• hydroelectric energy

    Hydroelectric engineers just dam it.

    Photograph by Volkmar K. Wentzel

    Hydroelectric Nations
    Hydroelectric power provides almost all the energy for some nations. Norway, Brazil, and the Democratic Republic of Congo all get more than 90 percent of their electricity from hydroelectric power plants. Plans for a new hydroelectric plant in the Democratic Republic of Congo may link homes and businesses in Europe with the African power supply.

    Washington's Energy
    The state of Washington is the largest consumer of hydroelectric power in the United States. The state used almost 58 million watts of hydroelectricity in 2009, more than double the next-largest state consumer, Oregon.

    Hoover Dam
    The Hoover Dam was built during the Great Depression, a period when most people had little money and jobs were very scarce. Building the dam seemed like an impossible task. Many people said it could not be built.

    Workers labored long, hard days for two years, building tunnels that are 15 meters (50 feet) widebig enough to fit a commercial airplane without its wings. The Hoover Dam is 221 meters (726 feet) tall52 meters (171 feet) taller than the Washington Monument in Washington, D.C.

    Building the dam gave hope and dignity to many victims of the Great Depression. It gave people a job and a way to earn money. The Hoover Dam is still in use, providing power to 1.7 million people in Arizona, California, and Nevada. It is often considered an engineering milestone and is named for Herbert Hoover, the U.S. president who helped make the project happen.

    Hydroelectric energy is made by moving water. Hydro comes from the Greek word for water.

    Hydroelectric energy has been in use for thousands of years. Ancient Romans built turbines, which are wheels turned by flowing water. Roman turbines were not used for electricity, but for grinding grains to make flour and breads.

    Water mills provide another source of hydroelectric energy. Water mills, which were common until the Industrial Revolution, are large wheels usually located on the banks of moderately flowing rivers. Water mills generate energy that powers such diverse activities as grinding grain, cutting lumber, or creating hot fires to create steel.

    The first U.S. hydroelectric power plant was built on the Fox River in 1882 in Appleton, Wisconsin. This plant powered two paper mills and one home.

    Harnessing Hydroelectricity

    To harness energy from flowing water, the water must be controlled. A large reservoir is created, usually by damming a river to create an artificial lake, or reservoir. Water is channeled through tunnels in the dam.

    The energy of water flowing through the dam's tunnels causes turbines to turn. The turbines make generators move. Generators are machines that produce electricity.

    Engineers control the amount of water let through the dam. The process used to control this flow of water is called the intake system. When a lot of energy is needed, most of the tunnels to the turbines are open, and millions of gallons of water flow through them. When less energy is needed, engineers slow down the intake system by closing some of the tunnels.

    During floods, the intake system is helped by a spillway. A spillway is a structure that allows water to flow directly into the river or other body of water below the dam, bypassing all tunnels, turbines, and generators. Spillways prevent the dam and the community from being damaged. Spillways, which look like long ramps, are empty and dry most of the time.

    From Water Currents to Electrical Currents

    Large, fast-flowing rivers produce the most hydroelectricity. The Columbia River, which forms part of the border between the U.S. states of Washington and Oregon, is a big river that produces massive amounts of hydroelectric energy.

    The Bonneville Dam, one of many dams on the Columbia River, has 20 turbines and generates more than a million watts of power every year. Thats enough energy to power hundreds of thousands of homes and businesses.

    Hydroelectric power plants near waterfalls can create huge amounts of energy, too. Water crashing over the fall line is full of energy. A famous example of this is the hydroelectric plant at Niagara Falls, which spans the border between the United States and Canada.

    Hydroelectric energy generated by Niagara Falls is split between the U.S. state of New York and the Canadian province of Ontario. Engineers at Niagara Falls cannot turn the falls off, but they can severely limit the intake and control the amount of water rushing over the waterfall.

    The largest hydroelectric power plant in the world is the enormous Three Gorges Dam, which spans the Yangtze River in China. It is 185 meters (607 feet) tall and 115 meters (377 feet) thick at its base. It has 26 turbines and will be able to generate more than a billion watts of power. The Three Gorges Dam is operating, but engineers are still working on the system. They are adding even more turbines and generators to the project.

