Lock No 66 is a Grade II listed building in the Brecon Beacons National Park local planning authority area, Wales. First listed on 28 August 1998. Lock.

Lock No 66

WRENN ID
weathered-stone-sepia
Grade
II
Local Planning Authority
Brecon Beacons National Park
Constituency
Brecon, Radnor and Cwm Tawe MP: David Chadwick (LD)
Country
Wales
Date first listed
28 August 1998
Type
Lock
Address
Lock No 66, Cwm Crawnon, Llangynidr, Powys
OS grid reference
SO 140 198
Coordinates
51.87057, -3.25006
Source
Cadw listing

Also on this page: flood risk · radon risk · weather exposure · detailed attributes ↓

Description

Lock No 66 is the lower lock in a group of three that completes a flight of five locks west of Llangynidr. This lock is part of a 37-kilometer stretch of canal and raises the water level by 17 meters towards Brecon. The lock chamber has been partly refaced in brick, and the gates were replaced in 1993. There is a by-pass overflow to the west.

Local climate

Lock No 66 sits in one of the wettest parts of the UK, with an average of 1,180 mm of rain a year. This makes it wetter than 90% of listed buildings in the UK. Its exposure to wind-driven rain is greater than that of 78% of listed buildings.

It experiences an average of 57 freeze-thaw cycles a year, more than 96% of listed buildings. Of these, 32 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.

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Nearby listed buildings

  1. Lock No 67 Grade II 132 m
  2. Lock No 68 Grade II 190 m
  3. Tofs Lock Bridge (Canal Bridge No 135) Grade II 315 m
  4. Coombes Lock Bridge (Canal Bridge No 134) Grade II 324 m
  5. Limekiln at Monmouthshire and Brecon Canal Sanitary Station Grade II 350 m
  6. Lock No 65 Grade II 378 m
  7. Embanked Aqueduct carrying Monmouthshire and Brecon Canal over Afon Crawnon Grade II 423 m
  8. Workhouse Bridge (Canal Bridge No 136) Grade II 612 m
  9. Workhouse Bridge (Canal Bridge No.136) Grade II 615 m
  10. Lower Lock Bridge (Canal Bridge No 132), including Lock No 64 Grade II 687 m