Mean sediment residence time in barchan dunes
Mean sediment residence time in barchan dunes
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DOI：
10.1002/2013jf002833
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发表时间：
2014-03
期刊：
影响因子：
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通讯作者：
Dongqi Zhang;Xiaoping Yang;O. Rozier;C. Narteau
中科院分区：
文献类型：
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作者：
Dongqi Zhang;Xiaoping Yang;O. Rozier;C. Narteau
当大沙丘迁移时，滞留在背风面的沉积物后来在暴露在沙丘面时被动员起来。然后，沙粒在沿着角部抛射之前可能会经历多次沙丘周转周期，但沙粒对沙丘地貌动力学的贡献时间尚不清楚。为了估计这样的停留时间，我们通过跟踪三维细胞自动机沙丘模型的单个细胞来分析稳定状态下沙丘中的泥沙颗粒运动。总的泥沙通量可以分解为平流通量和弥散通量，以估计底层物理过程对沙丘形状的相对贡献。从中心到角部的净横向泥沙输运表明，与背风坡上的雪崩相关的汇聚泥沙通量相比，在背风坡上扩散的泥沙通量更有效。这两个相互拮抗的弥散过程的综合作用，制约了中央地区沉积物颗粒的横向混合。然后，对于不同的水流强度和沙丘大小，我们发现泥沙颗粒在沙丘中的平均停留时间等于中央纵向沙丘切片的表面除以输入沙量。我们推断，这一中心切片包含了大多数关于丛林地貌动力学的相关信息。最后，我们利用颗粒示踪技术的优点，开始讨论在存在河床形态的情况下泥沙的输运和记忆问题。
When a barchan dune migrates, the sediment trapped on its lee side is later mobilized when exposed on the stoss side. Then sand grains may undergo many dune turnover cycles before their ejection along the horns, but the amount of time a sand grain contributes to the dune morphodynamics remains unknown. To estimate such a residence time, we analyze sediment particle motions in steady state barchans by tracking individual cells of a 3‐D cellular automaton dune model. The overall sediment flux may be decomposed into advective and dispersive fluxes to estimate the relative contribution of the underlying physical processes to the barchan shape. The net lateral sediment transport from the center to the horns indicates that dispersion on the stoss slope is more efficient than the convergent sediment fluxes associated with avalanches on the lee slope. The combined effect of these two antagonistic dispersive processes restricts the lateral mixing of sediment particles in the central region of barchans. Then, for different flow strengths and dune sizes, we find that the mean residence time of sediment particles in barchans is equal to the surface of the central longitudinal dune slices divided by the input sand flux. We infer that this central slice contains most of the relevant information about barchan morphodynamics. Finally, we initiate a discussion about sediment transport and memory in the presence of bed forms using the advantages of the particle tracking technique.