WATER QUALITY MODELING FOR THE FEITSUI RESERVOIR IN NORTHERN TAIWAN 1

Field data collected from the Feitsui Reservoir in Tai- wan indicate that the water is at a stage between mesotrophic and eutrophic. Recent measurements such as total phosphorus, chloro- phyll a and Secchi depth levels suggest that the water quality has been declining. A two-dimensional, laterally averaged, finite differ- ence hydrodynamic and water quality model was used to simulate the water quality in the Feitsui Reservoir in an effort to determine sound water quality management strategies. The model was cali- brated and verified using data collected in 1996 and 1997. The cali- brated model was used to simulate algal biomass (in terms of chlorophyll a) levels under various wasteload reduction scenarios. Model results show that 50 percent reduction of the total phospho- rus load will improve the existing water quality, shifting the trophic status from eutrophic/mesotrophic to oligotrophic. The modeling effort has yielded valuable information that can be used by decision makers for the evaluation of different management strategies of reducing watershed nutrient loads. KEY TERMS: water quality modeling; hydrodynamics; CE-QUAL- W2 model; phosphorus; chlorophyll a; Feitsui Reservoir.)