It happend the night the hurricane came through. Flooding takes time.
What happend was that the winds from the north raised the level of the lake erroded the levee and made it break.
This has always been the scenerio that people talked about beyond the Cat 5 Direct hit that pushed storm surge up the Mississipi river.
the water eroded a Concrete wall? The levee that breached at the 17th street canal was resenctly upgraded to a concrete wall. Also, television did not report on the break until tuesday morning. There was a seperate levee break on Monday on another canal.