Mississippi and Missouri River flood levels unde...( When it comes to calculating flood risk...)

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 doesnt 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.

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Contact: Ann Cairns
acairns@geosociety.org
303-357-1056
Geological Society of America
3-Apr-2002

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