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Ecosystem Restoration as Infrastructure–MRGO, Part 1

 

MRGO and its Spoil Bank Runs between Lake Borgne and Breton Sound

MRGO and its Spoil Bank Runs between Lake Borgne and Breton Sound

 

In 1965 the U.S. Army Corps of Engineers completed the Mississippi River and Gulf Outlet, a deep draft navigation designed to shorten the distance between the Port of New Orleans and the Gulf of Mexico. At completion it was 650 feet wide and 36 feet deep. The sides of its channel sloughed off into the bottom. By 2005 the wake generated by Ocean-going ships had widened MRGO’s channel to 2,200. The Corps of Engineers spent $22 million a year to maintain the depth of its channel, which had been increased to 40 feet.

 

MRGO at Shell Beach

MRGO at Shell Beach

 

 

MRGO extended 76 miles into the wetlands southeast of New Orleans, cut through the cypress swamps that protected New Orleans, shredded brackish and saline marshes that slow down and reduce storm surges, broke through ridge created by Bayou la Loutre, a speed bump for hurricane storm surges, and the hydrologic barrier between Breton Sound and Lake Borge, ripped up submerged vegetation that anchored the floor of marshes west and south of Lake Borgne, and coverted 20,000 acres of wetlands to open water and had a negative impact on another 618,000 acres.

 

MRGO Spoil Bank

MRGO Spoil Bank

MRGO Spoil Bank and Hurricane Levee: Shell Beach

St. Bernard Parish, Louisiana

The MRGO spoil bank: It’s six-tenths of a mile wide, wide enough to support a live oak forest at Shell Beach, but too exposed to open water to protect the hurricane levees of St. Bernard Parish.

When the Corps of Engineers dredged MRGO, excavators cast their spoil to the south side of the channel, building a wide spoil bank that filled all of Turiano, Grass, Nicks Lagoons, and part of Portman Lagoon, all near Shell Beach, and all a part of the 27,600 acres of estuarine wetland and lagoon habitat lost to open water and spoil. This is the mid-section of Reach 2 of the channel. This is the reach that cut through the Breton Sound Marshes, the natural levees of Bayou la Loutre and Bayou Yscloskey, and the cypress swamps that protected New Orleans. 

The Corps of Engineers constructed the St. Bernard Parish hurricane protection levee, part of the Lake Pontchartrain and Vicinity Hurricane Protection Project, of highly erodible sediment dredged from the channel, set it right out of the edge of the spoil bank. 

On the eve of Katrina sandy core of the levee offered no defense to the storm surge raging in from Lake Borgne. Parts of the levee reached the intended 17.5 feet, much of it was unfinished and reached only 15.5 feet or even 13.5 feet. The Corps of Engineers constructed the levee in stages, and waited for the soils to dry and settle before moving on to the next stage. The engineers completed the third stage in 1994-1995 and were waiting for funding from Congress for the final stage, which would have brought the levee to 17.5 feet. This is what faced Katrina’s storm surge, long, tall waves that plowed across Lake Borgne, breached the levee in many, many places, ripped across the declining wetlands, overtopped the back levee, and flooded St. Bernard Parish.

In January 2006 the Working Group for Post-Hurricane Planning for the Louisiana Coast ruminated on spoil banks and levees in their publication of that month. The “V” formed by spoil banks and levees of the MRGO and Intracoastal Waterway funneled the storm surge out of Lake Borgne into the Lower Ninth Ward and New Orleans East via the Industrial Canal. The straight spoil banks along oil and gas canals cut through meandering bayous, stop the sheet flow of water through the marshes, capture freshwater that might nourish the marshes, and send it directly toward the gulf. The spoil banks of navigation canals, like MRGO and the Houma Nav deliver saltwater to fresh wetlands, killing them.

But, what if we could analyze the effects of these artificial canals and ridges and incorporate them into coastal planning. 


          Day, John, Mark Ford, Paul Kemp, and John Lopez, “Mister Go Must Go: A Guide for the Army Corps’ Congressionally-Directed Closure of the Mississippi River Gulf Outlet,” Environmental Defense Fund et al., December 4, 2006, http://www.environmentaldefense.org/documents/5665_Report%20-%20Mister%20Go%20Must%20Go.pdf; Seed, R.B., et al., Investigations of the Performance of the New Orleans Flood Protection Systems in Hurricane Katrina on August 29, 2005, Berkley, California: University of California at Berkley, July 31, 2006, (2-6)-(2-7), http://www.ce.berkeley.edu/~new_orleans/report/CH_2.pdf; Working Group for Post-Hurricane Planning for the Louisiana Coast, A New Framework for Planning the Future of Coastal Louisiana after the Hurricanes of 2005, Cambridge, Maryland: University of Maryland, Center for Environmental Science, January 26, 2006, 17-18, http://www.umces.edu/la-restore/New%20Framework%20Final%20Draft.pdf.  

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3 Responses

  1. […] of New Orleans,  has been officially closed for several weeks now. It will remain a factor in the landscape for a long time, until a second closure is made at Bayou Bienville, close to New Orleans, and until […]

  2. […] Mississippi and cut a few miles off the trip between the Gulf of Mexico and New Orleans. Read more here and go to the categories section of this blog and scroll down to the MRGO category for other […]

  3. […] August 27, Rachel Maddow devoted her program to Louisiana’s coastal wetlands and the role MRGO, a navigation channel constructed in the 1960s to shortcut the trip between the Gulf of Mexico and […]

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