Mechanisms of Dune Growth and Decay in Rivers
Mechanisms of Dune Growth and Decay in Rivers
复制标题
河流沙丘生长和腐烂的机制
DOI：
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复制
发表时间：
2021
影响因子：
5.2
通讯作者：
J. Venditti
中科院分区：
文献类型：
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作者：
R. Bradley;J. Venditti
沙丘生长和腐烂的机制在河流动力学中仍然是一个主要未知数。两种理论已得到实验和数值模型的支持。流体动力学解释表明，生长和衰退的发生是由于床层地形和沉积物通量之间的相位滞后造成的。另外，运动学过程也被用来解释通过合并而产生的生长以及通过叠加的床型蚕食较大沙丘而导致的衰变。由于缺乏高分辨率地形，天然河流中的任何一种机制都缺乏论证。在这里，我们首次观察到沙丘在上升过程中通过运动过程快速生长，随后可能通过高流量的流体动力学过程进行逐渐调整。随着流量减弱，较小的沙丘会发展并蚕食较大的特征，最终在基流附近形成平坦的沙床。运动过程发生在共同的阈值剪切应力下。在水文下降过程中形成的叠加沙丘是沙丘腐烂的标志。
The mechanisms responsible for dune growth and decay remain a major unknown in river dynamics. Two theories have been supported by experiments and numerical models. A hydrodynamic explanation suggests that growth and decay occur due to phase lags between bed topography and sediment flux. Alternatively, kinematic processes have been invoked to explain growth by merger and decay by superimposed bedforms cannibalizing larger dunes. Demonstration of either mechanism in natural rivers has been lacking due to a paucity of high‐resolution topography. Here, we provide the first observations of rapid dune growth by kinematic processes during a rising hydrograph limb, followed by gradual adjustments likely through hydrodynamic processes at high flow. As flow wanes, smaller dunes develop and cannibalize larger features, eventually creating a flattened bed near base flow. Kinematic processes occur at a common threshold shear stress. Superimposed dunes formed during falling limbs of hydrographs are signatures of dune decay.