It was a simple solution that could have prevented one of the worst disasters in the nation's history: metal gates at the mouths of New Orleans' canals that closed automatically to block hurricane storm surges on Lake Pontchartrain.
But the gates were never built. Local officials objected to the Army Corps of Engineers' plans in the 1980s, saying they would interfere with the city's antiquated network of pump stations that drain rainwater from the city.
The broken levees that flooded New Orleans after Hurricane Katrina have their roots in decades of decisions like the one to abandon the floodgates. The decisions reach all the way to Washington, where Congress in 1992 ordered the Army Corps to abandon the gates and instead build the network of flood walls that failed, according to Al Naomi, a corps senior project manager.
One of four teams investigating the levee failures told the Senate Homeland Security Committee on Wednesday that some preliminary indications of the levee failures are beginning to emerge, but it's still too early to say what caused the massive breaches.
A USA TODAY analysis of government documents and interviews with investigators, public officials and independent engineers shows that the underlying reasons for the flooding are compromises that undercut safety, miscalculations that underestimated risk and poor relations between the patchwork of agencies that oversee the miles of flood walls around New Orleans.
...Critical problems that underlie the failures behind the most costly flood in U.S. history:
Ã¢â‚¬Â¢ The 40-year-old analysis that served as the basis for how big to build the levees badly underestimated the potential for a large hurricane to hit the city.
The Army Corps of Engineers opted in 1965 to protect against what it believed would be the worst storm in 200 years. Congress agreed. Ivor Van Heerden, the leader of a Louisiana investigative team examining the levees, says that at least two larger hurricanes other than Katrina have hit New Orleans in the past 100 years.
By contrast, the Netherlands decided to protect itself against the worst storm possible in 10,000 years after more than 1,800 people died in a massive levee failure in 1953.
Ã¢â‚¬Â¢ New Orleans' levees - the result of the city's gradual growth rather than safety or efficiency - are riskier than those in neighboring communities.
Jefferson Parish, which adjoins New Orleans to the west, relies on a simpler system of levees at the lakefront to keep high water out. The levees are higher and stronger than the levees that failed on New Orleans' drainage canals.
As a result, Jefferson remained dry during Katrina.
Ã¢â‚¬Â¢ Safety is compromised by the patchwork of governmental agencies and private firms that share responsibility for designing, building and maintaining the levee system.
Investigators found numerous leaks where two sections of levees controlled by different authorities joined, says Peter Nicholson, a civil engineering professor from the University of Hawaii who heads a levee investigation by the American Society of Civil Engineers.
The problem is symbolic of a broader issue that has undercut safety over the years, say the investigators: Safety is too easily compromised because no single agency is in charge.
"You have multiple agencies, some of which aren't on speaking terms with each other," says Raymond Seed, another Berkeley professor who heads the investigative team from the National Science Foundation.
Just as the gates at the mouths of the canals were opposed by local levee and pumping agencies, environmental groups in the 1980s derailed plans to erect a structure to block storm surges from Lake Pontchartrain. Engineers now say that undercut safety.
Ã¢â‚¬Â¢ Investigators found signs that poor maintenance of levees had compromised safety.
Bea says he believes large trees allowed to grow near levees may have contributed to the failures. Investigators say they also found leaks caused by portions of levees that had sunk and not been repaired.
Ã¢â‚¬Â¢ The corps, which oversees levee design and construction, has steadily lost expertise in the face of budget cuts. That's "as shocking as what happened in New Orleans itself," Seed says.