A rough reconstruction of the flooding based on anecdotal accounts,
interviews, and computer modeling, shows that the huge scale of the
overlapping floods – one fast, one slow – should have been clear to
some officials by mid-afternoon Monday, when city representatives
confirmed that the 17th Street canal floodwall had been breached.

At that point areas to the east were submerged from the earlier
flooding, trapping thousands, while gradually rising waters stretched
from the Lakefront across to Mid City and almost to the Central
Business District.

Federal officials have referred to the levee breaches as a separate
and much later event from the flooding to the east, and said that they
were unaware of the gravity of the problem until Tuesday, suggesting
valuable response time was lost.

“It was midday Tuesday that I became aware of the fact that there was
no possibility of plugging the (17th Street canal) gap and that
essentially the lake was going to start to drain into the city. I
think that second catastrophe really caught everybody by surprise,”
Homeland Security Secretary Michael Chertoff said Sunday, adding that
he believed the breach had occurred Monday night or Tuesday morning.
By that time, flooding from at least one of the two breached canals
already had been under way all day Monday, evidence shows.

Even on Tuesday, as still-rising waters covered most of New Orleans,
FEMA official Bill Lokey sounded a reassuring note in a Baton Rouge
briefing.

“I don't want to alarm everybody that, you know, New Orleans is
filling up like a bowl,” Lokey said. “That's just not happening.”

Once a levee or floodwall is breached by a hurricane storm surge,
engineers say, it often widens and cannot be quickly sealed. Storm
surge waters in Lake Pontchartrain may take a day or more to subside,
so they keep pouring into the city – most of which lies below sea
level – until the levels inside and outside the levee are equal.

Experts familiar with the hurricane risks in the New Orleans area said
they were stunned that no one had conveyed the information about the
breaches or made clear to upper-level officials the grave risk they
posed, or made an effort to warn residents about the threat after
storm winds subsided Monday afternoon.

“I’m shocked. I don’t understand why the response wasn’t
instantaneous,” said Louisiana State University geology professor Greg
Stone, who studies coastal storm surge dynamics.

“They should have been monitoring this and informed people all the way
to the top, (and) then they should have warned people,” said Ivor Van
Heerden, who uses computer models at the LSU Hurricane Center to study
storm surges and provided officials in the Louisiana Office of
Emergency Preparedness headquarters with data indicating the potential
for flooding that could result from Katrina.

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