Flood reduction through wetand restoration: the Upper Mississippi River Basin as a case history.

Synopsis: This article outlines how wetlands can significantly reduce flooding in the Upper Mississippi watershed. The authors first provide a historical context by estimating the original and lost wetland storage capacities of the Upper Mississippi and Missouri River Basins. Historically, about 10% of the basin would have been classified as wetland in 1780. By 1980, wetland acreage had been reduced to only 4% of the basin, representing about 26 million acres of wetlands eliminated since 1780. The area of wetland restoration required to reduce the risk of future flooding adequately was estimated based on the total amount of excess floodwater beyond bank-full discharge that passed through the City of St. Louis during the major flood event of 1993. Next, the approximate area of upstream wetlands that could have accommodated an equivalent volume of water was estimated. The authors conclude that by restoring 13 million acres of upstream wetlands within the watershed (approximate depth=1m), flooding would be adequately controlled. The authors therefore recommend that 7% of this watershed should be in wetland cover to provide adequately control flooding. Related water quality benefits of this amount, including lower turbidity, excess nutrients, and toxic substances were also described, as supported by research at the Des Plaines River Wetlands Demonstration Project, Illinois.