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THE EIGHTH WONDER OF THE WORLD
The Thames Barrier has been protecting London from flooding for more than 30 years now. Robert Williams reports.
Large publically funded engineering projects often have a bad reputation in Britain. They are associated with grandstanding, waste, delays, incompetence and poor planning. Critics insist that big bridges and long tunnels, supersonic airliners and high-speed railways should instead be funded by the private sector.
The greatest rejection of this argument is about six miles east of the City of London, near Greenwich, an elegant and perfectly engineered study in stainless steel, zinc and concrete which in terms of value for money may represent the most effective use of taxpayers’ cash anywhere in the world.
Built at a cost (in today’s money) of around £1.6 billion and finished in 1983, the 1700ft Thames Barrier has paid for itself many times over in the 31 years it has been operating, in terms of lives saved and of properties not flooded across 50 square miles of a city built on a soggy flood plain which is slowly sinking into the North Sea. No wonder that the Thames Barrier has been described as the eighth wonder of the world.
After the wettest winter on record and after the Thames has risen to its highest levels in 60 years in some parts, the Thames Barrier breached the recommended annual limit of 50 closures for the first time this winter, In the whole of the 1980s, it closed on just four occasions. About half of these closures were to protect central London and the rest to regulate river flooding and damage upstream. The flood defence closure on 7 February was the 500th closure of the barrier (including test closures).
The Thames Barrier was built to protect London from storm surges coming from the North Sea – very high tides exacerbated by high winds and low pressure systems which can add several feet to sea levels locally. Climate change was not on the agenda in the 1950s but it was known that south-east England was sinking, albeit very slowly, into the North Sea as the result of geological settling following the last Ice Age. This sinking, coupled with rising sea levels means that, over time, London is more at risk than before.
And, in 1953, a particularly disastrous flood occurred. Over 300 people drowned and about 160,000 acres on Canvey Island, near the mouth of the Thames, were flooded. A government appointed committee recommended that a barrier be built across the Thames. The main problem was that the volume of shipping using London Docks was at its peak, and that ships were getting bigger. This meant that an opening in the barrier of around 1400 feet would be required. A number of schemes were put forward, but failed to come to fruition.
Then cargo began to be shipped in containers, a new container port was opened downstream at Tilbury and the old London Docks became redundant. It was decided that openings only 200 feet wide, the same as Tower Bridge, would be sufficient, and the site of the barrier could be further upstream than originally envisaged.
The Thames Barrier was designed for the Greater London Council by Rendel, Palmer and Tritton, and was officially opened by the Queen on 8 May 1984.
A map released by its operator, the Environment Agency, in December showed how London would look if sea levels continued to rise and there was no barrier. The Houses of Parliament, the O2 arena, Tower Bridge, and areas including Southwark, the Isle of Dogs, Whitechapel and West Ham were shown to be flooded.
For most of its history, London lacked such protection. In 1928, 14 people drowned when a swollen Thames overflowed between the City and Southwark to the east and Putney and Hammersmith to the west. According to contemporary reports, the streets were filled with water up to 4ft (1.2m) deep.
Balancing the tide and the river
The barrier, made up of 10 steel gates, reaches 520m (1700ft) across the river. When open, the gates lie flat on the river floor and close by being rotated upwards until they block the river. The four main gates span 61.5m (200ft) and weigh more than 3000 tonnes each. The barrier is closed just after low tide to create an empty ‘reservoir’ for the river flow to fill up. The process of closing the barrier – from making the decision, physically shutting it, waiting for high tide to come and go and re-opening it – takes eight or 10 hours, starting with the gates on the outside until the middle gates are shut.
With no barrier, at high tide, the sea would normally flow up the estuary and into London, pushing the river water back. With all the extra rainfall, this could worsen the flooding. The barrier prevents this from happening. The gates are left shut and the river water is held until the tide turns. Staff wait for the water on both sides to ‘equalise’ – reach the same level – and then the gate is opened and the river water can rush out into the estuary.
The barrier was originally designed to last up to the year 2030. Recent studies suggest that even with sea level rises from anticipated climate change, the barrier will be sufficient protection for London until 2060–70.
The Barrier has already become London’s unsung saviour. London did not flood, even during a massive storm surge in 2007, which was comparable in scale to that in 1953. The Barrier has survived 15 ship collisions and it even played a backstage role in the 2012 Jubilee celebrations, turning the tidal Thames into a gigantic lake, safe for the hundreds of small boats, including the royal barges.
But the frequency of closures in recent months could suggest that the Barrier is operating close to the limits of what it can do to protect central London and at-risk upstream areas. Also, as it ages, and the more it is used, the more likely it is to run into mechanical problems.
So there are growing calls for this wonderful piece of engineering, Brunellian in imagination and scale, to be replaced – and quickly. Current plans by the Environment Agency, which operates London’s flood defences, to keep the Barrier operational until the 2070s are not enough, in the face of climate change that is producing rising sea levels and more powerful storms of the kind that have made this winter catastrophic for so many. So is it time for Thames Barrier 2?
A replacement Barrier – larger, higher and to be built closer to the mouth of the Thames, would be built around the site of the M25 crossings at Dartford. It would cost tens of billions of pounds but, the argument goes, compared to the devastation that would result if a storm surge overwhelmed the current Barrier this would be a bargain.
The increasing use of the Barrier as a defence against fluvial flooding west of London means that not only must rising sea levels be taken into account (an estimated 40–60cm by the 2070s) but also more extreme weather. Can London afford not to invest in a new barrier?
Whatever decision is taken, the original barrier – an incredible work of engineering – will still be doing its job for the next 40 years. Brunel would be proud – as should be the taxpayers of the 1970s who paid for it. n
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