You are here


The "levees" vs. "floodwalls" distinction

As I've been trying to point out, when the media refers to "levees" in some cases they're refering to floodwalls. Now, from the It-takes-a-DUmmie category comes this picture-heavy thread showing the difference and the distinction between them.

Soil heaves, structural problems caused flooding, not overtopping?

There's more on that possibility in "Pile of mud may be clue to levee failure". Also see the links here.

ACE backtracks on levee conclusions

From "Ground Shifted Beneath Levees":

...Within days of the flooding, federal engineers asserted that the flood-control system was simply never designed for such a powerful storm.
Now, with evidence suggesting Katrina's intensity fell within the range the levees should have handled, corps spokesmen are saying the organization wants to conduct a full-scale analysis of the design and construction of the levees.
The levee system was designed to withstand a Category 3 hurricane. Katrina's winds had weakened to 125 mph by the time it reached New Orleans, consistent with a Category 3 storm, according to meteorologist Chris Landsea of the National Hurricane Center in Miami.
Surges from the Gulf of Mexico and Lake Pontchartrain spilled over the walls at the 17th Street Canal, London Avenue Canal and the Inner Harbor Navigation Canal, say Army officials and experts at the New Orleans Sewerage and Water Board, which operates the city's pumping stations.

Sinking, bad design caused floodwall failure?

From "Ground Shifted Beneath Levees":

...Levees and storm walls may be as much as 2 feet lower than they were designed to be, both because elevation data were outdated when the levees were built and because the land has continued to sink, [some experts] say.
...Experts also are studying the Army Corps of Engineers' 1990s project that topped existing earthen levees with concrete walls to strengthen New Orleans' hurricane defenses. The approach was economical but may have left the walls weaker than intended. Three concrete walls failed after Katrina hit Aug. 29, to catastrophic result.
Engineering experts [including Ivor L. van Heerden, deputy director of the Louisiana State University Hurricane Center] say the designs failed to use the most modern technology, had almost no redundancy to compensate for minor problems during a storm, and were further undermined by weak clay soils in the New Orleans area...
...In other areas, including eastern New Orleans, overflow destroyed many miles of levees.
...[Louisiana State University engineering professor Roy K. Dokka] had warned in the last two years of an approaching disaster. "The most recent data shows that all of the previous subsidence work was faulty," he said.
On average, coastal Louisiana has been sinking half an inch annually, he said. But New Orleans East, which saw devastating flooding when levees overflowed, is sinking faster. Many levees are at least 6 inches lower than they were designed to be, and those in New Orleans East and badly damaged Plaquemines Parish are perhaps 2 feet lower.
...Geological and human forces are causing land elevations to drop, said Virginia R. Burkett of the U.S. Geological Survey's National Wetlands Research Center in Louisiana.
Over thousands of years, coastal subsidence was offset by Mississippi River sediment deposits, Burkett said. But dams and other water projects on tributaries have halved river sediment since 1950, and levees on the main river channel now carry the remaining sediment deep into the gulf rather than spreading it along the coast.
Offshore oil and gas extraction have accelerated subsidence in some areas, Burkett said. And swamp drainage, particularly under New Orleans, has caused organic soil matter to decay and compact, adding even more to the subsidence.
As levees have sunk, melting glaciers have lifted ocean levels globally, she added.
The problem is expected to worsen in the coming century...
...In 2001, the National Geodetic Survey warned Congress that elevation surveys for Louisiana were "obsolete, inaccurate and unable to ensure safety."
...Two years ago, the agency began recalibrating Louisiana elevation data using the Global Positioning System, Deputy Director David Zilkoski said. But Katrina struck before the project could make a difference.
In the year before Katrina, Zilkoski said, he went from town to town to warn local officials that elevation data in the region were inaccurate, including those that showed evacuation routes.
...Meanwhile, LSU's Van Heerden expressed concern that the 1990s work to place concrete walls atop levees might have contained fundamental design flaws.
The new walls were tied into existing steel sheeting inside the earthen levees. In some cases, the tops of the steel and the footings of the new concrete walls overlapped by just 2 feet. Steel reinforcement bars were welded or looped into the sheeting to tie the structures together, he said.
Van Heerden said he believed the walls on the 17th Street and London Avenue canals failed because they could not resist the water pressure, not because of overflow or foundational erosion.
He said the storm walls snapped where the steel sheeting met the concrete walls. He said it was generally bad practice to use old sheeting as a foundation.
Katrina would also have weakened the levees' clay soils, a further potential cause of failure.
Geotechnical engineering professor Dobroslav Znidarcic of the University of Colorado at Boulder said he was surprised concrete walls were used for the levees.
Few retaining walls are made of reinforced concrete anymore, he said. Instead, "mechanical stabilized earth" can provide greater strength and resistance to total failure. The system, developed in the late 1980s, sandwiches fabric grids between layers of soil.
"I am concerned their design is prone to catastrophic failure if anything goes wrong," he said. "It does not have a sufficient level of redundancy."

