The Thames Barrier - flood defences on the river Thames

The Thames Flood Barrier, a stunning piece of engineering by anyone's standards, was a long time in coming. Ideas for some kind of barrier or barrage across the Thames had been floating around for nearly a century, but it was only the devastating floods of January 1953 that really galvanised the authorities into action. Even then, it would take another three decades before the Barrier was finally in place.

The river Thames has always played a key, if mysterious, role in the life of London. Archaeologists have found many precious items dating back to the Iron Age in the river, placed there to placate the capricious gods. The Battersea Shield, dating to the first century BC, is just one of many such items that have been found in the river. It is currently on display in the British Museum.

As time went on people living along the river learned how to tame it, or so they thought. For there are times when the Thames can be as capricious as ever. As Jonathan Schneer put it in his book The Thames: England's River, “human control of the river was always illusory.” The historical record is full of stories of Thames floods, that of 1953 being far from the least of them.

A number of factors have to be in place for the worst of the floods to occur. Known as a North Sea Surge, they occur when storms in the Atlantic are driven across the ocean by easterly winds, a great hump of water hitting the North Sea and then being channelled southwards into the relatively narrow gap between the Continent and England's east coast, coinciding with a high “spring” tide, produced by the combined gravitational forces of sun and moon in a straight alignment with the earth.

This happened on 31 January 1953, with the result that an onslaught of water surged up the Thames Estuary, flooding low-lying Canvey Island. Two hundred and fifty acres of east London lay 3 and a half feet under water. The tide even briefly threatened central London, reaching just to the top of the parapet running along the Victoria and Chelsea embankments. In Essex alone, the surge tide drowned more than three hundred people.

There were a variety of proposals for the type of barrier to be erected across the Thames. One called for a lifting bridge with barrier gates that could be lowered on tot eh river bed when the bridge was in the down position. Another proposal called for erection of a swing bridge barrier. All of the initial proposals aroused objections of various kinds.

The Thames Barrier as it now stands rests on a concrete sill on the river bed. Each gate is attached a t a right angle to a metal disc fitted to a pier. Hydraulic cylinders rotate the disc, which when turned pulls the gate up to face the river, rising a little more than 50 feet above the surface of the river. It has ten gates in all, each gate weighing 3,300 tonnes.

After much delay, the Thames Barrier was officially opened in 1984, and is one of the largest moveable flood barriers in the world. Situated at Woolwich, it has been raised over 100 times to protect London from flooding (2010 figures), and is projected to act as a high standard barrier until 2070. The Thames Estuary 2100 project is looking at ways of managing flood risk in the estuary after this date, which will take into account different tidal surge patterns and higher sea levels.

The Thames Barrier is an impressive monument to both modern civil engineering and man's ongoing battle with nature. It has become a tourist site in its own right - there is a visitor centre at Woolwich, and a number of boat trips along the Thames visit it. Well worth a trip.