The life of a meander bend: Connecting shape and dynamics via analysis of a numerical model
The life of a meander bend: Connecting shape and dynamics via analysis of a numerical model
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DOI：
10.1002/2014jf003252
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发表时间：
2015-04
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影响因子：
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通讯作者：
Jon Schwenk;S. Lanzoni;E. Foufoula‐Georgiou
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作者：
Jon Schwenk;S. Lanzoni;E. Foufoula‐Georgiou
弯曲尺度曲流河动力学分析是一个具有重要理论意义和实用价值的问题。这项工作介绍了一种方法，用于提取和分析的历史，从成立到截止（称为“原子”）通过跟踪向后通过时间的一组两个截止节点的数值曲流迁移模型的个人曲流弯曲。将这种方法应用于简化的物理模型，可以在长时间内以高时间分辨率访问以前不可用的弯曲尺度曲流动力学。我们发现，截止前，内禀模型动力学总是模拟一个原型截止原子形状，我们称之为简单的。一旦发生来自截断的扰动，另外两个原型截断平面形状出现，称为长形和圆形，其分别通过沿着其长轴和垂直轴的拉伸来区分。三个措施的曲折迁移增长率，平均迁移率，质心迁移率，引入捕捉个别弯曲的动态寿命，并揭示类似的截止原子几何形状共享类似的动态历史。具体而言，通过三种形状类型的透镜，可以看到简单的具有最高的生长和平均迁移率，其次是圆形，最后是长形。使用最大平均迁移率作为度量描述原子的动态过去，我们显示了它和两个度量的截止几何之间的强连接。这一结果表明，早期形成的动力学可以推断从静态截止planforms和存在一个关键时期的早期曲流弯曲的生活时，其动态轨迹是最敏感的截止扰动。这些结果可以应用到密西西比河牛轭湖与未知的历史动态的一个例子。结果表征的基础模型，并提供了一个框架，比较更复杂的模型和观察到的动态。
Analysis of bend‐scale meandering river dynamics is a problem of theoretical and practical interest. This work introduces a method for extracting and analyzing the history of individual meander bends from inception until cutoff (called “atoms”) by tracking backward through time the set of two cutoff nodes in numerical meander migration models. Application of this method to a simplified yet physically based model provides access to previously unavailable bend‐scale meander dynamics over long times and at high temporal resolutions. We find that before cutoffs, the intrinsic model dynamics invariably simulate a prototypical cutoff atom shape we dub simple. Once perturbations from cutoffs occur, two other archetypal cutoff planform shapes emerge called long and round that are distinguished by a stretching along their long and perpendicular axes, respectively. Three measures of meander migration—growth rate, average migration rate, and centroid migration rate—are introduced to capture the dynamic lives of individual bends and reveal that similar cutoff atom geometries share similar dynamic histories. Specifically, through the lens of the three shape types, simples are seen to have the highest growth and average migration rates, followed by rounds, and finally longs. Using the maximum average migration rate as a metric describing an atom's dynamic past, we show a strong connection between it and two metrics of cutoff geometry. This result suggests both that early formative dynamics may be inferred from static cutoff planforms and that there exists a critical period early in a meander bend's life when its dynamic trajectory is most sensitive to cutoff perturbations. An example of how these results could be applied to Mississippi River oxbow lakes with unknown historic dynamics is shown. The results characterize the underlying model and provide a framework for comparisons against more complex models and observed dynamics.