Drying of the American West
Part A: Reservoirs on the Colorado River
The Colorado River drains a huge area of the arid southwestern United States. While the source of much of its water is from the high forests on the western side of the Rocky Mountains, the main river flows through desolate canyons and dry desert areas. By building dams across the river, we have been able to hold back some of the water that would otherwise flow downstream. The result of each dam is a reservoir of "saved" water that can be tapped as it is needed. The mighty river that carved the Grand Canyon is now responsible for providing water for growing numbers of people and agriculture across the southwest.
- Click the map image, left, for a larger view. Examine the map to get familiar with the location and setting of the Colorado River Watershed. Focus in on the locations of the large reservoirs formed by Glen Canyon Dam (Lake Powell) and Hoover Dam (Lake Mead).
- Skim through the press release titled Lake Mead Could Be Dry by 2021. The article is a synopsis of a scientific paper. Look for the main ideas, including the reasons that the authors conclude are responsible for the water deficit.
- Read How Low Can It Go? (Acrobat (PDF) 2.1MB Jul10 08), a 3-page article from the journal Southwest Hydrology. Pay particular attention to the graphs that show the elevation (a measure of how full reservoirs are) of Lake Powell and Lake Mead over time.
The image on the right shows a portion of Lake Powell in the fall of 2003, a time when the reservoir was filled to just 35 percent of its capacity. The whitened canyon walls or "bathtub ring" above the water indicates the reservoir's highest level. Photo courtesy of U.S. Bureau of Reclamation Lower Colorado Regional Office.
Stop and Think1. Consider what the "squiggly lines" on the graphs of page 2 in the "How Low Can it Go?" article really mean... Use the graph of Lake Mead levels to describe a brief history of the reservoir. Tell when and how the reservoir got started, how long it took to fill, and mention events that affected its level.
2. Beginning in 1964, how long did it take to capture enough water to fill both of the large reservoirs?
3. The levels of Lake Powell and Lake Mead both show steep declines in the past decade. What are the two things that control the level of a reservoir?