Strengthening flood defences in New Orleans

The challenge: a huge flood risk demanded stronger protection measures

Located on the Mississippi River between the Gulf of Mexico and Lake Pontchartrain, New Orleans has a high risk of flooding and devastation.

The city’s flood defences are vast, including 350 miles of levees and barriers. But when Hurricane Katrina struck in August 2005, it became clear those defences were insufficient to protect the city and needed to be strengthened.

During Hurricane Katrina, 80% of New Orleans was flooded – severely damaging over 200,000 homes and businesses and causing over 1,000 deaths.

The United States Army Corps of Engineers (USACE) realised it needed to redesign the entire Hurricane Storm and Damage Risk Reduction System (HSDRRS). And it wanted to provide a 100-year level of protection for the region.

The solution: strengthened flood defences and new predictive technology

The USACE commissioned Royal HaskoningDHV to advise on the project, including hydraulic modelling and design, flood forecasting, GIS-based mapping, and risk management.

We conducted a detailed analysis of areas of weakness in the original levees – uncovering limitations in their back slopes and transition points between materials – and designed structures to strengthen them.

As well as enhancing the city’s physical defences, we also developed a Levee Information Management System to improve operational processes around the structures. And we created the innovative Hurricane Surge Atlas, which helped emergency managers quickly assess the expected storm surge levels of approaching hurricanes.

Our work included many innovative approaches, concepts, and technologies. For example, we developed a probabilistic method to determine levee and floodwall elevations, so spatial variability could be considered in the hydraulic design of flood protection systems, and through our analysis we showed that a lower crest level of the Lake Borgne Storm Barrier would provide sufficient safety to the City of New Orleans, reducing the construction cost by some $400 M compared to the original designs.

We also advised on how the marshlands around the city could be restored to create a habitat for local wildlife and act as a natural defence for New Orleans.

The result: better protection for New Orleans and the surrounding area

The redesign of the HSDRRS means New Orleans is better prepared for future hurricane threats. The entire system now has a 100-year level of protection – a key step towards better flood protection for low-lying areas in the Mississippi river delta, too.

Together, the technologies and structures we put in place are contributing to a more resilient and operable system that is helping to reduce flood risk for current and future residents of New Orleans and its surrounding area.