Last year engineers were surveying a part of London's Victorian sewer network and made a surprising discovery when they were confronted with a vast concrete blockage that was rapidly nicknamed the 'Concreteberg'.
Nearly 105 tonnes of concrete had inadvertently been dumped into the sewer network to create a 100 metre-long mass, which then took several weeks to excavate.
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While the Concreteberg was remarkable for its whale-like scale, there have been other grim blockages in the London sewer network – most famously the 'Fatberg' made up of cooking fat and baby wipes, dubbed the 'Monster of Whitechapel', which became enough of a celebrity that part of it ended up in the Museum of London.
Somewhat fittingly, the engineers who found the Concreteberg were actually surveying the network for telecoms company SSE Enterprise Telecoms before installing new technology which could not only deliver 5G and broadband, but also create a fibre-optic monitoring network to help spot such blockages in the future.
London's Victorian sewers have served as a route for broadband cables for a couple of decades. Using the sewers rather than digging up the road is a much more efficient way of extending broadband services, and as much as ten times cheaper than digging up the road.
SSE Enterprise Telecoms has a 131km London network and recently rolled out a 20km fibre network in the London sewer to support 5G trials. "Previously you'd have had to close all the roads down and dig up the roads," said Paul Clark, director for the utility sector at the company. "In our 20km, we had about 1km that required traditional digging and road closures – everything else was done within the sewers."
But what's newer is using those fibres to make it easier to monitor what's going on underground, which makes being involved with these projects more attractive to water companies. "The benefit we can add is that it helps them and helps us run fibre across areas that are very costly," Clark said.
The telecoms fibres monitor the sewer network using acoustic technology that listens for changes in sound, while thermal monitoring technology picks up temperature changes – the sort that might happen if a tunnel was filing up with water due to a new blockage.
"The fibre is the monitoring device," Clark explained. "If there is damage in the pipe, that will change the sound in that particular point in the network and that's picked up by these devices so it helps pinpoint where the damage is."
If the technology had been in place at the time of the Concreteberg, it could have picked up the sound as the concrete was poured into the sewer and indicated that something was going on.
"Without the sensing technology there could be a lot of this happening," Clark said. "If we'd had the sensing technology in there already it would have picked up that something was happening at the time it was happening."
The Concreteberg wasn't the company's only discovery; later in the year a telecoms chamber installation dig uncovered human remains dating from the 1600s beneath a church near St Mary Axe, in the heart of the City of London; after the authorities established there was no foul play, the bones were re-interred close to where they were discovered.
While it's easy to visualise the cables in London's massive Victorian sewers, cabling can also be run through much smaller pipes using robots.
"Once you've got the technology in there you don't have to send people down in an environment that is really hostile, and with the smaller pipes you can't send people in anyway, so there's no way they can tell if the pipe is damaged," said Clark.
Last month, the government said it is looking for new ways of getting high-speed broadband delivered as widely as it can across the country, and is exploring ways to make it easier to run cables through the electricity, gas, water and sewer networks that span the UK, or along road or rail networks. All of this means that getting your broadband out of the sewer pipe might become a lot more common in future.