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Dams

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What is a dam? A dam is something that stops water from flowing in a stream. A plug. They can be big or small and are made from a variety of materials. But, most importantly, they must be strong enough to hold back the water. Build your own dam from Popsicle sticks in this Zoom activity.

How many types of dams are there? The PBS web site Building Big - Dams lists four major ones- arch, gravity, buttress, and embankment and describes the forces that operate on each. An arch dam, usually constructed in narrow, rocky places, is built in a curve facing the water. The water pushes against the dam, squeezing it and helping to hold it in place. A buttress dam consists of a slab and supporting buttresses or walls. The water pushes against the slab and the buttress or walls push back keeping the dam in place. An embankment dam is made of dirt and rocks and its heavy weight keeps the dam in place against the force of the water. A gravity dam is large and heavy with a wide base. The weight of the dam prevents it from toppling over.

The National Geographic web site Geoguide/Dams explores what factors need to be taken into considered before a dam is built and what impact a dam can have on the surrounding environment. For a real life example of what the National Geographic's web site is talking about, take a look at the PBS web site Great wall across the Yangtze . China is in the process of damming the Yangtze, a fifteen-year project. The web site states that "...When the dam becomes operational, over a million people will have been relocated, over a thousand archeological sites will be submerged beneath the reservoir, and endangered species may be driven to extinction..." Quite an impact.

As mention above, a dam has to hold back the water. But dams can leak or crack. Crackling dams looks into why dams crack. It is a very entertain site written on three levels - beginners, intermediate and advance. And this is not just idle theory. Dams do crack and several examples are given.

Like to visit a dam? It is just a click away. The Hoover Dam is an arch type dam built on the Colorado River during the depression in only five years. For additional information about the Hoover Dam, check out the PBS web site Hoover Dam.

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