下荆江急弯段凸冲凹淤演变过程与机理  

Analysis of evolution processes and mechanisms of sharp bends in the Lower Jingjiang Reach

作　　者：刘鑫 夏军强[1] 邓珊珊[1] 周美蓉[1] 毛禹 许全喜 Xin Liu;Junqiang Xia;Shanshan Deng;Meirong Zhou;Yu Mao;Quanxi Xu(State Key Laboratory of Water Resources and Hydropower Engineering Science,Wuhan University,Wuhan 430072,China;Bureau of Hydrology,Changjiang Water Resources Commission,Wuhan 430010,China)

机构地区：[1]武汉大学水资源与水电工程科学国家重点实验室,武汉430072 [2]长江水利委员会水文局,武汉430010

出　　处：《科学通报》2022年第22期2672-2683,共12页Chinese Science Bulletin

基　　金：国家自然科学基金(51725902,U2040215,52009095);湖北省自然科学基金创新群体项目(2021CFA029)资助。

摘　　要：三峡工程运用后,下荆江急弯河段出现凸冲凹淤的弯道演变现象,威胁防洪与航运安全.下荆江8个弯道为急弯(相对曲率B/R>0.5),6个急弯段的弯顶上游区域发生了明显的凸冲凹淤过程,且主要表现为凸岸边滩冲刷下切、河岸持续崩退,凹岸深槽回淤并形成长条形心滩,导致断面形态由不对称的三角形变为W形.本文采用水沙及实测流场资料,从水流流速重分布、来沙组成变化及河岸土体组成等3个方面研究了急弯段凸冲凹淤的演变机理.结果表明:(1)急弯段水流流速重分布规律有利于弯顶上游凸冲凹淤现象的形成,在弯顶上游段流速分布主要受曲率变化控制(贡献率占67%),导致主流长期偏靠并冲刷凸岸,凹岸流速较小且易形成水流分离区,利于泥沙落淤;(2)由于上游来沙量减少约82%,细沙比例减小,粗沙比例增加,导致弯顶上游凸岸边滩冲刷后,无法及时回淤,故凸岸边滩总体呈冲刷下切趋势,但粗沙可在流速较小的凹岸侧落淤形成心滩;(3)在凸冲凹淤过程长期作用下,河床横比降减小,曲率变化对流速横向分布的贡献率增大,主流继续向凸岸摆动,进一步促进了凸冲凹淤过程的发展.因此,在水沙条件相对稳定的情况下,下荆江急弯河段凸冲凹淤过程会继续发展,在没有限制的情况下,急弯段逐渐下移.After the operation of the Three Gorges Project(TGP),the patterns of erosion and deposition invert in most of the sharp bends of the Lower Jingjiang Reach(LJR),which threatens the safety of flood control works and navigation channels.The sinuosity coefficients of 10 river bends in the LJR were around 1.1–3.0,and 8 river bends belonged to sharp bends with the relative curvature(B/R)greater than 0.5,and 3/4 of the sharp bends displayed abnormal deformation processes,which was characterized by the erosion of point bars attached to the convex banks and the deposition of longitudinal benches close to the concave banks upstream of the apexes,and the cross-sectional profiles changed from the asymmetrical triangle shape to the“W”shape.In addition,measurements of flow and sediment were used to clarify the reasons which accounted for the change of deformation patterns caused by flow velocity redistribution,compositions of incoming sediment and river bank soils.The results indicate that:(1)The redistribution of flow velocity was beneficial to the inversion of deformation processes.Flow redistribution upstream of the apex was mainly controlled by the term(Ⅱ)related to the abruptness of curvature change,with the average contribution rate of 67%,which resulted in such a phenomenon that the highest velocities occurred along the convex banks and the point bars suffered from continuous erosion.Furthermore,the flow separation zone with small velocities formed along the concave bank,in which the coarse sediment particles easily deposited;(2)as the total amount of incoming sediment decreased by about 82%,the proportion of fine sediment fraction decreased and the proportion of coarse sediment fraction increased,the recovery of the point bars attached to the convex banks upstream of the apexes was restricted after these bars were scoured.However,the coarse sediment particles deposited in the flow separation zones adjacent to the concave banks and the longitudinal benches formed consequently;(3)driven by the deformation pattern

关 键 词：急弯河段 凸冲凹淤 流速重分布 来沙条件 下荆江 

分 类 号：TV147[水利工程—水力学及河流动力学]