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The River Giedd (Welsh: Afon Giedd) is a river in Powys, Wales and which lies almost wholly within the Brecon Beacons National Park (Parc Cenedlaethol Bannau Brycheiniog). 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 (Y Mynydd Du) 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. 〔British Geological Survey 1:50,000 map sheet 231 'Merthyr Tydfil' & accompanying memoir〕〔Ordnance Survey Explorer map OL12 'Brecon Beacons National Park: western area'〕 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. 〔Gascoine, W. in Ford, T.D. (ed) 1989 'Limestones and Caves of Wales' Cambridge University Press〕 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'). == External links == * (images of upper River Giedd ) * (and of lower River Giedd and area on Geograph website ) 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「River Giedd」の詳細全文を読む スポンサード リンク
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