diamond geezer

 Tuesday, October 07, 2014

Once a year the Environment Agency checks that the Thames Barrier is working by giving it a full tidal closure. They haven't really needed to do this in 2014, which is by far the most uppy downy year in the barrier's 30 year history. The gates rose only four times throughout the 1980s, whereas this year the tally is already 48 and there are still twelve weeks to go. Nevertheless the planned annual exercise must always go ahead, invariably on a post-equinoctial Sunday morning, and precise times can be determined by checking the official website in advance. This year, October the fifth.

Events always begin at low tide, in this case quarter to four in the morning, at which point the gates are raised one by one to stem the river's flow. Over the next six hours the tide is prevented from passing upriver and a height differential is created on either side of the barrier. Upstream the river level stays low, while downstream the river rises three metres, which looks simply unnatural. There is alas no viewing position from which both sides can be seen simultaneously, not unless you're standing on top of the barrier itself, which only employees and their special guests can do. There did seem to be a roaring trade in special guests this Sunday, parading out across the first bridge in their official black helmets before burrowing onwards to a central vantage point. Lucky them.

Those of us not fortunate enough to be a Thames Barrier special guest could only stand on the banks and gawp. Admittedly the view from the banks was fantastic (and better from the south side than the north because the sun was behind you). The barrier's seven streamlined silver piers stretched out across the river, their gates twisted into full defensive position, creating an artificial glassy sea. Normally the Thames is never still, but on closure day the water is becalmed and spectacular reflections spread across the surface with barely a ripple.

I'd turned up at high tide, an hour early for the main event or so I thought, and the paltry number of observers suggested others had thought the same. But then a siren went. The tide was running early (such phenomena are rarely as precise as nautical tables would have you believe) so the engineers in the control room had decided to move to the next phase an hour earlier than scheduled. One of the central 61m gates moved slowly into underspill mode, that's to an angle of 118°, creating a three foot gap beneath the water. This was enough to restart the flow, thereby beginning a three hour journey to eventual equilibrium. Protecting the capital is slow and steady, never speedy.

A second siren followed a quarter of an hour later, this the signal for a second gate to swivel into underspill. As the high tide trickled through, cleaning out the sills on the river bed, so a large flock of seagulls flocked and swooped above the waves. The churning water made for easy pickings, of whatever tasty aquatic morsels they could find, and even after a further hour the aerial display showed no signs of stopping. Further upriver the Greenwich Yacht Club were out on the water in force, taking advantage of the unnatural conditions and the absence of all other river traffic. And steadily the crowd of spectators grew, too late for the start of the flood but in plenty of time to watch it grow.

The rise in water level was almost imperceptible, it taking millions of cubic metres to fill a river half a kilometre wide. But still the tide squeezed in, creating choppy ripples across the upstream side (but still flat as a millpond on the other). Over the subsequent couple of hours this crystal pool gently sank as the high tide receded, eventually matching the rising level on the opposite side and allowing the gates to be heaved back into horizontal position. The event was an awesome sight, indeed it was hard to point a camera anywhere and get a less than amazing photo. And it all ran like clockwork, which is exactly what you want to hear if you live or work anywhere near the river between Silvertown and Putney. Sunday's closure confirmed the taming of the Thames, and all with consummate style, a tribute to 30-year-old technology that still protects and inspires.

My Thames Barrier closure gallery
There are 20 photos altogether [slideshow]

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