My last post dealt with Louisiana's plan to divert the Mississippi below New Orleans to save coastal wetlands. The picture below shows the river at New Orleans; Algiers Point is on the right and the city proper is on the left, so we're looking downstream.
To provide some perspective on the flow of the Mississippi, its average annual discharge is about 450 million acre-feet (MAF) or 17,700 cubic meters per second (cms). Contrast that to the Columbia (about 200 MAF or 7,900 cms), and the Colorado (14 MAF; 550 cms). Among world rivers, in terms of average annual discharge, it ranks 8th behind the Amazon (4900 MAF; 190,000 cms), Congo (1100; 42,000), Yangtze (890; 35,000), Orinoco (740; 29,000), Brahmaputra (510; 20,000),La Plata (500; 19,500), and Yenesei (460; 17,800). Yeah, it's a big one!
So why is a hydrologist who's done most of his work in the arid western USA blogging about the "Father of Waters"? Why not? My curiosity about the Mississippi River started early in life, but piqued in high school, when I got a copy of a new book, Modern Hydrology, by the late Raphael G. Kazmann, a legendary engineering professor at LSU in Baton Rouge. The book covered far more than just the Mississippi, but I was intrigued by Kazmann's discussion of the river's discharge and flood control.
Later, as a graduate student at the University of Arizona, I heard Kazmann tell a fascinating tale about the river and its "desire" (forgive the anthropomorphism - a trait of water nerds like me) to change its course - "delta switching" - which it had done a number of times over the past many thousands of years.
He described how the river really wanted to flow down the Atchafalaya River, a distributary of the Mississippi, formed by the confluence of the Red River with the Mississippi's main channel at the Louisiana-Mississippi stateline. It's about 170 miles (270 km) long and also serves as a shipping channel.
The Atchafalaya is actually building a delta into the Gulf of Mexico, one of the few places where the Louisiana coast is growing (see below).

If the Mississippi were left to its own devices, it would "prefer" to flow predominantly down the Atchafalaya, a more direct (190 miles or 300 km shorter) route to the Gulf of Mexico, leaving much less water in the main channel. This, of course, would leave the major ports
of Baton Rouge and New Orleans "high and dry", or nearly so. Suffice it to say that's not an option - these are two of the biggest ports in the USA and, along with the associated oil and petrochemical industries, are critical to the USA's economy. So maintaining the status quo is not just important to Louisiana, but to the USA.
The "ideal" (from society's standpoint) flow distribution is to have about 30% of the combined Mississippi River + Red River discharge flow down the Atchafalaya and about 70% down the main channel of the Mississippi. To maintain this distribution, at the behest of Congress the U.S. Army Corps of Engineers constructed an elaborate system, the Old River Control Structure Complex, which was completed in 1963. I have never seen these engineering works in person, but I've heard people, including engineers not impressed by just anything, describe this complex as something amazing.
This complex "keeps things right" - maybe not for the natural system, but for humankind's needs. In the above picture of the complex, the Mississippi is to the left, curving to the right in the background. The view is towards the east-southeast.
Kazmann felt strongly (see If the Old River Control Structure Fails? Louisiana Water Resources Research Institute, Bulletin 12, 1980, pages 1-8) that the river would eventually win out, and that most of the flow would wind up in the Atchafalaya's channel. The current mainstem would become an estuary, or perhaps "bayou" might be more appropriate.
John McPhee's book The Control of Nature has an excellent discussion on this issue. Katherine Kemp has a short article on "The Mississippi Levee System and the Old River Control Structure" that's very informative.
"One who knows the Mississippi will promptly aver...that ten thousand River Commissions, with the mines of the world at their back, cannot tame the lawless stream, cannot curb it or confine it, cannot say to it 'Go here or go there' and make it obey, cannot save a shore that it has sentenced." -- Mark Twain, Life on the Mississippi
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