Floodwall evidence not that "incredibly damning"?

Regarding the NBC report discussed in "Incredibly damning" evidence found about flood walls, commenter GeoBandy says the following here:

"Out of tolerance" in this context means "not plumb" (or straight) and has absolutely nothing to do with the strength or adequacy of the levee... in fact the contractor admitted and agreed that the levee was adequate for its intended purpose...
...There's nothing in these documents that indicates anybody ever claimed the contractor (or the completed levee) didn't meet specs, resulting in a "weak" levee (or wall)...
But there's NOTHING in these documents that says ANY party ever said the levee as completed was "weak" or in any way inadequate or defective. It may have been defective in some way, I obviously don't know that. But these documents certainly don't lead to that conclusion.

Did a barge cause the Industrial Canal breach?

Here are some links. Please summarize:
thread: "The story from those that lived in the area is that the 17th street levee was breached because the construction company working on the old Hammond bridge left a big barge in the canal and the hurricane tossed it around and it busted out a section of the wall."
link "there appears to be a dangerous confusion of damage done to the Industrial Canal, which is the issue here, and damage done to the 17th Street Canal, which is a red herring" (links to this)
9/14 "Mystery Surrounds Levee Breaches"
link "One additional component which as been virtually ignored as the cause of much of the catastrophic flooding in New Orleans was not the topping of the levees by storm surge but the collapse of them by barges. According to a story in The New Orleans Times-Picayune: "A loose barge may have caused a large breach in the east side of the Industrial Canal floodwall. . . " Quoting Army Corps of Engineers project manager Al Naomi: "(The breach is) ultimately in my opinion what got (the Lower Ninth Ward and St. Bernard Parish) flooded." That same story also noted the potential that "small pontoon barges" in the 17th Street Canal "are still unaccounted for" and originally were moored alongside the Old Hammond Highway bridge over the canal, that ironically were in the process of being "hurricane-proofed" as Katrina struck August 29th. . . The Time-Picayune story closes with a quote questioning the Army Corp project manager: "Leonardo Ramirez, a construction worker and Metairie resident who lives on the Jefferson Parish side of the levee near the breached area, said that he thought he heard a barge hitting the levee early Monday, although he did not see it happen: "At quarter to six in the morning, we head a huge bang, and then we heard another. It was so loud. It scared us."
link to video at this site

"Incredibly damning" evidence found about flood walls

Lisa Myers of NBC reports in "New Orleans levee reported weak in 1990s":

