Island Barn Reservoir


The Island Barn Reservoir lies south of the River Thames in England at West Molesey and north of Lower Green Esher. The reservoir is large with a capacity of 992 million gallons and is managed by Thames Water. It is within the borough of Elmbridge and is surrounded by the River Mole to the west and the River Ember to the east. Queen Elizabeth II Reservoir is a larger reservoir to the West.

History

Island Barn Reservoir was authorized by the Lambeth Water Act 1900 . It was built by Sir Robert McAlpine for the Metropolitan Water Board, and opened in 1911. The contract was valued at £152,727.

Construction

The embankment walls have a puddle clay core extending down through a gravel layer to the underlying blue London clay. The outside face of the embankment is grassed, the inner face is lined with concrete slabs.
The key dimensions of the Island Barn reservoir are as follows.
ParameterValue
Capacity900 million gallons
Surface area121 acres
Perimeter1 mile 1,200  yards
Base to top of bank35 ft
Base to top water level30 ft
Height of bank24 ft to 34 ft
Depth of puddle core15 ft to 25 ft
Embankment volume1.27 million tonnes
Maximum height of water17.59 m AOD

Operation

Raw water, from the River Thames, is pumped 2.7 km through a 54 inch diameter pipeline from the pump house at Walton Water Works adjacent to the Knight reservoir. The reservoir can also be filled by gravity from the Bessborough and Knight reservoirs.
The reservoir allows some settlement of suspended solids; biological cleaning through exposure to sunlight; and provides a buffer storage volume to maintain capacity at times of low flow in the river.
Water is supplied to the Surbiton water treatment works.
For several years leakage through the embankment had been observed. A survey identified three areas of leakage. In 2017 interlocking sheet piling 18.5 m long was driven vertically through the centre of the embankment into the London clay to stop the leakage.
Between 1992 and 1998 1.3 million tonnes of gravel were removed from the base of the reservoir.

Sailing Club

Island Barn Reservoir Sailing Club hosts dinghy sailing races and training at the reservoir. Among many successful current and past members has been Fireball world champion and ISO designer John Caig and British Olympic, European Champion and World Cup sailor Nicola Groves.
The reservoir is a bird watching site and Black-necked grebes have been sighted here.

Gallery