Abstract:

Qingcaosha Reservoir is the main water source for Shanghai, providing approximately 55% of its high-quality raw water needs, and effectively guarantees the safety of water supply for Shanghai. The waters near the Qingcaosha Reservoir experience saltwater spillover from the North Branch into the South Branch; the nearby waters, moreover, suffer from direct saltwater intrusion from the open sea. In this study, a large number of measured salinity data in the upstream and downstream sluice was used to statistically analyze the characteristics of direct saltwater intrusion near the Qingcaosha Reservoir waters in recent decades. The analysis results show that direct saltwater intrusion neat the Qingcaosha Reservoir waters in recent decades was closely related to the river discharge, tide, and wind. There were a total of 16 instances of direct saltwater intrusion at the upstream sluice that occurred from September to March of the following year; likewise, there were a total of 41 instances of direct saltwater intrusion at the downstream sluice that occurred from September to May of the following year. The direct saltwater intrusions at the upstream and downstream sluices appeared primarily in December, January, and February of each year. We found that saltwater intrusions occurred most commonly when the river discharge was less than 18 000 m³/s during neap tide and middle tide (after neap tide) accompanied by persistent northerly or northwesterly winds. We found that the strength and duration of the northerly or northwesterly winds in the days preceding saltwater intrusion had an important role on direct saltwater intrusion.

Key words: Changjiang Estuary, Qingcaosha Reservoir, saltwater intrusion, river discharge, tidal type, wind