20 June 2018
Welsh Bridges: 7. Craig Goch Dam
The other Elan Valley dams are also well worth visiting, but in the absence of bridges I won't be featuring them here. Someone else will have to start their own blog. "Weir Weirdos", I suggest.
The Elan Valley dams and reservoirs were constructed under the direction of engineer James Mansergh on behalf of the Corporation of Birmingham, a city some 75 miles away. Water carried from the Elan reservoirs apparently takes about a day and a half to reach Birmingham, all by gravity flow.
The dam is some 156m long, 36m tall, and 32m thick at its base, a masonry giant surmounted by 13 segmental arch spans. Note that I've taken the 156m figure from an information board nearby - the plaque picture above gives a shorter length for the "length of weir".
It's a beautiful and very well-put-together structure. The viaduct piers merge smoothly into the curved profile of the dam spillway, and the contrast between the spillway's smooth stone facing and the viaduct's rough stone facing is effective (although I think this is the effect of many years of water flow, not an original feature).
The detailing of the viaduct is admirable in pretty much every respect, and doubly so on the lovely octagonal valve tower.
The viaduct is masonry faced on its elevations, but with a narrow band of brickwork forming the arch barrels in between. There are drain holes at every span in the roadway, and surface water drains out through the piers directly onto the dam spillway.
The view downstream from the dam is spectacular, and the road journey from here westwards through the beautiful hills to Cymystwyth is also recommended (I had come that way after visiting Llanilar Suspension Bridge).
The Coflein website has aerial photos, as well as some photographs of the dam under construction.