PHOTOS, VIDEO: Preserve is good example of how floodplains manage water

Naturally functioning Cedar River floodplains like the Swamp White Oak Preserve in Muscatine County can improve water quality and reduce flood damage, say scientists studying the rare ecosystem's hydrology.

The 700-acre preserve's effective cleansing and retention of floodwaters could serve as a model for flood plain restoration projects along the 300-mile course of the Cedar River, said Keith Schilling, a hydrologist with the Iowa Geological Survey.

“We would see a huge improvement in water quality and a steep reduction in the height of floods” if the Cedar River were reconnected with its flood plain, said Schilling's collaborator, Grinnell College associate biology professor Peter Jacobson.

In most reaches, the Cedar has been effectively cut off from its flood plain by agricultural practices and urban development. While it may be impractical in cities to leave large capital investments unprotected by flood walls, “we ought to pull back from the river where we can and let its flood plain function naturally,” Jacobson said.

Since 2004, Jacobson and Schilling have been studying the Cedar flood plain at the Swamp White Oak Preserve, an open savanna dominated by swamp white oak and bur oak trees growing in a sand terrace west of the river.

Understanding how the region's geology, topography and vegetation affect flooding can help determine how to restore flood plain habitat and natural water systems for maximum environmental and public benefit, they believe.

In agricultural watersheds like the Cedar's, Jacobson and Schilling have found that natural floodplains sharply reduce levels of nitrogen and phosphorus, improving river water quality.

Their observations also show that flooding at the preserve occurs over land and through the water table - an indication of the porous nature of the surface and the preserve's ability to hold excess water above and below ground.

The project is supported in part by a $100,000 grant from the Alliant Energy Foundation.

Video by Jim Slosiarek

“Our interest, apart from just being good stewards of the environment, is to increase understanding of flood plain management as a means to minimize damage from future floods,” said Elliot Protsch, Alliant Energy chief operating officer.

During the Cedar's record flood in June 2008, water covered the preserve, which extends more than a mile from the river, to a depth of 12 feet. Even naturally functioning floodplains are not immune to flood-caused damage, said Matt Fisher, East Iowa project manager for the Nature Conservancy, which owns the Swamp White Oak Preserve.

Floods of that magnitude jeopardize some of the preserve's rarest species, such as the stinkpot turtle, Illinois mud turtle, smallmouth salamander and massasauga rattlesnake. Fisher said last year's flood has also hastened the spread of reed canary grass, an invasive species that threatens the preserve's more than 320 documented plant species.