When the Romans built Londinium circa AD 50, they chose a good place to start. The land on the north side of the river latterly known as the Thames sloped upwards; that on its swampy southern bank did not. The threat of flooding seems not to have been lost on those imperial adventurers whom Boris Johnson has termed a “bunch of pushy Italians”. Today, the high ground we call the City of London would still stay mostly dry if the river burst its banks. The same cannot be said of much else of the capital lying close to its aquatic spine.



The Environment Agency’s “at risk” list includes the Houses of Parliament, Whitehall, City Hall, Canary Wharf, Westminster Abbey, the Tower of London, Kew Gardens, the O2 Arena, 51 railway stations, 35 Underground stations, eight power stations, more than 1,000 electricity substations, 400 schools, 16 hospitals and over half a million of Greater London’s roughly 3.3 million homes – not to mention 1.5 million of its people. Large areas of Southwark, Lambeth, Tower Hamlets, Hammersmith, Fulham, Wandsworth, Barking, Dagenham, Woolwich and Newham could find themselves under water, along with many settlements along the estuary in Essex and Kent.

Put it this way: Londoners have a lot to thank the Thames’s flood defences for. Chief among these is, of course, the Thames Barrier, the huge, vaguely sci-fi string of mini-piers and silver pods that spans the eastern gateway to the capital between New Charlton and Silvertown.

Areas of east and south-east London with a one-in-1,000 risk of tidal flooding without the Thames Barrier and associated tidal walls. Illustration: Environment Agency

Last winter, from early December 2013 to the end of February last year, its steel gates were closed a record-shattering 50 times, preventing the river from running riot. Previously, the barrier had closed only 124 times since it began operating in 1982. The agency described this sharp increase in demand as a “blip” and, apart from routine testing, the barrier hasn’t been closed since. However, during its lifetime there’s been a strong, overall upward trend: it was closed four times in the 1980s, 35 times in the 90s, and 75 times in the 2000s. There have been 65 closures since 2010, suggesting this climb is continuing.

Is a watery end nigh? Not in the foreseeable future, says the agency – but the need to look far ahead was recognised early this century with a project entitled Thames Estuary 2100, established to manage flood risk through to 2100. A plan produced in November 2012 primarily addressed the biggest threat: surges in the twice-daily North Sea tides that drive water past Southend and Sheerness, right through the centre of London and out the other side as far as Teddington in its south-western suburbs.

… the greatest tide that ever was remembered in England to have been in this river, all Whitehall having been drowned Samuel Pepys, 1663

The plan set out options for a whole new flood barrier, the most promising location (option 3.2) being further east, beyond London’s boundaries at Long Reach, Dartford. But it anticipates the present barrier continuing to do its job until 2070, four decades longer than originally thought, thanks to improved maintenance and revised predictions about sea levels.

The exceptional winter of 2013/14 did, though, prompt the agency to review its impacts on the barrier’s present and future operations. A report produced last August noted that the first closure of the period, completed during the first half hour of 6 December, had protected London from “the highest tide seen at Southend in over 30 years of operations”.

The other exceptional element of the 50 closures cluster was that the great majority – 41 of them – were prompted not by tidal surges from the east, but by prolonged heavy rainfall in the Thames catchment area to the west of the capital. The resulting increases in “fluvial flow” downstream created the second type of reason for closing the barrier – protecting vulnerable locations just upstream from Teddington, such as the village of Thames Ditton and the residential Trowlock Island.

Flooding near Staines-Upon-Thames in February last year. Photograph: Peter Macdiarmid/Getty Images

These are put at risk when the pressure of the tidal Thames waters arriving from the other direction further boosts already high water levels. But that risk is reduced if, over on the opposite side of the city, the barrier is closed just after low tide. This effectively turns the London stretch of the river into a temporary reservoir with spare room into which the extra fluvial waters can freely pass. Once the tide has receded and levels on either side of the barrier match, the barrier is opened again, and the contents of the “reservoir” released to resume their journey towards the sea.

