『Abstract
　The Three Gorges Project (TGP) is a transcentury project that has aroused world attention. It is expected that the flow velocity and runoff of the Yangtze River will be changed after the project has been accomplished. Consequently, however, the ecological environment in the Yangtze River Basin, particularly in the estuary region, will be affected. Salinity intrusion into the Yangtze River estuary, in general, is mostly affected by the Yangtze River discharge and its external tidal level. This paper focuses on examining the influence of changes in runoff on salinity value. The question, to which should be paid attention is: how is the interaction between changes in runoff of the Yangtze River and salinity distribution in the Yangtze River estuary, China? In this research, a three-dimensional model has been used to identify the effects of runoff change on salinity distribution. The drawn conclusion is that the change of salinity is influenced by discharge variation. Positive and negative impacts of TGP would both turn up but in different period. In sum, TGP is in favor of restraining saltwater intrusion. Nevertheless a suitable method should be found to resolve its negative influences.

Keywords: Three Gorges Project; Yangtze River estuary; Saltwater intrusion; ECOMSED model』

Introduction
Yangtze River runoff and changes
Model set-up
　Hydrodynamic module
　Study area and computational grid
　Data source
　Model configuration
　Boundary conditions and initial conditions
Results and discussions
　Verification of tidal level and flow field
　Outputs in October
　　Overall influence of runoff on salinity in October
　　Effects on salinity in the south branch of Yangtze River in October
　　Effects on salinity in the north branch of Yangtze River in October
　Outputs in February
　　Overall influence of runoff on salinity in February
　　Major effects on the freshwater supply for Shanghai in February
Conclusion and discussion
Acknowledgments
References