Abstract: Sedimentation and sediment delivery in the Three Gorges Reservoir (TGR) has always been a hot issue during its demonstration and operation. In this study, long-term series field measured hydrological and terrain data before and after the TGR’s impoundment are used to investigate the trend of runoff and sediment load transport into the TGR. The effect of sedimentation on the TGR is discussed. The result demonstrates that despite rare changes in annual runoff, the total amount of sediment load transport into the TGR shows a significant reducing trend (by 60%) after the impoundment of the TGR. Analysis of the field data shows that the average sediment delivery ratio of the TGR is 24% during 2003-2018 and the annual loss in storage capacity is about 0.3%. Annual sedimentation is in a linear relation with incoming sediment, and the slope of the relation is larger when water level gets higher in flood season. Sediment mainly deposits in river reaches with wide cross sections, especially in the permanent backwater area where the flow velocity is relatively small.In some branching reaches,the river pattern develops towards unification.It is expected that this study will help optimizing the TGR operations and improving its comprehensive function.

Key words: sedimentation, sediment delivery ratio, river pattern conversion, sediment inflow, Three Gorges Reservoir