Friday, April 16, 2021

a bridge too far

Sticking with the subject matter of the previous post for a minute: let's assume that the current rather tenuous claim of the Basseleg Viaduct to the title of "oldest still in use" lapses, by virtue of it being no longer economically sensible to keep the track and infrastructure maintained for the very occasional trains that run up to the quarry. Questions arise at this point: firstly, which viaduct takes over the title? And the answer to that is: I don't know. A very quick scan of the Wikipedia page linked in the last post suggests it might possibly be the Sankey Viaduct between Liverpool and Manchester, which already makes the vague but grandiose claim of being "the earliest major railway viaduct in the world".

The second question is: what happens to the structure then? And the answer is: it depends. If it's lucky it might get repurposed to carry a cycleway following the course of the old line, like the one at Garndiffaith I rode across many years ago. If it's unlucky enough to be in the way of the relentless march of progress then it may get blown up, like the Thirteen Arches Viaduct in central Bristol (which had to make way for the M32) or the much earlier demolition of the Pwll-y-Pant viaduct near Llanbradach, immortalised on film with some splendid Mr. Cholmondley-Warner commentary here and here

That's all well and good for the spectacular big-ticket items that span vast distances, but what of all the little over- and under-bridges that crop up along a stretch of disused railway? Well, the bridges that carried the railway itself over obstructions like roads can just be demolished, if that's what you want to do and the old line hasn't been repurposed in a way that means a through route needs to be kept. Over-bridges are more of a problem, since they tend to carry something you want to keep (again, most likely a road) over the course of the old railway. 

There has been a certain amount of hoo-hah on Rail Infrastructure Enthusiast Twitter in recent weeks at the announcement by The Man of an intention to divest himself of responsibility for the continuing upkeep of these structures by burying a good many of them under many tons of earth. The Man in this case is the body responsible for the monitoring and upkeep of all the remaining bits of old line, former trackway, bridges, tunnels etc. This is now known as the Historical Railways Estate, but formerly rejoiced in the rather more Eeyore-ish name of the Burdensome Estate. And you can see why, to be fair, as the job basically involves keeping an eye on some crumbly old stuff while someone figures out what to do with it, while also ensuring it doesn't get so crumbly that bits of it fall off and injure people.

It is certainly true that infilling structures like this precludes the possibility of the old trackbed being used for other things, like cycle routes, or even revived rail routes, and moreover that some of them have historical and/or aesthetic and/or architectural value in themselves, and moreover that it's not deranged to be suspicious of government's stated motives for doing stuff, nor to question their cost/benefit calculations. I suppose you do have to ask of the advocacy groups, though, as persuasive as the case they make seems: is there in fact any bridge or part of old pre-Beeching railway infrastructure that they would be prepared to let go? Is this (points at randomly-selected structure) particular farm track overbridge so valuable that it must be preserved in perpetuity? 

Is a compromise solution sometimes acceptable if it keeps the route open? And are the ambitious future plans of wild-eyed oil-bespattered train nerds to run their heritage railway route along an old trackbed really a good enough reason to commit government funds to infrastructure upkeep? 

I leave those questions with you. As blunt and aesthetically-unpleasing as burying stuff under kilotons of sand and rubble is, though, it has been applied as a solution to structural concerns with some much larger structures, including some that you would assume were far too large to bury, or at least not without the resulting pile of stuff having an impractically wide footprint (but where just blowing the whole thing up wasn't an option because of a desire to keep trains running across the top of the structure). But that didn't stop engineers in the early 20th century burying the impressive Kilton Viaduct in North Yorkshire under what was calculated to be 720,000 tons of mining spoil.

A couple of what appear to be even larger ones are available in Connecticut, USA: the Lyman Viaduct towered 137 feet above the valley it traversed before it was entombed inside a giant embankment (oddly, in the same year - 1913 - as the Kilton Viaduct), as was the nearby Rapallo Viaduct. Obviously before you dump all the dirt you have to provide a means for the waterway(s) to continue flowing, unless you want to create a reservoir as well; generally this was done with some massive concrete culverts. The ones under the Lyman Viaduct are big enough to walk through

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