All you need to know about London's Thames Barrier on its 40th anniversary

Wednesday marks the 40th anniversary of London’s Thames Barrier, inaugurated by Queen Elizabeth II on May 8, 1984, steadfastly protecting the capital for over four decades.

The barrier has prevented London from flooding more than 200 times, protecting four World Heritage sites, 4,000 listed buildings, and 1.5 million people.

However, changing climates and rising sea levels could see the barrier put to more frequent use to keep people safe in the future.

Today’s anniversary coincides with the Thames Barrier's operations manager’s last day at work.

Andy Batchelor, who has worked there for 25 years, told the BBC: "Having witnessed and worked on the Thames Barrier's opening, I am immensely proud of the protection it has provided London for the past 40 years and will continue to provide for years to come.

"Its reliability and effectiveness demonstrate the sophistication of its design by a very talented group of engineers and the continued maintenance and operation carried out by the barrier team."

Here’s the history behind the impressive engineering feat as it marks another memorable milestone.

When was the Thames Barrier built?

London has consistently struggled with flooding throughout its history, with hundreds of people being killed or displaced.

One of the most noteworthy instances was a tidal surge in 1953 that reportedly killed 307 people across the east of England. It caused thousands to flee the flooded capital.

Construction on a barrier that could protect London from further tidal surges did not start until 1974.

Work on 10 steel gates that can rise to the height of a five-storey building was finished in 1982. The barrier came into use the following year before its 1984 inauguration.

Apart from standard maintenance sessions, it has served as the main defence for flooding in London ever since.

How does the Thames Barrier stop flooding?

The Thames Barrier spans a 520-metre section of the River Thames, close to Greenwich and London City Airport.

The main sections of the gate weigh around 3,300 tonnes and usually lie flat on the river bed, allowing the tide to move naturally and boats to cross.

When detection systems identify a surge of water, hydraulics raise the gates into place. It takes around one and a half hours for all the gates to be lifted 20 metres high.

When in place, the barrier stops the flow of water to prevent flooding from reaching the capital.

After the risk has subsided, the gates open from the bottom to let water gradually flow back in, basically operating like a canal lock. The gate can be opened only once the water level on both sides is equal.

How many times has the Thames Barrier been used?

Since its opening, the Thames Barrier has protected the capital from tidal and fluvial flooding 221 times.

It is also part of a more robust flood protection system that includes walls, embankments, flood gates, and pumps up the estuary.

Between 2013 and 2014, the barrier was reportedly used a record-breaking 50 times. Discussions are being held about how to reinforce the structure in the future.

How long will the Thames Barrier last?

The Thames Barrier is expected to last another 46 years, quietly protecting London and its inhabitants until 2070.

However, in 2023 the UK Government admitted that the threat of flooding in the future means it may need to raise defences in inner London, upstream of the Thames Barrier, by 2050.

Concerns about the threat of flooding led to ministers bringing the Thames Estuary 2100 Plan forward by 15 years.

“Flooding is devastating for communities — and its impacts will become more extreme as we contend with a changing climate. We will need to be more adaptive and flexible to deal with these threats,” Flood Minister Rebecca Pow said in 2023.

“The Thames Estuary 2100 Plan is a perfect example of this: a world-leading climate adaptation strategy which allows us to react to changing circumstances and ensure people living in the Thames estuary are protected well into the future.”

Decisions about what lies in store for the barrier have not yet been made. The Government is waiting until 2040 to confirm whether it plans to reinforce or replace the existing barrier with a new defence system.

The BBC reported that the Environment Agency, which operates the barrier, said greater defences against flooding would be needed in the coming decades.