Coastal Resiliency. Its very definition means protecting coastal waterfronts from catastrophe through artificial and natural means. With a rising sea level, climate change and other natural disasters such as hurricanes and tsunamis, COWI North America has a track record of resiliency work around the coasts of North America especially the eastern seaboard, gulf coast and western United States.
With the damage caused by Hurricane Katrina (2005) and the Tohoku tsunami (2011) local and federal agencies were forced to consider more robust structures. This would improve resilient protection to coastal communities from extreme events.
When Hurricane Katrina made landfall on August 29, 2005, what followed became the most costly natural disaster ($80 billion) in the history of the United States. The U.S. Army Corps of Engineers awarded the largest civil works Design-Build contract ($1.3 billion) to design and construct the 1.7 mile long Inner Harbor Navigation Canal Lake Borgne Surge Barrier. This barrier, located where the greatest threat of incoming storm surges may occurred, should prevent the kind of flooding seen that August.
In addition to protecting local residents, the city of New Orleans was at risk of losing its 100-year flood insurance certification. This forced the design and construction of the surge barrier to be fast-tracked. As part of a joint venture, COWI began work in earnest in 2008.
COWI employed a number of innovative techniques in the construction:
- Designed the wall for overtopping – the pre-bid conceptual wall elevation was originally estimated at 32 feet above sea level. By allowing for more water, the barrier doesn’t need to be raised. We reduced the height to 25 feet, resulting in a major cost savings.
- “In-the-wet” construction technology – the use of offsite prefabrication allowed for in-the-wet construction to proceed on a fast-track basis. This also helped maintain vessel navigation, fish passage, and tidal water exchange.
- Plunge pool behind the floodwall allowed for the efficient dissipation of wave overtopping energy. Furthermore, the project life of the barrier could be extended by operating the polder to allow for greater future wave overtopping.
In 2012, Hurricane Isaac was the first major storm to hit Louisiana since Hurricane Katrina. It is estimated that the Inner Harbor Navigation Canal Lake Borgne Surge Barrier prevented $5 billion in damages.
Over the course of its development (from 2010 to 2014), the surge barrier has won 22 annual awards in engineering for excellence.
Similar preparations for resiliency also took place across the continent in California. This time, however the danger was not hurricane related – it was the possibility of a debilitating tsunami that prompted action.
Crescent City Marina Replacement – Crescent City, CA
Crescent City is located in northern California near the Oregon border. Commercial and sport fishing boats operate out of the harbor at the Crescent City Marine. Several fish houses are located on the pier, where fishing boats unload their catch.
Crescent City has a long history of being exposed to tsunami events that occur along the Pacific Rim –– dating back to 1946 and as recent as 2011.
The probability that a tsunami would occur during the 25-year life of the replacement marina drove the Crescent City Harbor District team to consider the design requirements of a tsunami resistant marina.
COWI Marine implemented a number of ground-breaking techniques throughout the design process:
- Developed a methodology to estimate the tsunami loads and apply them to the marina structural elements prior to the development of the new ASCE 7 Tsunami Standards for buildings and waterfront structures. Some of these considerations were incorporated into the new standard such as wave celerity, water density due to suspended sediment, and embankment erosion.
- Numerical modeling was used for specific project site. By limiting the wave height to 15-ft and running the waves, the expected loading was calculated. The Tohoku tsunami in 2011 collaborated the results from the 2010 analysis.
- The float design included various applied wave loads and special detailing for float and guide connections.
- Geotechnical recommendations included several alternative studies for pile support and performance.
Over the course of its development (from 2014 to present), the marina saved a significant amount of money and time and has won two awards of excellence in engineering.
Learn more about COWI’s resiliency engineering here.