The federal government's verdict on the future of New Orleans is in: The city is much safer than before Hurricane Katrina but faces a 1-in-100 chance each year of significant flooding.
Since Hurricane Katrina struck nearly two years ago, killing 1,293 and causing an estimated $100 billion in damage, the Army Corps of Engineers has overseen a vast construction program to reinforce levees, repair damage and upgrade pumping stations.
The effort has improved the city's prospects significantly but has not eliminated the huge risks.
A computer analysis - the final part of the Corps' investigation into the levee failures during Katrina - found that residents in many sections of the city faced the likelihood of flooding as deep as 8 feet one year out of every 100.
That means that homeowners would have to expect that during the course of a 30-year mortgage, they have a greater than 25 percent chance of enduring a serious flood if their home is in an area of the city below sea level and vulnerable to hurricane surges.
The risk analysis provides a valuable tool for residents, businesses, insurers and home lenders to understand the risks they face in the city, said Lt. Col. David Berczek, the Corps' program manager for risk and reliability. The projections were based on a complex mathematical model of 152 hypothetical hurricanes bearing down on New Orleans.
The Corps is being careful not to suggest that its repairs and upgrades will prevent flooding or that the city should redevelop areas below sea level where homes were submerged by Katrina.
"Everybody has to answer that for themselves," said Ed Link, the University of Maryland civil engineer who led the investigation.
But Link says that the current levee system is providing the city with the best protection it has ever had and that it will continue to improve. By 2011 the Corps hopes to complete repairs and upgrades to the 350-mile levee system that would further protect the city.
Such efforts would not, however, guard entirely against another Katrina. The Corps' analysis shows that although Katrina did not have extremely high wind speeds, it produced a bigger surge than any hurricane on record to have previously hit New Orleans.
It was both intense and large, pushing a mound of water up the Gulf Coast that washed away miles of levees. In New Orleans the surges reached 19 feet with additional waves of 8 feet.
The improved system would be more resistant to such a storm, meaning that even when levees were overtopped by waves, they would not completely fail as they did in Katrina. Indeed, the Corps' risk assessment assumes that its levees would not suffer the huge breaches caused by Katrina.
At a news conference in New Orleans, the Corps released maps of each of the 37 sub-basins in metropolitan New Orleans. The maps show the depth of water that homeowners could expect in a flood with a 1 percent annual chance of occurring.
The maps show, for example, that the affluent Lakeview neighborhood would be subject to 5 feet less flooding because the nearby levees on the 17th Street Canal have been improved. But the area could still get up to 8 feet, depending on the street.
In many other areas of the city, improvements since Katrina have been modest. In much of Gentilly, St. Bernard Parish and the 9th Ward, flooding would be nearly as bad as before the improvements were made.
Ralph Vartabedian writes for the Los Angeles Times.