The Army Corps of Engineers has officially taken the blame for the New Orleans levee failures.

Serious work began on New Orleans' hurricane protection system in the 1960s after Hurricane Betsy flooded the city in 1965. But over the decades, funding slackened and many parts of the system were not finished by the time Katrina hit.

The result was a disjointed system of levees, inconsistent in quality, materials and design, that left gaps exploited by the storm, the report said.

Also, engineers did not take into account the poor soil quality underneath New Orleans, the report said, and failed to account for the sinking of land, which caused some sections to be as much as 2 feet lower than other parts.

Four breaches in canals that run through New Orleans were caused by foundation failures that were "not considered in the original design of these structures," the report said. Those breaches caused two-thirds of the city's flooding.