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PART 3 - The Surge!

No 9 adit, spring 1993

March 1993......

No 9 Adit, late 1993!November 1993!

What had happened? Clearly an overwhelming flood: after all there had been heavy rain on and off through the autumn. But this surge had come from above. It had come down the drainage gully that takes the discharge from the No 6 adit. Higher up it had scoured to bedrock and washed away several trees. The next step was to try to find out why so much water had suddenly entered the workings to exit from No 6. It didn't take long...

Nant Bwlchgwyn above Ystumtuen has broken into the workings!
Here it is - the stream known as Nant Bwlchgwyn to the east of Ystumtuen. The course of the stream follows in part the outcrop of the lode. Subsidence has occurred and the entire stream has entered old workings. Since all of these workings - Ystumtuen, Penrhiw and Bwlchgwyn - are drained by No 6 adit at Cwmrheidol, here we have the culprit.

Bridging the subsidence, Nant Bwlchgwyn
In the Spring of 1994 we therefore set out to repair Nant Bwlchgwyn, by culverting it straight over the subsidence. Here we are digging the culvert into place and have just turned the water-flow back on its correct course...

Nant Bwlchgwyn restored to its correct course
And here is the nearly-completed job. However, caution is advised, as there are other workings in this area and the potential for further subsidence needs to be assessed and dealt with, if Cwmrheidol is to avoid further surges like that of late 1993!

Deep inside No 6 adit another shale-dam is holding back water
Attention then turned to the No 6 Adit at Cwmrheidol, where a shaly dam had developed in an area where the roof was steadily crumbling close to the adit's intersection with the lode. This image depicts the general scene at this point, way in underground.

Clearing the dam in No 6 adit, Cwmrheidol mine
The dam was gradually lowered bit by bit to avoid any sudden water surges. Beyond lay tunnels left and right driven along the lode. The left-hand one was walled-up but archival work by Simon Hughes had already determined that it connected down to No 9 by a winze. Such tunnels are driven with a slight gradient "outbye" - that is, towards the adit, to allow water to flow outwards. But, because the water level was so high, it had overcome the gradient, so that it was able to escape down the winze into No 9. The removal of the dam allowed the correct direction of flow to be re-established.

Pipes laid after the dam was removed, permitting unimpeded water flow
After removing the dam, action was taken to ensure that water flow and human access would be possible in the event of further falls of ground. Strong twin-wall pipes were deployed: two at ground level to take the water, which were then buried, and a third bigger-gauge one, here being put into place. This too was buried. The pipes extend well out into the tunnels beyond, to avoid roof-falls blocking them.

That concluded the works at Cwmrheidol back then. The aim was to maintain the
status quo with respect to underground drainage. The longer-term treatment of this drainage is a problem of much greater magnitude which, it is hoped, will be tackled eventually. The risks of potential subsidence and more sudden water surges, due to the juxtaposition of old stopes and rivers in the Ystumtuen area, is a problem that will not go away until it is fully assessed and dealt with in an appropriate manner.