Tidal asymmetry and velocity skew over tidal flats and shallow channels within a macrotidal river delta
Tidal asymmetry and velocity skew over tidal flats and shallow channels within a macrotidal river delta
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DOI：
10.1029/2011jc007384
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发表时间：
2012-03
影响因子：
--
通讯作者：
N. Nidzieko;D. Ralston
中科院分区：
文献类型：
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作者：
N. Nidzieko;D. Ralston
[1]人们通常认为，在短期内，浅河口，在领先的顺序速度和海拔是完全不同的阶段，使持续时间的不对称的上升和下降的潮汐应表现为倾斜的速度。我们观察到交替落潮和洪水占主导地位的速度偏斜的春小潮调制事件的不对称性所产生的混合，主要是半日天文潮汐内的大潮汐斯卡吉特河三角洲在普吉湾，华盛顿。我们描述了可能导致局部不对称的三个因素：（1）由表面梯度和局部深度之间的相位滞后引起的落潮优势，（2）由于河流排放引起的落潮优势，以及（3）由于斜压性引起的近床洪水优势。大的大潮导致更大的潮汐产生的相位滞后，并导致在退潮占主导地位的速度偏斜。这种退潮优势所造成的潮汐排水加强了河流排放潮滩在较低的低水位。然而，这种放电的斜压分量，产生洪水占主导地位的近床速度偏斜，反击的摩擦效应的落潮优势。这些过程的平衡在很大程度上取决于春小潮周期，河流流量的大小，以及在潮滩和河道系统内的位置。我们的观察结果在以前描述这些过程的研究中是值得注意的，因为我们的分析表明，这些机制在只有几公里的非常短的空间尺度和非常浅的系统中是相关的。
[1] It is often assumed that, in short, shallow estuaries, at leading order velocity and elevation are exactly out of phase, so that duration asymmetries in the rise and fall of the tide should be manifest as skewed velocities. We observed alternating ebb- and flood-dominant velocity skew in response to the spring-neap modulation of incident asymmetry generated by the mixed, mainly semidiurnal astronomical tides within the macrotidal Skagit River delta in Puget Sound, Washington. We describe three factors that may contribute to local asymmetries: (1) ebb dominance caused by phase lags between the surface gradient and local depth, (2) ebb dominance due to fluvial discharge, and (3) near-bed flood dominance due to baroclinicity. Large spring tides led to greater frictionally generated phase lags and resulted in ebb-dominant velocity skew. This ebb dominance caused by tidal drainage was reinforced by fluvial discharge across the tidal flat at lower-low water. The baroclinic component of this discharge, however, produced flood-dominant near-bed velocity skew that countered the ebb dominance of the frictional effects. The balance of these processes depends strongly on the spring-neap cycle, magnitude of river discharge, and position within the tidal flat and channel system. Our observations are notable in the context of previous studies describing these processes because our analyses indicate that these mechanisms are relevant over very short spatial scales of just a few kilometers and in very shallow systems.