Debris Flow Source Evolution And Sensitivity Assessment In Typical Areas Of The Middle And Lower Reaches Of Minjiang River

The Wenchuan earthquake produced a lot of landslides,which provided abundant source for debris flow activities after the earthquake.On July 9 to 10,2013,persistent heavy rain caused the "7.10" debris flow group incident in Mian County,Wenchuan County,washed down the highway and blocked the Minjiang River,and seriously threatened the safety of the residents and vehicles.Now,the Wenchuan earthquake has been in the past 10 years,its provenance has undergone different intensity changes,but the danger of geological hazards still exists.Based on the large amount of source and different activity intensity of the post earthquake landslides,this paper selects the main research area of Miansi town in Wenchuan County,analyzes and summarizes the changes of the source of the landslides in the basin based on the change of different activity rates,and finds out the distribution and evolution characteristics of its source activity and the rate of activity based on the different activity rates.It is necessary to evaluate the sensitivity of the multistage landslide and analyze the evolution of the sensitivity of the study area to effectively stop the hazard of debris flow and restore the reconstruction work of the earthquake stricken area.The study area is about 32 kilometers away from the epicenter of Yingxiu town,and the peak acceleration of ground motion(PGA)is between 0.76 and 0.84,which belongs to the strong earthquake zone.There are two faults in the territory: the Mao-Wen fault zone and Jiudingshan fault zone.Natural disasters such as material looseness,slope deformation,shallow surface looseness,collapse and landslide are very common in the study area caused by earthquakes.The study area are Huaxigou,Anjiagou,Mozigou,Wayaogou et al which eight debris flow gully,the debris flow in the basin of the topography of the south north high low form on the whole,give priority to with erosion landscape of hills and zhongshan,terrain is steep,airport development conditions,conducive to the basin of collapse disasters occur and loose material collection,cause the threat of mountain disasters continues after the earthquake a few years.Based on this problem,in order to explore the landslide activity and the sensitivity of the evolution law after earthquake,collecting five phase of high resolution remote sensing images in the study area(2008,2009,2011,2009,2011),and combined with the existing data and field investigation,using GIS technology to the collapse of every period in the study area with interpretation,the landeslide assigned to activities,the evolution of landslide activity rate in the study area over the years was obtained and the prediction analysis was made,At the same time,the evolution of landslide with different activity rates on control factors such as height,slope,slope direction and distance from water system are analyzed.According to statistical results generate new landslide to predict the future trend is less,but the landslide activity is still high,with the extension of time,under the effect of no powerful external forces,the landslide activety will flatten out fell,the active development of slope vegetation ecology also gradually restored,further reducing the landslide activity,The analysis predicted that the landslide activity rate in the study area would reach a low level and below 10 years later.However,at the present stage,most of the landslide bodies are still in the active state,and the possibility of debris flow is still relatively high.It is still necessary to strengthen the engineering prevention and control of debris flow,early warning and prediction,and risk area zoningBased on the above interpretation of the results,the use of probability comprehensive judging method to calculate the landslide activity probability value under each control factor,and using the analytic hierarchy process(ahp)to each control factor weighted superposition,get different landslide activity rate sensitivity values,then the collapse body sensitivity values for different activity rate in different activity ratio weighted superposition,is based on the rate of different activities landslide sensitivity zoning maps,finally get a 2008-2017 period sensitive area chart.In not before the outbreak of debris flow,low sensitivity area ratio is the largest in the study area,high risk minimum,but from 2008 to 2014,with gradually increase the proportion of the dangerous area,until in 2013 under the condition of heavy rainfall caused mudslides group events.After mudslides,between 2014 and 2017,the activity of the landslide in the study area is gradually reduced,in the absence of heavy rainfall,earthquake and other powerful outside dynamic condition,the dangerous area gradually reduce,but in 2017,the evaluation results,the study area is 15.06% of the area ratio of highly sensitive areas,is still dealing with highly sensitive areas related to disaster prevention and mitigation measures.