crossriver

With the Thames eternally flowing past, London invites contemplation but doesn't easily give out conclusions. Like the river, the city is in continuous flux and changing all the time, from day to night, from summer to winter, and from one year to the next. Even the simple things run deeper than the shallow surface suggests.

Ask, for example, which way the Thames runs. To a simple person, the answer is similarly simple: Water runs down the hill. There's fine logic to this and a grave flaw: The gradient that the water follows doesn't need to be based on gravity. Pressure can drive water up the hill, and so can the brute force of a steam engine.

For the river, these options are irrelevant, and yet there's more that meets a cursory glance. The Thames is a tidal river, one of the most elevated in the world. There's no competing with the Bay of Fundy (between Nova Scotia and New Bunswick) where the difference between low and high tide is a hardly believable 55 feet or the Severn Estuary (between England and Wales) where the tidal rise is close to 50 feet. But the Thames isn't exactly lying low, and for a waterway traversing a major metropolis, the numbers are baffling: Outside the Houses of Parliament, there are 25 feet between low and high water, each reached twice a day.

The tides do more than just go up and down: The alter the character of the riverfront with confusing irregularity. As the time of high tide shifts by an hour each day, areas near the river change in appearance all the time. Sometimes the sublime Millennium Bridge barely rises from the tired waters; sometimes it stands up as if on stilts. Sometimes brown waves lap on Southbank; sometimes the intrepid relax on thin slivers of silty beach, far below at the foot of the flood wall.

With these aquatic goings on, I was wondering what was actually going on. How do the tides get into London? The North Sea is a good 40 miles away. There are two possibilities, and I have been in heated discussions arguing the merits of either theory. The rising sea could push the water up the river. Or it could merely block its flow, its rising water level creating an barrier to prevent the river's emptying into the Channel. To put it simpler, and more dramatic: Which way does the Thames flow? Does the sea push upriver into London, or does everything come to a total standstill as the river hits the rising sea?

Wouldn't it be the coolest story if I had set out to answer this question by submerging myself in the chilly floods and feeling for myself the force of the mighty river. I could have taken this blog to a new level, had I transnavigated the fluid band by the power of my flapping arms and legs. Alas, I didn't. I've never even stuck my toe inside. But the other day, the feat was achieved nevertheless, and my question answered.

On one of the last nights of July, Matthew Parris, a 60-year-old newspaper columnist for The Times and former conservative politician, did the feat I was thinking of. Flouting common sense and positively endangering himself, he hopped into the quiet river of the night at Rotherhithe and went for the blinking torch a friend had placed on his apartment's balcony. It was a pioneering stunt, though not as literally groundbreaking as what had taken place a good 180 years earlier.

In the early 1800s, the father-and-son team of Marc Isambard and Isambard Kingdom Brunel, oddly named but renowned as giants of civil engineering, proposed the first tunnels underneath navigable rivers, and in London they put their plan into execution. Simultaneously digging with blunt shovels and stabilizing the developing hole with a wooden scaffold, they made their way from Rotherhithe to Wapping, slowly, laboriously and extremely miserably. As the bed of the Thames is not hard rock but soft clay and quicksand, liquid kept seeping into the building site without respite. Back then, the Thames was little more than an enormous open sewer; the workers were literally shoveling shit. Finished and lined with shiny glazed bricks, the tunnel provided an eerie underground promenade for Victorian aristocrats.

How times have changed. These days, Overground trains run through the tunnel at a rate of eight an hour, hardly slowing down to honor the daring feat. The water above has improved dramatically. The feces are long gone, and pollution has eased as heavy manufacturing has disappeared from English shores. Sea horses now roam the Thames Estuary, salmon make their way upriver, and sometimes a stray whale makes the river his home.

All this was good for Mr Parris, who could enter the water without a hazmat wetsuit and savor the exquisite quietness of the early-morning river with all his senses. It didn't help him with his navigation, though. He ended up three quarters of a mile upriver, swept along haplessly by a tidal current that he had seriously miscalculated. He emerged on the other bank coated in mud like a sow in heat, but he had proved a point. The sea does indeed push mightily into the river.