5.2 Water
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There are six reservoirs on the Taf Fawr and Taf Fechan which flow from the Brecon Beacons to Merthyr Tydfil to form the River Taff. One of these is the Upper Neuadd, built in 1902 to the design of G. F. Deacon. The dam is of the gravity type, 77 ft 5 in. high and 1385 ft long on the crest, and is unusual in that the entire darn is of a thin masonry section buttressed with earth fill over most of its length.
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Another tributary of the Taff, the Afon Cynon, has several interesting reservoirs on it above Aberdare. One of these, built in 1875 on a side stream at Nant Hir, has an earth dam some 63 ft high and 328 ft long on the crest, with a puddle clay core, a grassed downstream slope and stone pitched upstream slope.
It was the work of J. F. La Trobe Bateman, one of the most active water engineers of his day.0 Other examples of his work are mentioned in Chapters 5 and 8. He was the son-in-law of William Fairbairn worked on tubular bridges in association with Robert Stephenson.
Across the Nant Hir reservoir is a notable reinforced concrete open-spandrel arch bridge carrying the A465 Heads of the Valley Road.