Engineer Manual No. 1110-2-2502 is not a publication that would normally excite interest from the general population. But in the weeks and months ahead, as New Orleans struggles to rebuild from the floods of Hurricane Katrina, Section 4 of that Army Corps of Engineers book could be scrutinized intensely by city and state officials.
The manual sets the performance standards for, among other things, inland floodwalls: the kind the corps built along the city's drainage canals and that failed spectacularly during Katrina, flooding much of the city and leading to many of the 1,100 deaths thus far confirmed from the storm.
...Forensic engineers investigating the levee failures say the layman's translation of that section amounts to a "gotcha" clause for those who believe the walls failed through faulty design and not because they were overwhelmed by a storm that exceeded design limits.
"It says what every engineer knows: If you build walls to 14 feet, regardless of the design specifications for the expected storm -- 12 feet or 10 feet or 13 feet -- those walls must hold water to their tops," said J. David Rogers, a forensic engineer on the National Science Foundation team investigating the failures.
..."So, yeah, this was a human failure, not a natural disaster."
Since overtopping has been ruled out as the cause of failure along some canal walls, experts in and out of the corps have debated whether the water inside the failed floodwalls was higher than the 12.5 feet maximum listed as the design capacity. But Rogers and other engineers said Section 4b makes that discussion moot. Because the walls were built to 14 feet, to account for wave splash, any collapse below that level means the design failed.
"Their own manual makes it pretty clear this was a failure, " Rogers said, "although they might try to argue it was something else."
...But the debate continues, because the stakes are high. If the walls yielded to forces lower than their design specifications, the city will be on firmer moral and legal footing in asking Congress to pay for the all the property damaged and destroyed when the waters of Lake Pontchartrain poured into the city. If not, the government can say the cost should be borne by flood insurance and homeowners.
Much more at the link.
This page has pictures of the measures that various countries take to protect their coastlines from being flooded, ending with the New Orleans levee system. Point taken, but it's not exactly fair to blame the Army Corps of Engineers for fault that, once again, is shared by various levels of government as well as the public.
A termite expert is questioning whether tiny, voracious Formosan termites played a role in the failure of levee walls in New Orleans during Hurricane Katrina.
Louisiana State University entomologist Gregg Henderson said there are clear signs that the destructive insects were present, and he wants the opportunity to dig into the levees beneath the walls to find out if termite nests contributed to their weakening.
Army Corps of Engineers officials, however, say no evidence has been found to indicate that termites undermined the integrity of the levees.
Henderson, a world-renowned expert on termites, found evidence of insects -- both Formosan termites and fire ants -- in the joints between wall panels on both the London Avenue and 17th Street canals. Fire ants, an enemy of termites, tend to invade the channels created by the wood-destroying insects...
At the London Avenue Canal, where several engineering teams believe the pressure of water in the canal undermined a weak layer of sand beneath levee walls and caused them to slide and fail, Henderson found insects in 73 percent of the joints, he said...
...Jerry Colletti, corps manager for completed public works, said engineers determined that the pinholes created by termites in the plastic joint spacers and in some cases in concrete were not dangerous...
..."The corps did an evaluation to determine how much water would come through those little pinholes," he said. "The decision was made not to take any action on the joints. We looked into sealing the joints, and it was going to be expensive and we didn't see a purpose to it; the pinholes didn't cause a structural integrity problem."
"We don't have anybody at the corps who's a termite expert," he said...
A difference in soil boring data transferred from one chart to another may have played a key role in engineering decisions that led to the breach on the 17th Street Canal floodwall that flooded much of New Orleans during Hurricane Katrina, National Science Foundation investigators say.
A cross-section drawing in the project design documents shows a weak layer of peaty soils running between 11 feet and 16 feet below sea level in the area that failed during the storm. But information in the individual soil borings that were used to draw the cross section show the peaty layer extending as deep as 30 feet below sea level.
Investigators said their own borings taken at the site this week confirm the 30-foot depth, leading them to believe that designers used the flawed cross section drawing to set the sheet pilings beneath the floodwalls at 17.5 feet below sea level - a choice that allowed water to migrate to the land side of the wall, causing the breach.
"It's pretty obvious the depth of the organic deposit shown on that cross section is what determined the sheet piling depth ... for the whole canal," said J. David Rogers, a member of the National Science Foundation team, and a leading authority on levee and dam failures. "They saw this marshy deposition, they recognized it as potentially dangerous, so they specified sheet piles that went just beyond the bottom of that line.
The Army Corps of Engineers did a design review of the New Orleans levees in 1990. Apparently the engineers on the project thought the soil under the 17th Street Canal was stronger than it was, and one of their offices discovered this at that time:
Corps documents show the mistake of overly optimistic levee strength was detected by its Vicksburg, Miss., office, which directed local engineers to make changes. But when the chief engineer in New Orleans replied that the results were based on "engineering judgment," his superiors dropped the issue.