    Hydroelectric Energy and the Environment

    Hydroelectricity relies on water, which is a clean, renewable energy source. A renewable source of energy is one that will not run out. Renewable energy comes from natural sources, like wind, sunlight, rain, tides, and geothermal energy (the heat produced inside the Earth). Non-renewable energy sources include coal, oil, and natural gas.

    Water is renewable because the water cycle is continually recycling itself. Water evaporates, forms clouds, and then rains down on the Earth, starting the cycle again.


    Reservoirs created by dams can provide large, safe recreational space for a community. Boaters and water skiers can enjoy the lake. Many reservoirs are also stocked with fish. The area around a reservoir is often a protected natural space, allowing campers and hikers to enjoy the natural environment.

    Using water as a source of energy is generally a safe environmental choice. Its not perfect, though. Hydroelectric power plants require a dam and a reservoir. These man-made structures may be obstacles for fish trying to swim upstream. Some dams, including the Bonneville Dam, have installed fish ladders to help fish migrate. Fish ladders are a series of wide steps built on the side of the river and dam. The ladder allows fish to slowly swim upstream instead of being totally blocked by the dam.

    Dams flood river banks, destroying wetland habitat for thousands of organisms. Aquatic birds such as cranes and ducks are often at risk, as well as plants that depend on the marshy habitat of a river bank. Operating the power plant may also raise the temperature of the water in the reservoir. Plants and animals near the dam have to adjust to this change or migrate elsewhere.

    The OShaughnessy Dam on the Tuolumne River in the U.S. state of California was one of the first hydroelectric energy projects to draw widespread criticism for its impact on the environment. The dam, constructed in 1913, flooded a region called Hetch Hetchy Valley, part of Yosemite National Park. (The lake created by the OShaughnessy Dam is called the Hetch Hetchy Reservoir.) Environmental coalitions opposed the dam, citing the destruction of the environment and the habitats it provided. However, the power plant provided affordable hydroelectric energy to the booming urban area around San Francisco.

    The Hetch Hetchy Reservoir is still a controversial project. Many people believe the OShaughnessy Dam should be destroyed and the valley returned to its native habitat. Others contend that destroying a source of energy for such a major urban area would reduce the quality of life for residents of the Bay Area.

    There are limits to the amount of hydroelectric energy a dam can provide. The most limiting factor is silt that builds up on the reservoirs bed. This silt is carried by the flowing river, but prevented from reaching its normal destination in a delta or river mouth by the dam. Hundreds of meters of silt build up on the bottom of the reservoir, reducing the amount of water in the facility. Less water means less powerful energy to flow through the systems turbines. Most dams must spend a considerable amount of money to avoid silt build-up, a process called siltation. Some power plants can only provide electricity for 20 or 30 years because of siltation.

    Hydroelectric Energy and People

    Billions of people depend on hydroelectricity every day. It powers homes, offices, factories, hospitals, and schools. Hydroelectric energy is usually one of the first methods a developing country uses to bring affordable electricity to rural areas.

    Hydroelectricity helps improve the hygiene, education, and employment opportunities available to a community. China and India, for instance, have built dozens of dams over the past decade, as their development has quickly grown.

    The United States depended on hydroelectric energy to bring electricity to many rural or poor areas. Most of this construction took place during the 1930s. Dams were a huge part of the New Deal, a series of government programs that put people to work and brought electricity to millions of Americans during the Great Depression. The Bonneville Dam on the Columbia River, the Shasta Dam on the Sacramento River, and the Hoover Dam on the Colorado River are some dams constructed as part of the New Deal.

    The most famous hydroelectric power project of the New Deal is probably the Tennessee Valley Authority (TVA). The TVA constructed a series of dams along the Tennessee River and its tributaries. Today, the TVA is the largest public power company in the U.S., providing affordable electricity for residents in the states of Alabama, Georgia, Kentucky, Mississippi, North Carolina, Tennessee, and Virginia.

    However, hydroelectricity often comes at a human cost. The huge dams required for hydroelectric energy projects create reservoirs that flood entire valleys. Homes, communities, and towns may be relocated as dam construction begins.

    Egypt began construction of the Aswan Dam complex on the Nile River in 1960. Engineers realized that ancient temples of Abu Simbel were going to be flooded by the reservoir, called Lake Nasser. These monuments were built directly into cliffs several stories tall. The Abu Simbel temples are a part of Egypts cultural heritage and a major tourist destination. Rather than have the monuments flooded, the government of Egypt relocated the entire mountainside to an artificial hill nearby. Today, Abu Simbel sits above the Aswan Dam.

