Rivers change course. They meander, they cast off oxbow lakes, they cut new channels, they merge, they split. They find the low ground and the fastest way to the sea as it calls them, Oshun returning to Maman Yemaya. It does no good to tame them; you can't - if Oshun doesn't slip out of your grasp, if Yemaya does not swell onto the land to claim her wayward child, then Oya will shake her skirts and blow a storm to send the river where she wills.
For upwards of sixty years, the Army Corps of Engineers has been in a protracted battle with the Father of Waters, that he should stay in his current course instead of swallowing his daughter, the Atchafalaya, and following her much shorter course to the Gulf of Mexico. The upshot of this struggle is that he has been held, just barely, at the cost of raising the floor of his current channel - such that when he does change course, instead of merely switching positions, with the Atchafalaya becoming the main stream and the current one being the distributary, instead the current channel will be too high to maintain a flow that will keep the salt water of the Gulf at bay, and will become a brackish estuary. Needless to say, this will be bad for New Orleans, and (not incidentally) nearly as disastrous for Baton Rouge.
The current flood may be the one that shakes him loose. But even if it isn't, that flood will come one day; the only question is when. Well, that's not quite true. Then will come other questions, like "Is Lake Pontchartrain (which is itself brackish) capable of supplying enough water for New Orleans by itself?" and "If the Mississippi is no longer navigable to the Port of New Orleans, are the Ports of Houston and Mobile big enough to handle the increase in shipping traffic?" and "Is the Tennessee-Tombigbee waterway big enough to handle the sudden shift in river traffic?" (No, no, and no, as far as I can tell so far. Having said that, the Tenn-Tom does take some of the flood pressure off of the Mississippi by diverting some of the Tennessee's flow down to Mobile.)
Some interesting reads on the topic:
The Control of Nature: Atchafalaya is a fantastic article by John McPhee from the New Yorker - in 1987. It's long. Read it anyway. Katrina haunts the edges, of course, but the article is mostly about the interplay between the river, the Corps, and the people of southern Louisiana. There are moments of
phenomenal writing scattered through the article, as well. (Warning: it reads like it was OCRed and re-edited in haste, which I suspect is the case - there are some odd spelling errors.)
The Flood Last Time: Almost Apocalypse, at the Daily Impact, is from earlier this month, and is much shorter - just a review of the Flood of '73 and what
almost happened at the Old River Control Structure. It's a very succinct summary, though. And I have to say, that title was effective - sent a shiver down my spine, and I've not been in that faith for nearly two decades.