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King George V Reservoir
Enfield and Chingford, London, UK
associated engineer
William Booth Bryan
date  1908 - 15th March 1913
UK era  Modern  |  category  Dam/Reservoir  |  reference  TQ372966
ICE reference number  HEW 2222
The King George V is one of a group of reservoirs in the lower Lea Valley. It stores water for subsequent treatment downstream and has the largest surface area of any London reservoir. It is bounded to the east by the Lee Navigation and by the diverted River Lea to the west.
The reservoir was constructed as part of an overall strategy for the Lea Valley, subject to a Royal Commission in 1893. At that time the site was marshland used for pasture, owned by the East London Water Works Company (founded 1807), which became part of the Metropolitan Water Board in 1904. King George V led the inauguration ceremony for the reservoir on 15th March 1913.
The non-impounding reservoir is supplied from the River Lea by a pumping station (TQ373979) at its north west corner. Both were designed by William Booth Bryan (1848-1914), Chief Engineer from 1882 onwards to both the East London Water Works Company and later the Metropolitan Water Board.
The reservoir consists of two basins (north and south) divided by an earth embankment that has three large-diameter uncontrolled culverts through it. The combined surface area is some 170ha. The 6.5km long perimeter embankment encloses 12,500 million litres of water, 7.5m deep. This embankment has a puddled clay core and is a maximum of 8m high. Its external slopes are formed from river gravels and alluvial deposits and it's founded on soft clay over sandy gravel above London clay.
Four cast iron outlet pipes from the pumping station discharge water through vertical bar screens into a weir that forms the inlet to the reservoir. This structure consists of a brick chamber with a chamfered granite sill, flanked by stepped brick walls with granite copings. It was given Grade II listing in 1991.
The outlet tower (TQ374951) at the south east corner of the reservoir discharges untreated water through a tunnel under the embankment into the open channel of the River Lea diversion. This flows downstream via another pumping station at Chingford Mill (TQ362926), now disused.
During the drought years of 1933-4, the reservoir was empty at times and was only ever quarter full at most. In World War II (1939-45) it was drawn down by 1.5m for safety but on refilling after the war, it leaked.
The Metropolitan Water Board was abolished in 1974 and Thames Water Authority (now Thames Water) assumed responsibility for its undertakings, including the Lea Valley reservoirs, the water of which is now treated at the Coppermill Water Treatment Works (TQ354882). In 2004 the reservoir was drained for improvement works to the outlet facilities.
Following a statutory inspection, in 2008 a safety recommendation was made to increase the reservoir's existing emergency drawdown capacity significantly, to make possible a 1m drawdown in 24 hours. This effect this, twin siphon pipes fitted with submerged discharge valves were installed. Each valve is 8m high with a bore of 1.2m and a flow rate of 7,000 litres per second.
This reservoir and the later William Girling Reservoir (TQ366940) to the south are known collectively as the Chingford Reservoirs. They are designated a Site of Special Scientific Interest for their varied bird life. The King George V Reservoir is particularly noted for populations of great crested grebe.
Siphon valves (2008): Blackhall Engineering Ltd
Research: ECPK
"Obituary: William Booth Bryan, 1848-1914", in ICE Proceedings, Vol.199, pp.447-449, London, 1915
"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

King George V Reservoir