Tropical Storm Barry has officially taken shape in the Gulf of Mexico and is scheduled to make landfall on the Louisiana coast early Saturday morning as a Category 1 hurricane, posing a serious flood threat to communities in the Lower Mississippi Valley, including New Orleans and low-lying coastal parishes.
It’s bad timing. The storm is set to buzz by the mouth of the Mississippi River during a record-breaking season of high water. A storm surge from Hurricane Barry could push the river (currently at 16 feet) over the levees (at 20 feet). Earlier this week, the National Weather Service predicted the river would crest at this 20 foot threshold, but a subsequent forecast Thursday morning gave New Orleans a little more breathing room, dropping the crest to only 19 feet.
Still, there are legitimate fears that a combination of storm surge, wind, and rain brought in by Barry could overtop levees. While the Army Corps of Engineers has downplayed the possibility of overtopping near New Orleans, it has admitted that intermittent instances of overtopping could occur in surrounding areas.
Overtopping does not mean levee failure of the type that occurred in 2005 during Katrina. A lot of water would have to rush over, really fast to create meaningful structural damage. According to Clinton Willson, a professor of environmental engineering at Louisiana State University, the “roots and grass” and vegetation of the earthen levees along the Mississippi River are specifically meant to keep overtopping water from “scouring,” or eroding the levee exposing vulnerabilities. As long as levees have been regularly maintained, Willson explains, “some areas could probably have overtopping for hours and there would never be any scouring.” As long as the Army Corps has kept up with its maintenance of the levee system, the risks associated with overtopping should be reduced. The storm surge is only expected to last for a few hours.
“You can’t flood-fight miles and miles and miles of levee,” said Dave Ramirez, the water management chief for the New Orleans District of the Army Corps of Engineers. “They’re just looking to flood-fight those areas that are low and also have higher population and possible damage behind those levees.” The real concern with overtopping, Ramirez said, is not the threat to the levees but the task for the pumps.
Willson agrees. “It’s more about the potential to get double-digit rainfalls over the next 36 hours and whether we have massive pulses of rain that overwhelm the local storm water infrastructure.” The drainage systems in New Orleans and other parishes are likely to be overwhelmed by the torrent. According to the National Hurricane Center, Barry is expected to drop 10 to 20 inches over the coastal part of the state, with 25 inches in some places.
The sustained rainfall will no doubt pose a challenge to New Orleans’ antiquated pumping and drainage system, which has already struggled this week.