中文摘要：

三峡水库蓄水后沙量骤减使得荆江河段河床剧烈冲刷调整,下荆江急弯段＂凸冲凹淤＂,部分弯道凹岸侧淤积形成水下潜洲。这种不同于弯曲河道一般性演变规律的异常现象势必给下荆江的行洪、航运及江湖关系变化等带来新的影响,其内在成因急需揭示。基于原型观测资料分析,通过研究滩槽冲淤量及分布、滩体及河道形态特征等,全面揭示了近期下荆江急弯段＂凸冲凹淤＂的演变特征及河道形态响应。结果表明,流量年内过程重分配、来沙量及组成突变是下荆江急弯段＂凸冲凹淤＂的决定性因素。

英文摘要：

The sediment discharge has been reduced sharply since the operation of Three Gorges Project in 2003, leading to the severe erosion of Lower Jingjiang Reach （LJR） , a representative meandering channel located in the middle of Yangtze River. Some sharp bends in LJR are unusually undergoing convex bank erosion and concave bank deposition resulting in submerged shoal, which are contrary to the basic fundamentals of curved riverbed evolution. These abnormal riverbed deformations induce changes in flood control, waterway condition and the relationship between Yangtze River and Dongting Lake, and indeed the corresponding mechanism needs to be investigated. In the paper, based on a number of field data, the characteristics of riverbed evolution and channel morphology adjustments are fully demonstrated by quantitative statistics of erosion-deposition distribution and channel morphology for selected curved reaches. The results indicate that the annual redistribution of flow, the reduction of sediment discharge and mutation of sediment gradation are the dominant causes.