Variation in water and sediment conditions and erosion and deposition characteristics in the reach between Three Gorges Dam and Gezhou Dam

A correct understanding of the variation pattern of water and sediment conditions as well as erosion and deposition characteristics in the reach between Three Gorges Dam and Gezhou Dam is essential for studying the many engineering problems in the reach. In this study, abundant water-sediment topographic data were analyzed, and the application of the theory of sediment incipient motion in erosion prediction was discussed. Owing to reservoir construction in the upper reaches of the Yangtze River and the successive operation of the two major hubs, the annual runoff in the reach was slightly reduced, the monthly average runoff was redistributed by "peak load shifting, " the annual sediment discharge declined considerably, and the water-sediment relationship in the reach was significantly changed. The cumulative erosion and deposition quantity in the reach was under short- and long-term control by the extreme hydrological conditions and scheduling of the hubs. In terms of time, there were apparent phased characteristics; in terms of space, some sub-reaches were in an active state. The bed sediment was refined and coarsened successively with the operation of the hub. The incipient critical condition curve was drawn based on Sha's incipient velocity equation, and the estimation of the maximum particle size of movable bed sediment or critical water flow of the cross-section provided a reference for predicting the possibility of riverbed erosion.