Its very definition implies strength and the ability to withstand or recover from challenging situations. In coastal and maritime environments, it means introducing practical, engineered solutions using artificial and natural means to allow regions to recover from catastrophic events. With rising sea levels, climate change and other natural disasters such as hurricanes and tsunamis, COWI North America has gained an extensive record of successful resiliency work around the coastal areas of North America, especially the eastern seaboard, gulf coast and western United States.
In 2005, when Hurricane Katrina made landfall, southern Louisiana’s protective floodwalls and barriers collapsed from the force of the record-breaking storm surge. The defense system designed to protect people and property in the low-lying areas in New Orleans and the surrounding area failed catastrophically, resulting in the most costly natural disaster in U.S. history ($80 billion).
In the aftermath of this disaster, the federal government authorized the U.S. Army Corps of Engineers to design and construct a Hurricane Storm Damage System around greater New Orleans. The first line of defense in this system is the Inner Harbor Navigation Canal – Lake Borgne Surge Barrier.
This massive $1.8-billion infrastructure project was designed to not only resist and reduce the risks associated with intense storm systems but to adapt to new future conditions around New Orleans. Storm surge events have a 1% chance of occurring any given year. This level of protection is more commonly known as 100-year risk reduction.
What made this project especially challenging was its location 30 miles south of New Orleans in the soft and muddy clays deposited by the Mississippi River, which demanded an experienced engineering firm that could provide innovative foundation and structural design work.
In 2008, this $1.3-billion design-build barrier project was awarded to leading international marine infrastructure consultants – COWI North America.
Inner Harbor Navigation Canal (IHNC)- Lake Borgne Surge Barrier
The design and construction of the IHNC barrier was the largest civil works Design-Build project ever awarded by the U.S. Army Corps of Engineers. At nearly 2 miles (3 km) long and 26 feet (7.9 m) high, this barrier is a state-of-the-art defense system to protect southeast Louisiana’s vulnerable areas from Lake Borgne and the Gulf of Mexico from the effects of a future storm surge events.
At COWI, each project offers unique challenges requiring practical innovations. Creative and practical solutions reduce construction costs without compromising structural performance. Some of the innovative solutions COWI introduced at the IHNC barrier include:
During Katrina, the magnitude of water flowing over or overtopping protective barriers and levees caused collapsed, leading to catastrophic damage.
Initially, the IHNC barrier’s design specified a 32-foot-high-wall (9.6 m) be built. Using state-of-the-art modeling, COWI found a 26 foot wall made of reinforced concrete could not only create a protective barrier strong enough to withstand 100-year-storm-protection requirements, it could reduce overall project delivery time, operate more cost effectively and be esthetically pleasing.
Floodwall Plunge Pool
By definition, plunge pools are formed under the force of a natural source, such as a waterfall or rapids. They are also formed as the result of water flowing over man-made objects such as spillways and bridge abutments. During Katrina, the force of water flowing over barriers and levees caused damaging erosion to the soft clays and soils along the Mississippi
Always keeping nature top of mind, COWI calculated the magnitude of downfall forces of overtopping waves and incorporated a plunge pool and spillway into the IHNC’s design. This plunge pool and spillway significantly weakened the force of the overflowing water, making them important features that increased the overall resilience, integrity and longevity of the IHNC barrier.
Now the water that flows over the IHNC barrier during heavy storms is stored in a basin area located behind the floodwall. Once the storm clears and the surrounding area is able to absorb water once again, it can be released back into the environment.
Because the IHNC barrier project was fast-tracked, COWI employed In-The-Wet method of construction to speed up construction time.
This method allows the majority of the construction of large-scale precast concrete segments to be built on land and then floated or lifted into place on pre-installed foundations. In-The-Wet is the ideal construction choice for large-scale projects being built in challenging marine environments.
In comparison to the more conventional cofferdam method, In-The-Wet offers several advantages including reduced project costs, decreased construction time, minimal environmental impact and enhanced construction safety. Perhaps most importantly, the use of In-The-Wet construction ensures minimal disruption of vessel navigation, fish passage and tidal water exchange.
All of the structural elements in these innovations provide 100-year durability life and they have been recognized with a multitude of design and engineering awards.
Today, COWI continues to build on its IHNC barrier experience introducing innovative and practical design solutions elsewhere in Louisiana and in other areas of the United States.
Our multifunctional project team takes great pride in knowing that the 1.4-mile-long IHNC wall will protect vital commercial arteries and more than 350,000 people living in New Orleans for many years to come.