Time running out on levee repairs for New Orleans
Published January 15, 2006
NEW ORLEANS - In New Orleans, the apocalyptic clock is ticking - again.
Ravaged last year by one hurricane and slapped by the fringes of another, the city faces a 2006 storm season that begins in less than five months - not much time to repair the tattered ramparts that keep New Orleans from being swallowed by the sea.
This year's hurricane season begins June 1. By that date, the U.S. Corps of Engineers says it expects to have the Crescent City's levees restored to pre-Katrina condition.
It's an enormous task. It will take about 4-million cubic yards of fill - a nearly Superdome-sized pile - to repair the 170 miles of levee destroyed or damaged by Katrina.
"So far we're on schedule and we're doing pretty good," said Col. Lewis Setliff, leader of the repair effort.
There are many who fear that may not be good enough.
"This is just a few Band-Aids, really," said Ivor van Heerden, a civil engineer at Louisiana State University.
"We really need to go the step further and start implementing projects now that would make New Orleans safe."
Setliff says he understands such concerns. But as commander of Task Force Guardian, his mission is to repair the levees in time for hurricane season, and that is what he vows to do. New Orleans will simply have to live through 2006 with about the same protection it has had for the past 30 - even though that wasn't enough to fend off Katrina.
"Everybody wants a lot of the long-term solutions overnight," Setliff said, but there is neither time nor funding to make major advances to the barriers by June.
The $1.6-billion repair effort will use some improved construction methods and materials compared to what was in place before, decreasing the chances that levees breached by Katrina will fail again. It will also bring levees that had gradually settled over the years back up to their original height.
But it will not raise the height of any levees or replace any sections that survived Katrina intact.
"We don't have the authority to just go in there and raise levees," Setliff said. "We are allowed to make some smart decisions."
For example, in every situation where it can, the Corps of Engineers is replacing the "I-walls" that top many levees with more stable "T-walls." An I-wall is simply a vertical concrete barrier anchored to the levee by steel sheet pile driven vertically into the ground.
A T-wall sits on a horizontal concrete base that protects the soil at the wall's base from crashing waves on the wet side and, in a worst-case scenario, from water pouring over the levee onto the dry side. During Hurricane Katrina soil erosion underneath floodwalls contributed significantly to a number of breaches by washing away the ground the concrete barriers sat on.
To make them even stronger, T-walls are also anchored by multiple steel beams, rather than a single sheet. Those beams are driven into the levee diagonally, providing more support.
Most challenging to repair are the breaches along the drainage canals that carry rainwater from the heart of New Orleans north to Lake Pontchartrain. Because so much of New Orleans is below sea level, pump stations have to lift water from the city's storm sewers into the canals, which then flow into Lake Pontchartrain.
During a hurricane the lake's surging waters reverse the flow in the canals, pushing water deep into the city.
Floodwall-topped levees along the canals rise as high as 14 1/2 feet above sea level, which should have been enough to contain Hurricane Katrina. But at three points on the London Avenue and 17th Street drainage canals, the floodwaters weakened the structures to the point that they gave way.
An emergency repair effort plugged the three breaches with massive sandbags weighing as much as 15,000 pounds each. But now the Corps is faced with the tricky task of removing the sandbags and replacing them with a new levee and floodwall - without inundating the city.
What they do is build temporary walls on both the canal and land sides of each breach. This surrounds the work area and keeps soil from collapsing into the hole that will be created during the next step, when the emergency sandbag levee is removed.
Then, a new levee and floodwall is built across the breach. After the new T-wall has been completed, the temporary walls, known as coffer dams, will be removed.
"This job will go right up to June," construction inspector Duke Ducarpe said of the repair at the 17th Street Canal breach. He said the two breaches on the London Avenue Canal might be repaired earlier than that.
Van Heerden said despite all that work, the Corps isn't doing enough. In many places, Katrina's storm surge overtopped an earthen levee and then began wearing it down, allowing an ever increasing amount of water to surge through the breach.
Along the Inner Harbor Navigation Canal, the torrent grew so powerful it swept away much of the lower 9th Ward neighborhood, washing houses off foundations and sending cars tumbling like pebbles in a raging river. The Corps plans to replace the I-wall along the canal with a T-wall.
Such measures may be enough to protect the lower 9th Ward during another Katrina. But there will be no improvement of levee segments that did not fail.
That leaves some of those segments vulnerable, unless additional, costly efforts are made to beef up the entire levee system.
"We've really got to look at doing more," van Heerden said.
[Last modified January 15, 2006, 01:48:18]
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