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Regional Basic Professional Training Course in Korea

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5.3.3.1. Mar<strong>in</strong>e floods<br />

❙ 335 ❙<br />

5. SITING CONSIDERATIONS<br />

In addition to modifications of the shore by erosion or by deposits of alluvia, which must<br />

obviously be taken <strong>in</strong>to account, various phenomena may occur on the shore: tides, swell<br />

and waves, currents, tidal waves, and seiches.<br />

The tides<br />

Tidal observations for a period of at least one year yield a solid knowledge of the<br />

amplitudes and situations of each wave <strong>in</strong> a given place and so make it possible to f<strong>in</strong>e‐tune<br />

the astronomic calculation. The extreme low and high tides are what must be considered.<br />

Swell and waves<br />

Swell and waves are wave tra<strong>in</strong>s most often <strong>in</strong>itiated by the w<strong>in</strong>d. Maritime works take<br />

these phenomena <strong>in</strong>to account <strong>in</strong> the design of jetties and site protection structures (water<br />

<strong>in</strong>take, platform). A calculation determ<strong>in</strong>es the residual agitation at the structures and<br />

beh<strong>in</strong>d them for various wave periods and sources, together with the amplitude of the<br />

oscillations (<strong>in</strong> a water <strong>in</strong>take channel, for example).<br />

Tsunamis or tidal waves<br />

Tsunamis are waves caused by an earthquake, volcanic eruption, or undersea or coastal<br />

landslide. One of the best known is the one that followed the Lisbon earthquake <strong>in</strong><br />

November 1755. It was felt as far away as the West Indies, and devastated the coasts of<br />

Portugal and Morocco.<br />

In most practical cases, the height of a tsunami <strong>in</strong> a given place can be deduced from its<br />

height <strong>in</strong> deep water offshore us<strong>in</strong>g energy refraction and transmission pr<strong>in</strong>ciples. At the<br />

approach to a coast, the shallower depth causes a reduction of velocity and wavelength<br />

and <strong>in</strong> consequence an <strong>in</strong>crease of height, s<strong>in</strong>ce the energy conveyed rema<strong>in</strong>s constant.<br />

There are mathematical models based on cont<strong>in</strong>uity equations that calculate the

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