The Colorado River flows from the Rocky Mountains in Colorado through the southwestern United States. Along its route, the river passes through an elaborate water-management system designed to tame the yearly floods from spring snowmelt and to provide a reliable supply of water for residents as far away as California. The system is both appreciated for the water it provides and criticized for the environmental and cultural losses it has created.

Among the dams on the Colorado is Glen Canyon Dam in Arizona, which creates Lake Powell—a deep, narrow, meandering reservoir—upstream in southern Utah. In the early twenty-first century, this modern marvel of engineering faced an ancient enemy: severe, prolonged drought in the American Southwest. Combined with water withdrawals that many believe are not sustainable, the drought has taken its toll on the water level in Lake Powell over the past decade.

NASA’s Landsat 5 satellite captured this series of natural-color images of the reservoir between 1999 and 2009. The images show the northeastern reaches of Lake Powell, where it fills Glen Canyon and connects with the Colorado River, flowing from the east, and the Dirty Devil River, flowing from the north (at normal water levels, both rivers are essentially part of the reservoir). The southward-reaching finger of land in the right half of the images is Mille Crag Bend; the Colorado River flows around the bend en route to Lake Powell. Sunlight brightens plateaus and southeast-facing slopes, casting shadows on the northern and western faces of the rugged landscape.

In the image acquired on March 25, 1999, water levels in Lake Powell were relatively high. Lake Powell, including the branch into Dirty Devil Canyon, was dark blue, a sign that the water was relatively clear. Flowing into Lake Powell, the sediment-filled Colorado River appeared green-brown. In the image acquired on April 20, 2000, the brownish hue extended deep into Lake Powell. Only in the south did side branches of the reservoir still appear deep blue. Lake levels, however, appeared roughly as high as in the previous year.

In the image acquired on April 23, 2001, Lake Powell appeared to have less sediment than in 2000 (the waters are more greenish than brownish), but lake levels had dropped slightly. The change is easiest to see in the side branches of the reservoir; all had thinned, and the side branch pointing toward the northwest (called North Wash) had even shortened slightly. The Dirty Devil Canyon appeared in earth tones. (At low water levels, the Dirty Devil River can be too narrow for Landsat to detect.) The image acquired on May 12, 2002, documented further drying, with more of the reservoir retreating from the canyon walls.

Dry conditions and falling water levels were unmistakable in the image from April 13, 2003. Lake Powell’s side branches had all retreated compared to the previous year’s extents. Water levels in Narrow Canyon had dropped enough to show canyon floor features not visible in earlier images. In the image acquired on May 1, 2004, water levels in Lake Powell had dropped enough to isolate the reservoir’s northwestern branch, where shallow water could not crest raised areas in the lake bed.

Lake Powell’s water levels plummeted in 2005, according to the U.S. Department of the Interior Bureau of Reclamation, and the lowest water levels seen in this time series appear in the image from April 2, 2005. In this image, the northwestern side branch of Lake Powell remained cut off from the rest of the reservoir. In the main body of Lake Powell, water pooled along its eastern edge, while the western portion showed large expanses of dry canyon floor.

Slight recovery showed in the image from April 26, 2006, as water filled much of the main body of Lake Powell. The northwestern arm, however, was still cut off from the reservoir, and the water in the reservoir appeared muddy brown. Water had risen enough to reconnect the northwestern branch to the main reservoir by May 17, 2007.

By April 26, 2008, water levels had once again dropped, although not to the same levels as observed in 2005. By April 13, 2009, however, water levels had significantly rebounded. Lake Powell’s northwestern branch was once again connected to the main reservoir, and water filled Dirty Devil Canyon and Narrow Canyon.

According to the U.S. Department of the Interior Bureau of Reclamation, Lake Powell’s water level hovered around 20 million acre-feet in 2000 (an acre-foot is a volume of water sufficient to cover an acre of land in a foot of water). By 2005, it had dropped to roughly 8 million acre-feet. Water levels rebounded somewhat over the next two years. As of mid-March 2009, conditions were projected to be slightly drier in 2009 than in 2008, but this was before significant snowfall around the Colorado River’s headwaters beginning in late March 2009. This springtime snowfall promised to provide ample water to the Colorado River in the short term. A 2007 report from the U.S. National Research Council, however, projected the American West could experience even worse droughts than the dry conditions seen from 2002 to 2005.

1. References

2. Committee on the Scientific Bases of Colorado River Basin Water Management, National Research Council. (2007). Colorado River Basin Water Management: Evaluating and Adjusting to Hydroclimatic Variability. National Academies Press. Accessed May 7, 2009.
3. Earth Observatory. (2004, December 12). Glen Canyon Dam. Accessed May 6, 2009.
4. Earth Observatory. (2007, October 17). Water Levels in Lake Powell. Accessed May 6, 2009.
5. Earth Observatory. (2009, March 30). Spring Snow Brings Moisture to Colorado Front Range. Accessed May 6, 2009.
6. Stokstad, E. (2007, February 21). Western drought: The worst is yet to come. ScienceNOW. Accessed May 6, 2009.
7. U.S. Department of the Interior Bureau of Reclamation. Upper Colorado Region Water Operations: Current Status: Lake Powell. Accessed May 6, 2009.
8. Wikipedia. (2009, May 3). Colorado River. Accessed May 6, 2009.

1. Links

2. Earth Observatory. (2004, August 6). Rainbow Bridge. Accessed May 6, 2009.
3. Riebeek, H. (2007, May 11). Global Warming. Accessed May 6, 2009.
4. Drought Monitor Classification Changes for Selected Time Periods. Accessed May 6, 2009.