    Chinas massive Three Gorges Dam project will bring safe, affordable electricity to millions of people. It will allow hospitals, schools, and factories to work longer, more reliable hours. It will also allow people to maintain healthier lifestyles by providing clean water. Construction of the dam directly benefited workers, too. More than a quarter of a million people have found work with the project.

    However, the project has forced more than a million people to relocate. Lifestyles were disrupted. Many families were relocated from rural towns on the banks of the Yangtze River to Chongqing, a major urban area with 31 million residents. Other people were relocated out of the province entirely.

  • Term Part of Speech Definition Encyclopedic Entry
    adjust Verb

    to change or modify something to fit with something else.

    affordable Adjective

    reasonably priced, not expensive.

    ancient Adjective

    very old.

    ancient Rome Noun

    civilization founded on the Mediterranean Sea, lasting from the 8th century BCE to 476 CE.

    aquatic Adjective

    having to do with water.

    bank Noun

    a slope of land adjoining a body of water, or a large elevated area of the sea floor.

    Bay Area Noun

    region surrounding San Francisco Bay in the U.S. state of California.

    block Verb

    to prevent something from happening.

    Bonneville Dam Noun

    series of hydroelectric dams and locks across the Columbia River in the U.S. states of Oregon and Washington.

    bypass Verb

    to go around or skip.

    cite Verb

    to give as an example.

    cliff Noun

    steep wall of rock, earth, or ice.

    Encyclopedic Entry: cliff
    cloud Noun

    visible mass of tiny water droplets or ice crystals in Earth's atmosphere.

    Encyclopedic Entry: cloud
    coal Noun

    dark, solid fossil fuel mined from the earth.

    continual Adjective

    ongoing or repeating frequently.

    controversial Noun

    questionable or leading to argument.

    crane Noun

    large wading bird.

    cultural heritage Noun

    traditions and customs of a specific population.

    dam Noun

    structure built across a river or other waterway to control the flow of water.

    delta Noun

    the flat, low-lying plain that sometimes forms at the mouth of a river from deposits of sediments.

    Encyclopedic Entry: delta
    destination Noun

    place where a person or thing is going.

    developing world Noun

    nations with low per-capita income, little infrastructure, and a small middle class.

    diverse Adjective

    varied or having many different types.

    dozen Noun

    a group of 12.

    duck Noun

    aquatic bird.

    electricity Noun

    set of physical phenomena associated with the presence and flow of electric charge.

    employment Noun

    job or work.

    engineer Noun

    person who plans the building of things, such as structures (construction engineer) or substances (chemical engineer).

    environmental coalition Noun

    group of people or organizations who are united in defense of the environment or an environmental issue.

    evaporate Verb

    to change from a liquid to a gas or vapor.

    factory Noun

    one or more buildings used for the manufacture of a product.

    fall line Noun

    imaginary line along which parallel rivers plunge, or fall.

    Encyclopedic Entry: fall line
    fish ladder Noun

    series of steps overflowing with water, where fish can migrate upstream around a barrier such as a dam.

    flood Noun

    overflow of a body of water onto land.

    Encyclopedic Entry: flood
    flour Noun

    ground grain, usually of wheat.

    gallon Noun

    unit of volume equal to four quarts (3.79 liters).

    generate Verb

    to create or begin.

    generator Noun

    machine that converts one type of energy to another, such as mechanical energy to electricity.

    geothermal energy Noun

    heat energy generated within the Earth.

    grain Noun

    harvested seed of such grasses as wheat, oats, and rice.

    Encyclopedic Entry: grain
    Great Depression Noun

    (1929-1941) period of very low economic activity in the U.S. and throughout the world.

    habitat Noun

    environment where an organism lives throughout the year or for shorter periods of time.

    Encyclopedic Entry: habitat
    Herbert Hoover Noun

    (1874-1964) 31st president of the United States.

    hydroelectric energy Noun

    energy generated by moving water converted to electricity. Also known as hydroelectricity.

    Encyclopedic Entry: hydroelectric energy
    hydroelectricity Noun

    power generated by moving water converted to electricity. Also called hydroelectric energy or hydroelectric power.

    hygiene Noun

    science and methods of keeping clean and healthy.

    impact Noun

    meaning or effect.

