A decade after Hurricane Katrina ravaged the Gulf Coast the land there is still sinking, sea levels are still rising and it's natural to ask the question: Is New Orleans doomed?
Probably not, say researchers from a wide variety of fields who have gathered this week in Baton Rouge for a symposium on the 10 years of research that have followed the 2005 disaster.
The researchers, primarily from Louisiana State University (LSU), have good reasons for their optimism, along with some hard-earned insights and advice that could help other coastal areas around the world facing the prospect of rising sea levels and sinking landscapes.
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"Louisiana will be the test case for how coastal areas all over the U.S. will deal with climate change and sea level rise," said Traci Birch, an environmental and land use planner with LSU's Coastal Sustainability Studio. "Landscapes aren't static" and so neither should our approach to living on them be.
First there is the matter of subsidence, or sinking, of the Mississippi Delta, in the heart of which is the city of New Orleans.
Since Katrina's assault on that city, scientists have improved their GPS monitoring and have a better picture of where and at what rates various parts of the delta are sinking. They also have a pretty good idea of how human and natural causes can affect the slowly dropping ground.
But try asking specifically what's causing a particular neighborhood to sink and how fast, and things get messy really fast.
"The discord among the researchers is pretty profound," said Joshua Kent, a geographer at LSU's Center for Geoinformatics (a.k.a. "C4G") in Baton Rouge. Kent has been involved in measuring subsidence and worked with the former director of the C4G, the late Roy Dokka, who proposed a connection between the sinking ground and what appear to be faults in southern Louisiana.
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The reason for the discord is that there are a lot of ways land can subside, Kent explained. The most basic is simply the settling of newer river sediments. As the grains of silt and sand pack together more tightly, they take up less space and the ground sinks. Helping this along is the pumping of water and oil from the ground.
Those fluids normally fill the spaces between soil particles and essentially keep the soil from packing too tightly.
Another source of subsidence is the weight of the sediments themselves. Mississippi River sediments have been piling up in the delta since the end of the last ice age, and their weight has caused the Earth's crust there to bow downward with the weight. This effect was shown by Dokka and his colleagues in 2007.
Then there is the matter of whether there are faults along which some of the land could be sliding into the Gulf. Dokka proposed that there was a sort of gigantic, slow-moving slumping of delta sediments into the Gulf. Adding to all these processes are the pumping of water and oil from the ground, which can cause the land to sink, as well as change how faults behave.
The problem is, figuring out exactly which process is at work in which area and to what degree is not easy. Different researchers have differing opinions, which is where the discord comes from.