The impacts report said that while vital maintenance work on the barrier had been able to continue throughout the three demanding months, “if 50 closures was to become the norm this would start to impact on the reliability of the barrier.” It concluded that a repeat was unlikely, noting that solar and lunar conditions contributing to higher tides will not recur before 2032 “then not again until 3182”. But it also underlined the expectation that the barrier will need to be closed more often against tides, and consequntly will be able to come to the Teddington area’s aid less frequently. A new scheme to augment the locks and weirs there is being worked on.

Computer-aided design didn’t exist [when the barrier was built]. It was put together from 13,000 pen and ink drawings Tidal defences manager Andy Batchelor

Localised flooding in London from Thames tributaries may be increasing as a risk in its own right, as experts told the London Assembly’s environment committee last January. It is estimated that 24,000 properties are under significant threat. Parts of Kingston, Barnet and Waltham Forest were top of the list. In response, the London Rivers Action Plan, supported by the mayor, has been restoring rivers previously constrained in artificial channels, giving them greater width and a safety margin for flooding into surrounding green space, improving habitats for plants and wildlife in the process. The river Quaggy, which passes through Lewisham, Greenwich and Bromley, is cited as a good example.

Exactly half of the Thames barrier’s 174 lifetime closures have been to help alleviate river flooding. But tides, the biggest worry, are its core business. Surges begin with bands of low atmospheric pressure originating in the Atlantic, which have the effect of raising sea levels. After passing north of Scotland, these high-water humps swing south down England’s east coast before funnelling into the Thames’s open mouth, sometimes heightened further by strong winds. “A surge tide entering the estuary can increase water levels by one to three metres,” the TE2100 plan explains.

The planners have put mitigating the effects of climate change at centre stage. They expect it to produce raised average sea levels, surge tide levels and wave heights in the coming decades, albeit by less than previously thought. Meanwhile, land levels in the south-east of England are falling – only by about 1.5mm a year, but over the course of a century it all adds up. In addition, development along the river’s banks is slowly invading its space, leaving less room within which its waters can expand.

The aftermath of flooding at Cheyne Walk, Chelsea, in 1928. Photograph: Associated Newspapers/Rex

The TE2100 plan sets out an action programme, already being put into effect, for building resilience into the floodplain environment. Setting new buildings back from the waterfront helps, as a buffer of green can double as an overspill facility. The space in front of the barrier’s visitor centre exemplifies the principle: when the barrier shuts out a high tide, the resulting build-up can put its picnic tables under water. The chancellor George Osborne allocated £196m for the Thames Estuary programme in December.

In the barrier’s operations centre, which looks out across that famous row of stainless steel-clad shells, tidal defences manager Andy Batchelor emphasises the integration of many elements is key to maintaining a safe level for the Thames. To the east they include a barrier at Barking Creek where the River Roding meets the Thames and, beyond the Greater London boundary, a floodgate at Tilbury Dock and the finely named Fobbing Horse barrier at Canvey Island.

Less conspicuous but just as vital to the system are the over 400 gates and smaller structures protecting homes, business and other buildings along the river’s length, and the more than 185 miles of embankments and walls. Hanging on the operations centre wall, a photograph shows the Queen’s visit there for at the barrier’s official opening in 1984.

As Batchelor observes, the power station look of the original control consoles is long gone. Today, the space is hushed and computerised, a monitoring hub for its own data and more from the Met Office and the UK National Tidegauge Network, enabling forecasts of dangerous conditions up to 36 hours in advance. Local flood warnings are issued too, enabling residents of places such as Richmond to anticipate water spilling across the towpath and up to their front gates.

“We’re modelling what is going to happen and what operations might be required to manage the water at different points along the river,” Batchelor explains. “If the level is going to be anything higher than 450mm from the top of the wall in the centre of London, then we will shut the barrier.”

