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UC Berkeley-led levee investigation team releases final report at public meeting in New Orleans

– A team of engineers conducting an independent investigation of the failure of New Orleans' levees during Hurricane Katrina issued a draft of its final report this week, concluding that the levees failed because of design and construction errors resulting from insufficient money and lack of appropriate oversight by federal, state and local agencies, in particular the U.S. Army Corps of Engineers.

Video simulation of levee breach
Levee breach video
This animation shows how the 17th Street Canal levee failed during Hurricane Katrina. Pushed by a storm surge, the rising water in the canal shoved the flood wall outward, cutting the levee in half. The water pressure was now sufficient to push the levee and floodwall horizontally, sliding along a weak layer of jelly-like clay. The inflowing water rapidly widened the breach. Credit: Trent Schindler/National Science Foundation
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The team, led by Raymond Seed, a University of California, Berkeley, professor of civil and environmental engineering, recommends in its May 22 report a broad reorganization of the Corps, which oversees most of the nation's dams, waterways and levees, and a restructuring of federal, state and local oversight of levees to prevent a similar disaster in the future.

The 700+-page report was funded with $230,000 from the National Science Foundation, another $50,000 from UC Berkeley's Center for Technology Research in the Interest of Society (CITRIS), and the donated time of 36 professional engineers and scientists from around the nation. The team studied every stretch of the levee system, either on the ground or from the air, conducted soil tests and ran computer simulations.

Its results differ from those of many previous reports, in particular that of the Corps' own Interagency Performance Evaluation Taskforce (IPET). According to Seed, the Corps always has maintained that the levees breached because they were overtopped by an unexpectedly high storm surge.

"These levees were not overtopped, they failed, primarily as a result of human error," Seed said. " The hurricane wasn't much bigger than the levees were designed for."

"One of our major findings is that the levee system protecting New Orleans was defective as a result of dysfunctional organizations," emphasized report coauthor Bob Bea, UC Berkeley professor of civil and environmental engineering. "The Corps needs to be modernized, and federal and state oversight of flood control restructured, because they can't build a safe levee with current processes."

Among the report's findings are that:

1. The 17th Street Canal levee was doomed to fail because of three weaknesses in the soil on which it was built, two of which should have been foreseen. As flood waters rose in the canal, they tipped the floodwall and flowed into the gap at its base, cutting the levee in two. Under the weight of the water, the outer half of the levee then slid horizontally along a weak layer of flocculated clay with a jelly-like consistency, perhaps laid down by a previous hurricane. Seed referred to this as a "peanut butter and jelly" failure.

Sticks mixed with the jelly-like clay probably concealed it during test borings done before the levee was built. But a close look at the borings should have revealed two other weakness: a layer of marshy material or peat, which would have failed had the jelly not failed first; and a deep layer of soft clay that also would have given way.

"The levee was going to fail anytime the water got up to eight or nine feet on the flood wall," Seed said. He noted that the IPET study found that the tipped floodwall failure could not have been foreseen, even though a full-scale test by the Corps in 1978 of a flood wall identical to that at the 17th Street canal concluded that such a failure was likely.

2. The flooding of New Orleans' Ninth Ward was a "failure in three acts," according to Seed. The levee along the Mississippi River Gulf Outlet was composed of highly erodable material, including shell sand, that was overtopped and washed away by 16- to 19-foot storm surges from Katrina. The surges continued across seven miles of treeless bayou to inundate the ward from the east.

Later, hurricane-pushed water surged up the Industrial Canal, overtopping the levees and flood walls in two spots. Failure, however, was not the result of overtopping, but rather, was due to seepage through the levee, which eventually led to blowouts that rapidly eroded the levee and undermined the flood wall. Flood waters poured in to meet the flooding coming from the east.

Tree growing on the levee
The southern breach of the London Avenue Canal was most likely caused by one or more trees growing on the levee. Tree roots provide an entry point for rising water, as illustrated in this drawing. (Illustration by Zina Deretsky/National Science Foundation)

This material "should never have been used in a levee," Seed said. "A lot of that material is still in the levee, and if it didn't fail during Katrina, it will fail next time."

3. The London Avenue South failure was not a result of overtopping, as claimed by the IPET report, but rather seepage through the levee that weakened it and led to a breach. The seepage probably was aided by one or more trees on the levee that should have been removed, the team concluded. A second breach resulted from unstable soils beneath the levee.

In its executive summary, the report says "a large number of engineering errors and poor judgements" contributed to the design failures of the London Avenue and 17th Street canals. "In addition, a number of these same problems appear to be somewhat pervasive," it says, "and call into question the integrity and reliability of other sections of the flood protection system that did not fail during this event."

The report also highlights the organizational problems that led to failure of the levees. The Corps did not adequately oversee the entire levee system, the report notes, and laid off many of its geotechnical engineers who could have effectively overseen its construction and maintenance. Instead, it says, levees were planned and built without adequate oversight.

"They took the engineering out of the Corps of Engineers," Bea said. "Much of this was a result of mandates by the White House, Congress and the state to be better, faster and cheaper, but you can't have all three at once without lowering the quality and reliability of the flood defense system."

According to the report, because the Corps allowed local levee districts to build and maintain portions of the levee system without proper oversight, these flood walls and levees were built to different standards that left weak links where the pieces met. "Many failures developed at interfaces or 'joints' in the New Orleans Flood Defense System," the report notes.

For example, the Corps had long fought to install floodgates to protect the three canals that cut through New Orleans, but it couldn't sway the local Levee Board or Water and Sewerage Board to agree. As a result, the long expanse of levees lining the canals had to be strengthened to withstand a hurricane.

"As a result of the decision not to install the floodgates, the three canals represented potentially vulnerable "daggers" pointed at the heart of the main metropolitan New Orleans protected basin," the report states. Without floodgates, the report says, the London Avenue canal suffered two breaches and the 17th Street Canal one breach as a result of Katrina, letting in 80 percent of the floodwaters that inundated downtown New Orleans.

The UC Berkeley-led team recommends changes from the White House to the local levee district that include a risk management council reporting directly to the President, a risk assessment office in Congress, and parallel offices at the state level. Seed said the team's main recommendation is not to replace the Corps, but to refocus it on engineering,

"The corps has lost its technical capability, and we want to build it back up," Seed said.

Links:

Draft final report of the UC Berkeley-led independent levee investigation team