The $7 Billion Super Sewer

The $7 Billion Super Sewer

What London’s new ‘super sewer’ is and how it will help alleviate the capital’s drainage problems by preventing sewage being discharged into the River Thames.

15 Mile Long Tunnel Under The Thames To Help London’s Sewage Overflow

To combat increasing pressure on the capital’s existing sewers, a huge tunnel running from Acton in West London through to Stratford in the east is being built at a cost of £4.2 billion. The new sewer, to be known as the ‘Thames Tideway Tunnel,’ will mostly follow a route under the River Thames at a depth of 200 feet along various sections before connecting with the newly constructed Lee Tunnel; from here sewage from the new tunnel is moved to the upgraded treatment works at Beckton.

London’s Overflow Problem

A combination of increased population and more hard surfaces as London expands means the capital’s existing sewer system, originally constructed in the 1860s, cannot cope when increased water from rainfalls enters the sewers. This excess water is discharged straight into the Thames effectively turning the capital’s main waterway into an open sewer. This used to happen only about once or twice a year, but increased demands mean it’s happening more like once or even twice a week on average now. Three main issues are causing the current overflow problem:

Original sewers overstretched

Designed by Sir Joseph Bazelgette, the original sewers still work perfectly but are simply trying to serve a population double the size they were designed to cater for. London’s population stands at around 8 million, a figure that’s growing whereas they were built at a time when the population was just 2 million. Sir Joseph did have the foresight to anticipate future expansion, so the sewers were designed to cater for around 4 million but that’s barely half of what’s required now.

London’s physical expansion

As more housing, buildings, roads and pathways are constructed it means more of the capital is covered with hard surfaces. As a result rainwater has nowhere to go except into the drains and thus the sewer system, as opposed to being absorbed naturally by softer ground previously not covered in concrete or tarmac.

Climate change

Generally, the UK is experiencing milder temperatures and lower rainfalls but the rain is falling in greater concentrated bursts placing heavy immediate demands on the sewer infrastructure. This is becoming noticeable in a general sense when sewer performance suffers through drains in poor condition finding it hard to cope; effective drain maintenance is becoming more and more important for domestic and commercial users alike.

How will the new tunnel help?

Instead of overflow water containing millions of tonnes of untreated sewage being discharged into the Thames each year, downpipes at various points will intercept it, divert it into the Thames Tideway tunnel and enable the 7.2 metre diameter sewer to transport the sewage underground to Stratford and ultimately to the Beckton treatment works. Along with the new tunnel, other upgrades to London’s sewage facilities have been completed or are under construction. The £635 million 4 mile long Lee Tunnel - mentioned above as connected to the new Tideway Tunnel - has been built, and all of the five major sewage treatment facilities in London are subject to a £675 million upgrading programme. The Tideway Tunnel and the other sewage facility upgrades are expected to help London’s sewage and drainage requirements well into the 22nd century (with a likely construction of some 600,000 new homes in the area) along with improving the environment through cleaner river water. The Thames has been cleaned up markedly over the past three decades; the vast reduction in sewage thanks to the new tunnel will enhance this further. There will be a boost in terms of employment in the area while work is being undertaken on the new tunnel with some 6,000 jobs being created during construction. Not everyone is convinced the new tunnel is the best way of alleviating London’s sewage problem. Some say alternative solutions should have been investigated, including the original assessor who recommended construction of the new tunnel in the first place.

Financing and ownership

Thames Water and the government will own, manage and finance the tunnel through a private company set up between them. Thames Water will meet one third of the cost with the remaining £2.8 billion being funded by private investors. Eventually, the private company will provide sewage services to Thames Water with the cost reflected in the water bills of its customers.