Sediment deposition trend in the Three Gorges Reservoir under the action of complex boundary conditions

Sedimentation in the Three Gorges Reservoir (TGR) is relatively complicated owing to the upstream water and sediment conditions and the reservoir scheduling process. In this study, based on a one-dimensional mathematical model of sediment, we investigated the comprehensive impact of changes in upstream and downstream boundary conditions on the sedimentation characteristics of the TGR. An empirical relationship between sediment inflow, average flood-season water level of the dam, and reservoir sedimentation was established, and their contributions and future sedimentation trends are discussed. We found that sediment inflow from upstream tributaries and the average flood-season water level of the dam are the main factors affecting sedimentation in the reservoir, causing the center of gravity of the sedimentation area to shift. Changes in sediment sorting and erosion/sedimentation in the downstream backwater and upper part of the perennial backwater zones are the most affected. In recent years, the contribution of sediment from the main stem to reservoir sedimentation has decreased, and the contribution from tributaries has increased. The recent impact of changes in the average flood-season water level of the dam on reservoir sedimentation is relatively small compared to the period from 2003 to 2012. In a normal hydrological year, the estimated sedimentation volume in the Three Gorges Reservoir is approximately 50 million tons, whereas in an unfavorable flood-combined hydrological year, especially when heavy rainfall in the tributaries causes the peak flow of the Minjiang and Jialingjiang rivers to exceed 30 000 m3/s, the estimated sedimentation volume in the Three Gorges Reservoir is approximately 160 million tons.