Classification of tidal response in estuaries from channel geometry
Classification of tidal response in estuaries from channel geometry
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从河道几何形状对河口潮汐响应进行分类
DOI：
10.1111/j.1365-246x.1985.tb05086.x
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发表时间：
1985
影响因子：
2.8
通讯作者：
D. Prandle
中科院分区：
文献类型：
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作者：
D. Prandle
总结。通过使用指数函数来近似航道几何形状，河口的潮汐响应可以直接分为三种类型之一。因此，用Boexp(αx)表示的宽度和用Exp(βx)表示的深度(x是河口沿岸的无量纲长度)由：(1)α+2β<；10，(2)α+2β≪10和(3)α+2β∼10来划分。用一个有阻尼简谐振子的自由振动作类比，α+2β表示‘衰减因子’。
类型(1)的河口是欠阻尼的，高程幅度在x轴上以振荡的方式变化。这类河口的响应峰值位于某一“自然频率”，大致接近四分之一波长的共振。类型(2)的河口对应于临界阻尼，并产生潮汐高程的最大放大。类型(3)的河口过度受阻，高程幅度向头部单调增加。在此类别中，通道几何结构以不发生四分之一波长共振的速率扩展。
上述发现源于分析方法和数值方法的结合。对10个主要河口的观测和计算的反应进行了比较，从而验证了这一理论。
第一次，芬迪湾和布里斯托尔海峡经历的大潮差被证明更多地是由它们的整体形状(即它们的值为α+2β∼10)而不是特定的共振长度造成的。在距河口头部一定距离x1处修建防潮屏障，有效地使α和β都增加了一倍(β1/2)。因此，障碍物对任何河口的影响是显而易见的，并解释了(2)型河口，如芬迪和布里斯托尔海峡对障碍物建造的高度敏感性。
研究了潮汐响应随不同潮汐种类的变化，特别强调了适当的线性化摩擦系数对每个分量的变化情况。河口对线性化摩阻系数变化的敏感性受到无量纲河口长度XL的强烈影响。
Summary. By using exponential functions to approximate channel geometry, the tidal response in an estuary can be directly classified into one of three types. Thus, with the breadth represented in dimensionless form by boexp(αx) and the depth by exp(βx) (x is the dimensionless length along the estuary) the three types are delimited by: (1) α+ 2β < 10, (2) α+ 2β≪ 10 and (3) α+ 2β∼ 10. Using an analogy with the free vibrations of a damped simple-harmonic oscillator, α+ 2β represents the ‘damping factor’.
Estuaries of type (1) are under-damped and the elevation amplitudes vary in an oscillatory manner along the x-axis. Such estuaries exhibit a response peak at some ‘natural frequency’ roughly approximating quarter-wavelength resonance. Estuaries of type (2) correspond to critical damping and produce maximum amplification of tidal elevations. Estuaries of type (3) are over-damped and elevation amplitudes increase monotonically towards the head. In this category, the channel geometry expands at a rate such that quarter-wavelength resonance does not occur.
The above findings stem from a combination of analytical and numerical methods. Validation of the theory follows from a comparison of observed and calculated responses in 10 major estuaries.
For the first time, the large tidal ranges experienced in the Bay of Fundy and Bristol Channel are shown to result more from their overall shapes (i.e. they have values of α+ 2β∼ 10) rather than from a specific resonant length. The construction of a tidal barrier at some distance x1 from the head of an estuary effectively increases both α and β by a factor exp(β1/2). Thus the impact of barriers on any estuary is readily apparent and the high sensitivity of type (2) estuaries such as Fundy and the Bristol Channel to barrier construction is explained.
The variation of tidal response with differing tidal species is examined with particular emphasis on how the appropriate linearized friction coefficient varies for each constituent. The sensitivity of an estuary to variations in this linearized friction coefficient is shown to be strongly influenced by the dimensionless estuarine length xL.