Photo by Claude Schneider -
The Thames Estuary, Claude Schneider
The construction of the Thames Barrier was an eventual result of the 1953 floods.
It took 29 years from the initial alarm to the final working barrier.
The history can be found in 'The Thames Barrier' by Stuart Gilbert and Ray Horner.
Various solutions and sites were examined during this time. The designs included -
1960s proposal for a Thames Barrier
Proposal for Thames Barrier, 1960s
A Lift Barrier
Thames Lift Barrier design
A Swing Barrier
Thames Swing Barrier design
A Retractable Barrier
Thames Retractable Barrier design
The design chosen in the end was the revolving rising sector gate. A scale model was built to show the principal -
A model showing a cross section through a gate, showing how the gate is revolved.
You can get an idea of the scale by looking at the scale figure in a white coat in the left hand service tunnel
The revolving rising sector gate in its four possible operating positions -
The revolving rising sector gate's four positions.
Note the top right closed position with the flood levels marked. The point has been made that if (when?) a surge overtops the closed barrier this will not necessarily be a disaster for London upstream of the barrier. There is so much room in the river above the barrier that if it has closed substantially before high tide the barrier could be overtopped by 0.8m and the level at London Bridge only rise by 0.3m. However the defences downstream would have been overtopped by 0.6m and this might well have caused unacceptable flooding. It would however clearly count as 'writing on the wall'! If this began to happen on a regular basis it would obviously mark a new urgency in finding a replacement strategy.
Reinforced concrete piers, founded on the solid chalk 16 metres (52.8 feet)
below the water line, support steel gates, which can be lowered,
to allow shipping to pass, or raised to block surge tides and prevent flooding
in central London.
Coffer dams (watertight boxes of interlocking steel plates) were first sunk into the bed of the river. The water was pumped out and the piers constructed.
A main working area was set up on the south bank to receive and distribute the vast amount of materials required.
On the north, a huge dry dock was built in which the concrete sills were cast. After manufacture, the dock was flooded and tugs towed the sills into position between the piers. They were then flooded and sunk to the level of the river bed, 16 metres (52.8 feet) below. The largest of these units measured 60 metres (194.7 feet) by 27 metres (89.1 feet) by 8.5 metres (28 feet) and weighed 10,000 tonnes. They had to be manoeuvred into a confined space, against a fast flowing current and placed within a maximum permitted tolerance of 10 mm (under 1/2 inch).
The piers and the sills form the supports and seating for the gates, and platform bases for the operating machinery, so they had to be accurately built.
Reversible hydraulic rams - one pulling and one pushing - are used to move rocker beams connected to discs at each end, and these rotate the gates into any of the four required positions.
Floating cranes were again used to accurately position this machinery.
one of the large sills being towed from the flooded dock out to the piers.
Others under construction beyond.
The Thames Barrier - A Systems Study, Chris Wallace -
This land-mark civil engineering project is one of the success stories of British civil engineering ...
Other difficulties encountered and countered were problems with the river-bed geology affecting the bed/pier interface; collision of a ship with a coffer dam and of course, bad weather.
One unanticipated problem arose in the sheeting of the roofs to the piers. The doubly curved roof had to be laid in narrow strips which were joined by turning the edge of one sheet up and folding the edge of the next sheet over it, in a direction to make the joint water proof. On one side a right handed plumber could do the job normally, but the other side could only be done by a left-handed plumber, or a right-handed plumber working upside down. Fortunately it appears that enough left-handed plumbers were recruited.
[ or right handed plumbers willing to be hung upside down! ]
1984: Queen Elizabeth II opened the Thames Barrier -
Thames Barrier Opening Letter Cover, 1984
The Thames Barrier has been closed 182 times since it became operational in 1982 (correct as of February 2018).
Of these closures, 95 were to protect against tidal flooding and 87 were to protect against combined tidal/fluvial flooding.
With continued maintenance, the current tidal flood defences will continue to protect London and the estuary for longer than originally planned.
These defences form a system which includes the Thames Barrier and 350 kilometres of flood walls and embankments, smaller barriers, pumping stations and flood gates.
Many of these defences were built more than 30 years ago, when engineers planned for sea level rise of 8 millimetres a year.
However, the sea level is currently rising by about 3 millimetres a year.
Tidal flood defences need to protect London and the Thames estuary from both a predicted rise in sea level and also potentially higher and more frequent ‘storm surges’ (temporary further rises in sea level caused by certain weather conditions over the North Sea).
Sea level rise in the Thames estuary over this century could be between 20 centimetres and 88 centimetres.
However, climate change is less likely than previously thought to increase the height and frequency of storm surges.
The maximum predicted sea level rise is more than 2.7 metres by the end of the century.
However, this is the worst case scenario, and highly unlikely.
CLIMATE CHANGE - The Met Office
BBC BARRIER NEWS
Click for TIDEWAY TIDES at this moment, barrier state etc
NORTH BANK Bugsby's Reach: Barrier to Dome