Tuesday, April 14, 2015

That Sinking Feeling: Land Lost and Land Gained in the Mississippi River Delta


By John Shepard

Meraux Foundationʻs Arlene Meraux River Observation Center at Docville Farm.
You might think that in one of America’s most important ports—the world’s fourth busiest by bulk tonnage—the crucial link to the sea would be prominent, obvious, maybe even celebrated. But in and around New Orleans, the Mississippi River isn’t much to be seen. I wonder how the fate of the river delta’s beleaguered natural systems might be different if the river, whose sediments have built and sustained one of most biologically rich coastal environments on the planet, were more accessible, or even just more visible. 

St. Bernard Port in-stream transfer terminal.
I write this from a rare window on the river where it flows past a shining new River Observation Center at the Meraux Foundation’s Docville Farm in St. Bernard Parish, where a CGEE River Institute is planned for this coming summer. The view before me from an upper level of the five-story building constantly draws my attention. The New Orleans skyline is visible about ten miles upstream. A parade of large cargo vessels pass by, visible over the top of the massive US Army Corps levee and the trees just beyond it that line the riverbank (a Panamanian crude oil tanker with the intriguing name Esteem Splendour just passed by heading downstream). These ships and their crews are in a world apart, and I can’t help but wonder what it’s like for the pilots as they keep an eye on currents and monitor other traffic while navigating the twisting river bends. I have met many people whose livelihoods are tied directly to the river delta’s amazingly fertile lands and waters—yet for almost all of them the river itself is not part of their direct experience.

The same levees that obstruct views of and access to the river protect human communities from the damages of river floods. But they have also been depriving the delta’s wetlands of sediment carried by the river. Here, in a nutshell, are the dynamics of the situation: 

Louisiana coastal wetlands from above.
For millenia, the slurry-like sediment that makes up the Delta’s land mass has been regularly replenished with vast amounts of new material every time the Mississippi flooded—usually, each spring and fall. This land naturally oozes into the Gulf of Mexico in a process called subsidence. For almost 100 years, however, levees have disrupted the land-loss/land-building process. Instead of replenishing delta wetlands, the levees contain the river-borne sediment, which is carried through the delta to the Gulf, where it disperses into the abyss off of the continental shelf. Sea-level rise compounds matters. While the world’s seas have been gradually rising for hundreds of years, our changing climate is exacerbating the rate at which shoreline is disappearing. The U.S. Fish and Wildlife Service’s coastal management plans anticipate a rise in sea level in the Gulf of 1.5 feet between 2000 and 2050. More recent studies suggest that these plans may be too conservative.

Diverting sediment from the river and transporting dredge material into the surrounding wetlands are widely recognized core strategies for saving the delta—strategies that are central to the current Louisiana coastal restoration Master Plan. However, there is much controversy over which strategy is best, and where and when they should be used. Last year we made an excursion by boat from a landing in Venice near the end of the Mississippi’s navigation channel to witness the land-building that diversions—in this case a half-mile-wide levee breech—can bring about. Here’s a short video of that trip to the West Bay Diversion:

It’s a shame more people can’t witness first hand such age-old processes that the river has wrought, and even sit a while by its banks to take in its swirling currents. When next summer’s contingent of teachers come together at Docville Farm, we’re planning to build into their experience a direct introduction to the river flowing with such power just beyond the levee.

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