Even with $15 billion dollars of work, the city is still vulnerable to a major storm. Experts feel it needs another $70 billion to be protected at the 500 year level called for due to its below sea level location and storm history.
An excerpt from the story from the Wall Street Journal.
“NEW ORLEANS—If Hurricane Katrina hit this city tomorrow, it would likely cause only light flooding, according to U.S. government and other engineers.
“A new ring of defenses costing nearly $15 billion—expected to be completed by the U.S. Army Corps of Engineers next June—will provide the Crescent City the best protection it has ever had from a storm, the Corps and other experts agree.
“The city's 350-mile flood-protection network is being upgraded to safeguard New Orleans from a so-called 100-year storm or flood, which has a 1% chance of arriving in any year. At that level of protection, which is designed to withstand a Category 3 hurricane like Katrina, Americans typically aren't required to purchase flood insurance.
“But many engineers and local politicians argue it may not be good enough. They say the city should be steeled for a 500-year or 1,000-year storm—roughly equivalent to a Category 5 hurricane.
“It isn't clear who will pay the tens of millions of dollars in annual maintenance costs for the system, which is being overhauled after storm surges from Katrina five years ago Sunday overwhelmed levees. Thousands were left homeless when 80% of the city was flooded.
“The Corps has completed much of a 1.8-mile-long, 25-foot-high surge barrier to the east of the city and has begun construction on a big pumping station to the south. Temporary pumping stations and flood gates are in place at three canals along Lake Pontchartrain to the north, already improving flood protection. …
“The view that a heavily populated and low-lying coastal area such as New Orleans—much of which lies below sea level—needs 500- or 1,000-year protection was echoed in two 2009 reports by the National Research Council. Three such Category 5 storms, which pack winds in excess of 155 miles an hour and large wave surges, have made U.S. landfall in the past century.
“Some experts have also raised the idea that residents of neighborhoods most vulnerable to flooding might be voluntarily relocated.
"We should be looking at a much higher level of protection in New Orleans. If that thing breaks, you've got people who are trapped in there," said David Moreau, a professor at the University of North Carolina who helped author one of the reports.
"Until we get to Category 5 protection, and do it in a way that's similar to what the Netherlands have done, we won't be adequately protected," New Orleans Mayor Mitch Landrieu, who is pressing for more federal help, said in an interview. He said he wouldn't consider relocating residents. "If the coast is rebuilt and the levees are strong enough, you can live anywhere," he said.
“The Corps estimates 500-year storm protection for the city would cost at least $70 billion, or nearly five times what Congress has authorized for post-Katrina improvements. Such an expansion might involve building additional defenses farther out on the metropolitan area's perimeter, such as along the north shore of Lake Pontchartrain, according to Corps estimates.”