River Giedd
Encyclopedia
The River Giedd is a river in Powys
, Wales
and which lies almost wholly within the Brecon Beacons National Park.
This river is perhaps unique in the British Isles in that there are in fact two separate rivers sharing the same name and occupying the same valley but which are not hydrologically connected. The upper Giedd rises on the southern slopes of the Old Red Sandstone
mountain, Fan Brycheiniog
in the Black Mountain
and heads south-southwest for about 3 km / 2 mi until, as it enters onto the Carboniferous Limestone
outcrop it disappears into its bed. A dry valley continues in the same direction beyond the sinks and, as it crosses the Millstone Grit
outcrop, gradually acquires a stream which is joined by others to become the lower Giedd. This separate river flows for about 6 km / 4 miles to its confluence with the River Tawe
at Ystradgynlais
in the Swansea Valley
.
Dye tracing
in 1970 revealed that the waters of the upper Giedd which disappear into the ground at Sinc y Giedd eventually re-emerge at Dan-yr-Ogof and do not contribute in any way to the flow of the lower Giedd.
The only significant tributary of the River Giedd is the Nant Cyw (translates as 'chicken stream') entering on its left bank and whose two tributaries are in turn, the Nant Iar ('hen stream') and Nant Ceiliog ('cockerel stream').
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...
, 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...
and which lies almost wholly within the Brecon Beacons National Park.
This river is perhaps unique in the British Isles in that there are in fact two separate rivers sharing the same name and occupying the same valley but which are not hydrologically connected. The upper Giedd rises on the southern slopes of the Old Red Sandstone
Old Red Sandstone
The Old Red Sandstone is a British rock formation of considerable importance to early paleontology. For convenience the short version of the term, 'ORS' is often used in literature on the subject.-Sedimentology:...
mountain, Fan Brycheiniog
Fan Brycheiniog
Fan Brycheiniog is the highest peak in the Black Mountain region of the Brecon Beacons National Park in South Wales. It is just inside the county of Powys, and also within the Fforest Fawr Geopark designated in 2005 in recognition of the area's geological heritage.The Beacons Way, a waymarked long...
in the Black Mountain
Black Mountain (range)
The Black Mountain is a mountain range in Mid and West Wales, straddling the county boundary between Carmarthenshire and Powys and forming the westernmost range of the Brecon Beacons National Park. Its highest point is Fan Brycheiniog at 802 metres or 2,631 ft. The Black Mountain also forms a part...
and heads south-southwest for about 3 km / 2 mi until, as it enters onto the Carboniferous Limestone
Carboniferous limestone
Carboniferous Limestone is a term used to describe a variety of different types of limestone occurring widely across Great Britain and Ireland which were deposited during the Dinantian epoch of the Carboniferous period. They were formed between 363 and 325 million years ago...
outcrop it disappears into its bed. A dry valley continues in the same direction beyond the sinks and, as it crosses the Millstone Grit
Millstone Grit
Millstone Grit is the name given to any of a number of coarse-grained sandstones of Carboniferous age which occur in the Northern England. The name derives from its use in earlier times as a source of millstones for use principally in watermills...
outcrop, gradually acquires a stream which is joined by others to become the lower Giedd. This separate river flows for about 6 km / 4 miles to its confluence with the River Tawe
River Tawe
The River Tawe is a river in South Wales. It flows in a principally south-westerly direction for some from its source below Moel Feity in the Old Red Sandstone hills of the western Brecon Beacons to the Bristol Channel at Swansea. Its main tributaries are the right bank Upper and Lower Clydach...
at Ystradgynlais
Ystradgynlais
Ystradgynlais is a town on the River Tawe in south west Powys; it is the second largest town in Powys, Wales. The town grew around the iron-making, coal-mining and watch-making industries....
in the Swansea Valley
Swansea Valley
The Swansea Valley , one of the South Wales Valleys is the name often given to the valley of the River Tawe area in South Wales, UK. It reaches southwest and south from the Brecon Beacons National Park down to the city of Swansea. Today, administration of the area is divided between the City and...
.
Dye tracing
Dye tracing
Dye tracing is tracking and tracing various flows using dye added to the liquid in question. The purpose of tracking may be an analysis of the flow itself, of the transport of something by the flow of the objects that convey the flow...
in 1970 revealed that the waters of the upper Giedd which disappear into the ground at Sinc y Giedd eventually re-emerge at Dan-yr-Ogof and do not contribute in any way to the flow of the lower Giedd.
The only significant tributary of the River Giedd is the Nant Cyw (translates as 'chicken stream') entering on its left bank and whose two tributaries are in turn, the Nant Iar ('hen stream') and Nant Ceiliog ('cockerel stream').