Thames tideway tunnel
The £4.2bn (at 2011 prices) Thames tideway tunnel project comprises a 24km long 7.2m diameter sewer 60m (average) below ground. The project plans were approved by the government on 12 September 2014. The tunnel will run from Acton in the west to Abbey Mills in the east. It will have a holding storage capacity of 1.6 million cubic metres.
Its purpose is to protect the River Thames from the frequent overflow of Victorian sewers designed for a much smaller population. Recently, flash flooding has caused sewers to back up and flood residences in west London.
Its route generally follows the Thames, at a fall of 1 in 790, it intercepts 34 overflow facilities and will require a number of significant connecting tunnels to other existing sewers. The project also includes new, expanded or replacement pumping stations, increased capacity storm water holding tanks and expanded sewage treatment works at Beckton which will capture the new tunnel contents via the newly constructed Lee Tunnel.
Thames Water (via a special purpose vehicle, Thames Tideway Tunnel Ltd) tendered the main tunnel work to the international market in three sections. UK consortia have been selected for all three projects:
- West section £300m - £500m, Nuttall and Morgan Sindall.
- Central section £600m - £900m, Laing O'Rourke and Ferrovial Agroman.
- East section £500m - £800m, Costain and Vinci and Bachy.
Construction is due to start in 2016 and complete by 2023. There are 23 construction sites. Some are on land already owned by Thames Water and others are on new sites still to be acquired, particularly those on the Thames foreshore.
The river will be used as much as possible to remove excavated material and deliver tunnel segments and construction material. At the combined sewer overflow (CSO) interception sites, construction of vertical cylindrical shafts some 60m deep will be built with internal diameters ranging from 7m to 20m to enable connecting culverts to be constructed that link existing sewers to the new tunnel. The main drive sites will require even larger 30m diameter x 60m deep shafts to allow the tunnel boring machinery to be lowered into position.
 Sites (west to east)
- Acton Storm Tanks - main tunnel starting point and combined sewer overflow (CSO) interception.
- Hammersmith - pumping station, CSO interception and connection tunnel drive site (CTDS).
- Barn Elms – CSO interception and CTDS
- Putney Embankment Foreshore – CSO interception and CTDS
- Carnwath Road Riverside – Main tunnel drive reception and connection tunnel from Dormay Street reception site.
- Dormay Street – CSO interception and CTDS.
- King George's Park – CSO interception and connecting tunnel reception site.
- Falconbrook – pumping station CSO interception and CTDS
- Cremorne Wharf Depot – CSO interception and CTDS
- Chelsea Embankment Foreshore – CSO interception and CTDS
- Kirtling St – main tunnel double drive site
- Heathwell Pumping Station – CSO interception and CTDS
- Albert Embankment foreshore – CSO interception andCTDS
- Victoria Embankment foreshore – CSO interception and CTDS
- Blackfriars Bridge Foreshore – CSO interception
- Shad Thames Pumping Station – system modification
- Chambers Wharf – main tunnel drive and reception site
- Earl Pumping Station – CSO interception
- Deptford Church St – CSO interception
- Greenwich Pumping Station – CSO interception and CTDS
- King Edward Memorial Park – CSO interception
- Bekesbourne St – system modification
- Abbey Mills Pumping Station – Main tunnel reception site.
Thames Water are to fund £1.4 billion by spreading the cost across its consumers. This could add £80 to average annual bills by 2020 across its 15m customers. Thames Tideway Tunnel Ltd will raise £2.8 Billion (2011 pricing) for the capital works based on future revenue income contracted with Thames Water.
In July 2015, it was announced that Bazalgette Tunnel Limited would finance, deliver and own the sewer. This is a consortium consisting of Allianz, Amber Infrastructure Group, Dalmore Capital Limited and DIF.
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