There is a report today that the whole flow of the Afon Lliedi has disappeared into a sinkhole in Llanelli.

I don't know the area at all, but the site in Llanerch appears to be on the Swansea member of the Pennant Sandstone. Although there is limestone far beneath, perhaps a more like explanation is drainage into old coal workings.

https://www.walesonline.co.uk/news/wales-news/llanelli-sinkhole-river-bridge-water-21328180

Looks like you're right. NLS shows a coal shaft 50m to the NW under the roundabout!

The Lliedi was at lowish flow and when a large diameter sewer pipe beneath the bridge (shown in news report photo) fractured, the sewer pipe captured almost the entire flow. It took a week for contractors to repair the broken pipe and restore normal flows. 

Graigfawr said:

The Lliedi was at lowish flow and when a large diameter sewer pipe beneath the bridge (shown in news report photo) fractured, the sewer pipe captured almost the entire flow. It took a week for contractors to repair the broken pipe and restore normal flows.

Click to expand...

At least it was not the other way round !

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