The Thames Barrier is a unique flood control structure on the River Thames at Woolwich Reach in East London. It is 520 meters wide and protects London against storm surges and rainfall swelling.

The barrier currently protects 125sq km (48sq miles) of London, including an estimated 1.25 million people, £200 billion worth of property and infrastructure, a large proportion of the London tube network and many historic buildings, power supplies, hospitals and schools.

Without the barrier the Houses of Parliament, the O2 arena, Tower Bridge and areas of Southwark, Beckton, West Ham, Whitechapel would all be submerged in flood water.

It took eight years to build the structure, costing £535m (£1.6 billion in todays money) and became fully operational in 1982.

The Thames Barrier is the second largest flood defence barrier in the world after the Oosterscheldekering Barrier in the Netherlands.

“Without the Thames Barrier, London’s flood defence walls would need to be considerably higher – the walls along the Embankment, for example, would have to be as high as the Victorian streetlamps, effectively depriving Londoners of their river”

Flooding in London, Greater London Authority 2002

Who is responsible for the Thames Barrier?

The Environment Agency is responsible for maintaining and operating the barrier and associated flood defences including the Barking and Dartford Creek Barriers. It costs around £6 million per year and needs 80 staff to operate and maintain the barrier.

The barrier closure is triggered when a combination of high tide forecasts in the North Sea and high river flows at the tidal limit of Teddington weir indicate that water levels would exceed 4.87 meters in central London.

Future sea levels and river flows are generated by Met Office computer models and forecasting systems. This service monitors tides along the east coast of England and as far away as the Western Isles in Northern Scotland.

The Thames Barrier has been closed 174 times since it first became operational in 1982 (correct as of March 2014). 87 of these closures were to protect against tidal flooding and 87 were to alleviate river flooding.

How does the Thames barrier work?

The barrier is a series of 10 separate movable steel gates, standing 20 meters tall and stretching 520 meters across the river.

Each of the main gates is a hollow steel-platted structure over 20m high and weighing around 3,700 tonnes, capable of withstanding an overall load of more than 9,000 tonnes of water.

When the barrier is closed, a solid steel wall sealing the upper part of the river from the sea is created, stopping water from flowing upstream towards the capital. The gates can also be part closed in the underspill position, allowing a controlled amount of water to pass under the gate and up the river.

Individual gates can be closed in ten minutes but the whole barrier takes around one hour and a half to close completely.

The barrier is only reopened once the water level upstream of the barrier matches the water level downstream. When not in use, the gates rest out of sight in curved recessed concrete cills in the riverbed, which allows river traffic to pass through.

Why was the Thames Barrier built?

The 1953 floods lead to a rethink of London’s flood strategy.

Before the barrier was built, the solution to flooding was to build higher and stronger river walls and embankments – a solution that became popular following the Thames Flood Act of 1879 and remained an accepted measure until midway through into the 20th century.

In 1953 the Thames Estuary experienced a widespread flood which claimed 307 lives and caused an estimated £50 million damage (£5 billion at today’s costs).

This lead to a dramatic rethink of the way in which flood defences were built to protect London.

Following a report in 1966 by Sir Herman Bondi, it was decided that the best solution was bank raising and a flood barrier with movable gates built across the Thames.

The Thames Barrier and Flood Protection Act 1972 gave powers to carry out this solution and led to the construction of the barrier.

Without the Thames Barrier, London’s flood defence walls would need to be considerably higher – the walls along the Embankment, for example, would have to be as high as the Victorian streetlamps, effectively depriving Londoners of their river.

The future of the Thames Barrier

The barrier was originally designed to protect London from a very large flood (1 in 100 years) up to 2030. As climate change and rising sea levels are creating a higher risk of flooding in London, improvements to the Thames Barrier and its flood management are needed to keep on protecting London from flooding.

In 2002 the Thames Estuary 2100 project headed by Dave Wardle was set up. It is a cross-regional Environment Agency project with the aim of developing a strategic flood risk management plan for London and the Thames estuary through to 2100.

The strategy will take into account increasing flood risk due to:

• Climate change
• Rising sea levels
• Changes in land levels
• The natural ageing of defence infrastructure
• New development in the tidal flood plain

The final plan will recommend what flood risk management measures will be required in the estuary, where they will be needed, and when over the coming century, based upon the climate change and sea level rise scenarios.

The Thames Barrier is not the only structure designed to protect London from flooding that will be improved in the Thames Estuary 2100 Project. Other tidal flood defence structures and measures include: the Barking Barrier, King George V lock gate, Gallions Flood Gate, Dartford Barrier, Tilbury Dock, Fobbing Horse, Easthaven Barrier, and Benfleet Barrier. In addition to these, the tidal Thames has 36 major industrial floodgates and 480 smaller moveable structures – mostly protecting residential property.

Read more about flood risk in the UK