Impacts of Three Gorges Reservoir on the sedimentation regimes in the downstream-linked two largest Chinese freshwater lakes

Abstract

We studied the impacts of Three Gorges Reservoir (TGR) on the sedimentation regimes in the downstreamlinked two largest Chinese freshwater lakes, Lake Dongting and Lake Poyang. Our results indicate that up to 1.73 × 109 t sediment was retained in TGR from June 2003 to December 2014. This resulted in a 145.9 × 106t yr-1 decline in the suspended sediment load at Zhicheng and a 16.8 × 106tyr-1 lower sediment flow from Yangtze River to Lake Dongting, which partially explains the 13.4 × 106tyr-1 lower sedimentation in Lake Dongting during the post-TGR period. Furthermore, TGR resulted in a 0.5 ± 0.3 m reduction of the multi-year mean water level at the Lake Poyang outlet Hukou, accelerating the suspended sediment export discharge from the lake. The reduced sedimentation in Lake Poyang during the post-TGR period was estimated to 6.3 × 106tyr-1. We estimate that a monthly mean concentration of sediment flow from TGR below 0.60 kg m-3 will lead to erosion in Lake Dongting and Lake Poyang. Better regulation of TGR may extend the life expectancy of the two vanishing large lakes.