Abstract: As a major project lying in the Changjiang Estuary, Qingcaosha reservoir leads to change of river regime in the North Channel markedly. The change of river regime could induce change of current field and sediment concentration, and then influence bed erosion and deposition. The three-dimensional hydrodynamic and sediment model were used to calculate and analyze the impacts of the project on current filed, sediment concentration, erosion and deposition in area around the reservoir. After the project, width of upper reaches of the North Channel was narrowed, which results in increase of both current speed and sediment concentration in the major channel on the north of Qingcaosha reservoir. On the contrary, the current speed and sediment concentration decrease in areas on east of the reservoir, lower reaches of the North Channel and sand bar due to the decrease of river discharge and tidal prism flowing into the North Channel. Using the formula of bed erosion and deposition based on experience and theory, and the modeled current, sediment concentration and water level, the erosion and deposition caused by reservoir project was calculated. Strong erosion occurs in the North Channel on north of reservoir, with maximum of 3 m, which matches well both in shapes and values with the observed depth change before and after the project. The numerical model simulated the distributions and magnitude of bed erosion and deposition fairly well caused by Qingcaosha reservoir project.

Key words: Changjiang Estuary, Qingcaosha reservoir, hydrodynamic, sediment concentration, erosion and deposition