Scotland's secret tunnel under the Forth, 50 years old and forgotten

Scotland loves a bridge. And this year it is dedicating a festival to three historic spans over the Firth of Forth: one old, one new and a third that is well into middle-age.

The Forth Bridges Festival, part of the Year of Homecoming 2014, is occasioned by the 50th anniversary of the Forth Road bridge – a worthy milestone that falls just a week or so short of the independence referendum.

But this year sees the 50th anniversary of an equally remarkable passage from the Lothians to Fife that has been almost entirely forgotten. On 30 April 1964 another Forth crossing was opened up – 500 metres below the sea, when miners from the Kinneil colliery on the south side of the Forth broke through a tunnel to meet their co-workers from the Valleyfield colliery in Fife.

For the first time in history, and before the Forth Road bridge was officially opened, it was possible to walk directly from the Lothians to Fife over five pitch-black kilometres.

It was, to be sure, no pedestrian byway; it was intended as an economic lifeline allowing Fife coal to be extracted southwards for processing in the modern facilities of Kinneil, rather than at the decaying plant at Valleyfield.

This in turn was to extend the life of three seams: the Blairhall Main, the Lochgelly Splint and the Jersey, names which have since passed into obscurity along with others – the Lochgelly Parrot, the Duddie Davie – that have their toponymic roots in the mining cultures of the Forth.

Alistair Moore, now 82, was the engineering mastermind that oversaw the construction of what is now a lost passage. He was working as a mining surveyor in Fife when in 1962 he was told to report the Kinneil colliery in Bo'ness where he still lives. He cautioned:

I can't be sure of the date, I'll need to check.

Though he bears a quiet pride about the subsea crossing, it says something about the unshowy culture of mining that the tunnel's anniversary might have eluded even its own designer.

The tunnel now has no visible existence. Both collieries have been demolished along with the entire industry of which they were a small part. Traces of the passage exist only in a few maps, plans and photographs – and in a diminishing pool of memories.

There is now nothing left above ground to mark the crossing; urban explorers hoping for a subterranean playground will also be disappointed. The mine shafts were backfilled with hardcore and capped with concrete. Where the tunnel went through coal, the iron props will have since buckled under the weight of gravitational settlement. In the harder rock sections, the tunnel will likely be intact albeit completely inundated with groundwater.

So it's not much of a heritage site – at least not in a conventional sense. But it's still a technical marvel. The digging was difficult enough: 18 months of back-breaking work by two teams inching towards each other often through difficult and, at times, uncertain geology.

Moore's burdens were more cerebral – he had to get the calculations right. It was one thing to align the direction of the tunnels but the greater challenge was to get the level correct. He recalls:

There was always the question: 'will it…?'

The opportunities for error were vast. Before the era of laser theodolites and mobile computing, he depended on endless manual measurements that started respectively from the door of the Old Kirk at Bo'ness and Blair Castle, Culross – both known Ordinance Survey benchmarks.

Piano wire was lowered down the shafts; readings taken and retaken, again and again.

As the teams grew closer, Moore was told to cancel his annual holiday so he could spend more time underground. At last, the mine-driver's boring rod punched through the sandstone from the Kinneil side into the cavity of the Valleyfield pit.

Through this narrow hole, 9cm wide and 8 metres long, cordial 'hullos' were exchanged between the two teams. But the relief was suspended until further calculations could ascertain exactly how well the levels matched. At a depth of 500 metres, the difference turned out to be 5 cm; bang on, in other words.

Alistair Moore didn't hang around for the official opening. He took off on his holiday, leaving his managers to grin for the cameras at the formal breaking-through ritual a couple of days later at 10.33am on 30th April 1964.
'Tunnels link bring pitmen secure jobs' ran the headline in the Coal News. While a measure of new life was given to Valleyfield, it only lasted until 1978.

The National Coal Board had intended that the tunnel, together with the modern processing facilities, might give Kinneil another century of working life, but the geology didn't work out as the miners had hoped. Nor, for that matter, did the outcome of the 1979 general election – 25 years ago this weekend. Kinneil was finally closed amid acrimony in Christmas 1982.
This was the brief window of history – two decades, more or less – in which humans could walk, shore to shore, under the Forth. It is no less a marvel for being ephemeral, invisible and forgotten.

But it raises the issue of how we should mark the landscapes and legacies of coal that have been buried by both the political traumas of the miners strike and our contemporary contrition over climate change. What little is left – the monumental towers of Cockenzie Power Station being a case in point – will soon be gone.

What remains are the stories, like Alastair Moore's insistence that he is the only person ever to have walked to Fife and back under the sea. No-one, it should be clear, will be following in his footsteps any time soon.