"Despite those ongoing controversies, we have tested those pumps again and again," said Karen Durham-Aguilera, director of Task Force Hope, the corps program to build a stronger protection system.
The corps has also raised levees throughout the system. Along Lake Pontchartrain, for example, levees are now about 17 feet above sea level, compared with 14 feet before Katrina, said Ed Link, a University of Maryland professor who led the post-Katrina investigation.
"Right now, the city in general is better protected, but it is still not adequate," Link said.
During Katrina, the Industrial Canal breached and flooded the 9th Ward when the storm surge moved up the Mississippi River-Gulf Outlet and struck the heart of the city. Despite repairs, its storm walls remain a weak point.
In recent weeks, the corps rushed to shore up a section of concrete wall on the Industrial Canal after corps members noted design weaknesses. Three-thousand-pound baskets of sand were brought in to reinforce the wall.
"The system is only as good as the weakest point," Durham-Aguilera said.
The corps has a plan to build large barriers along the canal, similar to those used in the Netherlands, said Durham-Aguilera. It awarded a $700-million contract earlier this year, but the structure will not be completed until 2011.
Long sections of levees along the Mississippi River-Gulf Outlet were washed away during Katrina. Corps officials say those sections, rebuilt with clay soils more resistant to erosion, are much stronger.
Not everybody accepts the corps' word.
Some critics have long contended that the corps used weak soils to rebuild levees and has taken other shortcuts. Corps officials acknowledged that their engineering failures had contributed to at least half the flooding that destroyed much of New Orleans.
Even though Katrina was a Category 3 storm in terms of wind speed, it produced a surge that would be expected, statistically, once every 396 years. The official corps investigation into Katrina concluded it was the biggest ocean surge to hit North America in recorded history.
The federal upgrade program is supposed to give the city protection against storms that have a 1% probability of hitting in any given year, or roughly once every 100 years.
But the probability figures may give the public a false assurance. The key issue is whether the public understands the forces of nature it is up against, said Gerry Galloway, a levee expert at the University of Maryland.
