Quotes of the Day

Mark Twain, the bard of the Mississippi River, was always skeptical of human efforts to control it. "Ten thousand river commissions, with the mines of the world at their back, cannot tame that lawless stream, cannot curb it or confine it, cannot say to it, 'Go here,' or 'Go there,' and make it obey," he wrote in 1883. Twain genuinely admired "the West Point engineers" who dreamed of caging the beast. He truly wanted to believe their confident pronouncements "that they can fetter and handcuff that river and boss him." But a life along the river convinced him that they "might as well bully the comets in their courses and undertake to make them behave, as try to bully the Mississippi into right and reasonable conduct."

More than a century later, as the beast wreaks havoc yet again, drowning farms and towns in its natural floodplain, forcing those gung-ho Army engineers to blow up levees and fling open floodgates to try to relieve its rage, it is clear that Twain was right. And also that Twain was wrong.

It turns out that Twain underestimated the ability of the Army to confine the Mississippi with earthen levees and federal dollars. In the flood of 2011, the engineers have fought the river to a heroic standoff, holding back a wall of water that would fill 25 Olympic-size swimming pools every second. Their mainline levees along the Mississippi have held firm. Most of the damage has come from backwater flooding where smaller tributaries have mutinied against their banks. The engineers sacrificed 130,000 acres (53,000 hectares) of farmland in a Missouri floodway, and they'll sacrifice more in a Louisiana spillway, but that was always their plan for a flood this scary.

"The system is under the most stress it's been under since it was designed," says Army Corps of Engineers spokesman Bob Anderson. "And so far, it's working."

But if human beings are winning this battle against the river, a proposition that some waterlogged communities might dispute, we're losing the war. It's not just bad luck that the modern Mississippi seems to have a 100-year flood every few years. It's not a coincidence that flood damage has been soaring for decades. It's because of what we've done to the river, to the floodplain and maybe to the climate. This flood may turn out to be a run-of-the-mill disaster rather than an epic disaster, but as Twain always understood, Mother Nature eventually gets the last word. "We're having disasters just about every year," says Robert Criss, a hydrogeologist at Washington University in St. Louis. "We like to think we control the river, but who's really in control?"

Twain's hometown, Hannibal, Mo., illustrates how flood fighting has become an almost annual Midwestern pastime. In a 2008 paper, Criss showed that in the previous 25 years, Hannibal had endured 10 floods at levels the Army Corps of Engineers expected only once a decade, including one 500-year flood and one 200-year flood. If that sounds like a fluke, Hannibal had to fend off another 10-year flood in 2009. And another in 2010. And now this.

Water Has to Go Somewhere
The Mississippi is a really big river system. Its watershed covers two-fifths of the continental U.S., draining all or part of 31 states. In its natural state, it rambled across that floodplain every spring, nourishing wetlands and recharging aquifers before drifting back to its channel. And it had a really broad channel, nearly a mile (1.6 km) wide at St. Louis when an Army engineer named Robert E. Lee mapped it in 1837. Today the Mississippi is a vibrant liquid highway with great cities along its banks and an agricultural empire in its 1.2 million-sq.-mi. (3.1 million sq km) basin. It doesn't ramble anymore. But all that water still has to go somewhere.

The straitjacketing of the Mississippi began with an obnoxious Army engineer named Andrew Humphreys, who lost 3,000 soldiers in the charge at Fredericksburg and later marveled, "I felt more like a god than a man!" He applied the same hubris to the river, enforcing a "levees only" policy that began cutting it off from its floodplain and squeezing it into a narrower channel. Today the Mississippi at St. Louis is less than half as wide as it was in Lee's day. Unfortunately, when more water has to stay in the tub and the walls of the tub move closer together, the water rises. In 1927, as the historian John Barry chronicled in Rising Tide, the river overwhelmed the patchwork of local levees that had sprouted along its banks, leaving a million people homeless and 16 million acres (6.5 million hectares) underwater.

After the deluge, the Army Corps devised a new plan that's still in place. It's a much better plan, providing much better protection. But it's also helped usher in an era of ever worsening floods that keep testing its defenses.

The new plan still relied on levees, but the corps took over responsibility for building them all along the river, so that poor towns and absentee landowners would no longer be weak links. These massive levees have kept the floodplain much drier. But their effectiveness has had perverse consequences, reducing the small levee failures in rural areas that once served as involuntary relief valves for the river in flood. Bigger and better levees have also attracted more intense agriculture and development in the floodplains behind them, so there's much more in harm's way. And the conversion of wetlands and prairies into tile-drained farms and asphalt exurbia has increased and accelerated the runoff pouring into the river and its tributaries, diverting even more water into the tub.

