Abstract: The aim of this study is to investigate into the law of erosion and deposition of downstream continuous sharp bend river channels in the lower Jingjiang River after the operation of Three Gorges Reservoir (TGR).According to the measured topographic data and hydrological data of Qigongling bend (in upper reach) and Guanyinzhou bend (in the lower reach), the river regime change and erosion and deposition characteristics under varying water and sediment condition are examined. Results reveal that: 1) due to the regulation and storage of upstream reservoirs, the amount of sediment coming from the upstream of TGR reduced by a large margin, and the water coming from the upstream is basically clear. Runoff redistributed as increasing in dry season, and declining in flood season in terms of flood peak. 2) After the operation of TGR, the upper and lower reach bends were scoured firstly, but then changed as scour in the upper reach while deposition in the lower reach, and subsequently went back to simultaneous scouring. In general, the two sharp bends were scoured in dry season, whereas deposited in flood season. But the upper reach bend and the lower reach bend showed opposite features: deposition in the upper reach while scouring in the lower reach in dry season, and erosion in the upper reach while deposition in the lower reach in flood season. 3) After the operation of TGR, the Qigongling bend tended to be narrow and deep, while the Guanyinzhou bend tended to be widened. The erosion and deposition performances of curved segments were opposite to those of transition segments. The research findings are expected to enrich the theory of bend reach evolution, and would offer technical support to the prediction of riverbed evolution as well as the regulation and protection of river channel.

Key words: sharp bend channel, scour and deposition characteristics, riverbed evolution, river regime change, Three Gorges Reservoir, Qigongling, Guanyinzhou