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News Release April 3, 2002
GSA Release No. 02-17
Contact: Ann Cairns
Director – Communications and Marketing, 303-357-1056

Mississippi and Missouri River Flood Levels Underestimated

When it comes to calculating flood risk, human influences that magnify flood hazards are often overlooked. The standard methodology for calculating flood risks for all rivers in the U.S. does not recognize long-term change in the river system, such as from land-use change, climate shifts, or engineering structures.

Nicholas Pinter, a geologist at Southern Illinois University, has been using a new technique that isolates the effects of engineering modifications of rivers. Looking at the Mississippi and Missouri Rivers, he's found that the same quantities of water have systematically caused greater floods because of the effect of human structures built along these rivers. These constructions push flood stages higher than they normally would be and cause more severe floods more frequently.

"Engineers have harnessed rivers worldwide for navigation and flood control, but engineering structures can cause larger and more frequent floods," Pinter said. "For example, record breaking flood crests on the Missouri River in 1993 can be expected to occur every 15-20 years at some locations, rather than every 100-500 years as widely estimated."

The current official level for the 100-year flood in downtown St. Louis is 47.1 ft. But Pinter has recently discovered that this flood height needs to be raised about four feet. The Army Corps of Engineers, however, has provisionally advised lowering it by half a foot. They obtained their results by using the standard methodology that doesn't consider systematic change in flood behavior over time.

"The difference between our results and the new Corps number is about 4.5 feet in flood height," Pinter said. "That's a lot of water."

Pinter and one of his students, Reuben Heine, will present these new findings in their respective presentations on April 4 and 5 at the Geological Society of America's North-Central Section and Southeastern Section Joint Meeting in Lexington, Kentucky.

It has been difficult to estimate precisely what the human impact on flooding has been because the factors that create severe floods overlap and are difficult to separate from year-to-year weather variations. These forces and mechanisms include climate change that drops more water into the river system, land use changes that cause more runoff to reach streams more quickly, and engineering changes that lowers a river's capacity to transmit flood water efficiently.

— by Kara LeBeau, GSA Staff Writer

Contact information:

Nicholas Pinter
Dept. of Geology
Southern Illinois University
1259 Lincoln Dr.
Carbondale IL 62901-4324 USA
Phone: 618-453-7375
Abstract available at:
Reuben Allan Heine
Environmental Resources and Policy
Southern Illinois University
Carbondale IL 62901-4637 USA
Phone: 618-453-7384 Heine
Abstract available at:

Geological Society of America
Southeastern Section and North-Central Section Joint Meeting
April 3-5, 2002
Hyatt Regency Hotel and Lexington Civic Center
Lexington, KY

For information and assistance during the meeting, please see the media assistant at the GSA registration table or call (859) 253-1234.


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