Protect New Orleans from storm flooding after Hurricane Katrina
The New Orleans metropolitan area is home to 1.2m people. Situated between the Gulf coast and the Mississippi river, almost half the area is below sea level.
The region is prone to heavy storms, with hurricanes building up in the nearby Gulf of Mexico every year. These can sweep inland - often causing flooding, damage and loss of life.
New Orleans has extensive defences against flooding, made up of 350 miles of floodgates and levees. A levee is an embankment or wall - usually made of earth and often running parallel to a river. Levees are designed to hold back rising waters in stormy weather.
Hurricane Katrina hit south-east Louisiana on 29 August 2005. Rated category 5 – the most destructive - the storm caused massive damage across New Orleans and surrounding areas, largely because of the failure of the city’s flood barrier system.
Water penetrated up to six miles inland and around 80% of the city flooded. Over 1,000 people died and 200,000 homes and businesses were destroyed or damaged. More than 800,000 residents had to flee the area.
Following the disaster, independent investigators established that New Orleans’ levees and floodgates had failed because of system design and construction flaws.
The US Army Corps of Engineers (USACE) – the government agency responsible for the system – commissioned engineering company Royal HaskoningDHV to help with the overhaul of the city’s flood defences.
"It's possible to protect New Orleans from a Category 5 hurricane... we've got to start. To do nothing is tantamount to negligence.”AL NAOMI Senior Project Manager For The US Army Corps Of Engineers
New Orleans flood
Leading flood resilience professional Jaap Flikweert tells us about the huge loss of life and economic damage that Hurricane Katrina caused and how engineers went about restoring the new flood defence system that was put in place as a result.
Did you know …
Hurricane Katrina was the third strongest hurricane ever to make landfall in the United States.
About 80% of New Orleans flooded – storm waters were up to 6m deep in some areas of the city.
Katrina’s total economic impact across Louisiana and Mississippi may eventually hit $150bn (£114m) – making the hurricane the costliest ever in US history.
Difference the project has made
Royal HaskoningDHV worked with USACE to advise on the redesign and rebuilding of the New Orleans flood defence system, which is known officially as the Greater New Orleans Hurricane and Storm Damage Risk Reduction System.
The six-year project collected data on the performance of the levees and used computer modelling to design improvements to the city’s network of floodgates and barriers.
Project engineers now believe that New Orleans is protected against hurricane and storm events for the foreseeable future.
How the work was done
Early tasks for engineers working on the New Orleans scheme included establishing a performance baseline for the city’s flood protection network.
The project team then used computer modelling to work out how the city’s floodgate and levee system had fallen short of these goals when it was hit by Hurricane Katrina.
One problem exposed by Katrina was that the back slopes of the levees had been eroded – especially where they were made of weaker materials, such as soil.
Transition points between different structures and types of material – for example at road or rail crossings - were another weak point.
Project engineers designed structures to support and strengthen the levees and transition points. They also advised on how to rebuild and strengthen the marshlands of the Louisiana coast, as these act as a natural barrier against the sea.
The scheme also saw engineers modelling the effects of diverting the course of the Mississippi. The project team predicted this would move more sediment into the area – strengthening flood defences overall.
People who made it happen
- Client: US Army Corps of Engineers
- Consulting engineers: Royal HaskoningDHV