The Mississippi was at major flood stage at St. Paul last week and more snow was falling. The Missouri and Ohio systems also are beginning to dump lots of water into the Mississippi and all of that will eventually get to us.
That makes people in Baton Rouge and New Orleans nervous, but the major danger to Acadiana when the Mississippi begins to flood is not from the Big River itself, but from the Atchafalaya, which is one of its major distributaries – that is, a stream that takes water from another one. (A tributary adds water to another stream.)
The Atchafalaya forks away from the Mississippi at Simmesport in Avoyelles Parish and presents a shorter and straighter course for a Mississippi flood to get to the sea. Dams and weirs control – at least for now – the amount of water that can get into the Atchafalaya from the Mississippi, but there are a number of pessimists who say that won’t last forever. The flood of 1973 nearly wiped out those structures, and they say another big flood could still do the job.
That would allow most of the Mississippi’s waters to flow down the Atchafalaya, something that nature has been trying to make happen for centuries.
The Atchafalaya probably established itself as a distributary of the Mississippi about 500 years ago, but it remained a small stream for the first 300 years because it was choked by a raft of logs that blocked all but a trickle of Mississippi water.
The biggest raft was made of 40 miles of logs jammed together, and it was not the only one. An 1805 survey found 11 other rafts varying in length, the shortest being about three football fields long. In some of them logs were piled as high as 12 feet above the water level.
When the steamboat trade began to develop in south Louisiana, planters and merchants pushed to have the logs cleared away so boats could use the Atchafalaya. Nobody did anything until 1839, which was a very dry year when the water was low. Planters took things into their own hands and set the rafts on fire.
According to one report the fires “burned much timber and several thousand alligators” but didn’t clear the river because logs were still jammed below the water line.
In 1842 the state finally cleared a narrow channel, hoping that it would generate enough current to clear out the rest of the rafts. Some logs were pushed downriver, but they just jammed in a different spot. “Snag boats” were finally sent in, using dragline-type grabbers to physically remove the logs.
That cleared the rafts, but created another problem: Water from the regular spring floods on the Mississippi now poured into the Atchafalaya, widening the river, wiping out farms in the Atchafalaya Basin, and creating a regular flood threat in places that had not seen one before.
In 1881 a commission reported to Congress that where once there had been farms in the basin, now they found “ruined dwellings and sugar houses ... fences deeply imbedded in the deposit of many floods. The live oak and other forest trees requiring the free exposure of their roots to air … smothered by sediment.”
There was some attempt to build levees in the basin but a big flood in 1882 wiped them out. Rebuilding of the levees began again in 1900 with some success in holding back the river, but a narrower channel caused it to scour itself an even deeper bed, allowing it to take more Mississippi water.
And there was another big consequence of that flood of 1882 and another later one: Water came down the Atchafalaya and flooded large areas east of Bayou Teche in 1882. But the flood did not cross a natural levee created thousands of years ago. This Teche ridge blocked another big flood in 1912, keeping it from Breaux Bridge and St. Martinville, even though Morgan City took a beating.
That’s why lots of St Martin Parish folks thought they were safe when the big flood of 1927 came pouring to the south. They thought the ridge would once again hold back the waters.
You can contact Jim Bradshaw at firstname.lastname@example.org or P.O. Box 1121, Washington LA 70589.