Effect of Dikes on Saltwater Intrusion Under Various Wind Conditions in the Changjiang Estuary

• Published in: Journal of geophysical research. Oceans 2020-07, Vol.125 (7), p.n/a
• Main Authors: Li, Linjiang, Zhu, Jianrong, Chant, Robert J., Wang, Chuning, Pareja‐Roman, L. Fernando
• Format: Article
• Language: English
• Subjects: Brackishwater environment; Changjiang Estuary; Coastal engineering; Coastal plains; Deep waterway project; Dikes; Dilution; Drinking water; Embankments; Estuaries; Estuarine dynamics; Freshwater; Geophysics; Inland water environment; Mathematical models; Morphology; Navigation; Numerical models; Saline water; Saline water intrusion; Salinity; Salinity effects; salinity variance; Salt advection; Salt water intrusion; Saltwater intrusion; strong northerly winds; Water intake; Water intakes; Water levels; Waterways; Wind; Winds
• ISSN: 2169-9275; 2169-9291
• DOI: 10.1029/2019JC015685

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. Plain Language Summary Coastal engineering projects such as channel deepening and dike installation always affect the length of saltwater intrusion in estuaries, but their effects may depend on the wind conditions. In this paper, we used a numerical model to explore the impacts of the dikes of the DWP on saltwater intrusion in the Changjiang Estuary under various wind conditions. Under climatic wind conditions, NC is occupied by freshwater for high discharge in the Changjiang Estuary. The dikes prevent the southward transport of relatively diluted low‐salinity water at the mouth of NC, resulting in an accumulation of diluted water and the weakening of saltwater intrusion and mixing in the NC. Under the strong north wind conditions, the salinity in the NC increases abnormally for the southward transport of high‐salinity water. Dikes blocked the southward transport and increased the landward water and salt transport in the NC. Although salinit