The Llyn Ystradau Deviation Ffestiniog Railway

tanygrisiau reservoir seen deviation. original route of ffestiniog railway beneath waters in foreground

between 1965 , 1978, ffestiniog railway deviation, 2 ⁄2-mile (4 km) long diversionary route, constructed between dduallt , tanygrisiau in order avoid ffestiniog hydro-electric power station , reservoir (llyn ystradau). deviation (this conventional name such railway works) built volunteers. @ southern end spectacular dduallt spiral formation (unique on public railway in united kingdom). including bridge, constructed entirely volunteers, , gains initial height rise of 35 feet (10.7 m) in order (after further 1 mile (1.6 km) of new volunteer-built railway , new tunnel) clear flooded track bed north of former moelwyn tunnel, plugged near usually-submerged northern end. between dduallt , old tunnel, parts of old railway formation can seen below new route.

the new 310-yard (280 m) tunnel constructed between 1975 , 1977 3 cornish tin mining engineers small team of employees. had blasted through granite spur of moelwyn mountain. tunnel plant included stone crushing , grading equipment, produced track ballast , other aggregates spoil use on railway. before opened rail traffic, new tunnel had lined throughout length liquid cement reinforced steel mesh in process called shotcreting .

from 26 may 1975, , on 2 summers, pull , push service, officially called shuttle, powered diesel locomotive moel hebog carriage 110, operated dduallt gelliwiog, enable tourists experience deviation route before new moelwyn tunnel opened.

north of new tunnel long stretch of track along west bank of new reservoir. on 25 june 1977, full-length passenger trains first ran dduallt through new tunnel now-dismantled temporary terminus known llyn ystradau . station alongside tanygrisiau reservoir but, because on central electricity generating board land without public access, passengers not leave station other train.

the remaining section included specialised engineering work @ summit (668 feet (204 m)) new line passes on power station pipelines. followed 2 public road crossings automatic signalling, on fr s reverse or down gradient, rejoin old route in tanygrisiau station (640 feet (195 m)), reopened on 24 june 1978.

the largely volunteer group building deviation officially called civil engineering group, members popularly known (and still remembered) deviationists, completed enormous task on 13 years.