Abstract: The measured salinity and numerical simulated current speed and direction in December 2013 and February 2014 were used to analyze the source of saltwater intrusion at the water intake of Qingcaosha reservoir. Under the general river discharge and wind case in dry season December 2013, the saltwater sources at the water intake during spring tide, medium tide after spring tide, early neap tide came from the upstream saltwaterspillover from the North Branch into the South Branch, whereas during late neap tide and medium tide after neap tide came from the downstream open sea, i.e., through the saltwater intrusion in the North Channel. It was found that the saltwater intrusion in the Changjiang Estuary in February 2014 was very severe and had never been happened in recent decades, which resulted in the not suitable take water days of the reservoir reach to 23 days, and serious threat of safety water supply in Shanghai. Under the general river discharge and long continue strong northerlies lasting 15 days in February 2014, the saltwater sources at the water intake of Qingcaosha reservoir during the all four tidal patterns came from the downstream open sea saltwater intrusion through the North Channel.

Key words: Qingcaosha reservoir, saltwater intrusion, tidal pattern, wind case