The silvery, 13-story-high piers of the $850 million Thames Barrier offer a clear view of the tall buildings in Canary Wharf, an East London business district that is home to the headquarters of major banks, financial services companies and media groups. Straddling the Thames River downstream of London, where 60 square miles of the central city is below the tide line, it is the world's second-largest movable flood barrier. (The largest is in the Netherlands.)
London's tides have been rising gradually since the 19th century, according to tide gauge, GPS, gravity and satellite measurements analyzed by researchers at the University of Nottingham. At the same time, the land itself is sinking because, like New York, London is slowly tilting downward as the countryside has adjusted to the melting of glaciers from the last ice age, scientists say. In the worst-case scenario today, storm tides 12 feet high or more could surge up river to flood London, unless blocked by the gleaming barrier.
Government planners are already debating proposals for much larger storm surge barriers on the Thames estuary in the century ahead.
Managing the river system became a national priority more than a century ago, in part due to what historians call "The Great Stink." In 1858, the summer stench of the Thames grew so rank that the odor almost forced Parliament to flee. Instead, the lawmakers commissioned London's first major sewers and the construction of the Thames Embankment to drain central London.
In the 1970s, when the Thames Barrier was being planned, scientists calculated London's sea-level risk based on historical measurements. Those estimates have been largely correct: The barrier has never been breached, and the original projections slightly overestimated the actual rise in sea level so far.
All told, the barrier has been closed 119 times since it became operational in 1982—including 75 times in the past decade, compared with just four times in its first decade of operation. However, its use has varied dramatically by year. It was closed a record-high 21 times in 2000, after high winter flows, but hasn't been used at all in the past two years, except for routine maintenance tests.
The U.K. Environment Agency has studied extensively how climate change, sea level rise and the aging of the barrier might increase tidal flood risk in the future and concluded that "we are unlikely to see major changes to the existing system for the next 25 years," according to a November report.
At that point, however, London's 180 miles of flood walls, nine tidal barriers, and 400 river gates will require a major overhaul, the agency said, to cope with a best-case scenario of a 35-inch rise in sea level by 2100 and worst-case scenario of nearly 9 feet.
"The key thing is an adaptable plan," said Tim Reeder, program manager for the Environment Agency's regional climate change program. "We know that science will continue to change in terms of storm surge."