Staines Reservoirs

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Stanwell and the Staines Reservoirs in 2011

The Staines Reservoirs are two large pumped-storage reservoirs that lie to the east of the King George VI Reservoir near Heathrow Airport in Middlesex. The village of Stanwell is to the north-east, and the town of Staines is to the south. The two reservoirs are situated between the A3044 and the A30. They were completed in 1902.[1]


To provide for a reliable and plentiful supply of water, three London water companies planned to jointly construct and operate two large reservoirs at Staines.[2] These would be pumped storage reservoirs to hold water abstracted from the Thames[3] and deliver it through aqueducts to the treatment works and supply pipes of the constituent companies. The three organisations were the New River Company, the Grand Junction Water Company and the West Middlesex Water Company.[4]

To obtain the legal powers required they promoted the Staines Reservoir Bill in Parliament in 1896.[4] The Bill was opposed by the London County Council, the Middlesex County Council and local landowners. Nevertheless, the Bill was enacted, with amendments, as the Staines Reservoirs, &c. Act 1896 (59 & 60 Vict. c.ccxli).[4] The companies formed a joint committee to oversee the construction.[2] The two reservoirs, North and South, are separated by a ⅔-mile-long embankment dam. The dams of both reservoirs have a 20ft- to 26ft-deep puddle clay core extending through the surface gravel into the underlying London Clay.[5] The reservoirs and have a combined capacity of 3,338 million gallons and were completed in 1902.[4] The valve towers for each reservoir are located at the west end of the dividing embankment.

Soon after completion of the reservoirs in 1902 the three water companies, and seven others, became part of the Metropolitan Water Board which was established under the provisions of the Metropolis Water Act 1902 (2 Edw. VII, c.41).


The reservoirs are filled from the Staines Reservoirs Aqueduct, built as part of the works. Water was originally lifted from the aqueduct to the reservoirs by five steam driven engines, each with a capacity of 16 million gallons per day.[2] The engines were housed in Staines pumping station south-west of the south reservoir. Under the original legal provisions, when the flow of the river at Bell Weir exceeded 265 million gallons a day, the joint company could abstract any surplus up to 100 million gallons of which 35 million gallons could be run directly to the filter beds at Hampton and the surplus pumped into the reservoirs.[6] The top water level in the North Reservoir is 10 feet higher than the South reservoir.[5] Water for treatment and use is drawn from the reservoirs through the valve towers and delivered to the aqueduct to flow south-east to several water treatment works.

The Metropolitan Water Board operated the reservoirs until the Board was abolished in 1974 under the provisions of the Water Act 1973 and ownership and control transferred to the Thames Water Authority, now Thames Water.

In 1992 there was a proposal to increase the capacity of the reservoirs by raising the height of the dam walls and removing the dividing embankment.[7] The work was estimated to take up to six years to complete.

From April 2020 a sheet pile cut-off wall was installed in two places to prevent leakage of water through the core of the south reservoir's embankment.[8]

The area has been designated a Site of Special Scientific Interest as it carries important wintering populations of tufted ducks, pochard, goosander and goldeneye.[9]

Staines Reservoirs Aqueduct

The Staines Reservoirs Aqueduct is a eight-mile aqueduct[10] that runs from the River Thames at Hythe End in Buckinghamshire (51°26'24.4"N 0°32'28.8"W) to the Red House distribution reservoir (51°25'11.6"N 0°23'20.4"W) near Kempton Park.[10] It was built by the Staines Reservoirs Joint Committee and originally completed in 1902.[6] The maximum flow capacity of the aqueduct is 475,000 cubic yards per day.[10]

Thames Water has historical images of the construction of the Staines Reservoirs Aqueduct.[11]

Water is drawn from the north side of the Thames about 300 yards above Bell Weir, at a decorative sluice house.[2] This is provided with sluices to control the flow and screens to prevent debris entering the aqueduct. The water runs underground for about 350 yards in a north-east direction, it then flows in two steel siphons under the Colne Brook. It continues in a concrete lined open conduit, before going under the Wraysbury river in steel siphons, then east across Staines Moor and another siphon under the River Colne to Staines pumping station. From here water is lifted into the Staines and King George VI reservoirs by pumps.[2]

