Characteristics of sedimentation and channel adjustment linked to the Three Gorges Reservoir

Abstract

Construction of large dams is attractive because of their great benefits in flood control, hydropower generation, water resources utilization, navigation improvement, etc. However, dam construction may bring some negative impacts on sediment transport and channel dynamics adjustments. Due to the effects of recent water and soil conservation projects, sediment retention in the newly constructed large upstream reservoirs, and other factors, the sedimentation in the Three Gorges Reservoir (TGR) is quite different from the amount previously predicted in the demonstration stage. Consequently, based on the measured data, characteristics of sedimentation and the related channel deformation in the TGR were analyzed. The results imply that sediment transport tended to be reduced after the Three Gorges Project (TGP). Sedimentation slowed dramatically after 2013 and indicated obvious seasonal characteristics. Due to the rising water level in the TGR in the flood season, the yearly sediment export ratio (Eratio) was prone to decrease. The water level near the dam site should be reasonably regulated according to the flow discharge to improve the sediment delivery capacity and reduce sedimentation in the TGR, and to try to avoid situations where the flood retention time is close to 444 h. The depositional belt was discontinuous in the TGR and was mainly distributed in the broad reaches, and only slight erosion or deposition occurred in the gorge reaches. Sedimentation in the broad and gorge reaches accounted for 93.8% and 6.2% of the total sedimentation, respectively. The estuarine reach located in the fluctuating backwater area experienced alternate erosion-deposition, with a slight accumulative deposition in the curved reach. Sedimentation mainly occurred in the perennial backwater area. The insight gained in this study can be conducive to directly understanding of large reservoir sedimentation and mechanism of channel adjustment in the reservoir region in the main channel of large river.