为探究三峡水库运用后下游连续急弯河道的冲淤调整规律,根据七弓岭、观音洲河段实测地形资料和水文资料,研究了水沙变异条件下河势变化和冲淤特性。研究发现:①三峡水库受上游水库调蓄作用,上游来沙量大量减少,上游来水基本处于清水状态;径流量重分配,枯水期流量增加,汛期洪峰削减。②三峡水库运行后,七弓岭、观音洲上下2个急弯河段首先冲刷,然后转变为“上冲下淤”的相反的冲淤性质,后又恢复为同时冲刷的状态;年内表现为枯水期冲刷,汛期淤积,上下弯道总是表现出相反的冲淤形态,即枯水期“上淤下冲”,汛期“上冲下淤”。③三峡水库运行后,七弓岭急弯河道趋向窄深,观音洲急弯河道则以展宽为主,弯道段与过渡段冲淤表现相反。研究结果以期完善弯曲河道的演变理论,并对下荆江河床演变预测、河道整治及河道保护工作提供技术支撑。

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.