Carno Adit is a tunnel driven by men working for Ebbw Vale Urban District in search of water. The tunnel entrance lies in Cwm Carno a small valley running northwards onto Llangynidr moor from Beaufort, Ebbw Vale. The valley lies just west of the road which crosses the moor and at present it contains two reservoirs feeding water to the Heads of the Valleys area.
I first entered the tunnel at the request of the Water Authority about twelve years ago and did a rudimentory exploration of the workings noting with interest several cave-type features, a dripping aven, a stream sink and several small phreatic passages blocked with sediment. I re-entered the tunnel in 1979 as part of the Southeast Wales Groundwater Survey with which I was involved, taking with me some geologists working as consultants for the WaterAuthority. We treated the stream sink in the tunnel with dyed lycopodium spores and proved a connection to Ffynnon Gisfaen, a spring in the Clydach Gorge some 3.5 miles distant to the east.
This dye test and its implications for cave exploration led me to negotiate with the Water Authority to dig in the phreatic passages to try and gain entry into the possible cave system leading to Ffynnon Gisfaen. Much discussion eventually has led to me digging in the tunnel and the results of the dig and the prior research work I give account of in this article.