The Wetlands Initiative estimates that restored wetlands and natural areas could store 39 million acre-feet of floodwaters -- the volume that caused the 1993 flood. This finding is reported in TWI's 2004 comprehensive study, Flood Damage Reduction in the Upper Mississippi River Basin: An Ecological Means.

Funded by the McKnight Foundation, the study looked in depth at data from 24 percent of the 100-year floodplain in Missouri, Iowa, Minnesota, Illinois and Wisconsin and identified 1.9 million acres that could be used to store emergency floodwaters. These areas are former or degraded wetlands or areas behind levees. (Leveed areas that protect more than 10 percent urban development were excluded from the study.) Researchers then extrapolated this known data to the 5-state region of the Upper Mississippi River Basin.

The study found that on average only about 7% of a county’s cropland is in the 100-year floodplain. Thus, the vast majority of a region’s cropland would remain in tact, even if all the cropland in the floodplain were restored to wetlands.

Restoring wetlands would increase bird diversity by 280%, as estimated by Audubon staff in this study. Currently 53 bird species use the existing cropland, but 145 species were estimated to use the restored wetland complex.

Tony Prato, economist at the University of Missouri at Columbia, estimated that society would save about $68 per acre by converting cropland to wetland and other native landscapes. Reducing flood damage and crop subsidy costs—while generating regional benefits in hunting, fishing, and recreation—would create the savings.

This is an unprecedented attempt to compile and analyze data from many sources across five states. Complete GIS data available as ArcView shapefiles is available on DVD for $20 by contacting The Wetlands Initiative.