Posted on 02/19/2008 8:30:19 PM PST by NormsRevenge
PARIS (AFP) - The Mississippi Delta is sinking fast, posing a challenge for the rebuilding of coastal Louisiana after the devastation wrought in 2005 by Hurricane Katrina, a study released Sunday confirmed.
Across large swathes of southern Louisiana, average annual subsidence of five-to-10 millimetres (0.2 to 0.4 inches) have contributed to sea-level rise, shoreline erosion and wetland loss, they said.
The findings have implications for delta regions around the world -- home to tens of millions of people -- already threatened by rising sea levels caused by global warming, the researchers told AFP.
But the study, published in Nature, also shows for the first time that the sinking of the Mississippi Delta is, geologically speaking, only skin deep, limited to a layer of peaty sediment less than 100 meters (300 feet) thick.
This is good news, say the researchers, because it means that flood-control structures -- if anchored in the rock-hard stratum below this softer, organic-rich layer -- stand a better chance of remaining stable and not subsiding.
The new findings could also help determine the effect of coastal restoration projects, such as plans to divert water and sediment from the Mississippi River to depleted wetlands.
The prevailing theory up to now has been that subsidence occurs deeper beneath the surface in Earth's crust due to the crushing weight of accumulating sediment.
But the study "shows that the high rates of subsidence at the land surface can be quite easily explained by what happens in the shallow subsurface, say 50 to 100 meters (150 to 300 feet)," Torbjorn Tornqvist, director of the Coastal Centre of the US Department of Energy's National Institute for Climate Change Research, told AFP.
Some parts of New Orleans, he said, had sunk more than two meters in five or six decades, caused in large measure by artificial drainage.
Tornqvist, a professor at Tulane University in New Orleans, and colleagues punched more than 100 holes up to 15 meters (50 feet) deep in the Bayou Lafourche region and used radiocarbon-dating to examine the sediment cores.
They found that rates of subsidence over the last 1,000 years were at least five millimeters a year, and up to twice that in shallower sediment.
Tens of millions of people around the world live in low-lying deltas caught between the scissors of land subsidence -- caused by depleted water tables and dense human habitation -- and rising sea levels driven by climate change.
"Compaction is a problem in many of these cities, often enhanced by human activities such as groundwater extraction," said Tornqvist, citing Manila and Bangkok as good examples.
Oil and gas withdrawal can also be factors in subsidence, he added.
Compaction is the process that squeezes water out of sediment, leading to a decrease in volume and accelerated sinking of land surfaces.
Other major delta areas already feeling the impact of rising sea levels include Mumbai and Kolkata in India, as well as Shanghai and Dhaka. "Tokyo also has a major subsidence problem," he added.
This is good news, say the researchers, because it means that flood-control structures -- if anchored in the rock-hard stratum below this softer, organic-rich layer -- stand a better chance of remaining stable and not subsiding.
“New Orleans is sinkin’ man, and I don’t wanna swim...”
Don’t give da cholat’ mayuh any ideas. Let him sink or swim on his own.
Well there's their agenda...and it taints their credibility.
Could be blamed on global warming. Oh, I forgot,global warming causes water level to rise and not land to sink.
But apparently not a major one, because this does not come from the first 300 ft.
Just remove all those sediment check dams upstream and let the dirt wash down the river and the accretion rate will increase, providing at least an annual layer of mud to offset the subsidence. That is how the delta got there in the first place.
We keep hearing about this. Anybody aware of any evidence that it is actually happening anywhere?
Now, if they’d just let the Mississippi go down the Atchafalaya Basin like it’s been trying to do all these years...
Flood control structures ARE the problem in Louisiana. Rip out the levees and the control structures, and the river silt would replenish the lost land.
Blashpemer!
Quite a relief to know that NOLA and the whole delta area can’t sink more than 300 feet below sea level!!! /s
Long Beach California was sinking in the 1950’s due extraction of oil. They discovered they could stop the subsidence by pumping seawater in to replace the oil they extracted. End of Problem.
When one builds a city on crap one shouldn’t be surprised when oneself comes up to the chin in sh#t.
“Flood control structures ARE the problem in Louisiana. Rip out the levees and the control structures, and the river silt would replenish the lost land.”
true in the aggregate
but some sort of flood control/diversion measures are needed because even by letting the silt downriver more, major hurricane floods will crest above those restored levels
maybe lake ponchitrain should be kept, by some means, far below its natural level, if so many people are going to occupy land that will always have floods and hurricanes
Oh, I thought this story was going to be about the real Mississippi Delta (running from Vicksburg up to the lobby of the Peabody Hotel).
Oh brother.
What a load; this person is an idiot!
There are no rising sea levels. There is no man-made Global Warming. Environmentalists aren't scientists, but political campaigners for total government.
Disclaimer: Opinions posted on Free Republic are those of the individual posters and do not necessarily represent the opinion of Free Republic or its management. All materials posted herein are protected by copyright law and the exemption for fair use of copyrighted works.