Effects of channel regulation on salt intrusion and residual circulation of Keelung River

摘要

A vertical (laterally integrated) two-dimensional numerical model was applied to study the hydrodynamic characteristics, salt-water intrusion and residual circulation in the Danshuei River estuarine system. The cross-sectional profiles measured in 2001 and 1990 respectively represent the conditions after and before channel regulation in the Keelung River. The model was re-verified with the available hydrological data measured in 2001. Detailed model re-verification has been conducted with water surface elevations, tidal current, and salinity distributions measured. The overall performance of the model is in qualitative agreement with the available field data. The model was then used to investigate the change in tidal ranges, salt-water intrusion, and residual circulation as a result of channel regulation in the Keelung River. The model simulations indicate that more tidal energy propagates into the estuarine system before channel regulation because of the substantial increase in river cross-sections. The residual circulations before channel regulation are greater than those after channel regulation and result in the limits of the salt intrusion before channel regulation being extended farther inland than those after channel regulation. This may show that channel regulation for flood control in the Keelung River did not contribute to the expansion of the mangrove areas and the disappearance of freshwater marshes at the Kuan-Du wetlands.