Debris Flow Susceptibility Assessment And Runout Prediction Of Datong And Taicun Gullies Near The First Bend Of The Yangtze River

Catastrophic debris flow events frequently occur in mountainous areas around the globe,which poses a serious threat to human society,economy,life,property,and safety.Debris flow often occurs under conditions triggered by heavy rainstorms,making it one of the most destructive geological disasters because it does not have any warning signs.With the speedy development of mountainous areas in China,debris flow events frequently occur,making China the worst-hitting country by debris flow in the world,especially the mountainous areas in the southwest of China.Therefore,it is of great importance to evaluate susceptibility assessment and Runout prediction of debris flow in mountainous areas.Taking Datong and Taicun gullies near the first bend of the Yangtze River as an example,this thesis evaluates susceptibility assessment and the potential runout distance of these two debris flow gullies by comprehensive methods of field investigation and numerical simulation.Through field investigation,the formation,circulation,and accumulation mechanism of debris flow gullies have been basically understood and grasped.The basic geometric parameters of debris flow gullies are obtained through GIS and remote sensing techniques.By referring to previous studies and combining with basic characteristics of debris flow gullies in the study area,eight causative factors including slope,topographic wetness index,sediment transport index,ground roughness,basin area,bending coefficient of the main channel,source material,and normalised difference vegetation index,were selected as susceptibility assessment indexes of debris flow gullies.Relative importance of the eight causative factors was determined by using the Analytic Hierarchy Process: slope(0.314)> topographic wetness index(0.249)> sediment transport index(0.168)> ground roughness(0.091)> basin area(0.078)> bending coefficient(0.042)> normalised difference vegetation index(0.025).According to the combined weight coefficient and single correlation degree of eight causative factors,the comprehensive correlation degree of Datong and Taicun debris flow gullies is calculated using the Extension method.Based on the evaluation results,the susceptibility level of both gullies is found moderate.The complex geological problem of debris flow susceptibility assessment has been well solved by combining AHP with extension theory.The development process and the Runout prediction of the debris flow gullies were made using the SFLOW software based on the shallow water flow model developed by the College of Construction Engineering,Jilin University.Debris flows events with return periods of 10-,20-,50-,and 100-year were simulated in Datong and Taicun gullies respectively.The runout distance of these two debris flow gullies can reach the main highway and even can block the Jinsha River completely.The above susceptibility assessments and Runout prediction can provide guidance to decision makers for disaster prevention and debris flow management.