Fifteen years after Hurricane Katrina struck the Gulf Coast on Aug. 29, 2005, storm planners and engineers are still applying the lessons learned from the catastrophic failure of New Orleans’ levees and the resulting flooding of the city. Yet, in an era of more frequent and unexpected storms – Hurricane Laura’s rapid acceleration is one example — the thinking has shifted toward risk reduction, not elimination.

“It was a watershed moment for us on how we approach flood risk management for the future,”  says Ricky Boyett, spokesman for the U.S. Army Corps of Engineeers’ New Orleans district.

Lewis “Ed” Link, a University of Maryland senior research engineering professor who helped guide the $14.6 billion New Orleans Hurricane and Storm Damage Risk Reduction System  (HSDRRS) efforts, says more money is needed to address long-term vulnerabilities. Currently about 90% of federal disaster funding goes toward recovery and rebuilding, but only about 10% is allocated for mitigation and risk reduction. “Unless we start spending more on mitigation, we’re in trouble. We are just moving from one disaster to the next.” says Link, ENR's 2007 Award of Excellence winner for his work on the failure analysis.

Since Katrina, many of the Corps’ policy documents have been rewritten to incorporate disaster risk and resilience. In 2009, the Corps’ established its Risk Management Center of expertise to advise on infrastructure decisions and assess the risks of dams and levees.  

Lessons from Katrina have been incorporated into the United Nations’ Sendai Framework for Disaster Risk Reduction, a 15-year roadmap that U.N. member states adopted in 2015 for making communities safer and more resilient to disasters.

UNESCO has also published guidance on how designated historic sites around the world can reduce disaster risk.

A walled city

Before Katrina, the prevailing approach to storm defense focused on protection – the idea that a region could shield itself from disaster. Katrina forced a shift in that way of thinking.

In the months immediately after Katrina, Link oversaw the Interagency Performance Evaluation Task Force (IPET), which the Corps commissioned to perform a forensic analysis of the levee and floodwall failures that caused flooding of 80% of the city after the storm. The analysis concluded the region’s hurricane protection system was a “system in name only” that lacked redundancy and consistency, was built with erodible materials and had entire sections that were incomplete. The task force recommended a risk-based approach to planning and designing infrastructure to account for variables such as sea-level rise, climate change, population fluctuations and subsidence.

“Risk is a dynamic thing. And your ability to reduce risk depends on maintaining cognizance of the situation,” Link says.

The IPET analysis informed the Corps’ design of  the HSDRRS to defend against a storm surge from a 100-year level hurricane, meaning a storm that has a 1% chance of occurring in any given year. Experts used computer-generated models of 152 different hurricanes of varying speeds, paths, sizes and intensity to calculate what a 100-year surge would look like. Before Katrina, they relied on only one model.

“Unless we start spending more on mitigation, we're in trouble. We are just moving from one disaster to the next.”

– Lewis "Ed" Link, University of Maryland senior research engineering professor

The now complete HSDRRS consists of 350 miles of levees and floodwalls, 78 pumping stations and a series of gated structures.

Whereas the region previously relied on a piecemeal system of interior levees and floodwalls as its primary line of defense, the Corps designed the new system with 133 miles of perimeter features surrounding greater New Orleans, with the goal of holding back storm surge.

“When a storm is approaching, you can close it down, and it effectively becomes a walled city,” says Boyett.

Resiliency features were essential to the new system, which was designed to be overtopped to prevent erosion and subsequent levee failures. Levees and floodwalls were raised and widened in some areas, while the Corps also fortified 77 miles of earthen levees with armoring features, consisting of a layer of turf matting and Bermuda grass planted on top.

The system features the world’s largest surge barrier of its kind, the Inner Harbor Navigation Canal-Lake Borgne Surge Barrier, built to hold back a 26-ft surge. “The system is immensely more robust than the previous system,” says Traylor Bros. project manager Wayne Jones, who led the construction of the $1 billion, 1.8-mile concrete wall that forms the barrier’s backbone. Jones was ENR's 2013 Award of Excellence winner for his work on the barrier.

Just three weeks after the barrier’s completion, Hurricane Isaac put the structure to the test, pushing 13 ft of water against it. “Had the wall not been functioning, there would have been mass flooding again,” Jones says. 

Living with water

Beyond sophisticated engineering, Katrina forced people to rethink water management in terms of urban planning and architectural design to complement pumps and drainage.

Urban and environmental architect David Waggonner has spent the 15 years since Katrina championing the idea of “living with water,” which focuses on sustainable stormwater management and the Dutch model of investing in water as an asset, rather than working against it.

A decade ago, Waggonner and his New Orleans-based architecture firm, Waggonner & Ball, led a team of local and international water management experts in developing the Greater New Orleans Urban Water Plan, a series of urban design strategies to slow, store and use rainwater through green infrastructure, instead of relying solely on forced drainage.

The plan helped guide the city’s Resilient New Orleans plan for green infrastructure, which helped the city secure a $141 million federal grant to create a stormwater retention district in the Gentilly neighborhood. The project’s centerpiece is the 25-acre Mirabeau Water Garden, a public space that will be able to contain nearly 10 million gallons of stormwater.

“The history of New Orleans was to hide the water. When the Dutch came down here they said, ‘You say you have a water problem. But where is it?’” Waggonner says. “We really had created a non-sustainable urban form. So we’re doing a lot of remediation.”

A new approach to storm prep

Even with more than $14 billion in safeguards in place to lower its risks, Boyett says a key to making the storm system work is the willingness of residents, businesses and city officials to take responsibility for their lives and property by purchasing flood insurance and evacuating if the orders call for it. “We’re better than we were before, but that’s not to say there is no risk,” Boyett says.

To that end, the region has changed the way it prepares for and responds to storms. The city of New Orleans developed its NOLA Ready system to provide emergency alerts, city-assisted evacuation and resources for storm preparedness and response.

Improvements in communications have been important to Boh Bros. Construction. The company was one of the first responders at the 17th Street Canal floodwall breach and helped put temporary pumping measures in place immediately after Katrina. At the time, the company was able to mobilize its employees with limited communication, but only because many of them showed up in Baton Rouge on the assumption they would be called into work. “Technology and communications are greatly improved from where they were,” says Robert S. Boh, president and CEO. “I imagine that in the aftermath of a storm of widespread devastation as Katrina was, we would be much more able to communicate with our employees and respond.”

Applying lessons to the future

Although lessons learned from Hurricane Katrina have informed engineering and policy decisions on how to prepare for and mitigate disaster risk and climate events, questions remain as to how much officials are willing to put that knowledge into action.

“If we have learned only one lesson from Hurricane Katrina — it is that it is far less expensive to prepare for a hurricane in terms of dollars and lives than it is to rebuild after the damage has occurred,” Jones says.

In fall 2021, the Corps will request $3.2 billion from Congress to maintain the levees’ ability to provide 100-year protection through 2073. Link and others have been critical of Congress’ continued reliance on the 100-year storm risk standard to guide levee designs. He questions whether that level of protection is sufficient to protect New Orleans given that Katrina was a 400-year storm, and that climate change is resulting in larger, stronger hurricanes.

“That’s something we have to get rid of and start using tolerable risk. The challenge is finding what is tolerable – what level of risk you’re willing to live with,” Link says. “And that’s not something our society is willing to grapple with.”