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The Thames Barrier consists of 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.

Thames Barrier Control Zone

A permanent Control Zone, encompassing the Thames Barrier, is established between Margaretness and Blackwall Point. All vessels navigating within this Zone are subject to the requirements of current General Directions as summarised below.

Navigation through the Barrier Control Zone

Under normal conditions navigation is through one span in each direction, which will be indicated by green arrows and red crosses on the piers of the Barrier.  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 and red crosses. Information regarding spans available for navigation will be broadcast in routine broadcasts at quarter past and quarter to the hour.

In addition to VHF radio, London VTS communicates with river traffic through illuminated Thames Barrier Notice Boards.  These are fitted with flashing red and amber warning lights and are situated on the embankment at the western and eastern limits of the Control Zone.  When either the red or amber lights are flashing, the Notice Board will display a message directing vessels to call London VTS on VHF Channel 14 for more information and instructions.

No vessel is to pass Margaretness inward bound or Blackwall Point outward bound during a Thames Barrier closure unless authorised by a Harbourmaster at the Thames Barrier Navigation Centre (London VTS).

Spans Open to Navigation

Light Signals

Each navigational span of the Barrier has an array of traffic signals on the ends of the adjacent piers to indicate whether the spans are open or closed to navigation.  The light signals will be displayed both by day and by night. Spans are open only to traffic in a single direction at anyone time.

Green Arrows will be exhibited from the ends of piers either side of the span(s) open to navigation. The arrows point inwards towards the span open to navigation from a particular direction.  Red Crosses will be exhibited from the ends of the piers either side of span(s) closed to navigation from one or both directions.

Spans Permanently Closed to Navigation

Span A to the south and spans H, J and K to the north are permanently closed to navigation and display at their centres the signals prescribed in the River Byelaws for closed bridge arches (see Thames Bridges – Lights and Shapes)

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:

a) comply with any signals exhibited on the Thames Barrier Notice Boards; and
b) navigate inwards through the northern most span and outwards through the southern most span open to navigation and having sufficient depth of water.

Further information about navigation through the Thames Barrier, including information on procedures for Barrier Closures is included in the PLA publication ‘Permanent Notices to Mariners’. Click here for more information.


PLA, London River House, Royal Pier Road, Gravesend, Kent DA12 2BG Tel. +44(0)1474 562200
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