The U.S. Army Corps of Engineers issued a 6,113-page report last week to explain why its hurricane-protection system in Louisiana failed during Katrina. In brief, here's what it said:
Why did the levee system fail? The Corps's system suffered from faulty design that was based on outdated scientific data. The network of canals and levees, built piecemeal over 40 years, was constructed to withstand relatively weak hurricanes, not the Katrina-size monsters that scientists had more recently warned of.
Why didn't the backup protection work? The pumping system meant to mitigate post-hurricane flooding worked at just 16% of capacity during the storm. The pumps that did work were scattered across four parishes, vastly reducing their efficacy. Once electricity was lost and operators evacuated, the system was quickly overwhelmed.
Why weren't the levees high enough? Engineers failed to account for how quickly the soil in Louisiana had sunk in recent years, so levees were in some cases 2 ft. lower than they were meant to be.
Has the system been fully repaired? About half of the state's 350-mile protection system was damaged in the hurricane, and much of that has been fixed. But experts caution that the levees may still be in a pre-Katrina state--that is, subpar.
What does the report recommend? The Corps must dramatically strengthen backup systems, keep up with the latest scientific developments and do a better job of risk assessment to prevent another disaster.