Channel Migration in Experimental River Networks Mapped by Particle Image Velocimetry
Channel Migration in Experimental River Networks Mapped by Particle Image Velocimetry
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DOI：
10.1029/2021jf006300
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发表时间：
2021-11
期刊：
影响因子：
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通讯作者：
A. Chadwick;E. Steel;R. Williams‐Schaetzel;P. Passalacqua;C. Paola
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作者：
A. Chadwick;E. Steel;R. Williams‐Schaetzel;P. Passalacqua;C. Paola
随着相互连接的河道移动，三角洲河网自然地重组，在整个三角洲平原上重新分配水、沉积物和养分。数十年的卫星图像和实验室实验记录了网络变化，但我们测量和理解河道运动的能力是有限的：现有方法难以有效利用，并且很难区分逐渐运动（河道迁移）和河道突然变化（河道撕脱）。在这里，我们提出了一种使用粒子图像测速（PIV）从平面图像中提取通道偏移的方法。虽然 PIV 最初设计用于跟踪流体中移动的颗粒，但基于通道宽度、迁移时间尺度和干湿界面图的输入估计，PIV 可以适用于跟踪三角洲表面上移动的通道。 Delta 实验的结果表明，与手动绘制的地图和独立的图像配准技术相比，PIV 导出的矢量场可以准确捕获河岸运动。与其他方法不同，PIV 针对的是河道迁移过程，排除与河道撕裂和溢流相关的变化。实验得出的 PIV 迁移率跨越了一个数量级，并且在沉积物供应减少和海平面上升期间降低，支持了最新的模型。总之，结果表明，PIV 提供了一种快速可靠的方法来测量河网中的河道迁移，非粘性条件下的河道迁移速率可以在增加约 10% 河道深度所需的时间内使河道移动与其宽度相当的距离，并且迁移方向约 60% 与平均水流方向正交，约 40% 与水流平行。
Deltaic river networks naturally reorganize as interconnected channels move to redistribute water, sediment, and nutrients across the delta plain. Network change is documented in decades of satellite imagery and laboratory experiments, but our ability to measure and understand channel movements is limited: existing methods are difficult to employ efficiently and struggle to distinguish between gradual movements (channel migration) and abrupt shifts in river course (channel avulsions). Here, we present a method to extract channel migration from plan‐view imagery using particle image velocimetry (PIV). Although originally designed to track particles moving in a fluid, PIV can be adapted to track channels moving on the delta surface, based on input estimates of channel width, migration timescale, and maps of the wet‐dry interface. Results for a delta experiment show that PIV‐derived vector fields accurately capture channel‐bank movements, as compared to manually drawn maps and an independent image‐registration technique. Unlike other methods, PIV targets the process of channel migration, excluding changes associated with channel avulsions and overbank flow. PIV‐derived migration rates from the experiment span an order of magnitude and are reduced under lower sediment supply and during sea‐level rise, supporting recent models. Together, results indicate that PIV offers a fast and reliable way to measure channel migration in river networks, that channel migration rates under non‐cohesive conditions can displace channels a distance comparable to their width in the time needed to aggrade ∼10% of the channel depth, and that migration direction is ∼60% orthogonal to mean flow direction and ∼40% flow‐parallel overall.