In summer 1858, when foul odors from the polluted River Thames forced the British Parliament to suspend its activities, legislators allocated funds to build London's first main sewers. A century and a half after the notorious Great Stink, the river is again under threat, this time from storm overflows.

Thames Water
TUNNEL TIME Thames geotechnical work platform rises from the river as Londons Big Ben loom onshore.
Thames Water
FOLLOWING THE RIVER The Tideway project comprises three proposed routes, all of which will feed the main tunnel. The River Lee tunnel, now under construction, will connect to the Abbey Mills route, and the River Thames route will connect to the Rotherhithe route.

Construction is starting on London's $7-billion Tideway program, which will include 39 kilometers of deep tunnels to intercept around half the 32 million tonnes of effluent that annually spills from the combined-sewer overflows.

Contractors are sinking huge shafts to accommodate 7 km of tunnels that will transfer combined-sewer overflows from the River Lee drainage in east London to a nearby Beckton treatment plant.

The $1-billion Lee interceptor will form the eastern extension of the main 32-km, 7-meter-dia collector tunnel, now in design, which will follow the Thames from the western boroughs and intercept 34 of the most polluting combined-sewer overflows (CSO) along the way.

Now estimated at $5.9 billion, the Thames tunnel will be many times bigger than any previous U.K. wastewater job, says Phil Stride, Tideway project leader with Thames Water Utilities, London.

While the budget is more than 60% above the desktop estimates made in 2007, it could have been as much as $1.6 billion more without the fine-tuning done in the past few years, says Jim Otta. As head of the utility's program management team of CH2M-Hill Inc., Englewood, Colo., Otta is acting as the Thames tunnel interim managing director.

Reducing the number of shafts reduced the Thames tunnel's budget and helped Stride fulfill his main responsibility of securing regulatory approval for the megasewer. With shaft sites dotting the riverbanks, some in prominent and high-value locations, the project has its detractors. “It's a ridiculous location,” said a borough councilor recently, when Thames Water identified a shaft site in his west London neighborhood. The sewer would stall the area's development plans for a decade, he claimed.

Cutting the number of worksites by 12 entailed a major review of how London's complicated drainage system functions. “When we first arrived, they were thinking they would have 34 shafts,” says Otta. “We said no. Each site [would pose] risks and problems. We used our own expertise to look at the network,” he adds.

The city's drainage system, which includes numerous covered rivers and streams, is “far from a typical network,” explains Otta. By monitoring outfalls, the team could “calibrate” the hybrid system and make it amenable to modeling. Additionally, the engineers put more emphasis on the quality of discharges rather than their frequency and volume, prime drivers in earlier planning, he adds.

With Thames tunnel planning and design well advanced, Stride aims to publish by fall the final route proposals, incorporating public comments. He hopes to secure final approval in about two years, aiming for a 2020 completion. In the meantime, Otta is turning more of his attention toward procurement.