Editing Thames Barrier (section)

===Background===
Flooding in London has been a problem since [[Roman Britain|Roman]] times.<ref name=":1">{{cite journal |last=Kendrick |first=Mary |author-link=Mary Kendrick |date=1988 |title=The Thames Barrier |journal=Landscape and Urban Planning |volume=16 |issue=1–2 |pages=57–68 |doi=10.1016/0169-2046(88)90034-5|bibcode=1988LUrbP..16...57K }}</ref> In 1954, the Waverley Committee, established to investigate the serious [[North Sea flood of 1953]] which affected parts of the [[Thames Estuary]] and parts of London, recommended that "as an alternative to raising the banks, the possibility and cost of erecting a structure across the Thames which could be closed in a surge should be urgently investigated".<ref>
{{cite hansard |title=Coastal Flooding (Committee's Report) |url=https://api.parliament.uk/historic-hansard/written-answers/1954/jun/03/coastal-flooding-committees-report |house=House of Commons |date=3 June 1954 |volume=528 |column_start=104 |column_end=5W |speaker=[[David Maxwell Fyfe, 1st Earl of Kilmuir|D. Maxwell Fyfe]] |position=[[Home Secretary]] |hansard=Written Answers (Hansard)}}</ref> A number of designs were put forward, from a huge road viaduct with two 500 foot (150 m) [[sluice gate]]s crossing the Thames at [[Crayford]]ness to flap gates lying on the [[river bed]] and floated up by [[compressed air]].<ref name=":0">{{cite book |last1=Gilbert |first1=Stuart |last2=Horner |first2=Ray |title=The Thames Barrier |year=1984 |publisher=T. Telford |location=London |isbn=978-0-7277-0182-4 |oclc=11594001}}</ref>{{page needed|date=March 2021}} By 1965, when the [[Greater London Council]] (GLC) took over responsibility, two major schemes were under consideration, costed at £24 million and £41 million respectively (£500 million and £800 million at 2020 prices).<ref name=":0"/>{{page needed|date=March 2021}}

In 1966, Sir [[Hermann Bondi]] was asked to take an independent view of the situation. He considered the estimated construction costs and the probability of a flood and of damage if the barrier was not built. He strongly recommended that a barrier should be built in order to avoid the catastrophe of flooding central London, and a site was agreed at Woolwich.<ref name=":0" />{{page needed|date=March 2021}}

The barrier protects central London against a [[storm surge]], caused when a deep depression forms to the north of Scotland and progresses across the [[North Sea]] and south-easterly towards southern Scandinavia. When such a surge coincides with a high [[spring tide]], the high winds associated with the depression can funnel the water up the [[Thames Estuary]] and cause surges of up to 3.5 metres (11.6 feet). The planners assessed that in the absence of a barrier, such a surge could inundate 45 square miles (117&nbsp;km<sup>2</sup>) of land, put hospitals, power stations and the [[London Underground]] out of action and cause damage estimated in 1966 at £2 billion<ref>''The Thames Barrier: The Background and Basic Engineering Requirements''. D Ayres Director of Public Health Engineering, GLC. 1983. Paper presented to a meeting of the Institution of Mechanical Engineers, 8th June 1983</ref> (about £50 billion at 2020 prices). The barrier was designed to provide a flood defence capable of resisting a once in 1000 year surge tide at a base date of 2030.