GM395

Neath Abbey Ironworks Dam  

18/12/1978  

Designated  

Neath Port Talbot  

Dyffryn Clydach  

273909  

198767  

Water Supply and Drainage  

Dam  

Post Medieval/Modern  

The monument, also known as Cwm Clydach Dam, consists of a masonry and earthen dam, built across the River Clydach in 1840-41 to impound water for the purposes of power generation at the Neath Abbey Iron Company works to the south. The Price and Fox families, Quaker industrialists from Cornwall, established Neath Abbey Ironworks in 1792. They made a range of well-regarded engines, locomotives, plant and ships which were exported around the world. The dam was constructed to reserve water to supply their expanding business and was large for the time, impounding a water surface area of c. 5.8 acres. The designer is not known, but the design was innovative and sought to progress beyond a simple gravity dam that was reliant on mass and weight to hold the water back. It was deliberately located and occupied a natural narrowing of the river valley, measuring c. 10m in height, up to 6m in width and 90m in length. The western part of the dam was built from finely jointed and coursed solid masonry and contained most of the architectural features. The air face was supported by two masonry buttresses and a corner buttress. In plan, the dam curved towards the impounded water to form a primitive version of a gravity-arch dam. The curve and buttresses were designed to spread thrust from the wall to the abutments and the toe beyond the air face. Two circular outlets at the base of the dam and the four spillways at the top released a flow of water regulated by the machinery still surviving on the north, slighter, side of the dam. The eastern outlet was fed by a dropshaft and maintained the water level in the reservoir. The western outlet was a sluice and operated by the surviving geared mechanism above to provide a controlled flow of water. The spillways comprised rectangular openings with setts laid on cast iron trays and with cast-iron posts at their upstream openings, inset to receive stop planks. The eastern part of the dam is simpler in design, built from a clay core protected by more roughly coursed masonry retaining walls. The parapet has mainly been replaced and recapped. The dam supports a minor road and the section over the spillways is supported on more recent reinforced concrete. The monument is of national importance for its potential to enhance our knowledge of nineteenth century water supply, power and industrial practices. It retains evidence of the innovation, operation and organisation of one of the leading ironworks and engineering companies during the Industrial Revolution in Wales. The structure itself may be expected to contain archaeological information concerning chronology and building techniques. It retains significant archaeological potential and features, particularly the associated sluice gear mechanism, which is rare in-situ physical evidence of mechanical engineering designed and produced by the Neath Abbey Iron Company. The significance of the monument is increased by the survival of original documentation and design drawings relating to the commissioning and construction of the dam. The group value of the dam is enhanced by its association with the charging ramp, blast furnaces and manufactory at Neath Abbey Ironworks (GM389) and their calcining kilns (GM635); collectively, these features make Neath Abbey Ironworks one of the best places in the UK to understand the integrated management of the iron industry during the Industrial Revolution. The scheduled area comprises the remains described and areas around them within which related evidence may be expected to survive. It is located at OS NGR 273940 198756. It is an irregular polygon in shape and measures 110m in length E-W by 15.5m transversely. First scheduled in 1978, the scheduled area has been expanded to incorporate additional features, including the earthen and masonry dam wall to the east, and the buttresses and the flared base of the dam wall to the south.