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CAMBRIAN CAVING COUNCIL Proposal to Dwr Cymru Welsh Water plc for access into the Ogof Carno cave system Management Summary The Ogof Carno cave system was found by cavers exploring an abandoned tunnel which was intended to enlarge the water supply for Ebbw Vale steel works in the early 1900s. The tunnel later passed into Dwr Cymru Welsh Water ownership. A number of natural passages leading off the tunnel have been expanded and explored by cavers since 1982, though progress has been intermittent due to diversions of interest into other nearby cave discoveries. Access had to be withdrawn in 2013 due to the major A465 roadworks and there were also health & safety concerns. Cambrian Caving Council would now like to negotiate a new access agreement for the Ogof Carno cave. We think this is a fitting project under the Welsh Government’s Year of Adventure 2016 initiative which promotes physical activity and healthy lifestyles, while the H&S aspects can be managed successfully with appropriate methods and precautions. History In 1905 the expanding steelworks at Ebbw Vale needed water in ever larger quantities. So Ebbw Vale Urban District Council began to drive a tunnel, starting in Cwm Carno and heading through Mynydd Llangynidr, in order to capture a large spring in Cwm Claisfer about three miles away without pumping. But tunneling contractors met with geological problems and their efforts were halted two miles underground in 1912 following an unfavourable survey by a geological consultant. The adit (tunnel) began in boulder clay and some coal measures for the first 200m, but then entered hard millstone grit for the next kilometre before continuing through the Dowlais limestone. The tunnel rises gradually by eight metres over its considerable length, and it is a dead straight line for the first 2kms in which the entrance can always be seen as a pin-prick of light in the distance. The geological problems arose when the tunnel reached a band of weak shale which caused the roof to collapse repeatedly. However, the roof was shored up, as in coal mines, and good hard limestone was found again beyond the shale. Simply to give up after conquering the physical difficulty points more to financial and timescale issues than to geotechnical concerns. The only current use of the tunnel is to make occasional discharges from the Carno and Llangynidr reservoirs via an underground pipe which emerges into the first 100m of the adit. The entrance to the adit was moved and re-engineered during the widening of the A465 to dual carriageway standard in 2013. The discharge pipe used to emerge around 50 metres into the old tunnel at a dam about one metre high which kept the tunnel beyond it completely dry. This pipe is now perhaps 100m inside the augmented adit. Caving, or exploring for new caves, through the old adit entrance was permitted by Dwr Cymru Welsh Water (DCWW) from 1982 to 2013 via an authorised access scheme run by Brynmawr Caving Club (BCC) who managed the key loans. The letters sent between DCWW and Cambrian Caving Council (CCC) along with minutes of a round-table meeting between DCWW and BCC are attached in the appendix to this proposal document. - 1 - Fig. 1. Adit (grilled) with service road under dualled A465 road in 2014 Fig. 2. Cavers using the old adit entrance in 2010 Fig. 3. Signing-in book at start of the brick-lined dry tunnel in 2010 - 2 - Hydrology An extensive research study was carried out by Bill Gascoine, a member of BCC, in partnership with DCWW who bought the water-tracing materials that he used. Sadly, Bill died in 2013 but his research is written up in the chapter he contributed to "Limestones and Caves of Wales" edited by Trevor Ford, 1991, Cambridge University Press, ISBN 0-521-32438-6, pages 40-55. Bill worked as a chemistry lecturer at Ebbw Vale College. He utilised an unusual method to trace multiple sinks simultaneously using inert lycopodium spores dyed in various colours. These spores are not native to the UK and therefore unusual to find. They can travel through underground watercourses to become trapped in plankton nets placed across the resurgences of interest. The nets are then examined by microscope for the characteristic spore shape and the specific dye colours used. Only a handful of coloured spores emerging provides a certain hydrological result. Thus the water flows within a wide area were easily revealed without compromising the public water supply. This is important because the land immediately to the west of Chartist Cave (see map below) drains to the Ffynnon Shon Sheffrey resurgence between Trefil and Shon Sheffrey’s Reservoir. Water sinking at Chartist Cave and Ogof Cynnes and Carno Adit all flows to Fynnon Gisfaen in