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Hydroelectric Power


HYDROELECTRIC POWER. The capability to produce and deliver electricity for widespread consumption was one of the most important factors in the surge of American economic influence and wealth in the late nineteenth and early twentieth centuries. Hydroelectric power, among the first and simplest of the technologies that generated electricity, was initially developed using low dams of rock, timber, or granite block construction to collect water from rainfall and surface runoff into a reservoir. The water was funneled into a pipe (or pen-stock) and directed to a waterwheel (or turbine) where the force of the falling water on the turbine blades rotated the turbine and its main shaft. This shaft was connected to a generator, and the rotating generator produced electricity. One gallon (about 3.8 liters) of water falling 100 feet (about 30 meters) each second produced slightly more than 1,000 watts (or one kilowatt) of electricity, enough to power ten 100-watt light bulbs or a typical hairdryer.

There are now three types of hydroelectric installations: storage, run-of-river, and pumped-storage facilities. Storage facilities use a dam to capture water in a reservoir. This stored water is released from the reservoir through turbines at the rate required to meet changing electricity needs or other needs such as flood control, fish passage, irrigation, navigation, and recreation. Run-of-river facilities use only the natural flow of the river to operate the turbine. If the conditions are right, this type of project can be constructed without a dam or with a low diversion structure to direct water from the stream channel into a penstock. Pumped-storage facilities, an innovation of the 1950s, have specially designed turbines. These turbines have the ability to generate electricity the conventional way when water is delivered through penstocks to the turbines from a reservoir. They can also be reversed and used as pumps to lift water from the powerhouse back up into the reservoir where the water is stored for later use. During the daytime when electricity demand suddenly increases, the gates of the pumped-storage facility are opened and stored water is released from the reservoir to generate and quickly deliver electricity to meet the demand. At night when electricity demand is lowest and there is excess electricity available from coal or nuclear electricity generating facilities the turbines are reversed and pump water back into the reservoir. Operating in this manner, a pumped-storage facility improves the operating efficiency of all power plants within an electric system. Hydroelectric developments provide unique benefits not available with other electricity generating technologies. They do not contribute to air pollution, acid rain, or ozone depletion, and do not produce toxic wastes. As a part of normal operations many hydroelectric facilities also provide flood control, water supply for drinking and irrigation, and recreational opportunities such as fishing, swimming, water-skiing, picnicking, camping, rafting, boating, and sightseeing.

Origins of the Hydroelectric Industry 1880–1930

Hydroelectric power technology was slow to develop during the first ten years of the hydroelectric era (1880 1889) due to the limitations of direct current electricity technology. Some pioneering hydro power developments using direct current technology are described below.

The Grand Rapids Electric Light and Power Company in Michigan connected a dynamo to a waterwheel for the Wolverine Chair Factory in July 1880 and this installation powered 16 brush-arc lamps. A dynamo was connected to a hydro power turbine at Niagara Falls in 1881 to power the arc lamps for the city streets.

The first hydroelectric power facility in the western United States was completed in San Bernadino, California, in 1887. By 1889 there were about 200 small electric generating facilities in the United States that used water for some or all of their electricity production. The potential for increasing hydroelectric development was dramatically enhanced in 1889 when alternating current technology was introduced, enabling electricity to be conveyed economically over long distances.

The next 30 years of the modern era of hydroelectric development, 1890 to 1920, began with the construction of individual hydroelectric facilities by towns, cities, cooperatives, and private manufacturing companies for their own specific needs, and ended with the organization of the first utility system in the country. Cities and towns used hydroelectric facilities to provide electricity for trolley systems, streetlights, and individual customers. Cooperatives

brought together groups of individuals and businesses to establish a customer pool that could finance and construct hydroelectric facilities for their own needs. Hundreds of small factories and paper mills in New England, the South, and throughout the Midwest constructed hydroelectric facilities for their own specific industrial use. Just prior to World War I, Southern Power Company purchased a large number of hydroelectric facilities from cites, towns, cooperatives, and factories, and consolidated them into the first regional utility power system in the United States. By 1920 hydroelectric facilities supplied 25 percent of the electricity used in the United States.

