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26 Feb 2019

Flicking through the channels the other evening, I found myself watching a programme about a sewer. It was soon obvious, however, that this wasn’t just any old sewer, but the Thames Tideway Scheme, a 25km tunnel passing through central London at a depth of between 35-65 metres. It is an incredible feat of Civil Engineering and I was soon hooked, marvelling at the enormity of such a project.

London’s original sewerage system was designed in the mid 19th century by Sir Joseph Bazalgette. At this time the population of the city was 2 million (although astute Bazalgette designed his system to be able to cope with double this number.) The population of London is now 8.5 million and the system, whilst still in good condition, simply can’t cope. It is a ‘combined’ sewerage system which collects not just waste from toilets, sinks, showers and washing machines, but also rainwater and run off from roads, gutters and pavements. At times of heavy rainfall overflow goes into the Thames, and in the 1850’s this happened maybe once or twice a year. Nowadays, with more people, more waste water and more buildings covering the green spaces that soaked up excess water, it happens every week.

Although new sewers have been built to serve outer London the contamination of the Thames reached crisis point and work commenced in 2016 to build the UK’s largest ever infrastructure project. The main tunnel has a diameter of 7.2 metres and starts in Acton in the west, winding up at Beckton Sewerage Works in the east, from where recycled clean water will be released into the Thames. When the project is completed in 2023 it is claimed that the ecological balance of the river will be restored, there will be less aesthetic pollution due to sewage derived ‘litter’ and those enjoying the river for recreational purposes will be better protected from disease.

This enormous project claims to reach out into the wider community and ‘re-connect’ London with its river. Much of the transportation of materials and spoil is by barge in order to reduce its environmental impact, and street art will follow the course of the tunnel above ground. The scale and complexity of the engineering involved will be harnessed to promote STEM subjects in local schools. Detractors counter this with the argument that the Thames Tideway is merely an expensive ‘stop gap’ and that, in the longer term, the real solution is to reduce building in the city and improve education as to what we should and shouldn’t be pouring down the sink or flushing down the toilet.