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Street-level flooding is more likely
Closing gates for tropical storm would be culprit
Tuesday, July 04, 2006
By Mark Waller

Heavy rain from a tropical storm could fill more streets with water this year than residents were used to seeing before Hurricane Katrina, according to new government projections.

The Army Corps of Engineers has drawn up maps showing parts of Gentilly, Lakeview and Uptown that can expect rainwater accumulation this hurricane season even if they did not typically flood in previous tropical storms. Closing the floodgates under construction at the 17th Street, London Avenue and Orleans Avenue canals in advance of a tropical system is what would trigger the extra flooding from rain.

However, the likelihood of closing the gates is slim: Corps officials have estimated they would have closed them only three times in the past 45 years, based on a historical analysis of weather data. And the gates would not be closed for rain events unrelated to storms that bring a surge -- meaning even a record rainfall such as the one the New Orleans area received on May 8, 1995, would not trigger gate closures.

The problem will ease by next season because more repairs to the flood control system will add drainage capacity to the canals when the gates are closed.

While the maps do not specify depths, a Corps spokesman said they show areas that would see inches of water and not the several feet that could result from a levee failure.

"This is a lower amount of water that's not going to be standing there for weeks like we had in Katrina," said Todd Hornback, a Corps spokesman based in New Orleans.

While the gates at the canal mouths on Lake Pontchartrain might block a devastating surge from getting in, the complication is that they will also stop some rainwater from draining. But Washington-based Corps spokesman Gene Pawlik argued that rainwater flooding is a lesser evil than flooding from another catastrophic levee rupture.

"A surge from Lake Pontchartrain is a bigger risk overall than rainfall inundation," Pawlik said.

The Corps will close the floodgates at the 17th Street and London Avenue Canals in the unlikely event a 5-foot surge threatens to invade the damaged canals from the lake, officials said. The Orleans Avenue Canal, which proved sturdier than the others in Katrina, can take up to 9 feet of surge before the gates close.

Corps officials said they issued the projections of rainwater accumulation to keep residents in New Orleans and parts of East Jefferson informed about the changed conditions they will likely see in tropical storms.

"It's really to make people aware, so they have a chance to prepare," Pawlik said. "In some areas where they have not traditionally had severe rainfall inundation, there is that chance now."

As time passes and the Corps adds more capacity to pump out water despite the closed gates, the amount of flooding from rain will decrease, the projections show. By next year's hurricane season, pumping capacity should be back to a level where an intense rain would have no greater impact than before Katrina, the Corps said.

Some areas will still suffer street flooding, but the vulnerable areas will be smaller than they are now.

"It's a system in progress," Pawlik said. "It's a work in progress."

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Mark Waller may be reached at or (504) 717-7706.