NEW ORLEANS -- As investigators and residents have
picked through the battered New Orleans levee system's breaches,
churned-up soil and bent sheet pile in the months since Hurricane
Katrina struck, they have uncovered mounting evidence that human
error played a major role in the flood that devastated the city.
Floodwall breaches linked to design flaws inundated parts of the
city that otherwise would have stayed dry, turning neighborhoods
into deathtraps and causing massive damage. In other areas, poorly
engineered gaps and erosion of weak construction materials accelerated
and deepened flooding already under way, hampering rescue efforts
in the wake of the storm.
These problems turned an already deadly disaster into a wider man-made
catastrophe, and have made rebuilding and resettlement far tougher
and more expensive challenges.
That's the picture that emerges from investigations of the levee
system by teams sponsored by the Louisiana state government, the
American Society of Civil Engineers and the National Science Foundation,
as well as dozens of interviews with local residents, officials
Experts say the New Orleans flood of 2005 should join the space
shuttle explosions and the sinking of the Titanic on history's ill-fated
list of disasters attributable to human mistakes.
The evidence points to critical failures in design and construction,
as well as a lack of project oversight and responsibility that allowed
small problems to metastasize into fatal errors. Twisted lines of
authority led to cursory inspections, communications snafus and
even confusion over such basic information as wall dimensions.
Outside engineers, political leaders and many New Orleans residents
now question the judgments and even the once-unassailable competency
of the Army Corps of Engineers, which had final authority over the
system. The corps and some of the same firms involved in the original
design and construction are spearheading the current effort to repair
the system and already planning to build stronger protections.
Sen. David Vitter, R-La., who sits on two Senate committees investigating
the levee failures, says the U.S. system for building flood defenses
is broken. The corps, he said, should be overseen by outsiders who
can assure it will do the job right.
"We need a new model, a new structure, a new process to get
this done which has to include outside, independent review of the
corps by outside, independent engineering experts," he said.
The levee flaws also raise troubling questions about the integrity
of flood defenses elsewhere.
"Everybody who has a levee out the back door now has to look
out and wonder, is this going to fail? Was it designed right?"
said Steve Ellis, vice president of Taxpayers for Common Sense,
a Washington fiscal watchdog group critical of the corps' priorities.
Corps spokesman David Hewitt said the agency has multiple experts
and engineers from outside agencies, private firms and academia
to aid its investigation. "We are determined to find out exactly
what happened both in the technical engineering and the planning
and execution process so that we can prevent another occurrence,"
Hewitt said. "We are engaging the best minds and professional
expertise in this important effort."
Engineers say that most structures that fail do so not because they're
hit by overwhelming forces, but due to flaws that creep in unnoticed
during design, construction and upkeep. A paper published this month
by Robert Bea, an engineering professor at the University of California
at Berkeley who is studying the levee failures, concluded that 80
percent of 600 structural engineering failures he studied over the
past 17 years were due to "human, organizational and knowledge
Bea said everything he has seen about the New Orleans levee system
so far tells him it belongs in that category.
The levee system's overall design dates to the 1950s, when understanding
of hurricane risks and flood dynamics was primitive compared to
today. The system was never built to take a hit from the most powerful
hurricanes -- storms in Categories 4 or 5 on the Saffir-Simpson
scale. The levees were designed by congressional mandate to fend
off floodwater heights -- up to around 11 or 13 feet, depending
on location -- that Category 1, 2 and some Category 3 storms would
But the investigations show that it did not even live up to that
billing. When Katrina's storm surge rolled in from the Gulf of Mexico
before dawn Aug. 29, the huge dome of water washed over levees on
the southeast side of New Orleans and flowed into the heart of the
city via two waterways. Some flooding was inevitable in those areas,
as evidence shows the water flowed over the tops of the levees.
Later that morning, as surge water rose in Lake Pontchartrain, which
is linked to the Gulf, floodwalls along the 17th Street and London
Avenue canals breached, even though water was well below their tops.
Investigators say those breaches shouldn't have happened.
Investigators say the walls broke when floodwater, pushing through
the soft, porous earth under the steel sheet pile foundations, started
moving the soil. The flood inundated much of central New Orleans
over the course of the day and night.
Engineers say some systemic design problem caused the breaches --
not merely a localized fluke -- because walls gave way in two canals
and some appear to have been close to breaching at other points.
"There does appear to be a systemic failure along the drainage
canals because the failure occurred at two places simultaneously,"
said J. David Rogers, a geotechnical engineer at the University
of Missouri-Rolla who studies levee failures. "There's got
to be something big that's causing that. ... This is a very bad
failure mark. It's telling you they missed the mark by a country
mile on the design."
While it's always easy to second-guess after a disaster, outside
engineers say that the depth of the sheet pile foundation appears
too shallow. A survey by Team Louisiana, the state-sponsored forensics
group, found -- and the corps confirmed last week -- that the sheet
pile depth was about 10 feet below sea level in the breached areas
at both canals, much shallower than the 18.5 feet-below-sea-level
depth of the canals and seven feet shorter than the corps thought.
Modjeski & Masters, the firm that designed the 17th Street canal
wall, said last week it had initially recommended a 35-foot depth
for the piling on the 17th Street canal, then shortened it at the
corps' behest, but offered no documentation to back the claim.
It's still unclear exactly what went wrong, though engineers suggest
the soil's resiliency was overestimated.
New Orleans soil is swampy and mushy, with alternating layers of
peat, clay and sand. Over the length of a floodwall it varies wildly
in consistency and strength.
