Bed shear stress estimation on an open intertidal flat using in situ measurements
Bed shear stress estimation on an open intertidal flat using in situ measurements
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DOI：
10.1016/j.ecss.2016.08.028
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发表时间：
2016-12
影响因子：
2.8
通讯作者：
Q. Zhu;B. C. Prooijen;Z. Wang;Yanxia Ma;Shi-lun Yang
中科院分区：
文献类型：
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作者：
Q. Zhu;B. C. Prooijen;Z. Wang;Yanxia Ma;Shi-lun Yang
河床切应力的准确估计是预测河口海岸冲淤过程的基础。本研究利用高频原位水深和近床流速测量，估算了长江三角洲一个开阔潮间带的床面剪切应力。为了确定水流引起的河床剪切应力（τc），首先使用两种方法将现场近床速度从湍流速度分解为单独的波轨道速度：然后用对数剖面（LP）、湍流动能（TKE）、修正的TKE（TKEw）、雷诺应力（RS）、和惯性耗散（ID）方法。波浪引起的床面剪应力（τw）采用经典线性波浪理论估算。基于Grant-Madsen波流相互作用模型（WCI）确定总床面切应力（τcw）。结果表明，当有效波高与水深之比（Hs/h）大于0.25时，由于大风产生的表面波污染了垂向速度脉动，τ cw被显著高估。此外，风的作用使波浪高度增大和垂向湍流增强分别导致τ和τ c增大，从而使床面总剪应力增大。通过对这些不同方法的比较，发现与ESA分解相关的TKEw方法是最佳方法，因为：（1）该方法产生最高的平均一致性指数;（2）它使用受多普勒噪声影响较小的垂直速度;（3）它对近床分层结构以及床位置和粗糙度的不确定性不太敏感。
Accurate estimations for the bed shear stress are essential to predict the erosion and deposition processes in estuaries and coasts. This study used high-frequency in situ measurements of water depths and near-bed velocities to estimate bed shear stress on an open intertidal flat in the Yangtze Delta, China. To determine the current-induced bed shear stress (τc) the in situ near-bed velocities were first decomposed from the turbulent velocity into separate wave orbital velocities using two approaches: a moving average (MA) and energy spectrum analysis (ESA).τcwas then calculated and evaluated using the log-profile (LP), turbulent kinetic energy (TKE), modified TKE (TKEw), Reynolds stress (RS), and inertial dissipation (ID) methods. Wave-induced bed shear stress (τw) was estimated using classic linear wave theory. The total bed shear stress (τcw) was determined based on the Grant–Madsen wave–current interaction model (WCI). The results demonstrate that when the ratio of significant wave height to water depth (Hs/h) is greater than 0.25,τcwis significantly overestimated because the vertical velocity fluctuations are contaminated by the surface waves generated by high winds. In addition, wind enhances the total bed shear stress as a result of the increases in bothτwandτcgenerated by the greater wave height and reinforcing of vertical turbulence, respectively. From a comparison of these various methods, the TKEw method associated with ESA decomposition was found to be the best approach because: (1) this method generates the highest mean index of agreement; (2) it uses vertical velocities that are less affected by Doppler noise; and (3) it is less sensitive to the near-bed stratification structure and uncertainty in bed location and roughness.