Operational since 1982, its purpose is to prevent the floodplain of all but the easternmost boroughs of Greater London from being flooded by exceptionally high tides and storm surges moving up from the North Sea.
London is vulnerable to flooding and from heavy tides closing in. A storm surge generated by low pressure in the Atlantic Ocean sometimes tracks eastwards past the north of Scotland and may then be driven into the shallow waters of the North Sea. The surge tide is funnelled down the North Sea which narrows towards the English Channel and the Thames Estuary. If the storm surge coincides with a spring tide, dangerously high water levels can occur in the Thames Estuary. This situation combined with downstream flows in the Thames provides the triggers for flood defence operations. The report of Sir Hermann Bondi on the North Sea flood of 1953 affecting parts of the Thames Estuary and parts of London was instrumental in the building of the barrier.
When needed, it is closed (raised) during high tide; at low tide it can be opened to enhance the river’s flow towards the sea.
Built approximately 3 km due east of the Isle of Dogs, its northern bank is in Silvertown and its southern bank is in the New Charlton area of the Royal Borough of Greenwich.
The concept of the rotating gates was devised by (Reginald) Charles Draper. In the 1950s, from his parents’ house in Pellatt Grove, Wood Green, London, he constructed a working model. The novel rotating cylinders were based on a small household appliance — a brass gas tap which could be found in most post-war houses in the UK. The barrier was designed by Rendel, Palmer and Tritton for the Greater London Council and tested at the Hydraulics Research Station, Wallingford.
The site at New Charlton was chosen because of the relative straightness of the banks, and because the underlying river chalk was strong enough to support the barrier. Work began at the barrier site in 1974 and construction, which had been undertaken by a Costain/Hollandsche Beton Maatschappij/Tarmac Construction consortium, was largely complete by 1982. The gates of the barrier were made by Cleveland Bridge UK Ltd at Dent’s Wharf on the River Tees.
In addition to the barrier, the flood defences for 11 miles down river were raised and strengthened. The barrier was officially opened on 8 May 1984 by Queen Elizabeth II. Total construction cost was around £534 million with an additional £100 million for river defences.
Built across a 520-metre wide stretch of the river, the barrier divides the river into four 61-metre and two, approximately 30 metre (100 ft) navigable spans. There are also four smaller non-navigable channels between nine concrete piers and two abutments. The flood gates across the openings are circular segments in cross section, and they operate by rotating, raised to allow ’underspill’ to allow operators to control upstream levels and a complete 180 degree rotation for maintenance. All the gates are hollow and made of steel up to 40 millimetres thick. The gates fill with water when submerged and empty as they emerge from the river. The four large central gates are 20.1 metres high and weigh 3,700 tonnes. Four radial gates by the riverbanks, also about 30 metres wide, can be lowered. These gate openings, unlike the main six, are non-navigable.
