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Lower‐Stage Plane Bed Topography Is an Outcome of Rarefied, Intermittent Sediment Transport
Journal of Geophysical Research: Earth Surface ( IF 3.9 ) Pub Date : 2021-04-23 , DOI: 10.1029/2020jf005754
Thomas C. Ashley 1 , Suleyman Naqshband 2 , Brandon McElroy 1
Affiliation  

Sedimentary bed configurations that are stable under weak fluid‐driven transport conditions can be divided into two groups: (1) mesoscale features that influence flow and sediment transport through roughness and drag partitioning effects (“mesoforms”) and (2) grain‐scale features that can effectively be ignored at the macroscopic scale (“microforms”). In practice, these groups delineate ripples and dunes from quasi‐planar bed configurations. They are thought to be separated by a transition in processes governing the relief of the bed; however, the physical mechanisms responsible for this transition are poorly understood. Previous studies suggest that planar topography is unstable when interactions between moving particles lead to stabilized bed disturbances that initiate morphodynamic pattern coarsening. This study presents a kinetic interpretation of this hypothesis in terms of parameters describing particle motion. We find that the microform/mesoform transition corresponds to a critical transition in particle behavior associated with increasing importance of particle collisions. This transition also corresponds to the point where continuum‐based morphodynamic models are permissible at the most unstable wavelength predicted from linear stability theory, providing a link between descriptive and mathematical theories of bedform initiation.

中文翻译:

低阶平面床地形是稀疏的,间歇性泥沙输送的结果

在弱流体驱动的运输条件下稳定的沉积床构造可分为两类:(1)中尺度特征,其通过粗糙度和阻力分配效应(“中型”)影响流量和沉积物的运输(“中型”)和(2)粒度特征在宏观尺度上(“缩微形式”)可以被有效忽略。实际上,这些组从准平面床构造中描绘出波纹和沙丘。人们认为它们是由控制床浮雕的过程中的过渡分开的。然而,人们对造成这种转变的物理机制知之甚少。先前的研究表明,当运动的粒子之间的相互作用导致稳定的床层扰动引发形态动力学模式变粗化时,平面形貌是不稳定的。这项研究从描述粒子运动的参数方面提出了这一假设的动力学解释。我们发现,微观形态/中间形态的转变对应于粒子行为的关键转变,与粒子碰撞重要性的增加相关。这种转变也对应于在线性稳定性理论预测的最不稳定波长处基于连续谱的形态动力学模型所允许的点,从而提供了床形描述的描述性理论与数学理论之间的联系。
更新日期:2021-05-18
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