中文摘要：

水库蓄水引发的下游河道再调整，对河流未来演变与人类活动均有重要影响．根据现场实测水文、地形与床沙资料，对三峡蓄水后下游宜昌一杨家脑河段的河床冲刷下切、粗化等现象进行了统计分析．结果表明，三峡水库蓄水后导致宜昌相同来流情况下来沙剧减，这是导致研究河段冲刷的根本原因．2002—2006年间主要冲刷区逐年下移，冲淤幅度逐渐变小．而2006年汛末与2008年汛末三峡水库水位的抬高均导致冲刷量的突增．2002--2006年各河段曼宁糙率值逐步增大，尤其是坝下河段．床沙组成中卵石含量迅速提高，坝下河段河床中值粒径亦明显增大，而枝城以下河段不明显．这种上、下游河段粗化过程的差异性与河道冲淤、糙率变化是一致的．

英文摘要：

The readjustment of reservoir-downstream channels is important to both local fluvial morphology and human activities. According to the observation of hydrology, landform and riverbed sediment, this study analyzed the scour, incision and bed matenal armoring of Yichang-Yangjianao channel, which is located at the downstream of the Three Gorges project （TGP）. The results show that the incoming sediment of Yiehang station is significantly decreased due to TGP impoundment, thus the study channel is scoured. The main erosion zone moved downwards every year and the scouring amount reached its peak in 2006 and 2008, when the reservoir stage was raised. The roughness coefficient increased during 2003 to 2006 （the near-dam section especially）. The proportion of cobbles on bed increased and the median diameter in the near-dam section also increase obviously, while the median diameter downstream of Zhieheng just changes slightly. The difference between the upstream and the downsteam in bed material armoring is coherent with the tendency in distribution of both scouring amounts and roughness coefficients.