As an engineer, Thomas O'Rourke can explain why the levees in New Orleans failed during Hurricane Katrina in 2005. But the real causes of the disaster are historical and political, he says. And we should not just build new protections for the Big Easy, but make all our communities "resilient" and better prepared to deal with catastrophe.

O'Rourke, the Thomas R. Briggs Professor of Civil and Environmental Engineering at Cornell, is an expert on the effects of natural disasters on infrastructure and a member of a National Academy of Engineering (NAE) team studying the effects of Hurricane Katrina. He reported some of his findings on Feb. 16 in a lecture at Cornell, "Hurricane Katrina: Geosystems in Crisis," a civil infrastructure seminar supported by the Charles L. Crandall Fund.

The first seeds of the disaster, O'Rourke reported, were planted over 200 years ago with the systematic building of longer and taller levees along the Mississippi River. The result was that less sediment was deposited at the mouth of the Mississippi, and wetlands that might have absorbed storm surges from the ocean were not created. After Hurricane Betsy flooded the city in 1965, Congress appropriated money to upgrade the levees to resist a one-in-a-hundred-year-hurricane -- a Category 3 storm like Betsy with 6 to 9 foot storm surges. Katrina was labeled Category 3 based on wind speed, but it was equivalent in pressure and surge to a Category 5 storm with surges 18 feet and higher at New Orleans and up to 30 feet along the coast in Mississippi.

"When I gave talks in Europe, people were amazed that we only planned for a hundred-year storm," O'Rourke reported. "Many said they planned for 1,000-year storms. The Dutch design for one-in-10,000-year events."

As soon as levees are built, O'Rourke pointed out, they become "wasting assets" as they sink into soft and compressible soil. He added that levee and flood wall systems are paid for by the federal government but must then be maintained locally, sometimes causing local governments to resist more effective designs that require higher maintenance costs. Instead of building flood gates at the head of the New Orleans drainage canals, the U.S. Army Corps of Engineers, under local political pressure, built "I-walls" by driving sheet piling into existing levees, and many of these failed during Hurricane Katrina, O'Rourke explained.

Levees along the city's London Avenue Canal were built on sandy soil, allowing water to seep under them and exert pressure that heaved and cracked the soil on the community side. In other locations water flowing over the top scoured out the levee soil, creating massive openings for the invasion of storm water. Meanwhile, large pipes designed to drain rainwater into Lake Pontchartrain worked in reverse, allowing water to back up from the rising lake into the center city. Pumps that were supposed to take water out of the city sat idle with no electricity to run them.

The resulting disaster caused $82 billion in direct damage but far more in damage to the local and national economy, as it disrupted the country's primary oil production, refining and transport facilities.

The event changed the policy of the U.S. Department of Homeland Security from a post-9/11 focus on protecting critical infrastructure to developing "resilient communities." O'Rourke said that "resilience" includes public education about risks, adequate leadership, sustained funding to maintain infrastructure after it is built, and planning that prepares communities to improvise and deal with the unexpected.

In repeated visits to New Orleans to fulfill his NAE responsibilities, O'Rourke said he experienced déjà vu, recalling the devastation he had seen in the aftermath of the 1988 Armenia earthquake, the 1995 earthquake in Kobe, Japan, and the Kocaeli earthquake of 1999 in Turkey.

"How often," he concluded, "do we have to experience the tyranny of déjà vu and repeat the cycle of destruction, rethinking, forgetting and more destruction?"