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12.11: Hydroelectric Power

Difficulty Level: Basic Created by: CK-12
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What do dams do?

If you take a trip out of Las Vegas toward Phoenix you can visit the Hoover Dam. Completed in 1935, the dam provides power to over a million homes. It also stores water for use by the residents of the desert southwest. Hoover Dam is one of the engineering marvels of the 20th century.

Water Power

Water flowing through a dam.

Moving water has energy (Figure above). That energy is used to make electricity. Hydroelectric power, or hydropower, harnesses the energy of water moving down a stream. Hydropower is the most widely used form of renewable energy in the world. This abundant energy source provides almost one fifth of the world’s electricity. The energy of waves and tides can also be used to produce water power. At this time, wave and tidal power are rare.

Hydropower Plants

To harness water power, a stream must be dammed. Narrow valleys are the best for dams. While sitting in the reservoir behind the dam, the water has potential energy. Water is allowed to flow downhill into a large turbine. While flowing downhill, the water has kinetic energy. Kinetic energy makes the turbine spin. The turbine is connected to a generator, which makes electricity.

Hydropower as a Resource

Many of the suitable streams in the United States have been developed for hydroelectric power. Many streams worldwide also have hydroelectric plants. Hydropower is a major source of California’s electricity. It accounts for about 14.5 percent of the total. Most of California’s nearly 400 hydroelectric power plants are located in the Sierra Nevada mountains.

Benefits and Problems of Hydropower

Water power does not burn a fuel. So it causes less pollution than many other kinds of energy. Water power is also a renewable resource. Water keeps flowing downhill. Although we use some of the energy from this movement, we are not using up the water.

The Colorado River backs up behind Hoover Dam. See the river coming in at the top of the photo.

Water power does have problems. A large dam stops a stream's flow, which floods the land upstream (See Figure above). A beautiful location may be lost. People may be displaced. The dams and turbines also change the downstream environment. Fish and other living things may not be able to survive. Dams slow the release of silt. Downstream deltas retreat and beaches may be starved of sand. Seaside cities may become exposed to storms and rising sea levels.

Tidal power stations may need to close off a narrow bay or estuary. Wave power plants must withstand coastal storms and the corrosion of seawater.

KQED: Harnessing Power from the Sea

Although not yet widely used, many believe tidal power has more potential than wind or solar power for meeting alternative energy needs. Quest radio looks at plans for harnessing power from the sea by San Francisco and along the northern California coast. Learn more at: http://science.kqed.org/quest/audio/harnessing-power-from-the-sea/


  • Hydroelectric power is clean and is important in many regions of the world.
  • Hydroelectric dams change the river's ecosystem.
  • Hydropower utilizes the energy of falling water.


Use this resource to answer the questions that follow.

http://www.hippocampus.org/Earth%20Science \begin{align*}\rightarrow\end{align*} Environmental Science \begin{align*}\rightarrow\end{align*} Search: Hydroelectric Power

  1. How is hydroelectric power generated?
  2. What does the height of the water determine?
  3. How is the turbine rotated?
  4. What are the advantages of hydroelectric power?
  5. What are the disadvantages of hydroelectric power?


  1. How does energy change forms as it goes from behind a dam to downstream of a dam?
  2. How is hydroelectric energy collected?
  3. What are some of the downsides of using hydropower?

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Difficulty Level:
6 , 7
Date Created:
Jan 04, 2013
Last Modified:
Aug 29, 2016
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