U.S. Water News Online
NEW ORLEANS -- The U.S. Army Corps of Engineers has decided to proceed with proposed floodgates as a way to prevent storm surge from building up in three of the city's major drainage canals, two of which breached during Hurricane Katrina.
"We just don't have the confidence in the canal levees at this point," Corps spokesman Jim Taylor said.
Normally, the 17th Street, Orleans and London Avenue canals drain rainwater pumped from New Orleans streets into Lake Pontchartrain. But during Katrina, storm surge pushed from the lake into the canals, ultimately causing levees along the 17th Street and London Avenue canals to break open from the unusual pressure. The result was flooding across western and central parts of the city, much of it catastrophic.
The new floodgates will remain open to allow rainwater to drain out of the canals unless a major storm begins to reverse the flow of water from the lake into the canals. In that case, the gates would close to prevent water from coming into the canals while temporary pumps would continue to move rainwater out.
"The level of protection is greater if you stop the surge at the lake," Taylor said.
That was what the Corps wanted to do long ago, but the city's sewerage and water board, which is in charge of draining the city, fought that proposal, fearful the gates would interfere with the drainage of rain water.
Instead, a compromise plan called for building up the canal levees and reinforcing them with concrete floodwalls anchored by steel sheet pilings driven into the ground. Since the water from Katrina's storm surge never ran over the top of the 17th Street and London Avenue canal walls, those levees should have held, many civil engineers studying the damaged flood control system have said.
The breaches have raised questions as to whether the canal levees were weakened by design flaws that could continue to leave them vulnerable in future large storms. Many engineers studying the system see the best long-term solution as building new, permanent pumping stations at the mouths of the canals. That would allow drainage pumping to continue at full capacity while the gates were closed. The Corps must first get authorization from Congress to pursue such a plan, however.
In the meantime, if heavy rain hits while the canal gates are closed, some rainwater flooding could occur in the city, but that would be preferable to the catastrophic flooding from Lake Pontchartrain, Taylor said.
"If lake is high and it's raining hard, there's likely going to be some interior flooding, maybe some homes flooding," Taylor said. "We're analyzing that now to see what areas would be flooded based on various scenarios ... and we'll be warning people to get out of the way."
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