Thames Barrier: Difference between revisions

The Thames Barrier is a flood control structure on the River Thames at Woolwich Reach in London. It is the world's second largest movable flood barrier after the Oosterscheldekering in The Netherlands.

River Thames Flood Barrier

The gate in the middle of this view has been raised to the maintenance position and a barge is in attendance.

Built across a 523 metre wide stretch of the river, the barrier divides the river into six navigable and four smaller non-navigable channels between nine large concrete piers. The flood gates across the openings are radial, i.e., half-cylindrical, and they operate by rotating, raised by hydraulics out of a horizontal sill below the water to form the barrier. They can rotate further to allow "underspill" for maintenance. All the gates are made of steel. The four large central gates are 61 metres long, 10.5 metres high (above local ground level) and weigh 1,500 tonnes; the outer two gates are 31.5 metres. Additionally, four radial gates by the riverbanks can be lowered. These gate openings, unlike the main six, are non-navigable. The gates are normally left open to allow ships to pass through, but can be rotated closed to stop water travelling up the Thames estuary.

Before 1990, the number of barrier closures was one to two per year on average. Since 1990, the number of barrier closures has increased to an average of about four per year.

The sea level rise threatens to exceed the Barrier's protection about the year 2030 (the time when the designers themselves thought improvements might have to be made), but it is possible that this could happen as early as 2010. This does not mean that flooding is certain, but it does alter the probabilities in the design calculation.

Design and Construction

The concept of the rotating gates was devised by Charles Draper. The barrier was designed by Rendel, Palmer and Tritton for the Greater London Council and tested at Harwell research lab in Oxfordshire. The site at Woolwich was chosen because of the relative straightness of the banks, and because the underlying river rock 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. In addition to the barrier itself the flood defences for 11 miles down river were raised and strengthened. The barrier was officially opened on May 8, 1984. Total construction cost was around £534 m (£1.3 billion at 2001 prices) with an additional £100 m for river defences. The barrier was designed to cope with sea level rises until around 2030–2050. Based on current estimates, it is expected to serve its full term. Since 1982 the barrier has been raised over 100 times; further, it is raised every month for testing. The barrier was operated by the National Rivers Authority until April 1996 when it passed to the Environment Agency.

In 2005, a suggestion that it might become necessary to supersede the Thames Barrier with a much more ambitious 16 km (10 mi) long barrier across the Thames Estuary from Sheerness in Kent to Southend in Essex was made public.

Previous flooding

Raising one of the gates (Mar 2007)

London is quite vulnerable to flooding. The threat has increased over time due to the slow but continuous rise in high water level over the centuries (20 cm / 100 years) and the slow "tilting" of Britain (up in the North and down in the South) caused by post-glacial rebound. This general rise in potential water levels combined with the tidal conditions of the Thames and with particularly severe weather conditions can create serious flood conditions — surge tides. Fourteen people died in the 1928 Thames flood, and after 307 people died in the UK in the North Sea Flood of 1953 the issue gained new prominence. Early proposals for a flood control system were stymied by the need for a large opening in the barrier to allow for vessels from London Docks to pass through. When containerization came in and a new port was opened at Tilbury, a smaller barrier became feasible with each of the four main navigation spans being the same width as the opening of Tower Bridge.

Sand Kite incident

On 27 October 1997, a dredger, MV Sand Kite, crashed into one of the main gates of the Thames Barrier. The ship dumped her 3,300 tonne load of sand and aggregate, then sank onto the gate where she sat for several days. This caused massive problems, resulting in premature corrosion of the flat side of the gate, and could have had potentially disastrous effects on London. One estimate of the cost of flooding damage, had it occurred, was around £13 billion.

The barrier gate could not be taken out of service, and had to stay on one hour readiness notice. The twice daily 21 foot tide and the fact the Thames was still heavily used caused logistical problems for any possible repair methods to the gate. Eventually the vessel was refloated and the barrier fixed, but not until mid-November 1997.

Popular culture

• In Series 5 Episode 10 of the BBC drama Spooks, environmental terrorists take control of the barrier in order to let London flood during a spring tide.
• In the Doctor Who episode The Runaway Bride, the secret agency Torchwood is revealed to have built a secret base beneath the Thames Barrier.
• In the graphic novel V for Vendetta, Evey Hammond recounts to V how the Thames Barrier had burst during the limited nuclear war, flooding London.

See also

• Thames Barrier Park

External links

• BBC News: On The Rise, The Thames in 2100

• Template:Mmuk phoetc
• Thames Barrier page at the Environment Agency
• Port of London Authority for information on Navigation through the Thames Barrier
• BBC report of potential outer barrier
• [1]
• [2]

Gallery

• 
  The Thames Barrier, picture 1
• 
  The Thames Barrier, picture 2
• 
  The Thames Barrier, picture 3
• 
  Lifted gate, from a distance
• 
  Lifted gate, medium view
• 
  Lifted gate, close up
• 
  Pier close up

51°29′52″N 00°02′12″E