|
The Overflow Spillway Weir & Conduits The overflow weir or "spillway" is of a type known as a side channel spillway. It was built in concrete at the eastern end of the dam and was faced with stone from Jumbles Quarry.
Overflow weir & channel leading to the overflow conduits under construction - temporary railway line in the channel
The overflow weir over which surplus water from the reservoir is discharged, is 300ft. long and empties into 459ft. of open channel cut in the hillside on the east side of the dam embankment. This open flood water channel originally fed into three 700ft. long discharge conduits, each 8ft. in diameter, which fall 110ft. down the 1 in 6.6 gradient embankment slope into the tailbay pool below the dam.
The Overflow Conduits under construction - Timber centring in place and stone facing being set
Withdrawing the timber centres
The downstream ends of the overflow conduits Stocks Reservoir first overflowed on 3rd March, 1933. Following an infamous cloudburst over the fells between Slaidburn and Wray in August 1967 which caused flooding and massive damage to Water Board installations in the Forest of Bowland area, major modifications were made to the Stocks dam overflow channel and conduits.
Overflow spillway conduits during heavy rain - 12th December 1964 Photograph used by kind permission of Mrs. J. Lawson
There was a fear that debris, fallen trees etc. from a similar catastrophic flood might choke the spillway conduits and cause the dam to overflow the top of the earth embankment and wash it away. As a means of reducing the risk, the level of the spillway weir was lowered 4 ft. by removing the top layers of masonry thereby reducing the capacity of the reservoir.
Spillway weir alterations as seen in 1974 Photograph used by kind permission of E. & M.C. Higham
These emergency alterations were eventually tidied up and the masonry of the overflow spillway weir was permanently fixed. Alterations to the overflow bywash conduits were also made at this time.
Altered spillway weir & overflow bywash Photograph used by kind permission of Ken Geddes © 2004. All rights reserved.
An open concrete spillway chute was constructed on top of the existing overflow conduits to carry more surplus water if required.
Altered overflow bywash - open channel above the conduit pipes Photograph used by kind permission of Ken Geddes © 2004. All rights reserved.
|