NBC News has obtained what may be a key clue, hidden in long forgotten legal documents. They reveal that when the floodwall on the 17th Street Canal was built a decade ago, there were major construction problems - problems brought to the attention of the U.S. Army Corps of Engineers.
A 1998 ruling, by an administrative judge for the Corps' Board of Contract Appeals, shows that the contractor, Pittman Construction, told the Corps that the soil and the foundation for the walls were "not of sufficient strength, rigidity and stability" to build on.
"That's incredibly damning evidence," says van Heerden, "I mean, really, incredibly damning."
Pittman won the contract in 1993. There already was an earthen levee made of soil. Embedded in that was a thin metal wall called sheet piling. The contractor was hired to pour concrete on top of all that to form the flood wall.
But the 1998 documents - filed as part of a legal dispute over costs - indicate the contractor complained about "weakness" of the soil and "the lack of structural integrity of the existing sheet pile around which the concrete was poured." The ruling also referenced the "flimsiness" of the sheet piling.
NBC showed the findings to engineering experts.
"That type of issue about the strength of the soils, of course, bears directly on the performance of a floodwall," says LSU engineering professor Joe Suhayda.
"I think it is very significant," adds Robert G. Bea, a former Corps engineer and professor at the University of California, Berkeley, who is part of a National Science Foundation inquiry into the failure of flood controls. "It begins to explain some things that I couldn't explain based on the information that I've had."
The construction company said as a result of these problems the walls were shifting and "out of tolerance," meaning they did not meet some design specifications. Nevertheless, the Army Corps of Engineers accepted the work.
"It seems to me that the authorities really should have questioned whether these walls were safe," says van Heerden.
The judge, in her ruling, blamed the contractor for the construction errors and turned down Pittman's request for more funds.

Pittman is now out of business. The ACOE says it will investigate, and it's preserving documents...
They provide this 6.4Meg PDF file with the ruling.

Did barges cause the floodwall breaches?

There are several pictures of a barge that ran into a levee here. Note that those are on the Mississippi River side of things, and apparently no flooding was caused by those barges. Here's an aerial shot.
However, a commentor at a previous post of his site had this to say:

I've been speaking with some evacuees that have been transplanted in my community and they say that there is a RUMOUR, and I do mean RUMOUR, that Beau Brothers Construction had some barges near the levees that were not tied properly; and as a result they banged against the walls and weakened them during the storm. I don't know anything more about it than what I just posted.

LSU: Faulty design or construction of floodwalls to blame

Ivor van Heerden and others from LSU's Hurricane Center now say that the flooding of New Orleans was caused by either faulty design or fault construction of the floodwalls, rather than overtopping or other explanations: "Experts Say Faulty Levees Caused Much of Flooding". (Note that the WaPo's headline is confused: they aren't talking about the levees).
LSU has constructed computer modeling showing that the surges did not overtop the floodwalls:

...[Van Heerden] said the real scandal of Katrina is the "catastrophic structural failure" of barriers that should have handled the hurricane with relative ease.
"We are absolutely convinced that those floodwalls were never overtopped," said van Heerden, who also runs LSU's Center for the Study of Public Health Impacts of Hurricanes.
In an interview Tuesday, [Army Corps of Engineers] spokesman Paul Johnston said the agency still believes that storm surges overtopped the concrete floodwalls near the lake, then undermined the earthen levees on which they were perched, setting the stage for the breaches that emptied the lake into the city.
Johnston said the Corps intends to launch an investigation to make sure it is correct about that scenario. But he emphasized that Katrina was a Category 4 hurricane when it smashed into the Gulf Coast, whereas Congress authorized the Corps to protect New Orleans against a storm only up to Category 3. "The event exceeded the design," Johnston said.


On a tour Tuesday, researchers showed numerous indications that Katrina's surge was not as tall as the lakefront's protections. They showed a "debris line" that indicates the top height of Katrina's waves was at least four feet below the crest of Lake Pontchartrain's levees. They also pointed out how the breached floodwalls near the lake showed no signs of overtopping -- no splattering of mud, no drip lines and no erosion at their bases. They contended that the pattern of destruction behind the breaches was consistent with a localized "pressure burst," rather than widespread overtopping.
The center has also completed a computerized "hindcast" of Katrina, which has confirmed the evidence before their eyes. Their model indicates that most of the surge around the lake and its nearby canals was less than 11 feet above sea level, and that none of it should have been greater than 13 feet. The Army Corps's flood-protection system for New Orleans was designed to handle surges of more than 14 feet above sea level.
"This should not have been a big deal for these floodwalls," said oceanographer G. Paul Kemp, a hurricane expert who runs LSU's Natural Systems Modeling Laboratory. "It should have been a modest challenge. There's no way this should have exceeded the capacity."

"Did New Orleans Catastrophe Have to Happen?"

This is from Aug 31, and discusses the funding for New Orleans' levees. I believe some of it has been contradicted by later reports, such as the news of what the levee board spends its money on.


Subscribe to RSS - floodwalls