New Orleans levees passed their first major test

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Published September 3, 2021

12 min read

The levees held. That’s the only good news out of Hurricane Ida, which left a trail of wreckage all the way to the northeastern United States, where it unleashed a deluge that caused historic flooding and so far, killed more than 48 people in five eastern states.

Even after Ida was downgraded from hurricane status, it remained an intense, rain-laden storm as it traveled cross-country from the Gulf Coast. In New York City’s Central Park, it dropped three inches of rain in an hour—a record. Most of the deaths along the eastern seaboard were caused after flood waters engulfed people in their cars and drowned them.

As the effects of climate change worsen and become more severe, Ida highlights the risks to a growing number of communities as the effects of climate change become more severe. The questions that Louisianans have wrestled with for decades, mostly without long-lasting solutions, can be asked now everywhere: How much can places where millions of people live be fortified? At what cost? And who pays for it?

In Louisiana, Ida finally answered the question that has haunted New Orleans ever since Hurricane Katrina flooded the city in 2005: Would the levees, rebuilt and fortified with $14.5 billion in federal dollars, stand up to a powerful storm? Storms and two hurricanes have come through in the years since, but Ida is the first storm event to rival Katrina.

Ida made landfall about 50 miles west of New Orleans as a Category 4 storm, one of the most powerful hurricanes to hit the state since the 1850s. After that, it closely followed a worst-case scenario track that had been modeled by engineers since Katrina, as they repaired and strengthened 350 miles of levees, pumps, floodwalls, and gates—including a 133-mile perimeter of levees that encircles the city.

“Ida was a very good test, let’s put it that way,” says Ed Link, a University of Maryland engineering professor who headed a multiyear, post-Katrina investigation into the failures of the levees. “Did it extinguish all doubts? That will never happen. You can never get rid of all the risk.”

Added Rene Poche, a spokesman for the Army Corps of Engineers, which rebuilt the system and finished the last part of the project in 2018: “There is no catastrophic flooding in New Orleans. The system performed the way it was supposed to. That’s a big deal.”

Outside the levees, the deluge

Even so, both New Orleans and the region remain vulnerable. Rainwater alone can still inundate the city, and as Ida showed, other infrastructure cannot stand up to powerful winds: The failure of the power grid plunged more than one million people into darkness. 

In rebuilding the levee system, the Army Corps repaired but did not replace the city’s antiquated plumbing system of drainage pipes that carry away rainwater. The system can absorb a half-inch of rain an hour, or 12 inches in a day. That’s not enough to keep up with the rain-laden storms in New Orleans’ future. The city need look no farther away than nearby Houston, where Hurricane Harvey rained by the foot and flooded the city in 2017.

Outside the perimeter levees, the rest of the New Orleans metropolitan region lacks the city’s level of protection. Levees are partial or non-existent. Five days after Ida, the emerging story of Ida’s destructive powers is being told in scenes of extensive flooding extending from Houma, southwest of New Orleans, all the way to Slidell, northeast of Lake Pontchartrain. Hundreds of thousands of residents—most of the region’s 998,000 residents live outside New Orleans—were still struggling with floodwaters days after the storm, just as they did after Katrina.

The sodden mess is even worse below New Orleans in the parishes closer to the coast. Grand Isle, a fishing community of 1,450 people perched on a barrier island in the Gulf of Mexico, was declared “uninhabitable” by Jefferson Parish officials.

The Coastal Protection and Restoration Authority, a state agency set up after Katrina to restore and protect Louisiana’s rapidly eroding coastline, has plans to fortify those areas. But most of what is envisioned is just that—plans. The project farthest along, the West Shore Lake Pontchartrain Extension, which extends levees across the east bank of St. John’s the Baptist Parish, had been in the works for 30 years and only got funded by Congress in 2018. Poche says it is scheduled to be completed by 2024.

“We need to be thinking about LaPlace and Grand Isle and the people living outside the perimeter walls and what do we do about them?” Link says. “The next thing to decide is which of these things will give us the most risk reduction and benefit to society and how the heck do we fund it. It’s going to be a big, big tax.”

Lessons of Katrina 

One of the biggest misconceptions about Katrina is that it was “only” a Category 3 storm. It was—but a horribly destructive one.

