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Midwest flood risks could be underestimated by five feet, study says

People pile sand bags to block the rising flash flood waters from Spy Run Creek in Fort Wayne, Ind. (Michelle Davies/The Journal Gazette via AP)

As states like California grapple with drought and water shortages, cities in the Midwest are facing the exact opposite problem: rising floods.

A new study published in the Journal of Earth Science says flood risk in the Midwest may be underestimated by as much as five feet, which could have a serious impact on flood insurance plans and development in the nation's floodplains.

Robert Criss, author of the study and  a professor at Washington University in St. Louis, warns that measurements for flood risk are "grossly inaccurate" because they are based on decades-old data and do not account for changes to watersheds, man-made river control systems and rising rivers due to climate change.

[California is burning again as its drought's vicious cycle takes its toll]

Rivers throughout the area, his study suggests, are swelling to record highs every year, skewing longstanding conceptions of flood risk, sometimes from as early as the mid-1800s.

"All this old data is being thrown in as if it's all the same," Criss said. "It's just wrong."

Flood risk has been measured by the National Flood Insurance Program since the 1960s based on "100-year floods." It's a complicated statistic, referring to a specific height a flood needs to meet or exceed to have a 1 percent chance of happening each year.

The 100-year flood concept was designed to balance the interests of protecting the public from floods and avoiding burdensome regulations. Most flood levees have been designed to withstand floods at 100-year levels, and the Federal Emergency Management Agency detail flood insurance maps based on those figures.

In St. Louis, for example, 100-year flood levels are about 46 feet, according to FEMA. But under Criss's analysis, which gives weight to modern river conditions, a 100-year flood event would actually reach 51.5 feet.

[Zoo animals loose in the streets after deadly floods hit Georgia]

The St. Louis flood wall was built in the 1960s at 52 feet to handle a volume last experienced in the city during 1844. In 1993, a massive flood reached within 2 1/2 feet of the wall system, which makes Criss question whether the city's wall would be able to handle another major flood any time soon.

The same goes for many other cities along the Mississippi, Missouri, Illinois and Ohio rivers, according to the study.

Any flood that rises a few inches above the levees has the potential to be catastrophic to a community, which is why Criss said flood insurance throughout the Midwest is "hopelessly underpriced."

The Midwest has been drenched by unrelenting rains throughout June, and forecasts say more rain is to come. Over the course of the next week, major and moderate flooding has been projected for areas along the Illinois, Mississippi and Wabash rivers, according to the National Weather Service, and in some areas, rivers are expected to exceed all-time records.

FEMA officials were unable to provide a comment by press time.

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