| To analyze the impacts of the impoundment and regulation of the Three Gorges Reservoir (TGR) on the hydrological regime of downstream river channels, this study utilizes daily average water level and discharge data from 1991 to 2021. A set of low-flow indicators, combined with the Mann-Kendall trend test and Pettitt abrupt change test, is employed to systematically investigate the spatiotemporal evolution characteristics and driving factors of low-flow conditions in the Yichang-Luoshan reach of the Yangtze River before and after the operation of the TGR. The results show that post-impoundment low-flow discharges at all stations increased significantly (Pm < 0.05), with abrupt changes detected in multiple flow-level series, mostly occurring between 2005 and 2009. The annual number of low-water-level days decreased notably at Yichang, Zhicheng, Jianli, and Luoshan stations after reservoir operation, while at Shashi station, it increased by 30.3 days. Compared to discharge series, water level series exhibited delayed mutation timing. A decline in water level under the same discharge conditions was observed primarily after reservoir impoundment, with maximum declines at Yichang (0.69 m at 8000 m3/s), Zhicheng (0.64 m at 8000 m3/s), Shashi (2.81 m at 6000 m3/s), Jianli (2.08 m at 6000 m3/s), and Luoshan (1.53 m at 8000 m3/s). The regulation effect of the TGR and channel erosion are identified as the primary drivers of low-flow evolution, though the hydrological responses varied spatially among stations. Specifically, the post-impoundment rise in low water levels at Yichang, Zhicheng, and Jianli is mainly attributed to reservoir regulation, while at Shashi, channel erosion led to a continued decline in low water levels despite increased low-flow discharge. Luoshan, influenced by the Dongting Lake system, showed relatively minor fluctuations in water level and discharge. |
