New Orleans 'risks extinction'
- From: alan@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxx (Alan)
- Date: Sun, 5 Feb 2006 01:43 +0000 (GMT Standard Time)
http://news.bbc.co.uk/1/hi/sci/tech/4673586.stm
By Helen Lambourne
Researcher, BBC Horizon
In the chaos that followed the worst natural disaster in American history, a
forensic investigation has been taking place to find out what went wrong and
why.
The BBC's Horizon programme has spoken to the scientists who are now confronting
the real possibility that New Orleans may be the first of many cities worldwide
to face extinction.
Modern day New Orleans was a city that defied the odds. Built on a
mosquito-infested swamp squashed between two vast bodies of water in what is
essentially a bowl, its very existence seemed proof of the triumph of
engineering over nature.
But on the 29 August 2005 New Orleans took a hit from Hurricane Katrina and
overnight was turned into a Venice from hell.
The delicate flood system in New Orleans, which so many relied on to protect
them was actually, year on year, adding to the risk of a catastrophe in the
city.
Coastal Geologist Shea Penland from the University of New Orleans knows every
inlet, every cove and every stretch of marsh that surrounds New Orleans.
He also knew that what had been thought of as wasteland for years were critical
to the survival of the city.
"The first line of defence isn't the levee in your backyard, the first line of
defence is that marsh in your backyard and we're learning what that means."
Coastal loss
The Mississippi River had been controlled over the years to stop the annual
floods with hundreds of miles of levees and dams. As a result sediments that
were naturally brought down to replenish the land, were cut off.
Gradually Louisiana started to lose its coast and today it has the highest rate
of coastal land loss in North America. An area the size of Wembley stadium is
lost to the sea every 20 minutes.
Professor Penland has no doubt about why the hurricane was so devastating: "What
we see, just played out there in the summer 2005 hurricane season was the
consequences of river control, living behind levees, living in a walled city
where we have to pump water up hill to get it out. How long can you live in a
bowl?
The loss of sediment to build up the land has led to another problem.
Much of the city is below sea level and continual pumping has caused the ground
to subside. Since 1878 the city has sunk by 4.6m (15ft), one of the highest
rates of subsidence in the entire United States.
Geologist, Professor Harry Roberts has spent the last 20 years watching his city
sink
"When you pump the water out of those kinds of soils they start to collapse and
more importantly the organic material oxidises and goes away so you've taken out
one component of the soil, and all that adds up to subsidence.
Precious wetlands
At the earliest opportunity after Katrina had passed, Shea Penland chartered a
seaplane to investigate the overnight loss to Louisiana's precious wetlands.
What he discovered sounded like the death knoll for the city. In just one night,
Louisiana had lost 3,885 hectares (15 sq miles) of wetlands, three quarters of
its annual loss in 24 hours.
Last Updated: Friday, 3 February 2006, 14:03 GMT
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New Orleans 'risks extinction'
By Helen Lambourne
Researcher, BBC Horizon
Residents brave the floodwaters in the Lower Ninth Ward, New Orleans. Image: AP
Venice from hell: New Orleans' delicate flood system was shattered
In the chaos that followed the worst natural disaster in American history, a
forensic investigation has been taking place to find out what went wrong and
why.
The BBC's Horizon programme has spoken to the scientists who are now confronting
the real possibility that New Orleans may be the first of many cities worldwide
to face extinction.
Modern day New Orleans was a city that defied the odds. Built on a
mosquito-infested swamp squashed between two vast bodies of water in what is
essentially a bowl, its very existence seemed proof of the triumph of
engineering over nature.
But on the 29 August 2005 New Orleans took a hit from Hurricane Katrina and
overnight was turned into a Venice from hell.
If you want New Orleans back you have to do some very fundamental things
Shea Penland, University of New Orleans
The delicate flood system in New Orleans, which so many relied on to protect
them was actually, year on year, adding to the risk of a catastrophe in the
city.
Coastal Geologist Shea Penland from the University of New Orleans knows every
inlet, every cove and every stretch of marsh that surrounds New Orleans.
