Water quality modeling of the Tanshui estuarine system in northern Taiwan

A vertical two-dimensional numerical model was developed to simulate water quality processes in branched estuarine systems. The model consists of hydrodynamic and water quality submodels. The model was applied to the Tanshui estuarine system of northern Taiwan, and calibrated and verified using field data collected from 1994 to 1996. Favorable model calibration and verification results were obtained. After calibration and verification, the model was used to predict future water quality conditions under various hydrological conditions as the result of the Tanshui River estuarine system clean-up project which is being implemented. Due to the clean-up project by the interception of a large amount of wastewater to the ocean outfall system, the freshwater flow in the estuarine system will decrease. On the basis of the model prediction the daily minimum dissolved oxygen (DO) concentration in the Tanshui River-Tahan Stream and Keelung River will not meet the water quality standard under low freshwater flow condition and 60% wastewater reduction. If wastewater reduction is up to 90% under low freshwater flow, the daily minimum DO concentration of three tributaries should meet the water quality standard(DO > 1 mg/l).