Over the course of a year, we conducted three field deployments in South San Francisco Bay to examine seasonal variability in bottom drag. Our data consisted of turbulence measurements both within and outside the bottom boundary layer and benthic characterization surveys adjacent to our study site. Our results suggest that canopies of benthic worm and amphipod feeding tubes, which were denser during summer, can increase the drag coefficient by up to a factor of three relative to the smoother beds found in winter and spring. The extent of the drag increase varied depending on the measurement device, with the greatest increase inferred by measurements taken further from the bed. The small scale and temporally varying population densities of these living roughness elements pose significant challenges for hydrodynamic models, and future work is needed to begin incorporating benthic biology statistics into drag coefficient parameterizations. Plain Language Summary Tidal flows in estuaries are affected by the properties of the seafloor. By taking flow measurements in South San Francisco Bay during three different seasons, we show here that feeding tubes built by organisms that live in the sediment bed during summer make the bed much rougher and slow down average flow velocities. The extent of the estimated difference in roughness depends on the instrument used for the measurement, but the overall results imply that these bottom‐dwelling populations should be taken into account when modeling flows in estuaries.

中文翻译：

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底部阻力随生物粗糙度的季节性变化

在一年的时间里，我们在南旧金山湾进行了三个现场部署，以检查底部阻力的季节性变化。我们的数据包括底部边界层内外的湍流测量以及与我们研究地点相邻的底栖特征调查。我们的结果表明，相对于冬季和春季发现的更光滑的床，底栖蠕虫和片脚类动物摄食管的檐篷在夏季更密集，可以将阻力系数增加多达三倍。阻力增加的程度取决于测量设备，通过离床更远的测量推断出最大的增加。这些生活粗糙元素的小规模和随时间变化的人口密度对流体动力学模型提出了重大挑战，未来的工作需要开始将底栖生物统计数据纳入阻力系数参数化。简单语言总结 河口的潮汐流受海底特性的影响。通过在三个不同季节对南旧金山湾的流量进行测量，我们在这里表明，夏季生活在沉积床中的生物体建造的进料管使床变得更加粗糙并减慢了平均流速。粗糙度估计差异的程度取决于用于测量的仪器，但总体结果意味着在模拟河口流动时应考虑这些底栖种群。简单语言总结 河口的潮汐流受海底特性的影响。通过在三个不同季节对南旧金山湾的流量进行测量，我们在这里表明，夏季生活在沉积床中的生物体建造的进料管使床变得更加粗糙并减慢了平均流速。粗糙度估计差异的程度取决于用于测量的仪器，但总体结果意味着在模拟河口流动时应考虑这些底栖种群。简单语言总结 河口的潮汐流受海底特性的影响。通过在三个不同季节对南旧金山湾的流量进行测量，我们在这里表明，夏季生活在沉积床中的生物体建造的进料管使床变得更加粗糙并减慢了平均流速。粗糙度估计差异的程度取决于用于测量的仪器，但总体结果意味着在模拟河口流动时应考虑这些底栖种群。