Saturday, October 12, 2002

Thomas Telford's great maybe

This is London Bridge . And for a bridge that has nursery rhymes about it, it is dazzlingly unimpressive. The area on the South Bank of the Thames around London Bridge is a fun place to walk however: it is full or narrow lanes, the remnants of docks, and markets that these days contain stalls that sell posh claret to rich people who live and walk nearby, nowadays, but it still has atmosphere. (These market stalls are under big signs saying "Turnips" and the like, however, so I imagine this was originally an agricultural market for produce that had just been unloaded from ships at nearby docks. I can imagine attempting to buy cucumbers there for ready money a century ago).

Of course, the nursery rhymes are about the original Medieval bridge (c 1600) of 19 piers, which did a substantial job of blocking the flow of the river. It was solid, but in danger of falling down in high waters. However, this bridge was the limit of navigability of the river, which is why it is the furthest upstream that you find the remnants of docks. When the medieval bridge was replaced with New London Bridge in 1831, the river could flow freely further upstream. This was both good and bad. Bad in the sense that bridges upstream were not designed for the tides, and many had to be replaced over the next few years. New London Bridge was not especially well designed, and was replaced with the present ugly structure in 1973.

The great "what if" in all this was that engineer Thomas Telford proposed a replacement for the original bridge in 1801, which would have been a single 200 metre cast iron span across the Thames. This would have been structurally sound and utterly beautiful, and would still easily do the job today. It was not built due to what seems to have been a mixture of conservatism and reluctance to spend money and effort on building the approaches. It's one of the great unbuilt projects of engineering history. (Sadly, I cannot find a picture).

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