长江中游宜都至松滋河口段近期河床演变分析

Study on recent riverbed evolution characteristics ofYidu-Songzi section of middle reaches of Changjiang River

近几十年来,受上游多座水库和各种涉水建筑物不断兴建的影响,长江中游宜都至松滋河口段河道边界条件和水沙条件相应发生了显著变化,河道将表现出新的演变特性,对下游河道防洪、航运、岸线利用、水环境、生态修复等可能产生一定影响。通过分析枝城水文站近期水沙变化特性和近20 a来河道地形实测资料以及开展一维水沙数学模型计算,探讨了长江中游宜都至松滋河口段近期河道演变特性。研究成果表明:多年来荆江三口分流比一直处于下降趋势,三峡水库蓄水运用前分沙比也呈现下降趋势,但蓄水运用后与蓄水运用前(1999~2002年)相比,分沙比平均值明显增加。受三峡水库蓄水后清水下泄影响,研究河段河床纵向冲刷剧烈,床沙粗化后中值粒径增大趋势明显,洲滩萎缩、深槽扩展,但2013年以来冲刷速率明显趋缓,且河道平面形态、水流主流和河势均保持基本稳定。预计今后一段时间内该河段河床冲刷幅度将有所减小并逐渐趋于平衡,研究河段河势不会发生重大变化。

In recent decades,affected by the continuous construction of multiple reservoirs and wading structures in the upper reaches of the Yangtze River,the boundary conditions and water-sediment conditions in the Yidu to Songzi River mouth reach of Yangtze River have undergone significant changes,and the river channels will show new evolution characteristics,which may have an impact on downstream river flood control,shipping,shoreline utilization,water environment,ecological restoration,etc.By analyzing the recent water and sediment change characteristics of the Zhicheng Hydrological Station and the measured data of the river topography in the past 20 years,and carrying out a one-dimensional water and sediment mathematical model calculation,the recent evolution characteristics of this river section were discussed.The research results showed that the diversion ratio of the three outlets of the Jingjiang River reach had been in a downward trend for many years,and the sediment separation ratio before the storage operation of the Three Gorges Reservoir also showed a downward trend,but the average sediment separation ratio after the storage operation had increased significantly compared with pre-impoundment period.Affected by the discharge of clear water after the impoundment of the Three Gorges Reservoir,the river bed in this section was eroded violently in the longitudinal direction,and the median particle size of the bed sand was coarsened obviously,the beaches shrinking and the deep trough expanding,but the erosion rate has slowed down significantly since 2013.In addition,the plane shape of the river channel,the main flow and the river regime remained basically stable.It is expected that the riverbed erosion rate of this reach will decrease and gradually tend to balance in the next period of time,and there will be no major changes in the river regime of the reach.