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Part 2: Tidenham Tunnel

(the GWR's 20th-longest tunnel)

 Name  Tidenham
 Opened  1876
 Closed  1981
 Length  1,180 yards
 Height  5.1 metres
 Width  4.6 metres
 No. of tracks  1 (still in place)
 No. of access shafts  1 (still in place)
 Southern portal  Located just north of Netherhope Lane and ¼ mile west of Tidenham (grid reference ST550963). Fenced off.
 Ventilation shaft  Located across a field south of the Offa's Dyke Path (grid reference ST549969). Surrounded by a high stone wall.
 Northern portal  Located just north of Offa's Dyke and 3 miles south of Tintern (grid reference ST547973). Fenced off.

Left: Prior to the installation of a fence, the south portal of the tunnel is seen in 2005.

Tidenham Tunnel was constructed to carry the Wye Valley Railway through a mass of limestone rock, allowing the railway to pass out of the Wye Valley before it enters a deep, tightly-curved gorge on the approaches to Chepstow. The line emerges into arable country and can head down to the mainline on a much straighter and cheaper route than would be possible if the tunnel had not been bored and the railway had followed the Wye down to Chepstow instead. One ventilation shaft was provided, slightly to the north of halfway through the tunnel. A distinct curve at each portal ensures that the bulk of the bore is in pitch blackness as it passes through the hill. Much of it is unlined, as the limestone was deemed to be solid enough to not require the additional expense of lining.

Following completion of the tunnel it opened to traffic with the line in 1876. For such a long tunnel on a railway with such a traumatic history it had a comparatively quiet time. The WVR was saved the expense and inconvenience of constant rock falls which disrupted the operations of other railways and the dry bore did not cause trouble because trains stalled inside or it flooded. By its very nature as a steeply-graded single track tunnel it was a confined space and unpleasant to work through with a steam-powered train but it didn't pick up the sort of reputation which its slightly shorter neighbour, Haie Hill Tunnel (about 30 miles further up the Severn) managed to obtain.

British Railways were left with the tunnel after nationalisation. The line cost a great deal to maintain and BR was keen to lose it in order to save money. The railway closed to passengers in 1959 but Tidenham Tunnel still had a fairly secure future with limestone traffic from Tintern Quarry. This could probably have gone on forever if it were not for the deteriorating state of the tunnel. The last serious attempt at maintaining it was probably carried out prior to 1959 (it is entirely possible that an overhaul of the tunnel was due when the line closed). Closing it to passengers had allowed less money to be spent on it; in December 1981 the maintenance requirement was reduced to virtually nothing by taking the line out of use. By this stage it was the 13th-longest active tunnel on the former Great Western network; this status now passed to Ardley on the line between Banbury, Bicester, High Wycombe and London.

The empty, two-thirds of a mile long hole now lies silent under Dennel Hill. A pile of rocks on the floor just south of the ventilation shaft suggest a simple reason for closure. Brambles, tree growth and rubbish made both portals increasingly inaccessible over the following 27 years, although neither was fenced off until August 2008. This necessitated clearing the portals; that at the south end used to be virtually inaccessible from Netherhope Lane. The old track remains in remarkably good condition - spared the pains of the Great Outdoors, the steel rails lead into the tunnel with only light oxidisation and the creosote in which they were intensively soaked seems to have helped the sleepers survive the following 50-odd years extreamly well. The tunnel is now inhabited by a population of bats.

The northern end of the tunnel, looking over the fence on a 15-second exposure. The slight green sheen is caused by the vegetation surrounding the approach to the portal.

The ventilation shaft. It sits on private land in a small patch of woodland, separated from the Offa's Dyke long-distance path by a cow field.

The southern portal is only about ten yards north of Netherhope Lane, but is barely visible from the overbridge. As at the northern portal, the track soon curves away into darkness.

Several websites interested in old railway tunnels carry pages on Tidenham; our pet pair are currently Sparhawk and Forgotten Relics (which also does a rather fine desktop background picture of the interior). (Both of these are external links.)

Planning for reopening the tunnel

The basic fact that there is track through the tunnel means that it is clearly a railway tunnel and much of the work which would need to be carried out in it could be carried out by rail-based vehicles. For example, one of Network Rail's test trains could be borrowed and taken through to get an in-depth analysis of the inside of the tunnel.

To begin with, it would be necessary to enter the tunnel with a group of engineers and surveyors. They would carry out an examination of the bore to ensure that it is structurally sound and could be restored to a suitable condition for the restoration of rail services. If it has started falling in on a large scale then re-opening is not an option and it would be preferable to liquidate the owning group so the Crown can deal with it.

If the tunnel is in moderately good condition then it would be necessary to carry out bat surveys and work out mitigation procedures. Once these are dealt with a handy group of official bat lovers will be brought round to the tunnel, shown it in detail and informed of the various benefits of the plans and the effects of mitigation in the hope that they will provide some advice, even if they do not wholly support it. Hopefully this should result in a first-time acceptance of the scheme by the bat inspection groups. Work will mostly be carried out by a group of bat-approved contractors and will take place during a period when bats are not in residence.

Natural England kindly provides information on the procedure for dealing with applications to interfere with bats; as the tunnel is in England this is a useful guide. It is mostly common sense (a phrase often used by Planning Department staff dealing with instructions mere minutes before they misconstrue them).

