Saturday, May 14, 2011

The Morganza spillway is not the story

The opening of the Morganza spillway for the first time since 1973 is at the top of the news. It's dramatic. A lot of people will lose their homes in order to save a lot more people from losing theirs.

But that is not the story. Or at least it shouldn't be.

The real story is a 35 miles upriver, near the town of Simmesport, Louisiana. There, in 1963, the U.S. army corps of engineers built a floodgate system very similar to Morganza called the Old River Control Structure, or ORCS. The reason the ORCS gets less attention is that water flows through it continuously, so the fact that water is flowing through it now isn't news. The ORCS controls the flow of water between the Mississippi and another river called the Atchafalaya. The Atchafalaya is not a tributary of the Mississippi, it is a distributory. The Mississippi forks at Simmesport, and part of its flow diverts into the Atchafalaya as part of a natural process called avulsion. It works like this: a river carries sediments. Over time those sediments are deposited in natural levees which periodically change the river's course. The Mississippi naturally changes course about once every thousand years or so. The next course change is overdue. When, not if, it happens, the Mississippi will divert into the Achafalaya, which follows a much shorter and hence steeper course to the Gulf of Mexico than the Mississippi does now.

The ORCS was built to prevent this course change from happening. The flow is carefully controlled to keep Mississippi from fully diverting. But in 1973, the last time a "hundred-year flood" happened on the Mississippi, the flow of water through the ORCS was so massive and turbulent that it undermined the structure's foundations and it very nearly failed. If it had failed, the water would have enlarged the Atchafalaya to the point where the process would almost certainly have become irreversible. The Mississippi River as we know it would have ceased to exist.

It is probably only a matter of time before the ORCS does fail. It was shored up after 1973, but water has a way of going where it wants to go. The Mississippi's sediments are building up, and the more they do the more attractive the Atchafalaya's shorter and steeper route becomes. This could be the year.

If it is, it would be an economic catastrophe of epic proportions. Morgan City, Louisiana would more or less cease to exist. The Mississippi would still flow through New Orleans, but it would not have enough water to support the deep-water river traffic it does today, and it would no longer be a suitable source of drinking water for the city of New Orleans. Most of the Gulf oil and fishing infrastructure would have to be rebuilt. It would be -- sorry, will be, because it's only a matter of time before it happens -- Really Really Bad (tm).

Despite this, I have yet to see any mention of the ORCS is any mainstream news outlet.

1 comment:

Peter said...

John McPhee wrote a long article about it in the New Yorker in 1987: