is a long tributary of the River Ely (), in the counties of Cardiff and Rhondda Cynon Taf, Wales. Its bedrock is predominantly of sandstone. Beginning on the western slope of The Garth () the river is fast-flowing, in clear shallow water with a hard substrate, flowing to the south of Llantrisant and generally west to its confluence with the River Ely at Pontyclun, falling over its course.
The river contains species such as stone loach, lamprey, eel, roach, chub and bullhead, and the Afon Clun valley is home to many species, including dragonflies and damselflies, badger, and the marsh fritillary butterfly, as well as the European Protected Species – bats, dormouse, otter and great crested newt. Birds in the area include bullfinch, kingfisher, linnet, reed bunting, skylark, and song thrush.
The valley is at risk of flooding between Cross Inn and Pontyclun and the river is liable to overflow its northern bank along its length downstream from the main A4119 (Tonypandy to Cardiff Bay ()) road at Talbot Green () to Pontyclun, providing a wetland wildlife habitat.
Many archeological sites are close to the river, from the Bronze Age tumuli on The Garth and an Iron Age hill fort at Rhiwsaeson, to the more recent industrial archeology of coal mines.
Course
The Afon Clun, a major tributary of the River Ely, drains an area of to the north-west of Cardiff in south Wales. The river's source is on the western slope of The Garth, a ) mountain of pennant sandstone midway between Cardiff () and Pontypridd, whose eastern slopes feed the River Taf by Taff's Well (). The Garth stands in the north western corner of the City and County of Cardiff (), above the village of Gwaelod y Garth, about north west of Cardiff city centre and about a mile or 1.5 km north of Pentyrch. The lower northern slopes of The Garth form the boundary with Rhondda Cynon Taf, about half a mile (800 m) north of the Clun's source. To the east the land falls away sharply from the summit, dropping more than over a distance of . The drop is less dramatic on the western slopes, the source of the Clun, but the river still falls to by the time it crosses the county boundary into Rhondda Cynon Taf at Rhiwsaeson, just under two miles (nearly 3 km) from its source. The Clun is fast-flowing, with clear shallow water and a hard substrate (gravel/cobble/pebble).
Near the Dŵr Cymru/Welsh Water water treatment plant at Rhiwsaeson the Afon Clun is fed from the north by Nant Myddlyn, which itself is joined from the east by Nant Dowlais. Nant Myddlyn rises in Tynant, Beddau about to the north of its confluence with the River Clun, between Beddau and Llantwit Fardre (), and Nant Dowlais rises in Church Village ().NGR: ST086958679 Nant Dowlais also has a tributary, which rises on Garth Isaf, two and a quarter miles (3.5 km) from it on the north western slopes of The Garth and about half a mile (800 m) north of the Clun's source.
Leaving Rhiwsaeson, about a mile (1.5 km) east of Cross Inn, the Clun widens to between about and and slows. Here, where the Clun flows to the south of Cross Inn, as well as along the banks of Nant Dowlais and Nant Myddlyn, evidence of otter activity has been noted. The river flows to the south of the A473 Pontypridd to Bridgend () road (Talbot Green By-Pass), where it is fed from the south by Nant Mwyndy. Nant Mwyndy flows over a bedrock of Carboniferous Limestone, rising in Creigiau and, flowing westwards, immediately north of Groesfaen, passing a small industrial estate at Mwyndy, feeding a lake resulting from Victorian opencast iron mining (see History below) and turning south to flow past Cefn-y-Parc Cemetery, Penygawsi, before reaching its confluence with the Afon Clun.Location of Cefn-y-Parc Cemetery The Clun then flows beneath the main A4119 (Tonypandy to Cardiff Bay) route about south of the roundabout by Glamorgan Vale Retail Park, Talbot Green. At this point, the river often overflows onto the meadows to the north, providing a wetland wildlife habitat, although drainage of floodplain grasslands, for industrialisation, housing and associated infrastructure, has affected wildlife by reducing its available area. To the south, the enclosed woodland of Coed-yr-Hendy follows the river's course for its final half-mile (800 m). The woodland's gentle slope, up from the Clun towards Miskin () and Pontyclun, prevents significant flooding over Afon Clun's southern bank.
After passing Y Pant Comprehensive School and Pontyclun Fire Station, the Clun flows under the bridge built for the Llantrisant to Cowbridge () main road, also known as the A4222, and gives its name to the nearby village, Pontyclun ("Clun bridge"). Immediately past the bridge, from its source, is the Afon Clun's confluence with the River Ely, which heads south, east to Miskin, almost encircling Pontyclun, then south on its way to Cardiff, where it flows into Cardiff Bay by Penarth Marina, which flows into the Bristol Channel.
Clun Valley The River Clun and its tributaries pass through the following towns and villages within Rhondda Cynon Taf, before merging with the River Ely at Pontyclun -
Efail Isaf (Llantwit Fardre) Tonteg (Llantwit Fardre) Church Village (Llantwit Fardre) Llantwit Fardre Beddau (Llantrisant) Rhiwsaeson (Llantrisant) Groes-faen (Pontyclun) Cross Inn (Llantrisant) Talbot Green Tyla Garw (Pontyclun) Pontyclun
Ecology Average annual rainfall in the area is .
Bedrock along the river's course is predominantly sandstone.
The Clun's water quality is generally class RE2 or better.
