Washington Week: Student Voices (O)

Land development partially to blame for Iowa flooding
By Christopher Patton
The Daily Iowan, U. Iowa
July 18, 2008

Iowa hasn't always been quite so flood-prone.

The state's native prairies originally absorbed most of the rainfall, but their development has led to increased runoff and flooding.

Wayne Peterson, an urban conservationist working for the Iowa Department of Agriculture and Land Stewardship, said the state's landscape processed rainwater quite differently before most of the natural habitats were developed into agricultural fields and urban areas. Peterson worked in the field of agricultural land conservation for more than 20 years before becoming involved with urban issues.

"Two hundred years ago, Iowa was full of prairies, savannas, and wetlands," he said. "The vast majority of the time when it rained, the rain infiltrated into the soil, moved through the soil matrix, and became part of the groundwater discharge into the river."

This process maintained a stable rate of water drainage, Peterson said, and Iowa's wetlands, streams, and rivers would not have seen water levels move quickly up or down nearly so frequently as they do now had the prairie remained intact.

Having written a book about the effect of development on Iowa's natural environment, Connie Mutel, historian and archivist of IIHR - Hydroscience and Engineering at the UI, agreed with Peterson that changes to the state's ecosystems radically altered how water drains from the soil.

"Iowa was 80 percent prairie, the heart of the tall-grass prairie," she said. "The prairie soils were very thick and extremely high in organic matter and mineral particles."

Those soil components held it together in small clumps that allowed for numerous air pockets between them, Mutel said, and the air pockets enabled the soil to act as a sponge and soak up significant amounts of water. However, killing the prairie grass and repeatedly plowing the soil collapsed those pockets, meaning the soil no longer absorbs water as it once did.

And with nowhere else to go, the water simply runs downhill and immediately enters the river system, she said. This causes water levels to rise more quickly and higher than they would have in a natural state, she said.

Lon Drake, a University of Iowa emeritus professor of geology, said changes in how water drains in the state call current floodplain maps into question.

"To make those maps, you measure and collect data over a long period of time," he said. "But the old data aren't really valid, because they apply to a different landscape that doesn't really exist anymore."

Mutel said the best way to repair Iowa's land would be to return 50 percent of it to native prairie.

But bringing back the prairie may not be politically or economically feasible.

"It's pretty hard to talk farmers into planting prairies when corn is so expensive," Peterson said. "A major social shift to no-till farming is the most realistic, fastest way to achieve results."

No-till farming would help curb runoff because it leaves more organic matter intact in and on top of the soil, he said, and this material absorbs water.

However, Peterson made clear he doesn't primarily blame farmers, saying that a more comprehensive study needs to be done to determine where runoff originates and find a way to absorb more of it at its sources. Everyone with land generating runoff is partially to blame for flooding at this point, he said.

"The bottom line is that we all have to work together," he said. "It's in all of our best interests to work on how to reduce peak flow."

E-mail DI reporter Christopher Patton at: chris-patton@uiowa.edu

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