中文摘要：

潮区界河段河势演变对三峡工程的响应是长江经济带建设中的重要问题。然而受观测手段所限,对三峡截流以来潮区界变动范围及其地貌演变的客观认识亟待探讨。对大通站洪季水位资料进行频谱分析,初步判断了近期长江洪季潮区界位置;对比1998年和2013年水下地形资料,分析了三峡大坝截流以来该河段河槽的冲淤演变特征;利用多波束测深系统对冲刷明显河段的微地貌进行了高分辨率观测。结果显示：（1）1998-2013年潮区界变动河段河槽整体冲刷5 649.7万m^3。其中,上段全面冲刷,太白、太阳两洲并岸,铜陵沙被冲开,主槽刷深达5.6m;中段主泓摆动,天然洲南冲北淤,黑沙洲中水道淤死,南水道左岸最大冲深达8.9m;下段近岸冲刷强烈,北岸最大冲深达15.4m;（2）该河段近期处于剧烈的冲刷环境,左岸冲刷尤为显著;（3）冲刷深槽分布在顺直河段,深达5.4-12.6m;冲刷坑分布在分汊河段平面形态突变处,最大冲深达28.1-30.5m;水下侵蚀陡坡分布在近岸侵蚀严重的顺直河段,坡度为0.59-0.62。

英文摘要：

The evolution of tidal limit and its river regime in response to the Three Gorges Project （TGP） is an im- portant issue in the construction of the Yangtze River Economic Belt. However, due to the limitation of the observation method, there has been no report about the comprehensive study on the change of position of the tidal limit and the geomorphic evolution in this area since TGP river closure. In this study, the average location of tidal limit in recent flood season was identified through spectral analysis of water level in Datong station, the evolution char acteristics of landform were analyzed by comparison of bathymetric data in 1998 and 2013 and the high resolution micro-geomorphology in typical erosional areas was carried out by the multibeam echo sounding data. The research shows that： （1） From 1998 to 2013, the overall channel erosion in tidal limit reaches was 5 649. 7× 10^4m^3. The upper segment was all-round eroded with the erosion depth in the main channel up to 5.6 m. Taibaizhou and Taiyangzhou merged into bank and Tonglingsha was scoured aside. The middle segment was deposited with small amplitudes and the main stream line swung. The north side of Tianranzhou, Heishazhou Middle Waterway was silted up while south side eroded up to 8.9 m. The lower segment was generally eroded with strong erosion near the northern shoreline where the max depth was 15.4 m. （2） The grain size of surface sediment was apparently coarsened, which indicates that the river channels are under severe erosional environment in the near future. （3） The erosional channels were mainly distributed in straight reaches, and the depth was 5.4- 12.6 m. The scour pits were distributed in braided reaches where the planform suddenly changed, and the max erosion depth was 28. 1- 30.5 m. The erosional subaqueous bank slope mostly appeared in straight reaches with serious nearshore erosion, and its slope was 0. 59-0. 62.