Engineers to Test Flood Defenses In New Orleans
Questions Surround Failure During Katrina

By Peter Whoriskey
Washington Post Staff Writer
Sunday, August 12, 2007

NEW ORLEANS -- A $3 million experiment by the Army Corps of Engineers this week will simulate the conditions that caused critical levee failures during Hurricane Katrina, leading to disastrous flooding.

In the test, engineers will gradually pump water into a section of the London Avenue Canal, one of two canals whose flood walls toppled in the storm two years ago, allowing in most of the inundation in the main part of the city.

As the canal waters rise, engineers will monitor the amount of seepage beneath the flood wall and how much the structure tilts -- while promising nervous neighbors that the test will not cause another breach. The measurements will tell them how much rising water the canal wall can withstand.

"Some computations show the wall is going to fail at certain water levels; some show it won't," said Ray Martin, a geotechnical engineer consulting with the Corps on the project. "This experiment will let us know."

The fact that such an experiment is necessary two years after the storm reflects the continuing uncertainty as to exactly what caused the city's flood defenses to fail.

Despite three investigations, disputes continue over a host of key questions. What exactly was the primary cause behind the toppling of the canal walls? Would deeper wall supports -- which, to save money, were built shorter than originally proposed -- have held the walls upright? Did earthen levees fail mainly because surging waters overtopped them, or did they crumble first because of flimsy materials? Did a major man-made shipping channel known as the Mississippi River Gulf Outlet allow the storm surge to slam the city?

Such questions must be resolved to ensure that the next set of flood defenses works as hoped, some experts say.

Equally as important -- and, perhaps more important to the thousands who are suing the Corps -- is the question of whether government agencies and contractors who built the levees and flood walls are guilty of negligence or wrongdoing.

"The bottom line is that this city was destroyed, and the public doesn't yet have an undisputed explanation," said Sandy Rosenthal, director of Levees.org, a local advocacy group. "There are a lot of questions that have yet to be answered."

Levees.org has been agitating for improved flood defenses and urging politicians to establish an "8/29 commission," a congressional body modeled after the Sept. 11 commission.

"There have been numerous studies about Katrina, without any clear direction of how to prevent a flood-control-system failure in the future," said Sen. Mary Landrieu (D-La.), who has embraced the proposal and sought to introduce it into legislation.

There have been three major engineering investigations into the disaster. The most ambitious, a $25 million effort, was sponsored by the Army Corps of Engineers and reviewed by the American Society of Civil Engineers. Another study was commissioned by the state of Louisiana. Still another was conducted by a team from the University of California at Berkeley and partially sponsored by the National Science Foundation. The reports generally agree that the catastrophe was, at least in part, an engineering failure as well as a natural disaster that overwhelmed the city.

But there are differences on significant issues and, as a National Research Council panel noted, those differences could affect how the city's new flood defenses are designed.

In its most recent review of the Army Corps' Katrina report, the Research Council panel noted the differing views of the "primary failure mechanism[s]" in the canal walls and warned that "the proposal of a single failure mechanism could lead future designers to focus on narrowly drawn conclusions, leading to neglect of other, equally plausible failure modes."

Robert G. Bea, one of the leaders of the Berkeley team of investigators, has called for an 8/29 commission "to truly understand why these failures developed" because "the Corps is still not designing things safely enough."

But Ed Link of the University of Maryland, who directed the Corps-sponsored report, said that although "there's lots more to learn and lots more analysis to be done, I don't see a lot of benefit in rehashing what's already being done. Fundamentally, there's a lot of agreement" about what happened in Katrina.

The canal walls that are the subject of the upcoming test, and ones like them, are relatively simple structures: concrete supported by steel sheet pilings driven deep into the soil.

The tricky element of their construction is the generally weak soils into which the walls and their supports are set -- part marsh, part clay, part sand. Much of the uncertainty regarding the walls' strength has to do with the varying soils.

"This is the Mississippi Delta, built up by hundreds upon thousands of years of sediments and the like being deposited," said Col. Jeff Bedey of the Army Corps, who is overseeing the canal experiment. "It's not simple."

Bedey noted that the canal walls are less critical to the city's protection than before because they are now a second line of defense. New floodgates are supposed to block a storm surge from entering the canals.

The strength of the canal walls remains important, however, because the canals will still be used to pump floodwater out of the city into Lake Pontchartrain. The Corps currently estimates that the canals can safely hold water to a level of four feet. Corps engineers are hoping, however, that the walls can sustain more than that so more pumping may be done.

Last week in the Gentilly neighborhood, as residents still rebuilding their homes watched construction workers section off a portion of the canal for the test, many alternately wondered and worried over whether such certainty is achievable.

"I worry that there's even a need for the test," said Virginia Bouvier, 42, a nutrition counselor who is fixing her home beside the canal. "We should have known about these walls before Katrina."