Hazard And Risk Assessment For Debris Flow About The Snow Making And Water Diversion Project In Yanqing Competition Area

With the increasing of hydropower,road,pipeline,bridge and other projects in mountainous areas,the number of debris flow disasters are increasing.Due to engineering functions and topography conditions,the engineering site area is a favorable geological environment for debris flow disaster,and the main hydraulic facilities are faced with high risk of debris flow.Firstly,the formation conditions,basic characteristics and susceptibility of debris flow in the are analyzed by means of field survey,remote sensing interpretation,UAV fine measurement and AHP.Secondly,we propose two indexes: the mean thickness of water yield in debris flow gully and mean thickness of stone produced by source under different rainfall recurrence period.And we simulated and predicted the potential debris flow disaster in engineering area.Finally,based on the risk assessment theory,the risk of debris flow in major hydraulic facilities is quantitatively assessed according to the simulated dynamic parameters such as mud depth and mud velocity,and corresponding prevention and control suggestions are put forward.This thesis mainly draws the following conclusions:(1)The snow-making and water-diversion project is located in a mountainous area of Beijing that has historically been prone to generate the disaster of debris flows.The evaluation results of the susceptibility of potential debris flow gully by AHP show that the susceptibility of N02,N08,N09 and N10 is high,that of N04,N06 and N07 is medium,and that of N01,N03 and N05 is low.The susceptibility of debris flow in gully with engineering disturbance is significantly higher than those natural gully.(2)At present,it is difficult to use debris flow dynamic numerical simulation method to simulate and predict sediment erosion thickness under multiple rainfall conditions.In terms of this issue,we propose two indexes: the mean thickness of water yield in debris flow gully and mean thickness of stone produced by source under different rainfall recurrence period(1%,2% and 5%).And we simulated and predicted the potential debris flow disaster in engineering area with above indexes.(3)The simulation results show that the 900 reservoir-dam and pumping station were mainly affected by N02 mudslide gully,the 1050 reservoir-dam was mainly affected by N03,N04 and N05,and the 1050 Reservoir-dam and 1290 reservoir-dam were mainly affected by N01 and N07,respectively;The mud flow depth and impact force near the1050 pond dam are larger,the 900 pond dam is faced with a larger sediment thickness,the 1290 pond is faced with a higher impact force,the 900 pump station and 1050 pump station is faced with a smaller sediment depth and impact force.(4)Based on the simulated dynamic parameters of debris flow in different rainfall scenarios,the risk levels of debris flow in major hydraulic facilities are quantitatively evaluated.The results show that: the risk of debris flow at 900 pond dam and 1050 pond dam is medium,medium and high,the risk of debris flow at 1050 pump station and 1290 reservoir is low,medium and low,and the risk of debris flow at 900 pump station is low under different rainfall situations.(5)The risk of debris flow in 900 pond dam,1050 pond dam,1050 pump station and1290 pump station cannot be tolerated and measures need to be taken.According to the damage modes of the main hydraulic facilities,it is suggested to build a retaining dam upstream for 1050 pond dam,a sand retaining pond at the tail of 900 pond dam,a retaining wall on the east side of 1050 pump station and a drainage channel on the east side of 1290 reservoir.