MELISSA BLOCK, Host:
This is ALL THINGS CONSIDERED from NPR News. I'm Melissa Block.
ROBERT SIEGEL, Host:
And I'm Robert Siegel. There is a new development in the investigation into why the floodwalls around New Orleans failed during Hurricane Katrina. An independent panel overseeing the investigation has sent a strongly worded letter to the Chief of the U.S. Army Corps of Engineers. And the letter says that in some places, the Corps did not leave enough margin for safety when it designed those floodwalls. NPR's David Kestenbaum has been following this story and David first who is this group that sent this letter?
DAVID KESTENBAUM: This is an independent group of 13 engineers picked by the American Society of Civil Engineers. It's the same group that helped figure out how the World Trade Centers collapsed. They're some of the most respected engineers in their field and they've actually been empowered by the U.S. Government to sort of look over the government's shoulder to keep them honest while they do their investigation into the failure. And their charter officially says they're suppose to stick to helping figure out the mechanism of what went wrong, but the panel members say in this letter that they know this oversteps their bounds, but the words they use are gravity and potential impact of their conclusions warrant immediate action.
SIEGEL: What are their conclusions about what happened with the floodwalls in New Orleans?
KESTENBAUM: The committee says that the 17th Street Canal wall, in particular, was built with too small of a safety margin. So the 17th Street Canal, when they were designing it, there's a certain amount of engineering judgment that comes into play. Basically they drill down these cylinders into the earth and they test the soil at different depths. And they say okay this layer is strong and this one's a little weaker. They do some calculations and they build the wall. But those walls, at least the ones in the 17th Street Canal, failed before they should've.
And the panel says, looking back, some of the judgment calls that were made at the time of design, were not the conservative judgments you would expect would be made for a system that's responsible for protecting an entire city. It's unclear if had, had the system been designed with a little more of a safety margin, if it would have survived. But they say the design should've been more conservative.
SIEGEL: Now this sounds like it's in conflict with the official government investigation a few weeks ago, which said that the failure of the floodwalls could not have been foreseen. It sounds at least implicit in what you're saying that it might've been foreseen?
KESTENBAUM: The official report does say that the particular cause of the failure was unforeseen. This letter says in essence, yes, well, you might not have foreseen this happening when you designed it, but you could have. And maybe you should have. One of the things that caused the 17th Street Canal wall to fail was this crack that opened. Basically the wall tilted out a little bit and this gap opened up with the earthen base, and allowed the water to press up against the entire wall. So this letter, and some other critics, point out that the Corps had done its own experiments in the 1980s suggesting that this kind of failure could happen. Another cause was a weak layer of clay out, sort of, in people's backyards just outside the wall. And the letter said the profession has known for decades that the clay would've been a lot weaker there. So the Corps did a lot of this work and they should've known about it.
SIEGEL: What does the Corps say about this?
KESTENBAUM: Well the official investigation, which a lot of the Army Corps people were working on has not been charged with looking back the original design. They've been charged with looking forward in trying to make sure the levies are safe for the future residents of New Orleans.
I've talked to Corps officials in the past about the original design, and they've all said, look, this is over 20 years ago. There are lots of reasons why those engineering judgments might have made sense at the time. And some of the research cited in this letter, to be fair, that could've raised red flags, that research was published in the late eighties. And the walls were already under construction or built by then.
SIEGEL: Thank you David.
KESTENBAUM: You're welcome.
SIEGEL: That's NPR's David Kestenbaum. Transcript provided by NPR, Copyright NPR.
