NEW ORLEANS — When he arrived three weeks ago, 80 percent of the city was under water, and the devastation was unfathomable. The damage is still "apocalyptic," but as he watches the last pockets of water drain from New Orleans' 9th Ward and anticipates a dry city by tomorrow, Col. Duane Gapinski said he feels a certain sense of satisfaction.

"It's pretty cool," said Gapinski, 46, who was brought in from the Army Corps of Engineers' Rock Island, Ill., office to oversee drainage efforts after Hurricane Katrina.

"You can see these big vortices as the water comes through these culverts under the railroad trestle. There's a sense of accomplishment. We've done something."

For Gapinski and others who came to help the undermanned New Orleans division, it has been nonstop madness. Operating out of a headquarters beside the Mississippi River, they have worked 18-hour days, monitoring progress in an operations center filled with laptops and maps coded in pink and blue to show areas that are drained and areas that aren't.

"They have nothing to be ashamed of," said Mitch Frasier, spokesman for the New Orleans corps' office, which is still missing three-quarters of its 1,200-person force, "and a lot to be proud of."

Questions raised

But as floodwaters recede, the corps is hearing more criticism than praise — ranging from questions about why the levee system suffered a massive failure in the first place, to suspicions that repair work was biased to favor upper-income neighborhoods, to concerns that planned repairs will leave it as vulnerable next year as it was a month ago.

The corps said yesterday it is launching a formal investigation into the failures of floodwalls and levees. The probe, by corps and outside experts, is expected to take eight months, a spokesman said.

But hurricane experts from Louisiana State University and others already have raised questions about the corps' initial assertions that floodwalls in two key drainage canals at 17th Street and London Avenue were overtopped by water from Lake Pontchartrain that eroded away their earthen bases.

Corps officials said that was the predictable consequence of government decisions decades ago to pay for a system that was only high enough and strong enough to protect against Category 3 storms — not a Category 4 hurricane such as Katrina.

The LSU experts, however, have concluded through computer modeling and inspections of the debris lines along the earthen levees lining Lake Pontchartrain that Katrina's surge was not, in fact, high enough to top the canals' 14-foot floodwalls.

They point a finger, instead, at possible design flaws.

"There's a number of ways levees can fail," said John Pardue, a civil-engineering professor at LSU's Water Resources Research Institute. "But overtopping — that was an act of God and not a design problem; that is not what happened based on what we saw."

Corps officers such as Gapinski and Col. Richard Wagenaar, commander of the New Orleans district, say they will await results of forensic studies. But they say they have seen other evidence — debris on the land side of the 17-foot lake levees, for example — that supports an overtopping theory, and are dismissive of the computerized storm-surge models.

"These are meteorologists," Wagenaar said, "reporting on concrete structural issues."

When Rita hit, the corps repairs of the 17th Street and London Avenue canal breaches sprung leaks but held. But similar repairs at a third major breach along the Industrial Canal failed, and water flowed over the top, reflooding the battered 9th Ward. And that produced a new round of criticism.

Officials complain

Officials in neighboring St. Bernard Parish, flooded along with the Ninth Ward, complained the government engineers had done more to protect the rich areas than the poor.

Wagenaar and Gapinski say there was no bias in repair efforts, but securing the navigational passage of the Industrial Canal is a harder engineering task because its depth made it impossible to wall off storm surge, as they did at the drainage canals.

The controversy, however, illustrated a deeper problem: After the deluge of Katrina, the people of New Orleans may want more than the corps has the capacity to deliver. When Wagenaar appeared before the New Orleans City Council on Tuesday night to outline his plan for restoring levees to their pre-Katrina capacity by June 1, some greeted the plan with dismay.

"Pre-Katrina is not going to work for us," Councilwoman Cynthia Morrell told him. "We need to go one step above."

That, experts say, isn't going to happen in eight months. Fuller protection of New Orleans, Pardue said, is going to cost tens of billions of dollars and take years. It will have to involve not only higher walls, but better walls, a system of sensors to let officials know about breaches when storms hit, and movable floodwalls to reduce surges into Lake Pontchartrain and the canals.

New Orleans will just have to keep its fingers crossed next year. And if another Katrina hits, corps officers such as Gapinski say they may be back.

Details on the corps' investigation were provided by the Los Angeles Times.