Jim Andrews

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Hurricane Isaac Reverses Mississippi River Flow

September 03, 2012; 8:17 AM

--Isaac's Storm Surge Overpowered the River's Drought-Shriveled Flow

Hurricane Isaac's storm surge triggered a powerful upstream flow on North America's greatest river, the Mississippi.

US Geological Survey gages on the Mississippi at Belle Chase, La., registered the backward-flowing tide on Tuesday, as Category 1 Hurricane Isaac landed in southern Louisiana, the BBC News website said.


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Upstream flow at Belle Chase was 182,000 cubic feet per second (cusesc). Normal downstream flow at this gage is 125,000 cusses.

The storm surge hiked the gage height nearly 10 feet above average.

Another 100 miles up stream, at Baton Rouge, an 8-foot rise in gage height was registered, the BBC said.


The Aug. 28-29 spike in gage height marks the storm surge of Hurricane Isaac at Belle Chase, below New Orleans, La. As the river gage height rose from 1 to 11 feet, the river actually flowed backwards (USGS Image).

Reversal of flow on the "Big Muddy," as the Mississippi is sometimes known, is not at all unprecedented. After all, the lower river has a very low gradient, the river being only about 60 feet above sea level where the Mississippi crosses the Arkansas-Louisiana line.

Hurricane Katrina caused backup on the river that boosted gages by 13 feet back in 2005.

Nor are hurricanes the only natural phenomenon known to reverse the Mississippi's flow. Great earthquakes on the New Madrid Fault Zone, Mo., are known to have caused backwards flow and even "waterfalls," back in 1812.

The views expressed are those of the author and not necessarily those of AccuWeather, Inc. or AccuWeather.com

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About This Blog

Jim Andrews
The International weather blog from AccuWeather.com is written by Jim Andrews who has more than 10 years experience forecasting outside the United States.