Evolution of shoal and deep‐water channel morphology and responses to human activities in the downstream section of the terminal hub of the Hanjiang River

The operation of cascade reservoirs in a watershed profoundly exerts river water‐sediment dynamics and topography evolution, and the terminal reservoir is the focus area for river and waterway management. This paper reveals the process and underlying factors of topography evolution and water level adjustment in the lower Hanjiang River under the action of cascade reservoirs. This study focused on the 263 km river channel downstream of the Xinglong Hydropower Conservancy Project on the Hanjiang River. Using measured flow, sediment, and topography data from 1977 to 2023, we analyzed the changing characteristics of riverbed scouring and deposition intensity, thalweg, and cross‐sections. Additionally, we evaluated the response relationship between riverbed scouring and deposition intensity and factors such as sediment transport, runoff, and human activities. From 1977 to 2023, the low‐water channel in the Xinglong–Estuary reaches showed a scouring and cutting tendency, and the riverbed slop initially decreased and then increased. The main cause of the riverbed scouring along the Xinglong–Estuary reaches was the reduced sediment load in the watershed, with waterway engineering having a slightly larger influence than runoff in the Xinglong–Xiantao reaches; by contrast, runoff exerted a more significant effect than both waterway engineering and the Yangtze River water level decline in the Xiantao–Estuary reaches. During the autumn flood season from 1983 to 2023, the water level differences between the Hanjiang and Yangtze Rivers at the same flow rate showed an increasing trend, leading to an increase in water surface slope, which intensified scouring forces and riverbed scouring. This study improves our understanding of the impacts of dam construction on river topographical evolution, water level changes, and deep‐water waterway resources.