"Those are the kinds of subsurface conditions that lend themselves
to having weak pockets or stronger pockets, and Mother Nature will
always find the weak pockets," said Joseph Wartman, a Drexel
University geotechnical engineer studying the levee failures. "What
makes levee design and engineering so challenging is you can have
a system that's many, many miles long and you only need the weakest
150 feet to rupture for the whole system to fail."
Another related factor in the breaches -- one with national implications
-- is the relatively low safety factor used in construction of the
levee banks and floodwalls. A safety factor is a kind of cushion
that engineers include in a structure's design to ensure it can
withstand all the punishment it's designed to take, plus a little
Corps standards for levees and floodwalls date back decades, officials
say, and were originally intended to protect sparsely populated
rural areas, not cities and billions of dollars of valuable infrastructure.
The safety factor of 1.3 used in the designs is significantly lower
than those used in structures with similarly large-scale tasks of
protecting lives and property.
With data from soil borings spaced at more than 300-foot intervals
along the canals, engineers could develop only a fragmentary picture
of what is underground. They were supposed to account for that uncertainty.
That's typically done either by raising the safety factor or by
making conservative estimates of soil conditions.
Team Louisiana investigators said last week that based on new calculations,
they believe engineers working for contractors Eustis Engineering
and Modjeski & Masters miscalculated the depths of the 17th
Street canal walls. The team has not yet released detailed findings.
University of California engineers say the designers may not have
accounted for storm surge water's effects on the soil.
According to project and court documents, those designs were reviewed
and approved by corps engineers.
It's not clear yet if additional factors such as cost-cutting or
specific on-site construction problems contributed to the levee
breaches, but the failures can also be linked to a chain of political
and managerial decisions.
The corps originally proposed building floodgates at the mouth of
each canal to block surge waters. But local officials insisted on
building floodwalls because floodgates would have made it difficult
to pump water out during a storm. Engineers say the obvious -- though
expensive -- solution is to build pumping stations at the lakefront
rather than miles inland.
A 1980s-era dredging project in the 17th Street canal adjacent to
the breached area left the levee wall much narrower than it was
on the unbreached side. Investigators say that change probably contributed
to the ultimate failure of the wall.
Pittman Construction, the contractor that built the 17th Street
wall, ran into trouble driving sheet piles in 1993. When the concrete
tops to the walls were poured, documents show, the walls tipped
slightly. Though the corps attributed this to Pittman's methods,
not the site conditions, and a judge agreed, some engineers say
the difficulty they encountered was an early warning sign.
Meanwhile, state and local officials have admitted they generally
skipped the canal floodwalls in annual inspections of levees --
and the levees they did inspect were examined in a cursory fashion.
To the east, where water flowed over levees, assessing the system's
performance is a more complicated task. In general, engineers say
that once a levee is topped, its structural integrity cannot be
guaranteed. But many walls breached or eroded as well. That and
the large scope of the damage have alarmed investigators. Levees
protecting St. Bernard Parish and the Lower Ninth Ward -- areas
still mostly uninhabitable -- were all but washed away by the storm,
One source of the scouring and multiple breaches is actually a corps
policy, dictated by Congress. Corps officials say they are not allowed
to put rip-rap, concrete or other forms of scour protection on the
dry side of levees. Doing that anticipates flood levels higher than
the walls are designed for, which is beyond the corps' mandate for
Category 3 protection.
A report published last month by the American Society of Civil Engineers
and National Science Foundation teams identified other unanticipated
weaknesses in the levee system. Builders used weak, sandy soils
in the now-obliterated St. Bernard Parish hurricane levee, and that
likely contributed to its rapid destruction. In areas where two
different levee sections came together, investigators found many
awkwardly engineered transitions that allowed water through.
A much larger problem lies in the overall design of the levees along
the city's southeastern flank. Unlike areas fronting Lake Pontchartrain,
southeastern areas are more or less directly exposed to waters from
the Gulf, and hurricane floods are more likely to strike there and
rise higher when they do.
The levee system forms a V-shape where two waterways meet that acts
as a giant funnel, driving water heights even higher and channeling
storm surge directly into canals leading into the city.
Computer modelers have complained for years that the corps had underestimated
the risk to those areas, and former corps modeler Lee Butler estimated
the actual risk was double the corps estimate in a 2002 study done
for The Times-Picayune of New Orleans. The corps only recently announced
it would stop dredging the Mississippi River-Gulf Outlet, a controversial,
little-used navigation channel linked to the high storm surges.
It will takes months, and possibly years, to arrive at a detailed
assessment of what went wrong and assess responsibility, engineers
familiar with the situation say. Investigators must not only determine
why individual wall sections failed, they must trace the roots of
decisions, untangling overlapping responsibilities of the corps,
private contractors and local agencies. A federal inter-agency team
investigating the system won't make its report until next June.
A National Research Council team is only now being formed.
So far, the scope of the disaster and the human element central
to it have only begun to sink in among political leaders and agency
heads, including the corps, which is at the center of all the inquiries.
The corps has declined comment on the causes of the levee failures,
pending the outcome of its own studies.
People familiar with the agency say that the disaster means things
may never be the same.
"In the old days the corps used to get criticized for being
way too conservative in their designs," said Don Sweeney, a
corps economist for 22 years who left after exposing irregularities
in the agency's economic impact statements and now teaches at the
University of Missouri.
"They would design a structure with a safety factor of 4 or
5. They did have that reputation of building things with integrity
that were built to last. And if they said it was built to do something,
it would do it."
Dec. 11, 2005
(John McQuaid, Bob Marshall and Mark Schleifstein are staff writers
for The Times-Picayune of New Orleans. They can be contacted at
firstname.lastname@example.org, email@example.com and firstname.lastname@example.org.)