| Taoshan reservoir is located at Qitaihe area, Heilongjiang province, which is a big reservoir to control flood and supply water to city, as well as agricultural irrigation and aquiculture, etc. It is built in August, 1990. Since then, it has displayed an important action to local economic development, city construction and guarantee of urban water supply, making acquired remarkable economic and social benefit. Up to the end of the year 2004, the total water quantity supplied to city has reached 3.24 hundred million m3, making industrial benefit of $8.10 hundred million, while the total water quantity used for agriculture has reached 11.8 hundred million m3 making agricultural benefit of $2.83 hundred million. It's the unique surface water source in urban area of Qitaihe City, but with the development of industry and agriculture in recent years, and the irrational utilization of water resources by residents, a series of ecological environmental problems has taken place in the reservoir, especially the eutrophication of the reservoir. Therefore, enhancing the protection of water resources of Taoshan reservoir is a long-time strategic task.Meanwhile, as the low velocity of flow in reservoir and the large error of observation value, in order to know the hydro dynamics and the movement & distribution law of contaminants, the numerical simulation has been widely used in lake current, acquiring lots of achievements. The thesis is based on the"948"project of"the introduction and application of hydro-ecologic protecting and managing technique in Songhua catchment"supported by the ministry of water resources. Based on Delft-3D system, the coupling simulation model of hydro-dynamics and water quality in Taoshan reservoir is established, which is used to predict the flow and water quality. The main contents of the research are as follows: (1) The key research object is the water quality simulation in Taoshan reservoir. The data of hydrology and water quality of the year 2000 is collected,providing necessary conditions for the research.(2) Through reading the domestic and foreign references, the common method of surface water numerical simulation is known. Combined with the data of actual measurement, using Bossiness assumption, assuming the static pressure, and ignoring the variation in vertical direction, the model is generalized, and the 2D conceptual model is established, then the numeric model is obtained.(3) Based on Delft-3D system and hydrologic data, the model's initial conditions (specified initial water level in hydrodynamic model; specific initial concentration in water quality model) and boundary conditions (specific flow quantity in hydrodynamic model; specific concentration in water quality model) are defined, and the numeric model is solved. Comparing the simulation results with the actual measurement (the comparison water level and concentration at the dam in hydrodynamic model; the comparison of concentration at location 1 in water quality model), the parameters of the model is identified, and the actual hydrodynamic model and water quality model suitable for Taoshan reservoir are obtained.(4) In the process of model parameters selection, the main influencing parameters of hydrodynamic model are Manning coefficient n and Eddy viscosity VH; For water quality model, as the selected indexes are ammonia nitrogen and dissolved oxygen, the main influencing parameters are diffusion coefficient, the degradation coefficient of ammonia nitrogen (first-order nitrification coefficient), and reaeration coefficient.(5) The finite difference approach is used to solve the numeric model, using orthogonal curvilinear grid to disperse space. ADI algorithm is used to solve the model. Contrast with traditional time-domain algorithm, the ADI algorithm is precise, flexible, efficient, stable, etc. (6) Hydrodynamic simulation results show that: the hydrodynamic field is mainly controlled by the location of inlet and outlet, wind, flux and the topography of lake bed. The locations of the inlet and outlet control the main flow direction, while the topography of lake bed and the flux control the partial direction and velocity of the flow; The flow of reservoir has a common property with lake current, that is the elevation difference is relatively small between upstream and downstream, and the flow velocity is relatively small, generally 10-3 magnitude. Only at the narrow cross section of the inlet, the flow velocity is relatively large. In some dead angle, the flow rate is extremelly small, the period of water cycle is long, and the metabolism is slow. In some partial area of the reservoir occurs circulation flow, which is mainly influenced by wind and topography. Water moving under the influence of inertia, and influenced by topography and wind, circulation flow occurs at corners.(7) The results of water quality simulation show that: Hydrodynamic simulation is the precondition of water quality simulation. Hydrodynamic field control the distribution variation of the concentration field. In addition, the variation of water quality movement in the reservoir is also influenced by diffusion, inlet concentration and degradation. Taoshan Reservoir is a shallow lake, with the average depth of 4 m, and the vertical scale is much smaller than its level scale. Under vertical diffusion, the concentration of contaminants in vertical is distributed uniformly. The results of water quality simulation show that: In spatial scale, the concentration of ammonia nitrogen decreases from upstream to downstream, while the concentration of dissolved oxygen increases; in time variation, the concentration of ammonia nitrogen decreases, while the concentration of dissolved oxygen increases.(8) According to the water problem most likely to occur, programs are designed for model prediction. Proper prediction programs are design to forecast, providing basics for further work of local management and decision departments of water resources, and some protection measures for water pollution problems in the future are suggested.Delft-3D is one of the best numerical simulation software of surface water at present, especially in modeling reservoir eutrophication, considering interaction and chemical reaction between indexes, walking in front of the world. But this study also has many lacks, because of the limitation of the measurement conditions and actual data, the established hydrodynamic model and water quality model are both two-dimension models, without considering the gradient variation of each elements in vertical and the action of circulation low, causing some errors. Therefore, it's necessary to extend the observation items, improve the observation methods and strengthen the research on three-dimensional model.
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