With the National Weather Service predicting that the Mississippi River will rise to 20ft (as of 4 a.m. on July 11, 2019), many residents are understandably concerned.
On Wednesday, a graphic published by Nola.com showed areas where the Mississippi River levees are below 20 feet – mostly along the Lower 9th Ward in New Orleans and St. Bernard Parish on the East Bank, and Algiers on the West Bank.
However, according to a spokesperson for the Army Corps of Engineers, the graphic isn’t entirely accurate according to their records. “They show the levee elevations for the 9th Ward between 20 and 21 feet,” spokesman Ricky Boyett said. “Our modeling does not show overtopping of the levees in the 9th.”
The same cannot be said for Plaquemines Parish, where the entire East Bank and portions of the West Bank are under mandatory evacuation orders. Evacuations there began at 6 a.m. on Thursday.
The Phillips 66 Alliance Refinery is preparing to shut down by early Friday morning, and they have already released all nonessential personnel from work. The 2,400-acre facility sits along the river south of Belle Chasse. Around 850 people (including contractors) work at the refinery.
The levees surrounding the river in Plaquemines Parish are part of what capture storm surge moving into the Mississippi and force it upriver towards New Orleans. Ordinarily, that isn’t as much of a concern, as the river is typically much lower in the summer months. However, flooding across the midwest has resulted in the Mississippi River remaining at or near flood stage for the past several months.
However, determining whether the Mississippi River will overtop the levees isn’t as simple as adding the three to six-foot storm surge to the 16 ft. current river elevation level. While at flood stage, the Mississippi River has a higher flow rate than it does under normal conditions. This can help prevent some of the storm surge from traveling as far upriver.
In addition, if the storm surge causes the Mississippi River to overtop the levees in Plaquemines Parish, it could lower the amount of storm surge to affect New Orleans.
For now, the Army Corps of Engineers remains confident that the system can handle the predicted impacts from what is expected to become Hurricane Barry.
“We’re confident with the integrity — the levees are extremely robust and designed to handle a lot of pressure.”
To prevent any risk of overtopping, Corps officials began installing “stoplogs” at the Harvey Canal Lock to add three feet to its height. They also began installing HESCO baskets along the river at the Army Corps headquarters on Leake Avenue, one of the lower spots in the levee system.
“We’re talking to the state to see if we need to take any precautionary measures,” Levee Authority Executive Director Derek Boese told WWL-TV. “Whether that would be internal assets or assets such as the national guard could provide. That’s all underway at this time.”