How Consistent Are Estimates of Roughness Parameters on a Rough Coral Reef?
How Consistent Are Estimates of Roughness Parameters on a Rough Coral Reef?
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DOI：
10.1029/2021jc017825
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发表时间：
2021-12-01
影响因子：
3.6
通讯作者：
Dunbar, R.
中科院分区：
文献类型：
--
作者：
Lindhart, M.;Monismith, S. G.;Dunbar, R.
珊瑚礁在水动力学上是粗糙的，产生了湍流边界层，输送和混合了影响珊瑚礁过程的各种标量，也可以用来监测珊瑚礁的健康状况。通常假定从单一仪器得出的礁石边界层特征能够准确地代表研究地点。这种方法依赖于两个假设：第一，边界层在感兴趣的区域内相对均匀；第二，在空间上移位或具有不同时空分辨率的两台仪器在对同一流动进行采样时会产生类似的结果。我们在查戈斯群岛10米深的15x20米的暗礁上部署了四个测速仪。该场地的潮差为1米，波浪主要是局部产生的风浪，H-RMS和lt；0.5m。深度平均流通常为0.2m/S。通过拟合壁面定律直接由雷诺应力测量得到的摩擦速度显示仪器之间的一致性(成对决定系数R-2在0.53到0.86之间)。因此，边界层似乎在空间上是均匀的，至少在我们阵列的尺度上是如此，而且在目前的情况下，来自一台仪器的摩擦速度确实大体上代表了该地点。我们使用曲线拟合法和运动结构摄影测量法来计算阻力系数，虽然我们发现估计值之间基本一致，但有一台仪器产生的阻力系数要大一个数量级。因此，观察到了仪器之间的一些变异性，特别是当高分辨率仪器测量局部流动特征时。
Coral reefs are hydrodynamically rough, creating turbulent boundary layers that transport and mix various scalars that impact reef processes and also can be used to monitor reef health. Often reef boundary layer characteristics derived from a single instrument are assumed to accurately represent the study site. This approach relies on two assumptions: first, that the boundary layer is relatively homogeneous across the area of interest, and second, that two instruments displaced in space or with different spatiotemporal resolution would produce similar results when sampling the same flow. We deployed four velocimeters over a 15 x 20 m reef at 10 m depth in the Chagos Archipelago. The site had a 1 m tidal range, and waves were primarily locally generated wind waves with H-rms < 0.5 m. Depth-averaged currents were typically 0.2 m/s. Friction velocities derived directly from Reynolds stress measurements by fitting the law of the wall show agreement between instruments (pairwise coefficients of determination R-2 ranged from 0.53 to 0.86). Thus, the boundary layer appears to be spatially homogeneous, at least at the scale of our array, and it appears that in the present case friction velocities from one instrument are indeed generally representative of the site. We calculate drag coefficients using curve-fitting and Structure-from-Motion photogrammetry, and while we find general agreement between estimates one instrument in particular produces drag coefficients an order of magnitude larger in comparison. Hence, some variability between instruments was observed, notably when high-resolution instruments measured localized flow features.