Dam-induced effects on downstream flood and low-water levels in large rivers: insights from the Middle Yangtze River

Dam-induced channel adjustments often reduce low-water levels but can paradoxically increase flood levels. The Middle Yangtze River (MYR) may serve as a representative example of dam-induced downstream fluvial responses. The cumulative channel scour volume in the MYR was 2.8 billion m3 after the operation of the Three Gorges Project. The flood levels exhibited a pronounced rise in some years owing to the combined effects of bed incision, increased channel roughness and local base-level rise, while the low-water levels declined consistently due to channel degradation. The total scour volume is predicted to reach 2.8 billion m3 in the next 30 years, with the low-water levels declining by 3 m in the Jingjiang Reach, and the flood levels would remain almost unchanged due to the balance between intensive channel degradation and increased channel resistance. The findings underscore the necessity of incorporating century-scale channel evolution predictions into the analysis of water level variations.