Assessing the Influence of Sea Level Rise on Salt Transport Processes and Estuarine Circulation in the Changjiang River Estuary

Global sea level rise has been greatly concerned by government and society with its effects on saltwater intrusion and material transport in estuaries, which threaten freshwater habitat and drinking water supplies. A semi-implicit estuarine, coastal, and ocean model (ECOM-si) was used to assess the influences of rising sea level on salt transport processes and estuarine circulation patterns in the Changjiang River estuary, China. The variations of intruding saltwater and residual salt transport were simulated according to the variations of several sea level rise scenarios, and results in typical year and dry year were demonstrated, respectively. The modeled results are in good agreement with the observed data, and statistics show good correlation coefficient and Skill Score values. Results from the numerical experiments show that the intensity of saltwater intrusion and stratifications both increase as sea level rises, while the increments are quite distinct between each channel. Furthermore, it shows obvious interannual changes following different river discharges. The residual transport of salt was used to analyze the changes in transport processes and estuarine circulation pattern. The computation results show that the Stokes drift transport is the major mechanism for up-estuary salt transport in each channel, whereas the seaward Eulerian transport is of the same order. The flux of saltwater spillover from the North Branch into the South Branch increases with stronger Stokes transport as sea level rises. The landward salt transport is strengthened in the North Channel and may further affect the upper reaches under strengthened tidal pumping and vertical shear transport with higher sea level. The overtopping flow affected by tidal pumping is the dominant mechanism for salt exchange between the North Passage and South Passage. This may increase the salt supply from the ocean into the South Channel.