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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."