Risk Assessment And Prevention Research Of Debris Flow In Yangjia Gully,Beichuan

For a long time,debris flow breaks out frequently in mountainous areas,causing great harm.However,there is a lack of preventive measures.Yangjia gully,located in Beichuan County,has eruptions of mountain torrents and debris flows of different sizes every year in rainy season.On the one hand,it directly endangers the lives,works and production of the residents along the gully.On the other hand,debris flow rushes into the main river,blocking the river course and raising the river bed,causing secondary disasters along the coast,which has a huge impact.This paper takes the debris flow in Yangjia gully,where in Chenjiaba Township of Beichuan County as the research object.The geological environment conditions and formation conditions of Yangjiagou debris flow basin were studied in depth by investigating,using Arcgis and CAD software and referring.The risk assessment of debris flow is carried out by selecting specific parameters and calculating mathematical modelling.And the results are compared with the actual investigation results.Based on the comprehensive analysis and evaluation results,the prevention and control suggestions are put forward.The main research results are as follows:(1)A detail field investigation of physical geography and geological environment conditions had been made in Yangjia gully.The reasons for the high frequency of debris flow in Yangjia gully are analyzed:(1)In terms of topographical conditions,the study area is eroded and dissolved in low-middle mountainous landforms,with a relative altitude difference over 1km.The steep and deep valleys can provide sufficient kinetic energy,and the 25.0 km~2 watershed area has a very strong catchment capacity.(2)In terms of material sources,the Weijiashan landslide and the gully have a large amount of solid loose deposits,which could directly involved in the activity when the debris flow starts.(3)In terms of water sources,the rainfall intensity leading to debris flow become lower after the earthquake.Rainfall is concentrated and abundant in Yangjia gully every year.Rainstorms and persistent heavy rainfall often occur in the rainy season.(2)Combining the three basic factors and the parameters of the movement characteristics of debris flow in Yangjia gully,nine evaluation indexes are selected.After the combination of AHP and entropy method,the fuzzy comprehensive evaluation of the risk of debris flow in Yangjiagou is carried out,and the result is extremely dangerous.Finally,the result is compared with Liu Xilin's model and actual survey results.It is considered that the fuzzy comprehensive evaluation method of combination weighting is better than the traditional model,and the evaluation result is more realistic.(3)The vertical slope of Yangjiagou is relatively large.Slope with serious deep cutting and erosion results in larger slope gradient,and the channels are either wide or narrow.The debris source is mainly provided by Weijiashan landslide and channel loose material.According to the specific situation and the evaluation results,two schemes are proposed.It is proposed to adopt the prevention and control scheme of“Fixed trench bed is the main method,and blocking works are the auxiliary method,accompanied by trench cleaning”.