长江中游曲流河段河道的近代演化过程研究

曲流河是冲积平原河流中的重要河型之一,曲流河的河道演变对冲积平原的建设与演化起着非常重要的作用。地处江汉平原的长江中游藕池口至城陵矶段河道是最典型的曲流河段,其曲流河道的几何形态和变化过程较为复杂,对该段河道演化过程的研究在河流的开发利用及水利工程建设中具有很好的理论指导意义。本研究通过对历史资料和多期卫星遥感影像的解译与分析,表明长江中游藕池口至城陵矶河段的曲流河道演化在受自然和人类活动双重影响的情况下,该河段河道的演化仍然维持曲流河特征。受大洪水的切滩作用及松滋口、太平口和藕池口3个分流口对洞庭湖的分水分沙的影响,该段河道的演化过程较为复杂。自然裁弯取直和人工裁弯取直在一定程度上改变着河道演化的进程,但由裁弯取直及上游水利工程引起的纵坡降增加产生的冲淤变化将会维持河道的稳定,同时在该河段实施的护岸工程也会抑制河流的横向侵蚀,曲流河段河道演化进入自调整和自组织过程。

TEMPORAL AND SPATIAL EVOLUTION OF MEANDERING RIVER IN THE MIDDLE REACHES OF THE CHANGJIANG RIVER

River meanders present some degree of form regularity.They play a major role in floodplain construction and evolution and are major components of the fluvial landscape.They are varying from highly dynamic to stable under present conditions.Typical meanders of a fluvial river channel are characterized by eroding their outer banks and depositing sediments on their inner bands,producing new sinuous curves.The lower Jingjiang section between Ouchikou and Chenglingji in the middle reaches of the Changjiang River is a typical meandering river.In this paper we document the temporal and spatial changes of this river based on analyses of historical data and satellite imageries.Results show that the evolution of meandering channel is influenced by the natural processes and human activities.The natural processes include deposition of fine-grained silt and clay carried by river and development of sinuous curves.Lower velocity may promote sediment deposition during dry season.However,higher velocity simultaneously will erode the concave bank and deepen the curve into hairpin-shaped meanders during the flooding season fromMay to October.Sometimes the river may cutoff meander,and continued erosion and deposition may cause migration of meanders.The three outlets of Songzikou,Taipingkou,and Ouchikou may divide water and sediment to the Dongting Lake,and the evolution of the sinuous curve may become more complicated.Natural cutoff and human cutoff of the river may change the processes of the river evolution,but the higher vertical drop in level may maintain new balance between erosion and deposition,bank-protection work constructed may restrict the transverse erosion of the Changjiang River,and meandering rivers may become self-adjusted.