All About Dams

People build dams to control water—to make sure the right amount is at the right place at the right time.

River water rises behind dams, forming artificial lakes called reservoirs. The stored water can be used to generate electricity or to supply water for homes and industries, for irrigation or for navigation. Reservoirs also are good places to fish, swim and play.

How are Dams Built?

Engineers use models and computers to figure out how much water a dam will have to support and how big and strong it must be. Then they can decide what sort of dam to design.

There are four main types of dams:

• Embankment dams are the most common type in the United States. They are massive structures made of earth and rock that rely on their heavy weight to resist the force of the water. A layer of clay or concrete may be used to stop leaks through gaps in the rocks. TVA’s Cedar Creek Dam is an embankment dam.
• Gravity dams are concrete dams that also hold back the water entirely by their own weight. Usually the side of the dam that faces the oncoming water is straight. Most gravity dams are expensive to build because they require so much concrete. TVA’s Norris Dam is a gravity dam.
• Buttress dams have a series of supports, or buttresses, that brace the dam on the downstream side. Buttress dams may be flat or curved. Most are made of reinforced concrete. There are no buttress dams in the TVA system.
• Arch dams are good for narrow, rocky locations. Their curved shape holds back the water in the reservoir. Arch dams are thin and require less material than any other type of dam. There are no arch dams in the TVA system.

Do Dams Ever Break?

If a dam is well designed, it will be strong enough to hold back the water behind it, whatever happens. But tragic accidents still occur, often caused by the unimaginable power of natural forces such as earthquakes, landslides or floods.

The worst dam disaster happened over a century ago. A huge dam in Johnstown, Penn., burst in 1889, killing more than 2,200 people.

More recently, in 1976, the Teton Dam in Idaho broke as the reservoir behind it was being filled for the first time. Eleven people were killed. The Teton Dam disaster resulted in new government rules to ensure that dams are safe.

Dam Safety at TVA

Every TVA dam is checked regularly to make sure it that it is safe and the equipment used to operate it is working properly. Read more about dam safety at TVA.

Because many of these dams were built in the 1930s, TVA has had to do a lot of work on them to make sure that they meet modern safety regulations. These ensure that TVA’s dams can stand up to the biggest flood or earthquake that we would ever expect to see in the Tennessee Valley.