Gyfylchi tunnel (Tonmawr) at The Black Mountains

Background and History

This 1124 yard tunnel seems to be one of many names; Gyfylchi is the most common, and occurs on OS maps. Tonmawr is the next most popular name, but I have also seen the the tunnel referred to as the Gyfalcha, and Gyfwlchau tunnel, and in the ‘Railway Engineer’ report of 1902 (following an accident in the tunnel) as the Gyluchy tunnel. It was the only tunnel on the South Wales Mineral Railway, a mere 12mile stretch of track that ran down from Glyncorrwg, via Tonmawr to the docks at Briton Ferry, in Neath. Work on the line started in 1853, and it was opened in sections between 1861 and 1863. When opened it was a broad 7′ 1/2″ gauge, but in 1872 the line was adjusted to standard gauge. This allowed junctions with the Great Western Railway, just north of the Cymmer tunnel, and the Port Talbot Railway at Tonmawr junction. There is evidence on the 1:25,000 scale OS map, that just south of the tunnel there was a junction built that saw a track running back down the valley side to connect with the Rhondda and Swansea bay Railway at Pontrhydyfen.

The 5 locomotives served the mines, collieries and quarries around Glyncorrwg and the mines in the Pelenna valley, taking the minerals (for example, limestone, dolomite, coal) to the docks at Briton Ferry. Although there was never a passenger service on the line, people from the isolated Glyncorrwg valley commonly were allowed to ride in the empty wagon or in the brake carts for free, to visit Neath in order to trade. The line was single track apart from 2 passing places, one at Cymmer and one at Tonmawr; it was standard practice fro trains to pass at Cymmer unless special instructions had been given. On August 16th 1902 the train leaving Glyncorrwg intended to pass at Tonmawr, but without the proper authorisation. Due to this, the train leaving Briton Ferry was expecting to pass at Cymmer as normal and the two trains collided head on inside the tunnel, both drivers suffering injuries and many of the villagers who were riding in the wagons were injured, 2 of them fatally. Following the report on this incident, a telegraph system was set up between Tonmawr and Cymmer to stop a repeat occurrence.

In 1910 the section of track between Tonmawr and Briton ferry was dismantled, and all traffic went now to Port Talbot. In 1925 the Glyncorrwg colliery closed, although the line still served quarries in other parts of the valley. In 1947 the Tonmawr end of the tunnel collapsed and it was never reopened.

I’d like to acknowledge IR Society, whos website provided most of this information

The tunnel today

The southern portal, in the Afan valley, is tucked away on the hillside and is gradually being consumed by ivy. People seem very determined to get in to the tunnel; although the door was welded shut, the wall next to it has been knocked in instead, and there are cutting discs on the floor outside. Inside the tunnel, the immediate bend to the right means that the portal is not visible from early on, but after this the tunnel is straight. There is a definite feeling of sadness in this tunnel, it seems to be very still and tense inside, perhaps due to its turbulent past and sudden closure; there is also evidence of heavy solvent abuse here (aerosols, glue, plastic bags) which is a shame to see.

The trackbed is still very corrugated, showing where the sleepers once lay, and walking down the tunnel involves striding along the crests of these ridges. The walls are cut rock for the most part, with brickwork here and there, and the roof is a wavy strip of dark brick resembling a cobbled street. Although there was little water ingress visible, after around 500yards the tunnel becomes flooded, the depth of water gradually increasing. I gave up once it covered my walking boots, and I’m glad I didn’t both going any further as report suggest the water gets steadily deeper. A report of a visit in the 1970’s estimated the water depth at the far end to be around 12ft, but also that it started to flood after only 300yds from the southern portal; we got much further in than that so I would assume the water level has dropped somewhat since then. When standing at the start of the flood, you can hear water pouring in somewhere in the distance.

The northern poratl has been totally obliterated. We found the causeway where the track crosses the river Pelenna, just north of the tunnel, and the swampy cutting (now thick with trees), but this cutting ends in a muddy, uneven hillside. The only evidence of the railway up here is a small section of stone wall at the start of the cutting.