Three years ago, Hurricane Katrina smacked almost directly into New Orleans. After a brief initial thought that the city had survived without severe damage, levees failed along the channels that carried water from Lake Pontchartrain to the Mississippi. We all know the rest of the story: ~1,500 dead, tens of billions of dollars in damages, a city decimated that even now, three years later, is still a shadow of its former self and may never fully recover.
Now we hear that another Hurricane, Gustav, is headed in the same general direction. To a devastated city that still hasn't fully repaired the creaking infrastructure that was insufficient to protect the city 3 years ago. With a ~40% probability of making landfall as a Category 3 or greater storm.
But that doesn't worry me. For one thing, the latest tracking forecasts have the storm missing New Orleans to the west.
And second, the place where the storm is now projected to go is potentially much worse.
Southern Louisiana is a creation of the Mississippi River. Carrying soil and silt and sand from most of the upper reaches of North America, the Mississippi has, thanks to regular flooding and simply slowing down as it approaches the Gulf, deposited that treasure from the rest of the country along its banks and floodplains. Without that, the bayous would not exist.
But there's a reason that there is a shoreline, rather than a long fingerlike extension reaching most of the way to Mexico. Over the centuries, the river has regularly jumped its banks and abruptly changed course, like a poorly held firehose. The Mississippi, like all rivers, carries the seeds of its own displacement every day. The sediment in its current gradually builds up a delta and raises its channel, making the path to its eventual destination that much longer and the river itself higher than the surrounding land. As water obeys the laws of gravity, it constantly seeks the shortest, steepest route to its goal. Hence the Mississippi's shifts from one channel to another, infrequent by our standards but in geologic time occurring in the blink of an eye: about once every thousand years. The last time this happened was...almost a thousand years ago. Is there a reason it's not happening now?
It's called Old River Control. It is situated at the juncture of the Mississippi and Atchafalaya. Its importance can be summarized in this sentence: from Old River Control, it is 314 miles via the Mississippi to the Gulf of Mexico, via the Atchafalaya, it is only about 175.
The Atchafalaya was already a distributary of the Mississippi before large settlements of people came along with steamships and commerce, but ironically enough, we are responsible for making the problem worse. Dredging projects caused the Atchafalaya to fully capture the Red River and made it easier to capture part of the Mississippi. Fortunately, the mouth of the Atchafalaya was blocked by a giant logjam that had existed for centuries...until we took the time to clear that out to render that river more navigable. And so the stage was set for the Missisippi to once again change course.
Except for the fact that, by now, we had built a large, intricate infrastructure along the Mississippi's current route, one that was of vital importance to our nation's economy. Were the river to move away from that, the impacts would be enormous. And so starting in the 1950's the Army Corps of Engineers undertook it's most audacious battle against nature yet, and by 1963 had created Old River Control, a structure designed to give the Atchafalaya 30% of the Mississippi's flow and deny it the rest.
But what Mother Nature lacks in speed, she makes up for in endurance. She can be patient, secure on the knowledge that time is on her side. There have been other times and other floods that which have pushed Old River to its limits (1973 was the closest call yet). It's only been 45 years, and it's likely we've barely seen the extremes which can be thrown at it.
If Old River Control were to fail, the Atchafalaya would capture the Mississippi. In plain language, it would become the Mississippi, and the current channel, like many before it, would become a muddy ditch before finally drying up entirely. The mouth of the river would be a salt water estuary along the Gulf. The ecosystems would change dramatically, severely impacting the seafood industry until both nature (the regions shrimp and crawfish, among countless others) and ourselves could adapt, likely not for 2 or more generations.
And New Orleans and every port structure around it would become useless.
Eventually we would adjust. A new port and new facilities would be built, maybe somewhere not too far from the current location of Morgan City (which would be destroyed in a flood of biblical proportions were the Atchafalaya to reign supreme). Commerce would begin anew, and the "new" Mississippi could once again return to being the lifegiving artery to our Nation's economy that it is today.
But not for many long, difficult and expensive years. All this happens if Old River Control, a large and imposing structure in isolation but a flimsy child's toy in the face of the forces that could come down upon it, were to fail.
And as of now, THAT appears to be where Gustav is headed.
So no, I'm not worried about New Orleans, not primarily. My worries are elsewhere.
(As a final note, if you want to learn even more about the Mississippi, the Atchafalaya, Old River Control, and the impacts of all of these on Southern Louisiana, I strongly suggest you read this excellent New Yorker Article, which was expanded to be part of this book.)