中文摘要：

三峡水库蓄水后,葛洲坝枢纽下游近坝河段内枝城枯水位降幅较小,但宜昌及宜都等位置枯水位降幅较大,且随时间变化显示出非均匀下降的特征。为揭示该现象成因,依据宜昌至枝城河段内枯水位、地形、河床组成等实测资料分析了各因素的时变特征,并采用分离变量法计算分析了枯水位非均匀下降的机理。结果表明：宜昌枯水位在2008年前降幅小且下降速度慢,2008年以后降幅增大且下降速度加快;宜都至枝城区间冲刷是引起宜昌枯水位下降的主导因素,宜都以上河床变形、枝城水位下降为次要因素;宜都以上河床粗化引起阻力调整,是导致2008年前宜昌枯水位降幅小的主要原因;2012年后,宜昌至枝城段河床变形和阻力调整余地都已不大,未来宜昌枯水位稳定性主要取决于枝城水位变幅。

英文摘要：

Since the impoundment of the Three Gorges hydroproject,the decline of the low-water level along the Zhicheng river reach near the dam downstream of the Gezhouba hydrocomplex is small,but the falling amplitude of the low-water stage along the Yichang-Yidu river reach has greatly decreased. And the changes of the low-water level show the characteristics of non-uniform decline with time. This paper analyzes the time-variation characteristics of each factor in order to reveal the causes of this phenomenon,on the basis of the prototype observed data,including the water level,topography and composition of river bed of the Yichang river reach and its downstream,and a separation of variables method is applied to analyze the mechanism of the non-uniform drop in low-water level.The analysis results show that the falling process of the low-water level along the Yichang river reach was different before and after 2008. The decline in the low-water level along the Yichang river reach was small and slow down before 2008. After 2008,the falling amplitude of the low-water level increased and its falling speed was quicker.The scour from the Yidu reach to the Zhicheng reach is the main cause of the decline of low-water level in the Yichang river reach,and the deformation of the riverbed above the Yidu reach and the decline of water level in Zhicheng reach are the secondary causes. The adjustment of riverbed resistance caused by riverbed material armoring was a main cause of the decreasing amplitude of the low-water level along the Yichang river reach before 2008. After 2012,there was a little room for river bed deformation and resistance adjustment in the Yichang to Zhicheng river reach. The stability of the low-water level along the Yichang reach depends mainly on the fluctuation of water level along the Zhicheng river reach.