Environmental Engineering Reference
In-Depth Information
reservoir can extend over many hundreds of square miles, providing an
abundant and inexhaustible supply of organic debris.
Dams can last for many decades, but their life span can be rapidly cut
short by the accumulation of sediment behind the dam. Abundant sand
and mud are continually deposited in the reservoir. More sediment in
the reservoir means less room for water, and dredging reservoirs is
expensive. As water depth decreases, the ability of the dam to generate
electricity also decreases.
A more futuristic source of power and electricity from moving water
involves harnessing the oceans that cover 71 percent of the earth's
surface. There is nearly 900 times more energy in a cubic foot of water
as in a cubic foot of air because of the difference in density. But there
are signifi cant technological obstacles to harnessing wave and tidal
movements for human use. Some have been overcome, but diffi culties
remain. Past governments in the United States have not been supportive
of developing electricity from ocean power, in contrast to Europe, Aus-
tralia, and elsewhere. Fourteen countries now operate wave- or tidal-
power stations, but most are tiny, experimental, and expensive.
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It is
diffi cult to build devices that can survive storm damage, seized bearings,
broken welds, and snapped mooring lines. The amount of overbuilding
required as a safety factor to overcome these dangers is uncertain, and
overbuilding increases costs.
Wave Power
The best areas for harnessing wave energy to generate electricity are
where the waves form far out at sea and are driven shoreward as the
winds pump energy into them. The areas of strongest winds are between
latitudes 40º and 60° in both the Northern and Southern Hemispheres
on the eastern sides of the oceans. In the United States, the most
favorable areas are along the Pacifi c coast.
No commercial wave power generators are operating in the United
States. The world's fi rst wave farm opened in 2008 in Portugal. It con-
sists of three machines, and expansion to twenty-fi ve machines is
planned, but it generates only 2 megawatts of power, an order of mag-
nitude too small for the farm to be considered commercial. Other farms
are in the planning or development stage in Scotland, England, and
Australia. Environmental dangers to the commercial development of
wave energy include displacement of commercial fi shers from productive
fi shing grounds, alterations in the pattern of beach sand nourishment,
and possible hazards to safe navigation.
