Llanishen Reservoir Dam is a Grade II listed building in the Cardiff local planning authority area, Wales. First listed on 24 July 2009. Reservoir dam.
Llanishen Reservoir Dam
- WRENN ID
- ruined-moat-burdock
- Grade
- II
- Local Planning Authority
- Cardiff
- Constituency
- Cardiff North MP: Anna McMorrin (Lab)
- Country
- Wales
- Date first listed
- 24 July 2009
- Type
- Reservoir dam
- OS grid reference
- ST 186 814
- Coordinates
- 51.5262, -3.17429
- Source
- Cadw listing
Description
The Llanishen Reservoir Dam is a significant structure built to enclose a flat lowland site, covering an area of 238,000 square meters and stretching almost a mile in length. Like other reservoir dams in the area, including Cantref, Beacons, and Llwyn Onn, it features a clay core and mass earth bund construction with sloping embankments. The inner embankment is faced with pitched stone, while the outer embankment is turfed.
Notable features include the inlet gauge chamber from the Taff Fawr and the outflow control valve platform, both of which are faced in rusticated ashlar with heavily dressed plinths, string courses, and copings. Similar dressed stone is also used for the Nant Fawr wash channel and spillway, the culvert exits, the stepped weir, and the scour tunnel exit.
Local climate
Llanishen Reservoir Dam sits in a wetter-than-average part of the UK, with an average of 1,080 mm of rain a year. This makes it wetter than 86% of listed buildings in the UK. Its exposure to wind-driven rain is greater than that of 87% of listed buildings.
It experiences an average of 22 freeze-thaw cycles a year, fewer than 77% of listed buildings. Of these, 8 follow at least 1 mm of rain in the preceding 48 hours. Average temperatures at this location have risen by 0.3°C per decade since 1991.
Averages for 1991–2020; temperature trend 1991–2025. Figures describe the wider area (a grid cell of roughly 10 km), not the individual site. Contains modified Copernicus Climate Change Service information 2026.
More on this building
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- No EPC on record for this property
- No sale records on file
- No related consent applications matched
- Detailed attributes — period, style, materials, features
- Flood risk assessment
- Radon risk assessment
- Weather exposure and heating demand — rain and frost month by month and year by year, wind direction, solar and humidity
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Similar buildings
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- 2 Dam, valve tower, bridge and outflow on Pontsticill Reservoir
- 3 Caban Coch Dam (partly in Llanwrthwl community)
- 4 Dam, valve tower, bridge and outflow on Pontsticill Reservoir
- 5 Dam and drive across Nant Meigan on Baron Hill estate
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