Seabrook storm surge gate gets environmental OK
http://www.nola.com/hurricane/index....ate_gets.html#
Construction of the proposed Seabrook storm surge gate at the Lake Pontchartrain entrance to the Industrial Canal has been given environmental approval by the local Army Corps of Engineers commander, clearing the way for work to begin by June.
The structure, which is expected to cost $155 million, will include two lift gates, or metal structures that will be lowered in place before a storm. The lift gates will be on each side of a sector gate, two wedge-shaped structures that will swing closed to block the channel used by barges and ships to enter the lake.
"This is the last gap that needs to be closed in the east bank hurricane risk reduction system," said Col. Robert Sinkler, commander of the corps' Hurricane Protection Office, which is overseeing the project. "It is the only true gap that still exists."
The gates are being designed to protect from surges created by a hurricane with a 1 percent chance of occurring in any year, a so-called 100-year storm.
The structure would be a record-breaking project for any corps district, Sinkler said. But it only ranks third in terms of size and complexity among post-Katrina improvements in the New Orleans area, behind the $1.3 billion combination of gates and surge barrier walls being built along the eastern edge of Lake Borgne and the $1 billion West Closure Complex that will block surge from entering the Harvey and Algiers canals on the West Bank.
Combined with the Lake Borgne surge barrier, improvements to floodwalls along the Industrial Canal, and levees and floodwalls along the Gulf Intracoastal Waterway, the gate will complete protection from storm surges entering the Lower 9th Ward and eastern New Orleans from the east side of the canal and entering the Upper 9th Ward and Pontchartrain Park areas on the canal's western side.
The environmental approval, which came last week, includes commitments by the corps to assure that two endangered species won't be hurt by construction. The canal will be monitored for the presence of Gulf sturgeon and West Indian manatees, and if any are found to be present, biologists will determine how to get them to move out of the channel before work resumes.
The Gulf sturgeon spends part of its time in the lake and in interior wetlands, with some using the canal to move into the Gulf of Mexico during its life cycle.
Manatees often are found in the lake in summer months, and may use the canal to reach the Gulf on their way to warmer waters in the fall.
The environmental report outlines a number of temporary impacts, including reductions in the number of fish larvae able to move through the canal and possible fish kills when the canal's lake entrance is shut down for 6 to 12 months during construction.
The project also is expected to impact a number of businesses along the canal.
In December, a Port of New Orleans official warned that the project could cost the area's economy more than $150 million and nearly 3,000 jobs.
Col. Robert Sinkler, commander of the corps' Hurricane Protection Office, which oversees the gate project, said shipping will still have access to much of the waterway from the canal lock at the Mississippi River and from the Gulf Intracoastal Waterway.
He said the corps considers the project's effects to be legally similar to the effects of street reconstruction projects to adjacent businesses.
The businesses are all tenants of the Port of New Orleans, which must still agree to provide access to its land for the construction project, Sinkler said. He said those negotiations are not expected to delay a June start date for construction.
In October, the corps awarded an initial contract for $495,000 to design and build the gate structure to Alberici Constructors of St. Louis, Mo. A challenge of that award by a competing bidder resulted in negotiations between Alberici and the competitor, which cleared the way for the Government Accountability Office to clear the project for construction, Sinkler said.
Under the terms of its early contract, Alberici is expected to be awarded two contract options that will account for the majority of the estimated $155 million in construction costs.
The complicated construction process will begin with the filling of a scour hole on the canal's bottom that stretches into the site of the new gate. The hole will be filled with sand barged to the site from another location.
Then a special mixture of Portland cement and other ingredients that allow concrete to cure under water will be poured on the canal bottom to form a "tremie slab." A coffer dam will then be constructed around the slab and drained to allow construction of the gates.
When the coffer dam is completed, its walls will be at the same height as the completed gates, blocking surges from the lake from entering the canal.
The corps environmental report, titled "Individual Environmental Report #11 Tier 2 Pontchartrain," was conducted under an expedited process approved in the aftermath of Hurricane Katrina. A copy is available on the Web at
http://www.nolaenvironmental.gov.
Mark Schleifstein can be reached at
mschleifstein@timespicayune.com or 504.826.3327.
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They couldn't even accept clay with too much gravel in it, so I doubt clay full of 200-year-old pipes, bricks, pottery pieces, and newspapers will make the grade. That's also our tax money the Army Corps would use, so that's not really a good way to recoup costs.
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