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The Louisiana Coast: Last Call
Tue May 14, 2013
The Louisiana Coast: Last Call — How We Got This Way: The Mississippi River
Anyone flying into New Orleans on a clear day now looks down on a panorama of delicate marsh floating like green lace on the brown waters of the Mississippi delta. Those wetlands seem endless — stretching to the horizons.
But scientists tell us we’re really looking at the skeletal remains of a vast wetland ecosystem that presented huge challenges to European explorers back in the 16th century.
But to understand what Louisiana was lost, and how quickly that disaster has happened, we need to take a look back on how nature built this area, and how long that took.
When Bienville was searching for the main stem of the Mississippi back in the early 1700s, he was paddling through the Amazon of North America, an immense wilderness of swamps, marshes and high natural ridges that had been under construction by nature for thousands of years.
“If you go back roughly 12,000 to 18,000 years, basically the Gulf Coast would have formed a smooth bite from Florida, Alabama, Mississippi through Louisiana roughly south to right around Baton Rouge, north shore of Lake Pontchartrain, south of Lafayette, and coming out where the Texas coast [is] now,” says Tulane University geographer Richard Campanella. “Global temperatures start to warm, and the ice sheets — which covered roughly 50 percent of the North American continent started to recede — they started to melt.”
Campanella says this melting released immense amounts of water, and that water re-sculpted North American topography and hydrology.
“Coming down this sort of down-warping in the earth’s crust, called the Mississippi embayment now, which is now the lower Mississippi Valley, you have this radically increased water flow and sediment component in that water,” Campanella says. “So it hits the Gulf of Mexico just south of Baton Rouge, loses its kinetic energy and dumps vast amounts of alluvium at the edge of the continent.”
So, a huge river with an immense supply of sediment was pushing into the very flat and shallow Gulf of Mexico, and it started dropping all the sediment.
“It’s open salt water, so it deposits this sediment on the sub-alluvial surface, basically the bottom of the Gulf of Mexico,” Campanella says. “So, that accumulation starts to break sea level and starts to turn water into land to the point that the river could no longer go through its own deposition. So what it does, it leans over to the side and sorts depositing here — and this starts subsiding.”
Campanella says the river is so huge, and the sediment so dominant, that it wins the battle — and it dominates the relatively weak tides and along-shore currents of the Gulf of Mexico.
“That’s why we pro- grade and protrude,” Campanella says. “What’s happening in the opposite direction, now, we do have along-shore currents — they’re sweeping some of these sediments westward — and this forms south central Louisiana and the chenier plains of the southwest, so there’s land building going on all around.”
But one of the greatest, and saddest, paradoxes of history is that while the Mississippi has always been New Orleans’ most important feature — the very reason for its existence — for almost 300 years it was also seen as its biggest problem.
“There were always challenging elements to making peace with this deltaic geography, fundamentally because it is existentially a product of dynamism and humans resist this,” Campanella says. “We evolved in continental environments with hard earth beneath our feet, and so we imposed hardness and rigidity on an environment that is fundamentally fluid and dynamic.”
But the Mighty Mississippi wasn’t going to give in without a fight. The first levees around the new French colony were easily breached. Floods were common, as historian Larry Powell of Tulane University explains.
“Well, the levee system was born as an afterthought, and for many years it was very piecemeal,” Powell says. “It was an afterthought because, when Bienville first flung a few shacks down on this land and called it New Orleans, he didn’t think about building levees until the whole settlement was underwater for about six weeks.”
Powell says that would have been in 1719, the very first year after the city’s founding.
“The very first year, and the place went underwater, and they said, ‘Oh, we better build some levees,’” Powell says. “And, you know, in 1728, there was a bigger flood, in 1735, a real bad one in 1785, one in 1790, ’91… I mean, they were recurring.”
But the river’s days of being a free flowing force of nature were already marked. Young America was consumed with the ideal of a manifest destiny, and controlling the Mississippi was a challenge it wouldn’t resist.
By the mid-1800s, a patchwork of taller, wider levees stretched almost 500 miles from New Orleans to Greenville, Miss. They were poorly designed, often collapsed and breached during big rivers.
But more importantly, the federal government was now involved, and an engineering debate about how to deal with high rivers was nearing a conclusion that would have grave consequences for all time.
“You had one report by a civil engineer named Charles Ellet that advocated a multi-tiered response to flood control, with not just levees, but also diversions and spillways and reservoirs and that kind of thing,” says historian Powell. “And then you had Andrew Humphries, who was this fanatical believer in levees only — and Humphries won out, partly because it was less costly to build levees than to do all this other stuff.”
The upstart nation had made a decision to control nature by putting this beast of a river in a straight jacket. It wasn’t easily accomplished, of course, and the battle between river and nation continued for decades until the Great Flood of 1927. With the nation shocked at seeing half the lower river valley under water, Congress ordered the U.S. Army Corps of Engineers to never let this happen again, to build the biggest, best levee system ever.
And by the mid-1930s, the job was done.
The Mississippi, that great feature of nature that had drained a continent for thousands of years, was now squeezed into a pipe.
That system was considered one of the great engineering feats in the nation’s history. But it was also a death sentence for most of southeast Louisiana.
“This land is built of mud, millennia of mud, and it sinks, it compacts,” says Powell. “And if it’s not replenished by this formidable land-producing machine — which is what the river really is, among other things — it’s going to continue to subside until it’s well below sea level.”
Yet, as big a mistake as that was, it wouldn’t be a quick death for this area. The subsidence would come mostly at a snail’s pace. Researchers say if the levees were all we had done, the river delta would have lived a long, productive life for hundreds of years, and the wetlands that were in place in the mid-1930s would still be in pretty good shape today.
But that’s not all we did.
About the time those levees were being completed in the 1930s, a signature event was taking place on the delta that would compress that disaster time frame from hundreds of years to a single human lifetime.
Oil and gas were discovered in our wetlands.
Support for The Louisiana Coast: Last Call comes from the Greater New Orleans Foundation, an organization that addresses the challenges facing people who live and work in the coastal communities of Southeast Louisiana.
The Louisiana Coast: Last Call is written and reported by Bob Marshall, and produced by Fred Kasten.
The Louisiana Coast: Last Call
The Louisiana Coast: Last Call