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
Unplanned Barrier closures - the figures are complex.
Ignoring the test exercises and closures initiated
for other than tide/surge and river flow causes gives this graph which uses the figures
(numbers from Environment Agency, Hansard):
Barrier Closures against tidal surges and river flows.
However the following Hansard (Parliamentary reporting) question and answer reveals a rather more complex situation - (quoted from Hansard June 2005)
Norman Baker: To ask the Secretary of State for Environment, Food and Rural Affairs
if she will list the occasions on which the Thames Barrier has been closed in each year
since its inception; and what estimate she has made of the number of occasions when
it will be closed in (a) 2010, (b) 2020, (c) 2050 and (d) 2100.
Mr. Morley: The Thames Barrier is closed to protect London from high water levels in the River Thames. These high water levels result from tidal surge conditions in combination with high freshwater flows following rainfall over the Thames catchment.
The Barrier closures may be characterised as predominantly tidal-influenced (T)
or predominantly rainfall/fluvial-influenced (F).
Since inception, the Thames Barrier has been closed to prevent flooding during the winter flood season (generally October to April) on 92 occasions as follows:
Forecasting the frequency of future closures of the Thames Barrier depends on two principal factors:
(a) The impacts of climate change on sea and river levels based on the climate change scenarios currently available; and
(b) The extent to which these levels may be reduced by other flood risk management measures used within the Thames Estuary in conjunction with operation of the Thames Barrier.
Depending on the balance of factors described above, The Environment Agency's early studies indicate that the estimated frequency of closures will be as follows.
2010: 10—20 closures per year
2020: 20—35 closures per year
2050: 6*—75 closures per year
2100: 30*—325 closures per year
The lower figure for each year indicates the best predicted outcome based on lowest climate change scenario impacts and maximum use of flood management mitigation measures implemented from 2030 (shown by *).
The higher figure for each year indicates the worst potential outcome based on maximum climate change predicted impacts with no additional flood management mitigation measures implemented from 2030.
The Environment Agency is currently planning for the future of flood risk management within the Thames Estuary. For this purpose, it has established a project called Thames Estuary 2100 based at the Thames Barrier. The purpose of the project is to produce a flood risk management plan for the tidal part of the Thames Estuary covering the next 100 years.
Since the above figures were given:
2005-6 total 3?
18-JAN-07 2030-0300 [high river flow, storms]
21-JAN-07 1100 [high river flow, storms]
22-JAN-07 1200-1730 [high river flow, storms]
18-MAR-07 0930-1530 [Surge 0.8m, 6.55m at Sheerness]
24-JAN-08 1400-1500 [high river flow, Spring tide]
2007: total 7
The Thames Barrier and the future risks of flood
Met Office Climate change and the Thames Estuary, September 2008
BBC BARRIER NEWS
Bugsby's Reach: Barrier to Dome
; Frost Fairs
Cannon St Rb
The Great Stink
Charing Cross Rb
Magna Carta Is
Black Potts Rb
New Thames Br
Angel on Br
Papist Way Slip
Clifton H Br
Culham Cut Fb
Head of River
Medley Weir Site
Arks Weir Site
Old Mans Fb
Radcot Cradle Fb
Radcot New Br
Radcot Old Br
Bloomers Hole Fb
St Johns Br
Castle Eaton Br