How protected is London from flooding?

“People have this idea about the River Thames, the sheer beauty of it, the sparkling sunshine on the water. But the river can turn nasty,” says Professor Hannah Cloke from the University of Reading.

On a freezing January morning 70 years ago, residents of Canvey Island in the Thames Estuary woke to gale-force winds and the terrifying spectacle of water overcoming the sea wall. There had been no warning, it was bitterly cold, the wind howled and the waters rose so quickly that residents who could not escape fast enough, had to cling on to their rooftops. Those that could not hold on slipped into the icy waters and were carried away.

The North Sea Flood of 1953 took the lives of 58 people on Canvey Island, while the entire population of the island – about 13,000 – had to be evacuated. In total, 307 people were killed in England, while in the Netherlands, 1,836 people lost their lives. The combination of wind, high tide and low pressure caused the sea to flood land up to 5.6m above sea level and most sea defences facing the surge were overwhelmed – with dire consequences.

As the UK reeled from the floods and investigations were launched, planners realised that without the construction of a great barrier, such a surge could inundate 45 square miles (120km2) of land, shut down hospitals, power stations and the London Underground, and cause damage estimated at about £50bn in today’s prices.

Thus, an engineering masterpiece was born – the iconic Thames Barrier, a retractable barrier system spanning the Thames river near Woolwich. Officially opened in 1984, the barrier was designed to protect central London against surges like the one seen in 1953, caused when a deep depression forms to the north of Scotland and progresses across the North Sea towards southern Scandinavia. When these surges coincide with high spring tides, high winds can funnel the water up the Thames Estuary and cause powerful surges.

“We definitely cannot control nature, but we can take the edge off it sometimes,” says Cloke, who is an environmental modeller and forecaster and lectures about flood risk at the University of Reading.

It’s not just the barrier that protects London and the south-east of England from tidal and fluvial flooding. There is a network of more than 330km of walls and embankments, nine major barriers and gates, including the Thames Barrier, and over 400 other structures including flood gates, outfalls and pumps.

The Environment Agency (EA) recognises the challenge of keeping this all up-to-date. “Predictions show that by 2050 the UK could see 59 per cent more winter rainfall and once-a-century sea level events could become annual events by 2100,” it said in a recent consultation document.

“The climate is changing and causing sea levels to rise. As sea levels continue to rise, these structures are having to work harder, and a growing population means more people are living in the floodplain. These factors, combined with ageing flood defences, means the risk of tidal flooding will increase over time, unless we all work together to manage this risk carefully.”

In May, the regulator published an updated plan setting out how it aims to protect more than 1.4 million people and £321bn of property until the end of the century. It is estimated it will cost £16bn to implement. 

In the plan, known as ‘Thames Estuary 2100’, the EA said defences upstream of the Thames Barrier in inner London would need to be raised 15 years earlier than originally intended because improved climate models had illustrated the “heightened risk of flooding from a warming climate and rising sea levels”.

What to do about the barrier itself also features heavily in the plan. It was originally designed to protect London against a very high flood level until 2030, after which protection would decrease, “while remaining within acceptable limits”, according to the EA. However, at the time of its construction, the barrier was expected to be used just two to three times per year. In reality, since the mid-2000s it has been forced to close six to seven times a year on average.

It was closed four times in the 1980s, 35 times in the 1990s and 75 times in the 2000s. There have been 88 closures since 2010; in 2013/14, the UK experienced an exceptionally wet and stormy winter, forcing the EA to close the barrier 50 times in a single year. The EA’s own guidance says the barrier should not be closed more than 50 times a year.

Despite this, the EA says it now anticipates the present barrier will continue to do its job until 2070, four decades longer than originally thought, thanks to “improved maintenance and revised predictions about sea levels”.

The Thames Estuary 2100 Plan identifies several options to protect the estuary to the end of this century and beyond, and it expects to put the plan in place by 2070. The options include upgrading the existing Thames Barrier and wider defence system, constructing a new barrier with two sets of gates, as well as introducing multiple flood storage areas alongside the existing barrier. The EA says barriers with a second set of gates and locks are more expensive to build and “cannot be justified given current sea level rise projections”. However, it says it ultimately expects to need a barrier with a second set of gates and locks by 2120, regardless of which option it selects.

But experts warn this is not fast enough. Jonathan Bamber, professor of physical geography at the University of Bristol and an expert in sea level rises, says the 2040 target “is problematic not just because of the likelihood of more weather extremes, but also because sea level rise is occurring far faster than predicted when the barrier was designed and built.

“These two factors create a problem for the effectiveness of the barrier on the timescale the EA is working to,” he adds.

Cloke says she would feel much more comfortable if the EA decided before 2040, given the unpredictability of climate change-related weather events. She points out that the original barrier took 31 years to build after the North Sea flood. “I think we need to hurry up and make a decision because we’ve got an uncertain future ahead of us… and that’s not even taking into account potential political wobbles.”

Cloke says the 2013/14 floods should be seen as a wake-up call. “The 50 closures in 2013/14 were not planned for at all,” she says. “We had a combination of the tidal surge flooding coming up the river and the fluvial flooding coming down the river, brought on by heavy rainfall. This pattern of storms may be more likely with climate change. It could easily happen again that we would need to close it 50 times. I think it’s really concerning because the barrier wasn’t designed to do that.

“By not planning for future extreme weather events fast enough, we are shooting ourselves in the foot. We must invest now to save that money later,” she adds.

In response to these concerns, the EA has said it will create a roadmap for selecting an end-of-century option that will outline the steps and approval required, and that this “could result in a decision being made before 2040”.

