Abstract: The river system in Dongting Lake, originating from the Yangtze, has a flow-sediment regime that depends much on the Three Gorges Reservoir. A study on the scour and sedimentation in this system and its time changes can help understand the river’s flood control and the river-lake relationship. In this study, we develop a numerical flow-sediment transport model and simulate the scour and sedimentation and its changes in the river system in the period starting from the reservoir operation. The dominant factors are examined on the basis of the simulations and field observation data. The results show that in this period, a general scour has occurred over the system－a trend that will not change in the near future－but its intensity has been decreasing gradually. And no obvious change has been observed in the trends of the diverted flows, flow diversion ratios, or sand diversion ratios at the estuaries of the river system. In the period, the amount of diverted sediment has been reduced tremendously, as the flow from the reservoir is laden with much less sediment and thus has altered the scour and sedimentation conditions of the river system. In addition, sand mining has also imposed a significant impact on the river system.

Key words: Dongting Lake, flow-sediment transport model, Three Gorges Project, channel evolution