I thought my November column, "Protecting New Orleans (Part 2)," would end my series concerning flooding and that beleaguered city’s struggle to get back on its feet. But some recent news stories in the New York Times goaded me into writing another column on the subject. The articles2 were titled "Malfeasance might have hurt levees, engineers say" and "Louisiana’s levee inquiry faults Army Corps." As an impartial observer, it occurs to me that it is relatively easy to blame engineers who are involved directly in a project for lapses by "civilians" who sometimes meddle into technical matters of which they know little or nothing. Assuredly, politically appointed civilians who run the Federal Emergency Management Agency (FEMA) today could have done little to mitigate the Katrina disaster as far as flood protection devices are concerned, but the Times story pointed a well-watered finger at a number of facts that made the flooding worse than it had to be.
The "Official Louisiana Team," as it was called by the Times (also known as Team Louisiana), is investigating the hurricane Katrina flooding. It found that the 17th Street Canal levee, which suffered one of the more significant structural failures, was constructed with insufficient concern about the inherent weakness of the underlying soil in the area of failure. The deputy director of the Louisiana State University (LSU) Hurricane Center (the leader of the investigation team) said, "It should have been obvious [that the subsoil under the canal banks] was inherently weak." Another member of the team, an engineering consultant, was puzzled by what was actually constructed, since the design "was gone over by everyone at high and low levels of the Corps of Engineers staff members." This "going over" was done even before protection standards were upgraded in the 1980s.
An interesting detail of the investigation of the breaches in the levees is that the interlocking members of the sheet piles, which are driven down and intended to anchor the levees and prevent water from flowing underneath them, were apparently too shallow to prevent the passage of water under the levee.
Team Louisiana performed tests that apparently indicated that the bottom of the piles extended only to 10 feet below sea level in some places. However, when the Corps of Engineers (Corps) pulled several of the piles in mid-December, it found that they indeed extended to a depth of 17 feet below sea level.
But, even at that depth, they might have been too shallow to ensure the safety of the embankment and pile system, according to the team.
The Times story listed some hard-to-believe numbers: "In spots where the levees are being repaired, the Corps of Engineers is calling for sheet piles to be driven to a depth of [an incredible] 51 to 65 feet." It seems to me that if these numbers are correct, it would be difficult to prove by an unbiased benefit- cost analysis that such a construction plan was even feasible.
But the state manager for Team Louisiana, Edmund Preau, Jr., of the Louisiana Department of Transportation & Development, said the walls should never have toppled merely because the water levels reached 11 or 12 feet.
Interestingly, a spokesman from the Corps acknowledged that "its own sonar tests had confirmed the state’s findings of 10-foot sheet pile depths." In order to confirm this, some piles were pulled at the 17th Street Canal and measured more accurately.
But, a spokesperson noted that the pile depth is only one factor which might contribute to the strength of a levee; others involve levee height and width.
According to the Times article, the design standard set by the Corps for levees calls for them to be built at 130 percent of the strength needed to withstand a Category 3 hurricane. Design documents from the Corps reportedly stated that the New Orleans levees would meet that standard. However, preliminary calculations by Team Louisiana indicate that the levee in question (17th Street Canal) was actually constructed at 93 percent to 98 percent of that strength near the breached area.
In fairness to the Corps, another member of Team Louisiana, G. Paul Kemp, an associate professor at LSU, said outsiders might interpret the findings to be foisting blame for Louisiana’s problems onto the federal government and trying to avoid responsibility for local lapses in levee maintenance. However, Kemp argued, "The design and construction is a process that is overseen by federal people at every step." My interpretation of the Times stories is not that anyone is pointing fingers to blame the Corps, but Team Louisiana is interested in learning exactly what happened, what went wrong, and how a similar disaster can be prevented in the future. As I write this, data is still being collected, so engineers should follow this story with interest. Its outcome may have significance for all of us who encounter attempts by non-technical people to alter engineering designs without due consideration for the consequences.
Alfred R. Pagan, P.E., P.L.S., is a consulting engineer in Hackensack, N.J. He can be reached at 1-201-441-9719; or e-mail him at email@example.com.