Saturday, July 02, 2005

How is the way to build a Dam ?

With the exception of the Great Wall of China, dams are the largest structures ever built. Throughout history, big dams have prevented flooding, irrigated farmland, and generated tremendous amounts of electricity. Without dams, modern life as we know it would simply not be the same.

Since the first large-scale dam was built in Egypt more than 5,000 years ago, engineers have devised various types of dams to withstand the forces of a raging river.


El Atazar Dam
Arch dam:
El Atazar Dam
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Arch Dams...
are good for narrow, rocky locations. They are curved, and the natural shape of the arch holds back the water in the reservoir. Arch dams, like the El Atazar Dam in Spain, are thin and require less material than any other type of dam.

How does the force work in the arch dam ?


Arch Dam: Forces
The arch squeezes together as the water pushes against it. The weight of the dam also pushes the structure down into the ground.




Image of the Bartlett Dam
Buttress dam:
Bartlett Dam
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Buttress Dams...
may be flat or curved, but one thing is certain: a series of supports, or buttresses, brace the dam on the downstream side. Most buttress dams, like the Bartlett Dam in Arizona, are made of reinforced concrete.


How does the force work in buttresses dam?


Buttress Dam: Forces
Water pushes against the buttress dam, but the buttresses push back and prevent the dam from toppling over. The weight of the buttress dam also pushes down into the ground.



Image of an embankment dam
Embankment dam:
New Waddell Dam
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Embankment Dams...

are the most commonly built dams in the United States. They are massive dams made of earth and rock. Like gravity dams, embankment dams rely on their heavy weight to resist the force of the water. But embankment dams are also armed with a dense, waterproof core that prevents water from seeping through the structure. Tailings dams -- large structures that hold back mining waste -- are a type of embankment dam.

How does the force work in the Embankment Dam?



Embankment Dam: Forces
Water pushes against the embankment dam, but the heavy weight of the dam pushes down into the ground and prevents the structure from falling over.




Grand Coulee Dam
Gravity dam:
Grand Coulee Dam
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Gravity Dams...
are massive dams that resist the thrust of water entirely by their own weight. Most gravity dams, like the Grand Coulee Dam in Washington, are expensive to build because they require so much concrete. Still, many people prefer its solid appearance to the thinner arch and buttress dams.





How does the force work in gravity dam?




Gravity Dam: Forces
Water pushes against the gravity dam, but the heavy weight of the dam pushes down into the ground and prevents the structure from falling over.


All dams -- whether they're embankment, buttress, arch, or gravity -- must be maintained as they get older. Without proper maintenance, spillways can clog and concrete can crack. Some dams are even removed because they block the migration of fish.

When should dams be taken down? When should they be repaired? Engineers must consider the services that each dam provides and the environmental impact that each dam creates before they make this decision -- and this isn't easy. Oftentimes, there is no right answer.


Sources: Building Big/http:www.pbs.org