Abstract: The Three Gorges Reservoir, impounded since 2003 for 20 years, has played a crucial role in flood prevention, hydropower generation, navigation, water resource utilization, and ecological environmental protection. However, its operation has also impacted downstream hydrological regimes. We analyzed daily runoff and water level data from the Yichang hydrological station spanning from 1950 to 2022. Applying the MASH (Moving Average over Shifting Horizon), Sen slope, and IHA/RVA methods, we quantitatively assessed the alterations in hydrological regimes following the Three Gorges Reservoir operation. Findings revealed significant trends in moving-average runoff, with increases during January-May and decreases during September-November, as well as decreasing moving-average water levels from June to December. Fourteen IHA (Indicators of Hydrologic Alteration) showed substantial alterations, resulting in an overall alteration of 63.52%, classified as moderate. The Three Gorges Reservoir notably enhanced the median values of annual minimum flow components and the number of flow reversals while decreasing the median values of annual maximum 1-day flow through streamflow regulation. These adjustments reflect the reservoir’s multifaceted benefits for flood control and hydropower generation. The research outcomes offer valuable insights for managing water resources within the Three Gorges Reservoir.

Key words: Three Gorges Reservoir, hydrological regime, MASH method, IHA/RVA method, Yichang hydrological station