...The Army Corps of Engineers learned that the [17th Street Canal levee or flood wall] had broken early Monday even as the storm hit, but it was impossible to do anything about it before lake water cascaded unimpeded into the below-sea-level city for 36 hours, turning a really bad storm into an unimaginable abomination. There was no public announcement that the levee had broken until late Monday.
Lt. Gen. Carl A. Strock, the Corps' commander, told reporters at the Pentagon on Friday that Katrina had simply overpowered levees designed 30 years ago with a 99.5 percent chance of enduring for 200 to 300 years: "We, unfortunately, have had that 0.5 percent" happen, Strock said.
On Friday, the Corps was trying to close the 17th Street breach and another breach at London Avenue to the east. A third break -- two breaks actually -- in the Industrial Canal, were left alone because water levels in the lake and the surrounding wetlands had subsided so much that water was draining out instead of coming in.
Col. Richard P. Wagenaar, the Corps' New Orleans District commander who is the on-site commander at 17th Street, said a police officer called him Monday morning to tell him about the break, but he could not drive there. On Tuesday, the Corps tried to drop some sandbags into the breach, but "it didn't work real well," Wagenaar said. "They were too small, and the water velocity carried them away."
It was better on Friday, but there was a big, deep hole to fill, and the bags -- made to hold 20 tons of sand -- were only carrying five, because the helicopters that arrived every five minutes or so, Black Hawks, Sikorskys and even the Chinooks, could not haul more.
Still, the Corps had a plan. Michael Zumstein, action officer for the Corps' "unwatering team," said the canal had been sealed off from the lake with steel slabs, causing water levels in the canal to drop further. That should eventually make it easier to plug the breach.
While the preferred strategy was to plug the breach and allow the city's pumps to discharge floodwater into the canal, the Corps was also prepared to use emergency pumps to flush directly over the steel dam and into the lake if stopping up the hole proved too difficult.
Zumstein said engineers were using the same strategy at a 250-foot breach in the London Avenue Canal, where they were closing the canal mouth even as they tried to stopper the hole: "They're tearing up Lakeshore Drive and using the concrete as fill," Zumstein said.
Elsewhere, flood teams were taking advantage of the fact that the city is divided by internal levees and floodwalls into 13 "sub-basins" with their own drainage systems and pumping stations -- like separate basements with their own sump pumps.
Walter Baumy Jr., engineering chief for the Corps' New Orleans District, said water levels in the lake had subsided by mid-afternoon Friday to within a foot of normal levels, and "when the water inside the bowl is higher than the lake level, we want to drain the water out of the bowl as much as possible."
Baumy said engineers planned to cut new breaches, or "notches" in levees elsewhere in the city, creating makeshift gutters in flooded areas to let water leak out. "We'll see an immediate improvement," he predicted...