Abstract: Xiongjiazhou reach is located at the tail of the lower Jingjiang River in the midstream of Yangtze River. The morphology of Xiongjiazhou reach transited from straight to slightly sinuous and then gradually evolved into S-shape. It is currently the most sinuous segment in the Jingjiang reach. Subjected to incoming water and sediment load, and affected by riverbank boundary conditions as well as natural and artificial cutoffs, Xiongjiazhou reach has undergone frequent local adjustment in terms of river regime. Since the chute cutoff in the convex bank of Xiongjiazhou reach, a new anabranching channel was formed, leading to the coexistence of the main channel and the anabranching channel, which changed the flow conditions at the outlet of the Xiongjiazhou reach and further affected the bank collapse rate and riverbed erosion-deposition process in Qigongling bend. According to remote sensing imagery data and representative sections in dry season, the entire Xiongjiazhou reach has been creeping towards the downstream and the channel has been widened. The newly formed anabranching channel in the Xiongjiazhou bend is experiencing expanded scouring, with an average width of 70 m in seven years. The deep trough along the outflow section develops from the left bank to the right bank, and the thalweg of downstream Xiongjiazhou is deflected to the right bank. After the impoundment of the Three Gorges Reservoir, the thalweg has been moving close to the concave bank of Qigongling bend, whereas the original deep trough was deposited into two bars emerging above water surface. After reaching the apex of Qigongling bend, the thalweg gradually shifted to the concave bank. The results of this research provide reference for the implementation of the river regime control project in this segment, and offer ideas for the next step in the study of river regime control.

Key words: chute cutoff, morphology, riverbed scouring and deposition, anabranching channel, bend, bank collapse, Xiongjiazhou reach, lower Jingjiang River