Abstract: The operation of the Three Gorges Reservoir has significantly altered the original hydrodynamic conditions of the river and led to adjustments in the morphology of central bars. To further investigate the effects of Three Gorges Reservoir impoundment on the morphological adjustments of central bars, we selected five typical central bars in the reservoir area as study objects. Using Landsat remote sensing images and terrain and water-sediment data from 2003 to 2017, we quantitatively analyzed the spatial and temporal evolution characteristics of the morphological adjustments of the central bars at different stages. Results showed that with the fluctuation of the water level in the Three Gorges Reservoir, the exposed area of central bars gradually decreased, and the riverbed showed an accumulated siltation trend, which accelerated the morphological changes of central bars. The strongest siltation occurred at a water storage elevation of 156 m (October, 2006 to 2008), while siltation significantly attenuated after 2012. At spatial scale, the further away from the dam, the smaller the siltation intensity of central bars. Due to sand mining, central bars in the area affected by the backflow of the reservoir were subjected to irregular changes in local riverbed topography. Meanwhile, the backflow of the Three Gorges Reservoir changed the development mode of central bars. Specifically, the downstream end of the bars developed and was silted towards the downstream, while the upstream end was eroded by clear water flow.

Key words: central bar, scouring and silting adjustment, flow-sediment variation, Landsat remote sensing image, morphological spatial and temporal evolution, Three Gorges Reservoir