A general contractor is installing two 550-ton sector-gate leaves in a $1.3-billion barrier designed to reduce the risk of a hurricane’s storm surge on New Orleans’ exposed eastern side. The leaves will plug a big hole in the city’s armor for the 2011 hurricane season.

Photo: Courtesy of USACE

Ring wall shields two 550-ton sector-gate leaves when open and braces them against storm loads when closed.

Massman Construction Co., Kansas City, Mo., is installing the two 75-ft-wide, 42-ft-tall sector-gate leaves to form an armored door for a 150-ft-wide navigable passage through the 1.8-mile-long, 26-ft-plus-elevation barrier, known as the Inner Harbor Navigation Canal-Lake Borgne Storm-Surge Barrier, or IHNC. It is part of a much larger defense system designed to reduce flood risk for the entire city.

The gate will help the system meet the U.S. Army Corps of Engineers’ design standards to reduce risk from a storm surge that has a 1% chance of occurring in any given year—often referred to as a 100-year storm.

The IHNC surge barrier also includes a 150-ft-wide bypass barge gate, adjacent to the sector gate, and an already installed 56-ft-wide vertical-lift gate opening for recreational craft on another channel to the south. The barge gate—a concrete-loaded barge designed to be submerged to block another pass in the event of a surge—will be on-site by June 1 so it can be pulled into place if needed.

The gate is massive. “It has the highest storm design load of any structure in the world,” says retired Col. Vic Zillmer, the Corps project manager on the IHNC.

A joint venture of TetraTech INCA, Metairie, La., and Ben C. Gerwick, Oakland, Calif., designed the gate and supporting structure, including a 20-ft-wide ring wall that curves from the gate junctures to abutments to fortify the gate.

From its sill under the channel to the roadway surface on top, the 120-ft-long ring wall is 42 ft high. It has a 3-ft-thick outer wall, a 2-ft-thick inner wall and 20-in.-thick connecting walls, Zillmer says.

The gate leaves, fabricated at Shaw Global in Delcambre, La., are 42 ft tall, and the floodgate shield has an arc length of approximately 103 ft, says Larry Haser, vice president of operations management for Shaw Environmental & Infrastructure, Baton Rouge, the prime contractor.

The leaves are to being set “in the wet,” rather than inside a dry cofferdam. “The gates will be moved into final position using push boats, winches and guides,” Haser says. All three gates are expected to be operational for this hurricane season, but they will not completed until 2012.