Density Current Sediment Transport Test And Its Application To The Dredging Of Wang Yao Reservoir

China is the world’s most serious reservoir siltation country,the annual loss of reservoir capacity due to siltation is about 10 billion m³,some reservoirs due to the loss of reservoir capacity of more than 30%,serious siltation poses a great threat to reservoir flood control,operation and ecological safety.In the current reservoir dredging technology,the use of jet erosion siltation surface shaping density current sand transfer and drainage method has achieved relatively good results in engineering practice,and is an effective way to solve the reservoir dredging problem.Accordingly,in order to understand the movement law of density current more deeply,the movement process and law of open-gate density current were investigated through physical model tests,the influence of different factors on the movement characteristics of muddy water density current was analyzed,and the theoretical model of density current sand transport and discharge was analyzed and deduced,and to predict the variations in key parameters of the density current of muddy water formed during the jet dredging operation.The main contents and conclusions of this paper are as follows.Firstly,the physical model of the open gate muddy water density current was established,and the head of the density current was the key object of study,and the movement process and law of the open gate density current,the shape of the head,and the variation law under the influence of different factors were analyzed.The results show that:after the gate is opened,the muddy water quickly dives into the ambient water to form the density current;after the density current runs for a certain distance,a stable head structure is formed;when Re>1000,the density current goes through the slumping and inertial phases;when Re<1000,the density current changes directly from the slumping phase to the viscosity phase;in the slumping phase,the head of the density current has a Froude number F_rh=0.72 and a dimensionless velocity u_f^*=0.42;at the same dimensionless moment,the morphology of the head of the density current is similar;the slope and density differences have a large effect on the velocity of the density current;water depth has a large effect on both the velocity and thickness of the density current.Secondly,the equations of motion at different stages of the density current at different stages were derived and compared with the experimental results.The results show that:when the term related to the turbulence of water flow is introduced and the variation of the thickness of the density current along the course is taken into account,the relationship between the flow velocity and the variation of the sand content along the course is in good agreement with the experimental results;in the slumping stage,the sand content of the density current decreases slowly along the course,and in the inertial,the difference in density between the clear and muddy water has little effect on the rate of variation of the sand content of the density current.Finally,field dredging test results based on Wang Yao Reservoir jet dredging technology,the results of the tests and theoretical analysis were combined to analyze and predict the sand transport and discharge of the density current.The results show that:the density current formed during the jet dredging operation moves towards the funnel-shaped zone;the sand content of the density current is 35kg/m³after running for about 180m,and the sand transport rate reaches 87.5%;the speed of the density current movement is basically synchronized with the along-range variation of the sand content;the jet dredging technical scheme and dredging method proposed in this paper have certain effect.