A seagull lands on the 17th Street levee near a breach repaired with metal reinforcements (behind the birds) on Saturday, Feb. 18, 2006, in New Orleans. (AP Photo/Carolyn Kaster)

In the face of the threat of a developing tropical system in the Gulf of Mexico, the New Orleans area dikes are about to get a near-failing grade from the new Army Corps of Engineers rating system.

“Preliminary rankings… show that the corps believes there’s still a significant risk of flooding from major hurricanes or river floods that are greater than the design heights of Mississippi River levees and hurricane levees on both the east and west banks,” Mark Schleifstein with the Times-Picayune reported Monday.

Schleifstein stressed, however, that the near-failing grades applied to storms larger than what the levees are built for.

“The hurricane and river levees are designed to protect from surge created by a so-called 100-year hurricane, or a storm with a 1 percent chance of occurring,” Schleifstein explained. “The ratings show that 500-year events, with a 0.2 percent chance of occurring in any year, will overtop the levees and cause significant flooding.”

“The chances of failures for flood events involving water levels below the authorized 100-year heights were adequate,” he went on to say.

So while it would take an extremely rare hurricane, such as Katrina, to cause the levee systems in New Orleans fail, there are still major concerns about the flood potential from the system currently developing in the Gulf.

“From 10 to 20 inches of rain may fall on part of the north-central Gulf Coast beginning late this week and continuing into next week, and could in itself result in disastrous flooding,” warned AccuWeather.com Expert Senior Meteorologist Alex Sosnowski.

Schleifstein explained that New Orleans’ internal drainage system can only handle 10-year rain events. “The pump system handles an inch of rain per hour for the first few hours. After that, all bets are off,” he said.

“There is potential for some places to get rainfall rates of an inch per hour or more for a prolonged period,” Sosnowski stated.

If the pumps are overwhelmed, that could have an effect on the levees.

Sosnowski pointed out that there are other issues to consider with a long-duration, meandering tropical system, including potential for long-duration storm surge.

AccuWeather.com Meteorologist Mark Mancuso expressed concern that New Orleans could be hit with more than a foot of rain, which may put pressure on the levee system.

“It’s not just the rainfall, but perhaps days of pressure on levees, as storm surge water could be driven into Lake Pontchartrain if a tropical storm or hurricane hangs out over the north-central Gulf of Mexico,” Mancuso said.