Hydrological dynamics of the Yangtze river-Dongting lake system after the construction of the three Gorges dam.

The Yangtze River-Dongting Lake link has gotten a lot of attention as a because of the Three Gorges Project. However, the hydrological dynamic process and future direction of the river-lake interaction in the context of sediment reduction are yet unknown. Based on Dongting Lake Basin runoff and sediment data from 1961 to 2020, as well as field monitoring data of turbidity and flow velocity from Yichang to Chenglingji section of the Yangtze River, this paper examines the runoff and sediment variation law and hydrological dynamic process of Chenglingji, the only outlet connecting Dongting Lake to the Yangtze River, and reveals the development trend of the river-lake relationship. After absorbing high-concentration material from Dongting Lake, Chenglingji's turbidity and energy per unit water body alter dramatically. When the high-speed flow from the mainstream of the Yangtze River and the gentle flow of Dongting Lake pass through the "deep trough" of Chenglingji, the two streams of high and low flow velocity intersect and decelerate to dissipate energy, and the flow structure becomes more complicated. Dongting Lake has experienced three stages: deposition (1961-2007) -erosion (2008-2017) -deposition (2018-2020). The river-lake relationship will tend to a new dynamic equilibrium state in the future.