The hydroelectric industry matured between 1920 and 1930. During this period, electrical grid systems expanded, reaching more customers who were eager to receive and use electricity. Industrial production grew to satisfy the demand for consumer goods, requiring additional electricity. To meet the increasing demand, town and city electrical systems and regional utility systems grew in number and size throughout the more populated areas of the country. By 1930 hydroelectric facilities were delivering almost 30 percent of the nation's electricity needs.

The Hydroelectric Industry Prospers 1930–1980

The hydroelectric industry prospered from 1930 to 1980 for a number of reasons. Considerable federal funding was provided from 1930 through the 1960s for the construction of large federal dams and hydroelectric facilities. A major percentage of the massive increases in electricity required for wartime production during the 1940s was met by the construction of a sizable number of hydroelectric facilities; and to meet escalating electricity needs in response to the dramatic expansion of consumer demand and industrial production throughout the decades of the 1950s, 1960s, and 1970s, many new electric generating facilities, including hydroelectric developments, were constructed.

In the 1930s, major federal funding for new dam and hydroelectric facility development was allocated for three locations: the Tennessee River under authority of the Tennessee Valley Authority (TVA), the Colorado River under authority of the U.S. Bureau of Reclamation (Bureau), and the Columbia River under authority of the Bureau and the U.S. Army Corps of Engineers (COE). The TVA was established during the Great Depression in 1933 to develop multiple-use water resource projects in the Tennessee River system and spur economic development in Tennessee. It began construction in 1935 on a series of dams with hydroelectric facilities, which included almost 30 dams by the time the system was completed in 1956. Most of the TVA growth took place during World War II when the electrical demand necessary to develop the atomic bomb in the region surged by 600 percent between 1939 and 1945.

The Bureau, established in 1902 to promote the development of the western United States through the construction of federal irrigation dams, completed the world famous Hoover Dam on the Colorado River in 1936. Hoover Dam, which opened three years ahead of schedule, was a public works project intended to relieve unemployment during the Great Depression and provide critical electricity to meet the growing needs of the City of Los Angeles, California. At the same time, the Bureau and COE undertook the development of the great dams on the Columbia River in the northwestern United States. Within six years of the initial operation of Hoover, the Bureau completed Grand Coulee Dam on the Columbia River, still the largest dam in the northwestern United States. During the mid-1940s, Grand Coulee supplied the electricity needed to produce planes and other war material to support U.S. victory in World War II. Bonneville Dam, completed in 1938 by the COE and also located on the Columbia River, was a public works project to help relieve regional unemployment during the Great Depression. Like Grand Couleee, Bonneville also supplied critical electricity in support of World War II production efforts. In 1940 hydroelectric plants supplied more than 35 percent of the nation's electricity.

Grand Coulee and Bonneville, along with the other large hydroelectric projects constructed in the northwest region from the 1940s through the 1960s, supplied between 80 and 90 percent of the electricity consumed in the states of Washington and Oregon by 1980. However, the portion of the nation's electricity supplied by hydroelectric facilities had declined to 12 percent. Federal support for constructing dams where a hydroelectric plant could be included was declining and initial steps were being taken to alter the primary mission of the Bureau and COE from developing new projects to operating and maintaining existing facilities.

