We’ve covered several times in Erosion Control the problems of Louisiana’s shrinking coastal marshes. The reining-in of the Mississippi River with levees, channels, and other structures has certainly reduced flooding and made the areas adjacent to the river more manageable, but over the last century and a half it has also prevented the river from depositing silt—about 400 million tons of it a year—as it had done for millennia.  

This recent article from the New Yorker explains the process in detail—how the river periodically changed direction before we prevented it from doing so, how the deposition of silt along these new routes created the Louisiana coastline, and why—as the soft soils along the water’s edge dry out and become compacted—that coastline is disappearing. The Mississippi River essentially “assembled the Louisiana Gulf Coast out of bits and pieces of Illinois and Iowa and Minnesota and Missouri and Arkansas and Kentucky,” but it’s no longer doing so. If either Delaware or Rhode Island had lost as much land as Louisiana has in the last few decades, the article notes, the US would now have only 49 states.  

There’s a potential solution on the horizon, but it involves undoing some of the work we’ve so carefully crafted over the years. Louisiana’s Coastal Protection and Restoration Authority, which has undertaken several marsh-creation projects, has a plan to knock holes in some of the levees along the Mississippi and Atchafalaya Rivers. “The openings will be gated and channelized, and the channels will themselves be leveed,” the article explains. “C.P.R.A. likes to characterize the effort as a form of restoration, a way to reestablish natural processes. And that’s true, but only in the sense that trucking salmon upstream, or using planes to train whooping cranes to migrate, is natural.” Still, if the plan works, it will divert water, and the sediment that water carries, toward Barataria Bay and start building up land. A second plan diversion project will divert more water and sediment to another area of the shrinking Plaquemines Parish. The projects will cost, respectively, $1.4 billion and $800 million, and most of that money would come from the BP oil spill settlement fund.  

You can read more on the sediment diversion projects here.