During the 80’s and 90’s, Frank and I were blessed with the opportunity to vacation in England several times. On a couple of those occasions, one of our sight-seeing highlights was a visit down the Thames River to the spectacular Great Thames Barrier. We had never heard of the barrier before and first encountered it on a trip to Greenwich, where the mean time used historically as the prime basis of standard time throughout the world was determined (now replaced by COORDINATED UNIVERSAL TIME). Greenwich is also the site where the British clipper ship Cutty Sark is moored. The Cutty Sark, built in 1869, was one of the last tall clippers to be built (also one of the fastest at the end of a long period of design development, which came to an end as sailing ships gave way to steam-powered vessels.
We were fascinated by the magnificent Great Thames Barrier whose huge shining steel structures looked to us as if they had been dropped from outer space. Here’s a bit of what we’ve since learned about the Barrier. The Thames River is a tidal river. By that I mean that the river is directly impacted by the ocean’s tides. Throughout the centuries, London was deluged by the river many times.
The most severe flooding incidents in recent history occurred in 1928, when the river burst its banks, inundating parts of central London and drowning 14 people; and in 1947, when a sudden thaw after a severe winter added to the river already swollen by torrential rain. These two events, plus a disastrous North Sea flooding of 1953 that devastated Canvey Island, killing 53 people, led to the construction of the Thames Flood Barrier at Woolwich.
The Thames Barrier prevents the floodplain of most of Greater London from being flooded by exceptionally high tides and storm surges moving up from the North Sea. It has been operational since 1984. When needed, it is closed (raised) during high tide; at low tide it can be opened to restore the river’s flow towards the sea. Built approximately 1.9 miles due east of the Isle of Dogs, its northern bank is in the London Borough of Newham and its southern bank is in the New Charlton area of the Royal Borough of Greenwich.
Design and construction
This diagram shows 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 rotating gates was devised by (Reginald) Charles Draper. In 1969, from his parent’s house in Pellatt Grove, Wood Green, London, he constructed a working model. The novel rotating cylinders were based on the design of the taps on his gas stove. 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 was largely complete by 1982.
The barrier was officially opened on May 8, 1984 by Queen Elizabeth II. Total construction cost was around £534 million ($2.3 billion at 2016 prices).
Built across a 570 yard wide stretch of the river, the barrier divides the river into four 200 ft and two approximately 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” so operators can control upstream levels.
All the gates are hollow and made of steel up to 1.6 inches thick. The gates are filled with water when submerged and empty as they emerge from the river. The four large central gates are 66 ft high and weigh 3,700 metric tonnes. Four radial gates by the riverbanks, also about 100 ft wide, can be lowered. These gate openings, unlike the main six, are non-navigable.
A Thames Barrier flood defense closure is triggered when a combination of high tides forecast in the North Sea and high river flows at the tidal limit at Teddington Weir indicate that water levels would exceed 16.0 ft in central London.
During the barrier’s entire history up to October 2017, there have been 179 flood defense closures. The barrier was closed twice on November 9, 2007 after a storm surge in the North Sea comparable to the one in 1953. The main danger of flooding from the surge was on the coast above the Thames Barrier, where evacuations took place, but the winds abated and, at the barrier, the November 9th storm surge did not completely coincide with high tide.
The barrier was originally designed to protect London against a very high flood level (with an estimated recurrence interval of one hundred years) up to the year 2030. At the time of its construction, the barrier was expected to be used 2–3 times per year. It was actually used 6–7 times per year.
The projected defense level included long-term changes in sea and land levels as understood at that time (c. 1970). Recent analysis extended the working life of the barrier until around 2060–2070. From 1982 until March, 2007, the barrier was raised one hundred times to prevent flooding. The 10 steel gates are raised monthly for testing; with a full-test closure over high tide once a year.
Released in 2005, a study by four academics contained a proposal to supersede the Thames Barrier with a more ambitious 10 mile long barrier across the Thames Estuary from Sheerness in Kent to Southend in Essex.
Note: The Thames Barrier Information Centre is currently closed for refurbishing, which is due to be finished in the spring of 2018.
Sources: visitlondon.com; ibtimes.co.uk; Wikipedia; gov.uk