how many levees was broke in hurricane Katrina?

Answer 1

Overall, approximately 28 levee failures were reported.

TIMELINE:
http://www.npr.org/templates/story/story.php?storyId=5200940
A timeline released by a Senate investigative panel shows 28 reports of levee failures the day Katrina made landfall in New Orleans. The information is at odds with contentions from Bush administration officials who say they didn't learn about the levee failures until the following day.

ARTICLE (breaks/investigations/misc):
http://en.wikipedia.org/wiki/Levee_failures_in_Greater_New_Orleans%2C_2005