The Hydraulic Geometry of Evolving Meandering Rivers
The Hydraulic Geometry of Evolving Meandering Rivers
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DOI：
10.1029/2019jf005309
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发表时间：
2019-11
期刊：
影响因子：
--
通讯作者：
F. Monegaglia;M. Tubino
中科院分区：
文献类型：
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作者：
F. Monegaglia;M. Tubino
我们研究了不断发展的曲流弯道的平滩水力几何。分析的驱动力是认识到，迄今为止介绍的模型都没有考虑到泥沙质量的守恒，这导致了不切实际的泥沙输运能力下降，而曲折变得更长。为此，我们提出了一种新的模型来预测河道宽度和坡度在不断变化的河曲中的适应性，该模型由河道宽度的阈值关系和坡度的常微分方程组成，该方程来自Exner方程的积分平均公式。后者占三个主要过程：（i）曲流延伸，（ii）宽度的变化，和（iii）床加积由于减少的运输能力。我们的模型预测减少的渠道宽度和坡度，其幅度是由参数RT代表的时间尺度的河流平面形状和河床的比例。当此比值较大时，平滩水力几何形状基本不变;相反，当RT较小时，随着河道弯曲度的增加，平滩宽度和坡度发生显著变化。通过遥感分析和公布的数据，我们提供了几个曲流河段的参数RT的估计。我们还跟踪的变化，在亚马逊流域的四个动态弯曲的河流通过一个创新的多时弯曲-尺度分析的河岸宽度。观察到的进化轨迹令人满意地再现理论预测。
We study the bankfull hydraulic geometry of evolving meander bends. The analysis is driven by the recognition that none of the models introduced so far accounts for the conservation of the sediment mass, which leads to an unrealistic drop of the sediment transport capacity while the meander becomes longer. With this aim we propose a novel model to predict the adaptation of channel width and slope in evolving meanders, which is composed of a threshold relationship for the channel width and an ordinary differential equation for the slope, arising from an integral, meander‐averaged formulation of the Exner equation. The latter accounts for three main processes: (i) meander elongation, (ii) width change, and (iii) bed aggradation due to reduction of the transport capacity. Our model predicts a reduction of both channel width and slope, whose magnitude is regulated by the parameter RT representing the ratio between the timescale of river planform and that of riverbed. When this ratio is large, the bankfull hydraulic geometry keeps nearly invariable; on the contrary, when RT is small, as channel sinuosity increases, the bankfull width and slope experience a significant change. Through remote sensing analysis and published data we provide estimates of the parameter RT for several meandering river reaches. We also trace the changes of the bankfull width of four dynamic meandering rivers in the Amazon basin by means of an innovative multitemporal bend‐scale analysis. Observed evolutionary trajectories are satisfactorily reproduced by theoretical predictions.