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

Yongqiang Zhou,Xinping Zhang,Erik Jeppesen,Yunlin Zhang,Jingbao Li,Xichun Li

doi:10.1038/srep35396

Abstract

We studied the impacts of Three Gorges Reservoir (TGR) on the sedimentation regimes in the downstream-linked 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 × 106 t yr−1 decline in the suspended sediment load at Zhicheng and a 16.8 × 106 t yr−1 lower sediment flow from Yangtze River to Lake Dongting, which partially explains the 13.4 × 106 t yr−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 × 106 t yr−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.

Highlights

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
Considering the large area of the ungauged regions, the contribution of ungauged suspended sediment to the sediment budget of the Yangtze River is an important factor to consider. This contribution has been quantified[19,26] and estimated in some studies[25,33], but the ungauged sediment source and its impact on the river-lake system has often not been element of investigation in previous studies[22,34,39], resulting in an underestimation of the sediment deposition in downstream river reaches and lakes. This means that an accurate estimation of the suspended sediment budgets of Lake Poyang and Lake Dongting impacted by the operation of TGR is not available
We evaluated to which extent the establishment of TGR has simultaneously affected the sediment budgets of Lake Dongting and Lake Poyang by comparing the observed sediment budgets in the two lakes with a calculated non-TGR scenario

Summary

Introduction

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. Considering the large area of the ungauged regions, the contribution of ungauged suspended sediment to the sediment budget of the Yangtze River is an important factor to consider This contribution has been quantified[19,26] and estimated in some studies[25,33], but the ungauged sediment source and its impact on the river-lake system has often not been element of investigation in previous studies[22,34,39], resulting in an underestimation of the sediment deposition in downstream river reaches and lakes. How to best regulate dams to maintain an erosion state in downstream-linked lakes has been a subject of limited investigation[4,22]

Methods

Results

Conclusion