Abstract: An improved three dimension numerical model of saltwater intrusion in the Changjiang Estuary was applied to this numerical simulation. The model was validated with the salinity observed in 2007—2008 at the 10 hydrological sites, and the results showed that the model calculated salinity are well consistent with the observed ones. We considered the extremely drought year 1978—1979 as a hydrological calculation year, adopted the observed topography in 2008, and considered the effects of tide, wind stress and mixing in the model. The measured daily river discharge at the Datong station was modified by the Three Gorges Project, the eastern water diversion project from the South to the North, and the water intake and drain along the river. The conclusion is that the longest continuous days unsuitable for water intake in the Dongfengxisha reservoir are 26 days. This important parameter has been adopted in the build of the reservoir, providing scientific and technological support for the construct of ecological Chongming island and the ensure of freshwater resource safety.

Key words: Changjiang Estuary, saltwater intrusion, Dongfengxisha reservoir, the longest continuous days unsuitable for water intake, numerical calculation