Backwater controls on the evolution and avulsion of the Qingshuigou channel on the Yellow River Delta
Backwater controls on the evolution and avulsion of the Qingshuigou channel on the Yellow River Delta
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回水对黄河三角洲清水沟航道演变与撕脱的控制
DOI：
10.1016/j.geomorph.2019.02.032
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发表时间：
2019-05
期刊：
影响因子：
3.9
通讯作者：
Han Shasha
中科院分区：
文献类型：
--
作者：
Zheng Shan;Edmonds Douglas A.;Wu Baosheng;Han Shasha
当河流接近基准面时，它们的水和沉积物动态受到称为回水区的过渡河段的影响。在低流量时，回水区会导致水流减速和河道内沉积，但在高流量时，回水区会导致水流加速和侵蚀。在许多洪水中，回水区的沉积和侵蚀动力学被认为控制了一些大型三角洲河道上的撕脱位置。然而，在各种研究中，回水的作用往往是推断或建模，并直接观察到的证据回水如何影响信道动态在撕脱网站仍然很少。在这项研究中，我们展示了回水区如何影响清水沟河道的演变和撕脱，这是黄河三角洲最近的一个瓣，使用了四十年（1976-2015）的数据，这些数据来自系统的流量，泥沙负荷，横截面剖面和水面高程的调查。结果表明，该河道在汛期普遍发生侵蚀，在非汛期普遍发生淤积。在汛期，沿下游河道沿着的侵蚀速率一般呈下降趋势，这主要是由于下游河道拓宽以及随后输沙能力的降低。在最下游的横截面处，侵蚀率达到零，这与在水动力回水效应下的预期相反，在水动力回水效应下，水位下降导致高流量期间下游侵蚀增加。在非汛期，最大的沉积发生在回水区上游，可能是由于当地地形的曲折弯曲或从堤防收缩的影响。1985年至1996年，形态动力学回水伴随着河口坝的沉积和逐渐变浅，导致下游沿着下游河道河段的沉积、超高和侧向迁移率增加。预测的撕脱位置在Q6或Q7横截面附近，撕脱长度在海岸线上游约20-30 km，这与历史上的撕脱位置一致。我们强调回水效应和通道几何形状之间的密切相互作用，并认为，形态动力回水可能发挥更重要的作用比水动力回水在建立和触发黄河三角洲的撕脱。
As rivers approach base level, their water and sediment dynamics are affected by a transitional reach known as the backwater zone. At low flows, backwater zones cause flow deceleration and in-channel sedimentation, but at high flows, they cause flow acceleration and erosion. Over many floods, the dynamics of deposition and erosion in the backwater zone are thought to control the locations of avulsions on some large deltaic channels. However, in various studies, the role of the backwater is often inferred or modeled, and directly observed evidence of how backwater affects channel dynamics at avulsion sites remains scarce. In this study, we show how the backwater zone impacts the evolution and avulsion of the Qingshuigou channel, a recent lobe on the Yellow River Delta, using four decades (1976–2015) of data from systematic surveys of water discharge, sediment load, cross-sectional profiles and water surface elevation. The results show that the channel was commonly eroded during flood seasons and aggraded during nonflood seasons. Erosion rates generally decreased in the downstream direction along the lower channel reach during flood seasons, primarily due to downstream channel widening and the subsequent decrease in sediment transport capacity. The erosion rate reached zero at the cross-sections farthest downstream, which is contrary to expectations under hydrodynamic backwater effects, where drawdown causes erosion to increase downstream during high flows. During nonflood seasons, maximum sedimentation occurred upstream of the backwater zone, possibly due to impacts of local topography of meandering bends or constriction from dikes. Morphodynamic backwater accompanied by the deposition and gradual progradation of a mouth bar resulted in downstream increasing sedimentation, superelevation, and lateral migration rates along the lower channel reach from 1985 to 1996. The predicted avulsion location was near cross-sections Q6 or Q7 with an avulsion length of ~20–30 km upstream of the shoreline, which was consistent with those for historical avulsions. We emphasize the close interplay between backwater effects and channel geometry and argue that morphodynamic backwater may play a more important role than hydrodynamic backwater in setting up and triggering avulsions on the Yellow River Delta.
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