For years, the smart money has bet that, in the protracted wrestling match on the Mississippi between man and nature, nature will ultimately come out on top. The decision, going back to the 19th century, to imprison a naturally meandering river between levees — parallel Great Walls of China, to use the common analogy — has the inevitable effect of raising the water level downstream. Even at normal stages, the river stands up “like a vein on the back of a hand,” as John McPhee wrote in his 1989 best-selling book “The Control of Nature.”
Levee failures can be killers. National Guards now walk the levees day and night. They want to pounce on small problems before they become big problems.
A week ago, an enormous sand boil appeared just north of the Louisiana border, in Arkansas. It measured more than 120 feet across. Soon surrounded by sandbags, it became an instant swimming pool. The downward pressure of the pooled water counterbalanced the pressure from the nearby river.
“I’m feeling vigilant. Literally saying prayers every day,” said Garret Graves, chairman of the Louisiana Coastal Protection and Restoration Authority. “The potential disaster here is real, and we’re doing everything we can to make this go down in history as simply a record-high-water event rather than a record disaster.”
The system is designed to limit the river stages at Baton Rouge and New Orleans during a major flood. The solution is diversion. First, the Corps opened the Bonnet Carre spillway north of New Orleans, dumping a portion of the river flow into Lake Pontchartrain. Then the Corps opened the Morganza spillway, north of Baton Rouge. That relief valve, completed in 1954, has been opened only once before, during the 1973 flood.
The moves do not come without a cost. Fresh water is surging into normally brackish Lake Pontchartrain, with potentially devastating effects on the marine life there. And to the west, the Atchafalaya River basin is slowly filling with water diverted at Morganza. Residents have evacuated, some unhappy to have their lives disrupted to spare the big cities and industries to the east.
Day by day the water surges Niagara-like through the Morganza spillway and advances through the kingdom of crawfish.
Perhaps the trickiest part is ahead: Once the water hits Morgan City, it will be pinched by levees and floodwalls and will begin to “stack up.” As the water rises in the floodplain, it will find ways to spill into adjacent areas in a process known as backflooding.