Thames Water has invited contractors to bid for the Thames Tideway Tunnel, a £4.2bn, 15-mile (24km) long, 200ft (61m) deep tunnel that will capture 39 million tonnes of untreated sewage, currently flushed into the Thames every year.
The London sewer system, designed by Joseph Bazalgette in 1858, can no longer cope with present volumes of waste. Thames Water has proposed a solution in the form of a giant sewer to be built under the Thames. According to Thames Water, “The Thames Tideway Tunnel is needed to give greater capacity to a system built in 1850s to take both sewage and rainwater. London's population growth and the covering over of open land which could once absorb rainfall mean that a system designed to discharge to the river only occasionally, after exceptionally heavy rainfall, now discharges untreated sewage to the river on average once a week.”
There are 57 sewage overflow points into the Thames which discharge 16m tonnes of waste into the river each year.
The main tunnel will run from Acton to Abbey Mills, and at a further cost of £600, the Lee tunnel will connect it to the Beckton sewage works in the east. Six custom-built tunnel boring machines will drive under the capital’s existing infrastructure, including bridges, transport and utility tunnels, in-river structures, river walls and buildings. In addition to the tunnel and new pumping stations, contractors also need to intercept or control 34 combined sewer overflows that discharge into the river.
Work is expected to start in 2016 and take up to seven years. 24 construction sites will need to be built along the river. Thames Water has stressed the company hasn't asked the Government for a loan to for the works.
The plan is not without its critics: Hammersmith and Fulham Council says the main construction site will blight the Fulham riverside. It argues that there are much cheaper and greener alternatives available; Sir Ian Byatt, former head of the water regulator OFWAT doubts whether the city needs the Tideway Tunnel, and whether it will provide value for money. A Planning Inspectorate examination began on Thursday 12 September is expected to deliver its decision next autumn.