Correction appended.

Looming 26 feet over the bayou, the Inner Harbor Navigation Canal-Lake Borgne Surge Barrier stands as a concrete and steel sentinel against the rising and heaving ocean.

The 1.4-mile-long wall, also known as the IHNC barrier, protects vital commercial arteries and more than 350,000 people in New Orleans. An ambitious and expensive project built on soft soils and hard lessons, this Great Wall of Louisiana is a bulwark against once-in-a-century storms.

Coast Guard search and rescue

The $1.1 billion initiative, commissioned by the Army Corps of Engineers and turned over to local managers last year, includes three gates to allow shipping and navigation through the Mississippi River Gulf Outlet and the Gulf Intercoastal Waterway, respectively the first- and third-busiest water routes in the United States.

The IHNC barrier fills a critical niche in a $14.45 billion hurricane and storm risk reduction system that marshals 350 miles of levees and 73 pumping stations. "This [niche] was considered the soft underbelly of the storm protection system," said Dale Berner, vice president of Ben C. Gerwick Inc., the major design firm behind the project. "The flood wall is unique in the world. There is no other flood wall like it."

Its novelty lies in its scale, scope and design, but other cities like New York are eyeing the IHNC barrier as a model while they look to protect themselves from a changing climate and rising waters. The future of coastal metropolises may lie in these megaprojects, which defend growing populations and prevent even more costly damages.

However, the eventual cost and durability of these structures remain open questions. This week, two separate studies showed that previously underestimated ice melting in Western Antarctica could as much as triple forecast sea-level rise over the next two centuries. Thus, the definitions of projected 100- and 500-year storms may now be under revision.

In April, the American Society of Civil Engineers (ASCE) granted the sea wall its Outstanding Civil Engineering Achievement Award, the highest honor the group bestows on infrastructure initiatives. Former ASCE President Blaine Leonard, the chairman of the awards committee that selected this project, noted that one of the key selection criteria is sustainability.

What is the measure of sustainability?

"We look at sustainability in what is known as the triple bottom line: social, environmental and economic sustainability," Leonard said.

The IHNC barrier exemplified important trends in infrastructure projects during its construction, especially mitigating environmental harm and accounting for future changes in the ecosystem. "We're certainly seeing elements of environmental considerations in projects that you wouldn't have seen 20 years ago," Blaine said.

USACE Dam construction

However, one of the most important aspects of the IHNC barrier came even before workers started pouring concrete; engineers used an approach known as design-build.

The old-fashioned method for civil engineering projects involved completely designing a road, bridge or wall, then soliciting bids from contractors and then building the project.

The newer method involves engineers partially designing the project and then soliciting bids. The contractors then fill in the blanks using their own discretion. It's a strategy that's catching on because it drastically cuts development time, so projects that used take up to a decade to complete can finish in two or three years. This is incredibly important for disaster mitigation projects that have to overcome flaws exposed from the last big storm and be ready in time for the next one.

Design-build also spreads the financial burden from the government to the contractor. "They take on the responsibility to work within their budget and they get very innovative as a result of that," Leonard said. "The [IHNC] contractor learned to do things that had never been done before."

As it stands, the IHNC barrier is the largest design-build project in the history of the Army Corps of Engineers.


Ben C. Gerwick's Berner explained that the structure above the water is only the tip of the iceberg; the main wall consists of 144-foot-long concrete piles extending 130 feet below the mud line underwater.

More to be done

The design draws on past lessons from hurricanes like Katrina and Betsy and accounts for future changes in the climate. The Army Corps' temporary Hurricane Protection Office developed 152 simulated storm surges based on conditions measured in 2007 and projected sea-level rise out to the year 2057. The results guided designers to the final height of the wall.

The goal is not just to resist the 100-year storm, but to survive the 500-year flood, where the barrier will remain standing even as water crests over the top, according to Berner. "Our barrier met the same performance standard as the rest of the [storm mitigation] system, but the rest of the system was not built through a marsh," he added.

However, walls to keep the water out are only part of the solution. The Mississippi Delta, home to more than 2 million, is itself washing away, and up to 13,500 square kilometers of land could erode by 2100 (ClimateWire, April 12, 2012). The sediment helps dissipate energy from the ocean, and losing it as a barrier means the walls and levees will take a heavier beating.

The state of Louisiana's Coastal Master Plan aims to address this by engineering and restoring the delta, but the price tag lies between $50 billion and $150 billion.

Timothy Doody, president of the Southeast Louisiana Flood Protection Authority-East, which now manages the IHNC barrier, said Gulf Coast denizens still need to take precautions to protect their property. "Local officials need to change building codes and ordinances," Doody said. "We live within a 'bowl,' and we shouldn't be building on grade any longer."

Though the new wall is an engineering marvel, Doody said that people behind it still face risks from storms. "I think we should be aiming toward a much higher level of protection," he said. "My concern is that complacency is going to creep back in."

"There will always be the chance of a bigger storm," echoed Army Corps spokesman Ricky Boyett. "We're hoping when the storm comes, [the barrier] is defending vacant property. We don't want anyone to get too complacent."

But pulling back completely isn't an option, either. The water that flows around New Orleans drives commerce in the city and for much of the United States. The region is a waypoint for 20 percent of commercial shipping in the country, provides one-third of the nation's seafood tonnage and is a major hub for offshore oil.

"Water is the lifeline in New Orleans. You have to be able to allow it to go in and out on a daily basis," Boyett said.

Hence, the massive IHNC barrier, the marvel that it is, will spend most of its time trying to be as unobtrusive as possible but remaining vigilant for rising water.

Correction: An earlier version of this story misstated how far the barrier extends underwater.