Water And Sediment Separation Method And Its Effect On Sediment Reducing In Lower Yellow River

Yellow river is one of the river with highest sediment discharge. It also the complexity river in sediment controlling. The traditional sedimentation reduction model including two type. The first one is soil and water conservation project based on sediment source. The second one is water and sediment regulation engineering based on the hydrodynamic conditions. However, as the result of natural and social conditions limit, nether of the two models can achieve the massive sediment utilize. Our work analyse the boundary condition of water and sediment transport and the flow and sediment transport characteristic. We also analysed the key theory in water and sediment separation model. Based on that, we used the one-dimensional unsteady flow mathematical model discuss the effect of water and sediment separation model on the sediment erosion and siltation quality in the the lower reaches of the yellow river. The main contents of this paper are as follows:(1) The introduction expounds research background and significance of the the Yellow River sediment reduction, summarized limitations of existing deposition reduction models. The application of water and sand separation model in the Yellow River based on water and sediment boundary condition analysis. The research content and method has been introduced in this part.(2) Sediment concentration and sediment grain size are researched to compare the sediment particle diameter. In this work, we analysed of the flocculation conditions of fine sediment, sediment particle collision influence and the internal and external flocculation factors. Mechanics of the three flocculation and sedimentation ways, including single particle sedimentation, particle flocculation and floc sedimentation are expatiated. Four sediment stages of fine particle flocculation in low and high sediment concentration, including floc settlement period, control-group settlement period, flocculent net period and consolidation settlement period are research.(3) Yellow river sediment hydrodynamic properties in different sediment concentration are discussed. The existing colloidal models are used to preliminary interpretated floc stability mechanisation. The floc growth process of yellow river sediment is expounded with DLVO theory, compression mechanism of electric double layer, adsorption and charge neutralization mechanism, adsorption bridging mechanism, capture mechanism. From the mechanical hand, effects of Brown motion, Gravitational system forces, flow shear stress on the fine sediment were discussed.Combining with fractal growth theory, it introduced the sediment fractal dynamics. The existing fractal dimension calculation methods were all based on two dimensional and uniform sediment. Three calculation methods, density function method (3D), radius of sphere gyration method and sedimentation method, were used to calculate the floc fractal dimension. It deduced the sediment particle and floc settling velocity with consideration of gravity force, drag force, buoyancy force and Brown motion. The existing group settling velocity formulas were researched and the ZHANG Hongwu formula were chose to build the one-dimensional unsteady flow and sediment model.(4) Based on fractal theory, the particle and floc force characteristics were disccused. Using the balance of internal and external force, the limited diameter under uniform sediment and un-uniform sediment were calculated. With this, the reason for supernatant-sediment interface forming was expounded. With the force analysis, the supernatant-sediment interface settling velocity in initial section was calculated. Combining with the research of FEI Junxiang, Kynch, Roberts, Yoshioka, Toty and Shannon, the settling velocity in straight section, transition section and the compression section all have been calculated.(5) It is difficult to dynamical observe the fine particle growing to floc. With analysing the actual Yellow river situation, The diffusion limited flocculation model was built to simulate the floc growth process of uniform and non-uniform sediment. With consideration of particle surface electrochemical action, a simulation based on Brownian dynamic for perikinetic flocculation of fine sediment under the ionization is presented. The Langevin equation is used as dynamical equation for tracking each particle making up a floc. Monte Carlo method was used for simulate random variation in particle movement. It simulated the particle number, radius of gyration, fractal dimension.etc. The floc growth process with charged particle and uncharged particle were compared to analyse the effects of electricity on flocculation. From the mathematical view, it explained the reason that flocculants accelerate sediment flocculation. Based on limited diameter, the supernatant-sediment interface settling velocity was calculated in different sediment concentration.(6) The experimental samples in this work were taken from the Huayuankou of Yellow River. The sediment properties including sediment grain size, dry density, dry unit weight, density, bulk density and settling velocity were measured in experiments. It analyzed the incoming water and sediment data, sediment grain size of riverbed in the lower reaches of Xiaolangdi Dam. The model proposed in this work were verified using the previous data. The calculated values and experimental values were coincided well with each other.(7) To study the effects of water and sediment separation model on sediment lower reaches. Based on the existing one-dimensional mathematical model of the lower reaches of the Yellow River, a one-dimensional mathematical model for unsteady flow was introduced, which included the newest theory of particle settling velocity formula, group settling velocity formula and sediment-carrying capacity of flow formula. After the test for function and stability of each module, the date from2006Yellow River flood and sediment regulation were used to rating roughness coefficient and coefficient of sediment transport capacity. The date from2007Yellow River flood and sediment regulation were used to verify the model. The results show that the numerical diffusion process of water stream and sediment concentration are close to that of real value.According to the flow and sediment data of2006, some data series with different sediment concentration, different particle diameter distribution and different flocculation situation, were drawn up to study the effects of each factor on sedimentation reduction on the lower reaches of Xiaolangdi Dam using the previous one-dimensional mathematical model. This work could provide cognitive basis for the water and sediment separation in lower reaches of Xiaolangdi Dam.(8) Research result is summarized and the present unsolved questions as well as the future research were listed.