Work starts on London's super sewer
Haven Seajack 2 is seen conducting site investigations work outside the MI6 building on the Thames at Vauxhall, London.
The Thames Tunnel project in London, now in the preliminary stages of site investigation, will be one of the biggest civil engineering projects in the UK.
Designed to handle the regular discharge of sewage into the metropolitan River Thames, the tunnel is Thames Water’s £4bn answer to the problem that sees London’s original Victorian sewers overflow around 50 times a year, sending some 39m tons of rain water overflow and sewage into the river. The water company predicts that this could rise to 70m tons in the next 10 years if not dealt with urgently.
The Thames Tunnel will be a ‘super sewer’, 8m wide, and up to 75m beneath the river bed. It will be about 20 miles long, running from the Hammersmith/Barnes area in west London under the river past Tower Bridge to Limehouse, before being diverted towards Beckton sewage works in Newham via Abbey Mills or Greenwich. It will absorb the content of 34 of the most polluting combined sewer overflows as identified by the UK Environment Agency.
To carry out ground investigations, jack -up rigs have been deployed along the river through central London to identify the various conditions the tunnel boring machine will come up against. The contract to provide jack-up facilities was awarded to Red7Marine, whose Haven Seajack rigs have been moved about the waterway by their own tug, Haven Supporter, and other vessels supplied by General Marine.
The previous government approved the scheme in 2007 and in 2008 Thames Water started discussions with the riparian boroughs, the Environment Agency, the Port of London Authority and Greater London Authority, all of whom provided input into the methodology and the choice of preferred route and construction sites.
A second phase of public consultation will begin this September when information resulting from the site investigation will be published in accordance with the Environmental Impact Assessment needed to support the planning application, which is due for submission in mid-2012. Thames Water says it will review the plans in the light of public reaction to the scheme.
The most vocal objections will centre on a series of riverside ‘shaft sites’ where access shafts and permanent pumping stations will be constructed. As well as extending into the river, these will consume scarce and valuable waterside amenity sites in Putney, Wandsworth and Chelsea, which are expected to be passionately objected to by various resident groups.
Objections to the overall scheme, which will raise metropolitan water bills by at least £1 per week, are unlikely to have any effect as the scheme is intended to meet EU directives on waterways, despite fears that under extreme circumstances the tunnel will not totally eradicate the problem and polluted overflows will still occur.
Once construction starts, Thames Water claim they will make the best use of the river, including wharfs and jetties, to transport construction equipment and excavated materials. They expect to deploy a ‘significant’ number of barges to ferry materials in and out of the sites. Initial construction of the tunnel is provisionally scheduled to start in 2013 and finish in 2020.
by Graeme Ewens
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