Wednesday, December 19, 2007

London's Beer Challenges

Sometimes the oddest things are connected - like beer and ground subsidence. According to Philip Ball in Life's Matrix: A Biography of Water, "London subsided by an average of two and a half to three inches between 1865 and 1931 as a result of the lowering of its water table. There is now a rumor, however, that at least some parts of London's water table are rising again because the big breweries, which consumed much of the water in the city's aquifers, have moved out of town (or out of business). Londoners are warned of an impending threat of flood rising from the deep because the capital no longer makes its own beer." I can't find anything to corroborate this, but the basic idea is plausible and a good example of connections between unlikely events.

In looking for something to back this up, I did find reviews of a report that said, among other things, that London is subsiding generally as the land mass of England responds to the unloading of the last ice sheet, with the north tipping up and the south tipping down. The weight changes as tides come and go up the Thames are dramatic enough to change the level of the ground by 10 mm twice a day, and the seasons load the ground differently, so that measuring true subsidence is tough. All this is relevant because the Thames is rising over time, about 1 mm annually, leading to increasing flooding. So even if the lack of local beer doesn't flood London from below, the Thames is likely to take care of the job.

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