Saturday, September 23, 2017

The Thames Barrier: Protecting London

In early 1953 a storm out of the North Sea drove the sea up the Thames estuary towards the capital. A storm tide, low pressure and high tide, overwhelmed London's defences and water poured onto the streets.

It was a wake up call and the response was the magnificent Thames Barrier (above), formally opened by the Queen in May 1984. A series of radial gates can be rotated into position to halt the waters and protect the city's gleaming towers and vulnerable tube tunnels.

Once a month there is a test in which all gates are raised and once a year an open day (also part of Totally Thames) when you can talk to staff, so I went along.

When I arrived all but one of the gates were in the up position but as I watched the final one, D span, started to rotate:

Within a few minutes it joined the others to a full raised barrier, stretching the 520 metres from bank to bank:

Each of the four main gates are over 20 metres high and, with counterweights, weigh about 3,700 tonnes.

The visitors centre gave further information, such as a moving cut-away model that showed inner workings. It also reveals some hidden features of the barrier - such as how the gates can be rotated beyond 90 degrees to create an underspill that allows the water flow to remove silt and avoid its build-up.

Most of the structure is purely functional, to ensure that there is as near as possible 100% availability, with back-up power supplies and in-house repair workshops.

But the silver arched roofs on the piers are not just functional but also architecturally elegant. They are self-cleaning and are built in a similar way to cathedrals.

A remarkable structure, which alas due to global warming, is increasing being called upon to protect London.


bonnie said...

Lots of studies on doing that here in NYC but no action yet...

JP said...

I imagine the engineering challenge for NY is greater - but then maybe the storm risk (e.g. Sandy) is also higher