Google+ London Architecture Blog: Week 36 13 Feature #29 Thames Barrier

Saturday, 7 September 2013

Week 36 13 Feature #29 Thames Barrier

Thames Barrier
Project Team: Rendel, Palmer and Tritton (Design Engineers), Greater London Council (client), Costain/ Hollandsche Beton Maatschappij/ Tarmac Construction consortium (construction), Cleveland Bridge UK (manufacturer of the gates)
Date Constructed: 1974-1982
Location:  Thames Barrier Information Centre, 1 Unity Way, Woolwich, London, SE18 5NJ

The Thames Barrier is a flood defence system located on the River Thames in the Docklands, beside the Victoria Docks and to the east of the Greenwich Pensinsula. The Barrier protects the city from flooding by high tides from the North Sea. The barrier was designed by the engineers Rendel, Palmer and Tritton and opened in 1982.

High tides from the Thames Estuary have always proved to be a problem for London. When the Romans began building on the north bank of the River Thames (on what is now the City of London) slight flooding occurred around the River Banks but the small settlements remianed safe in their raised position. However, with expansion of the city for maritime trade and increases in population, combined with rising sea levels, flooding occurred much more frequently. Large scale flooding began to change the landscape of the city, and impacting on the maritime trade into and out of the city.This created a need for a stronger and more robust defence system.

The creation of the Land Drainage Act of 1930 led to proposals being drawn up for a unified flood defence system. Although the existing defences were upgraded, large scale flooding occurred in 1953, and in the 1960s a far more advanced moveable barrier system and advanced warning system was proposed ( to replace the existing barage). In 1968, the GLC (Greater London Council) was presented with designs for a moveable barrier which would offer a robust and economic solution, which provides protection but also allowed access for river traffic. The heights of the River banks were raised and in 1974, the GLC started work on the new flood defense system between Silvertown to the north and Woolwich to the south. The barrier was completed in 1982 and was officially by HM Queen Elizabeth II in 1984.

Since it has been in operation, the barrier has been raised 100 times to protect the city from flooding. It is anticipated that the current barrier will protect the city until 2070, when rising sea levels will mean the level of protection will no longer be sufficient. However, the Environment Agency has already began to research plans for a replacement which will protect the city up until 2100.

The barrier stretches 520m across the River Thames and provides flood protection for London from the Thames Estuary in the east. The barrier functions as a series of gates, some of which are fixed and some which can be open and closed to allow water flow and river traffic to pass through. The Falling Radial Gates adjoining the River bank at each end are only for flood protection and do not allow river traffic. They are positioned above the water surface and drop down when required for protection from high tides. Between these are the semi-circular Rising Sector Gates which are positioned on the River bed allowing river traffic to pass through and the water flow. During times of high tide, these gates rise up in a curve and block the flow of water from the East, creating a protective barrier. When the levels are safe, the barriers are raised further allowing water to pass underneath the barrier. The gates can also be raised to enable maintenance and inspection.

The gates are 20m high and are of a hollow steel construction which can fill with water when the gates are lowered and then drain when they are raised. The gates are powered by hydraulic cylinders located above water in small sculptural structures, designed in a fin like form, open at one end to expose the working mechanisms including the yellow arms which move the gates into their open and close positions. These enclosures are clad in zinc and provide a subtle contrast to the heavy machinery which they enclose.

Further details and a video of how the barrier works (links to the Environment Agency website).

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