| Summary: | 博士 === 國立臺灣大學 === 土木工程學研究所 === 96 === In this study, a three-dimensional hydrodynamic and water quality model was developed to simulate the circulation pattern and the trophic level of reservoirs with highly variable bathymetry in Taiwan. As reservoirs in Taiwan are characterized by the rapid changes in bathymetry and the transient variations of the storage volumes (i.e. surface elevations), this presents various challenges for the modelers.
Preliminary model results obtained for the Feitsui Reservoir show that the transient variation of the storage volume can be reproduced by the model, whereby the dynamic fluctuation of the surface elevation at the dam site is replicated by the model for a two-year period (from 1999 to 2000). Subsequent tests conducted using the model include hydrothermal simulations to ensure the accurate predictions of the spatial and temporal variations of temperature in the reservoir, with particular focus on matching the thermocline structure during the summer stratification period. Results of the temperature simulation reveal that a stratification phenomenon occurred during summer and early autumn in 1999 and 2000, and subsequently led to an overturn phenomenon. The hydrodynamic results derived were then used to run the water quality modeling subprogram.
An eutrophication model that can simulate eight water quality variables was also developed in this study. Biological variables were incorporated, including four groups of phytoplankton such as cyanobacteria, green algae, diatom, and all the others. The hydrodynamic and water quality simulation uses the same grids and time steps in order to handle the complexity of the geometry of Feitsui reservoir. Simulation results indicate that the temperature, light, and nutrient are the growth limiting factors for phytoplankton. A new temperature function used in CE-QUAL-ICM was applied in this model. The results shown that this function is suitable for temperature-limiting phytoplankton simulation in Feitsui Reservoir. Both the field data and model simulation results also show that each algae has its own growing period. It was found that phosphorus is the nutrient limiting factor for most phytoplankton, except for diatom, which is controlled by both phosphorus and nitrogen. Lastly, the carbon-phosphorus-nitrogen ratio for the four groups of phytoplankton was made distinct so that the interaction of nutrients could be emphasized.
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