New Orleans Sinking Faster Than Thought
May 31 8:02 PM US/Eastern
By SETH BORENSTEIN
AP Science Writer

WASHINGTON

Everyone has known New Orleans is a sinking city. Now new research
suggests parts of the city are sinking even faster than many
scientists imagined _ more than an inch a year.

That may explain some of the levee failures during Hurricane Katrina
and it raises more worries about the future.

New Orleans Sinking Faster Than Thought
May 31 8:02 PM US/Eastern
By SETH BORENSTEIN
AP Science Writer

WASHINGTON

Everyone has known New Orleans is a sinking city. Now new research
suggests parts of the city are sinking even faster than many
scientists imagined _ more than an inch a year.

That may explain some of the levee failures during Hurricane Katrina
and it raises more worries about the future.

The research, reported in the journal Nature, is based on new
satellite radar data for the three years before Katrina struck in The
data show that some areas are sinking four or five times faster than
the rest of the city. And that, experts say, can be deadly.

"My concern is the very low-lying areas," said lead author Tim Dixon,
a University of Miami geophysicist. "I think those areas are death
traps. I don't think those areas should be rebuilt."

The blame for this phenomenon, called subsidence, includes
overdevelopment, drainage and natural seismic shifts.

For years, scientists figured the city on average was sinking about
one-fifth of an inch a year based on 100 measurements of the region,
Dixon said. The new data from 150,000 measurements taken from space
finds that about 10 percent to 20 percent of the region had yearly
subsidence in the inch-a-year range, he said.

As the ground in those areas sinks, protection from levees also falls,
scientists and engineers said.

For example, the Mississippi River Gulf Outlet, built more than three
decades ago, has sunk by more than 3 feet since its construction,
Dixon said, explaining why water poured over the levee and part of it
failed.

"The people in St. Bernard got wiped out because the levee was too
low," said co-author Roy Dokka, director of the Louisiana Spatial
Center at Louisiana State University. "It's as simple as that."

The subsidence "is making the land more vulnerable; it's also screwed
up our ability to figure out where the land is," Dokka said. And it
means some evacuation roads, hospitals and shelters are further below
sea level than emergency planners thought.

So when government officials talk of rebuilding levees to pre-Katrina
levels, it may really still be several feet below what's needed, Dokka
and others say.

"Levees that are subsiding at a high rate are prone to failure," Dixon
said.

The federal government, especially the Army Corps of Engineers, hasn't
taken the dramatic sinking into account in rebuilding plans, said
University of Berkeley engineering professor Bob Bea, part of an
independent National Academy of Sciences-Berkeley team that analyzed
the levee failures during Katrina.

"You have to change how you provide short- and long-term protection,"
said Bea, a former engineer in New Orleans. He said plans for concrete
walls don't make sense because they sink and can't be easily added
onto. In California, engineers are experimenting with lighter weight,
reinforced foam-middle levee walls, he said.

Dixon and his co-author Dokka disagree on the major causes of New
Orleans' not-so-slow fall into the Gulf of Mexico.

Dixon blames overdevelopment and drainage of marshlands, saying "all
the problems are man-made; before people settled there in the 1700s,
this area was at sea level."

But Dokka said much of the sinking is due to natural seismic shifts
that have little to do with construction.

Dokka also thinks all is not completely lost. Smarter construction can
buy New Orleans some time.

"We've made the pact with the devil by moving down here," he said. "If
we do things right, we probably can get another 100-200-300 years out
of this area."

The Army Corps of Engineers is adding extra height to earthen levees
to compensate for sinking and is setting benchmark measurements of all
levees for regular monitoring of how much they sink, corps spokesman
Gene Pawlik said.

"It's something post-Katrina, we're much more focused on," Pawlik said
Wednesday. "It's certainly an engineering challenge."


--
"Science is the record of dead religions." -- Oscar Wilde

"There are no absolute certainties in this universe. A man must try to
whip order into a yelping pack of probabilities, and uniform success is
impossible." -- Jack Vance

"Civilization is the interval between Ice Ages." -- Will Durant.

"War is God's way of teaching Americans geography" -- Ambrose Bierce

"Progress is the increasing control of the environment by life.
--Will Durant

Joseph R. Darancette
daranc@NOSPAMverizon.net