JACKSON, Miss. -- The Coast Guard reopened the swollen Mississippi River north of New Orleans on Tuesday, allowing cargo vessels on the nation's busiest waterway to pass one-by-one in the latest effort to reduce pressure from rising floodwaters.
A 15-mile stretch at Natchez, Miss., was closed entirely earlier in the day, blocking vessels heading toward the Gulf of Mexico and others trying to return north after dropping off their freight. Had the channel remained closed, it could've brought traffic to a standstill up and down the river, which moves about 500 million tons of cargo each year.
That sort of interruption could've cost the U.S. economy hundreds of millions of dollars for every day of idled barges carrying coal, timber, iron, steel and more than half of America's grain exports.
Coast Guard officials said wakes generated by passing barge traffic could increase the strain on levees designed to hold back the river. Authorities were also concerned that barges could not operate safely in the flooded river, which has risen to the level of some docks and submerged others.
"We're closely monitoring traffic along the river and all vessels must stay to the center of the river," Coast Guard Cmdr. Mark Moland said.
It's not clear how long barges would only be able to move one at a time through the section. The river is expected to stay high in some places for weeks.
The Coast Guard did not have comprehensive figures on how many vessels were immediately affected, but the agency stopped at least 10 near Natchez on Tuesday.
In past closures, the numbers have grown quickly. In 2008, the agency halted 59 ships within a day of shutting down a stretch of the river near New Orleans because of a barge and tanker collision.
Shipping companies had hoped for a swift reopening.
On a typical day, 600 barges move up and down the river, according to Bob Anderson, spokesman for the Mississippi Valley Division of the Army Corps of Engineers. A single barge can carry as much cargo as 70 tractor-trailers or 17 rail cars.
"When it shuts, there's really no alternative," said Jim Reed, president of the Illinois Corn Growers Association.
The Coast Guard's traffic-management division hoped to prevent barges from piling up on either side of the closed zone by requiring them to be at least 1,200 feet apart.
Also Tuesday, at least 10 freight terminals along the lower Mississippi between Baton Rouge and New Orleans suspended operations because of high water. Vessels scheduled to use the terminals will either have to wait out the high water or divert elsewhere. Delaying a vessel by even a single day often costs $20,000 to $40,000, port officials said.
Throughout the spring, the Mississippi is a highway for barges laden with corn, soybeans and other crops headed from the Midwest to ports near New Orleans, where they get loaded onto massive grain carriers for export around the world.
The closure helped push corn, wheat and soybean prices higher Tuesday.
Traders were already nervous about tight supplies of all three crops. Farmers are behind on their planting because of cold, wet weather. At the same time, global supplies have been depleted by rising demand from ethanol makers and livestock producers.
The price of corn jumped 22.75 cents to $7.20 a bushel, while soybeans rose 14.5 cents, to $13.41 a bushel. Wheat rose 27.5 cents to settle at $7.64 a bushel.
While prices might spike in the short-term, flooding and port closures along the Mississippi River probably will not affect crop prices for long, said John Sanow, an analyst with DTN Telvent.
Traders are more worried that flooded acreage won't be replanted with corn, he said.
If the closure had persisted, the crop exports most likely to be affected are corn and soybeans, said Jason Ward, analyst with Northstar Commodity in Minneapolis.
The port, the largest in terms of tonnage in the United States, handles 54 percent of the nation's annual grain exports. It handles about 60,000 barges a year, along with 4,500 to 5,000 deep-draft vessels that carry grain and other bulk cargo such as steel.
The Mississippi also conveys most of New England's home heating oil and gasoline, along with 20 percent of America's coal, according to the American Waterways Operators, the trade group of the barge operators.
The closure was the third in a series of recent moves designed to protect homes and businesses behind levees and floodwalls along the river.
Over the weekend, the Army Corps opened the Morganza Spillway, choosing to flood rural areas with fewer homes to protect Baton Rouge and New Orleans. Another spillway near New Orleans was opened earlier, but it did not threaten homes.
The river is expected to crest Saturday in Natchez at 63 feet, down a half-foot than earlier predictions. But that level is still nearly five feet above a record set in 1937. It could take weeks for the water to recede.
Natchez Mayor Jake Middleton said if the city's levees were damaged, it could endanger hospitals, a convention center and historic buildings both in Natchez and across the river in Louisiana.
The floodwaters have displaced more than 4,800 people in Mississippi, including 80-year-old Leslie J. Sherwin, who was pushed out of his house in Tunica County three weeks ago and into a shelter.
"The road is cutoff. The house is flooded, and I can't even go home," Sherwin said. "But hey, nothing lasts forever. I've been knocked down many times. I'm just going to do what I've got to do, day by day."