Abstract Morphodynamics and hydro-sedimentological processes in meandering rivers are one of the most complex phenomena observed in alluvial channels. Because of the complex nature of the interaction between flow structure, morphology, sediment transport, and bank roughness, a better understanding of these morphological units is needed, particularly for low-gradient rivers characterized by large meandering bends with high width-to-depth ratios. The present research provides an accurate description of the interaction between suspended bed-sediment transport, flow structure, and bed morphology on three consecutive bends characterized by width-to-depth ratios higher than 50. The study focuses on a selected reach of the Colastine River, which is a secondary channel of the Parana River, Argentina. Acoustic measurement techniques with high spatial-time resolution were employed during two different events - a bankfull and a medium-flow stage event - to capture the three-dimensionality of the flow velocity, suspended bed-sediment transport, and variations in bed morphology. Although the core of maximum velocity shifts from bank to bank at the bend entrance, following the thalweg shifting, the suspended bed-sediment concentration remains in the center of the channel because of the strong influence of the secondary currents and the bed morphology. Two types of secondary flows are well-defined in the cross section: a unidirectional flow toward the outer bank generated by the topographic steering effect along the point bar, and the classical helical motion confined to the thalweg zone. Close to the outer bank, the core of maximum velocity shifts toward the center of the channel because of the presence of macro-roughness induced by banklines and downed trees, which in turn generate high turbulence patterns along the outer bank. The bed morphology shows an extended point bar occupying almost half of the channel width (in the cross section apex) and spreading downstream to the entrance of the following bend. The thalweg shows an abrupt change from bank to bank, producing high curvature at each bend entrance. The findings reported herein show a lack of correlation between the cores of maximum velocity and suspended bed sediment, exhibiting different behaviors than those observed in smaller alluvial channels with lower width-to-depth ratios.

中文翻译：

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具有高宽深比的大曲折弯道：来自水文沉积过程的见解

摘要 蜿蜒河流的形态动力学和水文沉积过程是在冲积河道中观察到的最复杂的现象之一。由于水流结构、形态、泥沙输运和河岸粗糙度之间相互作用的复杂性，需要更好地了解这些形态单位，特别是对于以高宽深比大曲折弯道为特征的低梯度河流. 本研究准确描述了三个连续弯曲处的悬浮床-沉积物输运、流动结构和床形态之间的相互作用，这些弯曲的宽度与深度之比高于 50。该研究侧重于 Colastine 河的选定河段，这是阿根廷巴拉那河的次要航道。在两个不同的事件中采用了具有高空间时间分辨率的声学测量技术 - 满岸和中等流量阶段事件 - 以捕获流速、悬浮床-沉积物运输和床形态变化的三个维度。尽管最大速度核心在弯道入口处从岸边移动到岸边，但随着thalweg移动，由于二次流和床形貌的强烈影响，悬浮床沉积物浓度仍然保留在通道中心。在横截面中明确定义了两种类型的二次流：由沿点杆的地形转向效应产生的朝向外岸的单向流，以及局限于 thalweg 区的经典螺旋运动。靠近外岸，由于岸线和倒下的树木引起的宏观粗糙度的存在，最大速度的核心向通道的中心移动，这反过来又会沿着外岸产生高湍流模式。床的形态显示了一个延伸的点杆，几乎占据了通道宽度的一半（在横截面顶点），并向下游扩展到下一个弯道的入口。thalweg 显示从一个岸到另一个岸的突然变化，在每个弯道入口处产生高曲率。本文报告的发现表明，最大速度的核心与悬浮床沉积物之间缺乏相关性，表现出与在具有较低宽深比的较小冲积通道中观察到的行为不同的行为。这反过来又会沿着外岸产生高湍流模式。床的形态显示了一个延伸的点杆，几乎占据了通道宽度的一半（在横截面顶点），并向下游扩展到下一个弯道的入口。thalweg 显示从一个岸到另一个岸的突然变化，在每个弯道入口处产生高曲率。本文报告的发现表明，最大速度的核心与悬浮床沉积物之间缺乏相关性，表现出与在具有较低宽深比的较小冲积通道中观察到的行为不同的行为。这反过来又会沿着外岸产生高湍流模式。床的形态显示了一个延伸的点杆，几乎占据了通道宽度的一半（在横截面顶点），并向下游扩展到下一个弯道的入口。thalweg 显示从一个岸到另一个岸的突然变化，在每个弯道入口处产生高曲率。本文报告的发现表明，最大速度的核心与悬浮床沉积物之间缺乏相关性，表现出与在具有较低宽深比的较小冲积通道中观察到的行为不同的行为。thalweg 显示从一个岸到另一个岸的突然变化，在每个弯道入口处产生高曲率。本文报告的发现表明，最大速度的核心与悬浮床沉积物之间缺乏相关性，表现出与在具有较低宽深比的较小冲积通道中观察到的行为不同的行为。thalweg 显示从一个岸到另一个岸的突然变化，在每个弯道入口处产生高曲率。本文报告的发现表明，最大速度的核心与悬浮床沉积物之间缺乏相关性，表现出与在具有较低宽深比的较小冲积通道中观察到的行为不同的行为。