Thames Tideway Scheme

The Thames Tideway scheme is a proposed 25 km (16 mi) tunnel running mostly under the River Thames through central London, intended to provide storage and conveyance of combined raw sewage and rainwater discharges that currently overflow into the river. On 12 September 2014, the UK Government approved the plans, overriding some of the findings of the Planning Inspectorate. The decision has given rise to at least three Judicial Reviews.The Thames Water project involves construction of a tunnel (the Thames Tideway Tunnel) running from Acton in the west of London through to Abbey Mills in the east, controlling 34 of the most polluting combined sewer overflows (CSOs) via transfer tunnels along the way or system modifications. The captured sewage will then be transferred to Beckton Sewage Treatment Works (currently being upgraded to increase capacity) via the Lee Tunnel (already under construction) for treatment before being released. The main tunnel will be approximately 25 km (16 mi) long and have an internal diameter of 7.2 m (24 ft). It will run through the centre of London, mostly under the River Thames, at a depth of 30 m (98 ft) in the west through to 70 m (230 ft) in the east.Once constructed the system is expected to reduce the number of overflow events to a maximum of four per CSO per year at time of commissioning, increasing gradually due to effects of climate change and population growth.Starting in 2016, construction of the Thames Tideway Tunnel would take seven to eight years. Its current planned target completion date is 2023.The current estimate of its capital cost - excluding unknown financing costs and ongoing operations and maintenance costs - is £4.2 billion in 2012 prices. The budget for the scheme has steadily increased since it was first put forward - for example, the stated budget in 2004 was estimated at £1.7bn, which included the Lee Tunnel and sewage treatment works upgrade costs. In the words of the Consumer Council for Water:""The estimated cost of the project has escalated, from £1.7bn in 2004 (including Lee Tunnel and sewage treatment works (STW) costs) to £2.2bn in 2007 (also including Lee Tunnel and STW costs) to £3.6bn now for the shorter Thames Tunnel as far as Abbey Mills, plus some £1bn for the Lee Tunnel and upgrade of works at Beckton. The total costs of all the Tideway schemes have therefore increased from £1.7bn six years ago to £4.6bn today (all costs at relevant year prices). There is no guarantee that the current estimate will not be subject to further escalation.""Less than a year after this writing, a further £500m was added to the estimate.