Click for TIDEWAY TIDES, barrier state etc
THAMES BARRIER
from Boating on the Thames - the Thames Barrier - which should be referred to if actual navigation is proposed!
The Thames Barrier has ten spans lettered A to K from south to north:
Spans B to G are open to navigation subject to the restrictions described in current General Directions.
Spans C, D, E and F are 61m wide with a depth of 5.8m below Chart Datum.
Spans B and G are 31.5m wide with a depth of 1.2m below Chart Datum and have depth boards on Piers 3 and 9.
Spans A, H, J and K are permanently closed to navigation.
Under normal circumstances, and subject to the requirements of partial closures,
the northern spans E, F and G are used for inward bound traffic
and the southern spans B, C, and D are used for outward-bound traffic.
(The piers of the barrier are numbered 1 to 9, from north to south.
There are signs indicating the number of the pier on both east and west sides of the barrier)
Thames Barrier Control Zone
A permanent Control Zone encompassing the Thames Barrier is established between Margaretness
(next to the entrance to Barking Creek) and Blackwall Point (at the O2 Dome).
See
Recreational Users Guide
Thames Barrier Control Zone
.JPG)
Thames Barrier Schematic
Usually, traffic is routed through one span in each direction, which will be indicated by green arrows.
Spans which are closed to navigation will be indicated by red crosses on the piers of the Barrier.
*Do not navigate through a span which is closed to navigation –
the gates may be under the water or rotating to a defence position*.
Vessels intending to pass through the Barrier should contact London VTS on VHF Channel 14
at either Margaretness Inward bound or Blackwall Point Outward bound.
London VTS will then allocate a span which will be indicated as being available by the green arrows.
Occasionally, all the spans at the Thames Barrier may be closed either for test purposes
or because of a predicted tidal surge
(the EA promulgates test closures in advance.
See either the PLA’s
Notice to Mariners or the EA’s website
https://www.gov.uk/guidance/the-thames-barrier).
When this is the case, you should remain clear and not enter the Thames Barrier Control Zone
due to the unpredictable eddies and currents that are produced.
Spans Open to Navigation
Light Signals:
Each navigational span of the Barrier has traffic signals on the ends of the adjacent piers
to indicate whether the spans are open or closed to navigation.
Spans are only ever open to traffic in one direction at a time.
Green Arrows will be shown from the ends of piers either side of a span(s) open to navigation.
The arrows point inwards towards the span open to navigation.
Red crosses will be shown from the ends of the piers either side of span(s) which are closed to navigation.
Spans Permanently Closed to Navigation
Span A (the southern most span) and spans H, J and K (the northern most spans) are permanently closed to navigation and display closure signs which are also used on closed bridge arched (3 red discs in an inverted triangle)
Overtaking and Manoeuvring Restrictions
Any vessel wishing to overtake another vessel, or any vessel wishing to carry out manoeuvres in the Thames Barrier Control Zone, may only do so with the express permission of the Harbourmaster at London VTS.
Vessels Under Sail
Vessels proceeding under sail between the Woolwich Ferry Terminal and Hookness must keep to the starboard side of the fairway and are not to impede any other vessels. Whenever possible, such vessels should take in their sails and use motor power to navigate through the Thames Barrier.
Small Vessels (under 13.7 metres in length)
All small vessels and craft such as yachts, dinghies, power boats, sculls, rowing boats
and canoes not fitted with VHF radio are to navigate inwards through the northern most span
and outwards through the southern most span which is open to navigation (indicated by green arrows)
and which has sufficient depth of water.
Further detailed information about navigation through the Thames Barrier is included
within the PLA’s General Directions publications.
Click here to find our publications.
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
Thames Barrier, © Doug Myers 2005
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 BBC THAMES FLOOD NEWS