Modernizing London’s Sewers
As rain pours down onto a London street, umbrellas pop open and pedestrians scatter. Small fast-moving rivers race down the street, eventually flowing into sewers beneath the city. The storm runoff quickly overtaxes the Victorian-era combined sewer system, parts of which are the “lost rivers of London” that were covered over as the city grew. Because the sanitary and storm sewers are combined, storm runoff quickly becomes more than the system can handle. Untreated sewage flows into the tidal River Thames, creating an unsightly mess and damaging the river’s ecosystem.
“People don’t realize what’s happening in the river,” says Bernard Woolfe, hydraulic lead on the Thames Tideway Tunnel (TTT) project that will modernize the London sewer system. “When they’re told, they’re pretty horrified.”
River Thames Pollution
This sewer overflow scenario happens many times each year. The result is a significant environmental and aesthetic problem. According to the Thames Tideway Tunnel website, about 39 million tons of combined sewage and stormwater discharge into the river in a typical year. The environmental impacts of these discharges are enormous for plants and animals — including humans.
“I’ve been down there at low tide,” says IIHR Research Engineer Jacob Odgaard. “It’s really bad. You have to hold your breath.” Odgaard, along with IIHR Engineers Andy Craig and Troy Lyons and a sizable crew of shop staff and students, are part of a massive effort to make London’s sewer system fit for a world-class capital city. It is, engineers say, one of the largest wastewater infrastructure projects in the world.
The Thames Tideway Tunnel Project at IIHR
Laboratory modeling related to the TTT project has been underway at IIHR since 2011, bringing in nearly $1 million in funding and requiring thousands of hours of work. “IIHR has remained at the forefront of research on deep tunnels and related hydraulic structures, working on projects in the United States and abroad, including Washington, D.C., Cleveland, Indianapolis, Toronto, Atlanta, Akron, and Abu Dhabi in the last 10 years alone,” Lyons says.
The TTT plan calls for the construction of a 19-mile tunnel system, more than 20 feet in diameter, deep beneath the river to intercept and store the combined sewage until it can be transferred for treatment at an expanded wastewater treatment works. IIHR is a key partner in the TTT project, conducting physical modeling to simulate movement of water and air through the many interception chambers, control gates, dropshafts, and deaeration chambers required to move the flow from the surface into the tunnel system.
Why did TTT turn to a contractor thousands of miles away for these services? IIHR brings unique expertise, experience, and facilities to the project, says David Crawford, chief engineer for systems integration on the TTT project. “There are not many laboratories in the world that can do it,” he says. “The quality of [IIHR’s] work is fantastic for us.”
Crawford says the IIHR team has proven competitive economically and technically. IIHR staff members are also able to meet a tight schedule, provide sophisticated testing, and cope with numerous changes to the models. Crawford says the relationship between IIHR and TTT, which includes staff members for CH2M Hill and Thames Water, has definitely evolved. “We don’t consider ourselves client and contractor,” he explains. “We’re here to solve our problems, and we’re all one team.”
“The people we’re working with [at IIHR] really understand our objectives,” adds TTT Hydraulic Engineer Joss Plant.
Dropshafts and More
IIHR researchers construct the physical models required to improve and verify the design of the various hydraulic structures and to particularly verify the computational fluid dynamics (CFD) modeling. In fact, design specifications for some of the components were originally developed at IIHR. These include the vortex drop arrangement, in which flow spirals down a vertical shaft from street level to the tunnel, and the so-called baffledropshaft, in which flow cascades down a number of baffles before entering the tunnel.
Dropshafts are just one important aspect of the project’s complex network of tunnels, conduits, and interception chambers. Each structure is unique and presents its own design difficulties, thanks to the complex infrastructure entangled beneath the city of London, Odgaard explains.
Despite its significant cost, Craig says the Thames Tideway Tunnel is crucial for the water environment and economic resources of London and the U.K. Odgaard agrees. “It’s not glamorous research,” he admits. “But it’s one of those projects that you really like to be involved with because it has such an impact.”
Lyons agrees, and points out that many larger cities are adopting similar strategies to deal with combined sewer overflows. And IIHR is ready with expertise and experience to help.
Plant adds that the TTT team has come to depend on IIHR. “We know we’re going to get quality results back,” he says. “Here, no problem is too big.”