中文摘要：

三峡水库蓄水利用已有13年,对坝下游洪、枯水位和河道形态调整的影响已初步显现,通过对1955-2016年长江中游水位、河道地形等资料的分析,结果表明：（1）坝下游各水文站同流量枯水位下降、洪水位变化不大,最低水位上升,最高水位下降趋势;（2）2002年10月-2015年10月枯水河槽冲刷量占平滩河槽冲刷量的95.5%,冲淤分布由蓄水前＂冲槽淤滩＂转为＂滩槽均冲＂,不同蓄水阶段存在差异;（3）河槽冲刷过程中,上荆江及以上河段枯水位下降趋势趋缓,下荆江及以下河段下降速率增加,应采取防控措施遏制河道水位下降趋势;（4）枯水河槽冲刷是长江中下游航道水深提升的基础,枯水位降幅小于深槽下切深度,在河道和航道整治工程综合作用下航道尺度提升,提前5年实现了2020年航道尺度规划目标;（5）平滩水位以上河槽形态调整不大,在河床粗化、岸滩植被、人类活动等综合作用下河道综合阻力增加,出现了中洪水流量—高水位现象,应引起足够重视。三峡水库汛期调蓄作用可有效提升中下游洪水防御能力,但不排除遭遇支流洪水叠加效应,中下游洪水压力仍然较大。

英文摘要：

In this study, data measured from 1955-2016 was analyzed to study the relationship between the water level and river channel geometry adjustment in the downstream of the Three Gorges Dam （TGD） after the impoundment of the dam. The results highlighted the following facts： （1） for the same flow, the drought water level decreased, however, flood water level changed little. The lowest water level increased, while the highest water level decreased at the hydrologic stations in the downstream of the dam; （2） the distribution of erosion and deposition along the river channel changed from ＂erosion at channels and deposition at bankfulls＂ to ＂erosion at both channels and bankfulls＂; the ratio of low water channel erosion to bankfull channel erosion was 95.5% from October 2002 to October 2015, with variations in different impoundment stages; （3） the drought water level decrease slowed down during the channel erosion in the Upper Jingjiang River and the reaches ahead but sped up in the Lower Jingjiang River and the reaches behind; concrete measures should be taken to prevent the decrease in the channel water level; （4） erosion was the basis for channel dimension upscaling in the middle reaches of the Yangtze River; the drought water level decrease was smaller than the thalweg decline; both channel water depth and width increased under the combined effects of the channel and waterway regulations; and （5） the geometry of the channels above the bankfulls did not change much; however, the comprehensive channel resistance increased under the combined effects of the river bed coarsening, bench vegetation, and human activities; as a result, the flood water level increased markedly and moderate flood to high water level phenomena occurred, which should be considered. The Three Gorges Reservoir effectively enhances the flood defense capacity of the middle and lower reaches of the Yangtze River; however, the superposition effect of tributary floods cannot be ruled out.