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Abstract: [Purposes] There are three tributaries connecting the Dongting Lake and the Yangtze River. The water and sediment status were measured at five hydrologic gauge stations along the three tributaries, i.e., the Xinjiangkou, Shadaoguan, Mituosi, Kangjiagang, and Guanjiapu station. This study investigated the days of occurrence of runoff cutoff and change of streamflow and water level at the five hydrologic gauge stations, and their interrelationship with runoff and sediment transport. This study also investigated the impact of human activities on the changes of water and sediment in Dongting Lake in conjunction with the construction of water conservancy projects. [Methods] Based on the measured water and sediment data from 1961 to 2017 at the main control stations at the inlet and outlet of Dongting Lake, the Mann-Kendall test and the Pettitt mutation test were used to analyze the evolution characteristics of water and sediment flowing into and out of Dongting Lake during different periods. [Findings] 1) The average annual diverted flow at five hydrologic gauge stations continued to decrease. The annual total runoff and the runoff during the flooding period at the five hydrologic gauge stations changed abruptly in 1985. The water level at the five hydrologic gauge stations raised significantly, and the amount of sediment at the five hydrologic gauge stations decreased along with the reduction of the diverted flow. The most remarkable decrease of sediment occurred at the Ouchikou, and the total amount of sediment transported into the lake at the five hydrologic gauge stations had a significant abrupt change in 1990. 2) Although the runoff of the four major rivers flowing into the Dongting Lake did not change significantly, both the annual sand sediment transport and the amount of sediment transported during the flooding season decreased significantly after 1985; 3) The total runoff flowing into and out of Dongting Lake exhibited a decrease trend. The annual sediment flowing into and out of the lake exhibited a decrease trend. The decreasing rate of the annual sediment flowing out of Dongting Lake is relatively slow. Specially, the sediment flowing out of Dongting Lake is larger than that flowing into Dongting Lake after 2008. [Conclusions] The lower Jingjiang River meander cut-off Gezhouba hydropower complex, Three Gorges Project and the control project constructed for the four major rivers flowing into the Dongting Lake are the main causes for the change of water and sediment process of the Dongting Lake. Among them, the operation of Three Gorges Reservoir led to 90.0% decrease of the diverted sediment at the five hydrologic gauge stations and the diverted flow at the Mituosi, Kangjiagang, and Guanjiapu station. The changes of water and sediment in the four major rivers flowing into the Dongting Lake were more strongly influenced by the large- and medium-sized reservoirs constructed in Hunan Province.
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