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The Ratio of the Atchafalaya to the Mississippi

The Mississippi at the Old River Control Structure

The Mississippi at the Old River Control Structure

The New Orleans District of the Corps of Engineers has initiated a study that would change the ratio of Mississippi water and sediment that could be diverted to the Atchafalaya River, which is the only functioning distributary of the Mississippi, that is a river that carries water from the big river to the Gulf of Mexico, particularly come floodtime.

Several months ago I wrote a history of the Old River Control Structure and the Flood of 1973 and about the need for Atchafalaya water and sediment for rebuilding wetlands in the Terrebonne Basin. Len Bahr at lacoastpost explains the role of the Atchafalaya in Corps’ thinking and in the future of Louisiana’s wetlands far better than I can

Bayou Lafourche at Donaldsonville, Louisiana

Bayou Lafourche at Donaldsonville, Louisiana

When Europeans settled Louisiana the Mississippi had several distributaries: Bayou Lafourche, Bayou Plaquemine, Bayou Manchac, and the Atchafalaya. As people settled along the bayous, we closed the distributaries at their heads to prevent flooding the new communities. Not long ago I wrote about efforts to divert freshwater and sediment along Bayou Lafourche to wetlands in the Barataria and Terrebonne Basins south of Donaldsonvile.

When the Corps of Engineers ran the Mississippi River levees clear to Venice, the engineers left the Atchafalaya open to carry of Mississippi floodwater and protect New Orleans from flooding. They turned the Atchafalaya into a floodway and bracketed the river between between levees between levees set seventeen miles apart.

By the 1950s it became clear that the Mississippi had become too long and too flat and was going to do its river thing: divert to the Atchafalaya and leave Baton Rouge high and dry without a deep draft Mississippi to service their ports, because the Mississippi south of the Atchafalaya would fill with silt.

When the Corps built Old River Control in the 1950s it rationed 30% of the Mississippi to the Atchafalaya through the structure. That ratio has not change in 50 years, even  though it has become clear in the last 50 years that Louisiana’s wetlands desperately needed the freshwater and sediment the Atchafalaya could carry to them.

The Atchafalaya, which is building land at its mouth, offers many possiblities for land building in other places. In 2006 the Lake Pontchartrain Basin Foundation and the Coalition to Restore Coastal Louisiana published the first issue of the Multiple Lines of Defense Strategy. In the assessment team’s response to the publication of Louisiana’s Comprehensive Master Plan for a Sustainable Coast, configured in the wake of Katrina and Rita, the scientists suggested diverting the Atchafalaya through East Protection Levee and Lake Palourde and into the fresh marshes of the Penchant Basin in the northwestern region of the Terrebonne Basin. They even upped the ante, suggesting that all of the Atchafalaya be diverted to the Terrebonne Basin. Check out page 23 in the pdf report.

Fresh Marshes along Bayou Carencro in the Penchant Basin

Fresh Marshes along Bayou Carencro in the Penchant Basin

Finally, Keith Magill published an editorial in Houma Today last sunday about the choices Louisiana faces in light of the LSU report on rising sea levels and sinking land across the coast. To get a feel for what we will lose if we lose the Louisiana coast, go to Bayou Woman, where Wendy Wilson Billot, details life along the bayous of the Terrebonne Basin.


2 Responses

  1. It won’t be impossible for the rivers silt to reclame the wetlands, it will just take centurys. As long as man tries to change what mother nature needs to do, man will lose. Take your pick on what you want, let the rivers have the swamps back and let them rebuild them or loose them all together. Look what we have done in 50 years.

  2. […] Red River and its sediment to the Gulf of Mexico, where it is building new land. Last summer the New Orleans District of the Corps of Engineers announced it would study changing the ratio of Mississippi to the Atchafalaya with an eye to […]

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