The Army Corps of Engineers did a design review of the New Orleans levees in 1990. Apparently the engineers on the project thought the soil under the 17th Street Canal was stronger than it was, and one of their offices discovered this at that time:
Corps documents show the mistake of overly optimistic levee strength was detected by its Vicksburg, Miss., office, which directed local engineers to make changes. But when the chief engineer in New Orleans replied that the results were based on "engineering judgment," his superiors dropped the issue.
[Robert Bea, a University of California-Berkeley professor] said the discussion in the 16-year-old "design memo" points to the key decision that created fatal problems on the 17th Street Canal levee and could reveal a systemic problem that will show up during investigation into the London Avenue and Industrial Canal levees, which also breached during the Aug. 29 storm.