Effect of dikes on saltwater intrusion under various wind conditions in the Changjiang Estuary

To improve navigation, the deep waterway project (DWP) was implemented in the North Passage of the Changjiang Estuary in 1998, which includes a deep channel and two dikes protecting it. By altering estuarine morphology, the DWP can affect saltwater intrusion and mixing, with implications for drinking water intake and supply. In this study, we employ a numerical model to study the influence of dikes of the DWP on saltwater intrusion in the estuary under the climatic and persistent strong northerly wind conditions that occurred in February 2014. The model results show that the dikes prevent the southward transport of relatively low-salinity water at the mouth of the North Channel (NC) under climatic wind conditions, resulting in the weakening of saltwater intrusion and mixing in this channel. Under persistent strong northerly wind conditions, relatively high-salinity water is transported southward to the mouth of NC and blocked by the dikes causing a water level rise at the mouth of the NC. As a result, a large amount of high-salinity water advected into the NC and then out to the sea from the South Chanel, forming a counterclockwise horizontal circulation. The salinity increases abnormally, but mixing decreases in the NC for no more salinity variance input with the implementation of the DWP. Overall, the DWP favors water intake for the reservoir in NC under climatic wind conditions and is unfavorable to water intake under persistent strong northerly winds (>9 m/s), which can lead to extremely severe saltwater intrusion.