A family evacuated in Whitstable, Kent, in 1953. The floods killed 307 people in eastern England – the catalyst for the construction of the Thames Barrier. Photograph: Popperfoto

Without it, London would get its feet wet and much worse. Recorded history of the Thames banks bursting goes back a long way. In December 1663 Samuel Pepys recorded “the greatest tide that was ever remembered in England” and “all White Hall having been drowned, of which there was great discourse”. The last major flood affecting central London occurred in January 1928, when defences in Chelsea and Victoria were overwhelmed at dead of night, with a section opposite the Tate Gallery in Millbank collapsing. Among the paintings damaged as a result were works by Turner, famous for his boiling seascapes.

Parliament and the Tower were swamped too, as were the then fairly new Blackwall and Rotherhithe tunnels and, most tragically, the basement homes of some of the capital’s poorest residents, largely in Southwark and on the Westminster side of Lambeth Bridge. Fourteen people drowned and thousands had to leave their homes. It occurred thanks to a perfect combination of storms, with a tidal surge meeting a doubling of inflow from the west caused by heavy rain and snow thawing in the Cotswolds, where the Thames has its source.

The catalyst for the barrier’s construction was the North Sea flood disaster of winter 1953, when a huge tide saw sea levels rise by more than 18 feet and overwhelm coastal defences in Scotland, Belgium and, most horrifically, the Netherlands where 1,836 lives were claimed.

In eastern England there were 307 fatalities, as large parts of Lincolnshire, Norfolk, Suffolk and Essex were washed over. Canvey Island’s sea walls collapsed, leading to 58 of those deaths, and a further 35 perished at Jaywick in Clacton. The waters coursed upstream through the then busy docks, swamping factories, gasworks and electricity generating stations from Tilbury all the way to the East End, where the Thames spilled on to the streets of West Ham and into 1,000 homes. The centre of London just about escaped, but there are photographs of people in Richmond marooned on towpath benches. There were no warning systems. Victims were caught completely unawares.

The Thames Barrier closed at high tide. Surge tides can raise water levels by up to 3m. Photograph: Andrew Holt/Getty

Plans to build a barrier began soon after. The design for its rotating gates had been created by engineer Charles Draper, reportedly working from his parents’ home in Wood Green and inspired by the domestic gas taps that were common at the time.

A civil engineer, Batchelor has worked on the barrier since joining its maintenance team in 1984, becoming its manager in 1999. He’s a founder member of the International Network of Storm Surge Barriers, a group of highly specialised experts whose membership includes those responsible for protecting waterside cities as varied as Venice, St Petersburg and New Orleans. Batchelor explains that the Thames Barrier’s technological evolution has followed tried-and-tested routes, with new elements only being introduced after they’ve proven reliable elsewhere. The current system earned its spurs in the North Sea oilfields.

Walking the warrens within the barriers is an education. Piers are connected by passageways built below the water. Pipes and bundles of cable run like friezes along the walls. Two metres of concrete separate you from the river overhead, though when a boat passes apparently its propellers can be heard. Up above, vast hunks of muscular, yellow-painted hydraulics stand ready to open and close the 10 gates.

The six in the deepest water lie flush with the riverbed when closed, to allow boats and shipping through. The widest four gates each span 61m of the river, whose width is 520m at that point, and weigh more than 3,000 tonnes each. Batchelor remains full of professional admiration: “This was on the drawing board in the 1960s, constructed in the 70s. Computer-aided design didn’t exist then. It was put together from 13,000 pen-and-ink drawings.”

The full effect of the barrier is the same as if the floodwalls along the Victoria Embankment were 3m higher. Without this line of defence, those walls would have to be built up accordingly, rather spoiling the view. A decision about building a new barrier is expected to be made in 2050. The present one is widely seen as a beacon of farsighted public investment – one it would be wise to learn from.