Cwm Du (Pont Rhyd-y-cyff) Viaduct

Cwm Du (Pont Rhyd-y-cyff) Viaduct

In 1894, the Port Talbot Railway and Docks Company obtained Parliamentary approval to redevelop the town’s existing harbour and docks, construct a new dock with a deep water lock and piers, and equip them with the best handling facilities available at the time. The intention was to open up the extensive and practically untouched coalfields of the Llynvi, Garw and Dyffryn valleys by providing unrivalled shipment facilities, Port Talbot being much closer than the existing docks at Swansea, Barry or Cardiff.

To transport the coal for export, the second element of the scheme involved the laying of a meandering 17-mile railway linking Port Talbot with Pontyrhyll via Bryn, Maesteg and Lletty Brongu. Loaded trains faced a stiff climb on a ruling gradient of 1:75 as far as the line’s summit, thereafter enjoying a 1:40 descent. The tightest curve was of 10 chains radius.

Work on the railway – with an estimated price tag of £200,000 – got underway on 1st March 1895 and was fulfilled by Messrs S Pearson & Son, contractors based in Westminster. Scheduled for completion in March 1897, the single track actually opened for traffic five months late, on 31st August. The PTR&D extended its reach by opening two other connecting lines during 1898; its new docks were also inaugurated that year.

To the north-west of Lletty Brongu Station, the line crossed a stream, Cwm Du, by means of an imposing brick viaduct. Comprising seven 40-foot arches and an eighth of 20 feet within its eastern abutment, the deck reached a height of 80 feet above the water at the centre span. The red brick arches are supported by piers and abutments built of cement concrete faced with brindles. Still apparent half way up the piers are supports for the rakers that helped to brace the arches’ timber centring during construction.

Now owned by the Highways Agency (formerly British Railways Board (Residuary)), Cwm Du Viaduct is referred to by its structure number PTP/10m 20ch. In recent times, the Board carried out repairs to the parapet which resulted in the refuges – located on both sides above the piers – being removed. The brick corbelling which used to support them is now protected by covers, preventing water penetration and associated freeze/thaw action. The deck has also benefited from the installation of a waterproof membrane, with ballasting taking place thereafter.

The Port Talbot Railway effectively became a long branch line on New Year’s Eve 1951 with closure of the eastern section from Lletty Brongu to Pontyrhyll. From that date, the line over the viaduct was used mainly for wagon storage. The track was removed in June 1959 although it was not until 9th May 1960 that the section from Cwmdu was officially closed.

(John Finch’s photo, taken from Geograph, is used under this Creative Commons licence.)

October 2013