The Des Moines River in Iowa is rising higher and more often, which means floods like those that swamped the city in 1993 and 2008 are more likely to occur again than experts had previously estimated, according to a study released Jan. 20 by the U.S. Army Corps of Engineers.
“We want to let the people know that there is a greater risk of flooding,” said corps spokesman Ron Fournier.
After the 2008 flood, the corps requested funding for the study to increase its understanding of the river at the reservoirs at Saylorville Lake, north of Des Moines, and Lake Red Rock, in southern Iowa. The reservoirs were built using water flow information before the 1960s, Fournier said.
“The reservoirs still provide benefits for downstream from the reservoirs, but not as much compared to those old flows. The new flows means the reservoirs are going to get higher, more often,” he said.
Completed in November, the new study includes river gage data from 1917 to 2008. The most recent update before this study had been made after the 1993 flood using information from 1994.
But the current study does not address why the river is rising higher and more often.
“You may now be in a flood plain or a flood zone and you may not be protected by a levee that you thought you might have been,” Fournier said.
The next step, he said, will be to find ways to make the reservoirs more effective.
After the city came close to flooding last year, then-Gov. Chet Culver asked federal leaders to examine changes to flood management plans at Iowa’s four reservoirs, which also include Coralville and Rathbun lakes. The reviews could cost $8 million. Iowa has asked Congress to include the funding for a reservoir study in the corps’ budget for 2012.
Fournier said if the funding is approved, the corps will look at the reservoirs to determine the options.
“The new flows mean that it’s flooding more often and at higher elevations,” he said.
Fournier said the corps shared the study with local, state and federal officials. The Federal Emergency Management Agency will use the new data in a project to redraws flood maps in Iowa and across the country.
“It better reflects any changes that have been made since the last flood map revision, whether the flood plain has been widened, there’s more water rolling down the flood plain, that type of event,” said FEMA spokesman Josh deBerge.
Bill Stowe, public works director in Des Moines, said the corps’ study offers immediate information on the city’s levee system, which was tested during last summer’s flooding. Part of the system is being refurbished. Stowe says given the corps’ study, some revisions may be needed.
“We’re going to take heed the risk elevation that these reports are providing us and use it to provide greater protection to Des Moines residents,” he said.
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