    Industrial Revolution Noun

    change in economic and social activities, beginning in the 18th century, brought by the replacement of hand tools with machinery and mass production.

    intake system Noun

    process engineers use to control the flow of water through a dam.

    lumber Noun

    precisely cut pieces of wood such as boards or planks.

    marsh Noun

    wetland area usually covered by a shallow layer of seawater or freshwater.

    Encyclopedic Entry: marsh
    migrate Verb

    to move from one place or activity to another.

    mouth Noun

    place where a river empties its water. Usually rivers enter another body of water at their mouths.

    Encyclopedic Entry: mouth
    natural gas Noun

    type of fossil fuel made up mostly of the gas methane.

    Encyclopedic Entry: natural gas
    New Deal Noun

    (1933-1938) series of U.S. government programs intended to provide economic "relief, recovery, and reform" to Americans during the Great Depression.

    non-renewable energy Noun

    energy resources that are exhaustible relative to the human life span, such as gas, coal, or petroleum.

    obstacle Noun

    something that slows or stops progress.

    oil Noun

    fossil fuel formed from the remains of marine plants and animals. Also known as petroleum or crude oil.

    organism Noun

    living or once-living thing.

    power Noun

    ability to do work.

    province Noun

    division of a country larger than a town or county.

    Encyclopedic Entry: province
    public Adjective

    available to an entire community, not limited to paying members.

    quality of life Noun

    satisfaction with the material, cultural, and technological conditions of a region or population.

    rain Noun

    liquid precipitation.

    Encyclopedic Entry: rain
    recreational Adjective

    having to do with activities done for enjoyment.

    recycle Verb

    to clean or process in order to make suitable for reuse.

    reduce Verb

    to lower or lessen.

    relocate Verb

    to move a residence or business from one place to another.

    rely Verb

    to depend on.

    renewable energy Noun

    energy obtained from sources that are virtually inexhaustible and replenish naturally over small time scales relative to the human life span.

    reservoir Noun

    natural or man-made lake.

    Encyclopedic Entry: reservoir
    reuse Verb

    to use again.

    river Noun

    large stream of flowing fresh water.

    Encyclopedic Entry: river
    rural area Noun

    regions with low population density and large amounts of undeveloped land. Also called "the country."

    Encyclopedic Entry: rural area
    severe Adjective

    harsh.

    silt Noun

    small sediment particles.

    Encyclopedic Entry: silt
    siltation Noun

    process where sediment and silt build up on the bottom of a reservoir, reducing the amount of water it can hold.

    spillway Noun

    dam structure that allows excess water to flow directly into the river or other body of water below the dam.

    steel Noun

    metal made of the elements iron and carbon.

    stock Verb

    to supply.

    sunlight Noun

    visible radiation from the sun.

    temperature Noun

    degree of hotness or coldness measured by a thermometer with a numerical scale.

    Encyclopedic Entry: temperature
    temple Noun

    building used for worship.

    Tennessee Valley Authority (TVA) Noun

    largest public utility in the U.S.

    Three Gorges Dam Noun

    electrical power plant along the Yangtze River in China.

    tide Noun

    rise and fall of the ocean's waters, caused by the gravitational pull of the moon and sun.

    Encyclopedic Entry: tide
    tourist Noun

    person who travels for pleasure.

    tributary Noun

    stream that feeds, or flows, into a larger stream.

    Encyclopedic Entry: tributary
    turbine Noun

    machine that captures the energy of a moving fluid, such as air or water.

    upstream Adjective

    toward an elevated part of a flow of fluid, or place where the fluid passed earlier.

    urban area Noun

    developed, densely populated area where most inhabitants have nonagricultural jobs.

    Encyclopedic Entry: urban area
    water cycle Noun

    movement of water between atmosphere, land, and ocean.

    Encyclopedic Entry: water cycle
    waterfall Noun

    flow of water descending steeply over a cliff. Also called a cascade.

    Encyclopedic Entry: waterfall
    water mill Noun

    large mechanism powered by flowing water.

    watt Noun

    unit of power. Abbreviated w.

    wetland Noun

    area of land covered by shallow water or saturated by water.

    Encyclopedic Entry: wetland
    widespread Adjective

    affecting a large area or community.

    wind Noun

    movement of air (from a high pressure zone to a low pressure zone) caused by the uneven heating of the Earth by the sun.

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