He also knew that what had been thought of as wasteland for years were critical
to the survival of the city.
"The first line of defence isn't the levee in your backyard, the first line of
defence is that marsh in your backyard and we're learning what that means."
Coastal loss
The Mississippi River had been controlled over the years to stop the annual
floods with hundreds of miles of levees and dams. As a result sediments that
were naturally brought down to replenish the land, were cut off.
Gradually Louisiana started to lose its coast and today it has the highest rate
of coastal land loss in North America. An area the size of Wembley stadium is
lost to the sea every 20 minutes.
Helicopter drops sandbag during repair of levees. Image: AP
New Orleans highlighted the fragile balance of living behind levees
Professor Penland has no doubt about why the hurricane was so devastating: "What
we see, just played out there in the summer 2005 hurricane season was the
consequences of river control, living behind levees, living in a walled city
where we have to pump water up hill to get it out. How long can you live in a
bowl?
The loss of sediment to build up the land has led to another problem.
Much of the city is below sea level and continual pumping has caused the ground
to subside. Since 1878 the city has sunk by 4.6m (15ft), one of the highest
rates of subsidence in the entire United States.
Geologist, Professor Harry Roberts has spent the last 20 years watching his city
sink
"When you pump the water out of those kinds of soils they start to collapse and
more importantly the organic material oxidises and goes away so you've taken out
one component of the soil, and all that adds up to subsidence.
Precious wetlands
At the earliest opportunity after Katrina had passed, Shea Penland chartered a
seaplane to investigate the overnight loss to Louisiana's precious wetlands.
What he discovered sounded like the death knoll for the city. In just one night,
Louisiana had lost 3,885 hectares (15 sq miles) of wetlands, three quarters of
its annual loss in 24 hours.
New Orleans' wetlands are crucial to its future survival, say scientists
"If you want New Orleans back you have to do some very fundamental things", says
Professor Penland.
"You're going to have to bring the land back that protects the city from the
ravages of hurricanes. If we don't incorporate that then the city will be faced
with extinction.
Local urban planners believe that the survival of the city is dependent on
preserving its lowest lying areas, its devastated residential areas, as
parkland.
Areas like the Lower Ninth Ward built 2.4m (8ft) below sea-level - and where
hundreds of people died - may not be part of the city's future.
Instead they could be turned into green spaces, serving both as buffers against
future flood waters and as a reminder that nature sometimes should be left
alone.
Future predictions
Even if some residential areas are not rebuilt, the city will still need hugely
increased defences. In order to assess that task, engineers at Louisiana State
University have investigated why the floods were so devastating.
By collecting residents eye-witness testimonies and stopped clocks from their
flooded homes Professor Ivor Van Heerden and his team pieced together a timeline
of the levee breaches.
Their initial results suggest the levees were breached while the waters were
still rising. They found faulty design in the levees and weakness in the soils
underneath.
According to Van Heerden: "The system wasn't even capable of withstanding a
Category One hurricane".
To make New Orleans safe to withstand a Category Five hurricane, his proposal is
for a vast barrier system stretching from Mississippi all the way to Texas.
It could take 20 years to build but Van Heerden believes this is the only way to
guarantee the safety of the city's people.
Without adequate protection, subsiding nearly an inch per year, with devastated
wetlands and a disappearing coast the future looks dismal for New Orleans.
The future of this sinking city is further compounded by the effects of global
warming; rising sea-levels and an increased intensity of hurricanes.
"New Orleans' future is very hard to predict," says Van Heerden.
"The big unknown is global warming. If sea level rises come up by another metre
in the next 50 to 60 years, if we see far more of these major hurricanes we
could well reach a point where we see we need to abandon these cities like New
Orleans."
http://news.bbc.co.uk/1/hi/sci/tech/4673586.stm
Alan
http://www.veloceraptor.free-online.co.uk/enigma.html
http://veloceraptor.blogspot.com/
http://www.bushflash.com/pl_lo.html
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