History in Structure

Canal Aqueduct over Afon Twrch, including weir

A Grade II* Listed Building in Ystradgynlais, Powys

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Coordinates

Latitude: 51.7683 / 51°46'6"N

Longitude: -3.78 / 3°46'47"W

OS Eastings: 277270

OS Northings: 209240

OS Grid: SN772092

Mapcode National: GBR Y5.ZT6J

Mapcode Global: VH5G2.FTJ8

Plus Code: 9C3RQ69C+82

Entry Name: Canal Aqueduct over Afon Twrch, including weir

Listing Date: 4 December 2001

Last Amended: 20 December 2002

Grade: II*

Source: Cadw

Source ID: 25953

Building Class: Transport

ID on this website: 300025953

Location: Situated some 50m N of Twrch Bridge between Ystradgynlais community and Ystalyfera community, reached by footpath along river from Gurnos Road.

County: Powys

Town: Swansea

Community: Ystradgynlais

Community: Ystradgynlais

Locality: Ynyscedwyn

Built-Up Area: Ystradgynlais

Traditional County: Glamorgan

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Ystradgynlais

History

Canal aqueduct carrying former Swansea Canal over the Afon Twrch, 1794-8 by Thomas Sheasby, engineer, the largest aqueduct on the canal. This was the first aqueduct to use hydraulic lime for waterproofing. The aqueduct stands on a 4m high stone-faced weir which diverted water into a canal feeder. The 16-mile Swansea Canal was opened in 1798 to Hen Neuadd, Abercraf, declined after the railway opened in 1852 and closed in 1931. The course of the canal around Ystradgynlais is substantially lost under the bypass. The aqueduct was restored 1993-4.

Exterior

Canal aqueduct of 21 m span, 9 m broad, squared rubble stone with 3 broad low arches, each of 7m span, 2.7 m height, the arch soffits and voussoirs rendered over. String course under deep walling to canal sides and later C19 rock-faced stone coping. Downstream side has 2 small triangular cutwaters carried up as triangular piers with 2 offsets. Upstream side has been reinforced in C19 with 2 big stepped rounded stone piers covering earlier cutwaters. This side has a concrete spillway in centre, and parapet top courses in red brick. Under E abutment is circular tunnel for the tailrace of a former mill, with stone voussoirs to entries.
Canal channel 3.35 m wide and 1.25 m deep, has tow-path on S side, canal bed concreted in restoration, canal sides rubble stone, probably rebuilt in 1993-4. There is a cast-iron mounting for a small emptying sluice on the N side and the broad concrete overflow to centre has slots for sluice gates each side.

Reasons for Listing

Included as the principal surviving engineered structure of the Swansea Canal.

Scheduled Ancient Monument GM 396(NEP).

External Links

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