November 30, 2021

Hurricane Ida in New Orleans: Will levees protect Louisiana from flooding years after Katrina hit?

NEW ORLEANS — New Orleans finds itself in the trail of Hurricane Ida 16 years to the day after floodwalls collapsed and levees had been overtopped by a storm surge pushed by Hurricane Katrina. That flooding killed greater than 1,000 individuals and precipitated billions in harm. However Ida arrives on the doorstep of a area reworked since 2005 by a large civil works mission and nearer consideration to flood management.

The system already has been examined by a number of storms, together with 2012’s Isaac, with little harm to the areas it protects. Each storm raises questions on New Orleans’ defenses, although, and as Ida approaches, listed below are some solutions:

What’s modified since Katrina?

The federal authorities spent $14.5 billion on levees, pumps, seawalls, floodgates and drainage that gives enhanced safety from storm surge and flooding in New Orleans and surrounding suburbs south of Lake Pontchartrain. Except for three drainage initiatives, that work is full.

“The post-Katrina system is so different than what was in place before,” stated U.S. Military Corps of Engineers spokesperson Matt Roe.

Beginning with a large surge barrier east of town, the system is a 130-mile (210-kilometer) ring constructed to carry out storm surge of about 30 ft (9 meters). The Nationwide Hurricane Middle on Friday projected Ida would carry a surge of 10 ft to fifteen ft (3 to 4.6 meters) on the west financial institution.

At that degree, it might come over the levees in some areas, stated emergency supervisor Heath Jones of the Military Corps of Engineers’ New Orleans District.

“They’re designed to overtop in places” with protections in opposition to worse harm, together with armoring, splash pads and pumps with backup turbines, he stated.

“We’ve built all that since Katrina,” and so they’re designed for a worse storm than the Ida is anticipated to be, he stated.

Jones stated there doesn’t look like any hazard of storm surge coming over the levees on the east financial institution, which makes up a lot of the metropolis. It was the east financial institution levees that broke after Katrina.

Governments as of Friday weren’t ordering individuals protected by the levees to evacuate, displaying their confidence in the system.

Quite a lot of floodgates are being closed because the storm approaches. That features huge gates that ships can usually sail by means of, resembling ones that shut off the Inside Harbor Navigation Canal close to the Decrease ninth Ward. That has lowered the chance of flooding in an space lengthy considered as among the many metropolis’s most uncovered. Not less than one smaller floodgate on land has been eliminated for upkeep, although, with officers planning to shut the hole with sandbags.

What about rainfall flooding?

Contained in the ring of levees, rainfall have to be pumped out. The New Orleans space has an elaborate system of canals and pumps to take away water, however it may be overwhelmed by persistent heavy rainfall, like in 2017 and 2019, when two storms every dumped greater than 9 inches (23 centimeters) of rain in some areas. Heavy downpours have been a continuing on the soggy Gulf Coast, however some distinctive rainstorms have been noticed in latest years, with specialists saying such torrents have gotten extra frequent as a warming environment carries extra water vapor.

Capability in some areas has been improved since 2005 by means of greater than $2 billion in drainage work, permitting elements of the system to take away as a lot as 4.7 inches (120 millimeters) of rain in three hours – what designers accounted as a rainstorm that might come solely as soon as each 10 years.

Town of New Orleans drainage system has 24 pumping stations with a mixed capability of over 50,000 cubic ft per second (cfs), which is sort of 400,000 gallons (1.5 million liters) per second. That does not embody pumps in neighboring suburbs.

However a few of the pumps in addition to the facility system supplying them in town are antiques plagued with reliability issues. On Friday, officers had been attempting to carry {an electrical} turbine again on-line to supply reserve energy for the system. Three of 99 pumps had been additionally out of fee, however New Orleans Sewerage & Water Board Govt Director Ghassan Korban stated there’s sufficient redundancy to again them up.

One of many classes of the 2017 and 2019 storms has been that upkeep of drains, pipes and canals has been uncared for. Officers urged residents Friday to brush up round storm drains, underlining a priority that even the very best pumps will not work if drains are clogged.

“Our mission is obviously to stay ahead of the storm, stay ahead of the rain and keep the city dry,” Korban advised reporters Friday. “But at one point, once our system is overrun, our mission shifts from keeping the city dry to just pumping the city as fast as we can.”

Will the levees maintain up over the long term?

Consultants notice that the levee system was constructed to protect in opposition to a 100-year degree of storm surge – a surge that has a 1% probability of taking place any given 12 months. With rising seas from local weather change and the sinking of Louisiana’s spongy coast, there’s concern that merely is not sufficient.

Reviews issued in 2021 suggest spending a projected $1.7 billion to boost levees and floodwalls to maintain offering the 100-year safety by means of 2078. That features elevating the peak of 99 miles (159 kilometers) of levees, changing greater than 1 mile (1.6 kilometers) of floodwall and constructing 3.2 miles (5.15 kilometers) of recent floodwall.

What are the dangers in outlying areas?

Areas exterior the city core that the levee system protects could have little or no safety in opposition to storm surge. Hurricane Isaac in 2012 flooded about 7,000 houses in LaPlace and different areas upriver from New Orleans after 8 ft (2.5 meters) of storm surge entered Lake Pontchartrain. The Corps of Engineers has began development on a levee to protect that space, however Corps of Engineers spokesperson Rene Poche stated it is not projected to be accomplished till 2024.

Quite a lot of native governments have ordered individuals to evacuate from low-lying and uncovered areas exterior of protecting levees, together with elements of New Orleans.

Suburbs north of Lake Pontchartrain are additionally not protected by levees or floodgates, though enhancements for St. Tammany Parish are being studied. Areas near the shore, in addition to the rivers that feed into the lake and the Mississippi Sound, are susceptible to storm surge.