Taff's Well thermal spring is in Taff's Well (Welsh: Ffynnon Taf) north of Cardiff, south Wales () at an elevation of about . It is the only thermal spring in Wales. The spring emerges on the eastern bank of the River Taff and has been contained within a brick well structure. Access is via Taff's Well park, a public park owned and maintained by Rhondda Cynon Taff Council.

The spring is enclosed inside a well and stone building constructed in the 19th century. The well built to contain the spring waters is brick-lined and approximately deep. The building has an internal dimension of , and water fills this area. A brick-built spiral staircase is incorporated in the inside of the well. There is one visible overflow pipe, which emerges several metres to the west of the spring on the bank of the River Taff.

A recent conceptual model considers that the water has journeyed from the limestone outcrops on the north crop of the coalfield over a period of at least five thousand years, but possibly ten thousand.

The site is a registered Regionally Important Geological Site and a Grade II listed building.

History The early history of Taff's Well spring is not documented; in fact the first recorded visit to the spring was in 1760 by the chemist D. W. Linden. Roman settlements and roads occur throughout the Taff Valley but there is no evidence that the Romans knew about, or used the spring. A local tradition suggested that a flood in 1799 had uncovered Roman masonry at the site; however, no trace of the masonry survives today, and Natur Cymru state there is no evidence of Roman activity at the site. Ffynnon Dwym ("tepid well") was an alternative name for the well.

19th-century dictionaries mention the reported medicinal properties of the water, especially for the cure of rheumatism. The spring reached its height of popularity during the mid- to late 1800s, visitors arriving in the village in large numbers hoping to cure their ailments.

The following excerpt is from The Book of South Wales the Wye and the Coast, published in 1861. It is a description of people's beliefs in the healing powers of holy wells in the 19th century.

Hall concluded that the waters relieved and occasionally cured chronic disorders, citing a young man who came as a cripple and left after a fortnight's bathing able "to run about the green meadow and enjoy life." Another patient was described, an Irishman who was unable to move without the aid of crutches.

The growing popularity of Taff's Well spring as a tourist destination was again reported in 1877 by the chemist J. W. Thomas who said "the well waters have long since obtained some celebrity, especially the well water as a curative agent for rheumatism." Thomas concludes "we do not feel encouraged by this story (which, by the way, we rather fancy we have heard before) to insist very much upon the curative properties of the Water of Taff's Well."

During the 19th century, a weir was constructed across the River Taff. This caused the widening of the river, which moved eastwards towards the spring with floodwaters often covering the spring.

The well building fell into disrepair at the beginning of World War I, and in 1929 the Taffs Well villagers decided to repair the well and it re-opened in 1930 complete with a small swimming pool. It was around this time that the famous travel writer H. V. Morton visited the well, dedicating several pages of his 1932 book to it. A large flood in the 1950s caused the pool, and well, to fall into disuse once again. In 1978 the well's waters were used to rescue the village bowling greens from drought. It was not until the 1990s that a redevelopment of the area was undertaken by Rhondda Cynnon Taff Council.

Taff's Well spring is not currently used for water supply or recreational use. The council had plans to reinstate the spring and to develop it as a tourist attraction but these have not been fully realised.

The Grey Lady of Taff's Well

Taff's Well is not considered to be a holy well, although there are many of these in Wales. The best-known myth or legend associated with the spring (apart from its healing properties) is that of the "Grey Lady":

Geology

Taff's Well spring emerges from the southern limb of the south Wales Coalfield, Carboniferous "Millstone Grit" (Marros Group) occurs in the immediate area of the Taff's Well thermal spring. The underlying Carboniferous Limestone can be seen outcropping just south of Taff's Well. The underlying Devonian Old Red Sandstone outcrops over southeast, just north of the M4 motorway.

The superficial geology in the area of the Taff's Well spring comprises an unknown thickness of river alluvium and river terrace deposits.

The Taff's Well sub-unit is bound to the southwest by the Tongwynlais or Taff's Well Fault, which runs north–south, crossing the River Taff, and passing very close to the spring. The Taff's Well Fault is a continuation of the Daren-ddu fault, a major northwest–southeast-trending fault in the Coal Measure rocks of the South Wales Coalfield.

The Tongwynlais Fault is a normal fault and affects both the Carboniferous Limestone and underlying Devonian Upper Old Red Sandstone. The fault has a downthrow of 85m to the west.

The water is hypothesised to flow largely within the Carboniferous Limestone Group but partly within the Marros Group from sources on the north crop of the coalfield. At the lowest levels of the syncline within the Coal Measures it is heated geothermally before rising to the surface.

Temperature

Environment Agency Wales have monitored the temperature of the well since 2008, using a Solinst LTC logger.

During this period the maximum recorded temperature was and the average temperature . The temperature varies +/- about the average temperature of . The temperature can, on the whole be described as constant, with lower temperatures on occasion being attributed to mixing with Taff water or groundwater after heavy rain.

The average temperature at Taff's Well Spring, , is over warmer than the average groundwater temperature of in Wales.

Temperature °C Date Reference 18.61 1877 13 1969 22 1969 18.5 1969 19.6 1980 20.6 1988 22.12 2008 Environment Agency Wales. Publicly held water quality and temperature data from WIMS system and assorted compilation of references on Taffs Well - unpublished data

Water flow

Measurements of flow from the overflow pipe are rare. Slaters Dictionary mentions the well is close to the river into which the waters are continually flowing. In 1877 the well was described as "very powerful, and appears from rough calculation to afford about 800 gallons per hour" (or about 0.001m3/s).

Ecology

Ecological data from thermal waters is limited in the UK; however, an Irish Survey has been undertaken which looks at both flora and fauna associated with thermal and warm waters.

A survey of thermophillic cyanobacteria identified abundant growths of Phormidium ambiguum GOM which formed conophyton-like pinnacles up to high in the still water.

During periods when the well floods, water flows out onto the park forming a shallow pond next to the well building. Algae flourishes in the overflow water, which stands stationary exposed to light and oxygen, of which there is little in the thermal waters inside the well building. Filamentous algae Melosira variants and Spirogyra have both been identified and are very abundant in the flooded pool area outside the well building.

See also List of hot springs

References

External links