Regulation of the Hydroelectric Industry 1899–1986

Hydroelectric power development has always been closely linked to political influences. Federal recognition of the necessity to control development on the nation's waterways began with the passage of the Rivers and Harbors Act in 1899, less than twenty years after the appearance of the first hydroelectric facility. The rapid expansion of interest in natural and water resources led to the creation of the Inland Waterways Commission in 1907. This Commission issued a report advocating a national policy to regulate development on streams or rivers crossing public lands. A White House Natural Resources Conference the following year proposed increased development of the nation's hydroelectric resources. As a result, the Federal Water Power Act (FWPA) was passed in 1920, establishing the Federal Power Commission (FPC) with the authority to issue licenses for non-federal hydroelectric development on public lands and waterways. Recognizing that the FWPA did not extend to all waterways, Congress enacted the Federal Power Act (FPA) in 1935 to amend the FWPA. The FPA extended the FPC's authority to all hydroelectric projects built by utilities engaged in interstate commerce. The FPA also required that the effects of a project on other natural resources be considered along with the electricity to be produced by the project.

From 1940 to 1980, twenty-two federal laws were passed that affect the hydroelectric licensing decisions of the FPC (renamed the Federal Energy Regulatory Commission [FERC] in 1977). Included among these laws are the Fish and Wildlife Coordination Act, Wilderness Act, National Historic Preservation Act, Wild and Scenic Rivers Act, National Environmental Policy Act, Endangered Species Act, Federal Land Policy and Management Act, Soil and Water Resources Conservation Act, Public Utility Regulatory Policies Act, and Energy Security Act. The enactment of these laws coincided with increasing concerns that negative environmental consequences result from dam construction. These concerns included flooding large land areas, disrupting the ecology and the habitat of fish and wildlife, changing the temperature and oxygen balance of the river water, creating a barrier to the movement of fish upstream and downstream, and modifying river flows. By 1980 concerns that the salmon runs in the Columbia River system were in jeopardy prompted congress to pass the Pacific Northwest Power Planning and Conservation Act. This Act established the Northwest Power Planning Council, which is responsible for the protection and recovery of salmon runs in the Columbia River system. The implementation of many of these laws resulted in a more complex and expensive process to obtain a license for a hydroelectric facility.

The Hydroelectric Industry Stabilizes 1986–2000

The Electric Consumers Protection Act (ECPA) of 1986, which increased the focus on non-power issues in the hydroelectric licensing process, has contributed to an increase in development costs to the point where new hydroelectric facilities are often only marginally competitive with other conventional electric generating technologies. Since 1986, the time required to obtain a hydroelectric license has grown from two years to four years and the licensing cost has doubled for projects of all sizes. Even with more efficient technology, hydroelectric generation increased only slightly between 1986 and 2000. By 1986, the average size of all hydroelectric projects in the United States was about 35,500 kilowatts. After 1986, new projects completing the licensing and construction process average less than 5,000 kilowatts in size.

The recent availability of cheap natural gas and the minimal permitting requirements for gas-fired electricity generating plants has resulted in a dramatic increase in the construction of these plants. These gas-fired plants are meeting the increasing electricity demand more economically than other generating resources.
In today's climate of increased environmental awareness, the construction of new dams is often viewed more negatively than in the past. Therefore, the construction of a new dam for hydroelectric generation is rare. Only six hydroelectric projects were constructed between 1991 and 2000 with new dam or diversion structures and all of these structures are less than 30 feet (10 meters) in height. Hydroelectric facilities are installed at only about 2 percent of the nation's dams.

Present Geographical Distribution of the Industry

Almost 70 percent of all U.S. hydroelectric generation is produced in the western United States during an average water year. The northwestern states of Washington, Oregon, Montana, Wyoming, and Idaho generate about 50 percent of all hydroelectric output. The mountains are high and water is plentiful in this region, yielding optimal conditions for hydroelectric generation. Another 20 percent of the nation's hydroelectric output occurs in the southwestern states of Colorado, Utah, Nevada, California, Arizona, and New Mexico. While these states have terrain similar to those in the northwest, the climate is drier. The southeastern states of Virginia, North Carolina, Tennessee, South Carolina, Georgia, Alabama, Mississippi, and Florida contribute about 10 percent of U.S. hydroelectric production. This region includes large TVA and utility dams with hydroelectric plants. The State of New York produces over 8 percent of the nation's hydroelectricity. At a capacity of 2,500,000 kilowatts, the New York Power Authority's Robert Moses Niagara hydroelectric project is the primary contributor of this electricity. The remainder of the country produces 12 percent of U.S. hydroelectric generation.