Water for treatment and use is drawn from the Staines and King George VI Reservoirs and flows along the Staines Reservoirs Aqueduct in an east-south-east direction to Ashford, then around the north side of Queen Mary Reservoir, water discharged from the reservoir enters the aqueduct at this point. The aqueduct continues across Ashford Common with a connection to Ashford Common water treatment works and then across Sunbury Common.[12] From Sunbury Common the aqueduct changes direction to the north-east, it curves around the north side of Kempton Park race course with connections to Sunbury and Kempton Park water treatment works, and flows in a south-east direction into the Red House distribution reservoir (51°25'11.6"N 0°23'20.4"W).[13] From here a pipeline and an open aqueduct takes water south to the reservoirs at the west end of Hampton waterworks.[14] From 1916 experiments were undertaken to pre-treat the water in the aqueduct with chlorine added to the water from the Staines reservoirs.[14]  

To increase the supply of water the aqueduct was paralleled underground in the 1960s by the Staines–Kempton aqueduct tunnel.[15] This was built by the Metropolitan Water Board between 1960–63 and runs from Little Hythe on the Thames to the water treatment works at Kempton Park. It is five miles long and eight feet wide.[10] The tunnel is lined with 150,000 expanded concrete wedge blocks, the contractors for the project were Edmund Nuttall, Sons and Company Limited.[16]

In February 2014 after a sustained period of heavy rain the River Thames was at a high level which caused water to back up in the River Colne.[17] This then spilt into the Staines Reservoirs Aqueduct which channelled the water to Staines. The aqueduct spilt over into the River Ash which over topped its banks and flooded about 80 houses in the Leacroft and Priory Green area and damaged the aqueduct.[18]


  1. British History on line
  2. 2.0 2.1 2.2 2.3 2.4 Hunter, W. (1 October 1901). "Visit to the Staines Reservoir Works". Journal of the Sanitary Institute 22 (4): 571–73. 
  3. Bell, F. G. (1979). Engineering Geology and Geotechnics. Butterworth-Heinemann Ltd,. pp. 268–9. ISBN 9780408003551. 
  4. 4.0 4.1 4.2 4.3 London Metropolitan Archives (1897-1902). "Staines reservoir joint committee: water supply and distribution". Retrieved 16 June 2020. 
  5. 5.0 5.1 "Long-term stress measurements in the clay cores of storage reservoir embankments". Retrieved 17 June 2020. 
  6. 6.0 6.1 "The Staines Reservoirs". The Times: p. 5. 18 June 1901. 
  7. "Water Resources Development Options". September 1992. Retrieved 17 June 2020. 
  8. "Reservoir work to keep London's taps flowing for another 120 years". 14 April 2020. Retrieved 18 June 2020. 
  9. Colne Valley Park
  10. 10.0 10.1 10.2 10.3 "Staines-Kempton Tunnel Aqueduct". 1960. Retrieved 16 June 2020. 
  11. Thames Water. "Staines Aqueduct". Retrieved 17 June 2020. 
  12. Ordnance Survey Six-inch map, Middlesex XXIV.NE, dated 1920
  13. Ordnance Survey six-inch map, London Sheet Q, dated 1920
  14. 14.0 14.1 Wray, Anthony (December 2015). "Water Quality, Morbidity, and Mortality in London,1906-1926". Retrieved 16 June 2020. 
  15. Cuthbert, Eric William and Frank Wood (1962). "The Thames-Lee tunnel water main". Retrieved 19 June 2020. 
  16. "A new water tunnel". New Scientist 8 (no. 201): 788. 22 September 1960. 
  17. Surrey County Council (20 April 2015). "Flood Investigation Report River Ash and Knowle Green Area". Retrieved 19 June 2020. 
  18. Goble, R. A.. "Staines aqueduct Flooding 2014". Retrieved 19 June 2020. 

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