Humans have been altering the environment to suit their needs for thousands of years. One significant type of alteration is the building of dams to stop or divert the flow of streams and rivers. We build dams to prevent downstream flooding, to create reliable sources of drinking and irrigation water, to generate power, and to provide recreational opportunities such as boating and fishing.

Humans are not the only animals to alter their environment by building dams. Beavers are master dam builders and because of their innate ability to create these highly effective structures, are sometimes referred to as nature's first engineers. Unlike humans, who must be taught or learn through trial and error how to design and build dams, beavers know instinctively how to interweave sticks to create a strong and durable structure, as well as how to seal a dam with mud to make it impermeable to water. Their lives depend on it. The ponds created by beaver dams provide refuge from predators as well as underwater access to food throughout the winter.

Beavers construct their dams using relatively simple techniques along with materials readily available in their environment. These techniques and materials are adequate for a dam created to hold back a small pond, especially if the builder is willing and able — as beavers are — to work constantly to maintain the dam. In contrast, constructing a dam capable of withstanding the force of millions of gallons of water requires more advanced materials and careful planning. Materials such as concrete and steel are highly resistant to forces that squeeze and stretch. They also can be shaped to fit a particular set of circumstances.

Determining what form a large dam will take and how it will be constructed requires careful planning. Engineers often use scale models and detailed drawings and calculations to help them determine which design and materials will work best for a dam in a particular situation. By doing so, they avoid large-scale experiments with various designs and materials, an approach that would be both costly and potentially dangerous.

The children featured in this video segment follow many of the steps engineers use to solve problems, including those that arise from their initial design solutions. In this case, one dam is collecting all of the water in the stream, leaving none for the dam downstream. The children need to find a way to create two pools from only one stream of water. This requires that they modify their original design so that the new upstream dam collects a portion of the water in the stream and lets the other portion continue to the downstream pool. By carefully assessing their initial design and the needs of others, the children are able to make small but important design modifications so that in the end everyone is happy.

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