The Financial Picture of the Hydroelectric Industry

The financial status of the hydroelectric industry is generally healthy due to long equipment life and low maintenance and operating costs. Hydroelectric facilities in the United States had total capital value in 2000 of about $159 billion based on average new facility costs compiled by DOE of $1,700 to $2,300 per kilowatt of capacity. The gross revenue for the industry in 2000 was about $18 billion based on U.S. electricity production of 269 billion kilowatt hours and DOE's $0.066/kilowatt hour estimate for the national average value of electricity. Using DOE's data, net profit for the industry in 2000 was calculated to be about $11 billion after deducting licensing and regulatory costs (about $500 million), capital costs (about $4.6 billion), and operation and maintenance costs (about $1.9 billion). In the mid-1990s, the hydroelectric industry directly employed nearly 48,000 people and their earnings totaled approximately $2.7 billion according to DOE. Another 58,000 people indirectly provided services and material needed to operate and maintain hydroelectric dams and generating facilities. Few businesses that are 125 years old are as efficient and as important to the U.S. economy as the hydroelectric industry.

Future Directions for the Hydroelectric Industry

The hydroelectric industry has been termed "mature" by some who charge that the technical and operational aspects of the industry have changed little in the past 60 years. Recent research initiatives counter this label by establishing new concepts for design and operation that show promise for the industry. A multi-year research project is presently testing new turbine designs and will recommend a final turbine blade configuration that will allow safe passage of more than 98 percent of the fish that are directed through the turbine. The DOE also recently identified more than 30 million kilowatts of untapped hydroelectric capacity that could be constructed with minimal environmental effects at existing dams that presently have no hydroelectric generating facilities, at existing hydroelectric projects with unused potential, and even at a number of sites without dams. Follow-up studies will assess the economic issues associated with this untapped hydroelectric resource. In addition, studies to estimate the hydroelectric potential of undeveloped, small capacity, dispersed sites that could supply electricity to adjacent areas without connecting to a regional electric transmission distribution system are proceeding. Preliminary results from these efforts have improved the visibility of hydroelectric power and provide indications that the hydroelectric power industry will be vibrant and important to the country throughout the next century.


Barnes, Marla. "Tracking the Pioneers of Hydroelectricity." Hydro Review 16 (1997): 46.
Federal Energy Regulatory Commission. Hydroelectric Power Resources of the United States: Developed and Undeveloped. Washington, 1 January 1992.
———. Report on Hydroelectric Licensing Policies, Procedures, and Regulations: Comprehensive Review and Recommendations Pursuant to Section 603 of the Energy Act of 2000. Washington, May 2001.
Foundation for Water and Energy Education. Following Nature's Current: Hydroelectric Power in the Northwest. Salem, Oregon, 1999.
Idaho National Engineering Laboratory and United States Department of Energy—Idaho Operations Office. Hydroelectric Power Industry Economic Benefit Assessment. DOE/ID-10565.Idaho Falls, November 1996.
———. Hydropower Resources at Risk: The Status of Hydropower Regulation and Development 1997. DOE/ID-10603.Idaho Falls, September 1997.
United States Department of Energy, Energy Information Administration. Annual Energy Review 2000. DOE/EIA-0384 (2000).Washington, August 2001.
United States Department of Energy—Idaho Operations Office. Hydropower: Partnership with the Environment. 01-GA50627. Idaho Falls, June 2001.
Richard T.Hunt
See alsovol. 9:Power .
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Hydroelectric Power

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The damming of streams and rivers has been an integral part of human civilization from its early history. Controversy paralleled this use because impounding and diverting water for upstream users affects those who live downstream, and also modifies the local habitats of plants and animals. Dams are built to control floods, improve navigation, provide a drinking-water supply, create or enhance recreational opportunties, and provide water for irrigation and other agricultural uses. A small percentage of dams (less than 3 percent in the United States) are used to generate power.