the Clydach Gorge 5kms away where DCWW can abstract 4,000 cu.m. daily for the Brynmawr public supply. Water sinking at Blaen Onneu Cave and Llangattock Mountain cave systems resurges at Pwll-y-Cwm much lower down in the Clydach Gorge and later joins the River Usk and out to sea. The invention of dyed lycopodium spores as a water-tracing agent is attributed to [Drew, D.P., Smith, D.I., 1968, Techniques for the Tracing of Subterranean Drainage. British Geomorphological Research Group Tech. Pub. Ser. A, p.2-36]. Fig. 4. Carno Adit in relation to the local area - 3 - Fig. 5. Carno Adit (blue) and the Ogof Carno cave (red) in relation to surface features Geology Mynydd Llangynidr is one of Britain’s finest examples of interstratal karst (i.e. limestone beds in between other rock types). Doline fields (i.e. surface collapses and depressions) within the grit outcrops are a special feature on gently dipping escarpments in South Wales, and Llangynidr has the densest, largest and most spectacular assemblage of these dolines. Collapsed dolines, broad shallow subsidence basins and large masses of foundered grit all occur within a small area here. Caves form in the limestone beds, which in this case dip to the south. Water entering from the land above through exposed limestone or breaks in the gritstone cap will follow small cracks and faults in the limestone, widening them through solutional action, and running away down the dip. It is possible, as shown in the diagram below, that a large cave system has few if any direct connections to the present land surface which has been sculpted many times by glaciations. Fig. 6. Stratification, surface collapses and solutional cave development beneath - 4 - Fig. 7. Surface geology of Mynydd Llangynidr There are two small caves in the middle of Mynydd Llangynidr: Ogof Cynnes is a cave with 900m of rift passages formed in the top beds of the limestone just beneath the grit cover, and Ogof Fawr (Chartist Cave) is another small cave accessible from the boundary of the limestone and grit. So both of these have grit roof at their entrances, soon leading down to rift passages and large internal collapse chambers which have no surface expression. About 9kms of cave passages lie in Ogof Carno in the Dowlais Limestone at a depth of up to 100m and they appear to be the down- dip continuations of influent caves such as Ogof Cynnes. But Ogof Carno is only accessible from inside the DCWW adit by sheer luck and it is not connected to any natural surface entrance. Fig. 8. Chartist Cave entrance with its thin gritstone roof over the limestone - 5 - Spelaeology Cave features become evident in Carno Adit almost immediately it enters the Dowlais limestone at 1200m from the entrance. For example, at 1290m a side passage is met on the right which can be entered through a hole in the brick tunnel lining. This passage is 10m long and it formed while fully submerged in water. It now has shelved walls and a cap-mud floor. The mud has flowed in from the surface under high pressure during various glaciations to occupy a pre-existing cave. The geological consultant’s report of 1912 mentioned the presence of a strongly draughting fissure in the limestone wall of the tunnel. This likely corresponds to a strongly draughting hole in the wall found by cavers. Their study of this draught, its dependence on weather conditions and its lack of moisture or surface smells, prompted the cavers to widen this hole and so access a natural cave chamber beyond it. But unfortunately there was no continuation into man-size passages. A little way beyond the draughting fissure is a small area of collapse in the floor which sinks water in wet weather, again suggesting natural caves. The next 120m of the tunnel has some pools of water on a rough boulder-strewn floor and another sink for water at its northern end. The water is also ducted away from the tunnel by a small pipe laid in the floor. It was into this pipe that the dyed Lycopodium spores were introduced that gave the positive water trace to Ffynnon Gisfaen. Just beyond this floor sink, access can be gained through a hole in the tunnel brick lining to a dripping aven (i.e. a blind vertical passage) some 6m high and 2m in cross-section at its lower end. Water issues from a small crack in the aven, cascades down the wall and flows along the tunnel to the sink. The vertical difference in height from here in the adit to the land surface is 65m. There are a few more natural side passages in this area, dug out when tunnel contractors followed cave features, presumably hoping to chance upon and tap any underground water source that would be vastly cheaper than tunneling for another 1400m to reach the Claisfer valley.

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