The impressive Thames Barrier was built between 1974 and 1982 to protect central London from flooding at abnormally high tides. It runs from Silvertown on the north bank (London Borough of Newham) to Charlton on the south bank (Greenwich).
The total length of the barrier is 520 metres, and provision is made for four large navigable channels (61 metres wide) and two smaller ones which measure 30 metres. All the channels can be closed by hydraulically operated gates. The navigable channels have rising radial gates and smaller gaps closer to the bank are operated by falling segments.
Running the full length of the barrier through the concrete foundations are two parallel tunnels - named upstream and downstream. These carry essential services (and personnel) to the mid-river piers. Sub Brit was lucky to be given special permission to visit in January 2009, when around 120 members were guided round, including a climb to one of the piers from within. Access is no longer possible for the public.