Spatio-temporal variation of thalweg in Jingjiang River section since operation of Three Gorges Reservoir

The operation of Three Gorges Reservoir has markedly altered the downstream water and sediment conditions, leading to continuous adjustments in the thalweg of Jingjiang River section. To investigate the adjustment process and patterns of Jingjiang River thalweg following the impoundment of Three Gorges Reservoir, this study analyzed the spatial and temporal evolution of thalweg elevation based on measured data from 162 cross-sections from 2003 to 2021. The results indicated that since the operation of the Three Gorges Reservoir, the thalweg of the Jingjiang River had generally experienced erosion, with an average annual rate of (-0.08±0.28) m/a. The most intense erosion occurred between 2014 to 2019, reaching (-0.18±0.51) m/a. After 2019, influenced by major flood events, the thalweg elevation shifted to deposition with the average change of (0.27±1.08) m/a, but whether this represented a trend reversal requires further investigation. Spatially, the heterogeneity in thalweg changes was significant, with the Gong′an section showing the minimal changes since 2007, the Shishou section experiencing the strongest erosion, the Jianli section alternating between erosion and deposition, and the Zhijiang section showing intensified erosion in the later period. This study revealed a "erosion-deposition-reerosion-redeposition" chain response pattern in the middle Yangtze River′s channel evolution process, which held significant theoretical importance for understanding longitudinal sediment transport processes in large alluvial rivers, and providing a scientific basis for flood control and waterway management in the middle reaches of Yangtze River.