Tide‐Storm Surge Interactions in Highly Altered Estuaries: How Channel Deepening Increases Surge Vulnerability
Tide‐Storm Surge Interactions in Highly Altered Estuaries: How Channel Deepening Increases Surge Vulnerability
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DOI：
10.1029/2019jc015286
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发表时间：
2020-04
期刊：
影响因子：
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通讯作者：
R. Familkhalili;S. Talke;D. Jay
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文献类型：
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作者：
R. Familkhalili;S. Talke;D. Jay
我们发展了理想化的分析和数值模式来研究风暴潮幅度在摩擦、弱收敛、无反射河口中的变化。摩擦是用切比雪夫多项式来处理的。风暴潮用两个正弦分量之和表示，第三个分量表示半日潮(D2)。风暴潮的经验拟合表明，两个正弦分量足以代表基线以上的风暴潮(R=0.97)。研究发现，涌浪幅值的空间转换取决于河口的深度，以及涌浪的时间尺度、幅值、不对称性和潮汐相对位相等特征。分析模型结果表明，在所有涌浪时间尺度上(12-72小时)，涌浪幅度在较深的航道中衰减较慢(e折叠较大)。河口越深，涌浪幅度越大。敏感性研究表明，初级幅度较大(或时间尺度较短)的浪涌比幅度较小(或时间尺度较大)的浪涌衰减得更快。此外，结果还表明，存在一个对水深、近岸涌浪幅值和时间尺度变化最敏感的位置，沿简单形式河口观测到的涌浪幅值最大变化的位置随着深度的增加而向上游移动。此外，涌浪与潮汐的相对位相和涌浪的不对称性可以改变涌浪变化最大的空间位置。随深度增加变化最大的是短时间尺度的大涌浪。结果表明，海平面上升和航道加深也可能改变涌浪幅度。世界上许多河口的自然状态都发生了很大的变化。湿地被开垦，航运渠道被拓宽和加深，以容纳大型集装箱船。对风暴潮和洪水风险的影响才刚刚开始探索。在这篇文章中，我们使用理论方法来理解风暴潮的特征--如它移动的速度有多快，它的规模有多大，它是在涨潮还是落潮时发生--如何改变它在河口的行为。我们的结果表明，当航道疏浚和加深时，风暴潮通常会变大；在高摩擦的河口内，观察到最大的放大作用是时间尺度较短的快速移动的风暴。其他特征--如相对于潮汐的时间和河口的形状--也影响着对变化条件的敏感度和幅度。我们发现，在沿海和远上游，航道加深的影响可以忽略不计。在这两者之间，出现了对疏浚最敏感的区域。因此，河道加深和海平面上升引起的洪水风险变化在空间上可能是可变的，即使在一个单独的河口内也是如此。
We develop idealized analytical and numerical models to study how storm surge amplitudes vary within frictional, weakly convergent, nonreflective estuaries. Friction is treated using Chebyshev polynomials. Storm surge is represented as the sum of two sinusoidal components, and a third constituent represents the semidiurnal tide (D2). An empirical fit of storm surge shows that two sinusoidal components adequately represent storm surge above a baseline value (R = 0.97). We find that the spatial transformation of surge amplitudes depends on the depth of the estuary, and characteristics of the surge wave including time scale, amplitude, asymmetry, and surge‐tide relative phase. Analytical model results indicate that surge amplitude decays more slowly (larger e‐folding) in a deeper channel for all surge time scales (12–72 hr). Deepening of an estuary results in larger surge amplitudes. Sensitivity studies show that surges with larger primary amplitudes (or shorter time scales) damp faster than those with smaller amplitudes (or larger time scales). Moreover, results imply that there is a location with maximum sensitivity to altered depth, offshore surge amplitude, and time scale and that the location of observed maximum change in surge amplitude along an estuary of simple form moves upstream when depth is increased. Further, the relative phase of surge to tide and surge asymmetry can change the spatial location of maximum change in surge. The largest change due to increased depth occurs for a large surge with a short time scale. The results suggest that both sea level rise and channel deepening may also alter surge amplitudes. Plain Language Summary Many estuaries around the world are heavily altered from their natural state. Wetlands have been reclaimed, and shipping channels widened and deepened to accommodate large container ships. The effects on storm surge and flood risk are just beginning to be explored. In this paper we employ a theoretical approach to understand how the characteristics of a storm surge—such as how fast it is moving, how big it is, and whether it happens on flood or ebb tide—change how it behaves in an estuary. Our results show that storm surge generally gets larger when channels are dredged and deepened; the largest amplification is observed for fast‐moving storms with a short time scale, within estuaries that are highly frictional. Other characteristics—such as the timing relative to the tide and the shape of the estuary—also impact the amplitude and the amount of sensitivity to changing conditions. We find that channel deepening effects are negligible at the coast and far upstream. In between, a region of maximum sensitivity to dredging occurs. Thus, changes in flood risk due to channel deepening and sea level rise can be spatially variable, even within a single estuary.