Biomedical Engineering Reference
In-Depth Information
It has been calculated that the sale of electricity from the Three Gorges Dam in China will
cover the construction costs after 5
e
8 years of full generation.
Since hydroelectric dams do not burn fossil fuels, they do not directly produce carbon
dioxide. While some carbon dioxide is produced during manufacture and construction of
the project, this is a tiny fraction of the operating emissions of equivalent fossil-fuel electricity
generation. Hydroelectricity produces the least amount of GHGs and externality of any
energy source. Coming in second place was wind, third was nuclear energy, and fourth
was solar photovoltaic (PV). The extremely positive GHG impact of hydroelectricity is found
especially in temperate climates.
Reservoirs created by hydroelectric schemes often provide facilities for water sports and
become tourist attractions themselves. In some countries, aquaculture in reservoirs is
common. Multiuse dams installed for irrigation support agriculture with a relatively
constant water supply. Large hydro dams can control floods, which would otherwise affect
people living downstream of the project. This is a welcoming change for the sustainability of
the ecological system “locally”.
However, hydroelectric power stations that use dams could submerge large areas of land
due to the requirement of a reservoir. Large reservoirs required for the operation of hydro-
electric power stations result in submersion of extensive areas upstream of the dams, con-
verting fertile agricultural, forest, or grasslands to wetland and even aquatic system. As
such, biologically rich and productive lowland and riverine valley forests, marshland, and
grasslands are forever lost to an entirely different ecological system: wetland. The loss of
land is often exacerbated by the fact that reservoirs cause habitat fragmentation of
surrounding areas. One can imagine the consequences of shifting from one sustainable
ecological system to another entirely different ecological system. Still, the change in sustain-
able state is not limited to simply the small “dry” area that converted to “wet” area but to
a larger area around the reservoir.
Especially for large hydroelectric facilities, a reservoir stores large amount of water and
occupies a large area of land surface. The ecological change is also associated with a potential
climate change. As more evaporation is from the reservoir surface than from “dry” land surface
with plant coverage, more precipitation is expected in the surrounding area. The increase in
precipitation and its affected area depend on the size of the reservoir. Thus, there is the poten-
tial to alter the local climate from more arid to more temperate moist. Again the landscape or
ecological system surrounding the large reservoir is altered because of the water storage.
Hydroelectric projects can be disruptive to surrounding aquatic ecosystems both
upstream and downstream of the plant site. For instance, studies have shown that dams
along the Atlantic and Pacific coasts of North America have reduced salmon populations
by preventing access to spawning grounds upstream, even though most dams in salmon
habitat have fish ladders installed. Salmon spawn is also harmed on their migration to sea
when they must pass through turbines. This has led to some areas transporting smelt down-
stream by barge during parts of the year. In some cases, dams, such as the Marmot Dam, have
been demolished due to the high impact on fish. Turbine and power plant designs that are
easier on aquatic life are an active area of research. Mitigation measures such as fish ladders
may be required at new projects or as a condition of relicensing of existing projects.
Generation of hydroelectric power changes the downstream river environment. Water
exiting a turbine usually contains very little suspended sediment, which can lead to scouring
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