After Katrina, gates were installed at the mouths of the drainage canals in New Orleans to keep Lake Poncthartain storm surge from coming in. These pumps were installed by the Corps of Engineers to pump the water over the gates.
My worry is that with a slow moving Isaac possibly dumping copious amounts of rain on New Orleans, that the pumps at the mouths of the canals can't keep up with the old original pumps farther inland and New Orleans has serious "rain water flooding". See graphic.
The new pumps at one of the canals has had hydraulic problems and two of them are out for repair until September. The Corps even admits that they can't match the pumps built in the 1800s!