Modelling hydrodynamics and water quality in the separation waterway of the Yulin offshore industrial park, Taiwan

Numerical models are often used to evaluate the potential impact of human alternation of natural water bodies and to help the design of the alternation to mitigate its impacts. This paper describes a case study in which an estuarine hydrodynamic and water quality model was used to help the design of the artificial waterway for an offshore industrial park. Yulin offshore industrial park is located at the central western coast of Taiwan. To mitigate its impacts on the nearby coastal area, the industrial park is buffered by a waterway separating it from the main island. The original design of the separation waterway has a width of 500 m. However, this width has been a controversial issue for the past 10 years. Since the separation waterway receives discharges from two streams in the main island, the Shu-Chu-Liao Stream and Hsin-Hu-Wei Stream, the potential inundation during flood events and water quality conditions during low flow periods are two of the major considerations for the width of the waterway. A vertical two-dimensional, real-time model of estuarine hydrodynamics and water quality was modified and used to determine the rational width of the separation waterway. The model modification is necessary to account for the multiple outlets into the sea when the whole system of the separation waterways is completed. Model calibration and verification were conducted with current, residual velocity, salinity, and water quality variables measured in the completed portion of the waterway. The overall performance of the model was in qualitative agreement with the available field data. The model was then used to evaluate several scenarios of different widths for the yet-to-be completed system of separation waterways. Based on the model simulation results, a 200 m wide waterway, bordered by 300 m wide flood plain, is recommended for adoption. The model simulation indicated that coastal water quality standard may be attained and inundation by the 50-year flood may be avoided by such a separation waterway.