Study On The Developmental Characteristics And Risk Assessment Of Debris Flow In Xiangxi Prefecture,Hunan Province

China is one of the most intense and frequent debris flow hazard in the world,the unique energy gradient?complex geological structure,concentrated precipitation?in mountainous area makes it the main distribution area of debris flow activities.Xiangxi Tujia and Miao Autonomous Prefecture,the center hinterland of Wuling mountain area,with the increasing hidden dangers of debris flow threatening the safety and property of peoples.However,the research on debris flow in Xiangxi Prefecture has not been reported in detail,which is an urgent need for risk assessment.Based on the field survey data of debris flow,with integrating the empirical formula,geomorphic parameters,model comparison and ArcGIS statistical evaluation,the development characteristics,impact factors and risk area division of debris flow have been systematically analyzed in this dissertation.The main research conclusions are as follows:?1?Illustrate the spatiotemporal distribution of debris flow basically.Debris flows are most concentrated in Longshan County,Huayuan County and Baojing County,mainly distributed in Yuanshui River valley,Wushui River valley and both sides of their tributaries.Debris flows mainly occur from May to September every year,June,July and August are the high frequency periods,May and September are the low frequency periods.Debris flows are all triggered by rainstorm,dominated by gully-type development,which mostly in the prime and active at present.?2?Determine the impact factors of debris flow initially.At an elevation of200¹000m,with steep slopes of 20⁴0°and valley density of 1.1¹.4km^-1;annual precipitation up to 1218¹357mm;fractured concentrated zones of fault zones and secondary faults;weathered Cambrian limestone and dolomite,Silurian shale and siltstone,Permian,Ordovician,Sinian shale,siliceous rock,Cretaceous sandstone and mudstone,Qingbaikouan slate bedrock;accumulation of waste residue from mining activities;cumulative effects of seismic activity.?3?Establish the debirs flow risk assessment system,with adapting the information method,coupling information method and BP neural network model,maximum entropy model,theoretical test and field test methods are also introduced.The results show that the maximum entropy model has higher evaluation accuracy,which is suitable for the risk assessment of debris flow in Xiangxi Prefecture.?4?Debris flow risk areas are divided.Annual precipitation,lithology,slope and fault structure are considered the main factors affecting the risk of debris flow;debris flow risk is generally increasing gradually from southeast to northwest,mainly in the form of flakes and strips;divide the debris flow risk areas into 5 areas,which including extremely low risk area,low risk area,medium risk area,high risk area,and extremely high risk area.?5?The prevention measures of debris flow are discussed.Divide the debris flow prevention regions into 8 key prevention regions,3 sub-key prevention region and 8general prevention regions.It is recommended to prosecute a comprehensive risk assessment of debris flow disasters during construction of the projects,and further improving the group measurement and prevention monitoring network.For residential areas that are severely threatened by debris flow,but not suitable for engineering measures,proactive avoidance and relocation should be implemented,combining with relevant poverty alleviation and ecological migration policies.Disaster prevention publicity,knowledge training,related drills in various communities should be strengthened,the prevention and control of disasters could be transformed into the conscious behavior of the whole society.