Technical Information on Scammonden Water
The catchment area in the Scammonden Valley is 1650 acres supplemented by an area in the Colne Valley of 3350 acres, making a total of 5000 acres.
The average rainfall over the catchment area is 52" per annum, but 18" of this escapes in deep percolation and evaporation, leaving only 34" to fill the reservoir.
The rainfall over this area gives approximately 8.7 million gallons per day (mgd).
After allowing for the compensation water and the yield of the Deanhead reservoir (which was built in 1840) the amount of water available from Scammonden Water is 6mgd.
- The area of the water surface when the reservoir is full is 104 acres
- The level of the bellmouth spillway above sea level is 826 feet
- The reservoir holds 1,730 million gallons
- Its maximum length is 0.9 miles, and the maximum depth is 170 feet
- The dam's maximum height above the valley floor is 242 feet
- The length of the motorway section is 2,050 feet
- The width of the dam wall at its highest point is 180 feet
- Over 5 million cubic yards of material were used in the construction
- The overflow shaft by the tower is 175 feet deep (equivalent to a 20 storey block of flats)
The fixed concrete arch of Scammonden Bridge has a span of 410 feet and rises to 120 feet above the motorway.
The Bradshaw Tunnel
The entrance to the Bradshaw tunnel is concealed under the water at the stream end of the reservoir and is only visible when the water level falls. It is nearly 1 ¾ miles long and links the Colne Valley with Scammonden. At its deepest it is 360 feet just below Nont Sarah's Hotel. Under flood conditions it can carry up to 30 million gallons of water per day.