Dynamics of Willapa Bay, Washington: A highly unsteady, partially mixed estuary
Dynamics of Willapa Bay, Washington: A highly unsteady, partially mixed estuary
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DOI：
10.1175/jpo2637.1
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发表时间：
2004-11-01
影响因子：
3.5
通讯作者：
Newton, JA
中科院分区：
文献类型：
--
作者：
Banas, NS;Hickey, BM;Newton, JA
从3年的水文时间序列的结果显示了威拉帕湾，华盛顿，一个大潮汐，部分混合河口，其河流和海洋末端成员都是高度可变的。海洋条件的波动——由风驱动的上升流和下升流之间的交替，以及哥伦比亚河浮力羽流的侵入——显示出在事件（2-10天）尺度上迫使盐度梯度发生数量级变化。计算了有效的水平扩散系数作为河流流量的函数，参数化了河口上游的全部盐通量。结果表明，威拉帕的体积综合盐平衡几乎总是远离平衡。在非常高的河流流量（观测值的前15%），河口平均失去盐，而在所有其他河流流量水平，它获得盐。事实上，在夏季低河流量条件下，有效扩散系数K大到足以驱动盐度净增加3-6倍于向海、河流驱动的盐通量。与斜压交换的预期相反，由于潮汐强迫的增加，扩散过程被放大，而不是被抑制。此外，K沿河口长度的变化近似于平均潮汐速度乘以河道宽度的5%，这与潮汐残差对密度无关的搅拌一致。为了总结Willapa的事件尺度和季节尺度变异性，提出了一个简单的非定常河口盐平衡诊断参数空间，这是Hansen和Rattray稳态方案的推广。
Results from 3 yr of hydrographic time series are shown for Willapa Bay, Washington, a macrotidal, partially mixed estuary whose river and ocean end members are both highly variable. Fluctuating ocean conditions-alternations between wind-driven upwelling and downwelling, and intrusions of the buoyant Columbia River plume-are shown to force order-of-magnitude changes in salinity gradients on the event (2-10 day) scale. An effective horizontal diffusivity parameterizing all up-estuary salt flux is calculated as a function of riverflow: results show that Willapa's volume-integrated salt balance is almost always far from equilibrium. At very high riverflows (the top 15% of observations) the estuary loses salt, on average, while at all other riverflow levels it gains salt. Under summer, low-riverflow conditions, in fact, the effective diffusivity K is large enough to drive a net increase in salinity that is 3-6 times the seaward, river-driven salt flux. This diffusion process is amplified, not damped, by increased tidal forcing, contrary to the expectation for baroclinic exchange. Furthermore, K varies along the length of the estuary as similar to5% of the rms tidal velocity times channel width, a scaling consistent with density-independent stirring by tidal residuals. To summarize Willapa's event- and seasonal-scale variability, a simple diagnostic parameter space for unsteady estuarine salt balances is presented, a generalization from the Hansen and Rattray steady-state scheme.