Waves on Beaches
Waves on Beaches
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DOI：
10.1006/rwos.2001.0131
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发表时间：
2019
期刊：
影响因子：
--
通讯作者：
R. Holman
中科院分区：
文献类型：
--
作者：
R. Holman
Wave motions are one of the most familiar of oceanographic phenomena. The waves that we see on beaches were originally generated by ocean winds and storms, sometimes at long distances from their final destination. In fact, groups of waves, generated by large storms, have been tracked from the Southern Ocean near Australia all the way to Alaska. Open ocean waves can be thought of as simple sinusoids that are superimposed to yield a realistic sea. Waves entering the nearshore, called incident waves, can have wave periods (T, the time between consecutive passages of wave crests) ranging from 2 to 20s, with 10s a typical value. Wave heights (H, the vertical distance from the trough to peak of a wave) can exceed 10m, but are typically 1 m, rep-resenting an energy density, of 1250 Jm² (p is the density of sea water, g is the acceleration of gravity) and a flux of power impinging on the coast of about 10kW per meter of coastline. Although this is a substantial amount of power, it is not enough to make broad commercial exploitation of wave power economical at the time of writing. Of interest in this section are the dynamics of waves once they progress into the shallow beach environment such that the ocean bottom begins to restrict the water motions. Most people are familiar with refraction (the turning of waves toward the beach), wave breaking, and swash (the back and forth motion of the water's edge), but are less fa-miliar with the other types of fluid motion that are generated near the beach. Figure 1 illustrates schematically the evolution of ocean wave energy as it moves from deep water (top of the figure) through progressively shallower water toward the beach (bottom of the figure). Offshore, most energy lies in waves of roughly 10 s period (middle of the figure). However, the processes of shoaling distribute that energy to both higher frequencies (right half of the figure) and lower frequencies (left half) including mean flows. In general, these processes can be distinguished as those that occur offshore of the surf zone (where waves become overly steep and break) and those that occur within the surf zone.
