River Rhiangoll

The Rhiangoll north of Cwmdu

The Rhiangoll is a river in the Black Mountains, within Brecknockshire. The course of the river is also within the Brecon Beacons National Park.

The riser rises on the western slopes of Waun Fach in the Black Mountains and drops steeply down to the west into the north-south valley through which the A479 runs between Talgarth and the hamlet of Tretower and through the village of Cwmdu.

The Rhiangoll is joined by various minor tributary streams on its left bank including the Ffinnant, Nant yr Ychen, Nant-y-fedw and Nantygarreg, all of which rise on the flanks of the ridge extending between Pen Trumau and Pen Gloch-y-pibwr. Two tributary streams flowing from Mynydd Troed and Mynydd Llangorse enter on its right bank as does Nant Ewyn east of the village of Bwlch.

The Rhiangoll enters the River Usk near Glanusk Bridge a mile south of Tretower.

Paleogeology

The main valley was excavated by glacial ice during the course of the ice ages as it breached the watershed at Pengenffordd. Its broad lower section was influenced by the merging of the Rhiangoll valley ice with that of the main Usk Valley glacier which swept down past Bwlch.

Outside links

("Wikimedia Commons" has material about River Rhiangoll)

• Location map: 51°52’33"N, 3°10’37"W
• Pictures of Rhiangoll Valley and the area on Geograph.co.uk