Homework - Environmental Issues with Dams - Caleb Guesno | Library

Most of the human activities that require water, require freshwater. Of all the water on Earth, freshwater makes up only 3 %. Traditional sources of freshwater include ground water, lakes, rivers, and other surface water. As the human population increases, some natural systems are pushed beyond their limits.

Changing the Flow of Surface Water People worldwide depend on sources of freshwater for their water supplies. Another method to obtain water is through dams. Streams and rivers are often dammed to create reservoirs that store water.

The large concrete structure shown to the right is the Hoover Dam in Nevada. The dam was built to control water flow and flooding along the Colorado River. Notice the large reservoir, Lake Mead, behind the dam. Freshwater from Lake Mead is used for recreational purposes, drinking water, irrigation, and hydroelectric power.

But dams can also have negative consequences on the environment and the biodiversity of ecosystems around the river. Dams can increase the rate of erosion along the banks of the streams. They also act as a geographic barrier for migratory fish. Because of dams, some rivers, such as the Colorado River, are nearly dry before they reach the ocean.

While dams can have positive effects for humans and other organisms living upstream, dams have many negative effects, particularly on ecosystems downstream of the dam.

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Environmental Issues Associated with Dams
Dams hold the promise of a nearly constant supply of electrical power with no associated emissions of greenhouse gases or toxic contaminants. They have some advantages compared to other ways of generating electricity, such as the ability to rapidly change the amount of electricity being generated, which reduces the amount of energy lost.

Unfortunately, dams have negative effects on the environment. When filling the reservoir any land located in the area where the reservoir will be, such as farm land, houses, or cities can be destroyed. The flooding will also destroy all the existing vegetation and animal habitat in that area.

Dams also interfere with the natural river dynamics, changing the natural flow patterns such as creating a more consistent flow. A dam traps sediment carried by the rivers and streams flowing into the reservoir, and the reservoir will eventually fill up with sediment. This blockage deprives the downstream river of sediment and associated nutrients. This can cause erosion and drastically change the downstream habitat, as clear, cold water from the depths of the reservoir replaces the warmer, muddy water that flowed down the river before the construction of the dam.

Dams are also lethal for migratory fish, such as salmon. Adult fish are blocked from migrating to upstream spawning areas. Juvenile fish die if they go through hydroelectric turbines.

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