Within a wave‐exposed mangrove forest, novel field observations are presented, comparing millimeter‐scale turbulent water velocity fluctuations with contemporaneous subtidal bed elevation changes. High‐resolution velocity and bed level measurements were collected from the unvegetated mudflat, at the mangrove forest fringe, and within the forest interior over multiple tidal cycles (flood–ebb) during a 2‐week period. Measurements demonstrated that the spatial variability in vegetation density is a control on sediment transport at sub‐meter scales. Scour around single and dense clusters of pneumatophores was predicted by a standard hydraulic engineering equation for wave‐induced scour around regular cylinders, when the cylinder diameter in the equations was replaced with the representative diameter of the dense pneumatophore clusters. Waves were dissipated as they propagated into the forest, but dissipation at infragravity periods (> 30 s) was observed to be less than dissipation at shorter periods (< 30 s), consistent with the predictions of a simple model. Cross‐wavelet analysis revealed that infragravity‐frequency fluctuations in the bed level were occasionally coherent with velocity, possibly indicating scour upstream of dense pneumatophore patches when infragravity waves reinforced tidal currents. Consequently, infragravity waves were a likely driver of sediment transport within the mangrove forest. Near‐bed turbulent kinetic energy, estimated from the turbulent dissipation rate, was also correlated with bed level changes. Specifically, within the mangrove forest and over the unvegetated mudflat, high‐energy events were associated with erosion or near‐zero bed level change, whereas low‐energy events were associated with accretion. In contrast, no single relationship between bed level changes and mean current velocity was applicable across both vegetated and unvegetated regions. These observations support the theory that sediment mobilization scales with turbulent energy, rather than mean velocity, a distinction that becomes important when vegetation controls the development of turbulence.

中文翻译：

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毫米级湍流与沿海红树林边缘的米级潮汐侵蚀和增生相关

在波浪暴露的红树林中，提出了新颖的野外观测资料，将毫米尺度的湍流水速波动与同期潮下河床高程变化进行了比较。在两周的时间内，在多个潮汐周期（洪水退潮）期间，从无植被的滩涂，红树林边缘和森林内部收集了高分辨率的速度和水位测量值。测量表明，植被密度的空间变异性是亚米尺度下泥沙输送的控制。当方程中的圆柱直径被致密气生菌团的代表性直径所取代时，通过标准的水力工程方程，对规则气瓶周围的波浪诱发的冲刷，可以预测单个或密集的肺气团簇周围的冲刷。波浪在传播到森林时会消散，但是观察到在非重力时期（> 30 s）的消散小于在较短时期（<30 s）的消散，这与简单模型的预测一致。交叉小波分析显示，床面重力流频率波动偶尔与速度相关，这可能表明重力流强化潮汐流时，在密集的气生菌斑上游冲刷。因此，次重力波很可能是红树林内泥沙输送的驱动力。根据湍流耗散率估算的近床湍动能也与床位变化相关。具体来说，在红树林和无植被的泥滩上，高能事件与侵蚀或接近零的床位变化有关，而低能事件与吸积有关。相反，在植被带和非植被带上，床位变化与平均流速之间没有单一的关系。这些观测结果支持这样一个理论，即动员的泥沙是由湍流的能量而不是平均速度决定的，当植被控制湍流的发展时，这一区别就变得很重要。