[Note: River Ecosystem Classification (RE) regulations and EU Directives for Bathing Water, Freshwater Fisheries, Dangerous Substances and Urban Waste Water Treatment;
RE1: 'Water of very good quality suitable for all fish species';
RE2: 'Water of good quality suitable for all fish species';
RE3: 'Water of fair quality suitable for high class coarse fish populations';
RE4: 'Water of fair quality suitable for coarse fish populations';
RE5: 'Water of poor quality which is likely to limit coarse fish populations.']
Afon Clun and its tributaries are designated 'salmonid waters and cyprinid waters' by the Department for Environment, Food and Rural Affairs (Defra) under the EC Freshwater Fish Directive (2006/44/EC), which sets physical and chemical water quality objectives to protect fresh water bodies suitable for sustaining fish populations
Rhondda Cynon Taf (RCT) has designated the Afon Clun Valley and Rhiwsaeson Hill as a Site of Important Nature Conservation, which is intended to provide the area with some protection from development. In addition, RCT has designated the undeveloped areas of the southern bank of Afon Clun (from Rhiwsaeson to Coed-yr-Hendy, including Mwyndy) and Efail Isaf, Garth and Nantgarw Western Slopes as Special Landscape Areas (SLAs). (SLAs) are intended to protect the visual qualities of "areas of fine landscape quality", when considering development proposals. Coed-yr-Hendy and Mwyndy consist mainly of "undisturbed" fields and woodlands. The south and west of the Efail Isaf, Garth and Nantgarw Western Slopes area consists of farmland – considered to be a buffer between The Garth and the urban area of Efail Isaf and Church Village. The eastern part is the prominent wooded slopes of the Taf Valley – a backdrop to the Treforest Industrial Estate. SLAs are identified using the Countryside Council for Wales' LANDMAP criteria, considering factors such as prominence, spectacle (dramatic topography and views), unspoilt areas (pre-industrial patterns of land use), remoteness and tranquility, vulnerability and sensitivity to change, and local rarity of landscape.
Diversity
The Afon Clun and Nant Dowlais contain minnow, stickleback, stone loach, lamprey, and eel. The species European bullhead (Cottus gobio) were also present, until a pollution incident in 2000 CE (see Industry below). In addition, the Clun contains roach and chub.
Among the species in the flood-meadows adjacent to the Afon Clun is the common orchid. The river's banks contain broadleaf woodland as well as invasive plants such as Himalayan balsam and Japanese knotweed.
Several species of dragonfly and damselfly hunt on the river. Other species present include bats, badger, dormouse, otter, great crested newt and the marsh fritillary butterfly, of which bats, dormouse, otter and great crested newt are European Protected Species. There is evidence that otters use Nant Dowlais and Nant Myddlyn, as well as the Clun and several species of bat have been sighted in the area, including Natterer's, long-eared, noctule and pipistrelle.
The Clun flows through, and close to, several areas defined in the UK Biodiversity Action Plan (BAP) as 'Areas of Ecological Significance'. Birds of 'conservation concern' recorded in surveys of the area are bullfinch, kingfisher, linnet, reed bunting skylark, and song thrush.
Hedgerows throughout the area qualify for protection, under the Hedgerows Regulations 1997.
Domesticated animals – horses and sheep – are kept in many of the fields bordering the river. Farmers have been encouraged to fence off access to the river for their animals, to prevent erosion of the riverbank and to prevent organophosphates (and the alternative synthetic pyrethroids) used in sheep dip, from contaminating the river.
Industry Two companies in the area around the Afon Clun valley are regulated by a system known as Integrated Pollution Control (IPC). They are Nipa Laboratories, at Llantwit Fardre, who operate processes involving the manufacture and use of organic chemicals, and Maxibrite, who produce smokeless fuels at Mwyndy, using carbonisation processes. IPC attempts to minimise the effect of industrial processes on the environment. Coal Products, who produced foundry coke at the Cwm Coke Works at Tynant, Beddau, were also regulated by IPC until the works closed in 2002. Under IPC the Environment Agency ensure that: "in carrying out a prescribed process the operator shall use BATNEEC (Best Available Techniques Not Entailing Excessive Cost) for:
i) preventing the release of substances prescribed for any environmental medium or, where that is not practicable by such means, for reducing the release of such substances to a minimum and for rendering harmless any such substances which are so released; and
ii) for rendering harmless any other substances which might cause harm if released into any environmental medium."
Since the end of coal mining in south Wales, the Afon Clun gradually returned to the condition in which it was before the Industrial Revolution, although it has been polluted several times since then. In 2000 CE ammonia discharged into Mwyndy Brook killed over 600 fish and eels, including the complete resident population of a conservation species known as bullheads, and many hundreds of small coarse fish fry, in the Clun. The coal briquetting plant that caused the pollution were fined a total of GBP31,816 in fines and costs, after a prosecution brought by the Environment Agency. Nant Myddlyn, a tributary on the Clun, suffered from a diesel spill near Llantwit Fardre, in early 2008 CE, which was raised at the Senedd.
Between 1994 and 1996, water quality at Nant Myddlyn, from Tynant to the confluence with the Nant Dowlais, was noted as RE5; at Afon Clun, from the confluence with the Myddlyn to Rhiwsaeson village, the quality was RE4. The deterioration of water quality was caused by the discharge of industrial effluent from Cwm Coke Works at Tynant. An effective effluent treatment plant was recommissioned to solve the discharge problem and water quality soon returned to RE2, until the works' closure in 2002 CE.
Since Coal Products' Cwm Coking Works closed, water abstraction from the Afon Clun area is minimal. The Works at Tynant had used up to 3.9 million litres per day (Ml/d) from Nant Myddlyn and a borehole and occasionally, water abstraction at the Works had caused Nant Myddlyn to dry up.
Floodplain