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Ecosystem Restoration as Infrastructure–Houma Nav, Part 3

To understand the reasoning behind the Houma Navigation Canal Lock, you must first understand the ebb and flow of freshwater and saltwater in the Louisiana coastal marshes before the construction of the levees along the Mississippi, which stopped the annual influx of freshwater into the marshes. 

Before the construction of the levees, the Mississippi flooded the Louisiana marshes with freshwater, sediment, and nutrients every time it flooded.  Every fall, the Gulf of Mexico washed saltwater into the marshes. The following spring, the Mississippi floods flushed out the saltwater. This went on until the construction of the levees stopped the ebb and flow of water in the marshes delivered the Mississippi floods straight to the Gulf of Mexico, where it is useless for landbuilding.

The Atchafalaya River still delivers freshwater to the western Terrebonne Basin, and much of it through the Houma Nav through a very round about way. 

The Atchafalaya is connected to the Mississippi through the Old River Control Structure, 200 miles north of New Orleans. The structure, which is set in the Main Line Levee, prevents the Mississippi from diverting to the Atchafalaya and rations 1/3  of the Mississippi to the Atchafalaya.

 

Freshwater from the Atchafalaya flows through the Avoca Island Cutoff to Bayou Chene and then the Intracoastal Waterway.

Freshwater from the Atchafalaya flows through the Avoca Island Cutoff to Bayou Chene and then the Intracoastal Waterway.

 

 

When the Mississippi floods every spring, so does the Atchafalaya, when it rises 3 to 4 feet above sea level, high enough to drive freshwater into the Intracoastal Waterway for a distance of up to fifty miles east of Morgan City. A lock in the Intracoastal Waterway prevents freshwater from flowing directly east along the waterway. So it flows around Avoca Island through the Avoca Island Cutoff, into Bayou Chene, and then to the waterway.

 

The Intracoastal Waterway Connects to the Houma Nav near Houma

The Intracoastal Waterway Connects to the Houma Nav near Houma

 

 

From the waterway it flows to the Houma Nav, which carries it south.

 

Lock on the Houma Nav

Lock on the Houma Nav

 

Which brings us to the proposed lock on the Houma Nav. The Louisiana and the U.S. Army Corps of Engineers would close the Houma Nav and bypass the closure with a new channel and a lock. It will be placed at the confluence of Bayou Grand Caillou and the Houma Nav.

The lock will be closed for about 90 days in the fall when saltwater in flowing into the wetlands. I will be opened for about 90 days in the spring to retain freshwater flowing into the canal from the Atchafalaya. 

And the lock will be closed when hurricanes threaten to stop storms surges from sweeping into the canal. 

What is stunning is the State of Louisiana does not consider the lock infrastructure but rather coastal restoration.

Restoration is infrastructure.

Congress authorized the lock in the 2007 Water Resources Development Act.

Source: The Louisiana Department of Natural Resources, Coastal Impact Assistance Program Application, Houma Navigation Canal Lock, May 22, 2006.

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