It occupies 350 acres (1.4 km2) and holds 3,493 million gallons (15,880,000 m3)[1] or, per The Times, 4,466 million gallons.[2] The top of its banks are 56 ft (17 m) above the surrounds. The enclosing bank crest measures 5.23 km.[2] Like its Lower Thames siblings, it is of earthen dam build: a puddled clay lining and embankments from materials excavated on site, particularly ballast (heavier aggregates).[3] It has been built-up from dry land as the eastern Thames Basin lacked sufficiently watered, largely unpopulated, agriculturally unprized vales to be dammed near to which conveniently coal-supplied treatment works and pipes to London could be built.
A tendered bid for the work – at £1,292,000, equivalent to £105,300,000 in 2023 – was accepted in July 1937. The contractor was John Mowlem and Co. Limited.[2]
The land purchase was likely connected with gravel extraction locally. Four such firms were digging for aggregates in Stanwell in 1956, employing nearly 100 people.[6]
Operation, sheep and notable birds
This and the Staines Reservoirs, built 1902, receive their input from the Thames at Hythe End, Wraysbury above Bell Weir Lock and the mouth of the Colne Brook. The reservoir's inlet valve tower is south, north of a pumping station; the outlet one is east, being gravity-fed. Input and output are to and from the Staines Reservoirs Aqueduct, feeding the Water Treatment Works at Kempton Park and another at Hampton.
To ease inspection of banks, a flock of sheep is kept on them which keeps them close-cropped.[7]
^Smith, Denis (2001). Civil Engineering Heritage. Thomas Telford, UK ISBN0-7277-2876-8
^ abcd"350-acre reservoir opening at Staines by the King today". The Times. 7 November 1947. p. 3.
^Hewlett, Henry (2004). Long-Term Benefits and Performance of Dams (Proceedings the 13th Conference of the British Dam Society held at the University of Kent, June 2004). Thomas Telford, UK.
^Gallop, Alan (2005). Time Flies: Heathrow At 60. Stroud: Sutton Publishing. p. 36. ISBN1-85310-259-8.
