This Drought Is So Bad Salt Water Is Flowing Up the Mississippi, Threatening NOLA's Water Supply

This Drought Is So Bad Salt Water Is Flowing Up the Mississippi, Threatening NOLA's Water Supply

by Brian Resnick

And that's the last thing the city needs as it braces for Hurricane Isaac.
Saltwater has been flowing from the Gulf up the Mississippi River, and that's as much of a problem as you might think.
Due to the historic drought still searing the Midwest and taxing the heart of our agricultural economy, the Mississippi River is at its lowest flow rate in years. In Memphis, for instance, the river is 8.9 feet below baseline. While the low flow has been grounding barges and creating pockets of quicksand, it is also allowing the Gulf of Mexico to flow nearly 90 miles upstream from the mouth of the Mississippi.
Why? Salt water is denser than fresh water, which means if you mix the two, the salt water sinks. The Gulf is salt water. The bottom of the Mississippi is lower than the surface of the Gulf. Following that gradient, the dense gulf waters actually flow up the Mississippi, crawling along the riverbed. Theoretically, the salt water can flow 350 miles from the mouth of the Mississippi, the point where the bottom of the river reaches an elevation higher than the surface of the Gulf. But the salty waters never makes it this far, as the downward flow of the Mississippi holds them back. http://www.theatlantic.com/technology/archive/2012/08/this-drought-is-so-bad-salt-water-is-flowing-up-the-mississippi-threatening-nolas-water-supply/261688/