THREE-DIMENSIONAL NUMERICAL MODELING OF THERMAL STRATIFICATION AND TURBID CURRENT REGIMES INDUCED INTO YONGDAM RESERVOIR (KOREA)

摘要

A persistent turbidity in reservoirs is typically caused by fine sediments (less than 20 /an), and their fate and transport in a stratified reservoir are greatly influenced by the thermal structure of the ambient water. Therefore, any numerical model selected for the simulation of turbidity flow in deep reservoirs should be fully validated using field data to confirm the model's reliability in simulating temperature and density flow regimes. The study was aimed to validate a coupled three-dimensional (3D) hydrodynamics and water quality model (ELCOM-CAEDYM) for Yongdam Reservoir (Korea). The model was tested for the simulations of hydrodynamics, seasonal stratification processes, and propagation of stream density flow contained suspended sediments (SS) for the period of June to December, 2005. Field data observed at four monitoring stations (ST1～ST4) were used to evaluate the models performance. Yongdam Reservoir was discretized, based on the Cartesian coordinate system, into 100 m in the horizontal direction, and 1.0 m in the vertical direction, forming 90,925 computational cells. For the simulations of turbidity (C_T), three different groups of SS classified by their particle size were used as state variables. Simulation results were compared with temporal and vertical profiles of observed temperature and turbidity. The model showed a good performance in reproducing the reservoir thermal structure and propagation of stream density flow. The magnitude and distribution of turbidity in the reservoir were consistent with the field data, although the turbidity in epilimnion zone was overestimated during the turn-over period because of the uncertainties involved in the input data and model parameters. In conclusion, ELCOM-CAEDYM is recommendable 3D model for water quality management of deep stratified reservoirs.