Distributions of current and chlorinity in the Chenhang Reservoir in the case of brackish water in-taking

Abstract

Brackish water (chlorinity slightly > 250 ppm) in-taking of the Chenhang Reservoir (CHR) from Changjiang Estuary during extremely dry season is an emergency method to ensure the freshwater supply in Shanghai. Mixed with freshwater previously stored inside the reservoir, the chlorinity of output water can below the criterion (250 ppm). In this study, a 3D numerical model was adopted to simulate the distributions of current and chlorinity in the CHR when the brackish water entered it, and their responses to the northerly wind. The results showed the circulations in the CHR were dominated by the inflow/outflow, wind-driven current and the density-driven current. The inflow/outflow currents were along the shore. Near the inlet, the baroclinic gradient force resulted in compensation flows at the upper layers due to the mass conservation. In the other area of the reservoir, the wind-driven currents were dominant at the upper layers and the compensate flows were formed at the lower layers. The wind stress tended to intensify the mixing in the water column. A patch of water mass with the chlorinity less than that of outflow water was formed in the northeast corner under the windless condition. If the artificial mixing was carried out, the chlorinity in the outlet would be decreased, and the quantity of the raw water supply would be increased.