The Army Corps of Engineers did in fact plead and whine and cry for years to be permitted to upgrade the flood system. And, the Sierra Club was instrumental in blocking the Corps' plans.
BTW - the canal that caused most of the flooding? Blame that on the New Orleans public works department. Some years prior to Katrina, they REMOVED some of those steel panels in the canal, to install some pumps or something. When finished, they put the very same panels, into the very same disturbed soil, without re-stabilizing the earth.
They SHOULD HAVE replaced the disturbed earth, compacting the dirt as it was put in the hold, THEN they should have jack hammered NEW PANELS, 4 feet longer than the panels they removed.
The canal didn't fail - that loosened earth washed out from under the canal.
Get your facts straight.