Louisiana’s Inner Harbor Navigation Canal (IHNC) Lake Borgne Surge Barrier is the central feature of the world’s largest Hurricane and Storm Damage Risk Reduction System (HSDRSS). Hurricane Katrina changed the morphology of New Orleans. The 18-foot storm surge overpowered the floodwall and the levee structure along the gulf of the Mississippi River. The natural disaster had an irreversible effect on the demographics of the city. More than a million people were dislocated and since then about only half of them had returned leaving the city empty. The fear of another storm is still consistent in the state of mind of the residents. The disaster led to the recognition of the need for an enhanced storm surge for the protection of this area. The federal government and The U.S. Army Corps of Engineers came together to ensure the city’s safety and raise the confidence of the residents to return home by building the navigational carrier. The IHNC surge barrier is the largest continuous barrier to be built in the world. This civil work project is the largest design-build project in the history of the U.S Army Corps. This project will fundamentally change the fights of New Orleans with the storms. 8 miles further to downtown New Orleans, the surge barrier that will act as a flood wall is built.
The Design
The disaster management infrastructure is synonymous to sturdiness but also the tectonics. The marine infrastructure is made to be resilient/resistant to climate change The 1.8 miles long flood wall is also known as the “great wall of Louisiana ”. TetraTech led the design of the barrier. The initial considerations were the navigational needs and the hydrological scenarios of the context. The final design is a massive feature of floodwall with three navigational passages.
The gates are pump-controlled. The operation of this passage is the derivation of local weather conditions. The gates can be raised to minimize the flood risk by allowing the water passage in the time of the surge. The idea was to design an infrastructure that is resilient/resistant to climatic conditions. The Gulf Intracoastal waterways require unobstructed bypass at all times. Hence the two separate gates were designed. The barge bypass gate was constructed first and it was used for the marine traffic movements during the construction of the surge barrier. The Gulf Intracoastal waterway hosts a 150-foot-wide sector gate which is the primary protection wall for New Orleans from the storm surge from the Gulf of Mexico. It is controlled by a 5714-ton concrete barge swing gate. The swing door can be closed or locked into place with the closure pins or can be rested into a seated position. The second 150-foot-wide gate is a hydraulically operated buoyant steel sector gate. The weight of the gate is mainly at the end of the 90-foot radius where the heavy skin plate assembly is placed. Finally, the Seabrook floodgate stops the storm surge from entering the Inner Harbor canal from Lake Pontchartrain. The Bayou Bienvenue is a 132-foot-wide liftgate that supports the vehicular bridge and provides protection from the storm surge from Lake Borge. The main purpose of this gate is to pass the commercial and recreational marine traffic. It has a 56-foot-wide opening where the walls of the barrier intersect the bayou. It provides 35 feet of clearance from water elevation when raised.
The construction
This project started in 2008 and was completed in 2013. It was accomplished through the design-build delivery method. The 26-foot tall flood wall is held up by the 628 batter piles. The fortification required the piles to be at exact depth and at an exact angle to hold back the thrust of the water. These piles are 288-feet long steel tubes that are inserted into the back of the wall. These piles transfer the load of the storm surge to the foundation. The 66-inch diameter piles were inserted using a custom made pile-driver which could only hammer vertically. There is no bedrock to hold the piles. Hence the flood wall is constructed 150-feet-tall with only 26 feet above the water elevation. This means 80% of the wall lies beneath the mud line. The piles were inserted into two sections. The first part was fairly quicker because of the soft texture of the mud, the 13 tons of weight slides itself with ease. The second half of it required almost 40-44 hammering to be inserted into the compacted ground located fairly beneath the earth’s crust. The project used temporary trestle construction transferring the segments. It ran across the length approximately 6 times each day. The design-build schedule helped the project to be completed faster. The project of this magnitude would usually take around a decade and a half to be accomplished. Whereas, IHNC Lake Borgne Surge Barrier was accomplished in 4 years. The engineering excellence was achieved by staying on schedule with minimal alteration. The steel and concrete project had very minute variations at different stages of the construction. The project efficiency was maximized by evaluating these various needs and decision making regarding the material procurement and fabrication were made before the design completion. The design complexity of the project was accomplished efficiently because of quick decision making and the close collaboration between the design team, U.S. Army Corps Engineers, and the State of Louisiana.
The Sustainability
The surge barrier has expectedly reduced the 100-year flood risk for the surrounding communities. The resilience to climate change is also enhanced by the construction of the buoyant gates. These gates are built with the ability to be manually operated in the condition of power break etc making it effective protection in the tougher times. This barrier relocated the focal point of the HDSSR infrastructure and moved it away from the city eliminating the need to raise the current flood infrastructure 30 feet higher.
The recovery of the city is a very non-linear and complicated issue that requires multiple aspects to be put into consideration. The surge barrier is the prima facie one. Without this project the survival of the city is questionable. Along with the surge barrier, various tasks are taken at hand for the city. New Orleans is also building hurricane resilient homes for the residents. The construction of the surge barrier was accomplished efficiently with minimum time taking. The project and the design team received many awards for its efficiency, tactility, and effective execution.
