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Understanding the developing Braithewaite situation
by ectopia
Monday, Sep. 01, 2008 at 11:46 PM
About two hundred residences in the Braithwaite subdivision along Highway 39 at the St. Bernard/Plaquemines Parish boundary southeast of New Orleans were threatened with flooding during the afternoon of Monday, September 1, 2008 as hurricane Gustav came ashore in southern Louisiana. The towns of Braithwaite and Port Nickel were ordered to evacuate. The status of this threat may have subsided somewhat tonight as the Army Corps of Engineers opened gates on the Caernarvon Mississippi River Diversion, thus lowering stress on the overtopped levee. Water in the Mississippi River is currently lower than the levels in the canals.
(this article continues to clarify the Braithwaite situation and history)
About two hundred residences in the Braithwaite subdivision along Highway 39 at the St. Bernard/Plaquemines Parish boundary southeast of New Orleans were threatened with flooding during the afternoon of Monday, September 1, 2008 as hurricane Gustav came ashore in southern Louisiana. The towns of Braithwaite and Port Nickel were ordered to evacuate. The status of this threat may have subsided somewhat tonight as the Army Corps of Engineers opened gates on the Caernarvon Mississippi River Diversion, thus lowering stress on the overtopped levee. Water in the Mississippi River is currently lower than the levels in the canals.
The compromised levee is adjacent and parallel to Clearwater Canal and is a Plaquemines Parish responsibility, not built by the Army Corps of Engineers. Crews have worked through the afternoon and evening to maintain the levee’s structure. Several national media report that parish officials evaluate the levee materials as “soft” and do not expect them to withstand the stress of Gustav’s storm surge and rainfall.
The Caernarvon diversion was constructed in the early 1990s in response to increasing invasion of freshwater marshland by the open waters of the Gulf of Mexico and decreasing levels of nutrients and sediment reaching the marsh from freshwater sources. About 3,400 acres of wetlands have been lost since 1956 in Caernarvon’s target area of 15,556 acres in the Breton Sound basin. Caernarvon expects to recover about a quarter of that amount of wetlands in the first twenty years of operation, commencing 1992.
The Caernarvon operation is NOT a pumping station built for flood water containment or displacement. It manages outfall from the Mississippi River into Big Mar and Bayou Mandeville. The project includes the diversion structure and water “control structures” (boxed flood gates) that were installed in existing “earthen closures” (levees) and can permit a maximum of 8000 cubic feet per second of fresh water, sediment and nutrients to enter wetland areas that had been previously isolated.
To displace canal water into the currently lower level Mississippi, this process will be allowed to flow in reverse.
Caernarvon was funded under the Water Resources Development Act of 1992. The “control structures” were installed along a roughly circular path of waterways west of Big Mar and north of Lake Leary, including the Delacroix Canal and D P Canal and Reggio Canal. The Mississippi River diversion gate is on the south bank between the towns of Braithwaite and Poydras, near St. Bernard State Park and Braithwaite Country Club Lakes subdivision and Hidden Oaks Golf course. The project takes its name from the Caernarvon plantation that once occupied the gate’s site. Prior to construction, a site survey found no historic structures or artifacts that would be displaced by the diversion project.
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