Research On The Development Characteristic And River-blocking Of Shiwulong Debris Flow,in Rangtang,Sichuan

Debris flows are the most common geological disasters in mountains and val eys,featuring sudden outbreak,short duration and strong disaster-causing ability.Rushing out of the valeys,debris flows often cause river-blocking when merging into the main channel,which finally induces the formation of barrier lakes.Such barrier lakes will inundate some upstream towns and infrastructure,the outburst of which could also destroy downstream houses,farmland,water conservancy and hydropower facilities,embankment,and bridges.As a result,it is concluded that the damage caused by secondary disasters from debris flows is often greater than that resulted from debris flows themselves.Shiwulong gul y,located on the right bank of Zongke River in Rangtang County,Sichuan Province,is an area with frequent burst of debris flow.After about 60-minute heavy rainfa ll in 2014,the debris flow broke out,the scale of which had never been observed in the past 20years,and the two-thirds of the river was blocked by the 6000m~3 sediments rushed out from the gul y.The river water actual y rose to the pavement and over-flowed into roadside residential houses,seriously threatening the safety of life and property of residents on the other side of this valey.On the basis of field investigation in Shiwulong gul y,this paper firstly summarized the formation conditions and development characteristics of debris flow.Through literature review,the degree of river-blocking in Shiwulong gul y was then estimated by the empirical formula of river blockage.Furthermore,the movement of debris flow was simulated by numerical simulation software CFX,and finally,the theory of fluid mechanics was applied to calculate the height of the backwater,on which this study was based to put forward suggestions on engineering harness.The main results of this study are as follows.(1)The geological background of debris flow development was expounded,and the surveys on the disaster history and scale of debris flow outbreak were conducted.Having analyzed and summarized the formation conditions from the aspects of water source conditions,topographic conditions and provenance conditions,it was determined that debris flow in Shiwulong gully is one kind of storm-valley debris flow,and the dynamic parameters of which were calculated.(2)Analyzed the degree of river-blocking caused by debris flow once in 20 years,or once in 50 years.By CFX,movement with different frequencies of the debris flow in Shiwulo ng gul y was simulated,after which the accumulation range was obtained.(3)Put forward a formula to calculated the degree of river-blocking by analyzing the influencing factors of debris flow blockage(4)The height of backwater after the different degree of river-blocking was calculated by hydrodynamic theory,and obtained the height of backwater.(5)The idea of“protection and pollutants disposal”was finally proposed to set up measures for engineering harness.Putting forward the scheme of planning the protective embankment,and the scope and scale of silt removal.