Meanwhile, there is mounting evidence that wing dikes, jetties and other river-training structures that the corps builds to aid navigation are raising flood levels as well. For example, Nicholas Pinter, a geomorphologist at Southern Illinois University at Carbondale, has concluded from historical data that navigation structures have elevated floods by about 8 ft. (2.4 m) near the small town of Olive Branch, Ill. The corps has rejected Pinter's research, but Olive Branch's levee was overtopped this month. "Floods wouldn't create the kind of damages we keep seeing without the changes that humans keep making to the system," Pinter says.

Finally, there's been a rapid increase in the frequency and intensity of unusual rain events, like the record Ohio Valley storms that drove the current flood. This increase could be a symptom of global warming, although there's not yet proof; some experts call it "global weirding." But it's dumping still more water into the tub.

Fortunately, the post-1927 plan went beyond levees. The corps also designed emergency measures to give the river room to spread out, including a plan to dynamite the Birds Point levee in Missouri in case high waters threatened Cairo, Ill., and to open several Louisiana relief valves to protect New Orleans. That foresight is paying off. The corps has just flooded the floodway behind Birds Point for the first time since 1937, easing the pressure on Cairo. "I don't have to like it, but we must use everything we have in our possession to prevent a more catastrophic event," Major General Michael Walsh wrote in his May 2 order approving the Birds Point blast.

Farmers in the floodway are suing the corps for damaging their property, as if their federally subsidized corn and soybeans in a federally protected floodplain would have survived had nature had her way. But the Birds Point plan was not a secret. They knew their land was in a designated floodway. And the Mississippi is no longer a natural river; it's a managed river. The Army engineers can't always bully it into right and reasonable conduct, but they don't want nature to have her way.

Retreat from the River
The mainline Mississippi levees that protect cities like New Orleans were built to withstand a "project design flood," essentially the worst the Army engineers could imagine. And the corps is about to use its Morganza Floodway for the first time since 1973, providing even more protection for the Big Easy. By contrast, the hurricane-protection design for New Orleans was based on a serious but not apocalyptic storm; it still failed during Hurricane Katrina, which wasn't even that serious by the time it reached the city. In fact, the levees along the Mississippi have made New Orleans even more vulnerable to storms from the Gulf of Mexico; by starving the river of sediment, the levees delivered less dirt to its delta, which has led to the disappearance of the coastal wetlands that once provided southern Louisiana's natural hurricane protection.

The metronomic recurrences of damaging 100-year floods may foreshadow a day of reckoning on the river as well. Jeffrey Mount, a geomorphologist at the University of California, Davis, says the corps is clinging to an outdated notion of "hydrologic stationarity," basing its strategy on the false assumption that historic floods will predict the future. "We can't keep ignoring the trends," says Larry Larson, executive director of the Association of State Floodplain Managers. "Everybody has this attitude that the system is invincible. We'll see."

The most obvious way to limit our vulnerability to the Mississippi, as with any ferocious beast, is to get out of its way. The federal government has bought out some 40,000 flood-prone properties across the country since the Mississippi flood of 1993, but Europeans have been far more aggressive about keeping development out of their floodplains and giving their rivers room to spread out. Still, the Obama Administration is finalizing an overhaul of the rules governing water projects, a rare opportunity to steer the corps away from the eco-destructive boondoggles that have been its lifeblood for years. After decades of monomaniacally moving dirt and pouring concrete, the corps has gone along with nonstructural efforts to reduce flood damage by restoring wetlands, buying out vulnerable properties and retreating from rivers in places like Napa, Calif., and Cedar Rapids, Iowa.

"We've learned a lot from failures in the past," Anderson says. "One thing we've learned is that where nature is too powerful, you've got to give it some sway."

The corps has been at war with the Mississippi for decades, and neither side has ever been big on retreat. But if there's a lesson from Katrina — not to mention the financial meltdown, the BP spill and the Japanese nuclear disaster — it's that black swans happen. One doesn't seem to be happening this time — but as they say in finance, past performance is no guarantee of future results. "The Mississippi River will always have its own way," Twain wrote. "No engineering skill can persuade it to do otherwise."

• Michael Grunwald