|Fig. 1: The Grand Coulee Dam on the Columbia River, Washington. (Source: Wikimedia Commons)|
Hydroelectricity is the production of electrical power through the use of gravitational force on flowing water. Hydroelectricity accounted for 12% of the United States electric power in 2010, and many countries have an even higher percentage because of the ability hydroelectric power has as an on-demand energy source. The two best aspects of hydroelectric power are the low cost to produce, and the flexibility of production.  The reason it is relatively cheaper form of energy is obvious in the fact of taking advantage of the power of our planet. The flexibility of production is also as simple as allowing more or less water to pass through the generators, to adjust to varying energy demands. Once a hydroelectric dam has been constructed there are no direct wastes that stem from the complex has a much less output of greenhouse gases compared to fossil fuel energy plants, as greenhouse gas emissions from natural-gas powered plants are 24 to 26 times greater than hydroelectric plants.  That being said, the act of damming has a large negative effect on the ecosystem of the river.
The environmental disadvantages of dams are numerous and diverse, including effects in the biological, chemical and physical properties of rivers ecosystems. With the largest dams in the world being constructed in the last 6 decades, the long-term effects on the rivers occupied by dams have yet to be discovered. The short-term effects caused the Marmot Dam in Oregon to be deconstructed due to the severe changes in salmon population in the Columbia River. Just as every river is unique in its size, landscape it flows through, and ecosystem it supports, so is the design and affect the dam can have on that river. 
A dam also traps sediments, which are critical for maintaining physical processes and habitats downstream of the dam (include the maintenance of productive deltas, barrier islands, fertile floodplains and coastal wetlands), which in turn can completely alter the chemical makeup of a river.  Dams have forced thousands of native people around the world to relocate their homes due to dam reservoirs. For example the Grand Coulee Dam in Washington was completed in 1942, and is the largest electric power producing facility in the U.S. The dam is built on the Columbia river and the creation of the Franklin Delano Roosevelt Lake, the reservoir at the mouth of the dam, forced the relocation of over 3,000 Native Americans whose ancestral lands where partially flooded. 
The Itaipu dam is another example of a dam physically altering the planet in a negative way. Built in 1982 in Guaira, Brazil, the Itaipu dam created a reservoir covering an area of 521 square miles. This reservoir covered the famous tourist attraction Guaira Falls, which had one of the largest water flow rates of any falls on Earth, with a discharge of 470,000 cubic feet per second.  Brazilian poet Carlos Drummond de Andre wrote a poem stating his displeasure of the falls:
|Here seven visions, seven liquid sculptures
vanished through the computerized calculations
of a country ceasing to be human
in order to become a chilly corporation, nothing more.
A movement becomes a dam.
While the subject of greenhouse gases has certainly taken a lead on the topic of the effects energy has on our planet, hydroelectricity certainly does not have clean hands on altering our planet. The short-term effects may seem small currently, but the long term may cause irreversible damages to the rivers of the world.
© Charlie Hopkins. The author grants permission to copy, distribute and display this work in unaltered form, with attribution to the author, for noncommercial purposes only. All other rights, including commercial rights, are reserved to the author.
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 P. C. Pitzer, Grand Coulee: Harnessing a Dream (Washington State University Press, 1994).
 J. P. Rafferty, Rivers and Streams (Rosen Education Service, 2011).