New Orleans lucked out when Katrina swept ashore east of the city. This meant its most powerful winds took aim on the Mississippi Gulf Coast, where the town of Waveland, less than 45 miles east of New Orleans, was leveled. All that was left standing in the business district, as one of Mother Nature’s cruel jokes, was a small sign commemorating Hurricane Camille’s equally destructive visit in 1969.

As the skies cleared in Louisiana in the minutes after Katrina passed through, many residents thought for a brief moment that New Orleans and the surrounding communities had survived intact. Within minutes that all changed. In St. Bernard Parish, residents described going outside after the winds lessened, only to face a wall of water heading directly toward them.

What Katrina lacked in wind speed at landfall, it more than made up for in size and surge. Offshore, Katrina had been a Category 5, and it had built up an enormous surge that did not diminish as the storm approached the coast and weakened.

“People said, ‘Katrina, no big deal.’ Well it was a big deal. It created the largest surge to ever hit North America,” says Link. “There were areas where the surge was over 25 feet.”

The surge pushed up the Intracoastal Waterway, into Lake Borgne, then Lake Pontchartrain, putting Gulf of Mexico water into the living rooms of homes in the Lakeview neighborhood. Of 50 breaches in the levee system, only four were attributed to structural failures—three in the London Avenue and 17th Street canals that normally serve to drain rainwater away from the city, and one in the Industrial Canal that bisects the city, separating the Lower Ninth Ward and St. Bernard Parish from downtown New Orleans.

The other 46 breaches occurred in places where the surge was so high it overtopped the levees. Floodwaters covered 80 percent of the city, as high as 15 feet in some areas. Some 70 percent of the city’s houses were destroyed or severely damaged.

Rebuilding defenses

Before Katrina, New Orleans’ levees were known as the city’s Hurricane Protection System. After Katrina, the rebuild was given a mouthful of a name, the New Orleans Storm Damage Risk Reduction System, to reflect a change in thinking about how to fortify storm defenses.

The rebuild began before the 2006 hurricane season with fixes to each of the 50 levee breaches. It continued with a series of major construction projects, including a $1.3 billion, 1.8-mile-long gated storm surge barrier along Lake Borgne that is 150 feet wide and known now as the “Great Wall of Louisiana.” Another major project was the Gulf Intracoastal Waterway West Closure Complex, which includes a 225-foot floodgate and the world’s largest pump drainage station, capable of filling an Olympic-size pool in four seconds.

The system has drawn criticism for being rebuilt merely to withstand a 100-year flood event—or what used to be thought of as one.

“Climate is going to make those numbers less relevant to the future,” Link says, as over time the 100-year event becomes a 50-year event, and so on, rendering existing infrastructure inadequate.

“What can you do with it?” he asks. “Can you afford to upgrade to a new level? That’s a pretty tough level for people in communities that have to fund it. But spread all over our rivers and our coastlines, we have this uncertainty where our past data no longer gives us a way to speculate for the future. We have to do it a different way and we’re still sorting that way out.”

Goodbye Mr. Go

One way to do the sorting, scientists argue, is to restore natural barriers and protections that have been disturbed or destroyed by modern development. That opportunity may have arisen out of the Katrina disaster with the permanent closing in 2009 of the Mississippi River Gulf Outlet, aka MR-GO, or Mister Go.

The 76-mile shipping channel,  was built by the federal government in the 1960s as a shortcut from the Gulf of Mexico to New Orleans’ inner harbor. It had been blamed, incorrectly it turns out, for funneling Katrina’s surge into the city. Link says the breaches elsewhere in the system, including the four structural failures of the levees, were responsible for the majority of the floodwaters.

“You can’t shove enough water up MR-GO to flood anything,” he says. “The analogy I use is it’s like trying to fill up a swimming pool with a garden hose.”

But the channel cuts through the St. Bernard Parish wetlands, and it had long been criticized by environmentalists for introducing seawater into those cypress swamps and freshwater marshes. The salty water has killed trees and plants—thus accelerating the decline of the wetlands and reducing the buffer they provide against storm surges.

Closing off the channel by building a rock wall at one end is already reducing salinization in the marshes, says Kimberly Reyher, executive director of the Coalition to Restore Coastal Louisiana, a nonprofit working to support a variety of coastal wetlands restoration projects. More of that is needed.

“The levees worked this time as intended,” she says. “But we need to think about other lines of defense. We can’t build walls around everything.”

The National Geographic Society, committed to illuminating and protecting the wonder of our world, has funded Explorer Ben Depp’s work. Learn more about the Society’s support of Explorers.

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