IIHR Modeling Helps Modernize London's Sewers

Friday, August 15, 2014

The fabled River Thames flows through London, one of the world’s greatest cities. As the population of London continues to grow, the overtaxed Victorian-era sewer system is simply unable to cope. Many times each year, heavy rains push run-off into London’s combined sewers, causing them to overflow and spew sewage directly into the Thames. The result is a significant environmental and aesthetic problem.

According to the Thames Tideway Tunnel website, about 39 million tons of combined sewage and stormwate are discharged into the river in a typical year. The environmental impacts of these discharges are enormous for the plants, animals, and fish living in and around the river — 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 students and shop staff, are part of a massive effort to modernize London’s sewer system and protect the Thames. It is, engineers say, the largest wastewater infrastructure project in the world. Laboratory modeling related to the Thames Tideway Tunnels (TTT) project has been underway at IIHR since 2011, bringing in more than $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 plan calls for the construction of a 19-mile tunnel system, more than 20 feet in diameter, deep beneath the river to intercept the combined sewage in order to transfer and store it until it can be treated and safely transferred. IIHR is a key partner in the project, conducting physical modeling to simulate movement of water and air through the many interception chambers, drop shafts, and orifices required to capture the flow into the tunnel system.

Craig says that IIHR researchers have unique expertise and facilities for construction of the physical models required to design the various tunnel components and to verify the computational fluid dynamics (CFD) modeling performed by the CH2M Hill team. In fact, design specifications for some of the components were originally developed at IIHR. These include the vortex drop arrangement, perfected at IIHR in the mid-1980s, in which flow spirals down a vertical shaft from street level to the tunnel, and the so-called baffle-drop shaft, in which flow cascades down a number of baffles before entering the tunnel. IIHR’s design specifications for baffle-drop shafts were published just last year. IIHR engineers have the facilities and capabilities to thoroughly test and prove the designs, which must take into account the tidal nature of the Thames at London.

The drop shafts are just one important aspect of the project’s complex network of tunnels, conduits, and interception chambers that transfers sewage to the tunnels and onwards for treatment before it is eventually released to the river. 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 will be ready, with expertise and experience to help.