Environmental Engineering Reference
In-Depth Information
Small hydro plants (mini hydro) usually generate between 1 and 30 Megawatts
and have flood areas smaller than 13 square kilometers.
There are more than 45,000 large dams around the world, and they have played
an important role in helping communities and economies harness water resources
for food production, energy generation, flood control, and domestic use. Current
estimates suggest that some 30-40% of irrigated land worldwide now relies on
dams and that dams generate 16.5% of the world's electricity.
From the 1930s to the 1970s, the construction of large dams became—in the
eyes of many—synonymous with development and economic progress, and they
were viewed as symbols of modernization. Thus, their construction accelerated sig-
nificantly. This trend peaked in the 1970s, when on average two or three large dams
were commissioned each day somewhere in the world.
Hydro plants usually use reservoirs to equalize the water flows that drive the
electricity-generating turbine. Water is stored behind the dam for seasonal, an-
nual, and, in some cases, multiannual regulation of the river. These dams are
built, ideally, in narrow gorges, with great depth and relatively small flood area.
Examples are the Hoover Dam near the Grand Canyon (which spurred the growth
of Las Vegas) and the dams built in the Alps. As there are few places offering
ideal dam-building conditions, dams of lesser height and longer lengths are often
built, flooding vast superficial extensions. Run-of-river dams often have no storage
reservoirs and operate with encapsulated electric generators, or bulb generators.
Large dams require significant financial investments. Estimates suggest that,
worldwide, at least US$2 trillion have been invested in the construction of large
dams over the last century. During the 1990s, an estimated US$32-46 billion was
spent annually on large dams, four-fifths of it in developing countries. Of the
US$22-31 billion invested in dams each year in developing countries, about four-
fifths were financed directly by the public sector. The immediate benefits of large
dams, including food security considerations, local employment and skills devel-
opment, rural electrification, and the expansion of physical and social infrastruc-
ture such as roads, were widely believed sufficient to justify the enormous invest-
ments made.
Presently there are approximately 1000 GW of hydroelectric power in operation
and more than 150 GW under construction. The theoretical potential for hydroelec-
tric generation is five times larger.
