diamond geezer

 Sunday, February 22, 2015

Twice a day, through central London, the Thames rises high enough to drown a house. From low tide to high tide, the height of the river can change by up to seven and a half metres, adding billions of gallons of water to the capital and than draining it all away again. And yet if you only walk down to the river's edge once, it's all too easy to overlook the variation. So yesterday, on the day of the greatest spring tides, I turned up twice.

Low tide, 10.23am (0.09m) [10 photos]
It sounds ridiculously low, nine centimetres, but the central channel of the Thames never gets that shallow and river traffic can easily continue. What changes is how much lower the boats are, passing the foot of the bridge supports, and with pebbly foreshore uncovered to either side. In front of the Tate Modern a shingle bank slopes down into the river, while down at Battersea a muddy expanse appears. And that's not unusual, these beaches appear every day, but at extremely low tides an additional strip of riverbed is revealed that would otherwise remain underwater. And this brings the mudlarkers out, scavenging the exposed beach for treasure, or at least some scrap of human detritus that might be of interest.

My favourite access point is at the foot of Cousin Lane, along the edge of Cannon Street station, immediately beside the terrace of The Banker pub. The steps here are always open, day or night, the first part of the descent in stone and then more modern metal treads. Be warned they're steep, and potentially slippery because the river was washing over them only a few hours earlier. But at the bottom you enter a world most Londoners overlook, the opportunity to walk along the riverbed of Old Father Thames. It's not the most welcoming of environments, so step carefully. The ground underfoot is rocky and pebbly, including chunks of built material and the occasional metal pole. Various piers and jetties have been embedded down here over the years, the most intriguing feature of which are the rows of wooden posts running parallel to the channel. You might spot the odd oyster shell or crockery fragment, but the most surprising omission is scattered modern litter. There are no plastic bottles, no cans, no unspeakable flushables, as if they've all been tidied up, or more likely washed away by the twice-daily tide.

When the tide's low you can easily walk beneath the tracks out of Cannon Street. It gets a bit up and down beyond, with a sandy dip and stony scramble, but a pair of stout shoes could see you most of the way through to London Bridge. I chose to head upstream beneath the City of London's refuse station at Walbrook Wharf. Normally it's unwise to wade past the two giant barges resting on the riverbed, but at particularly low tides a strip of shingle opens up below a long wooden beam and it's easy to slip through. A line of sodden wooden posts leads towards Southwark Bridge, beneath which the channel narrows slightly and it's possible to step out even further into the river. At Vintners Place a ladder and a set of steps give some indication of just how far down the riverbed is, while a concrete tunnel flows behind - dark, accessible and briefly Thames-free.

I wasn't here alone, a group of beachcombers were busy dislodging pebbles and poking in the mud, hunting for clay pipes and Roman tiles on this rarely-uncovered terrain. I heard no shouts to suggest that anyone had been successful. This part of the river is Queenhithe, once home to a Saxon port, and there are considerably more lines of wooden posts down here than I've seen anywhere else. There's also another access point here, a particularly steep set of stairs close to the Millennium footbridge. And yet I still caught sight of several pedestrians up on the Thames Path gazing down at us as if to wonder "How on earth did they get down there?" And we did it by knowing where the steps are, and more importantly precisely when the low spring tide was taking place. It is a wonderful feeling to be 'in' the Thames on an urban adventure, and walking along the very bottom of London. The river'll be almost as low at eleven o'clock this morning, if you're game.

High tide, 3.45pm (7.57m) [4 photos]
Five and a half hours later, what a difference. The spring tides bring extra high tides as well as extra low, and the Thames through London is looking particularly full. Normally the depth of the river at high tide is about six metres something, but that hits seven around the new moon, and this weekend over seven and a half. This means water lapping much higher than usual, still safely below the floodwall, but in places splashing over the top after a Clipper or rigid-inflatable passes through. Steps that previously gave access below are covered over, with water frothing at the top, and passers-by exclaim "ooh, that looks high" without really knowing why.

Extreme high tide isn't as impressive as extreme low tide because the Thames's defences are so stoutly built. They've been constructed to contain such spring tides as these, hence the river merely looks full rather than threatening. But there are spots that succumb, more generally out of the centre of town (eg at Putney), though not exclusively so. At Old Billingsgate the Custom House Walkway has signs at both ends warning of 'occasional flooding' although this is the first time I've ever seen it happen. Ripples wash gently across the pontoon, which probably remains crossable with care in waterproof boots, but nobody's giving conditions the benefit of the doubt. It's a stark reminder of how vulnerable London nearly is to major flooding, if only the Moon wasn't so damned predictable.

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