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Pont Briwet (1867), site of
River Dwyryd, near Penrhyndeudraeth, Gwynedd, north Wales, UK
Pont Briwet (1867), site of
associated engineer
Benjamin Piercy
Henry Conybeare
George Owen
date  1865 - 1867
UK era  Victorian  |  category  Railway Viaduct  |  reference  SH618383
photo   John Lucas and licensed for reuse under this Creative Commons Licence
The original Pont Briwet, also called Penrhyndeudraeth Bridge, was a Grade II listed timber rail and road bridge that crossed the River Dwyryd on the west coast of Wales north of Harlech. It was constructed as part of the Aberystwyth & Welsh Coast Railway, now part of the Cambrian Coast Railway network. Permission to demolish was granted in February 2012. A replacement bridge on the same spot opened to rail traffic in September 2014, and to road traffic in 2015.
The various sections of the Aberystwyth & Welsh Coast Railway were authorised in 1861-2, with Benjamin Piercy (1827-88) as chief engineer. The Cambrian Lines skirt the northern end of Cardigan Bay connecting Aberystwyth, Tywyn, Barmouth, Harlech, Porthmadog, Criccieth and Pwllheli. Pont Briwet is lies between Harlech and Porthmadog.
Henry Conybeare (1823-84) succeeded Piercy before construction commenced, after Piercy found himself on the wrong side of a boardroom struggle, and his role changed to consultant. Piercy's deputy, George Owen (c.1827-1901), became chief engineer after Conybeare was dismissed in November 1866. It's unclear which of them is directly responsible for Pont Briwet. The railway's contractor, Thomas Savin (1826-89), was declared bankrupt in February 1866 and the bridge opened the following year.
Timber pile viaducts are a notable feature of the Welsh coastal railways. They were once common all around the country but most have long been replaced. The best known on the Cambrian Coast network is Barmouth Viaduct (completed in October 1867 under Owen's stewardship), which combines a timber structure with trussed spans, one of which opens.
The original Pont Briwet accommodated a single rail track and a single lane of metalled toll road, later controlled by traffic lights at each end. It had 22 equal spans of 5.8m and its substantial battered abutments of rough slate blocks were more than 40m long.
The piers were composed of four or five timber piles, each roughly 350mm square in section, connected by crosshead timbers and braced with diagonals, making a series of frames. These supported 7.6m cross beams with substantial longitudinal beams above to carry the carriageways. The beams under the rail tracks were larger than those under the roadway. The bridge was decked with timber planks. Iron was used for bolts and bracing bars.
In 1932, the bridge was rebuilt extensively and half the piles replaced. Altogether, more than 183 tonnes of timber were removed and replaced piles, cross members and bracing using new creosoted pitch pine. Its overall width was then 8.5m.
By 2010, a speed limit of 30kph (19mph) had been imposed on trains crossing the bridge, and the single-lane roadway and limited access for other types of transport were causing difficulties. Vehicular traffic was restricted to 2 tonnes in weight, and pedestrians could not use the bridge. In July 2010, the Welsh Assembly announced a project to replace it by 2013. There were plans to retain the old structure for pedestrian use but a demolition permit was granted in February 2012.
In April 2013, work began on a new 18m wide structure for completion in the summer of 2015. It carries the single-track railway, plus a two-lane public highway and a 2.5m cycleway/footpath. The roadway's speed limit is raised to 65kph (40mph) and toll charges abolished.
Rail services over the viaduct were halted in November 2013, while the rail section of the new bridge was constructed to the west. Train services recommenced on 1st September 2014. The original structure was demolished by the end of November 2014 following diversion of the water main and telecommunications cables.
Access to road traffic closed in January 2014, resulting in a 13km detour for drivers. The roadway section of the new bridge mirrors the design of the rail section and is constructed on the line of the original bridge. Both are composed of prestressed concrete beams supported on reinforced concrete crossheads and large diameter concrete river piers, with abutments founded on widened and raised approach embankments.
The rail and road bridge superstructures are separate but the supporting crossheads are connected across the rows of piers of both bridges.
Contractor (2013-15): Hochtief (UK) Construction
Research: JJ, SKJ, ECPK
"The Cambrian Railways: A New History" by Peter Johnson, Oxford Publishing Company, Hersham, Surrey, 2013
"Timber Viaducts: Loughor and Pont Brewit" by Stephen Jones, in ICE Wales Cymru Newsletter, November 2013
"Design & Access Statement in Support of an Application for Listed Building Consent for Demolition at Pont Briwet, Penrhyndeudraeth" prepared for Network Rail, Gwynedd Council, TraCC for submission to the Snowdonia National Park Authority, undated
reference sources   BDCE2

Pont Briwet (1867), site of