My descent to the source of the Great Stink

12 April 2012

As I peered into the gloom 30 metres beneath the streets of Hammersmith, it wasn't hard to see why David Walliams had got sick swimming in the Thames.

From the top of the narrow hole down which I had descended in overalls, waders and miner's helmet, a noisome puddle had been visible at the foot of the ladder. "That's our bread and butter, mate," remarked the sewer worker hooking up my safety harness. At the bottom I walked gingerly down a passageway and into a huge underground chamber whose walls, roof and pumps were covered in raw sewage.

It's pretty dilute, and actually just smells foetid rather than anything worse. But that's the point: it's dilute because this is where the water surges through every time it rains heavily in west London - around 50 times a year - flushing the contents of the sewers into the Thames.

And that's a lot of overflow. The chamber I descended to is perhaps 70 metres long and eight metres high, and while only knee-deep in filth when I was there, it completely fills up when it rains. And keeps filling: at full tilt, the giant machines looming out of the murk can pump 24 tonnes a second into the river.

It's one of the bigger combined sewer overflows on the Thames. Each year they discharge a total of 39  million cubic metres of untreated sewage into the river, a figure that is rising fast. Hence a dodgy tummy for Walliams or anyone else in the water; and hence a lot of dead fish too.

The existing system has simply been overwhelmed by the size of our city. When Joseph Bazalgette built his famous brick sewers in the 1860s, he banished the "Great Stink" of the Thames by channelling waste to the east. His system is still the backbone of our sewer system. But since then the city's population has doubled, and its water use has increased enormously. The sewers can't cope.

Thames Water's answer is the Thames Tunnel, a giant new sewer planned to run up to 75 metres below the river bed. Wider than a Tube tunnel, more than 13 miles long and filled via outfalls along its length, it will cope with storm surges, storing and transfering waste to the east, to be pumped out there for treatment. If construction starts as planned in 2013, it will be complete in 2020.

When the second public consultation on the scheme begins at the start of November there will inevitably be arguments over the exact route and where the above-ground construction takes place.

There will be rows over the cost, too: £3.6 billion, paid for largely through water bills, at a cost of a little over £50 a year per household.

But despite the opposition of Conservative-controlled Hammersmith and Fulham council, nobody has yet come up with a workable, cheaper alternative. The Mayor and Environment Secretary Caroline Spelman both support the scheme. And until it happens, parts of the Thames will look like the unlovely picture that Hammersmith Labour MP Andrew Slaughter sends me from one of his constituents who lives by the river ("the stench is unbearable", she comments).

Meanwhile, it has started to rain outside my west London office. And I wonder where and when that
water will make its way out through the vast underground system beneath our feet.

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