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Canal Closure Works Proceed, Pump Stations Are Nexthttp://enr.ecnext.com/free-scripts/comsite2.pl?page=enr_document&article=20050902c
(enr.construction.com - 9/02/05 issue)The contractor working on the 17th St. Canal closure in New Orleans expected to complete the job by midday Sept. 2, then immediately move to stopper the London Ave. Canal in the same manner, according to a U.S. Army Corps of Engineers project manager.
Plugging the two canals will enable contractors to plug major canal breaches caused by overtopping from Hurricane Katrina's storm surge on Aug. 29. Floodwaters from Lake Pontchartrain overtopped the canal's 1-2-ft-thick steel and concrete-capped floodwalls, causing scouring from their earthen levee foundations. The water's force opened breaches of some 400 ft in each canal wall, allowing Lake Pontchartrain-at that point some five ft above flood stage to flow into the city which averages 6-14 ft below sea level in many places.
The lake is dropping toward its natural level of 0.5-1 ft above sea level, draining through the Rigolettes, Chef Mentour and Seabrook passes, according to gauge data monitored by the Corps. The level was at 2.1 ft on Sept. 1, said Al Naomi, program manager from the New Orleans District. He and several hundred employees from New Orleans were coordinating work from the Corps' Mississippi Valley Division headquarters in Vicksburg, Miss. "It's very difficult to maintain contact with our people on the ground in New Orleans," he said. Bell South provides the telecommunications backbone in the New Orleans area and is struggling to restore service in the 504 area code. Individual cell phone providers are replacing batteries in cell phone towers, Naomi added, but they restore service sporadically, typically from 24 to 48 hours. "One day the Cingular customers will have good service, but the next day they'll be down and the Nextel folks will be working. Communications is our biggest problem right now. It's nothing, compared to the people that need food and water and medical assistance, but it is a problem," he said.
Boh Brothers Construction Co., a New Orleans-based contractor, worked through the night, driving sheet piles into the 17th St. Canal base from the Hammond St. Bridge. Emergency generators provided light, said Tom Podany, a Corps project manager. As they were closing the flow of water into the canal from the lake, Blackhawk helicopters were placing some 120 sandbags of 3,000 lbs each into a 450-ft-long breach in the canal floodwall. As soon as Chinook helicopters-now in use to evacuate people from rooftops nearby-are available, 20,000-lb sandbags will be placed, said Podany. A convoy of contractors is also trucking rock to the site from a Bertucci Contracting Corp. bulk handling dock on the Mississippi River some five miles away, Podany said. "They're placing the material along the canal, about 500 ft from the breach," he said. "As soon as the sheet piles are in place, they'll start filling the breach with rock."
At the same time, the Corps and private contractors are building a "flexiboat bridge" from barges laid end to end across a flood area east of the 17th St. Canal. Its purpose is to provide access to the London Canal, so that Boh Bros. crews can drive sheet piles there and began to plug a breach nearly as long as the opening in the 17th St. Canal. Once both breaches are closed, Podany said, contractors will remove the sheet piles and the New Orleans Sewerage and Water Board will be able to restart its pumping stations and push the water from behind the flood protection system, back into the lake. The Corps will also strategically place five portable 42-inch pumps, each with a capacity of 1,000 cu ft per second, to accelerate drainage.
The Sewerage and Water Board is inspecting its pump stations, preparing to bring the flooded ones back online as soon as possible, Naomi says. "Some are already working, but they're in areas that are not affected right now," he added. A power station on Claiborne Ave., near the Jefferson Parish line, is critical to the effort, engineers said. The station, which was flooded and knocked offline, supplies 60% of the power to S&WB pumping stations. "It's a specially designed system, dedicated to the pumping system. It runs on 25 cycles. It's old, but the Corps and the Sewerage and Water Board just spent a lot of money making sure it's in good running order." The station, and a high-capacity pump station, took on water, but are on relatively high ground, he said. Crews will place about 1,000 bags of cement around the station's perimeter and pump it dry before restarting the power, Naomi said. He was not sure how soon that will be, however.