Waves of crushing water seem out of place along the River Thames, which lazily snakes its way through London, bisecting the city and drawing tourists from around the world.

But the water along this river has risen before, claiming hundreds of lives. Catastrophic flooding may well happen again although time, technology and the rarity of hurricane-like weather in the North Sea have conspired to make that possibility a small one.

"London is vulnerable to flooding be it from the Thames tide, from rivers as a result of heavy rainfall, or from our drainage system," warned Roger Evans who three years ago chaired a committee of the London Assembly on the issue.

British authorities have long conceded that London, home to nearly 8 million people, is vulnerable to sudden flooding and that has led to the creation of a set of barriers, embankments and levees that protect the city from surging tides and rising water.

London sits only a few feet (about a metre) above sea level and the Thames' backward flow at high tide would strengthen the effect of a sudden influx of water from the North Sea.

In 1953, more than 300 people were killed and 30,000 people evacuated because of flooding along the Thames and elsewhere in southeastern England. London itself was mostly spared but the damage, in today's costs, was more than 5 billion pounds (US$9.2 billion).

London was last directly flooded in 1928 with a loss of 14 lives. Were the capital to flood again, the damage would be massive, with insurance companies estimating the damage to be nearly 21 billion pounds (US$56.7 billion), if not more. The loss of life could also be very high.

"Quite simply put, we cannot allow the barrier to fail," said Sarah Lavery, of the Environment Ministry.

The most familiar part of London's protection network is the Thames Flood Barrier, finished in 1984 at a cost of 500 million pounds.

The barrier spans 520 metres in the Thames and is made up of 10 separate, moveable gates that are supported between concrete piers and abutments that house the machinery that lifts them up and down.

When the decision is made to raise the barrier, four main gates are lifted to the height of a five-story building and help block the water.

When the level of the river is normal, the round steel gates are left open and ships can pass through. But if ocean storms whip up strong currents and high waves, the gates go up.

"It's not exactly New Orleans," Lavery said of that city's levees, two of which broke. "But we are very conscious and there is always a risk of a bigger flood coming."

But there is also concern about global warming, which could raise Thames water levels and in a worst case scenario lead to a breach in the barrier that would send a wall of water spilling into London and covering the streets in nearly two metres of water.

Such a risk is not farfetched, warned Munich Re, the world's largest reinsurer, which ranked London No 9 on its list of top 10 megarisk cities.

"The city itself has a good degree of protection," said Andreas Siebert, head of the Geo Informatics department of Munich Re. But he added: "London is at risk by winter storms and thunderstorms and a storm surge."

That's why the city is looking at ways to keep the estuary protected and urging that Londoners take care of the green spaces in the city, said Kelly Flynn, a spokeswoman for the London Authority. "Flooding is a risk, a big risk," she said.

Last week, the authority warned that paving of gardens and parks was adding to the risk of flooding because rainfall had nowhere to soak into, save for the river.

Others are mindful of the need to protect the city and the future site of the 2012 Olympic Games from the threat of flooding by improving the barrier and augmenting it.

Source: China Daily