While it’s called the Mississippi River, it could well have been called the Ohio instead.
When the two great streams meet at Cairo, Illinois, it’s the Ohio that is carrying more water than the river that won the naming rights.
BY DAN SWENSON | Graphics Editor
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And at that juncture, the Mississippi has already incorporated the Missouri River, its longest tributary, into its flow. Despite the Missouri’s huge watershed, it drains a relatively arid section of the U.S. — and it has a series of dams that hold back water. So it’s a relatively small contributor to the Mississippi’s enormous volume, despite its length.
Why does any of this matter, if you’re not a geography nerd?
Well, it’s going to take a lot of rain upriver to turn back the the saltwater wedge that is threatening drinking water supplies around New Orleans (though maybe not the city itself). Most likely, that water is going to fall in the basins that are currently running at a trickle, compared to historical norms.
The Ohio River is the biggest culprit. Typically, fully half the water that flows past New Orleans originates in the Ohio. As Tulane geographer Rich Campanella put it in his essential book Geographies of New Orleans: “The Ohio River confluence at Cairo turns the Mississippi from a significant regional waterway into a world-class, continental-scale drainage.”
The Ohio hardly deserves such superlatives right now. As of Oct. 5, the Ohio is only contributing 8% of the river’s current (read: puny) flow, which works out to just 16,800 cubic feet per second. (On a normal day, the Ohio carries 16 times that much.)
So if you’re watching the weather reports from elsewhere and rooting for rain, pay special attention to the Ohio’s basin, which centers on Pennsylvania, Ohio, West Virginia, Kentucky, Tennessee, Indiana and Illinois. When heavy rain starts to fall up there, relief will be on the way.
Not all of the water in the Mississippi makes it to New Orleans. A complicated structure managed by the Army Corps of Engineers sends 30% of the river’s flow out the Atchafalaya, where it exits into the Gulf near Morgan City. (The Atchafalaya also carries the waters of the Red River, which drains much of Louisiana and parts of Texas and Oklahoma. Because the Red has been relatively robust during the saltwater crisis, the Corps is considering reducing the 30%to allow more water to get to New Orleans.)
While the Mississippi is by far North America’s largest river system, it hardly holds a candle to the world’s champion, the Amazon, which by volume discharges an average of 7.4 million cfs into the Atlantic Ocean. That’s nearly six times what the Mississippi sends into the Gulf of Mexico when it’s so full that the Bonnet Carre Spillway must be opened.
Right now, the Mississippi is barely putting out a tenth of that amount — meaning its current flow is about 2% of the Amazon’s on a typical day.
2023-10-06 09:30:00
#water #Mississippi #River #Environment
