Dol-y-Mynach Dam & Reservoir
Dol-y-Mynach Dam is the only unfinished dam in the Elan Valley Estate. The dam was meant to be one of three due to be constructed along the Afon (river) Claerwen as the second phase of the plan to develop a water supply for the City of Birmingham. Construction started but was paused thanks to the World Wars. After the conflicts, advances in construction technology meant it was no longer a viable solution and so the unfinished dam still stands to this day acting as a weir for the small Dol-y-Mynach Reservoir.
Key info
| Location | Elan Valley Estate |
| County | Powys |
| Construction halted | 1904 |
| Engineer | James Mansergh |
| Resident Engineer | George Yourdi |
| Maintained by | Dŵr Cymru Welsh Water |
Visiting guide
Open 24 / 7
Free entry
Free car parking (lay-by)
What can I expect when visiting Dol-y-Mynach Dam & Reservoir?
The dam is only accessible on foot. You can walk to the dam from the Elan Valley Visitors Centre; however, this guide will detail how to reach the dam by car. Drive west from the visitors centre and cross over the Garreg-Ddu dam. Follow the road left until you reach a double layby. This is the best place to park.
Follow the road south-west and take care. There are no pavements and the estate can get very busy with traffic during weekends, bank holidays, and when children are off school. If you are visiting in the winter, you will see the unfinished dam at the bottom of the valley to your left. Listed out for the sound of running water.
Continue down the road until you reach a gravel road with a gate to your left with the Dol-y-Mynach reservoir in sight. Enter the pedestrian gate and take this route along the reservoir.
Follow the track until you reach the Dol-y-Mynach valve tower. This is where water enters a 1.25 mile tunnel into the Garreg-Ddu reservoir, which is the start of the Elan Valley Aqueduct that supplies Birmingham. The Dol-y-Mynach valve tower you see before you provides a means to top up the Garreg-Ddu reservoir thereby maintain a water level required to avoid disrupting the supply.
Continue past the valve tower and you will see the Dol-y-Mynach dam remains to your right.
The dam has two piers of smooth stone blocks with a hollow centre. The remains you see would have been built during the first phase of construction with the other dams in the Elan Valley otherwise the dam site would have been flooded by the Caban Coch Reservoir.
Venture through the gate onto the stone platform for a closer look at the dam remains. You can see the pyramidal pediment over the circular outlet on the left. Immediately to the right is a cross section of the sloping rough dam face with smooth internal blocks. This is a brief example of what the dam would have looked like had it been completed. It now acts as a weir pushing back the Afon (river) Claerwen to form the Dol-y-Mynach Reservoir.
Unfortunately, you cannot proceed any further; therefore, head back to the gate at the start of the track where you will have the option to walk more around the Dol-y-Mynach Reservoir or return to your starting position.
How long does it take to visit Dol-y-Mynach Dam & Reservoir?
It will take you roughly 45 minutes to follow the visiting guide detailed above; therefore, you should extend your visit by exploring more of the Dol-y-Mynach Reservoir or the Elan Valley Estate.
Is Dol-y-Mynach Dam & Reservoir suitable for a picnic?
The Dol-y-Mynach Dam & Reservoir is located in the Elan Valley Estate, an area of pristine natural beauty with ample spots for picnics or a simple lunch.
How do I get to Dol-y-Mynach Dam & Reservoir?
The Dol-y-Mynach Dam & Reservoir is only accessible on foot. You can reach it from multiple walking routes from the Elan Valley Visitors Centre. If arriving by car, drive west from the visitors centre and cross over the Garreg-Ddu dam. Follow the road left until you reach a double layby. This is the best place to park.
If you are arriving by public transport, head for Rhayader. The town no longer has a railway station; however, you can catch a train to Llandrindod Wells and then take a 30 min bus journey to Rhayader. There are bus services from Rhayader to the Elan Valley Visitors Centre. Check out Traveline Cymru for travel info. You can always catch a taxi from Rhayader or Llandrindod Wells as an alternative option.
Dimensions
| Intended dam height | 101 ft (30.8 m) |
| Intended dam length | 938 ft (285.9 m) |
| Intended total reservoir capacity | 1,640,000,000 gallons (7,455 megalitres) |
| Intended top water area | 148 acres (0.6 km2) |
| Actual top water area | 26 acres (0.1 km2) |
Sources
- Brown, D. L. (2020) The Elan Valley Clearance. Eardisley: Logaston Press.
- Morton, R. (1997) The Building of the Elan Valley Dams. Walsall: Brian Lowndes Print.
- Coflein (2024) Dol-y-Mynach Reservoir, Elan Valley Water Scheme. Available at: https://coflein.gov.uk/en/site/309539/?term=dol-y-mynach (Accessed: 31 March 2024).
Cantlop Bridge