Feature: Londoners given chance to see gates that tame Father Thames

Londoners will be able to enjoy a close-up look on Sunday at one of the largest movable flood barriers in the world when the famous Thames Barrier throws open its doors, and its giant gates.

The government's Environment Agency is to carry out a rare full inspection of the structure built at a cost of 790 million U.S. dollars to protect Britain's capital from flood, or nearly 2.5 billion dollars at today's prices.

The operation will see the barrier gates fully opening over a full tidal cycle to test its sea and flood defenses.

The barrier currently protects 125 square km of London, including an estimated 1.25 million people, property and infrastructure worth 300 billion dollars. A large proportion of the London tube network and many historic buildings, hospitals and schools, including the Houses of Parliament, the famous Tower Bridge and areas of Southwark, Beckton, West Ham, Whitechapel would all be submerged in flood water without the barrier.

The 520-meter long barrier, opened by Queen Elizabeth in 1984, is hailed as an impressive example and celebration of British design.

The four largest of its 10 gates span 61 meters and weigh 3,700 tonnes each.

A spokesman for the Environment Agency said: "The Thames Barrier is quite a spectacle and makes an interesting and unique day out. The closure will offers visitor an insight into how London remains operational as a modern city."

The test starts at 6:30 a.m. local time when the barrier begins to close as the gates rise. As the high Spring tide starts its journey from the wide estuary towards London the barrier will hold back the water.

At around 1:45 p.m. the barrier will be partially opened for an underspill, causing a controlled rush, or surge, of water lasting for two hours.

The underspill shortens the time it takes for the upstream and downstream water levels to equal. It creates a white rush of water behind the gates, attracting many birds which come to feed in the white rush water and the food it provides.

A day of activities has been arranged for the public to see how London is protected from flood. The Thames Barrier cafe and information center is hosting a day of events, including meeting the barrier team, displays and arts and crafts activities for children, with souvenirs available.

The building of the barrier was prompted by the North Sea flood of 1953 which killed more than 300 people in England, mostly in the low lying areas around South West England.

Some experts have called for a new barrier to be built, fearing the existing defense system will be inadequate in years to come. They cite threats caused by a rise in high water levels at the rate of 20 centimeters a century and the slow "tilting" of Britain which is seeing north and west Britain rising and the London area dropping at a rate of up to five cm a century. Currently the barrier is raised around six or seven times a year. When it was built the expectation was it would be used just two or three times a year. A team is already working on a strategy to protect London into the 22nd century. Endit