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Washington (AFP) Aug 30, 2012
The Mississippi flowed backwards for nearly 24 hours when Hurricane Isaac roared off the Gulf of Mexico and made landfall in Louisiana, the US Geological Survey said Thursday.
In a statement, it said the Mississippi flowed upstream at 182,000 cubic feet (5,150 cubic meters) per second on Tuesday at Belle Chasse, downriver from New Orleans, where it surged 10 feet (three meters) above its previous height.
Average flow per second at that point on the 2,320 mile (3,734 kilometer) river, the mainstay of North America's largest river system, is 125,000 cubic feet -- equal in volume to about 90 standard 20-foot shipping containers.
"Although it doesn't happen often, hurricanes can cause coastal rivers to reverse flow," said the Geological Survey, a federal agency that constantly monitors the Mississippi's flow rate through a network of stream gages.
"Between the extremely strong winds and the massive waves of water pushed by those winds, rivers at regular or low flow are forced backwards until either the normal river-flow or the elevation of the land stop the inflow."
As Isaac creeped further inland, the agency said, it triggered surges along the Mississippi as far north as Baton Rouge, Louisiana, where the river crested eight feet (nearly 2.5 meters) above its prior height.
The Mississippi similarly went into reverse gear when Hurricane Katrina struck Louisiana with ruthless force in August 2005, cresting at 13 feet (nearly four meters) about its previous level.
Forecasters expect Isaac to remain to the west of the Mississippi as it moves north, bringing late-summer relief to grain-growing states in American heartland otherwise hard-hit by drought.
Severe floods hit central portions of the Mississippi last year, but a dramatic lack of rain this year has seen the strategic river fall to levels unseen since 1988, disrupting barge traffic.
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