Flood the farms to save the cities.

That’s the trade-off staring at the Army Corps of Engineers in Louisiana this week as a historically high Mississippi River rolls south, flooding towns in Mississippi on Wednesday, prompting evacuations farther south, and threatening the heavily industrialized petrochemical corridor running from Baton Rouge to New Orleans and beyond.

About a million people live along that corridor, in addition to the New Orleans residents who endured a flooding nightmare six years ago when levees failed after Hurricane Katrina.

So the corps is confronted with a Devil’s choice: cause a flood that would drown the livelihoods of central Louisiana farmers and fishermen, or let the high river roll and frantically sandbag 200 miles of levees to try to prevent flooding in the state’s two biggest cities.

If the swollen Mississippi is allowed to run full bore through the state, the water would eat away at levees and could overtop sections, drowning some districts of New Orleans under about 25 feet of dirty water — an inundation even greater than the Katrina disaster, according to a worst-case map prepared by Walter Baumy, chief of engineering for the corps’ New Orleans office.

But the corps has an ace up its sleeve. It can throw open a relief valve 35 miles northwest of Baton Rouge, the huge Morganza Spillway.

Designed to siphon a fifth of the Mississippi’s mightiest flow and sluice it west, the spillway has been opened just once in the 57 years since its completion, during the flood of 1973.

If thrown open again, the Mississippi would fall, as would the threat to Baton Rouge and New Orleans.

In exchange, a flood would shoot down the gut of central Louisiana and join the already high Atchafalaya River, which would further swell and flood. For 200 miles, farmers and fishermen would pay a steep price as a torrent greater than Niagara Falls would inundate crops, crawfish hatcheries and, possibly, the small cities of Houma and Morgan City. Sensitive oyster beds in the Gulf of Mexico would be imperiled by the pulse of freshwater.

On Wednesday, Louisiana Gov. Bobby Jindal (R) told residents in the path of the potential spillway flood to prepare for evacuation.

“These are very high stakes,” said Bob Thomas, a professor at Loyola University New Orleans who studies the politics and ecology of the spillway. “The Morganza will cause a lot of damage if it’s open, a major flood. But it’s designed for that.”

The Mississippi has flooded 3 million acres in Arkansas, Tennessee and Mississippi and has forced thousands from their homes. On Wednesday, the river set an all-time record at Natchez, Miss. Heavy snows in the upper Midwest this winter and record rains in April across the Ohio River valley triggered the historic floods.

In Louisiana, the Morganza Spillway decision rests with Corps of Engineers Maj. Gen. Michael J. Walsh, president of the Mississippi River Commission, which oversees the river’s flood-control system.

“The river is dictating what we need to do to protect the largest number of lives,” said Robert Anderson, Walsh’s spokesman.

On May 6, the head of the corps’ New Orleans district, Col. Edward R. Fleming, requested that Walsh open the spillway to protect the city.

Walsh is considering the request while keeping a close eye on river forecasts. He will make his decision between Thursday and Saturday, his spokesman said.

Forecasts suggest that Walsh will be forced to open at least some of the 125 gates that march across the 3,900-foot-wide spillway.

By Wednesday, the river had risen to just three feet below the spillway’s top, said Baumy, the corps engineer. And the National Weather Service projects the river’s flow will hit a preplanned trigger point early Friday. That’s when the service says the Mississippi will shoot past a spot called Red River Landing, just north of Morganza, at 1.5 million cubic feet per second.

Barge superhighway

For more than 50 years, the corps’ flood protection plan for Louisiana called for throwing open Morganza’s gates when the river hit that unlikely number. The whole river has been channeled as a superhighway for barges, with only two pressure relief points along the lower part — at Morganza and the already opened Bonnet Carre Spillway just north of New Orleans. Such a constraint leaves the corps with few options during a historic flood.

“They’re going to have to open up Morganza, not for the height, but for the pressure on the levees,” said Oliver Houck, a law professor at Tulane University who has long been involved with the spillway. “It’s going to remain high for weeks and weeks. And that’s the scare. All it takes is one weak spot” in a levee to flood New Orleans.

In the 1970s and ’80s, Houck led a fight to prevent real estate development in the spillway zone. His argument was simple: The corps designed the zone to be intentionally flooded. Allowing homes, farms and businesses to settle there would only make the decision to open the gates harder.

Environmentalists and sportsmen succeeded in stanching development in much of the spillzone. But farms and towns have still encroached. “A lot of places were developed because the USDA made subsidies to convert forest to cropland,” Houck said.

About 100,000 acres of soybeans, sugar cane, rice and corn are farmed in the spillway. Harvests are taken by barge to New Orleans for export, but all of this season’s crops are at risk, local farmers say.

Even if just half of the spillway opens this weekend, “the level of water is just too extreme” to save the crops, said Carlos Polozola, who farms corn, soybeans and wheat on 2,500 acres in St. Landry Parish.

The farmers who own the crops have insurance. But insurance covers only an act of God or natural disaster. Opening the spillway is a human decision made to try to avert a natural disaster, so the farmers would be out of luck.

“Some of our farmers would lose everything they have,” said Polozola, president of a district board representing St. Landry and two neighboring parishes. The farmers are appealing to the Army Corps of Engineers to write insurance companies a letter calling the spillway opening a natural event.

Not in ‘their lifetime’

In St. Landry Parish, pop. 2,000, residents are preparing for the worst flooding since 1927 as soon as Saturday, even if only some of the Morganza gates are opened. “It’s still going to send us a heck of a lot of water we can’t absorb,” said Sheriff Bobby J. Guidroz. A voluntary evacuation was in place, and many residents were leaving for shelter with friends and relatives.

Guidroz said that the Southern Louisiana community “is protected better than we were 70 years ago” but that most residents did not build their homes above flood levels. Building on pilings 10 feet aboveground is expensive. And residents “just don’t think it’s going to happen to them in their lifetime,” Guidroz said. “They’re willing to take the chance.”

To the east in Pointe Coupee Parish, the heart of French Creole plantation country, the thinking is that it’s not a question of if but when the spillway gates open. “We’re a lot more populated now than were were in ’27,” said the sheriff, Beauregard “Bud” Torres. “The flip side is, the levees are a lot better than they were then.”

He said that about 1,500 of the parish’s 25,000 residents whose homes are in a flood plain had evacuated.

“It’s the price you pay to live here,” he said. “Just as the river is not our friend now, it is a blessing the rest of the time.”

Fears of backflooding

Residents along the spillway are worried about a side effect of the opening called backflooding. This occurs when the waterway merges with other bayous and lakes, overloading the system and depositing water outside the levees.

“Everyone is panicking,” Polozola said. People are renting storage lockers and shelters and moving their belongings in.

At the spillway’s southern end, residents of Morgan City, pop. 13,500, 25 miles north of the Gulf of Mexico, are among the worried. This week, Mayor Tim Matte got the National Guard to raise the levees south and east of the city by three feet to protect against backflooding. But it won’t get to every section before the spillway is opened.

“We’re telling people they need to prepare themselves for whatever circumstances could come,” Matte said.

To critics who say people should not have built anywhere near the spillway, Matte said the Atchafalaya is a working river with fishing, timber, and offshore oil and gas industries that are vital to Southern Louisiana and the nation’s economy.

“This is a place where commerce takes place,” he said. “It’s a working coast. We need to be here.”