They were probably breached during the storm... the hole just got larger after.
Jeffers - can you please help with the question in post #2005?
They probably got a bit of overwash that started cutting a small ravine that suddenly deepened and widened as the gradient went to work. That's the problem with levees - you take a sluggish stream and give it a gradient if the levee fails.
Water seeps into the earthen barrier comprising the levees.
The soil becomes water soaked, weakens and eventually gives way. Or if it comes over the levy, the flow erodes the levy from the top, weakening it.
Similar to what happened in 93 along the Miss.
The LSU professor I saw on TV earlier said that the storm surges overspilling the levees caused the breach - apparently wearing them down until they gave.
Liquidfaction? Just my guess being that they were earthen levees.
"To: NautiNurse; seamole; Torie
My question: if the levees broke a day after the brunt of the storm...why did they breach?"
The storm moved extra water into the Lake, putting strain on the levees. Dynamic strain, not just like you pushing against them but with the added force of a moving weight.
This open cracks, and also, along with the rain, turns the earthen sections to wet toothpaste.
Once water finds a way through to the downstream face (as applied to an earthen dam), it's all over. The water will flow and trickle, enlarging the breach, until that section fails.
Many people feared this all along. Until it actually happened, we remained silent so as not to fuel panic. Let the reporters think that the City had dodged the bullet, they might have been right. Those who needed to know were fully aware of the potential years before this storm.
Looks like high < 20ft concrete wall. Looks like it cracked, then gave way. Maybe something big blew into it and started the crack propagating during the storm. It doesn't look that hard to fix. THey must have given up on it, or are mentally paralyzed.