm,and the velocity in gully is the highest;and the stacking thickness increases with the increase of rainstorm working condition,and gradually decreases from the central channel to the two sides of the stacking fan.(2)debris flow will not rush out of the gully in a rainstorm once in 10 or 20years;debris flow rush out of the gully during the rainstorm once in 50 years;the bailong river is blocked by debris flow that rush out of the gully during a rainstorm every 100 years.(3)when there is a rainstorm once in 10,20,50 or 100 years,the velocity,accumulation area and maximum accumulation thickness of debris flow in ganjia gully are the highest,and the maximum flow velocity is10.31m/s~12.43m/s,and the accumulation area is 0km~2~0.75 km~2,the maximum stacking thickness is 5.95m~8.24m;This three data of baicao gully are the smallest,with the maximum velocity of 6.28m/s~6.89m/s,and the accumulation area of 0km ~2~0.14 km~2,the maximum stacking thickness is 3.80m~4.90m.The reasons for the difference of the above data in each gully include the different flow rate of debris flow,the quantity of material source and the vertical gradient of flow area.2.after the construction of the blocking project:(1)the accumulation range of five debris flow gullies increases with the increase of rainstorm,and the accumulation thickness increases with the increase of rainstorm working conditions.Compared with no blocking project,the amount of debris flow rushing out will be reduced and the accumulation range will be narrowed too.(2)five debris flows will not rush out of the gully or only out of a small area when there is a rainstorm every 50 years;When there is a rainstorm every 100years,debris flows will rush out of the gully,but the area of accumulation area will be smaller than that of no blocking project.(3)when there is a rainstorm once in 10,20,50 and 100 years,the flow velocity,accumulation area and maximum accumulation thickness of debris flow in ganjia gully are the highest,and the maximum flow velocity is 10.3lm/s-12.43m/s,the accumulation area is 0km~2~0.62 km~2,the maximum stacking thickness is8.87m~9.16m;the flow velocity of zhaizi gully is the smallest,which is3.90m/s~9.18m/s.The minimum accumulation area of baicao gully is 0km~2~0.09km~2;The maximum accumulation thickness of the sancha gully is the minimum,ranging from 5.38m to 7.17m.The reasons for the difference of the above data in each gully include the different flow rate of debris flow,the quantity of material source and the vertical ratio of flow area,as well as the difference in the number and height of debris dams.