IHNC Lake Borgne Surge Barrier
The Great Wall of New Orleans
A storm surge barrier, 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). After Hurricane Katrina altered the structural arrangement of New Orleans in 2005, being 18-foot storm surge overpowered most of the floodwall and the levee structures along the gulf of the Mississippi River. The natural calamity had an irreversible effect on the demographics of the city. More than a million people were left displaced and since then about only half of them had returned.
The Surge Barrier made of concrete and steel is a complex system that is located at the intersection of the Gulf Intracoastal Waterway (GIWW) and the Mississippi River Gulf Outlet (MRGO).
It includes a monolithic flood barrier of 1,071 ‘soldier’ pilings at 140 ft in length, 26 ft above sea level, and 240 ft in length ‘battered’ piles extending to 200 ft underground. Connecting the barrier wall is a 150-foot-wide sector gate, a bypass barge gate and a 56 ft wide vertical lift gate.
Combined with other features of the Hurricane and Storm Damage Risk Reduction System, it is designed to prevent a 100-year storm surge from Lake Borgne, the Mississippi River Gulf Outlet (MRGO) and the Gulf Intracoastal Waterway (GIWW) from flooding the Metropolitan New Orleans area.
On 29th August 2012 (the seventh anniversary of Hurricane Katrina), the barrier was used for the first time, to protect the city from Hurricane Isaac.
Features
Typical flood wall and the MRGO closure flood wall (over a mile long)
150-foot wide navigable floodgate on the GIWW—a steel sector gate (42 ft tall)
150-foot wide navigable bypass floodgate on the GIWW— a concrete barge swing gate
56-foot wide navigable floodgate on Bayou Bienvenue—a steel lift gate
Concrete T-walls on land, at the north and south ends of the Lake Borgne barrier
Approach walls at the GIWW sector gate and the Bayou Bienvenue gate
Navigation gate in the Seabrook vicinity
Marsh enhancement with dredged organic material - as organic material is sorted from waterways in preparation for new construction, it will be deposited in nearby wetlands habitats to enhance environmental conditions
Design
The marine infrastructure is made to be resistant to climate change. TetraTech led the design of the barrier and the initial considerations were the navigational needs and the hydrological scenarios of the context. The final design was a gigantic feature of floodwall with three navigational passages.
The gates of the barrier are pump-controlled and the operation of this passage is based on 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 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.
Construction
Accomplished through the design-build delivery method, the project was completed from 2008-2013 from initiation to execution. 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 ft 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.
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 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 ft higher.
The recovery of the city is a very non-linear and complicated issue that requires multiple aspects to be put into consideration. Without this project the survival of the city is questionable. Along with the surge barrier, various tasks are taken at hand for the city. 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, tangibility, and effective execution.
Reference
https://www.floodauthority.org/the-system/lake-borgne-surge-barrier/#:~:text=The%201.8%20mile%2Dlong%2C%20%241.3,the%20 Flood%20Protection%20Authority%20%E2%80%93%20East.
https://www.re-thinkingthefuture.com/rtf-design-inspiration/a1633-ihnc-lake-borgne-surge-barrier-the-great-wall-of-new-orleans/
https://engineering-channel.com/the-great-wall-of-louisiana/
https://www.cakex.org/case-studies/inner-harbor-navigation-canal-lake-borgne-surge-barrier-resilient-storm-surge-protection-new-orleans
By -
Tuhina Chatterjee, Associate Editor - Civil Engineering and Construction Review
