The Corps designed and built the levees that failed. Their designs were flawed and the construction did not meet standards.
There is no one else to blame.
The lefties frown upon mention of this, because blaming an environmental group for *anything* reflects poorly on our political system. After all, trout are people, too.
Would the USACE plans from '76 have prevented all the flooding? Probably not, but it might've reduced it by two-thirds or so. Some blame definitely belongs to the plaintiffs who killed that project.