Nola.com: Levees get less scrutiny than dams
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Levees get less scrutiny than dams
Critics note disparity in corps' standards
Tuesday, March 21, 2006
By Bob Marshall
Staff writer
As they near the end of their investigations into
the deadly failures of New Orleans' hurricane
protection system, some of the nation's top
engineering minds have come to one unshakable
conclusion: If the Army Corps of Engineers had
built the region's levees to the same standards it
uses for dams, the city may well have survived
Katrina without catastrophic flooding.
Representatives of the American Society of Civil
Engineers and the National Science Foundation said
Monday that some of the problems they think played
key roles in the disaster -- low engineering
safety standards, lack of rigorous peer review and
shoddy maintenance -- are simply not tolerated by
the corps when building dams, but are commonplace
in levee projects.
"If you looked at a major earthen dam being
designed during the same time frame as the 17th
Street Canal (floodwall) was being designed, there
would have been boards of consultants and rigorous
outside peer review that probably would have
detected and caught many problems that are coming
to light with the 17th Street project," said Larry
Roth, deputy executive director of the society.
"There is a National Dam Safety Act that sets out
specific requirements to make sure dams won't have
these problems, that they are safe for the people
who live around them. There is no similar
legislation for levees.
"We're hoping one of the good things that comes
out of Katrina is that the country finally
recognizes the fact that levees protect as much
human life and property as dams."
Roth made his comments during a meeting of the
National Research Council, an arm of the National
Academy of Sciences, which is providing scientific
peer review of work being done by the Interagency
Performance Evaluation Task Force, the
corps-sponsored panel investigating the failures.
An appearance by task force team leaders at a
meeting of the council in New Orleans provoked an
update of its work to date, which will be part of
a comprehensive report scheduled to be completed
June 1.
But the council also asked for updates from the
society of engineers, which was designated to
provide ongoing review of the task force, and the
National Science Foundation, which is conducting
an independent investigation of the failures.
While spokesmen for both organizations had high
praise for the task force effort overall, they
urged the council and the corps to address what
they considered a major underlying cause for the
disaster: the low priority given to levee safety.
'A very huge issue'
Ray Seed, a University of California-Berkeley
professor who is a leader of the science
foundation investigation, said this was "a very
huge issue."
"The corps actually has a very elegant set of
policies set up for dam review and they do a very
good job of it," Seed said. "They bring in an
outside panel of experts with great knowledge and
experience in specific areas of science and
engineering critical to building dams.
"They are independent of the corps and they do
rigorous review of everything. Dams also have
outside review panels meet every few years to
review the safety of the dam and the maintenance
efforts.
"We would like to see the same thing in place for
levees, because they protect just as many -- maybe
more -- human life and property as dams."
National Science Foundation and American Society
of Civil Engineers team members, as well as the
state's Team Louisiana investigators, have pointed
to information uncovered by investigators that
they said is evidence of sloppy engineering and
weak peer review. Seed and Roth said those have
included floodwall sheet-piling supports that were
not driven below the bottom of the 17th Street
Canal; soil investigations that were not thorough
enough for the complicated soils, resulting in
overly optimistic estimates of soil strengths;
lack of soil borings at the levee toes, which
caused the design teams to miss a weak layer of
soils that contributed to the breach on the 17th
Street Canal; poor communications between outside
engineering firms and the corps; and poor levee
maintenance that allowed encroachment by trees and
swimming pools onto the rights of way.
A lesser standard
Even the basic engineering safety standards
applied to levees are more lenient than those for
dams, they said.
"Why have a factor of safety less rigorous for
levees?" Roth asked.
The "factor of safety" is the standard technique
engineers must use to account for unforeseen
variables that might affect their designs, such as
defects in materials or uncertain soil conditions.
That results in "over-engineering" or overbuilding
-- using components stronger than the physics of
the project call for, or including redundant
systems, just to be safe. The higher the factor of
safety, the less likely a design is to fail. For
example, a levee that uses a T-wall normally has a
higher factor of safety than an I-wall, which was
the design used in many of the areas that were
breached.
But because costs increase as the factor of safety
rises, the profession has established a scale of
appropriate factors of safety for different types
of structures, with the prime consideration being
the cost of failure -- in terms of dollars, and
lives. But while dams have a stringent factor of
safety, levees have had lower demands.
Traditionally, the factor of safety is 1.3 --
whether the levee is protecting a dairy farm or a
major city, such as New Orleans.
That difference, Seed and Roth agreed, points to a
systemic problem in the way the levees have been
built and maintained.
"It's very much like what was discovered in the
investigation of the space shuttle disasters,"
Seed said. "The system has to be changed to
prevent this from happening again.
"The problems the system created for New Orleans
can probably be found in every levee system in the
country," he said.
. . . . . . .
Bob Marshall can be reached at
rmar...@timespicayune.com or (504) 826-3539.