Prediction Of Typical Gully Debris Flow Activity Trend And Disaster Model In Longlin Town,Lixian County,Gansu Province

Gansu Province is one of the provinces with the most geological disasters in China.The Xihan river basin is located in the southeast mountainous area of Gansu Province,which is one of the geological disaster prone areas in Gansu Province.Longlin town is located in the middle and lower reaches of the West Han River Basin.Influenced by the geological environment and climate conditions,debris flow disasters occur frequently.Taking Longlin town as the research area,based on the 1:10000 geological disaster survey of Longlin town and its surrounding areas,this paper selects Wanjiagou,Tugou and Quanjia gully,the largest scale in Longlin Town,as the research objects,and uses the numerical simulation method to predict the activity characteristics and change trend of debris flow under the condition of material source and rainstorm intensity.1.Landslide is the main source of debris flow.Based on the evaluation results of TRIGRS and scoops3d models,which are suitable for shallow and deep landslides,it shows that with the increase of rainstorm intensity,the area of landslide instability area continues to increase,which is 0.31km~2,0.76km~2,1.37km~2 and 2.27km~2 respectively under the rainstorm conditions of 10-year,20-year,50 year and 100 year return periods.2.Based on the investigation data of landslides in Wanjia,Tu and Quanjia debris flow gullies in Longlin Town,the statistical relationship between landslide area and volume in Longlin town and its surrounding small watershed is established.Based on this,It is estimated that the starting material sources under four rainfall conditions are 47.6×10~4m~3,71.52×10~4m~3,162×10~4m~3 and200×10~4m~3 respectively.3.Based on the numerical simulation results of ramms software which can consider the debris flow provenance,the maximum velocity of the three gullies is 17.56m/s,19.37m/s,20.01m/s and19.26m/s respectively,and the maximum accumulation thickness of the accumulation area is3.76m,5.82m,9.15m and 9.48m respectively.Under the same rainstorm condition,the maximum velocity and accumulation range of debris flow in the three gullies are:Quanjia gully>Tu gully>Wanjia gully,and the frequency of debris flow in Quanjia gully is the highest.4.The possible disaster characteristics of the three debris flow gullies are as follows:(1)Wanjia gully:under the rainstorm conditions with 10-year and 20-year return periods,the gully is mainly silted,and the maximum siltation thickness is 2.5m and 9m respectively;Under the condition of 50 year and 100 year rainstorm,the area of debris flow impacting and silting gully mouth reaches 3.9×10~4m~2 and 4.6×10~4m~2 respectively,threatening 19 and 20 residential households respectively.(2)Tu gully:under the condition of rainstorm once in 10 years,the channel is mainly silted,and the maximum silting thickness is 3 m;Under 20-year,50-year and100 year rainstorm conditions,the areas of debris flow impacting and silting gully mouth reach11.6×10~4m~2,12×10~4m~2 and 12.5×10~4m~2 respectively,threatening 20-60 households.(3)Quanjia gully:under the four working conditions,the debris flow impacts and silts the gully mouth section,with an area of 9×10~4m~2,17×10~4m~2,17.5×10~4m~2 and 18.4×10~4m~2 respectively,threatening 6-16residential households and 3×10~4m~2-8×10~4m~2 farmland.