What Are the Costs and Benefits of Damming a River?
ESU401  Damming of the Colorado River

To live comfortably, humans need a reliable source of fresh water. Many population centers depend on rivers for a steady water supply. In the arid climate of the western United States, though, water can be scarce. Long periods without rain can cause rivers to dry up, interrupting the supply of water. People learned long ago that by building a dam across a river, they could hold back some of the river's water and store enough to meet their needs through a dry season. Land upstream of the dam had to be abandoned because it flooded, and the river would change downstream too, because it received less water and fewer floods. But building a dam helped ensure a steady water supply.

Early in the 1900s, the limiting factor for development of land in the western United States was the availability of water. Damming the Colorado River, which drains snowmelt and rain from the western side of the Rocky Mountains, was seen as a solution. In 1922, the Colorado River Compact outlined a plan to build a series of dams along the Colorado River that would control floods and ensure a steady water supply for southwestern states.

Glen Canyon Dam under construction in 1957.

Construction of Glen Canyon Dam, just south of the Arizona/Utah border, began in 1957. When it was completed in 1964, it was proclaimed as a major feat of engineering. It created Lake Powell, the second largest man-made reservoir in the United States.

Imagine some of the environmental changes that could occur upstream and downstream from the dam when it was completed and began holding water on its upstream side.

1. List three positive and three negative aspects of damming rivers.


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