Development Characteristics And Hazard Assessment Of Debris Flow In Upper Reaches Of Fu Jiang Shi Kan River Watershed

The upper reaches of Fujiang ShiKan River watershed is located in the northwest of Sichuan Mianyang,the transition area of Sichuan Basion to Qingzang-Tibet Plain.Affected by the Songpan earthquake belt and the Longmen Mountion Fault Zone earthquake are very developed and every earthquake induces a large number of secondary disasters.After the“5.12”earthquake the study area have broken many times debris flow disasters.These geological disasters have significant influence on the geomorphic evolution of the river valley and the human engineering activities.Consequently,it is great theoretical and ptactical significant to study the debris flow's forming conditions,Development characteristics and influence factors for the debris flow scientific management of the area.In this paper,ShiKan river watershed was research object in this paper.Combineed with field investigation and related geological data,study the debris flow formation condition,development characteristics,influencing factors and evaluate the possibility of debris flow activity in Maanshi landslide lake.On this basis,selected the main influencing factors of debris flow and established the risk assessment index system for debris flow.The risk of debris flow is evaluated by fuzzy analytic process and tradition model.The results of the two models compared and analyzed.Thus the risk assessment of debris flow in the research area is completed,research achievements and conlusions are as follows:(1)There are development a total of two main debris flow gullies(HongXi gully and XingPing gully)in the ShiKan river area.All of them belong to the post-style earthquake debris flow and its fluid property mainly water debris flow.There are three development debris flow gullies in HongXi gully,at the same time its the biggest gully in the study area.There are six development debris flow gullies in XingPin gully.The study area of debris flow are mostly high-frequency deris flow,and some of debris flow never even occurred had broken out after the earthquake.(2)After the“5.12”earthquake topographic condition have changed greatly in the study area,especially gully bed condition and source condition.Earthquake caused lots of landside collpses in watersheds,largely increasing loose substance reserve there.Besides there are also plntly of underlying landslides which is likely to be actived and enters into channels to block them under some disadvantage condition for example rainfall.The critical rainfall of debris flow in the study area is greatly reduced,and the characteristics of large scale,destructive and distribuction are shown.(3)“5.12”earthquake in the Shikan river fromed Maanshi,Wenjiaba two barrier lakes.Among them,Maanshi barrier lake is a whole slide on the left bank of the landslide.The total amount of accumulated is 599.6×10~4m~3,which is now washed away 258.6×10~4m~3 and still remains 341.0×10~4m~3.The amount of can mudslides dynamis reserves of about is 47.74×10~4m~3.Wenjiaba barrier lakes occurred when the earthquake happened to block the river,after the earthquake to conduct manual drainage.Now the tongue shape distribution,high stability,at the same time has been done on river rush prevention measures,will not provide source,only the channel slope is reduced,slows down the river flow,reduce the sediment carrying capacity.(4)A detil field investigation had been made in ShiKan river area.Statistics of the amount and distribution of the trench provenance,provenance total storage capacity of approximately 1087.99×10~4m~3,can mudslides dynamis reserves of about213.84×10~4m~3.There are mainly two types of debris flow in the study area:one is the block form when substances caused by landslides and collapse due to earthquakes block water channels and formed barrier lakes;the other is channnel start from when lots of solid substance of a certain amount of rainfall cause a large of debris flow disaster.After the earthquake,the increase of the source quantity,the decrease of starting condition and the mass accumulation of the sports energy gave brith to the development of debris flow in the study area.(5)The risk of debries flow is evaluated by fuzzy analytic hierarchy process and traditional model.Select the main factors which influence the debris flow actives,and9 debris flow ditch were evaluated.The results of the two models were compared and analyzed.There are 7 grooves belong to a high risk of debris flow gullies,2 grooves belong to the risk of debris flow gullies.The amended risk assessment results are consistent with expert on-site evalutions and the outbreak of the status quo.