Cyfarthfa balance pond and leat

Summary description and reason for designation

The monument comprises the remains of a major balance pond and leat serving a number of deep mines. Coal and ironstone were extracted from land leased by the Cyfarthfa Works by surface and patch workings until 1826. From that date deep mines where dug and worked with water balances. A line of these pits was supplied with water from this balance pond by the leat, which ran along the contour to the north, from which water was taken for each pit. The system probably dates from the 1830s and is shown complete on the Tithe Map for Merthyr Tydfil of 1850. This site is the largest water balance reservoir surviving on the former Cyfarthfa Estate and the only one which served a number of pits from a single leat. Morris and Williams, in their book The South Wales Coal Industry 1841 - 1875 (1958), note that "The water balance pit, used where there was an abundant supply of water, was peculiar to South Wales… In 1862, in Glamorgan alone, there were about sixty of these machines at work, all the great pits of the Cyfarthfa works being operated on this basis." The pond was created on a steep E-facing slope by building an earth and stone dam on three sides. The dam encloses an area of about 65m from N to S by 38m transversely and remains water-filled. There are the remains of a stone-lined sluice near the SE corner and a brick-lined spillway on the N side. The inner face of the dam is stone revetted. A leat runs from the NW corner of the pond. This leat is formed by a linear bank of earth and stone up to 4m in height, which creates a channel up to 3m in width between it and the slope to the W. The leat runs N for about 270m along the contour.

The monument is of national importance for its potential to enhance and illustrate our knowledge of the early 19th century coal mining and iron working industries of Wales. It is the largest and best preserved balance pond that survives on the Cyfarthfa estate, famous for its use of water balance technology in extracting coal and ironstone. The structures may be expected to contain archaeological information in regard to chronology, building techniques and functional detail.

The scheduled area comprises the remains described and an area around it within which related evidence may be expected to survive. It is irregular in shape on plan and measures 358m from N to S by up to 44m transversely.