San José State University
Thayer Watkins
Silicon Valley
& Tornado Alley

The Old River Control Structure
on the Lower Mississippi River

The Old River Control Project

The Mississippi River deposits millions of tons of sediment each year onto the continental shelf of North America in the Gulf of Mexico. As the writer Mark Twain observed, if this process continued unaltered the delta of the Mississippi would extend like a fishing pole from Louisiana to the Yucatan Peninsula. But instead the delta fans out from the lower end of the Mississippi. This occurs partly because the buildup of sediment encourages multiple channels that distribute the flow. But also every thousand or so years the Mississippi finds a new major channel.

There has been tremendous economic development along the present main channel which includes the cities of New Orleans and Baton Rouge as well as industrial plants elsewhere dependent upon the Mississippi for fresh water and deep water transportation. Three million people are depending upon the present channel of the Mississippi River.

The problem is that the Mississippi is on the verge of switching to a new channel along what is now the Atchafalaya River. The pronunciation of Atchafalaya is a bit troublesome because it is the French spelling of an Indian word. In French "ch" is pronounced as "sh" is in English. Thus "tch" is used in French to denote the English "ch" sound. Therefore the pronunciation of Atchafalaya is as though it were spelled "achafalaya."

The Atchafalaya River has already capture the Red River which flows from the west and used to be a tributary of the Mississipi. Already 30 percent of the flow of the Mississippi goes into a channel called the Old River and thence into the Atchafalaya River. The configuration is roughly in the form of an H in which the the Atchafalaya-Red Rivers form the left leg and the Mississippi the other with the Old River being the cross branch.

The Old River Control Project of the Corp of Engineers is working to prevent the capture of 100 percent of the Mississippi by the Atchafalaya. But the Corps of Engineers doesn't want to cut off all flow through the Old River because agricultural and marine development along the Atchafalaya River would be hurt. The Corps is committed to maintaining the 30 percent diversion that now exists.

Much of the present problem exists because of the past efforts of the Corps of Engineers. Until the nineteenth century about thirty miles of the channel of the the Atchafalaya was blocked by a prehistoric log jam. The Corps and others cleared away this plug of timber. The Red River was also cleared. The Red River had been a direct tributary of the Mississippi for two millenia, but due to the clearing of the Atchafalaya it was captured by the Atchafalaya in the 1940s. Fred Bayley, the chief engineer of the Lower Mississippi Valley Division of the Corp of Engineers, put this way, "The more water the Atchafalaya takes, the bigger it gets; the bigger it gets, the more water it takes."

The Old River was once part of the Mississippi. There a meander of the river where it almost looped back upon itself. The Corps decided to eliminate the meander by cutting a channel through the narrowest part. The Corps-made channel was quickly widened by the Mississippi and the meander virtually dried up. This is why the Old River has that name.

The Corps also blocked various distributary channels until now only the Atchafalaya diverts water from the main channel.

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