Saturday, 24 November 2012

An idea for surviving future storms: Raise coast

The San Antonio Express reports on a wizard wheeze to raise the coastline to combat "more frequent, intense storms and the kind of devastation recently seen with Superstorm Sandy" (alright, I know, I know).
People along the coast have a few options in an era of global warming expected to bring more frequent, intense storms and the kind of devastation recently seen with Superstorm Sandy: They can move back from the shore, elevate buildings or build levees to keep the floods at bay.
But a pair of scientists at Georgia Tech and Clemson suggest another alternative, although it sounds a bit like science fiction. Their research shows it is possible to raise the coastline itself.
Yes, it does sound "a bit like science fiction", as do all geo-engineering "wizard wheezes". This one's a real "cracker" - literally.
Leonid Germanovich of Georgia Tech and Lawrence Murdoch of Clemson, both environmental engineers, have worked out the math and are proposing a method of flood protection they call SIRGE, or solid injection for raising ground elevation.
The idea is relatively straightforward. They envision injecting sediment-laden slurry into hydraulic fractures in the ground. If repeated in adjacent areas and over a wide area, it works to push up the surface of the earth. They suggest a series of pumps and wells to force the material underground.
What could possibly go wrong?
After a 1900 hurricane devastated Galveston, Texas, killing an estimated 8,000 people, the city rebuilt after the ground level was raised as much as 17 feet. "It's been shown with the Galveston example, if you can increase elevations, that is your best bet in safeguarding areas against flood," Murdoch said.
While you can't elevate every building in a community, another approach might be to raise the level of the ground below it. A similar technique has been used on smaller scales.For example, when a tunnel is drilled under a city, a technique called compensation grouting is used above it, injecting material to keep the surface above stable so it doesn't sink. Perhaps the best-known example is the grouting done under Big Ben in London when a subway tunnel was built, Germanovich said.
Using SIRGE, the sediment would likely need to be projected 300 or more feet below the surface. The paper suggests that, in theory, at the upper end, it might be possible to raise the coast 10 meters, about 33 feet.
Ten metres? Along the entire coast, and over "a wide area"? Have they worked out just how much "sediment-laden slurry" would be needed, and how many "hydraulic fractures in the ground" would be required? The article does say they've "worked out the math", and presumably are not totally overawed by their figures.

"Fracking" involved in oil and gas extraction costs a lot of dollars, and for all the care taken, results in earth tremors and minor subsidence. If the pumping operations resulted in even a centimetre or so of difference in adjacent ground surface levels, water mains would fracture, roads and buildings and bridges would crack. How could local authorities possibly get permission from all land and building owners? What financial insurance would be needed? The cost of detailed geological surveys to identify possible problem "spots" would be immense.

First floor - future earthquakes, localised subsidence and endless litigation - Going up!

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