Protecting New Orleans From Future Katrina-Like Disasters
The Inner Harbor Navigation Canal (IHNC)-Lake Borgne Surge Barrier is a massive Hurricane and Storm Damage Risk Reduction System project (HSDRRS) that was completed under the direction of the U.S. Army Corps of Engineers (USACE). The 1.8-mile-long, 26-ft-high barrier provides surge protection to an elevation of 26 ft above sea level. The structure is located at the confluence of the Gulf Intracoastal Waterway (GIWW) and the (now closed) Mississippi River.
Gulf Outlet (MRGO), about 12 miles east of downtown New Orleans. The project reduces the risk for some of the areas hardest hit by Hurricane Katrina, including New Orleans East, metro New Orleans, Gentilly, the Ninth Ward and St. Bernard Parish. Its purpose is to substantially reduce the risk of flooding from a storm surge that has a 1% chance of occurring in any given year. “This project was the cork in the bottle needed to keep New Orleans safe,” says Larry Haser, vice president of engineering and construction with APTIM, who served as project manager for the entire design- build project. The $1.38-billion barrier is touted to be the largest design-build civil works project in USACE history. The barrier wall includes a concrete bypass barge gate and a buoyant, 42-ft-tall, hydraulically operated flood-control sector gate (both 150 ft wide) as well as a 56-ft-wide vertical lift gate. The surge barrier also provides floodwall tie-ins to the New Orleans East risk-reduction system to the north and the St. Bernard risk-reduction system to the south.
Big Leaf Challenge
The surge barrier sector gate offered particularly unique challenges, as it weighs more than 675 tons per leaf. Most of the gate’s weight is at the extreme of its 84-ft radius, where the heavy skin plate assembly is located. Buoyant tanks located behind the skin plates of each leaf provide perimeter support to relieve the operating loads on the supports and operating equipment.
To meet the timeline, design, procurement and construction were underway simultaneously—an approach that shortened the project-delivery schedule but also created challenges, which the team successfully managed. “Things were changing so fast that the schedulers had to make updates daily to keep up,” Haser says. “To successfully manage the project and coordinate the site activity, a high degree of communication with a one-team attitude was necessary.”
In addition, cost control, unstable soils and the need to minimize environmental impact—all while maintaining navigability and public safety—further influenced design and construction decisions. “We were creating something never built before and working almost exclusively from barges and other floating platforms on the water,” Haser adds. “We had to break the project into small enough elements to prioritize designs to keep up with long-lead-time items coordinated with construction sequences. We had as many items as possible prefabricated offsite to save time and ensure high quality, as it would have been so much more expensive and time draining to build them on the water.”
A Fully Operational Model
Advanced modeling techniques were used to confirm the reliability of the barrier’s potential. The project team constructed a fully operational physical model of the channel, the bypass gate, the sector gate and associated guide walls. Remote-control models of vessels simulated navigation within the channel under varied conditions. A floodwall model helped to verify that the overtopping rate was acceptable, and wave forces were studied to determine the size of the gate structures and associated mechanical equipment. Modeling also affirmed hydroelastic effects such as gate vibration, wave slamming and wave downfall.
In 2014, the project was recognized by the American Society of Civil Engineers (ASCE) with the 2014 Outstanding Civil Engineering Achievement (OCEA) award. In accepting the award, Lieutenant General Thomas P. Bostick, the commanding general and chief of engineers for the U.S. Army Corps of Engineers, said, “Everywhere that I go, I talk about this surge barrier, and I talk about the example that it shows of what America can do when it prioritizes and puts its mind to it.” He cites the federal funding, congressional support and local support of more than 300 organizations working together.
Haser concludes, “Our team [APTIM] was more than 100-people strong working on the project at any one time, and we all felt it was an immense privilege to work on something so important to the city—so unique and complex.”
APTIM. Expect the Extraordinary.