Abstract: The Songzi River serves as the primary channel linking the Yangtze River and the Dongting Lake. Since the 1950s, the water diversion from the Songzi River has gradually decreased due to the completion of artificial cutoffs in the lower Jingjiang River, the Gezhouba Project, and the Three Gorges Reservoir (TGR). Based on measured hydrological data and prototype channel observation data, we analyzed the change and influencing factors of water diversion at Songzi outlet after the impoundment of TGR. Results indicate the following: 1) The annual split ratio has stabilized at 7% with no significant changes. 2) The water diversion capacity of Songzi outlet noticeably increases when the discharge at Zhicheng Station exceeds 25 000 m³/s, particularly during the first ten years following the TGR impoundment. 3) Operations during main flood season have a minimal impact, while impounding water after flood season in the TGR negatively affects water diversion at Songzi outlet. 4) Riverbed erosion in the mainstream of Jingjiang River leads to a decline of middle-low water levels near the inlet, posing an unfavorable impact on the flow diversion at Songzi outlet. 5) To a certain extent, the construction of the channel improvement project in Lujiahe Shoal Reach helps maintain middle-low water levels, and the sand dredging in the entrance reach improves inflow conditions during specific periods.

Key words: water diversion, Three Gorges Reservoir, Jingjiang River, Songzi outlet, influencing factor