Thames Barrier (London, United Kingdom)
Back in 1663, diarist Samuel Pepys described London's vulnerability to flooding as the result of storm surges from the North Sea that cause the Thames Estuary to overflow its banks. Over the centuries, the threat has increased, due to a slow but continuous rise in high water level, as well as the slow tilting downward of the southern half of Britain as the island continues to rebound from the weight of ice age glaciers in Scotland. The Thames Barrier, a set of six massive, rotating floodgates designed by engineer Charles Draper, has protected London from disaster since the early 1980s. Since 1982, the barrier has been raised more than 100 times to thwart the rising Thames. Increasingly, however, scientists worry that global warming and its effect upon sea levels and weather may be too much for the structure to withstand. "Our Thames Barrier is built to cope with everything except an absolutely catastrophic, once-in-a-thousand-years freak weather condition," London Mayor Ken Livingstone told Reuters in May 2007. "But the trouble is freak weather conditions are becoming more and more common." There's also concern that the barrier's 13,000 seals may be starting to wear out. British environmental officials estimate that a devastating flood could inflict nearly $160 billion in damage upon London and necessitate the evacuation of more than 1 million people. That's why they plan to spend nearly $8 billion over the next 20 years to shore up the city's flood defenses.