Rhiangoll
Encyclopedia
The Rhiangoll is a river in the Brecon Beacons National Park in southern Powys
, south Wales
. It 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
. It 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 the Ewyn Brook east of the village of Bwlch
.
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. The Rhiangoll itself enters the River Usk
near Glanusk Bridge 1 mile south of Tretower.
Powys
Powys is a local-government county and preserved county in Wales.-Geography:Powys covers the historic counties of Montgomeryshire and Radnorshire, most of Brecknockshire , and a small part of Denbighshire — an area of 5,179 km², making it the largest county in Wales by land area.It is...
, south Wales
Wales
Wales is a country that is part of the United Kingdom and the island of Great Britain, bordered by England to its east and the Atlantic Ocean and Irish Sea to its west. It has a population of three million, and a total area of 20,779 km²...
. It rises on the western slopes of Waun Fach
Waun Fach
Waun Fach is the highest mountain in the Black Mountains in south-eastern Wales. It is one of the three Marilyns over 600m that make up the range, the others being Black Mountain and Mynydd Troed. To the north Rhos Fawr and the Radnor Forest can be seen.It is situated at the head of the Grwyne...
in the Black Mountains
Black Mountains, Wales
The Black Mountains are a group of hills spread across parts of Powys and Monmouthshire in southeast Wales, and extending across the national border into Herefordshire, England. They are the easternmost of the four ranges of hills that comprise the Brecon Beacons National Park, and are frequently...
and drops steeply down to the west into the north-south valley through which the A479 runs between Talgarth
Talgarth
Talgarth is a small market town and community in southern Powys , Mid Wales, with a population of 1,645. Notable buildings in the town include its 14th-century parish church and 13th century Pele Tower, located in the town centre, now home to the Tourist Information and Resource Centre...
and the hamlet of Tretower
Tretower
Tretower is a hamlet in the community of Llanfihangel Cwmdu with Bwlch and Cathedine in the southern part of the county of Powys in Wales. It lies on the A479 road within the Brecon Beacons National Park at the foot of the Black Mountains just off the Usk Valley...
and through the village of Cwmdu
Cwmdu, Powys
Cwmdu is a small village situated in the heart of the Black Mountains in Powys, Wales. Its name is derived from the Welsh language "Cwm Ddu", which means 'Black Valley'. It is located on the A479 Talgarth to Tretower road.- Amenities :...
. It 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
Mynydd Troed
Mynydd Troed is a hill in the Black Mountains of the Brecon Beacons National Park in Powys, south Wales. It lies 3 miles south of Talgarth and 2 miles northeast of the village of Llangors on the western side of the range...
and Mynydd Llangorse
Mynydd Llangorse
Mynydd Llangorse is a hill on the western edge of the Black Mountains in the Brecon Beacons National Park in Powys, south Wales. It lies two miles east of Llangors and its lake and 5 miles south of Talgarth. Its summit at 515m overtops the location 600m to the south at which a trig point is sited...
enter on its right bank as does the Ewyn Brook east of the village of Bwlch
Bwlch
Bwlch is a small village on a col between two hills, where the present day A40 road now runs, between Brecon and Crickhowell in Powys, southern Wales...
.
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
Glacier
A glacier is a large persistent body of ice that forms where the accumulation of snow exceeds its ablation over many years, often centuries. At least 0.1 km² in area and 50 m thick, but often much larger, a glacier slowly deforms and flows due to stresses induced by its weight...
which swept down past Bwlch. The Rhiangoll itself enters the River Usk
River Usk
The River Usk rises on the northern slopes of the Black Mountain of mid-Wales, in the easternmost part of the Brecon Beacons National Park. Initially it flows north into Usk Reservoir, then east by Sennybridge to Brecon before turning southeast to flow by Talybont-on-Usk, Crickhowell and...
near Glanusk Bridge 1 mile south of Tretower.