A decade ago Hurricane Katrina terrorized the Gulf Coast. What began as a tropical depression over the Bahamas quickly spun up into an unstoppable beast of wind and water that laid waste to parts of Louisiana, Mississippi and Alabama. New Orleans and its surrounding communities endured hours of surging water that quickly toppled inadequate defenses and flooded the region under more than three meters of water in some places. More than 1,800 people died during the storm and its aftermath, which left an estimated 600,000 families homeless.

The failure of New Orleans’s flood protection system was epic. The city, founded nearly 300 years ago, was built on low-lying marshland along the Mississippi River. After Hurricane Betsy battered New Orleans in September 1965 the U.S. Army Corps of Engineers began to build a network of levees and floodwalls—also called I-walls—to protect the Big Easy and adjacent parishes (counties). Unfortunately, planners never anticipated a storm surge of Katrina’s magnitude.

During and after that tempest billions of liters of water from the Gulf of Mexico, Lake Borgne and Lake Pontchartrain overwhelmed or outright destroyed the city’s flood protections. Storm water pouring over the concrete floodwalls in many places eroded away the soil on the other side that gave those structures their footing. As the bottom of the I-shaped walls was laid bare, the water pressure behind them toppled or pushed them aside. Meanwhile many of the pump stations installed to evacuate water from canals behind certain floodwalls were rendered useless, drowned by in the very water they were supposed to be siphoning away, according to a 2007 American Society of Civil Engineers (ASCE) report aptly titled “What Went Wrong and Why.”

The New Orleans hurricane protection system’s main shortcoming: It wasn’t actually a system. Instead, it was constructed as individual pieces based on bad math. “Levee builders used an incorrect datum to measure levee elevations—resulting in many levees not being built high enough,” according to the ASCE report. Some were nearly a meter lower than the intended design elevation, the report states. Add to that a poorly coordinated and executed disaster response plan—at both the national and local levels—and the stage was set for Katrina’s destructive rampage.

Surely, the U.S. is ready for the next Katrina or Hurricane Sandy, right? To find out Scientific American spoke with Robert Traver, a civil engineering professor at Villanova University and co-author of the ASCE report. Traver surveyed Katrina’s destruction firsthand after the storm, serving as a member of the ASCE External Review Panel that helped the Corps investigate the hurricane protection system’s catastrophic breakdown.

[An edited transcript of the interview follows.]

How did you get involved in the U.S. Army of Corps of Engineer’s investigation of the New Orleans hurricane protection system after Katrina?

A couple of weeks after Katrina the Corps contracted the American Society of Civil Engineers to provide quality control for the [Corps’s] study of the storm’s aftermath. We were there to make sure the right questions were being asked and the right processes were being used to understand what had happened.

The ASCE published a report with lessons learned after your post-Katrina work. What were the most important takeaways?

Three were especially important: The first is that there wasn’t an overall systems approach to the region’s hurricane protection system. One of the first questions I asked was: What was the plan for when water overtopped the levees? There wasn’t one. In addition, the water pumping stations were designed for heavy rainfall, not for hurricanes. They didn’t have alternate power sources or safe housing for the people working there. And in at least one of the levees that caused flooding, there were actually areas where the levee was intentionally built lower to the ground in order to protect the pump stations by relieving some of the water pressure. There were also inconsistencies in how the levees and pump stations worked together. That’s probably because the Army Corps of Engineers had built the levees while the city was in charge of the pump stations. I don't know how to say it nicely, but that [lack of coordination] was just incredible to me.

What were the other key observations?

The second important lesson to be learned is the great failure of communication in terms of making sure people understood how risky it is to live in New Orleans. Before Katrina the residents didn’t seem to fully understand this, even though the information was available to people making the decisions down there. The Corps pretty much described what would happen in the event of a major storm every year when they put out their request to Congress for funding. And the ASCE, in its Civil Engineering magazine, had published an article two years before Katrina that talked about exactly what would happen during a major storm. Still, people felt safe behind the levees so they wouldn’t leave.

The third lesson—and this applied to Sandy on the east coast a few years later, too—is that you need an analysis of the risk and consequences of failure. If you've never taken a close look at what would happen if water overtops your storm protections, then you won’t know what’s needed in terms of an evacuation plan and other emergency planning.

Have any of these lessons been taken to heart?

Since Katrina the Federal Emergency Management Agency (FEMA) has done a lot of mapping of storm surges along the coasts, trying to give themselves a sense of the risk of flooding during different sized storms. Somebody asked me a question recently about whether I’m worried about New Orleans or the New Jersey Shore in the event of another major storm. No, I’m not worried about them, because they’ve recently been through it. I’m worried about all the places that haven’t been hit.

What has the government done since Katrina to help avoid a similar catastrophe in that region?

Okay, this one is tougher. I am better at the engineering, but one thing they tried was the [Water Resources Development Act of 2007], which is supposed to give the Army [Corps] the ability to find the areas where we’re vulnerable. Unfortunately [the Corps’s] study was never funded or completed.

On the other hand, the Army Corps of Engineers did a lot of work to raise the levees higher and improve other storm protections down in New Orleans. And they’ve also redesigned all the pump stations so they can operate during a hurricane, by installing alternative fuel supplies, better communication systems and places where the workers can go when they need shelter during a storm. Where the canals empty at Lake Pontchartrain, they’ve added massive new pump stations that send water to Lake Pontchartrain if it starts to get too high on the levees in the canals. This takes some stress off the levees. That’s important because if a levee is destroyed, there’s nothing you can do to fix it right away.

Are the Gulf and east coasts better prepared for the next Katrina or Sandy?

These areas now know what the low-hanging fruit is when it comes to being ready. That includes improving the pump stations to protect the levees, raising the height of the levees and dunes, adding in overflow protection and raising the homes they’re protecting. Even adding sand dunes where they had never been built because people had wanted a good view of the ocean from their houses. But there are some places where you just can’t build or engineer your way out of danger. There are some low-lying areas where all you can say is, when this is eventually destroyed we should not rebuild in this area. But unless that is identified before the hurricane, that line of thinking is not always followed, because we’re a compassionate country and after a storm hits we want to help people rebuild their homes, regardless of where they were. As a nation we don't really do a very great job of tying in the consequences of building in a location to our zoning codes and building codes.