Impact of the Three Gorges Reservoir on the hydrologic regime of the river-lake system in the middle Yangtze River

Abstract The dynamic response of the river-lake systems to upstream reservoir regulation is one of the increasingly essential research issues of watershed management. In this paper, the Yangtze River and Dongting Lake, the third-longest river on the earth and the second largest lake in China, were selected as a case study on the river-lake system to quantitatively evaluate the reservoir operation impacts of the Three Gorges Reservoir (TGR) based on a 1D/2D coupled model and five statistical indexes. The results show that there was a noticeable flow decrease during the periods of peak flow regulation and reservoir impoundment, while the stage increase during the water supplement periods indeed contributed to the eco-environmental improvement of the Dongting river-lake system. In particular, this research indicated that the hydraulic gradient and riverbed incision downstream the dams were the critical influencing factors of the hydraulic interaction between the lake and rivers, which had a noticeable influence on the water exchange within the system. This work provides a new strategy for the future water resources and environmental management and facilitates the effective flow regulation of dams, which have significant implications for not only the Dongting river-lake system but also the similar lakes and rivers elsewhere.