Abstract: Since the Three Gorges Reservoir began impounding water, the Qigongling bend in lower Jingjiang River has experienced convex bank erosion and concave bank deposition. The narrowing of the Baxingzhou section due to bank collapses has created a risk of river channel cut-off. Drawing on observation data, we analyzed the precise location of the cut-off in the Qigongling bend, designed a new cut-off channel, and established a 1D-2D coupled, non-steady flow model covering the Dongting Lake and the middle reaches of the Yangtze River to assess the hydraulic effects of the cut-off under typical operating conditions. Results reveal that the cut-off at Qigongling bend will have a considerable impact on the water levels in upstream and downstream river sections and Chenglingji, the flow diversion and zero-flow days at the three outlets of Jingjiang River, as well as the confluence relationship between Jingjiang River and Dongting Lake. Our study provides technical support for assessing flood prevention measures near Chenglingji and for proposing relevant emergency plans. It is of reference value for safeguarding flood control safety in the region and managing and protecting the confluence area of the Jingjiang River and the Dongting Lake.

Key words: cut-off, hydrological regime effect, numerical simulation, non-steady flow model, Qigongling bend