Hydropower generates about 24 percent of the world's and 12 percent of the United States' electricity. Shown here are the massive turbines inside a hydropower plant along Washington state's Spokane River.
Above: Hydropower generates about 24 percent of the world's and 12 percent of the United States' electricity. Shown here are the massive turbines inside a hydropower plant along Washington state's Spokane River.

Waterpower was the impetus that powered manufacturers who were building a growing nation during the U.S. Industrial Revolution of the nineteenth century. Waterwheels used the power of river water flowing downstream to turn machinery. Water continued to produce the largest part of industrial power until after the Civil War (from 1861 to 1865) when it diminished in importance. Yet waterpower would soon experience a rebirth in the form of hydroelectric power. The modern terms "hydroelectric power" and "hydropower" generally have the same meaning.

Coming of Age

At the beginning of the twentieth century, hydroelectric power in the United States came of age with three events: the development of the electric generator; improvements in the hydraulic turbine; and a growing demand for electricity. The first commercial hydroelectric power plant was built in 1882 on the Fox River in Appleton, Wisconsin, in order to provide 12.5 kilowatts of power to light two paper mills and a residence. Paper manufacturer H. F. Rogers developed the plant after seeing Thomas Edison's plans for an electricity power station in New York.

Early Twentieth Century.

Commercial power companies soon began to install a large number of small hydroelectric plants in mountainous regions near metropolitan areas. By 1920, hydroelectric plants accounted for 40 percent of the electric power produced in the United States.

The creation of the Federal Power Commission in 1920 increased development of hydroelectric power plants. The development of larger and more cost-efficient power plants showed that monetary support by the federal government was necessary for such hydroelectric plants to compete effectively with other power-generating plants. Then in 1933 the government saw that besides power production, hydroelectric power plants could also be effectively used for flood control, navigation, and irrigation. As a result, the government created the Tennessee Valley Authority in the southeastern United States to develop large-scale waterpower projects. In the Pacific Northwest, the Bonneville Power Administration, created in 1937, similarly focused on electrifying farms and small communities with public power.

The Lower Granite Dam on the Snake River in Washington state is a "run-of-the-river" hydroelectric dam operated by the U.S. Army Corps of Engineers. The Bonneville Power Administration, a federal agency located in the Pacific Northwest, markets wholesale electricity and transmission from Lower Granite and twenty-nine other federal dams. From left to right is the dam's earthen embankment; locks; the spillway; and the powerhouse.
The Lower Granite Dam on the Snake River in Washington state is a "run-of-the-river" hydroelectric dam operated by the U.S. Army Corps of Engineers. The Bonneville Power Administration, a federal agency located in the Pacific Northwest, markets wholesale electricity and transmission from Lower Granite and twenty-nine other federal dams. From left to right is the dam's earthen embankment; locks; the spillway; and the powerhouse.


Hydroelectric power plants generally range in size from several hundred kilowatts to several hundred megawatts , but a few enormous plants have capacities near 10,000 megawatts in order to supply electricity to millions of people. According to the National Renewable Energy Laboratory, world hydroelectric power plants have a combined capacity of 675,000 megawatts that produces over 2.3 trillion kilowatt-hours of electricity each year; supplying 24 percent of the world's electricity to more than 1 billion customers.