However, it is unclear how the plan will be funded. The EA notes that since 2012, the estimated cost of putting the Thames Estuary 2100 plan into action has increased by around 50 per cent. This is due to inflation, flood defences deteriorating faster than expected and “a better understanding of the current defence system”, it says.

Currently, the main form of government investment to manage flood risk in England is the Flood Defence Grant in Aid (FDGiA). However, this will not be enough to fund all flood defence work needed in the Thames Estuary, the EA notes. “We need to fill this funding gap,” it says. Businesses, landowners, infrastructure providers and other groups who benefit from flood defences will be asked to contribute. The EA intends to publish an investment strategy by 2025.

Although the primary purpose of the Thames Barrier is to manage tidal flood risk in the estuary, the EA also closes it to protect low-lying properties in west London after heavy or prolonged rainfall – known as fluvial flooding. Yet the EA has a problem: it says it expects to have to close the Thames Barrier more frequently for tidal surges as sea level continues to rise and that if it continues to use the Thames Barrier to manage fluvial flood risk in west London after 2035, it will “cause wear and tear to the structure”, meaning “it may become less reliable, because it cannot be maintained to the required standards”.

The EA, therefore, says it will need to stop using the barrier for less significant fluvial events by 2035. It is developing models to understand “the complex interaction of the tidal and nontidal effects of flooding in west London”.

In its March report to Parliament, independent government advisers the Climate Change Committee (CCC) noted that developments are still being built in areas at future risk of flooding. “Most plans for new developments do not thoroughly regulate or track adaptation for future climate resilience … and there is insufficient funding to enable affected communities to adapt,” it adds.

The CCC argues that current planning guidelines are not sufficient to ensure new developments “are built in appropriate locations or with adequate climate change adaptation”. The EA estimates that over the next 50 years, the current number of properties on the flood plain is likely to double.

The University of Bristol’s Bamber says the problem with building on the flood plain is in the name – it floods. “More intense rainfall events are predicted with a warming climate alongside accelerating sea level rises. This will result in increased coastal and pluvial [rain-related] flooding, putting homes in the flood plain at more risk of flooding.”

The University of Reading’s Cloke says it is “appalling that we are building on the flood plain” and most people living on one “will suffer”, the costs will be astronomical, and poorer communities will suffer worse.

Peter Girard, spokesperson for Climate Central, a non-profit organisation that analyses and reports on climate science, agrees that “risks and costs will go up” if building continues on the flood plain.

“Wealthier communities can invest in defences and withstand losses that ruin others. Poorer communities face the risks with fewer protections and fewer options, including somewhere else to go when the waters rise,” he explains.

Climate Central creates maps showing regions potentially at risk during a coastal flood expected, on average, at least once per year. They do not factor in the UK’s network of flood defences and the Thames Barrier.

“It’s always in the back of my mind when I look at that really drastic map,” says Cloke. “If all these defences went, that’s the reality – that’s where we are living, we are living on the flood plain of the Thames, we’ve got all these complicated defences in place, and it is possible to manage some of that risk. But if we get a very big flood coming through, then there’s always this extra residual risk that the barriers will be overcome or fail and then those people will be flooded.”

Most respondents to the EA’s consultation said mitigation and adaption were crucial. Thames Water, for example, said “the challenge is so vast that both mitigation and adaptation interventions are required”. Experts agree that some communities will have to be relocated; Cloke says this could include places like Canvey Island, which suffered so badly 70 years ago.

“Canvey Island is basically a bathtub sitting in the middle of the river. Whenever it rains hard, the bathtub fills up and they pump water out and, of course, then there’s the threat of the river too. It’s a very difficult place to live. We do really need to consider the future of these places. They will become impossible to defend and therefore very dangerous places to live.”

But it’s not just Canvey Island, adds Cloke. “There are lots of [these vulnerable locations] along our coastlines. We saw this during the very heavy rainfall in the summer of 2022, when people’s cellars were flooding very quickly. So, it’s not just about the river; the rest of London is not very resilient to very heavy rainfall flooding.

“It’s a very difficult decision to move people away – these are their homes and people don’t want to give up their homes, for understandable reasons. But if it is too dangerous to live there and they cannot be defended, then sometimes there is no other option,” she says.

The Dutch government has already taken the step to relocate people at risk of flooding. As part of the Room for the River national flood prevention programme, which aims to increase the discharge capacity of the River Rhine, 50 homes were demolished in Nijmegen.

According to Cloke, places most at risk of flooding are where the rivers meet the sea. This creates a “double-whammy problem”, with potential for tidal surges to come up the river and fluvial flooding coming down the river. An important example is the Somerset Levels, much of which was under water in 2013/14, at the same time as the Thames was flooding. Farmers were greatly impacted, as much of the Levels is agricultural land.

Cloke says the Somerset Levels, which cover 250 square miles (650km2), is “too big an area to abandon entirely, it will be about using the land differently. It’s going to be very difficult to see the future looking exactly the same as it does now in 20 or 30 years’ time.”

Change is coming. But it is not clear whether communities are ready. On the Thames Estuary, only a third of respondents to the EA’s consultation said they felt equipped to prepare for the impacts of sea level rises.

“I think some people are aware of the risk of flooding, but I think many have other things on their minds now, particularly vulnerable communities who are struggling to feed themselves, or to heat their houses. Sometimes the risk of flooding doesn’t seem like the most important thing,” says Cloke. “That’s why we need to make sure we have a strong government that can make sure those risks are assessed for us.

“This is also why it is important to keep campaigning,” she says. Decisions about the barrier, and about all the flood defences across the UK, need to be made, and communities need to be prepared so that unlike 70 years ago “we are ready for the next big flood, not just waiting for it to strike us”.