The Nant Gwys is a river flowing off the Black Mountain (Y Mynydd Du) in

Powys Powys (; ) is a Local government in Wales#Principal areas, county and Preserved counties of Wales, preserved county in Wales. It is named after the Kingdom of Powys which was a Welsh succession of states, successor state, petty kingdom and princi ...

Wales Wales ( cy, Cymru ) is a Countries of the United Kingdom, country that is part of the United Kingdom. It is bordered by England to the Wales–England border, east, the Irish Sea to the north and west, the Celtic Sea to the south west and the ...

. Its tributaries Gwys Fawr and the Gwys Fach flow south from

Banwen Gwyn Banwen is a small village in Neath Port Talbot county borough in Wales. Banwen is part of the community of Onllwyn along with the village of Onllwyn itself and the adjacent parish of Dyffryn Cellwen. Banwen is in the Upper Dulais Valley, with vie ...

and

Bwlch y Ddeuwynt Bwlch (meaning ''a pass'' in Welsh) is a small village and an electoral ward in Powys, southern Wales. The settlement is strung out along the A40 road which crosses a low col above the Usk Valley at this point on its route between Brecon and Cr ...

respectively and join forces to form the Nant Gwys proper which then flows for about 5 km / 3 mi to its confluence with the

Afon Twrch The Afon Twrch is a river which rises in the Black Mountain in south Wales. It forms the boundary between the counties of Brecknockshire (currently administered as part of the unitary authority of Powys) and Carmarthenshire and, downstream of ...

at Cwm-twrch-Uchaf. The upper reaches of the river and its tributaries lie within the

Brecon Beacons National Park The Brecon Beacons National Park ( cy, Parc Cenedlaethol Bannau Brycheiniog) is one of three national parks in Wales, and is centred on the Brecon Beacons range of hills in southern Wales. It includes the Black Mountain (range), Black Mountain ...

(Parc Cenedlaethol Bannau Brycheiniog) and within

Fforest Fawr Geopark Fforest Fawr Geopark is a Geopark in the Brecon Beacons National Park, south Wales. It is the first designated Geopark in Wales having gained membership of both the European Geoparks Network and the UNESCO-assisted Global Network of National ...

. The river is one of several which run down the southward directed dip-slopes of the Black Mountain (Y Mynydd Du) passing from the Millstone Grit outcrop onto the mudstones of the

Carboniferous The Carboniferous ( ) is a geologic period and system of the Paleozoic that spans 60 million years from the end of the Devonian Period million years ago ( Mya), to the beginning of the Permian Period, million years ago. The name ''Carbonifero ...

Coal Measures In lithostratigraphy, the coal measures are the coal-bearing part of the Upper Carboniferous System. In the United Kingdom, the Coal Measures Group consists of the Upper Coal Measures Formation, the Middle Coal Measures Formation and the Lower Coal ...

.British Geological Survey 1:50,000 map sheets 230 'Ammanford' & 231 'Merthyr Tydfil' & memoir accompanying latter The name translates from

Welsh Welsh may refer to: Related to Wales * Welsh, referring or related to Wales * Welsh language, a Brittonic Celtic language spoken in Wales * Welsh people People * Welsh (surname) * Sometimes used as a synonym for the ancient Britons (Celtic peop ...

as 'sow stream', presumably in reference to the neighbouring

or 'boar river'.

External links

images of Nant Gwys and area on Geograph website

References

{{authority control Gwys Rivers of the Brecon Beacons National Park Rivers of Powys