Future Preparedness Lessons Found in Intentional Flood to Spare Illinois Town

Climate researchers used the intentional breach of a levee in near Cairo, Ill. in 2011 to get what they called a "once-in-a-lifetime" chance to study the damages of river flooding.

The levee was destroyed by the US Army Corp of Engineers to divert rising water in the Mississippi and Ohio rivers, which posed a threat to the town of Cairo. As a result, about 130,000 acres of Missouri farmland were inundated, creating the largest flood of the lower Mississippi ever recorded.

Writing in the journal Environmental Science and Technology, researchers from the University of Illinois report that landscape vulnerabilities can be mapped ahead of time to help communities prepare for extreme flooding.

"There is overwhelming scientific evidence that the characteristics of extreme rainfall under climate change are going to be different," said Praveen Kumar, a professor of civil and environmental engineering at Illinois and project leader on the study. "Forecasts of extremes of rainfall and flooding are not sufficient. The most urgent need is appropriate preparedness based on scientific assessment of landscape vulnerability."

The 2011 decision to breach the levees and allow farmland to be flooded was controversial because the land is agriculturally valuable and several hundred people lived along the floodplain, said the study's lead author Allison Goodwell.

By activating the Birds Point-New Madrid (BPNM) Floodway, floodwater was diverted for 35 miles before it was directed back to the Mississippi River.

"The consensus with BPNM is that it worked really well," Goodwell said. "It had a pretty immediate impact of lowering the levee stages all around the area."

Goodwell and her colleagues used sensors along the floodplain and LIDAR data from pre- and post-flood times to analyze erosion and deposition from the flood. The team also used a two-dimensional flow model, soil characteristics and information about vegetation to analyze the vulnerability of the landscape compared with observed impacts. They also compared sites that were heavily affected due to the flow with those that were not.

"You don't get the chance to do these huge-scale experiments very often," Goodwell said. "You could never do something like this in a lab. This was a chance to assess landscape impact and then back-predict that so before the next flood we have an idea of areas that might need protection. It can be broadly applied to areas along the Mississippi River basin or any area."