三峡工程蓄水后长江中游城陵矶—汉口河段过流能力变化及影响因素分析

受上游水库运行的影响,自2003年后长江中游河段河床调整,引起河道自身过流能力的变化.本文选取长江中游城陵矶-汉口河段作为研究对象,根据实测资料计算了2003-2016年两个水文断面的水位-流量关系及特征流量变化,并采用一维水动力学模型计算了河段尺度的平滩流量.结果表明:(1)螺山站及汉口站2003-2016年的水位-流量关系呈现枯水流量下水位降低、洪水流量下水位抬升的特点;(2)两站年最大流量下对应的水位整体抬升,警戒水位下对应的流量分别减小9%和16%;(3)2003-2016年城汉河段平滩流量有增有减,无明显单向变化趋势,2014年后呈减小趋势.分析断面的过流能力变化,发现螺山站与汉口站警戒流量与动床阻力呈明显的反比关系,过流能力由于河道阻力的增大而减小;床沙粗化、河道相对水深的减小及洲滩植被覆盖度的增大是引起河道阻力增大、过流能力减小的原因.

Variation in flood-discharge capacity of Chenglingji-Hankou reach in the middle Yangtze River and analysis of influencing factors since the onset of the Three Gorges Reservoir

Since the onset of the Three Gorges Project(TGP)in 2003,the sediment load entering the middle Yangtze River(MYR)has been reduced sharply,leading to remarkable channel degradation,which greatly influenced the flood-discharge capacity of this reach.In order to have a better grasp on this situation,there is a need to investigate the variation in flood discharge capacity in this area.Therefore,Chenglingji-Hankou reach(CHR)of the MYR was chosen as a typical reach for this study.Based on the cross-section profiles and hydrologic data surveyed annually from 2003 to 2016,the variations in the relationship between discharge and water-level,the corresponding water-level under the maximum discharge annually,and the characteristics of discharges under certain stages were analyzed at Luoshan and Hankou Stations.The results show that:(ⅰ)water-level under the same discharge decreased in dry season and changed slightly in flood season;water-level under the annual maximum discharge increased compared with that from 1954 to 2002;(ⅱ)the relative discharge under warning water-level at Luoshan and Hankou Stations decreased by 9%and 16%,respectively;(ⅲ)There is no obvious trend in the temporal variation of reach-scale bankfull discharge.The influence factors of the variation in the section-scale flood-discharge capacity were analyzed.It was found that the discharges under the warning water level(at Luoshan and Hankou Stations)were negatively correlated with the bed roughness,which implies that the increase in river resistance is probably one of the main causes of the variation in discharge capacity.Besides,the decrease in relative water-depth ratio and the increase in vegetation coverage on central bars may also show obvious influences on the discharge capacity of the study reach.