The London Tideway Tunnels are emerging into the spotlight, with the start of preparatory work in the centre of the capital.

Phil Stride, Head of London Tideway Tunnels, explains:

Lee Tunnel

The Lee Tunnel is the first of two we're proposing to substantially reduce the amount of untreated sewage discharged from London's Victorian sewers.

Subject to negotiating planning conditions known as a Section 106 agreement, the local authorities have this summer resolved to grant planning permission.

The Lee Tunnel construction contract will be the largest ever awarded in the UK water industry.

An extensive short listing process has whittled the bidders down to just two.

We are on track to appoint a preferred bidder later this year and plan to start work on site early in 2010.

Thames Tunnel

Meanwhile, detailed technical surveys for the longer and even more challenging Thames Tunnel are rapidly gathering pace.

Our team developing the tunnel's design are focussed on working out how it will connect to the 34 most polluting 'Combined Sewer Overflows'.

These are the points which the great Sir Joseph Bazalgette designed into the sewerage system to allow sewage to flow into the river after heavy rainfall, rather than back up on to the streets of London.

Our initial engineering challenge is to ensure we fully understand the ground conditions we'll need to negotiate during the construction, due to begin in 2012.

That's the reason why a large borehole rig appeared in the river outside the Houses of Parliament in July 2009. Over the next nine months a trio of rigs will be helping us understand the ground conditions deep beneath the river bed.

To ensure we have a complete picture, it's an exercise we're repeating at over 100 sites adjacent to the river too.

Another recent important milestone has been the publication of our Site Selection Methodology, following extensive consultation over the last year with the local authorities and other organisations potentially affected by the Thames Tunnel's construction.

Key planning consultees have also helped us develop our Stakeholder Engagement Strategy, which we will continue to refine this autumn in line with Government guidance for consultation relating to Nationally Significant Infrastructure Projects. (The Thames Tunnel has the potential to be considered by the new Infrastructure Planning Commission.)

The recent summer downpours, and their increasing regularity over time, have underlined just why the tunnels are so vital to London's future.

It's totally unacceptable for an average of 32 million tones of sewage to overflow into the nation's premier river each year.

There's a long way to go, but at last, after years of debate, we are now well on the way to getting an effective solution in place.

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