Were this year’s floods bad?
Not as bad as they could have been. Despite record-breaking water levels in Mississippi and Louisiana, the human toll has been lower than in earlier floods. About 10,000 people were displaced from their homes during May—far fewer than in the devastating floods of 1927, which left 600,000 homeless, or the 1993 floods, which destroyed 50,000 homes. This relative success came largely because the U.S. Army Corps of Engineers, which is tasked with controlling the Mississippi, quickly destroyed levees and opened floodways, allowing floodwater to flow over sparsely populated land before it reached built-up areas. The system “was designed to handle this,” said Col. Jeff Eckstein, commander of the Vicksburg, Miss., district of the Corps of Engineers. “We feel very comfortable with the system performing just as we thought it would.”

Why does the Mississippi keep flooding?
That’s what rivers naturally do after intense rain. But because mankind has built so many communities, power stations, and farms along riverbanks, we now funnel the flow through narrow, man-made channels, raising the water’s height and speed. Any excess water has nowhere to go but up. It’s a particular problem with the Mississippi due to its massive watershed, which covers 1,245,000 square miles in 31 states. Whenever there are big storms anywhere from western New York to Montana, the water drains into the Mississippi. Every three years on average, flooding results.

Why do we have to control it at all?
If we didn’t, the river would shift. In their natural state, rivers are dynamic systems. Over the course of hundreds of years, sediment builds up on the riverbed, forcing the river to meander. A river as large as the 2,300-mile Mississippi changes course radically every thousand years or so.
How do we prevent that?
The Corps and others have built 3,500 miles of levees, earthen mounds designed to keep the Mississippi from overflowing. More than 190 subsurface weirs alter the river’s flow. Much of the river’s southern course has been fitted with revetments, or reinforcements meant to keep riverbanks from eroding. “The Mississippi, Missouri, and Ohio rivers are largely man-made constructs,” says Nicholas Pinter, a geology professor at Southern Illinois University Carbondale.

When did this begin?
In 1724, shortly after the founding of New Orleans, when French settlers built three-foot levees upon which they could construct houses. Every time the city flooded, the settlers rebuilt the levees higher and higher. In 1879, Congress handed the job to the Corps, which over the following century oversaw the construction of more than 2,000 miles of levees of ever-increasing height, and stopped up tributaries and bayous to ensure that the river would not deviate from its route to the Gulf of Mexico. In 1973, a Corps general reassured Congress that “the Corps of Engineers can make the Mississippi River go anywhere the Corps directs it to go”—words somewhat undermined by that year’s extensive flooding.

What else can be done to thwart flooding?
Make the water flow elsewhere. The Corps began building a $13 billion system of spillways and channels after the 1927 floods to direct waters into floodplains or other waterways. For the first time since 1973, the Corps this year opened the Morganza Floodway, shunting water into Louisiana’s Atchafalaya River at a rate of 172,000 cubic feet per second and saving communities downstream from even worse flooding. A wiser approach may be to discourage settlement on vulnerable floodplains. “People who use protected floodplains forget the risk they face,” says Craig Colten, a geography professor at Louisiana State University. “It’s a fool’s errand to confine the river permanently.”

Is there a better alternative?
That’s an open question. If we were to let the Mississippi take its natural course, geologists say, it would flow down the Atchafalaya, a channel that takes a more direct southerly course to the Gulf of Mexico than the Mississippi’s current path toward New Orleans. The Old River Control Structure, a vast floodgate infrastructure built in the 1960s, prevents that from happening for now, but some warn that it will eventually fail. “The Mississippi is bound to find a new channel,” said engineer Raphael Kazmann. “It may be next year or 50 years from now, but it will happen.” The Corps of Engineers can only hope that the words of Mark Twain, back in 1883, do not come back to haunt them: We “might as well bully the comets in their courses,” he wrote, “as try to bully the Mississippi into right and reasonable conduct.”

How levees have hurt Louisiana
The levees lining the Mississippi have saved millions of lives over the years, but some argue they’ve also caused an ecological disaster in the Gulf of Mexico. The levee infrastructure siphons river sediment through a single waterway out into the sea, preventing it from building up to form natural defenses for Louisiana’s wetlands. As a result, the Gulf’s waters have steadily eroded the state’s coastline. More than a million acres of land have vanished over the past hundred years; by 2100, some scientists say, New Orleans could be an island. The only solution may be to demolish levees and let the river run wild, says Christopher D’Elia, dean of the School of the Coast and Environment at Louisiana State University, but that would displace thousands of people and harm industries that rely on the river. “We’re absolutely hamstrung by this situation,” he says.