A Study On The Risk Assessment Of Debris Flow In Yongsheng County, Yunnan Province

Yongsheng county is one of the high-risk areas of debris flow in Yunnan Province,where are the rainy season precipitation concentration and the influence of the Chenghai fault zone,the Jinsha River and its tributaries are deeply affected by the new tectonic movement,the geomorphology is complex and diverse,the mountain height,valley depth,steep slope,the cutting density,the rock weathering is serious,the erosion effect is strong.Therefore,the region is prone to debris flow disasters under the influence of interaction of topography,stratigraphic rock,geological structure and climate.After investigation,the county developed a total of 212debris flows,these debris flows seriously threaten the normal production and life of local residents and life safety,but also to a certain extent restrict the local economic development.According to the formation mode of debris flow,this paper is divided into three types of soil power-slip,earth power-removal and hydrodynamic-handling,and takes the Romrayan debris flow,Shaojin bay slope debris flow and the boss's landslide debris flow as a typical example,analyzes the different characteristics of the three debris flows from the formation conditions and the formation process,Used BP neural network to construct an evaluation model,quantitative evaluation of the risk of single ditch mudslides,and used Yongsheng County regional mudslide as the research scale,the application of AHP,multi-factor comprehensive evaluation method and Arcgis to divide the risk level of mudslide disaster in Yongsheng County,with a view to providing theoretical basis for the disaster prevention and mitigation work in Yongsheng County.The main results obtained are as follows:(1)Based on field investigation and related data analysis,this paper selects seven evaluation factors,such as mudslide scale,watershed area,maximum daily rainfall,main ditch length,relatively high difference in basin,frequency of debris flow and vegetation coverage,for the risk evaluation of single ditch debris flow.The five typical debris flow hazards were obtained:The moderate hazard of the water and stone flow in Shangenpu is 0.3728,the moderate hazard of the Romrasmudslide debris flow is 0.3728,the moderate hazard of the debris flow on the slope of Shaojin Bay is 0.5657,The boss's debris flow is moderately dangerous,with a risk level of 0.4349,and the Wangguan River debris flow is moderately dangerous,with a hazard level of 0.5473.Compared with the actual test,the relative error of the model is less than 10%,and the evaluation results are more reliable.(2)For the evaluation of the risk of debris flow in Yongsheng County,according to the historical factors and formation conditions of the debris flow disaster in the area,and combined with the local geological conditions,geological background and the induced conditions of debris flows,the risk evaluation of debris flow in Yongsheng County selected the distribution density of debris flows from the aspects of disaster historical factors,climatic factors and topographical geological conditions.The average annual rainfall,fault zone density,stratigraphic lithology,cutting density,slope,slope and curvature were 8 evaluation indexes to construct the mud flow hazard zoning evaluation system.The hierarchical analysis method is used to determine the weight,the multi-factor comprehensive evaluation method to calculate the hazard degree,through the Arcgis raster calculator to the grid layer overlay analysis,to obtain the Yongsheng County area debris flow risk level zoning map.(3)Analysis shows:There is a small area of extreme danger zone in Yongsheng County,the high risk area is mainly concentrated in the corner,the period,Chenghai,Yongbei,Sanchuan and Shunzhou and other places of the dam area and the Jinsha River Valley coastal areas,The area of land in the region is 1155.83 km~2,with a total of 133 development debris flow disasters,the moderate danger area is the periphery of the high-risk area and other places,the area of the region is 2070.00 km~2,a total of 67 development debris flow disasters,low-risk areas concentrated in the high mountain areas of Yongsheng County and the south-eastern areas of weak human activities,The land area is 1645.50 km~2,a total of 12 development debris flow disasters.By comparing with existing debris flow disasters,it can be seen that the higher the hazard level of the debris flow danger zone,the higher the density of the historical mudslide disaster,the lower the hazard level,and the smaller the density of the mudslide disaster,which is consistent with the actual characteristics.