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Geology plays big role in levee breaches, study finds

By Rachel Lippmann, KWMU

St. Louis, MO – This summer's flooding led to several levee breaks along the Mississippi River, and data presented at a conference Tuesday says the geology beneath levees has a lot to do with whether they hold or fail.

Two-thirds of the 60 levee breaks in 2008 happened near locations breeched by floodwaters in 1993, said David Rogers, an associate professor of geological engineering at the Missouri University of Science and Technology. Rogers was part of a team that studied the levee breeches.

The team found that most of the levees that broke were built right at the river's edge and made primarily of gravel or sand, meaning they can't handle water flowing over them for long periods of time.

"We had some clay dikes out there that were overtopped for two weeks and survived without even losing the weeds," Rogers said.

Continual levee breeches at those locations are likely, he said, unless engineers create more places for the water to go on the floodplain, perhaps by buying up some of the agricultural land on the riverbank. "We've diked off too much of the floodplain to be able to handle these maximum events without having a lot of failures," he said.

Rogers's presentation was part of a day-long scientific conference on the impacts of changing the river and the surrounding floodplain on flood levels.