From NO Times Picayune:
Meantime, five miles to the west, engineers worked to close a breach along the New Orleans side of the 17th Street Canal.

Huge drainage pumps ordinarily can drive millions of gallons of rainwater uphill through the canal, as it takes water from the low-lying city into Lake Pontchartrain. But the breach turned the canal into a major threat. Lake water flowed back through the breach, hemorrhaging into Lakeview and beyond.

The water had risen knee-deep during the storm, but despite the clearing skies, it had continued to rise one brick every 20 minutes, according to Kyle, continuing its ascent well into the night.

“We were good until the Canal busted,” said Sontag. “First there was water on the street, then the sidewalk, then water in the house.”

Officials of the Army Corps of Engineers have contingencies for levee breaches such as the one that happened Monday, but it will take time and effort to get the heavy equipment into place to make the repair. Breach repair is part of the Corps’ planning for recovery from catastrophic storms, but nobody Monday was able to say how long it would take to plug the hole, or how much water would get through it before that happened.