Editing Thames Barrier (section)

===Design and construction===
[[File:Thames Barrier - simple operation diagram.png|thumb|right|upright=1.2|Diagram showing how the gates work, though the barrier actually rises further than this to allow water to "underspill" under the barrier in a controlled fashion]]

The concept of the rising sector gates was devised by (Reginald) Charles Drapeer. In 1969, from his parents' house in Pellatt Grove, [[Wood Green]], London, he constructed a working model. The novel rotating cylinders were based on the design of the [[Tap (valve)|tap]]s on his [[gas cooker]]. The barrier was designed by Rendel, Palmer and Tritton for the [[Greater London Council]] and the concept tested at the [[Hydraulics Research Station]], Wallingford.<ref name=":1" /> 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.

The Thames Barrier and Flood Prevention Act, authorising construction, was passed in 1972. In 1974, the GLC placed the two major construction contracts. Civil construction was undertaken by a [[Costain Group|Costain]]/[[Royal BAM Group|Hollandsche Beton Maatschappij]]/[[Tarmac Group|Tarmac Construction]] consortium.<ref name=":0" />{{page needed|date=March 2021}} A separate contract for the gates and operating machinery was placed with the Davy Cleveland Barrier Consortium, formed by Davy McKee Ltd of Sheffield and [[Cleveland Bridge & Engineering Company|Cleveland Bridge UK Ltd]].<ref>{{cite web |url=https://www.gracesguide.co.uk/Davy_Cleveland_Barrier_Consortium |title=Davy Cleveland Barrier Consortium |author=<!--No author named.--> |date=30 July 2019 |website=Grace's Guide |url-status=live |archive-url=https://web.archive.org/web/20201124201649/https://www.gracesguide.co.uk/Davy_Cleveland_Barrier_Consortium |archive-date=2020-11-24}}</ref><ref name=":0" />{{page needed|date=March 2021}}

Work began at the barrier site in 1974 and progressed in two phases. The southern piers (9 to 6) were built first, with river traffic diverted to the north side, then traffic routed through the completed southern spans whilst the north side piers (1 to 5) were built. During construction of the piers, precast concrete sills were built in a [[cofferdam]] on the north side of the river and floated out and sunk between the piers to form the gate recesses, with access tunnels at the upstream and downstream ends.<ref>{{cite web |url=http://www.environment-agency.gov.uk/homeandleisure/floods/38355.aspx |title=Engineers and main contractors for the building of the Thames Barrier |author=<!--No author named.--> |publisher=Environment Agency |url-status=dead |archive-url=http://webarchive.nationalarchives.gov.uk/20090205134525/http://www.environment-agency.gov.uk/homeandleisure/floods/38355.aspx |archive-date=5 February 2009 |access-date=13 March 2021 }}</ref>

The gates of the barrier were fabricated in sections at Cleveland Bridge's [[Darlington]] works and assembled at [[Port Clarence]] on the [[River Tees]].<ref>{{cite journal |last=Horner |first=R. W. |date=July 1979 |title=The Thames Barrier Project |journal=The Geographical Journal |volume=145 |issue=2 |pages=242–253 |doi=10.2307/634390 |jstor=634390|bibcode=1979GeogJ.145..242H }}</ref>{{rp|251}} The gates, gate arms and rocking beams were transported from the Tees to the Thames by barge and lifted into position by two very large floating cranes operated by Neptun of Hamburg (now part of [[Smit International]]).<ref>Manufacture and Installation of the Barrier Gates and Operating Machinery – P F Harvey, Davy Cleveland Barrier Consortium – Institution of Mechanical Engineers – Paper presented at a meeting on 8th June 1983.</ref> The mechanical and hydraulic machinery was built by Davy Loewy, Henry Berry and Vickers and trial assembled in Davy's Darnall works. Delays to the civil works required changes to the construction and installation sequence, but commissioning was relatively uneventful and the first trial operation of all the gates together was carried out on 31 October 1982.<ref>{{cite news |last=Clayton |first=Hugh |date=4 November 1982 |title=All 10 gates being raised at the Thames barrier |url=https://www.thetimes.com/tto/archive/frame/article/1982-11-04/3/1.html |work=The Times |page=3 |access-date=2021-03-12}}</ref>

In addition to the barrier, the flood defences {{convert|11|mi|order=flip}} down river were raised and strengthened. The barrier was officially opened on 8 May 1984 by Queen [[Elizabeth II]].<ref name=Guardian>{{cite news |title=Better way to turn the tide |newspaper=[[The Guardian]] |date=9 May 1984 |page=2 |url=https://www.newspapers.com/image/259609689/}} {{subscription required|via=Newspapers.com}}</ref> The barrier cost £{{Format price|461000000}} (£{{Format price|{{Inflation|UK-GDP|461000000|1984}}}} now).<ref name=Guardian />{{Inflation/fn|UK-GDP}} Total construction cost was around £535 million (£2.4 billion at 2024 prices)<ref name="EnvironmentAgencyMay2024">{{Cite web |url=https://www.gov.uk/government/news/the-thames-barrier-protecting-london-and-the-thames-estuary-for-40-years |title=The Thames Barrier – protecting London and the Thames Estuary for 40 years |author1=<!--No personal author name given.--> |date=2024-05-08 |department=Environment Agency |website=[[GOV.UK]] |type=Press release |url-status=live |archive-url=https://web.archive.org/web/20240508014811/https://www.gov.uk/government/news/the-thames-barrier-protecting-london-and-the-thames-estuary-for-40-years |archive-date=2024-05-08}}</ref> with an additional £100 million for river defences.{{citation needed|date=December 2024|reason=Additional river defences not mentioned in Environment Agency press release}}

Built across a {{convert|520|m|ft|adj=on}} wide stretch of the river, the barrier divides the river into four {{convert|61|m|ft|adj=on}} and two approximately 30-metre (100&nbsp;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 segment]]s 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 {{convert|40|mm|in}} thick. The gates are filled with water when submerged and empty as they emerge from the river. The four large central gates are {{convert|20.1|m|ft}} high and weigh 3,700 [[tonne]]s each.<ref>{{cite web |url=http://www.environment-agency.gov.uk/static/documents/Leisure/Thames_Barrier_2010_project_pack.pdf |title=The Thames Barrier Project Pack 2010 |publisher=Environment Agency |url-status=dead |archive-url=http://webarchive.nationalarchives.gov.uk/20101216014218/http://www.environment-agency.gov.uk/static/documents/Leisure/Thames_Barrier_2010_project_pack.pdf |archive-date=16 December 2010 |access-date=18 October 2011 }}</ref> Four radial gates by the river banks, also about 30 metres (100&nbsp;ft) wide, can be lowered. These gate openings, unlike the main six, are non-navigable.{{citation needed|date=November 2021}}