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Queen Mary Reservoir
Staines Road, Ashford, Surrey, UK
associated engineer
Henry Edward Stilgoe
date  1922 - December 1924, 2007 - 2008
era  Modern  |  category  Dam/Reservoir  |  reference  TQ070695
ICE reference number  HEW 2226
Once the largest reservoir in the world, the elevated Queen Mary Reservoir, just north of the M3 motorway, stores water from the River Thames and supplies western London and Surrey. It is a popular location for water sports.
Queen Mary was the first large reservoir completed by the Metropolitan Water Board, who assumed responsibility for London’s water supply in 1904. Construction was authorised in the Metropolitan Water Board (Various Powers) Act 1921 and design carried out by the board’s Chief Engineer Henry Stilgoe (1867-1943).
The non-impounding reservoir is raised some 12m above the surrounding area. Water is pumped into it from the Thames via the Laleham intake channel by Littleton Pumping Station (TQ060696) at the western apex of the reservoir. In plan it is almost hexagonal and its embankment dam is 6.3km long, with a narrow core of puddled clay and gravel/earth shoulders at a slope of 1 in 3. Its capacity is 30,500 million litres with a surface water area of 286ha.
A central baffle breakwater extends 1km southwards from the north bank. This structure is another gravel/earth embankment capped with a concrete walkway, designed to limit wind-driven wave action. However, under south westerly winds algae accumulates on its west side.
The reservoir was completed in December 1924 and opened officially by King George V in June 1925. Referred to originally as Littleton Reservoir, it was renamed for the queen on opening day. It was the largest reservoir in the world when built and remained so for at least 25 years.
The embankment was damaged by World War II (1939-45) bombing. As the Metropolitan Water Board had taken the precaution of lowering all reservoir water levels by 1.5m at the outset of the war, no water was lost at this or any other similarly-damaged reservoir. Thames Water Authority (known as Thames Water after 1989) took over from the Metropolitan Water Board in 1974.
Following a statutory inspection, in 2007 a safety recommendation was made to increase the emergency draw-down capacity of the reservoir significantly — to achieve 750mm emergency draw down from top water level within 24 hours. This was done by installing twin siphon pipes fitted with submerged discharge valves in stilling chambers, which release water into Laleham Aqueduct west of the original pumping station.
Each computer-operated valve is 13m tall with an internal diameter of 1.6m, weighs more than 22 tonnes and has a flow rate of 13,000 litres per second. The 1.6m bore welded steel pipes between the valves and the aqueduct are each some 250m long.
Historically, aggregates have been dredged from the bottom of the reservoir, resulting in an uneven bed. Thames Water wanted to improve water circulation, so the reservoir and underlying ground were digitally modelled to locate suitable extraction areas. In 2008, planning approval was granted for the outer two thirds of the baffle to be removed and 1.25 million tonnes of sand and gravel to be extracted, increasing reservoir capacity by 1.26 percent.
The dredging arisings were transferred to a stockpile west of the reservoir by conveyor for recycling. Dredging will continue until the end of 2013 and the material will be processed until the end of 2033, after which the site will be restored and landscaped.
The land to the west of the reservoir and the reservoir itself are designated Sites of Nature Conservation Importance, covering some 360ha and noted for their varied bird life. The reservoir is not open to the public, though a sailing club (founded in 1972) uses it for wind-based water sports. The UK’s largest inland dinghy race — the Bloody Mary pursuit race — has been held here since 1973.
Contractor: S. Pearson & Son Ltd
Contractor (2007-8): David George Consultancy Ltd
Contractor (2007-8): Barhale
Siphon Valves (2007-8): Blackhall Engineering Ltd
Digital modelling (2007): Black & Veatch
Research: ECPK
"Obituary: Henry Edward Stilgoe, 1867-1943", in ICE Journal, Vol.20, pp.202-203, London, June 1943
"Queen Mary and King George V emergency draw down schemes" by Bryn Philpott, Yinka Oyeyemi and John Sawyer, in Dams and Reservoirs, Vol.19, pp.79-84, London, June 2009
reference sources   CEH Lond

Queen Mary Reservoir