graphic of the system for any below the "500-year storm" -they say...

"According to the map, most property inside the levees would remain dry or see minor flooding, even if half the interior pumping stations failed. Most remaining floodwaters within the levee system would reach less than 2 feet deep. By contrast, vast areas of New Orleans and St. Bernard Parish were submerged under 8 feet of water or more after Katrina." Some problem areas still remain, however. Pumping systems across the metro area will still be unable to keep up with the rainfall delivered by a 500-year storm, which could be more than 13 inches in 24 hours. That's the amount of rain in the New Orleans area by an average 100-year rain-only event.

http://www.nola.com/hurricane/index.ssf/2013/08/upgrated_metro_new_orleans_lev.html#incart_river