In many countries, hydroelectric power provides nearly all of the electrical power. In 1998, the hydroelectric plants of Norway and the Democratic Republic of the Congo (formerly Zaire) provided 99 percent of each country's power; and hydroelectric plants in Brazil provided 91 percent of total used electricity.
In the United States, more than 2,000 hydropower plants make hydro-electric power the country's largest renewable energy source (at 49 percent). The United States increased its hydroelectric power generation from about 16 billion kilowatt-hours in 1920 to nearly 306 billion kilowatt-hours in 1999. It runs a close second to Canada in the total amount of hydroelectric power produced worldwide. However, only 8 percent of the total U.S. electrical power was generated by hydroelectric power plants in 1999.
The largest U.S. hydropower plant is the 6,800-megawatt Grand Coulee power station on the Columbia River in Washington State. Completed in 1942, the Grand Coulee today is one of the world's largest hydropower plants, behind the 13,320-megawatt Itaipu hydroelectric plant on the ParanĂ¡ River between Paraguay and Brazil. *

Canada is the world's largest hydroelectric power producer. In 1999, it generated more than 340 billion kilowatt-hours of power, or 60 percent of its electric power, far outdistancing the U.S. hydropower percentage. The former Soviet Union, Brazil, China, and Norway are among the other top hydroelectric-generating countries.


Hydropower functions by converting the energy in flowing water into electricity. The volume of water flow and the height (called the head) from the turbines in the power plant to the water surface created by the dam determines the quantity of electricity generated. Simply, the greater the flow and the taller the head means the more electricity produced.

The simple workings of a hydropower plant has water flowing through a dam, which turns a turbine, which then turns a generator. A hydropower plant (including a powerhouse) generally includes the following steps:
  1. The dam holds water back, and stores water upstream in a reservoir , or large artificial lake. The reservoir is often used for multiple purposes, such as the recreational Lake Roosevelt at the Grand Coulee Dam. Some hydroelectric dams do not impound water, but instead use the power of the flowing river, and are known as run-of-the-river.
  2. Gates open on the dam, allowing gravity to pull the water down through the penstock. An intake conduit carries water from the reservoir to turbines inside the powerhouse. Pressure builds up as water flows through the pipeline.
  3. The water then hits the large blades of the turbine , making them turn. The vertical blades are attached through a shaft to a generator located above. Each turbine can weigh as much as 172 tons and turn at a rate of 90 revolutions per minute.
  4. The turbine blades turn in unison with a series of magnets inside the generator. The large magnets rotate past copper coils, which produce alternating current (AC).
  5. The transformer inside the powerhouse takes the AC and converts it to higher-voltage current so as to allow electricity to flow to customers.
  6. Out of every power plant exit four power lines consisting of three wires (associated with three power phases) and a neutral (ground) wire.
  7. Used water is carried through outflow pipelines, which reenters the river downstream.

Impacts and Trends

Hydroelectric power is a clean source of renewable energy where an adequate water source is readily available. Hydropower plants provide inexpensive electricity without environmental pollution such as air emissions or waste byproducts. And, unlike other energy sources such as fossil fuels , water is not consumed during electrical production, but can be reused for other purposes.

However, hydropower plants that rely on impoundments can negatively affect the reservoir site and the surrounding area. New reservoirs will permanently flood valleys that may have contained towns, scenic locations, and farmland. The permanent inundation also destroys fish and wildlife habitat that once existed at the reservoir site; however, new and different habitat is created. Hydropower operations that use run-of-the-river dams can block the passage of migrating fish, such as salmon. For example, many large dams in the Columbia River Basin impede Pacific salmon during their annual migrations through the river system.
Only 2,400 of the 80,000 dams in the United States are used for hydroelectric power. It is costly to construct a new hydroelectric power plant, and construction uses much water and land. In addition, environmental concerns have been voiced against their use. According to the U.S. Geological Survey, the likely trend for the future is toward small-scale hydroelectric power plants that can generate electricity for single communities.

William Arthur Atkins


Graham, Ian. Water Power. Austin, TX: Raintree Steck-Vaughn, 1999.
Kellert, Stephen R., ed. Macmillan Encyclopedia of the Environment, vol. 3. New York: Macmillan Library Reference USA, 1997.
Internet Resources
Hydroelectric Power Water Use - U.S. Geological Survey

Hydroelectric Power Water Use. Water Science for Schools, U.S. Geological Survey. <http://ga.water.usgs.gov/edu/wuhy.html> .
International Small-Hydro Atlas. <http://www.small-hydro.com> .
* See "Bureau of Reclamation, U.S." for a photograph of Grand Coulee Dam.

