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 Watch the talks from London under water [June 2008]

Will we need another Thames Barrier?

The Thames Barrier is a unique flood control structure on the River Thames at Woolwich Reach in East London. It is 520 meters across and protects London against flooding caused by tidal surges from the North Sea.

The barrier currently protects 125sq km of London, including an estimated 1.25m people, £80bn worth of property and infrastructure, a large proportion of the London tube network and many historic buildings, power supplies, hospitals and schools.

It took eight years to build the structure, costing £535m (£1300m at 2001 prices) and became fully operational in 1982.

Who is responsible for the Thames Barrier?

The Environment Agency is responsible for maintaining and operating the barrier, which is estimated to cost £6m per year, employing 80 staff in operating and maintaining the barrier and the associated flood defences including the Barking and Dartford Creek Barriers.

The decision to close the barrier is taken by the Barrier Controller, and the incoming tide is predicted using data from the barrier’s advanced computer analysis and Storm Tide Forecasting Service provided by the Met Office.

This service monitors tides along the east coast of England and as far away as the Western Isles in Northern Scotland.

How does the Thames barrier work?

The barrier is a series of 10 separate movable gates across the river.

Closing the barrier seals off part of the upper part of the river from the sea. When not in use, the gates rest out of sight in curved recessed concrete cills in the riverbed, which allows river traffic to pass through.

Each of the main gates is constructed as hollow steel-platted structure over 20m high and weighing around 3,700 tonnes, capable of withstanding an overall load of more than 9,000 tonnes.

The barrier is able to close in just a few minutes; however more time is allowed to reduce the chance of a reflective wave being created, which are capable of causing small scale floods downstream.

Figures from the Environment Agency show that over the last 25 years the Thames Barrier has closed  106 times, over half of which have occurred since 2000.

 How the Thames Barrier works - Environment Agency

A dramatic rethink - Why the Thames Barrier was built?

The 1953 floods lead to a rethink of London's flood strategy 

Before the barrier was built, the solution to flooding was to build higher and stronger river walls and embankments – a solution that became popular following the Thames Flood Act of 1879 and remained an accepted measure until midway through into the 20th century.

In 1953 the Thames Estuary experienced a widespread flood which claimed 307 lives and caused an estimated £50m damage (£5bn at today’s costs).

This lead to a dramatic rethink of the way in which flood defences were built to protect London.

Following a report in 1966 by Sir Herman Bondi, it was decided that the best solution was bank raising and a flood barrier with movable gates built across the Thames.

The Thames Barrier and Flood Protection Act 1972 gave powers to carry out this solution and led to the construction of the barrier.

The future of the Thames Barrier

The Thames Estuary 2100 (TE2100), headed by Dave Wardle, is a cross-regional Environment Agency project to develop a tidal flood risk management plan for the Thames estuary through to 2100.

The strategy will take into account increasing flood risk due to:

• climate change
• rising sea levels
• changes in land levels
• the natural ageing of defence infrastructure
• new development in the tidal flood plain  see Thames Gateway articles

The final plan will recommend what flood risk management measures will be required in the estuary, where they will be needed, and when over the coming century, based upon the climate changes and sea level rises the capital will face.

The project will produce a final plan in 2010 for submission to the Department for Food and Rural Affairs (Defra)

Thames Estuary 2100 Project

The Thames Barrier is not the only structure designed to protect London in the event of flooding.

Other tidal flood defence structures and measures include include: the Barking Barrier, King George V lock gate, Gallions Flood Gate, Dartford Barrier, Tilbury Dock, Fobbing Horse, Easthaven Barrier, and Benfleet Barrier. In addition to these, the tidal Thames has 36 major industrial floodgates and 480 smaller moveable structures – mostly protecting residential property.

 Watch the talks from London under water [June 2008]