Basically, the work must be in the overriding public interest (well, we think it is) with no other satisfactory alternative (bore another tunnel?) and a favourable conservation status (which sounds like somewhere else must be found for the bats). Proposals should be firm and confident with minimal dithering; only relevant information should be provided with no waffling; you should be precise about the number of bats being dealt with. They like to feel that you know what you are doing with their bats. There is also the query as to whether a licence is actually needed to deal with the bats; that will probably depend on whether it is decided that the bats need to go or not. The proposal should be clearly, although not too precisely, timetabled.

The ventilation shaft will undergo a cursory examination. Unless any notable problems come to light it will be left undisturbed. It is unlikely to be used by bats due to it being illuminated during the day. Ideally it would be either lined or filled in, but neither is particularly easy and the landowner above the shaft is understood to be uncooperative.

The actual work

With planning out of the way, work will begin on repairing the tunnel. While the rest of the line south of Tintern Quarry will be left with its current track for as long as possible (no point in bashing new track to pieces with construction trains when the stuff that's there can largely cope), the tunnel will need extensive works carrying out on it immediately to make it safe for trains and to protect the bats.

Bat protection and the condition of the tunnel come together rather nicely; the unlined bits of tunnel are falling apart and the lining does not comply with modern safety ideas. The tunnel was originally lined for about a quarter of its length from each portal with what is understood to be a stand-alone lining, protecting the railway from rockfalls but not holding up the roof. The central half remained unlined until a modernisation project inserted four lengths of wholly stand-alone lining - basically brick and stone arches protecting trains from rock falls again with lovely big voids between the crown of the lining arch and the roof of the bore. Nowadays these six sections of lining serve purely to hide the condition of the main bore from the eyes of maintenance gangs; should the bore decide to give way on a grand scale above one of these sections the warning signs would be hidden and the lining wouldn't offer much protection.

So the first phase will be to strip out the current lining in its entirety and replace it with a new one.The portals will be clad to look much the same as ever. The bore will be faced in bare concrete shaped in the same way as the current lining. This concrete will actually make contact with the bore and help to hold it together. There should be no further issues of piles of rocks appearing in the vicinity of the ventilation shaft.

The lining will naturally contain recesses for maintenance gangs at appropriate intervals (and consistent intervals - unlike the current lining, which is all over the shop). It will also be provided with recesses, holes and side tunnels as bat residencies. Some attempt will be made to ensure that they are nice quiet holes where the bats can sleep without being disturbed by passing trains - rubber linings around the entrances, for example, would help to deaden the noise.

Ideally the current track would remain in place on the grounds that it appears to be in excellent condition. On the other hand, doing a decent job at relining would involve digging out much of the ballast anyway, so the track will have to be disturbed so much that it may as well come out. The replacement will be a form of concrete slab track - a concrete base (with drainage channel down the middle) carrying rubber pads on which concrete blocks are installed; rails are then laid on the blocks in the style of 18th-century waggonways. The rubber pads help to deaden the noise of passing trains. Attaching the track to a fixed base guarantees that it won't move and therefore allows maximum use to be made of the tunnel's limited loading gauge. Using panels of this slab track will allow it to be readily removed and replaced if needs be.

If the original track, once removed, proves to be in decent condition it will be relaid at Tintern and Monmouth Troy stations to look a bit more authentic than continuously welded rail on steel or concrete sleepers. Line speeds at those locations will be low (15mph or less) which will minimise wear and tear and make using brand new track a bit of a case of overkill.

Arguably Tidenham Tunnel is the greatest obstacle to reopening. It includes a great deal of public relations work concerning the noise and the effects on the bat population; the bats and noise also provide environmental issues, while rebuilding such a long structure is a major engineering challenge. While the engineering challenges around the Tintern bridge and the viaducts at Monmouth and Penallt can be carried out in the open air, providing lots of space for heavy lifting equipment, track will have to be removed from and placed in Tidenham Tunnel in an enclosed space and all engineering equipment will have to fit into this bore with suitable evacuation procedures (which can make only limited use of the ventilation shaft). This results in a very difficult task with few precedents. Single-line tunnels are now quite rare, the branch lines which they were on having mostly closed, and very few have been subjected to full overhauls in recent years. Tidenham would be the longest UK tunnel to be reopened to rail traffic by a substantial margin; the current two longest reopened tunnels are double track bores.

One thing which we can claim is that people will only enter the tunnel on foot for maintenance, which we will try to schedule for out-of-season periods. Otherwise the bats will be left to enjoy life, except for the occasional passing train - which hopefully they won't notice. When trains are running people will be discouraged from entering the tunnel to disturb the bats by the proximity of an active station to the southern portal, the difficulties of accessing the northern portal and the inherent dangers in wandering around on railway lines. Provisions will be made for the tunnel to be securely gated overnight to keep out explorers, but the gates employed (which will be similar to, but slightly higher than, those protecting the southern portal of Tintern Tunnel) will provide plenty of space for the bats to fly in and out.

Home Wye Valley Jcn to Netherhope Tidenham Tunnel Tintern Quarry to Tintern Tintern Station Brockweir to St Briavels St Briavels to Redbrook Wyesham to Monmouth Signalling Rolling stock The Journey

Last modified 23/03/11

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