Page 537 - Geosystems An Introduction to Physical Geography 4th Canadian Edition

Chapter 16 Oceans, Coastal Systems, and Wind Processes 501
(a) The La Rance tidal generating station in France harnesses energy of the tides using a tidal (b) Turbine harnesses power from tidal currents barrage, similar to a hydroelectric dam. at Strangford Lough, Northern Ireland.
▲Figure 16.8 Tidal power generation. [(a) environment images/Uig/getty. (b) robert Harding Picture Library Ltd./alamy.]
turbines that are powered by the movement of flood and ebb tides to produce electricity. This is a more sustainable method with fewer environmental im- pacts, because a dam is not built within the tidal es- tuary. The first tidal stream generator was completed in 2007 at Strangford Lough in Northern Ireland (Figure 16.8b). In 2013, the first underwater turbines in the United States began generating power near Eastport, Maine, at the mouth of the Bay of Fundy. The main limi- tation of tidal power is that only about 30 locations in the world have the tidal energy needed to turn the tur- bines. However, many scientists suggest that this energy resource has huge potential in some regions. Pilot proj- ects are ongoing in Nova Scotia at the mouth of Minas Basin in the upper Bay of Fundy using tidal stream gen- erators, with research on the possible environmental ef- fects of new permanent installations also taking place.
Waves
Friction between moving air (wind) and the ocean sur- face generates undulations of water in waves, which travel in groups known as wave trains. Waves vary widely in scale: On a small scale, a moving boat creates a wake of small waves; at a larger scale, storms gener- ate large wave trains. At the extreme is the wind wake produced by the presence of the Hawaiian Islands, traceable westward across the Pacific Ocean surface for 3000 km. This is a consequence of the islands’
disruption of the steady trade winds, which also causes changes in surface temperature.
A stormy area at sea can be a generating region for large wave trains, which radiate outward in all direc- tions. The ocean is crisscrossed with intricate patterns of these multidirectional waves. The waves seen along a coast may be the product of a storm centre thousands of kilometres away.
Regular patterns of smooth, rounded waves, the mature undulations of the open ocean, are swells. As these swells, and the energy they contain, leave the generating region, they can range from small ripples to very large, flat-crested waves. A wave leaving a deep- water generating region tends to extend its wavelength horizontally for many metres (remember from Chapter 2 that wavelength is the distance between corresponding points on any two successive waves). Tremendous en- ergy occasionally accumulates to form unusually large waves. One moonlit night in 1933, the U.S. Navy tanker Ramapo reported a wave in the Pacific higher than its mainmast, at about 34 m!
Wave movement in open water suggests to an observer that the water is migrating in the direction of wave travel, but in reality only a slight amount of water is actually advancing. The appearance of move- ment is produced by the wave energy that is mov- ing through the flexible medium of water. The water within a wave in the open ocean is transferring en- ergy from molecule to molecule in simple cyclic