When you hear the word "dam", you may first think that someone is trying to use a dirty word. However, they may just be talking about a structure that is used to control water. There are a lot of reasons for dams to be built. They range from creating a farm pond to flood control to creating reservoirs to creating power, like the Hoover Dam.  Just like there are different reasons, there are different kinds of dams.

Arch Dam

Odds are that the picture in your head of a dam is an arch dam. These dams are shaped like a huge arch, with the arch facing upstream to take the force of the water. An arch is a very strong shape. It's often used in construction because of that. It's no different in a dam. The force and weight of the water is spread out along the arch, and then into the abutments that anchor the dam on either side and are dug down into the earth. The Hoover Dam is an example of an arch dam.

Barrage Dam

Unlike most other kinds of dams. a barrage dam isn't used to retain or contain water, it's used for flood control. That's because these dams are made of several gates spread out horizontally. The gates are in-between the supports of the dam. The gates can be opened or closed in order to control the amount of water that goes downstream. They are used to smooth out the flow of the river. The gates may be open all the way when there hasn't been a lot of rain so that the river downstream continues to flow at a reasonable rate. 

Fill Dams

These dams come in two basic types, earth fill and rubble fill. They are either constructed of two parallel concrete walls that are filled with soil or rubble, or they are the basis construction material of the dam. If they are used as the construction material, an impermeable material is often used on the upstream side so that water can't leak through. 

Gravity Dam

The biggest feature of a gravity dam is the fact that is just too big and heavy for the water to move. They take advantage of the earth's gravity, using it to give the dam strength, and having the force of the water run down into the earth. It also uses the weight of the water that it's holding back in order to strengthen itself. Gravity dams are often combined with arch dams to create a very strong dam. 

There are several sub-categories of each kind of dam, but these are the basic kinds of dam.

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