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Study shows more Missourians are vulnerable to river flooding than previously estimated

Arnold residents pile sandbags over a manhole to try to prevent sewage from mixing with floodwater. May 2017
File photo | Carolina Hidalgo | St. Louis Public Radio
A new study from The Nature Conservancy and University of Bristol shows that more people in Missouri and the continental U.S. are at risk from heavy rains and river flooding than previously measured by regulatory flood maps.

More people in Missouri are at risk of experiencing damage from heavy rainfall and river flooding, according to a study released Wednesday.

Researchers from University of Bristol, The Nature Conservancy and the Environmental Protection Agency found that about 41 million Americans are vulnerable to river flooding. That’s three times what Federal Emergency Management Agency maps estimate. The paper’s authors used a model that analyzed flood risks throughout the entire United States, whereas the FEMA maps cover only 60 percent of the land.

In Missouri, nearly half a million people are vulnerable to flooding — a nearly 25 percent increase over previous estimates — said Steve Herrington, director of freshwater conservation at the Missouri chapter of the Nature Conservancy. The study, published in the journal Environmental Research Letters, noted that factors such as climate change could make large flooding events more frequent.

The results are unsurprising, especially after residents along the Meramec River experienced damages after record flooding in December 2015 and May 2017, said David Stokes, executive director of the Great Rivers Habitat Alliance.

“I can’t tell you how many people we’ve met in the past two, three years who got severe flood damage who were told they were well out of the floodplain,” Stokes said.

The study also projected that the number of people at risk of being flooded by rivers will continue to rise. “[M]ore frequently inundated areas are experiencing faster population growth than less frequently inundated ones,” the authors wrote. “In other words, the more-hazardous areas in the floodplain are projected to experience a higher population growth rate than the floodplain as a whole.”

Floodplains tend to be attractive areas for developers to build, Stokes said.

“The land’s cheap, flat and generally easy to build on,” Stokes said. “For some strange reason, governments fall all over themselves to subsidize [floodplain development], which is completely immoral and offensive, but cities want to do it constantly.”

That eventually comes at a cost to people who choose to live in areas that are at risk of being flooded.

“We’ve got millions and millions of dollars worth of assets that are affected each year by flooding in these areas, not to mention the loss of homes and human lives,” Herrington said. “And I think our status quo for flood risk management in these communities is not working in the way it needs to.”

Communities have historically dealt with river flooding by building levees, a natural or artificial wall that prevents the overflow of the river from inundating people and properties.

The study noted that its findings did not consider the influence of levees on flood risk. “The USACE National Levee Database is incomplete, meaning that some of the areas we have identified as most at risk may be ‘false alarms’ where people and assets are actually defended from flooding,” researchers wrote.

However, levees can push flooding to other communities downstream, said Herrington. Some environmentalists and residents in St. Louis County have suspected that the levee in Valley Park contributed to increased flooding in the neighboring areas of Eureka, Fenton and Arnold. Further up the Mississippi, the Army Corps of Engineers’ Rock Island District released a study that indicated a significant portion of levees between northern Missouri and central Iowa were illegally raised. The Corps of Engineers is still working on its study to determine the effect levee heights have had on flooding along the Mississippi.

Herrington said that he would like to see parks built or wetland restoration in areas that experience frequent inundation.

“We, as taxpayers, we just can’t afford to keep building in these areas that are continually subject to flooding,” Herrington said. 

Follow Eli on Twitter: @StoriesByEli

Eli is the science and environment reporter at St. Louis Public Radio.