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首页> 外文期刊>Earth Surface Processes and Landforms: The journal of the British Geomorphological Research Group >Physical explanations of variations in river meander migration rates from model comparison
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Physical explanations of variations in river meander migration rates from model comparison

机译：模型比较对河曲迁移率变化的物理解释

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摘要

In meandering rivers, the local channel migration rate increases with increasing bend sharpness until it reaches a maximum at a certain critical value of the bend sharpness. Beyond this critical value, the migration rate decreases if bend sharpness increases. Similarly, reach-averaged migration rates attain a maximum at a certain river sinuosity. This work investigates the physics of these phenomena by comparing the results of two physics-based models of different complexity, in which the migration rates are proportional to the near-bank flow velocity excess. In the computational tests the river was allowed to meander progressively, starting from an almost straight planimetry. Both models reproduced the observed peak in the curve describing the local migration rate as a function of the ratio radius of curvature-channel width (R/B), with a rising limb at lower R/B values and a falling limb at higher R/B values. The rising limb can be explained by the decrease in relative lag distance between near-bank flow velocity and forcing curvature as R/B increases. The falling limb results from the decrease in local channel curvature and near-bank flow velocity excess. Since the models do not include flow separation, the results indicate that this phenomenon is not needed to explain the decrease of channel migration rates in sharp bends. The models reproduced also the peak in the curve describing the reach-averaged migration rates as a function of river sinuosity The increase and then decrease of reach-averaged migration rates as sinuosity increases appears to be mainly caused by the variation of the reach-averaged value of the ratio R/B.
机译：在蜿蜒的河流中，局部河道迁移率随弯曲锐度的增加而增加，直到在一定的弯曲锐度临界值达到最大值。超过此临界值，如果弯曲清晰度增加，则迁移率降低。同样，在一定的河流弯曲度下，河岸平均迁移率达到最大值。这项工作通过比较两种不同复杂度的基于物理学的模型的结果来研究这些现象的物理现象，其中迁移率与近岸流速过量成正比。在计算测试中，从几乎笔直的平面图开始，允许河流逐渐蜿蜒。两种模型均重现了曲线中观察到的峰值，该峰值描述了局部迁移率与曲率通道宽度（R / B）之比的函数，R / B值较低时上升肢，R / B值较高时下降肢B值。上升的肢体可以解释为随着R / B的增加，近岸流速与强迫曲率之间的相对滞后距离的减小。下降的肢体是由于局部通道曲率的减小和近岸流速度过剩引起的。由于模型不包括流分离，结果表明该现象不需要解释急剧弯曲中通道迁移率的降低。这些模型也再现了曲线，该曲线描述的是到达率平均迁移率随河流曲率变化的曲线。随着平均曲率的增加，到达率平均迁移率的上升和下降似乎主要是由于到达率平均值的变化引起的。 R / B之比。

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