Study On The Sediment Carrying Capacity Of The Middle And Downstream Yangtze River

The sediment-carrying capacity of flow, one of the key research contents of river dynamics fundamental theory, is of significance in the application to the areas of sediment-laden mechanism analysis, fluvial processes analysis and bed evolution calculation and so on. This thesis makes a study on the sediment-carrying capacity of the middle and downstream Yangtze river. Some basic conceptions of sediment-carrying capacity are introduced and the existing achievements are reviewed. The variation law of Kantian constant of sediment-laden flow, the influencing factors and the calculation of sediment-carrying capacity and the graded sediment-carrying capacity are investigated. The research findings are verified by the measured data of the middle and downstream Yangtze river.The existence of sediment in sediment-laden flow influences the flow structure. Based on the fact that the bed shear stress of flow is made up of the shear stress against the viscosity of bed surface and the shear stress accelerating the movement of bed load, influencing factors of Karman constant of sediment-laden flow are obtained by the mechanical analysis. The formula of Karman constant, which can be used to calculate Karman constant in the sediment-carrying capacity formula, is derived from fitting Karman constant with the experimental data.The various influencing factors of sediment-carrying capacity are summarized. Through the dimension analysis and the regression analysis under the corresponding conditions, several experiential formulas of sediment-carrying capacity are obtained. The formulas are verified with the measured data and the results reflect the mechanism of flow carrying sediment — the suspension of sediment is determined by the turbulent fluctuation of flow and the gravitation force itself.The turbulent energy equilibrium theory is reviewed. Some problems are pointed out for traditional simplified methods which can't reflect the effects of such as the viscosity of water and sediment mixture, sediment-carrying concentration, particle composition, especially the content of fine particle on the sediment-carrying capacity factually.Based on the analysis of the physical model of flow carrying sediment, the expressions of the terms of turbulent production and viscous dissipation are obtained taking the turbulent energy equation of sediment-carrying flow as a theoretical base under the conditions of two-dimensional, steady and uniform turbulent flow and the flow carrying sediment in equilibrium. Thereout a universal formula of sediment-carrying capacity for turbulent flow in the suspended zone is deduced. It has been indicated by the verification and the comparison with the typical existing formulas that the proposed formula is in a good agreement with the measured data in the Yangtze river.The calculating model of graded sediment-carrying capacity has been presented and the precision could be improved by calculating the size curve of graded sediment-carrying capacity, then a formula of graded sediment-carrying capacity is established. The formula is analyzed qualitively and verified by the measured data in the Yangtze river. The verification result is good.