Thames Barrier

thumb|300px|Far view of the River Thames Flood Barrier

The Thames Barrier is a retractable barrier system built to protect the floodplain of most of Greater London from exceptionally high tides and storm surges moving up from the North Sea. It has been operational since 1982. 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 about east of the Isle of Dogs, its northern bank is in Silvertown in the London Borough of Newham and its southern bank is in the New Charlton area of the Royal Borough of Greenwich.

History

Background

Flooding in London has been a problem since Roman times. 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". A number of designs were put forward, from a huge road viaduct with two 500 foot (150 m) sluice gates crossing the Thames at Crayfordness to flap gates lying on the river bed and floated up by compressed air. 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). (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.

Design and construction

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 Draper. 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 taps 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.

The gates of the barrier were fabricated in sections at Cleveland Bridge's Darlington works and assembled at Port Clarence on the River Tees. 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). 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.

In addition to the barrier, the flood defences down river were raised and strengthened. The barrier was officially opened on 8 May 1984 by Queen Elizabeth II. The barrier cost £ (£ now). with an additional £100 million for river defences.

Built across a wide stretch of the river, the barrier divides the river into four 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 thick. The gates are filled with water when submerged and empty as they emerge from the river. The four large central gates are high and weigh 3,700 tonnes each. Four radial gates by the river banks, also about 30 metres (100 ft) wide, can be lowered. These gate openings, unlike the main six, are non-navigable.

Predictions for operation

A Thames Barrier flood defence closure is triggered when a combination of high tides forecast in the North Sea and high river flows at the tidal limit at Teddington Lock indicate that water levels would exceed in central London. Though Teddington marks the Normal Tidal Limit, in periods of very high fluvial flow the tidal influence can be seen as far upstream as East Molesey on the Thames.

Barrier closures and incidents

{| class="wikitable sortable" style="text-align:right; float:right; margin:0 0 1em 1em;"

|+ Closures per season (Sept–May) and flooding source

! Season

! Tidal

! Combined <br> tidal/ <br> fluvial

! Total<br>

|1982–83

|1983–84

|1984–85

|1985–86

|1986–87

|1987–88

|1988–89

|1989–90

|1990–91

|1991–92

|1992–93

|1993–94

|1994–95

|1995–96

|1996–97

|1997–98

|1998–99

|1999–00

|2000–01

|16

|24

|2001–02

|2002–03

|12

|20

|2003–04

|2004–05

|2005–06

|2006–07

|2007–08

|2008–09

|2009–10

|2010–11

|2011–12

|2012–13

|2013–14

|41

|50

|2014–15

|2015–16

|2016–17

|2017–18

|2018–19

|2019–20

|2020–21

|2021–22

|2022–23

|2023–24

|11

|13

|2024–25

! Totals

|119

|102

|221

, there have been 221 flood defence closures. The main danger of flooding from the surge was on the coast above the Thames Barrier, where evacuations took place, but the winds abated a little and, at the Thames Barrier, the 9 November 2007 storm surge did not completely coincide with high tide.

On 20 August 1989, hours after the Marchioness disaster, the barrier was closed against a spring tide for 16 hours "to assist the diving and salvage operations".

The barrier has survived 15 boat collisions without serious damage.

On 27 October 1997, the barrier was damaged when the dredger MV Sand Kite hit one of the piers in thick fog. As the ship started to sink she dumped her 3,300-tonne load of aggregate, finally sinking by the bow on top of one of the barrier's gates, where she lay for several days. Initially the gate could not be closed as it was covered in a thick layer of gravel. A longer-term problem was the premature loss of paint on the flat side of the gate caused by abrasion. The vessel was refloated in mid-November 1997.

The annual full test closure in 2012 was scheduled for 3 June to coincide with the Thames pageant celebrating the Diamond Jubilee of Elizabeth II. Environment Agency said the pageant provided "a unique opportunity to test its design for a longer period than we would normally be able to", and performance under conditions of "a higher water level upstream than downstream"; also that the "more stable tidal conditions … in central London … will help the vessels taking part".

Ownership and operating authority

The barrier was originally commissioned by the Greater London Council under the guidance of Ray Horner. After the 1986 abolition of the GLC it was operated successively by Thames Water Authority (dissolved 1989) and then the National Rivers Authority until April 1996 when it passed to the Environment Agency.

Operations

The barrier was originally designed to protect London against a very high flood level (with an estimated return period of one hundred years) up to the year 2030, after which the protection would decrease, while remaining within acceptable limits. At the time of its construction, the barrier was expected to be used 2–3 times per year. By the mid-2000s it was being operated 6–7 times a year. In the 2010s, the barrier was generally (as a median) closed twice a year, but the average remained 6–7 due to the extreme of 50 closures in 2013–14 during the wettest winter in recorded history.

This defence level allowed for long-term changes in sea and land levels as understood at that time (c. 1970). From 1982 until 19 March 2007, the barrier was raised one hundred times to prevent flooding. It is also raised monthly for testing, with a full test closure over high tide once a year.

In November 2011, a new Thames Barrier, further downstream at Lower Hope between East Tilbury in Essex and Cliffe in Kent, was proposed as part of the Thames Hub integrated infrastructure vision. The barrier would incorporate turbines to generate renewable energy and include road and rail tunnels, providing connections from Essex to a major new Thames Estuary Airport on the Isle of Grain.

In 2019 architects Lifschutz Davidson Sandilands and marine engineers Beckett Rankine launched a proposal for a pedestrian and cycle bridge located next to the Thames Barrier; the scheme, called the Thames Barrier Bridge, was promoted as the only location in east London where a low-level opening bridge across the Thames could have relatively moderate opening spans of about .

Future

2012 debate on changing climatic conditions

In a January 2013 letter to The Times, a former member of the Thames Barrier Project Management Team, Dr Richard Bloore, stated that it was not designed with increased storminess and sea level rises in mind, and called for a new barrier to be looked into immediately.

The Environment Agency responded that it did not plan to replace the Thames Barrier before 2070, as it was designed with an allowance for sea level rise of per year, which has not happened in the intervening years. At the time, the barrier was around halfway through its designed lifespan. The standard of protection it provides will gradually decline over time after 2030, from a 1-in-1000-year event. The Environment Agency was examining the Thames Barrier for its potential design life under climate change, with early indications being that subject to appropriate modification, the Thames Barrier would be capable of providing continued protection to London against rising sea levels.

A decision on the best option for adapting to sea level rise to 2100 will be taken by 2040.