 water arrived at East Anglia (consisting of the counties of Norfolk, Suffolk and Essex) early on January 31st, continuing on to reach Canvey Island the following day. By this point over 100 people in coastal East Anglia had already been killed either by drowning or exposure to the freezing water. Canvey's defensive dykes were flattened by the 90 billion gallons of extra seawater and the island was completely submerged by the sea.
56 people died in this flooding. At this time there were no flood defences at all along the River Thames and further inland flooding killed another 150 people and ruined 160,000 acres of farmland. Almost 2000 people died along the British and Dutch North Sea coasts in total. This prompted an urgent inquiry by the British government into methods of flood prevention. The committee that conducted the investigation returned with a recommendation that a flood barrier be built on the River Thames to combat the risk of flooding from surge tides, one of which was responsible for the 1953 flooding.
Surge tides are "humps" of water up to 30cm higher than average sea level, caused by areas of low atmospheric pressure. They originate in the North Atlantic off the coast of Canada and usually pass north of the United Kingdom, but strong northerly winds can force them down through the North Sea, causing coastal flooding in Britain and Denmark.
The main problem with the idea of building a barrier on the Thames was the volume of shipping using the London Docklands. Ships were being built bigger and bigger at this time and it was felt that any barrier design would have to allow at least 1400ft clearance when open in order to not impinge on river traffic. This factor limited the points in the river at which the barrier could be built without widening the river itself. However, once the new container docks at Tilbury were built, river traffic diminished significantly in both size and quantity, and only a 200ft gap was necessary - the same as Tower Bridge. This made the design of the barrier system easier from an engineering standpoint (easier hold back 200ft of water than 1400ft of it), and gave more possibilities as to where to put it. The further downstream the barrier could be built, the more land it would be able to protect.
41 design proposals were submitted for flood prevention/control measures for the Thames. The design selected was created by Charles Draper, chosen for the minimal interference it would make to the normal flowing of the river and its traffic, its compactness, its relative simplicity and its looks (such as they are). Construction of the barrier began in 1974 and took eight years, at a cost of £535 million. It is worth noting that today it has an estimated value of over £10 billion, taking into consideration the cost of repairs after any significant flooding of the 45 km2 area it protects - including the now-redeveloped docklands, which is home to Canary Wharf, amongst others - which is estimated at £20 billion.
The design, the world's largest movable flood barrier, consists of nine concrete piers built into the solid chalk bed of the Thames. Between these piers are ten individual barriers. The piers contain rocker beams operated by push-pull hydraulic rams, which rotate the four main barriers between positions. There are two of these mechanisms on each pier - one for the barrier section on either side - meaning each barrier is operated by a movement beams at either end.
The simplest way to think of each of the main barriers is as a hollow cylinder with two-thirds of its sides removed. Flat rotating discs are at each end to support the barrier of which one side is flat and the other flush with the discs, between which it is fitted. Viewed in cross section, when raised each barrier looks something like this:
**** B |C**
** A |CCCC**
A - Central pivot point
B - Pivot point for rocker beam
C - Barrier section
Each of the four main barrier sections are 20 m high - about the height of a 5-storey
building - and weigh about 3,700 tonnes
each including their movement arms. Each section is capable of 