Last Friday at the invitation of Thames Water, I went underground to see the how Bazalgette sewer system copes with overflows at its Combined Sewer Overflows (CSO) in Hammersmith onto the Thames. It was certainly a sight to go down to the chamber some 70 metres long and 8 metres high and imagine what it must be like when it is completely filled up with rain and having to pump out 24 tonnes of muck a second.
All the CSOs along the Thames collectively pump out 39 cubic metres of untreated sewage into the Thames but the sewers can’t cope any more as London’s population has more than doubled since the famous brick sewers were built after the “great stink” in 1860. Ourr water consumption has also greatly increased, so the present infrastructure has been overwhelmed by our growing city.
The Thames Water solution to this predicament is the Thames Tunnel supported by the Mayor and DEFRA. It’s a giant new sewer some 75 metres under the Thames, 13 miles long and wider then a tube tunnel. It will cope with any storm surges, storing and transfering the waste east where it will be treated.
In November we will have the second stage of the public consultation on the preferred route and works sites, the latter issue having raised some contraversy in some neighbourhoods in London. Let’s hope all the work sites have been moved from green sites like Cremorne Gardens in Chelsea to brown sites nearby, causing a lot less bother to local residents during the works phase.
Other issues raised include the cost of the tunnel. The total project costs are some £3.6 million which will be paid from an additional £50 per household charge. This has not stopped some like Hammersmith & Fulham council objecting and suggesting a shorter tunnel option referred to as the Jacobs Babtie solution, which would be a better fix financially. But this proposal would still leave 19 of the 34 unchecked and not leave enough capacity in the existing sewers to be able to transfer the flows captured by a shorter tunnel to sewage treatment works in East London in any reasonable time scale. The result would be sewage sitting in the shorter tunnel for longer periods, creating the very odour problem for local resident they wanted to avoid. This is particularly so for the residents of Hammersmith & Fulham, where the shorter tunnel would still run along their boundary with the Thames. Whilst full, the tunnel would not be able to cope with flows generated by storms.
So all in all, barring any major revolts in the second stage of public consultation of the preferred route and in particular the location of the works sites, this looks like a welcome and long overdue addition to London’s sewage infrastructure.