Canal Aqueduct over Afon Twrch, including weir is a Grade II* listed building in the Neath Port Talbot local planning authority area, Wales. First listed on 4 December 2001. Aqueduct.
Canal Aqueduct over Afon Twrch, including weir
- WRENN ID
- stubborn-quoin-ochre
- Grade
- II*
- Local Planning Authority
- Neath Port Talbot
- Constituency
- Brecon, Radnor and Cwm Tawe MP: David Chadwick (LD)
- Country
- Wales
- Date first listed
- 4 December 2001
- Type
- Aqueduct
- Address
- Canal Aqueduct over Afon Twrch, including weir, Ynyscedwyn, Swansea, Ystradgynlais, Powys
- OS grid reference
- SN 772 092
- Coordinates
- 51.76835, -3.78002
- Source
- Cadw listing
Description
The Canal Aqueduct over Afon Twrch, which includes a weir, is a significant structure with a span of 21 meters and a width of 9 meters. It is built from squared rubble stone and features three broad low arches, each measuring 7 meters in span and 2.7 meters in height, with the arch soffits and voussoirs rendered over. A string course runs beneath the deep walling on the canal sides, topped with later 19th-century rock-faced stone coping.
On the downstream side, there are two small triangular cutwaters that rise as triangular piers with two offsets. The upstream side has been reinforced in the 19th century with two large stepped rounded stone piers that cover earlier cutwaters. This side also features a concrete spillway in the center and parapet top courses made of red brick. Beneath the eastern abutment, there is a circular tunnel for the tailrace of a former mill, with stone voussoirs at the entries.
The canal channel is 3.35 meters wide and 1.25 meters deep, with a tow-path on the southern side. The canal bed has been concreted during restoration, and the sides are made of rubble stone, likely rebuilt in 1993-1994. Additionally, there is a cast-iron mounting for a small emptying sluice on the northern side, and the broad concrete overflow in the center has slots for sluice gates on each side.
Local climate
Canal Aqueduct over Afon Twrch, including weir sits in one of the wettest parts of the UK, with an average of 1,490 mm of rain a year. This makes it wetter than 98% of listed buildings in the UK. Its exposure to wind-driven rain is greater than that of 95% of listed buildings.
It experiences an average of 43 freeze-thaw cycles a year, more than 81% of listed buildings. Of these, 21 follow at least 1 mm of rain in the preceding 48 hours. Average temperatures at this location have risen by 0.3°C per decade since 1991.
Averages for 1991–2020; temperature trend 1991–2025. Figures describe the wider area (a grid cell of roughly 10 km), not the individual site. Contains modified Copernicus Climate Change Service information 2026.
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