Controls of alluvial cover formation, morphology and bedload transport in a sinuous channel with a non‐alluvial boundary,Earth Surface Processes and Landforms

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Controls of alluvial cover formation, morphology and bedload transport in a sinuous channel with a non‐alluvial boundary
Earth Surface Processes and Landforms ( IF 2.8 ) Pub Date : 2020-11-03 , DOI: 10.1002/esp.5032
E. Papangelakis ₁ , M. Welber _{1,

2} , P. Ashmore ₁ , B. MacVicar ₃

Affiliation

The alluvial cover in channels with non‐alluvial beds is a major morphologic feature in these rivers and has important geomorphic and ecologic functions. Although controls on the extent of the alluvial cover have been previously researched, little is known about the role of channel meanders in shaping the three‐dimensional morphology and bedload transport rates in these rivers. Flume experiments were conducted in a fixed‐bed sinuous channel scaled from an engineered urban river. A fully graded sediment supply mixture was fed into the bare channel at rates ranging between 0.3 and 1.2 times the estimated channel capacity under constant discharge. The three‐dimensional morphology and surface texture of the alluvial cover were captured using photogrammetry, and the sediment output was periodically measured and sieved. A stable alluvial cover was achieved under all sediment supply conditions that coincided with a sediment transport equilibrium. The sediment supply rate controlled the final areal extent, mass and volume of the alluvial cover, while cover developed as a periodic series of stable bars ‘fixed’ by the channel planform. The alluvial cover development followed consistent trajectories relative to angular position around bends but developed to a greater degree and higher elevation with increasing sediment supply. The stable cover extent had a logarithmic relationship with the relative sediment supply, while the final mass, volume and bar height had linear relationships. The final channel morphology was characterized by fine‐textured point bars with flat tops and steep margins connected by coarse riffle features. The outside of banks between bend apexes remained bare, even at sediment supply conditions exceeding the channel capacity. The length of the exposed outer banks followed predictable linear relationships with the total cover extent. Insights from this study can provide guidance for the management of channels with non‐alluvial boundaries and provide validation for models of sinuous bedrock channel abrasion. © 2020 John Wiley & Sons, Ltd.

中文翻译：

在非冲积边界的弯曲通道中控制冲积层的形成，形态和床荷输送

具有非冲积层的河道中的冲积层是这些河流的主要形态特征，并具有重要的地貌和生态功能。尽管先前已经研究了冲积层覆盖程度的控制方法，但对于这些河流中河道在塑造三维形态和河床输水速率中的作用知之甚少。水槽实验是在一条固定河床中进行的，该河床是从一条经设计的城市河流定标的。在恒定流量下，将完全分级的沉积物供应混合物以估计通道容量的0.3到1.2倍的速率注入裸通道。用摄影测量法捕获冲积层的三维形态和表面纹理，并定期测量和筛分沉积物。在与沉积物输运平衡相吻合的所有沉积物供应条件下均实现了稳定的冲积层。沉积物的供给速度控制着冲积层的最终面积，质量和体积，而覆层则是由河道平面“固定”的一系列周期性的稳定条形成的。相对于弯道周围的角位置，冲积层的发育遵循一致的轨迹，但是随着沉积物供应的增加，冲积层的发展程度更高，海拔更高。稳定的覆盖范围与相对沉积物供应量呈对数关系，而最终质量，体积和钢筋高度具有线性关系。最终通道的形态特征是具有细密纹理的点形杆，其顶部平坦，边缘陡峭，由粗浅的浅滩状特征相连。即使在沉积物供应条件超过河道通行能力的情况下，弯曲顶点之间的堤岸外部仍然裸露。暴露的外堤的长度与总覆盖范围遵循可预测的线性关系。这项研究的见解可以为非冲积界河道的管理提供指导，并为弯曲的基岩河道磨蚀模型提供验证。分级为4 +©2020 John Wiley＆Sons，Ltd.

更新日期：2020-11-03

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