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can you name the top 10 countries powered by hydroelectricity

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Hydroelectric Power forum

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Water Science for Schools

Hydroelectric power water use

What percent of the nation's power do you think came from hydroelectric-power plants in 2006?
Hydroelectric power must be one of the oldest methods of producing power. No doubt, Jack the Caveman stuck some sturdy leaves on a pole and put it in a moving stream. The water would spin the pole that crushed grain to make their delicious, low-fat prehistoric bran muffins. People have used moving water to help them in their work throughout history, and modern people make great use of moving water to produce electricity.

Hydroelectric power for the Nation

Pie chart showing sources of electricity in the U.S. in 2006

Although most energy in the United States is produced by fossil-fuel and nuclear power plants, hydroelectricity is still important to the Nation, as about 7 percent of total power is produced by hydroelectric plants. Nowadays, huge power generators are placed inside dams. Water flowing through the dams spin turbine blades (made out of metal instead of leaves) which are connected to generators. Power is produced and is sent to homes and businesses.

World distribution of hydropower

  • Hydropower is the most important and widely-used renewable source of energy.
  • Hydropower represents 19% of total electricity production.
  • China is the largest producer of hydroelectricity, followed by Canada, Brazil, and the United States (Source: Energy Information Administration).
  • Approximately two-thirds of the economically feasible potential remains to be developed. Untapped hydro resources are still abundant in Latin America, Central Africa, India and China.
Producing electricity using hydroelectric power has some advantages over other power-producing methods. Let's do a quick comparison:

Advantages to hydroelectric power:
  • Fuel is not burned so there is minimal pollution
  • Water to run the power plant is provided free by nature
  • Hydropower plays a major role in reducing greenhouse gas emissions
  • Relatively low operations and maintenance costs
  • The technology is reliable and proven over time
  • It's renewable - rainfall renews the water in the reservoir, so the fuel is almost always there
Read an expanded list of advantages of hydroelectric power from the Top World Conference on Sustainable Development conference, Johannesburg, South Africa (2002)

Disadvantages to power plants that use coal, oil, and gas fuel:
  • They use up valuable and limited natural resources
  • They can produce a lot of pollution
  • Companies have to dig up the Earth or drill wells to get the coal, oil, and gas
  • For nuclear power plants there are waste-disposal problems
Hydroelectric power is not perfect, though, and does have some disadvantages:/p>
  • High investment costs
  • Hydrology dependent (precipitation)
  • In some cases, inundation of land and wildlife habitat
  • In some cases, loss or modification of fish habitat
  • Fish entrainment or passage restriction
  • In some cases, changes in reservoir and stream water quality
  • In some cases, displacement of local populations

Hydropower and the Environment

Hydropower is nonpolluting, but does have environmental impacts

Hydropower does not pollute the water or the air. However, hydropower facilities can have large environmental impacts by changing the environment and affecting land use, homes, and natural habitats in the dam area.

Most hydroelectric power plants have a dam and a reservoir. These structures may obstruct fish migration and affect their populations. Operating a hydroelectric power plant may also change the water temperature and the river's flow. These changes may harm native plants and animals in the river and on land. Reservoirs may cover people's homes, important natural areas, agricultural land, and archeological sites. So building dams can require relocating people. Methane, a strong greenhouse gas, may also form in some reservoirs and be emitted to the atmosphere. (EPA Energy Kids)

Reservoir construction is "drying up" in the United States

Line chart with year range on the bottom showing how since 1960, less reservoirs were being built.

