7/8/2011 4 min read
University of Illinois researchers are studying the hydrologic and environmental effects of intentional flooding.
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When the U.S. Army Corps of Engineers saved the town of Cairo, Ill., from flooding in May by using explosives to breach a protective levee and divert the rising waters of the Mississippi and Ohio rivers, about 130,000 acres of Missouri farmland was inundated. Calling the intentional flooding a “once-in-a-scientific-lifetime” occurrence, University of Illinois researchers are studying the hydrologic and environmental effects to determine the extent of the damage and develop recommendations to inform such decisions in the future.
“This is the largest flood that the lower Mississippi has seen—ever,” said Civil and Environmental Engineering Professor Praveen Kumar, who is leading the study. “The 1927 flood was comparable, but the damage was not as extensive because there were not as many people living there.”
High water levels in the Mississippi and Ohio rivers resulted from excessive snowmelt after an unusually long and cold winter, followed by persistent rainfall throughout April. The Corps of Engineers breached a levee south of Cairo to activate the Birds Point-New Madrid Floodway, diverting the water for 35 miles before directing it back to the Mississippi at New Madrid, Mo. They later opened the Bonnet Carré and Morganza spillways in Louisiana to ease pressure on the New Orleans levee system. Both of those spillways are mechanically controlled structures.
Property damage and economic losses are one side of the story, Kumar said, but another perspective focuses on the effect the flooding has had on the environment and the changes it made to the physical landscape. Flood waters cause erosion, scouring of the land, and the deposition of materials like chemicals and organic material. The landscape and the river itself can be reshaped, Kumar said. In addition to documenting those effects, the researchers plan to study the difference between the more controlled levee breaches of the Bonnet Carré and Morganza spillways, which involved the activation of engineered structures, and the Bird’s Point levee breach, which had to be blasted through.
The team includes experts in hydrology, geography and geology, in collaboration with the U.S. Geological Service and the U.S. Army Corps of Engineers. Traveling by boat and helicopter, they are observing changes on the rivers and throughout the flood plain. Using LIDAR mapping, an optical remote sensing technology, the team is observing and recording physical changes in the landscape. They are detecting chemical and other material deposited by the flood waters using hyperspectral imaging provided by the NASA’s Airborne Visible/Infrared Imaging Spectrometer (AVIRIS) and collected soil samples. What researchers learn during the one-year study could help other communities facing decisions about the activation of floodways in the future, Kumar said.
“When you have events of this magnitude, which happens once in a 100 years or less frequently, it’s like nature conducting a very big experiment,” Kumar said. “It’s a very unique opportunity for scientists to go and collect information as to what such a large event does to the landscape.”
The study, “RAPID: Mississippi Flood of 2011—Investigation of Initial Impact on the Landscape” is being funded by the National Science Foundation program, Grants for Rapid Response Research (RAPID).
In addition to Kumar, collaborators include: Professor James Best, U of I Department of Geology; Professor Robert Darmody, U of I Department of Natural Resources and Environmental Sciences; CEE Professor Marcelo García; Adjunct Assistant Professor Jonathan Greenberg, U of I Department of Geography; CEE Adjunct Assistant Professor Robert Holmes, Hydrologist, U.S. Geological Survey; Visiting Postdoctoral Researcher Jeffrey Nittrouer, U of I Department of Geology; CEE Professor Gary Parker; Professor Bruce Rhoads, U of I Department of Geography; CEE Research Assistant Professor Arthur Schmidt; CEE Professor Murugesu Sivapalan; and Associate Professor Michelle Wander, U of I Department of Natural Resources and Environmental Sciences.
Photo: Erosion scour in the farmlands of the floodway at O'Bryan Ridge, Mo., arising from the floods. Large floods extensively alter the landscape.