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How do Dams Work?

A dam allowing water through.
A ship going through a lock at the Three Gorges Dam, the world's largest hydroelectric dam.
The Hoover Dam.
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  • Written By: A Kaminsky
  • Edited By: Niki Foster
  • Images By: Belinda Pretorius, Harvey Barrison, Nofear4232
  • Last Modified Date: 28 July 2014
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Dams are one of humanity's oldest innovations. People may have borrowed the idea from the beavers, but human ingenuity has taken dam-building to incredible heights. These structures serve many functions: flood control, navigation, water supply, power generation and even recreation.

Essentially, dams are edifices, usually built of concrete, on a river to back up the water on one side. Depending on its purpose, it may have locks and a series of gates, called spillways, or it may have only a powerhouse and turbines. A good example of ones that serve all the aforementioned functions are those in the Tennessee Valley Authority system in the Southeastern United States. Many of the TVA dams have become vital parts of the river's ecosystem.

One hundred years ago, the Tennessee River was wild and narrow, running its 600 or so miles (around 965 km) from east Tennessee, down through northern Alabama, and then turning north, back into western Tennessee, before it emptied into the Ohio River in Paducah, Kentucky. The river flooded every spring, and the treacherous shoals in northwest Alabama made navigation hazardous. With the advent of the Tennessee Valley Authority, and the building of the dams on the river, the Tennessee became one of the country's largest shipping routes.

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Dams that assist in navigation have locks and spillways, which also aid in flood control. A lock is a gated chamber built on one side of the structure. Using gravity, the lock can be filled from the water above the dam, and emptied into the water below it. Boats can then navigate through the locks and continue on their journeys.

Spillways are gates built into the dams. They open and close, allowing water through, in order to lower the lake level above the structure. This aids in navigation because it helps keep a constant water depth in the main river channel. It also helps with flood control, since too much water from one portion of the river can be moved to other parts of the river that are not in danger of flooding.

Power generation is another primary purpose of dams. Water flows through the turbines, which turn the generators to produce power. The kinetic energy needed to turn the turbines comes from the force of the water falling into the turbines and turning their blades to power the generators. Hydroelectric power is much cheaper and more environmentally sound than many other generation methods.

Recreation on a river also profits from these structures. Again, since they keep the water level consistent, boaters and fishermen can count on safe water levels for their activities. The environment may also benefit, since lake levels can be lowered in the winter, for example, exposing mud flats and other land that helps support waterfowl wintering in the area. Dams also help keep water supplies steady, which is crucial in drought periods.

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Discuss this Article

amypollick
Post 12

@anon322042: The article explained it pretty clearly, I thought. Different dams serve different purposes. They *all* back up water behind the dam to form deep lakes. When the dam is finished, the river water quickly backs up behind the dam, flooding a large area around it.

From there, what happens next depends on the purpose. Some dams generate power, some control water levels and provide flood control, some assist in navigation, and some do all three.

anon322042
Post 11

But my question is what does the dam actually do? Like from start to finish?

chicada
Post 8

Why is the Hoover Dam at risk of shutting down? I live in California and I know that we get some of our water and power from the Hoover Dam Project. There is talk that if the dam shuts down, we will see something like a 20% increase in the cost of water and or electricity. This is potentially going to happen as soon as the next couple of years if something is not done. Can someone help me understand what is going on with the Colorado River and the Hoover Dam?

googie98
Post 7

@christym: If ever you get the opportunity to visit the Hoover Dam, it would be well worth it. It is a sight to see. The chief engineer, Frank Crowe was given the nickname “Hurry Up Crowe” because the dam was completed two years ahead of the anticipated finish date.

The Hoover dam was finished in 1935 and is 726 feet high, 45 feet thick at the top and 660 feet at the bottom. It is filled with over 3 million cubic yards of concrete.

While the dam was being built, the lowest paid workers made 50 cents an hour and the highest paid was $1.25 an hour.

Hoover Dam is named after Herbert Hoover, the country’s 31st president. The names “Boulder Canyon Dam” and “Boulder Dam” have also been used in reference to the dam.

christym
Post 6

Kudos to all of you who provide such great info! I am doing a science project on the Hoover Dam and I am looking for a little more info. Thanks in advance.

dega2010
Post 5

@momothree: Hoover Dam is located in Black Canyon which is right outside Las Vegas, Nevada. It has been named one of the Top 10 Construction Achievements of the 20th century.

Tourists can tour the dam for a fee of $30 per person. They do not allow children under the age of 8 to tour the dam and it is not accessible to wheelchairs.

momothree
Post 4

Where exactly is the Hoover Dam?

anon80439
Post 2

This helped.

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