Tuesday, June 23, 2015
Changes in the northeastern reaches of Lake Powell are documented in this series of natural-color images taken by the Landsat series of satellites between 1999 and 2015. The Colorado River flows in from the east around Mille Crag Bend and is swallowed by the lake. At the west end of Narrow Canyon, the Dirty Devil River joins the lake from the north. (At normal water levels, both rivers are essentially part of the reservoir.) Sunlight brightens plateaus and southeast-facing slopes, casting shadows on the northern and western faces of the rugged landscape. (Due to the angle of sunlight, this image may cause an optical illusion known as relief inversion.)
At the beginning of the series in 1999, water levels in Lake Powell were relatively high, and the water was a clear, dark blue. The sediment-filled Colorado River appeared green-brown. In the early years of this image series, water levels began to drop. The declines were first apparent in the side canyons feeding the reservoir which thinned and then shortened. By 2002, the lake level had dropped far enough that the exposed canyon walls created a pale outline around the lake.
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, the reservoir’s northwestern branch is isolated from the main reservoir; the shallow water upstream could not crest raised areas in the lakebed.
Lake Powell’s water levels plummeted in early 2005, according to the U.S. Department of the Interior Bureau of Reclamation. 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 large expanses of dry canyon floor were visible in the west.