Environmental Engineering Reference
In-Depth Information
Tides and Currents
Ocean waves, moved bywinds, are a form ofindirect solar energy.Yet, when we talk about
ocean energy another body of the solar system comes into play: the moon. The gravity of
our satellite is one-sixth that of the Earth, enough to cause slight fluctuation in the Earth's
orbit and to attract the Earth's waters (see
Figure 4.59
).
30
Figure 4.59.
How the moon influences the tides.
Seas and oceans experience two high tides and two low tides per day. The tidal range
depends on the dimension and depth of the water bodies. Enclosed seas, such as the Black
Sea or the Baltic, experience little or no tidal movement, while the oceans experience tides
up to several metres. At the top end of the scale is Wolfville, in Nova Scotia (Canada),
where tethered boats rise and fall 16 metres (the highest tidal difference on Earth) every
day.
Up to now, tidal energy has mostly been harnessed on estuaries closed off by a barrage
(see
Figure 4.60
). The principle at work is much the same as in a hydroelectric plant
(within the barrage are water turbines that generate electricity), except that the water basin
is replenished not through rainfall but through tidal flow.
