| Guolang gully is located at about 6km north-west of Yunlong County in Yunnan Province.It is a branch of the right bank of the Minjiang River which is a tributary of the Lancang River.The mouth of the gully is the key planning area of Yunlong County,and many public and administrative units are under construction.The landform of debris flow shows that massive debris flows have occurred in history.The recent massive debris flow occurred in the 1986.Debris flow has brought great threat to the construction of the town of the mouth of the gully.Therefore,it is of great significance to assess the hazard of debris flow on the basis of the formation conditions and basic characteristics of debris flow and to reduce the disaster in cities and towns.Based on the systematic investigation of the basic geological conditions and the development characteristics of the debris flow,this paper analyzes the formation conditions of the debris flow,the evolution history of the debris flow and the movement characteristics of the debris flow in 1986.The numerical simulation is used to simulate the movement process of debris flow under different rainfall conditions,and the main motion parameters of the debris flow(mud depth and maximum velocity)are obtained.The simulation results are analyzed and processed in conjunction with ArcGIS,and then to evaluate the risk of debris flow and propose the debris flow prevention measures.The main research results are as follows.(1)The Guolang gully area is 37.26km~2,the main gully is about 11.7km,and the average longitudinal slope is 132‰with 11 branch gully.Controlled by geological structure,the middle and upper reaches of the main ditch show a nearly EW trend.The middle and lower reaches are NNE trend,and the channel is lenient,and there are a large amount of loose solid materials.The main strata in the valley are from third to the Jurassic upper strata,and the lithology is mainly mudstone and sand mudstone interbedding,and the rock layer is steep,especially the left bank steep slope reverse slope development,the slope body bending and dumping deformation phenomenon is common,the slope is prone to bend and crack type failure and form landslides,and the sand mudstone in the ditch is weak and the fracture structure is also broken.The rock mass is more fractured and easily weathered and eroded.The main source of paleo debris flow is caused by landslide which is toppling and fracturing,and the second is the source of eroded material and the source of landslide.The damage of the old landslide accumulation,the unstable slope of strong toppling and bending deformation,the accumulation of old debris flow in the gully bed and the erosion of the slope surface constitute the source conditions of the modern debris flow of the gully.The survey and statistics show that the total reserves of the debris flow in the gully are about 1860.114×10~4m~3,and the dynamic reserves are about 60.5×10~4m~3.(2)Gullang gully is an old debris flow gully.During the geological history,large-scale debris flows have occurred,and the debris flow in the trench has also erupted in different scales.The outbreak of tributary debris flow in the gully has an important influence on the formation of the main gully debris flow.Most of the tributary debris flow scale is small,and accumulated in the mouth of the tributary,which is squeezing the main channel.At least two stages of large-scale debris flow have occurred in the N3Chenjiacun branch since the geological history.The debris flow has been fan-sleeved during the period.The stage I debris flow is larger than the stage II,and it can infer that the stage I sub-tributary debris flow caused a large-scale debris flow in the main gully,and this debris flow is the largest debris flow since the geological history of guolang gully.(3)The gully is a low-frequency debris flow ditch.In the recent rainy season in1986,the debris flow with a frequency of 50 years has been outburst in the rainy season.The total flow of debris flow is 12.6×10~4m~3,which is a large debris flow,but the scale is smaller than the early debris flow.According to the correlation criterion of debris flow,it is found that the total amount of solid matter in the main gully is 13.12×10~4m~3,which is similar to the actual solid matter of the debris flow.According to this,the amount of solid matter in the main branch gully in 50 years is calculated.The total amount of solid matter is 3×10~4m~3,the total amount of solid matter in the branch ditch Chenjia village is 4.99×10~4m~3.The mass calculation of the main gully and main branch in 100 years of rainstorm shows that the total amount of solid matter in the main gully is 15.25×10~4m~3,the total amount of solid matter is 3.49×10~4m~3,and the total amount of solid matter in the branch ditch Chenjia village is 5.8×10~4m~3.According to the scale of debris flow,the main branch gully are medium scale,and the main gully debris flow is large scale.(4)The recent debris flow occurrence and rainfall analysis showed that there was no debris flow in the main trench of Guolanggou in 20-year rainfall.In view of this,using the RAMMS::DEBRISFLOW software to simulate the debris flow movement process.The debris flow movement process was simulated under the frequency of one-time rainfall in 50years and 100 years.The main movement parameters(fluid depth,flow velocity)of debris flow were obtained,and a risk assessment model for debris flow in the study area was established.The evaluation model was combined with ArcGIS geographic information system for statistical analysis,and then get the distribution map of dangerous areas of debris flow.Under the conditions of P=2%and P=1%rainfall,there exist high?middle and low risk areas in the dangerous area of Guolanggou debris flow.Under the condition of P=2%rainfall,in the mouth of Chenjiacun to the mouth of main trench,the high-risk area is 4.6056×10~4m~2,which accounts for 30.3%of the risk area;the middle-risk area is 5.32×10~4m~2,which accounts for 35%;the low-risk area is 4.6664×10~4m~2,which accounts for 30.7%.Under the condition of P=1%rainfall,the high-risk area is 6.348×10~4m~2,which accounts for 38%of the risk area;the middle-risk area is 5.1576×10~4m~2,which accounts for 30.7%;the low-risk area is 5.2584×10~4m~2,which accounts for 31.3%.While there is more infrastructure in the trenches and in the trenches,the population density is high,and the outflow of mudslides may pose a greater threat to the lives and property of local residents.Based on this,comprehensive treatment measures are put forward. |
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