Gosh, hydroelectric power sounds great -- so why don't we use it to produce all of our power? Mainly because you need lots of water and a lot of land where you can build a dam and reservoir, which all takes a LOT of money, time, and construction. In fact, most of the good spots to locate hydro plants have already been taken. In the early part of the century hydroelectric plants supplied a bit less than one-half of the nation's power, but the number is down to about 10 percent today. The trend for the future will probably be to build small-scale hydro plants that can generate electricity for a single community.

As this chart shows, the construction of surface reservoirs has slowed considerably in recent years. In the middle of the 20th Century, when urbanization was occuring at a rapid rate, many reservoirs were constructed to serve peoples' rising demand for water and power. Since about 1980, the rate of reservoir construction has slowed considerably.

Typical hydroelectric powerplant

Hydroelectric energy is produced by the force of falling water. The capacity to produce this energy is dependent on both the available flow and the height from which it falls. Building up behind a high dam, water accumulates potential energy. This is transformed into mechanical energy when the water rushes down the sluice and strikes the rotary blades of turbine. The turbine's rotation spins electromagnets which generate current in stationary coils of wire. Finally, the current is put through a transformer where the voltage is increased for long distance transmission over power lines. (Source: Environment Canada)

Hydroelectric-power production in the United States and the world

Chart showing hydroelectric power generation by State in the United States, and the top countries in the world using hydro power.

As this chart shows, in the United States, most states make some use of hydroelectric power, although, as you can expect, states with low topographical relief, such as Florida and Kansas, produce very little hydroelectric power. But some states, such as Idaho, Washington, and Oregon use hydroelectricity as their main power source. in 1995, all of Idaho's power came from hydroelectric plants.

The second chart shows hydroelectric power generation in 2006 for the leading hydroelectric-generating countries in the world. China has developed large hydroelectric facilities in the last decade and now lead the world in hydroelectricity usage. But, from north to south and from east to west, countries all over the world make use of hydroelectricity—the main ingredients are a large river and a drop in elevation (along with money, of course).

Source: Energy Information Administration (EIA):

Sources and more information

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URL: http://ga.water.usgs.gov/edu/wuhy.html
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Tennessee Valley Authority - Hydroelectric Power

Hydroelectric Power

TVA hydroelectric facilities

Hydropower is America’s leading renewable energy resource. Of all the renewable power sources, it’s the most reliable, efficient and economical. TVA maintains 29 conventional hydroelectric dams throughout the Tennessee River system and one pumped-storage facility for the production of electricity. In addition, four Alcoa dams on the Little Tennessee River and eight U.S. Army Corps of Engineers dams on the Cumberland River contribute to the TVA power system.

Download a high resolution version of this video (37 mb, Quicktime)

What is hydroelectric power?

Water is needed to run a hydroelectric generating unit. It’s held in a lake behind the dam, and the force of the water being released from the lake through the dam spins the blades of a turbine. The turbine is connected to the generator that produces electricity. After passing through the turbine, the water reenters the river on the downstream side of the dam.
diagram of hydro plant

What is a pumped-storage plant?

A pumped-storage plant uses two reservoirs, one located at a much higher elevation than the other. During periods of low demand for electricity, such as nights and weekends, energy is stored by reversing the turbines and pumping water from the lower to the upper reservoir. The stored water can later be released to turn the turbines and generate electricity as it flows back into the lower reservoir.

Generating Plants

Find information on all the plants in the TVA generating system via our interactive map.

Department of Energy - Water - Hydroelectric Power

From A/Cs to carbon fiber, the research at the National Labs is having a big impact in our lives.


  • April 27, 2012
    Magna E-Car opens a new electric drive component facility in Grand Blanc Township, Michigan.
  • April 27, 2012
    April has been an exciting month for the Apps for Energy competition, so we want to take a few minutes to update Energy.gov readers on the competition and the plan for announcing the winners.
  • April 27, 2012
    According to a new report from Pacific Northwest National Lab, commercial building owners could save an average 38 percent on their heating and cooling bills just by installing a few new controls onto their HVAC systems.
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