(Photo 14 © Bill Blair)
To reach its junction with the South Wales Main Line, the Wye Valley Railway first had to penetrate a limestone outcrop beneath Wallhope Grove. This was achieved by means of the 1,188-yard Tidenham Tunnel which took trains from the steep-sided gorge at its northern end into green and pleasant farmland.
Constructed by Reed Bros of London, it consumed the lion's share of the route's £318,000 overall cost, taking two years to build at a rate of six feet per day and extending much further than its planned length of 715 yards. The south entrance is located immediately beyond the former site of Netherhope Halt and its adjacent overbridge. Curving immediately to the west, its straight central section is reached after around 250 yards. A lone ventilation shaft - the lower part of which is unlined - is encountered after a further ¼ mile, a little beyond the halfway point. Another curve then takes the track to the northern portal.
Opened on 1st November 1876, the tunnel was driven on a falling gradient to the north of 1:100. Much to the benefit of the line's financiers, the geology thereabouts was thought extremely stable and consequently the tunnel was built largely without a lining. Most of its central section remains so today. The discomfort experienced by passengers as they passed through was attributed to the rock floor, whilst this and its very tight gauge apparently caused excessive noise.
There are two areas where a partial free-standing lining was inserted - one immediately beyond the south portal and a second nearer the middle. These effectively act as masonry 'wallpaper' for the haunches and soffit, supported by shallow brick arches and stone pillars. It is not clear whether they were built during construction or installed later as a result of concerns over material falling into the four-foot. There are also a number of sections where a brick arch was later added - generally quite short and three rings thick.
During its later life, the condition of the tunnel deteriorated and it was the subject of some refurbishment in 1959, the year passenger services ended. The line through to Tintern Quarry, including the tunnel, was retained to serve limestone traffic. However its state was such that British Rail decided to mothball the route towards the end of 1981. Official closure came in 1986, although some reports quote 1988.
Today the tracks are still down but. unsurprisingly, rusted up. A couple of minor rock falls have occurred. Though generally dry, the tunnel features some remarkable localised mineral displays.August 2008 saw British Railways Board (Residuary), Tidenham's owners, erected palisade fences across both entrances. But access remains possible for the four species of bat found hibernating within it.
(Bill Blair's photo is used under this Creative Commons licence.)