Three teams of engineers studying the collapse of the New Orleans levee system agree that the design and construction of the protective girdle around Lake Pontchartrain caused the catastrophic flooding after Katrina passed through the city, and not the storm itself. Katrina only had Category-3 status when it hit the city, and the Army Corps of Engineers reported that the levees could withstand a hit of that magnitude, leading state and federal workers stunned when the walls collapsed anyway:

Investigators in recent days have assembled evidence implicating design flaws in the failures of two floodwalls near Lake Pontchartrain that collapsed when weakened soils beneath them became saturated and began to slide. They also have confirmed that a little-used navigation canal helped amplify and intensify Katrina's initial surge, contributing to a third floodwall collapse on the east side of town. The walls and navigation canal were built by the U.S. Army Corps of Engineers, the agency responsible for defending the city against hurricane-related flooding.

The preliminary findings -- based on physical evidence, Corps documents and hydrodynamic models run through a Louisiana State University supercomputer -- are the work of three teams of engineers and forensic experts conducting separate probes. The investigations are shedding light not only on the cause of the failures but also the scale of the rebuilding effort: The discovery of major flaws in the design of the city's levees and floodwalls could add billions of dollars to the cost of New Orleans' recovery.

Investigators already have rejected the initial explanation offered by Corps officials in the hurricane's aftermath that massive storm surges had overtopped and overwhelmed floodwalls on the 17th Street and London Avenue canals on the north side of town. The new findings for the first time point to a human role in all three of the major floodwall failures that left about 100,000 homes underwater and caused most of Louisiana's approximately 1,000 hurricane deaths.

Experts now believe that Katrina was no stronger than a Category 3 storm when it roared into New Orleans, and Congress had directed the Corps to protect the city from just such a hurricane.

"This was not the Big One -- not even close," said Hassan Mashriqui, a storm surge expert at LSU's Hurricane Center. He said that Katrina would have caused some modest flooding and wind damage regardless, but that human errors turned "a problem into a catastrophe."

Once again, this goes against all of the initial reporting in the immediate aftermath of Hurricane Katrina and the subsequent flooding. I covered this earlier when it first got raised as a possibility at the Washington Post, and it received only a small amount of attention in the Exempt Media. Now the Post reports again that the initial hypotheses by Louisiana State University researchers have been largely borne out by the physical evidence at the site of the collapses.

The bad news: the Corps of Engineers apparently knew better than to rely on the levees. They have had warnings over the years that the bases of river silt and peat could saturate under moderate conditions and weaken the levee structures, but have done little to address the situation. Since the newer levee systems simply got added to the top of older levees twenty years ago, some in the CoE have questioned whether their engineering models guaranteeing protection to Cat-3 hurrican strength actually applied. Eleven years ago, the question of soil composition and design flaws became the subject of a lawsuit -- one that was dismissed without ever addressing this issue.

Also, as reported earlier, the Post notes that the navigation canal along the levee system acted as a funnel, speeding up the water flow and allowing the water to eat away at this unstable base much more quickly than first thought. Again, the CoE understood the MRGO navigation channel could weaken the levees in a strong storm, but no effort has been made over the years to mitigate that.

Instead, everyone on site expected the levees to hold through a Cat-3 storm -- and when Katrina passed over New Orleans at that level, everyone breathed a sigh of relief. No one but the CoE expected to have problems with that level of storm, and apparently the CoE didn't tell anyone of their reservations.

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» Levee Failures from Don Singleton
Or maybe it will save billions of dollars if we think a little and decide why try to rebuild levees to protect land that is 7 to 15 feet below sea level, that has a mighty river on one side, a large lake on another side, and a huge gulf nearby. [Read More]

Tracked on October 24, 2005 1:16 PM