In the decades that followed, that approach has both protected numerous heartland communities from high waters and created a false sense of security for people who have increasingly populated flood plains. It also has led to agonizing decisions whenever monumental floods have come.

Now, as the rivers fed by a massive late-winter “bomb cyclone” churn south, the nation’s patchwork flood protection system is once again revealing its strengths, its vulnerabilities and the constantly competing interests of farmers, city dwellers, wildlife and industry. The ongoing disaster unfolding in the Midwest also has revitalized the long-running debate over whether to continue to try to control rivers or to make more room for them to swell.

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On Thursday in Missouri, Mike Parson (R) became the latest governor to declare a state of emergency, following Iowa, Wisconsin and Nebraska, where 96 cities, 79 counties and four tribal areas had made similar declarations.

Even as floodwaters continue to rise, the National Oceanic and Atmospheric Administration warned Thursday that a devastating spring lies ahead.

“We expect the flooding to get worse and become more widespread,” Mary Erikson, deputy director of NOAA’s National Weather Service, told reporters. “The stage is set for record flooding now through May.”

Erikson said the flooding “could be worse than anything we have seen in recent years,” including the devastating floods in 1993 and 2011, considered among the worst in U.S. history.

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Because of river levels that are already high, hefty snowpack in the Northern Plains and above-normal soil moisture, “conditions are primed” for more flooding, said Edward Clark, director of NOAA’s National Weather Center. “This is potentially an unprecedented flood season,” he said.

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And the levee system is not centralized under one governing body.

According to the National Committee on Levee Safety, approximately 85 percent of the 14,685 miles of levees in the National Levee Database are operated by local sponsors, not the Corps of Engineers. And that database accounts for only a portion of the estimated 100,000 miles of levees across the United States, most of which are not part of any federal program.

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In 2017, the American Society of Civil Engineers gave the nation’s levees a “D” grade, saying that “as development continues to encroach in floodplains along rivers and coastal areas, an estimated $80 billion is needed in the next 10 years to maintain and improve” aging levee infrastructure.

Rob Moore, a senior policy analyst at the Natural Resources Defense Council and a flood insurance expert, said devastating floods like the ones in the Midwest often lead to understandable calls to further fortify river defenses by building bigger levees.

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Moore said that levees traditionally have been built to withstand certain thresholds, such as a 100-year or 500-year flood event. But parts of the country have seen epic floods more often in recent years, and scientists predict that climate change could fuel more frequent and intense flooding.

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“We build all these levees on those assumptions, and we make lots of development decisions on those assumptions,” Moore said. “But if the 500-year flood happens twice in 30 years, have you really provided the protection that’s promised? Absolutely not.”

There are no easy answers, he said, because of the development that has taken place in many flood plains.

“What should happen is we need to have real discussions about rebuilding versus, in some cases, unbuilding,” he said. “How do we help people move out of these areas that are prone to this type of flooding and that are going to be more vulnerable to these types of events as climate change gets worse?”

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For those affected by the rising waters, the result is a confluence of competing interests.

“The water has to go somewhere,” said John Barry, author of “Rising Tide,” which recounts the story of the 1927 Mississippi River flood. “And what creates a problem or benefit right in front of you is going to have a counterbalancing problem or benefit somewhere else.”

Nicholas Pinter, a professor of geology and flood researcher at the University of California at Davis, said the current flooding in the Midwest presents both success stories and failures of levees.

For instance, the town of Niobrara, Neb., was rebuilt in the 1970s and moved almost entirely off the flood plain, he said. If it were still in its old location, Niobrara would have been washed away by the failure last week of a dam.

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But Pinter said that many towns along the Missouri River that were flooded in 1993 and 2011 continued to rely on their levees rather than relocating residents. Numerous levees have already failed or overtopped this year in Missouri, Iowa and Nebraska, he said.

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“We need new strategies, including giving rivers room and moving people out of harm’s way,” Bob Irvin, president of American Rivers, a conservation group, said in a statement.

In some spots around the country, including along the San Joaquin and Sacramento rivers in California’s Central Valley, officials have shifted from trying to merely control floodwaters to a philosophy of managing risks by allowing rivers room to swell.

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“People assume levees will protect them,” said John Cain, conservation director for California Floodplain Management at American Rivers, “and federal and state policies are on autopilot to rebuild after a flood, perpetuating the cycle.”

In densely populated areas where levees need to be reinforced, such an approach can make sense, he said. But in rural areas, Cain has been working on alternatives, including setting levees further back from the river banks and turning some flood plains into wetlands, which can filter water and improve its quality.

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“Flood plains can be sports fields, agricultural land or wetlands,” he said. “But residential use is not a good risk-management strategy.”

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Few people patrol the levees with guns anymore. But the floods have continued to create hard choices and hard feelings.

When the water surged to historic heights in 1993, federal officials told Illinois farmer Jeff Lorton not to continue sandbagging the levee that protected his 3,000 hogs. He saved his livestock, but his farm and others nearby flooded, reducing the impact downstream. During severe floods in 2011, the Corps blew open a two-mile stretch of levee in Missouri, sacrificing some 130,000 acres of farmland to save more densely populated parts of Illinois.

For Pinter, such episodes under­score a mantra in his field.

“There are two types of levees,” he said. “Those that have failed and those that will fail.”