BY HENRY PETROSKI
Orleans on higher ground could help
prevent future flood disasters.
THE PHENOMENON OF Grade inflation
has been widely discussed among
academics in recent years, but there
is another kind of grade raising
there that may have more relevance
after Hurricane Katrina's disastrous
flooding in New Orleans. There are
some historical precedents that
suggest grade raising as a possible
solution to the city's chronic vulnerability
due to its below-sea-level location.
In the mid-nineteenth century,
Chicago was prone to flooding, which
caused epidemics of cholera and
dysentery. To improve drainage,
Boston engineer Ellis Chesbrough
recommended that Chicago construct
a large-capacity sewer system, laying
the pipe directly on the existing
street grade and covering it with
6 to 10 feet of dirt. This raised
the grade of the city, of course,
and buildings had to be jacked-up
to conform to it.
Unfortunately, whatever the sewers
carried, including waste from Chicago's
large meat-packing industry, was
dumped directly into the Chicago
River, which carried it into Lake
Michigan, the source of the city's
water supply. To protect the lake,
the direction of the flow of the
river was reversed. This and the
grade raising were enormous undertakings
at the time, but they show what
can be done by a city with the will
to do it.
Galveston, Texas, was struck by
a huge storm surge in 1900, which
inundated the island city and killed
at least 6,000 people. An engineering
committee recommended building a
large sea wall and raising the grade
of the city to prevent such a disaster
in the future. To raise the city,
buildings and walkways were supported
on stilts while dredged-up sand
was pumped beneath them.
Moving large quantities of sand,
dirt, rocks or stones are familiar
construction tasks. It is how the
Egyptian pyramids were built. Even
today, structures large and small
begin with digging a foundation.
Similarly, large quantities of material
have to be moved in tunneling, canal
digging and other great projects,
such as Boston's Big Dig.
It would not take any great advances
in technology to raise the grade
of New Orleans. And given the recent
devastation caused by flooding,
this might be the time to do it.
Since the vast majority of the population
has been relocated and great numbers
of houses may have to be rebuilt,
a grade raising could proceed without
much additional disruption.
But what is technically possible
and logistically practical is not
necessarily the right thing to do
at a given time. The idea of raising
the grade of New Orleans may be
appealing to engineers, but it will
be politicians, civic leaders and
the citizens themselves who will
have the most to say about how the
city should be rebuilt.
Such extratechnical considerations
as the historical nature of the
city, its familiar grades and elevations
and even its cachet as a city that
parties below sea level are likely
to influence decision making at
least as much as technical assessments.
Just as there is no easy way to
resolve the debate over grade inflation
at colleges and universities, so
it would not be an easy matter to
get all interested parties in New
Orleans to agree on whether to raise
its street grade in low-lying areas.
Engineers know this, of course,
but it is still in their nature
to put all possible solutions on
Henry Petroski is the Aleksandar
S. Vesic Professor of Civil Engineering
and a professor of history at Duke
University. His latest book is "Pushing
the Limits: New Adventures in Engineering."