As drought continued to parch much of the United States in August 2012, the Mississippi River approached historically low water levels in several portions of its middle and southern reaches. As of August 20, a towboat and its barges had run aground in the main river channel, forcing its closure near Greenville, Mississippi. The grounding backed up shipping traffic—an occurrence that is becoming more frequent this summer—and left close to 100 vessels waiting for the channel to re-open and allow passage up and down the river.
The Advanced Land Imager (ALI) aboard the Earth Observing-1 (EO-1) satellite captured these views of the Mississippi River near Greenville on August 20, 2012. (The images are rotated so that north is to the left.) For scale, the barges and towboats are strung together into chains that can be up to 1,000 feet (300 meters) long and 100 feet (30 meters) wide. According to Steve Jones in the Vicksburg office of the U.S. Army Corps of Engineers, the grounding occurred about 6 miles (10 kilometers) south of the bridge that carries Route 82 across the river.
Many towboats and barges were tied up along the shores (top image), waiting for clearance to move north or south. Towboats must continually idle their engines while waiting, at a cost of nearly $10,000 per day according to Time magazine. Even before the closure, shipping traffic was limited to one vessel at a time due to the low water. The river last experienced similar closures during the drought of 1988.
The U.S. Army Corps of Engineers, which manages the Mississippi River, has been using dredges to try to move sand and keep the channels open, but only serious rainfall in the middle and upper Mississippi watershed will truly alleviate the problem. By law, the Corps is authorized to a minimum navigation channel that is 9 feet deep and 300 feet wide on the lower Mississippi River.
The Corps also builds and maintains rock dikes that are used to focus and increase the velocity of the low flow in order to provide an efficient channel for navigation, said Rick Robertson, also with the Army Corps. Several dikes are visible in the images above, sticking out into the river at right angles from the shore.
“The water is just so low this year that the dikes cannot provide the navigation channel without some dredging,” Robertson said. As of noon on August 22, 2012, the gauge at Greenville recorded a river stage of 7.62 feet, while the historic normal stage is 19.40 feet. One year ago, on August 22, 2011, the river stage was 26.92 feet.
Many sandbars are visible along the river’s edge; most are natural, though some form in the wake of dikes. “Sandbars are normal topography of the river,” said Jones. “They are just larger with extreme low water.” As the water level keeps falling, side channels are being cut off from the main flow, which can affect fish and wildlife along those old channels of the river.
NASA Earth Observatory image by Jesse Allen and Robert Simmon, using EO-1 ALI data from the NASA EO-1 team. Caption by Mike Carlowicz, with image interpretation from Rick Robertson, U.S. Army Corps of Engineers.