The catchment area in the Scammonden Valley is 670 hectares supplimented by an area of the Colne Valley of 1330 hectares, making a total of 2000 hectares.
The average rainfall over the catchment area is 132 cm per annum, but 46 cm of this escapes in deep percolation and evaporation, leaving only 86 cm to fill the reservoir.
The rainfallover this area gives approximately 39 million litres per day (mld).
After allowing for the compensation water and the yield of the Deanhead Reservoir (which was built in 1840) the amount of water available to Scammonden Water is 27 mld.
The area of the water surface when the reservoir is full is 42 hectares.
The level of the bellmouth overflow above sea level is 252 metres.
The reservoir holds 7800 million litres.
Its length is 1.4 km.
The maximum height above the valley floor is 74 m.
The length of the motorway level is 625 m.
The width at the is 55 m.
Over 4,600,000 cubic metres of meterial were used in construction.
The overflow shaft (by the tower) is 53 m deep (equivalent to a 20 storey block of flats).
The fixed concrete arch of Scammonden Bridge has a span of 125 m and rises to 37 m above the motorway. It was the longest single-span non-suspension bridge in the world when it was built.
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 2.8 km long and links the Colne Valley with Scammonden. At its deepest it is 110 metres underground, below the Nont Sarah's Public House. Under flood conditions it can carrry up to 135 milion litres of water per day.