The River Thames Flood Barrier, London

In 1953 a disastrous flood occurred along the Thames Estuary, caused by a surge tide off the North Sea, resulting in the drowning of some 300 people, and approximately 160,000 acres of farmland being swamped in seawater. An unpredictable phenomenon originating in the North Atlantic when areas of low pressure cause a sea mass beneath to rise slightly, these 'raised humps' of water normally travel North of Scotland. Occasionally, however, the northerly winds can force them into the North Sea and, ultimately, to the Thames Estuary. Further complications are experienced by the natural rise of sea levels, caused by the melting of the polar ice cap.

As it was becoming abundantly clear that the population of London were facing a serious threat of regular, and unpredictable, flooding, work began on the flood barrier in 1974. Taking a further eight years to construct, the Thames Flood Barrier was officially opened by Her Majesty the Queen in 1982.

The barrier itself comprises nine, huge piers set at intervals across the river, which form six main shipping lanes and four smaller channels. Between these piers are steel gates, up to 200ft (60.6m) wide, that lay in a concrete cradle on the sea bed (some 50ft - 15m below the surface). When the barrier needs to be raised, these gates are swung through 90 degrees by hydraulic arms to form the required barrier between the piers. A very impressive piece of engineering that is actually designed on the same basis as the everyday, domestic gas tap.

To ensure that the Thames Flood Barrier will, in fact, perform its required function in times of emergency, it is tested on a monthly basis at low tide for a couple of hours, and for a full day at high tide once a year. The testing dates are published well in advance to allow visitors to see the barrier in operation. For anyone living in and around London, this great construction provides not only a very impressive sight, but also a great feeling of comfort, and the reassurance that it will avert any potential disaster.

Further information on the barrier construction and operation can be obtained from the Thames Barrier visitor centre, which is situated on the South Bank of the river.