CP-1998-01
Near-field mixing of wastewater effluent from the Pali marine outfall, Northern Taiwan.
Liu, Clark C.K., Jing Li, and Huashan Lin
The Pali marine outfall, an important element of the Tansui River water pollution control project in Northern Taiwan, was designed to discharge wastewater at a rate of 37 m3/s, or about 840 mgd, into Taiwan Strait. To minimize the potential adverse impact of this discharge on the marine environment requires a thorough understanding of effluent mixing in receiving water. Generally, the negative environmental impact would be small if the waste materials in an effluent plume could be significantly diluted. The magnitude of near-field mixing depends on both waste effluent characteristics and ambient ocean conditions. Relevant ocean conditions include ocean current, density stratification, and ocean waves. The effect of ambient ocean waves on near-field mixing has been ignored by almost all existing mathematical models. In this study, the popular near-field mixing model UM was modified to include wave effect. The modified model was then used to predict effluent mixing in the Pali outfall area. Simulation results show that the minimum required initial dilution ration of 100 to 1 can be achieved when the ambient current velocity is 2 m/s or higher. Further, the simulation results indicate that ambient waves play an important role in near-field mixing. When the amplitude of ambient ocean waves is 2 m or higher, the Pali outfall effluent can achieve the required dilution, even in the absence of ocean currents.