OS Grid Ref: NH 22393 10846 (access tunnel portal)
Date opened: 1959
Date closed : Operational
The tailrace at Ceannacroc discharges into the river Moriston a little
distance from the power station. The road bridge in the foreground carries
an estate road over the tailrace channel, and doubles as the support structure
for the stoplog gates, used to hold the river water out of the tailrace
when it's dewatered for maintenance:
Photo: Ceannacroc Tailrace
Photo by: Mike
Ross
This drawing shows how the tailrace fits into the scheme of things:
Illustration: Ceannacroc Tailrace
Illustration by: Scanned by Mike Ross, from Proceedings of the Institution
of Civil Engineers, Sept. 1958
The tailrace tunnel is free-flowing; there's always airspace above the
water. It's a substantial tunnel. Just how substantial is only revealed...:
Photo: Ceannacroc Tailrace
Photo by: Mike Ross
...when it's dewatered for maintenance:
Photo: Ceannacroc Tailrace
Photo by: Mike
Ross
Another view at a different stage of maintenance. The ladders and scaffolding
for repointing the stonework give an idea of scale - it's horseshoe section,
19ft equivalent diameter, 1,700ft long. Descending the scaffold tower on
the right, into the tailrace, and looking back, we see...:
Photo: Ceannacroc Tailrace
Photo by: Mike Ross
...the road bridge/stoplog gantry, with the stoplog gates in place - the
other side of those gates is the River Moriston:
Photo: Ceannacroc Tailrace
Photo by: Mike Ross
Moving now to the other end of the tailrace, inside the power station. Since there is always airspace above the water in the tailrace, it was possible to drive an adit from the main chamber of the power station into the tailrace tunnel, for ventilation. Here's we're looking through the doorway, concealed behind some equipment rack on the main floor of the power station, which leads to the adit. Ahead, there's a concrete wall with climbing steps in it - this was put in to protect the station from flooding through this tunnel, in the case that a machine trip, surge and backsurge in the tailrace, occured at the same time as an enormous flood in the river outside:
Photo: Ceannacroc Tailrace
Photo by: Mike Ross
View from the top of the wall - a short, poorly lit, unlined adit runs
forward:
Photo: Ceannacroc Tailrace
Photo by: Mike Ross
Looking back from the wall into the power station:
Photo: Ceannacroc Tailrace
Photo by: Mike
Ross
Moving forward from the wall, after a short distance the adit turns sharp
right:
Photo: Ceannacroc Tailrace
Photo by: Mike Ross
Turning right, the adit ends after just a few feet, in a concrete plug
with a 'window', and a hole in the floor:
Photo: Ceannacroc Tailrace
Photo by: Mike
Ross
Quite a forbidding hole, with a very loud roar of surging water coming
up from it:
Photo: Ceannacroc Tailrace
Photo by: Mike
Ross
Ahhh... peering cautiously into the hole, it's revealed to be a 'window'
in the roof of the tailrace, immediately above the exit of the draft tube
from the 4MW machine. Water boils up from the draft tube and surges right-to-left
down the tailrace tunnel:
Photo: Ceannacroc Tailrace
Photo by: Mike
Ross
Leaning over still more cautiously, just a few feet downstream the right
wall ends, and the much larger discharge from the draft tubes of the main
22MW set is boiling up and surging away down the tailrace tunnel (the pipe
is the station dewatering pipe - seepage/leakage water collects in a sump
at the lowest level of the station, from where it is pumped 'overboard'
into the tailrace):
Photo: Ceannacroc Tailrace
Photo by: Mike
Ross
I returned to the same spot during refurbishment. Tailrace dry, cables
and hoses lying in the tunnel where the water is surging in the previous
picture:
Photo: Ceannacroc Tailrace
Photo by: Mike
Ross
Looking straight down from the 'window'. The normal water level is visible
as a 'tide mark' on the wall, but with no water there you can see the outlet
of the draft tube from the 4MW unit:
Photo: Ceannacroc Tailrace
Photo by: Mike
Ross
Descending the climbing staples gets us into the tailrace and allows us
to look back up at the 'window' from below:
Photo: Ceannacroc Tailrace
Photo by: Mike
Ross
Looking straight ahead from the above shot, the upwards-curving outlet
of the draft tube for the 4MW set:
Photo: Ceannacroc Tailrace
Photo by: Mike
Ross
Looking straight up at the 'window' to the adit from which we've just descended:
Photo: Ceannacroc Tailrace
Photo by: Mike
Ross
Finally, stepping back a few feet into the (very humid) tailrace proper,
we see the 4MW set tailrace and the 'window' on the left, and (through
the mist) the outlet from the 22MW draft tubes into the tailrace on the
right. The sharp edge of the 'splitter wall' which divides the two tailrace
channels is very clear. Directly behind me in this shot, the tailrace tunnel
runs straight for 1,700ft to the outfall:
Photo: Ceannacroc Tailrace
Photo by: Mike
Ross
