Abstract: Reservoir construction modifies the relationship between rivers and lakes and affects the downstream flow and sediment conditions, thereby impacting the river basin, human life, and social development. Using the 2003-2019 data series of runoff and sediment discharge in the Dongting region, variation trends in flow and sediment are analyzed using Mann-Kendall trend test and slip averaging, focusing on their abrupt changes through Mann-Kendall mutation analysis. The results show that for this period, significant variations with abrupt change points are noticeable in the annual sediment discharges at Dongting Three Entrances and the annual runoffs at the hydrological stations of Mituosi and Kangjiagang, while no significant variation can be detected in the annual runoff at the Entrances’ other stations or in the annual runoff or sediment discharge in the Dongting Four Tributaries. The abrupt change points of flow and sediment at Mituosi were in 2014 and 2010 respectively, while the rest were around 2008. The incoming flow and sediment from the Yangtze mainstream, which had been obviously affected by the 2008 test impoundment to 175 m of the Three Gorges dam, was an important factor of the variations in Dongting’s water and sediment. And sand mining and other factors were also possibly related to the scour and deposition in this lake.

Key words: sediment, water and sediment conditions, Mann-Kendall trend test, Dongting Lake, abrupt change