Monday, 23 April 2012

Garth Gwyn…a hill, a mine and a pipeline.

View towards Moel y Gest (1280x960)
This was supposed to be a relaxing stroll after several days of arduous slate tip and gorge yomping. We were going to follow an easy track to the top of Garth Gwyn, the hill that rises above Gelli-lydan, near Maentwrog. The expedition ended in yours truly staggering about exhausted. Why? Because we found a mine, of course!
Not a spectacular mine, rather one that needed the mine explorer's  "eye of faith" to see and understand, but a special place for all that. We'd struck up the track from the minor road through Gelli-lydan when Petra spotted what she thought might be an excavation above us. She'd previously noted a mine at the top of the ridge in Wilkinson's mining Gazetteer, called Pen-y-Foel. We ran up to the top of the ridge and found plenty of evidence of lead mining; a large spoil tip and traces of opencuts. A new wall had been built across the site, using the spoil from the tips. On some flat areas, small chips of quartz were scattered around, as if the rock had been smashed to get at the ore. The spoil contained traces of Galena and also some slag from a furnace.
 Garden Gate (991x1280)
Nearby on the ridge was a lovely old ruined farm house, although it's difficult to say whether this was connected to the workings. Yet, as we raked over the site, I became aware of a feeling that something was reading false. The tip was the wrong shape, somehow. It had a flat top, and was widely curved in plan form at the nose. Many of the large boulders in the tip bore marks of recent scraping by the tender caresses of a JCB's bucket. Then there was the lichen and moss, usually found on old mine tips. There wasn't any. We had to concede that this tip was modern, although there was no access road to speak of.
Moel Ddu from the Ridge (1280x960) The Tip (1280x960)
We trundled further down the hill on the supposed direction of the lode, to be surprised by two run-in adits. Again, the rock was similar. Perhaps these were adits that connected to the workings at the top of the hill. We'll never know. I am certain though, that for whatever reason, someone made a very serious effort to rake through the spoil on the hilltop, perhaps in the last twenty years.
Opencut (960x1280)
While at the top of the hill, we'd been intrigued by the course of the water pipe that carries the flow from Llyn Trawsfynydd to the Maentwrog Hydro station. It seemed to slither across the landscape like some monstrous python. We supposed that it wouldn't be far, so we set off to see it. Well, as the Sean Bean meme has it, one does not simply look at a section of pipeline. One follows it to the end. In this case, that involved another hill and some woodland bracken-bumping..
Pipeline (1280x960) Tree and Pipe (960x1280)
It's a strange thing, the pipeline. A victorian-looking, huge rivetted cigar tube supported by concrete plinths. We put our ears to it and could hear a strange vibration. All along it's length, dodgy bits of rivetting or rusty joins were highlighted in fluorescent paint. Somebody is keeping an eye on it. Then the pipe dived underneath the ground, below the summit of  Garth Gwyn. We portaged over the top, walking along a well-engineered incline that must have been used to build the pipeline. A concrete folly sat at the top. A sign proclaimed that it was the circular mouth of a surge shaft, whatever one of those is.
Tank on the Hill (1280x734)
This part is now designated a nature reserve, the Coed Camlyn reserve. It has a special atmosphere, as distant mountains surrounded the hilltop on all sides. Another walk down the coastwards side of the hill brought us to the other end of the pipeline, which emerged from a concrete valve house in two pipes, rather than one large one. There was no mistaking the sound of water speeding through these pipes. Even so, the sound of the birdlife all around was superb and the view down to the Dwyryd estuary and Moel-y-Gest were stunning, although the trees were too thick here to manage a decent shot.
We stumped back to the car just as the rain began to fall. It had been a super walk...if a little taxing on the knees.
Pipe Run 2 (884x1280)
Some Factoids:
The original Maentwrog Dam was commissioned in 1928, and was the largest of four dams which formed Lake Trawsfynydd to supply hydro electric generating sets at Maentwrog two miles to the North and some 183 m lower in elevation.
The reservoir is connected to the hydro station by two lengths of concrete lined tunnel with a length of low pressure steel pipeline between them. Twin high pressure pipelines lead from a valve house at the second tunnel portal down to the turbines. 
The Power Station below originally had an 18 megawatt output from three turbines but a fourth was added in 1934, increasing its output to 24 megawatts. It was "replanted" in 1991 further increasing capacity to 30 megawatts, and is currently operated by Magnox Limited Ltd.
The power station is painted in a hideous purple and cream colour scheme.
Dwr (1280x934)
Flange (960x1280)
Inspection Hatch (1280x991)
Surge Shaft (1280x1007)


Anonymous said...

That certainly is a monster pipe!

Dinorwig Power station also has a surge shaft, which exits at the surge pond above the quarry:,-4.090149&spn=0.002343,0.004812&sll=37.0625,-95.677068&sspn=50.244827,78.837891&oq=llanberis&t=h&fll=53.126435,-4.091211&fspn=0.002343,0.006856&z=18

I think that when the valves are opened to let water flow from the top reservoir down to the turbines, it is allowed to flow up the surge shaft in order to reduce the huge surge in pressure.

Iain Robinson said...

Thanks for the link, Graham. That is a monster at Dinorwig! We keep saying that we're going to go round on the guided tour, must do it this year. Went underground at Ben Cruachan power station a few years ago, that was some cavern, too. Thanks for the info about the surge shaft, it makes sense now.

Anonymous said...

We went on the tour last year and, even though touristified, guided tours are not really my thing, I really enjoyed seeing inside the place. No photography allowed though :-(

Iain Robinson said...

No photos allowed? Grrrr!

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