[Robert Bea, a University of California-Berkeley professor] said the discussion in the 16-year-old "design memo" points to the key decision that created fatal problems on the 17th Street Canal levee and could reveal a systemic problem that will show up during investigation into the London Avenue and Industrial Canal levees, which also breached during the Aug. 29 storm.
"In the Gulf, Katrina was a Category 5 storm, and the surge was still Category 5 when it hit the ground... It's the surge -- the pressure of water against those levee walls -- that's the most important factor, not the winds."
As previously discussed, there are questions over whether ACE's design of the levees and floodwalls was faulty or not.
And, the downgrading also affects LA's government:
"That storm was the biggest storm ever to enter the Gulf of Mexico," [Edmond J. Preau Jr., Louisiana's assistant secretary for public works] said in testimony before the Senate's Homeland Security and Governmental Affairs Committee. "I think it would be a real disservice to everyone if Katrina goes down in the history books as a '4' because the wind speed dropped at the last minute."
To some local experts, the report was further evidence that human error was primarily to blame for New Orleans's drowning.
"This is a further indictment of the levee system," Ivor Van Heerden, an LSU professor and leader of a team of Louisiana investigators probing the cause of the levee breaches. "It indicates that most of the flooding of downtown New Orleans was a consequence of man's folly."
Other engineering experts agree: Considering Katrina's weakened state at the time it reached New Orleans, the failure of the city's 17th Street and London Avenue canal floodwalls can be explained only as a failure of design or construction, said Robert Bea, a civil engineering professor at the University of California at Berkeley.
"The water level in the canals wasn't that high when the floodwalls breached," said Bea, a member of an investigating team funded by the National Science Foundation. "We had a premature failure of the defense system."
The Army Corps of Engineers said the plan for improved levees that is being pushed by President George Bush is a good one for the areas where levees breached but will do nothing to protect the Lower Ninth Ward, New Orleans East or St. Bernard Parish.
...The plan calls for closing off the levees at the London Avenue, Orleans Avenue and 17th Street Canals by June 1, 2006...
In addition the levees will be built over with concrete and pumping stations would be positioned near Lake Pontchartrain within two years.
The plans are based on the standard of a true Category-3 and Congress used 100 miles per hour winds as their gauge for satisfactory flood protection in the short term.
The Corps has also been given two years to come up with a proposal for Category-5 protection...
"Team Louisiana", the state-sponsored "forensic levee investigation team" with "six LSU professors and three independent engineers" says the floodwall on the 17th street canal was bound to fail due to improper design that didn't take into account weak soils below the levee.
And, they say that bad design should have been obvious to those responsible: the Army Corps of Engineers, Eustis Engineering (a local company) and Modjeski and Masters (national company).
That miscalculation was so obvious and fundamental, investigators said, they "could not fathom" how the design team of engineers from the corps, could have missed what is being termed the costliest engineering mistake in American history.
..."It's simply beyond me," said Billy Prochaska, a consulting engineer in the forensic group known as . "This wasn't a complicated problem. This is something the corps, Eustis, and Modjeski and Masters do all the time. Yet everyone missed it -- everyone from the local offices all the way up to Washington."
Reaction here and here.
Previously: "Floodwalls in Swampy New Orleans 'Like Putting Bricks on Jell-O'"
Sheet piling supporting the failed floodwall on the 17th Street Canal extends just 10 feet below sea level, 7 feet shorter than the Corps of Engineers has maintained, a team of investigators said Wednesday [11/9], strengthening earlier findings that faulty design and construction played a role in the canal breaches that flooded much of New Orleans during Hurricane Katrina.
An LSU forensic engineering team, working in conjunction with the state attorney general's office, began examining the levee foundation with ground sonar Wednesday. The first reading was taken about 150 yards south of the break that allowed water from Lake Pontchartrain to inundate the city.
Independent engineers have questioned whether the pilings, even at the corps' stated depth, went down far enough to support the floodwalls and prevent storm surge from penetrating beneath the earthen levees and causing structural failure...
When the Texas construction firm AquaTerra Contracting began work on an Army Corps of Engineers hurricane protection project on New Orleans' West Bank, it encountered a serious problem: Its floodwalls wouldn't stand up straight in the mushy soil.
AquaTerra workers tried driving steel sheet piling down to the 55-foot depth the design required for the walls' foundation, company CEO Clay Zollars said. But the piling began to lean inward.
Zollars said the corps decided to nearly double the depth of the steel foundation to 105 feet. That didn't work either.
"Before we completed the wall, it began to lean and sink also," Zollars said. "The pilings were inadequate. The corps corrected that by installing some additional reinforcing steel in the concrete, but the wall still is leaning."
The top of one section of the 10-foot wall is more than a foot off the vertical, he said. AquaTerra is seeking $5 million it says the corps owes it for the extra work on the $11.1 million contract. Corps officials won't comment on the case because of the dispute.
The problems illustrate one of the basic obstacles to building reliable levees -- or any heavy structure -- in south Louisiana: It's a swamp.