Impacts of wind stress on saltwater intrusion in the Yangtze Estuary

The observation at the Chongxi gauging station indicated the salinity of saltwater spilling over from the North Branch to the South Branch increased abnormally from November 10 to 12 in 2009 (during neap tide) and from February 11 to 12 in 2010 (during moderate tide). We found for the first time that the strong northerly wind was responsible for the above abnormal salinity increase. Previous studies indicated that the saltwater intrusion in the Yangtze Estuary is influenced mainly by the river discharge, the tide, and the wind stress, but the impacts of variations of wind speed and direction on it have not been investigated. In this study the impacts of wind stress on the saltwater intrusion were numerically simulated and the associated mechanisms were analyzed. The model results were consistent with the observed data obtained at six gauging stations during February and March in 2007 and four gauging stations in March 2008, and the abnormal salinity risings were well captured. Meanwhile, if the wind speed is reduced by half, the salinity there will be significantly decreased. Driven by the monthly mean river discharge of 11000 m3/s and northerly wind of 5 m/s from January to February, the model simulated the temporal and spatial variation of saltwater intrusion. The wind-driven circulation, as well as the net water and salt fluxes from the North Branch into the South Branch, was calculated and analyzed in the cases of different wind speeds and directions. The results indicated that the intensity of the saltwater intrusion in the Yangtze Estuary is significantly influenced by the wind speeds and directions.