Projects

The height of constructtion on the IHNC barrier will be reached this year. The IHNC Barrier or Lake Borgne Barrier is a significant part of the city’s hurricane and storm damage risk reduction system (HSDRRS). When completed in 2011, the $700M barrier will act as a key element in the defense against storm surges for Greater New Orleans’ most vulnerable areas, reducing the risk faced by the surrounding communities of St. Bernard, New Orleans East, Ninth Ward and Gentilly to a 1% chance in any given year.



New Orleans is protected against storm surges by 350 miles of levees and floodwalls. Construction of this system dates back to a hurricane in 1947 with additions following Hurricane Betsy in 1965. When Katrina hit the city in 2005, the levees failed due to a complex combination of technical and political factors, causing flooding for three weeks. On the eastside of the city, the 4m to 6m-high levees were no match for the surge produced by Katrina exceeding an elevation of +5m – floodwalls were overtopped and the city inundated.

Following the disaster, the US Army Corps of Engineers (USACE) was given the mandate to rebuild and revise the levees and floodwalls. The $14Bn HSDRRS programme to restore and improve defense works aims to provide the city with protection against storm surge flooding with 1% annual exceedance (a 100-year event). But while significant improvements have been made along some areas of New Orleans’ levees and floodwalls, other sections are still susceptible to a flood risk comparable to the pre-Katrina situation.


Team of Haskoning Inc. at the start of the construction of the barrier.

The IHNC project will seal off New Orleans’ Inner Harbor Navigation Canal from any powerful Gulf of Mexico storm surge in the event of future hurricanes – two navigation gates along the 3km floodwall can be closed to prevent water surging up the canal.
Construction of the barrier began in December 2008 with dredging of the access channel,

There are two main parts to the IHNC project:
1) The Gulf Intracoastal Waterway (GIWW) which includes the GIWW north floodwall, the GIWW gates and the GIWW to Bayou Bienvenue floodwall

2) Bayou Bienvenue (BB), which consists of the BB gate, the BB to Mississippi River Gulf Outlet (MRGO) floodwall and the MRGO south floodwall.

While the barrier is being designed for a 1% event, it's also being tested against a 0.2% event – normally known as a 500-year event. The design surge for a 1% hurricane is roughly 6m (18ft) above mean sea level, with design waves from 2m to 3m (7 – 9ft). The project's also taken into account the region's soft subsoil, which requires very long piles in order to withstand wave and surge forces – in this case, the floodwall consists of concrete piles 42.5m to 49m (140 – 160ft) long and 1.7m (66inch) in diameter, with 'batterpiles' behind it for additional strength. It's being produced offsite in individual sections of 4.9m (16ft), with each section being pre-strained before being shipped.



USACE is working with Shaw Environmental and Infrastructure on IHNC's design and build, subcontractors including Gerwick and INCA. Royal Haskoning has been appointed by USACE to provide guidance on various design elements, including the height of the structure and its capacity to withstand hurricane-induced waves. Experts from Royal Haskoning are also providing advice on how best to prevent soil erosion in the area and maintain navigation along the channel – and have also advised on using the storage capacity behind the structure to allow for some overtopping, thus reducing its height and resulting in significant cost reductions.

Today in 2010 the Construction of the barrier is still moving forward with an impressive speed. More than 90% of the main floodwall has been erected and is able to stop storm surge. The remaining openings are those where gates will be constructed and the pieces which tie the barrier into the levees on the mainland. Construction will go on during the 2010 hurricane season, and critical construction sites are protected against moderate storm surges.

Next to the large surge barrier in Lake Borgne a smaller surge barrier will be constructed at the Lake Pontchartrain entrance to the Industrial Canal; The Seabrook barrier. The structure, which is expected to cost $155 million, will include two lift gates which will be lowered in place before a storm. The lift gates will be on each side of a sector gate, two wedge-shaped structures that will swing closed to block the channel used by barges and ships to enter the lake.

The Seabrook barrier combined with the Lake Borgne surge barrier, improvements to floodwalls along the Industrial Canal, and levees and floodwalls along the Gulf Intracoastal Waterway, when finished in June 2011 will greatly reduce the risk of flooding for hundreds of thousands of residents in the St. Bernard, New Orleans East, Ninth Ward and Gentilly areas.

Today, a substantial part, but not all, of New Orleans’ HSDRRS project is completed. But while it's clear that progression has indeed been made to provide the city with better flood protection in the St. Charles and Jefferson areas – which with the New Orleans Metro and the West Bank have taken advantage of the closure of outfall canals and increased levee heights – on the east and south sides of the city, the flood risk is comparable to the pre-Katrina situation this 2010 season. All levees across the city need to be upgraded and combined into one effective surge protection system if it is to avoid future disasters. And there's still a lot of work to be done before the promised HSDRRS becomes a reality in 2011.

Below you can view an Animation video of the INHC Barrier project. This video is created by USACE Team New Orleans and can also be accessed together with other animations on http://www.youtube.com/user/teamneworleans.