Last week NPR had a story on Louisiana's plans to divert the Mississippi River to protect the coastal wetlands from further erosion. These wetlands, in addition to being important wildlife habitat, help protect Louisiana from hurricane damage. The erosion also threatens oil facilities, seafood production, and ports.
I have borrowed freely from that excellent piece in composing this post.
About every 30 minutes or so, a piece of southeast Louisiana the size of a football field vanishes into the Gulf of Mexico. Between 1932 and 2000, Louisiana lost about 1,900 square miles of land - the size of 1.5 Rhode Islands - and could lose another 700 square miles during the next fifty years if nothing is done. About 90% of all USA coastal wetland loss is borne by Louisiana.
The above map, from the U.S. Geological Survey (download below) shows the land loss from 1932-2000 in red with predicted land loss from 2000-2050 shown in yellow. Not a pretty sight.
The following is a USGS report describing historical and predicted Louisiana coastal land changes, 1978-2050.
http://www.lacoast.gov/landloss/NewHistoricalland.pdf
So what's the problem? Well, we've engineered the river system to such a degree that virtually all of its sediment load is dumped into the Gulf of Mexico. The river does not replenish its floodplain. Southern Louisiana was built over time as the river changed course, depositing sediment. But now, according to Denise J. Reed, a professor at the University of New Orleans, since we've constrained the Mississippi River within its banks, the only place it can deposit sediment, about 120 million tons per year, is in the Gulf of Mexico. As a result, as southern Louisiana erodes, there is nothing to replenish it.
State and Federal officials have tried to keep up with the erosion by dredging sediment and depositing it in critical areas - essentially trying to do what the river should be doing. But it's a losing proposition; for every one square mile created, five more vanish.
The state wants to alter the course of the Mississippi below New Orleans, to the east, west, or both, so that sediment is deposited in shallow water and used to rebuild the coastline. The legislature has approved the master plan; total cost could be $5 billion. Money from offshore oil leases will help pay for the project.
It won't be easy to do this. For one thing, keeping river traffic moving while the work is ongoing will be a daunting task. Oyster fishermen, whose livelihood may be threatened by the project, are none too happy. There is already talk of lawsuits delaying the project for years.
If you're wondering, "Why bother, I don't live in Louisiana?", remember that over half the nation's grain moves through Louisiana ports, and of course, consider all the petrochemicals and other goods that move through New Orleans and Baton Rouge, two of the largest USA ports.
In a forthcoming post I'll recount a prescient lecture I heard 35 years ago, in which I learned where the Mississippi River really wants to go.
And the river she rises
Just like she used to do
She's so full of surprises
She reminds me of you.
-- "Heart of the Night" by Poco (lyrics by Paul Cotton)
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