It’s not a reach to say New Orleans may be America’s most counterintuitive city. After all, we drive east to get to the West Bank. We bury our dead above ground. We gave our gridiron gladiators the fierce name “Saints” – then put a flower on their helmets.
So this latest piece of news should not surprise anyone: Street flooding is part of the city’s flood-prevention system, and it helps us qualify for federally subsidized flood insurance.
That feature was acknowledged by local and state officials after an Army Corps of Engineers press tour of the permanent pump stations its building, where three outfall canals empty into Lake Pontchartrain. Some journalists reported the new machinery protected the city against flooding during a 100-year storm.
Well, not exactly, officials later explained.
The city has two types of flood-prevention infrastructure to meet two very different threats: hurricane storm surge and rainfall.
The new, $14.5 billion system of levees, floodwalls, and permanent pumping stations encircling the East Bank is designed to protect against the surge from a 100-year storm — a storm that has a 1 percent chance of occurring each year.
When the corps says the new pumping stations are designed to withstand a 100-year storm, they aren’t talking about rainfall. They mean the structures will stand up to the surge, waves and wind of such a storm and will be able lift water coming from the city drainage system high enough to empty into the lake swollen by that surge.
The city’s drainage system, meanwhile, has been built to cope with the “100-year rainfall event,” meaning it can prevent homes and businesses from flooding even if 13 inches of rain falls in 24 hours.
The important term here is “drainage system,” and that includes our streets, parks and even empty lots.
The stormwater pipes and canals most of us think of are only parts of the system. They’re engineered to keep streets from flooding during just a 10-year rain, described as a storm that dumps 9 inches 24 hours.
The city gets FEMA’s stamp of approval for protection against a 100-year rain storm because engineers have shown its vast web of roadways and open spaces can store the rest of that deluge to prevent homes and businesses from flooding.
“That’s correct,” said Joe Becker, executive director of the Sewerage & Water Board of New Orleans. “The certification is based on the storage capacity as well as the volume we can actively be draining.”
And those massive new pumping stations at the end of the 17th Street, Orleans Avenue and London Avenue canals?
“They don’t change the capacity of the city to drain rain one way or the other,” he said. “They can only pump [into the lake] what we send to them.”
As anyone who has lived in The Big Easy long enough can tell you, the most frequent threat from flooding is rain. It can do serious property damage, as residents remember from the epic rainfalls of May 3, 1978 and May 8, 1995.
But hurricanes remain the more serious threat, flood-prevention officials said, because their consequences are more lethal and long-lasting.
“It’s the difference between being shot at by a slingshot and a .45-caliber pistol,” said Stephen Estopinal, president of the Southeast Louisiana Flood Protection Authority-East, which is charged with the operation and maintenance of the storm-surge system. “The slingshot will hurt, but that .45 can kill you.
“But there’s no doubt flooding from rain is the more constant threat, the one that causes the more frequent problem.”
But the street flooding should no longer be viewed completely as a problem. It’s actually helping prevent the situation from getting worse.
