Another one of the great things about traveling is that you get to learn all these random details about things that you would never normally take the time to research. One of those details has caught my eye every time I look at a map of London, and I have finally taken the time to look into it. It is called the Thames Barrier.

It was opened in 1984, took 10 years to build, and is the second-largest movable flood barrier in the world after the Oosterscheldekering (don’t you just love Dutch?) in the Netherlands. And it is really wild looking.

It’s built across a section of the river that’s about 1/3 of a mile wide and divides it into six sections with nine concrete piers. “The flood gates across the openings are circular segments in cross section, and they operate by rotating, raised to allow ‘underspill’ to allow operators to control upstream levels and a complete 180-degree rotation for maintenance.

“All the gates are hollow and made of steel up to 40 millimetres (1.6 in) thick. The gates fill with water when submerged and empty as they emerge from the river. The four large central gates are 20.1 metres (66 ft) high and weigh 3,700 tonnes.

“A Thames Barrier flood defence closure is triggered when a combination of high tides forecast in the North Sea and high river flows at the tidal limit at Teddington weir indicate that water levels would exceed 4.87 metres (16.0 ft) in central London. Forecast sea levels at the mouth of the Thames Estuary are generated by Met Office computers and also by models run on the Thames Barrier’s own forecasting and telemetry computer systems.

“About 9 hours before the high tide reaches the barrier a flood defence closure begins with messages to stop river traffic, close subsidiary gates and alert other river users. As well as the Thames Barrier, the smaller gates along the Thames Tideway include Barking Barrier, King George V Lock gate, Dartford Barrier and gates at Tilbury Docks and Canvey Island must also be closed.

“Once river navigation has been stopped and all subsidiary gates closed, then the Thames Barrier itself can be closed. The smaller gates are closed first, then the main navigable spans in succession. The gates remain closed until the tide downstream of the barrier falls to the same level as the water level upstream.


Photo courtesy of

Photo courtesy of


“All told, there have been 119 flood defence closures up to the closure on 20 March 2010. It costs £16,000 to close the Thames Barrier on each occasion .” (Wikipedia)

Interesting stuff, eh??