|Deviation | Dduallt|
Strictly speaking this page should be known as the Llyn Ystradau Deviation as there had been at least four previous deviations, the first at Old Moelwyn Tunnel, one at Garnedd Tunnel, one near Tanygrisiau and the deviation of the Dinas Branch.
In 1957 part of the line below Tanygrisiau was flooded by the CEGB (Electricity authorities) pumped storage scheme, having been compulsorily acquired in 1956. The last known use of the Old Moelwyn Tunnel was by a Moelwyn-hauled train on 12th January 1957. Full restoration of the Ffestiniog Railway to Blaenau Ffestiniog required the construction of a new route to avoid the new Tanygrisiau Hydro-Electric Power Station and lake (Llyn Ystradau) that the scheme had created.
In a Press Statement in March 1964, published in the FRS Spring Magazine, the FR announced its plans to build a deviation, detailing the background to their decision.
Other considered options
The first plan was to build the new route to the west of the reservoir (where it now goes), and a survey was undertaken by Mr A.R. Goodge in 1957. However, although the cheapest and easiest option, it revealed that there was insufficient room behind the power station.
A second survey was undertaken in 1958 by Livesey & Henderson (FR Consultant Engineers), the route running on the east side of the lake, passing through a (new) tunnel of 620 yards before running along the top of the dam (necessitating a new viaduct over the spillway). This second route would have cost twice that of the west-shore route.
The preferred option followed a third survey by Gerald Fox of an east-shore route. By the use of a spiral to raise the track level, the tunnel length could be cut to 75 yards, and therefore much cheaper. The statement said "The line is to be carried to a summit of 655 feet on the top of the high ridge between Moelwyn and Moel Ystradau, gaining some of the height by taking a spiral round a small hill to the east of Dduallt station, gradients being no steeper than the ruling Festiniog gradient of 1 in 80."
The concluding paragraph showed no sour grapes "It will provide a unique opportunity for the public to view the pumped storage scheme, the Power House and the Llyn Stwlan dam being seen to their best advantage across the waters of Llyn Ystradau. This exceptionally fine view of the first pumped storage scheme would not otherwise be possible for the public."
For an account of the various options considered by Gerald Fox and the logic for the ones the surveyors and the FR Company chose see FRM No 63. 
The adopted route
When work started on the Deviation it was along the lines of the published route, but the CEGB later acquiesced and agreed to let the line pass behind the power station on condition that the underground "bridges" needed to pass over the high pressure water pipes was undertaken professionally (McAlpine was to undertake this). The details of the West Side Route were published in the Winter 71/2 Festiniog Railway Magazine.  The resultant route, therefore, started with Fox's spiral, but instead of swinging to the east shore, kept to the west shore along a line similar to that of the first survey. The "exceptionally fine views" of the scheme were never to materialize, the line effectively passing through the power station's back yard.
The Deviation involved the building, almost entirely by volunteer labour over a 14 year period, 2½ miles of totally new railway involving embankments, cuttings, long hillside rock shelves, bridges and culverts, and starting with of a massive spiral track formation (the only one of its kind ever built in the British Isles) and a major feature in the landscape. The route had been surveyed and laid out (1961-64) by a team of volunteers led by Gerald Fox who was at that time engaged in the construction of London's Victoria Underground Line. Later Fox went to build modern tramways and rapid transit lines in the U.S.A.
Digging started on 2nd January 1965. Lots were drawn and the winner was Dr. M.J.T. Lewis to whom fell the honour of turning the first sod. Volunteer teams led by Michael Schumann (currently a member of the FR Trust). and others built the spiral and its bridge to gain sufficient extra height to take the railway above the level of the reservoir that was now flooding the railway and the old Moelwyn tunnel. Bunny Lewis, as resident site foreman, was the solitary employee for most of the time. Once the deviationists had reached and excavated the approach cutting to the new tunnel, work continued on the other side. These volunteer navvies came in their hundreds, men and women from all walks of life, a good number from the City of London. This deviation was a major undertaking involving several hundred volunteer days work per month for over fourteen years from 1965 to 1978 and its story was fully told in Ffestiniog Adventure by Brian Hollingsworth.
There was also the new tunnel, shorter but also, owing to modern regulations and a desire to increase the loading gauge, significantly wider and higher than the one it replaced. This had to be blasted through hard, abrasive syenite rock and after extensive planning, construction started in September 1975 and was carried out by three Cornish mining engineers, Robin Daniel, Bob Le Marchant and Pete Hughes, supported by generally less than 20 direct labour staff (12 engaged on a government subsidised employment scheme), plus volunteers, and with the aid of a substantial tourist board grant. The support work included the on-site crushing and grading of the excavated rock to make ballast in several sizes for use on the new railway. The new tunnel is 287 yards long and was opened on the 25th June 1977, with services running (from 8 July) to a temporary station called Llyn Ystradau at a spot previously known as Buarth Melyn.
The FR Deviation was completed along the shore of Llyn Ystradau (Tanygrisiau Reservoir) and over the pipelines behind the power station to reach the station at Tanygrisiau in 1978. The section behind the power station had to be done by contractors approved by the CEGB as previously noted, but the final task, Cwmorthin Bridge was Deviationist work. This officially completed the Deviation.
Reinstating the original sensitive route through the backyards of Tanygrisiau and Glanypwll to a new joint station with British Rail near the site of the FR's original Duffws station took a further 3 years. Mr Clough Williams-Ellis freely gave advice on landscaping matters. He had previously advised the old FR Co. in the 1930s when he landscaped Dduallt station at their request.
The Deviation was constructed starting at several sites as the work progressed. The early sites around the spiral were merely numbered, but the later ones were given names. These included (in order from Dduallt) Cei a'r Bont, Barn, Dingle, Midge, Rosary, Spooner's Hollow, Dragon, New Moon, Royal Oak, Gelliwiog, Bluebell, Two Trees, The Football Pitch, Tunnel South and Tunnel North. Most of these names are still in use, only Rosary, Royal Oak, Bluebell and The Football Pitch have been dropped.
Click on any location for more information
Many more pictures of the deviation works can be found at here.
The "Deviation Locator" panel at the top of this page, follows the above map sequentially from Campbell's Platform through to Tanygrisiau.