Water Quality Model For Sediment-laden Flow And Its Application To Simulation Of Riverside Water Quality In Three Gorges Reservoir

3D water quality model for sediment-laden flow is developed in thedissertation, which is based on pollutant transport-diffusion equationreflecting the sediment influence on environment. The simulation results ofseveral examples show that the model is suitable for numerical simulation ofpollutant transport and diffusion in sediment-laden flow. Therefore, the modelis applied to simulate the riverside water quality of Wanzhou reach in ThreeGorges Reservoir. The change of the riverside water quality after the storingof water in Three Gorges Reservoir and the influence of sediment on theriverside water quality are discussed according to the simulation results.The isothermal equation of adsorption is obtained according to the fieldmeasured water quality data of Qingxichang and Wanzhou section in ThreeGorges Reservoir. It comes to the conclusion which coincides with theadsorption experiment that the Langmuir isothermal equation can be used todescribe the adsorption of TP on sediment, and that the coefficients in theLangmuir isothermal equation vary with the sediment concentration andsediment gradation.The sediment adsorption and the influence of sediment movement aretaken into account in the water quality model for sediment-laden flow, and theadsorption quantity of TP is computed with the isothermal equation. Thenumerical simulation results of several typical examples show that thepollutant adsorbed on the sediment will move upward to the surface when thescour happens while it will move downward to the bottom when thesedimentation happens, so that the pollutant concentration along the verticaldirection is markedly affected by the sediment. The numerical results of theconcentration by this model vary distinctly from the traditional model whenintense scour or sedimentation happens. It is shown that the model cansimulate the pollutant transport and diffusion more accurately.The model is applied to simulate the concentration field of TP nearLongbaohe outfall of Wanzhou reach in Three Gorges Reservoir. After thestoring of water, the riverside water quality in Three Gorges Reservoir willget worse than before as the flow velocity slows down, and the change ofriverside water quality during the dry season is the most remarkable. Thepollutant adsorbed on the sediment will move downward to the riverbed andthe pollutant concentration at the water surface will be reduced whensedimentation happens during the initial stages of the storing of water.