Yet that hasn’t stopped the city from planning a $1.5 billion riverfront development along the Missouri’s banks, 120 acres of upscale shops, restaurants and apartments mostly in the river’s flood plain, an area that has been partly submerged this summer.

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Several hundred miles to the south, Louisiana is experiencing the fallout from decisions like that one — decades of rampant development behind tall levees that have cut the Mississippi and its many tributaries off from the vast open floodplains the rivers once carved for themselves. Tropical Storm Barry, which made landfall Saturday as a hurricane, is predicted to travel up the Mississippi toward St. Louis, deluging surrounding areas as it goes, with rainfall that will be channeled back toward the Louisiana coast in days to come — the latest potential catastrophe.

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“The major cause of record, recent flooding is entirely man-made — the dramatic constriction of our large rivers by oversized levees, flood plain development and structural narrowing for barge traffic,” said Robert E. Criss, professor emeritus with the Department of Earth and Planetary Sciences at Washington University in St. Louis.

This year’s historic floods throughout the Midwest caused billions of dollars in damages; washed out highways, bridges and dozens of levees; swamped crop lands and cities; sent residents fleeing for their lives; and left a death toll in several states.

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Decades of development have contributed to the problem. Claims to FEMA’s flood insurance program have increased rapidly in the past two decades and spread beyond coastal regions. Here in metropolitan St Louis, floods in 2013, 2016 and 2017 are among the city’s highest 10 crests, according to National Weather Service records.

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Regulation of flood plain building is a state-by-state patchwork, where Missouri is “the Wild West,” according to Olivia Dorothy of the environmental nonprofit American Rivers. Missouri’s neighbor Illinois has been more zealous about restricting building. The result: Missouri typically records a higher annual cost in flood claims per capita, according to a Washington Post analysis of National Flood Insurance Program data since 2010. Missouri ranks worse than its neighbor on several measures of flood damage tracked by the Natural Resources Defense Council, including average claim cost and number of claims per 1,000 people.

Yet with millions of people living in flood plains and shipping and tourism economies built on these key waterways, there is little political will for change. Environmentalists charge that jurisdictions hungry for tax revenue are continuing to plan risky projects without taking floods’ worsening intensity into account, heedless of the economic and human consequences.

“It’s lunacy,” said David Stokes, executive director of the Great Rivers Habitat Alliance. “They’re continuing to build in places where Mother Nature intended water to go. And there’s no end to it.”

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About 41 million Americans — more than 1 in 10 — live in what is known as the 100-year flood plain, areas with a 1 percent chance of flooding in any year, according to a study by the University of Bristol and the Nature Conservancy. About 500,000 flood plain dwellers live in Missouri, and there are almost 1.3 million more across the Mississippi River in Illinois.

The Army Corps of Engineers has responsibility for managing the country’s vast waterways, in many places re-engineering them to make them more navigable with deep, narrow channels, locks and dams. It has also come under fire from politicians, environmentalists and farmers.

While the Corps tries to reduce flood risk by finding ways to temporarily store water through diversions and preserving wetlands, it has little role in decisions about flood plain development. Decisions rest largely with states and vary widely.

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The nation’s main tool for reducing the impact of floods — the National Flood Insurance Program — shares risk through low-cost insurance and restricting construction by calculating how much higher the development would cause 100-year floodwater to rise. Illinois takes that further, allowing minimal impact in “worst case scenario” flooding.

But despite the state’s restrictive policies, some have built unauthorized levees higher than allowed, which keeps their properties dry but sends powerful water barreling toward neighbors. The Sny Island Levee Drainage District in New Canton, Ill., is among those that have raised levees higher than authorized heights, leading residents across the river in Missouri’s Pike County to complain that their land with lower levees is at risk.

“We see the impact from different regulatory regimes,” said Steven Sattinger, commander of the Rock Island District of the U.S. Army Corps of Engineers, which includes the Sny levees.

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Over the past few years, representatives of the levee districts have repeatedly put pressure on Illinois — to the consternation of hydrologists and environmentalists — to relax the regulations that have helped limit the size of levees and thus prevent flood plain development.

People up and down this part of the Mississippi and Missouri rivers still talk about the “Great Flood” of 1993, which followed a period of prolonged heavy rain and swamped 30,000 square miles of farms, wiped out whole towns and left more than 30 people dead.

In its wake, recommendations in a federal government report — including stricter limits on construction and establishing shoreline protections — have been largely ignored by federal and state governments, experts say, despite the growing danger of extreme weather, constricted rivers and runoff from new subdivisions, parking lots and strip malls.

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“We’re dealing with a problem that doesn’t seem to want to go away,” said Gerald E. Galloway, a retired brigadier general in the Army Corps of Engineers and now a professor of engineering at the University of Maryland.

“What was yesterday’s high water is now much higher,” said Galloway, lead author of the federal report.

One of Galloway’s recommendations was that homeowners be bought out of flood-prone areas and their homes razed. FEMA has spent $2.8 billion in the past 30 years doing just that — but not everybody wants to move.

Residents in Valmeyer Ill., a community of about 1,200 that was swept away in the ’93 floods, took FEMA buyout payments to rebuild homes on a hill about a mile and a half away, along with a school and its Corner Pub.

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Those residents stayed dry in the recent flooding, but 28 families who remain in the old Valmeyer, along with farmers with 60,000 acres, were asked to voluntarily evacuate when the Mississippi rose perilously in June and sandbagging began anew.

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“This is the worst since ’93,” said Valmeyer Mayor Howard Heavner. “It gives you flashbacks.”

What’s more, the National Flood Insurance Program has not kept up with development and climate change, experts say, with outdated mapping of flood-prone areas and slow-to-come buyout payments for homeowners who want to move.

“Our building codes and zoning need to keep pace and account for growing risk,” said Carolyn Kousky, director of the Wharton Risk Management and Decision Processes Center at the University of Pennsylvania.

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Congress called in 2016 for more systemic flood-damage reduction in the region, and the five states of the Upper Mississippi are holding public meetings to discuss common themes of river management. But there’s little appetite for spending the money it will take to revamp the system, analysts say.

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Some legislators have moved to reduce flood risk. Missouri state Sen. Andrew Koenig (R) introduced legislation this spring limiting local tax breaks for new developments in flood plains. The legislation did not pass. He intends to reintroduce it.

“If you want to build in a risky area, you should risk your own money,” Koenig said, “not ask taxpayers to risk theirs.”

Meanwhile, even as the floodwater remains, local jurisdictions in Missouri are moving forward with mega-developments that are too close to the Mississippi and Missouri rivers for comfort, Stokes said, racing to get them in place before a law like Koenig’s is passed by the legislature.

Aside from the project in St. Charles, there is also a proposed hotel and retail complex, called Lighthouse Landing, slated for land in St. Louis that was a golf course before the 1993 flood. In nearby Maryland Heights, city officials hope to approve a plan in an area once known as the Missouri River “bottoms.”

The area has flooded in three of the past five years and again in recent weeks from runoff from a nearby lake that couldn’t be channeled into the Missouri River because the river’s water was too high.

“If you have water in a bowl, it can’t get out,” said Maryland Heights Mayor Mike Moeller. But he defended the new project: “We’re working on a plan to develop it in a safe and proper manner.”

For days this summer, huge swaths of the riverfront area — just south of Interstate 70 in St. Louis — have been underwater.

Over at tiny Creve Coeur Airport, pilots waded through foot-deep water and did not hide their skepticism at Maryland Heights’ plan.