The Seymour and Capilano reservoirs supply 70 percent of metro Vancouver. But to get the water to Vancouver’s new Seymour-Capilano Filtration Plant, a roughly decade-long project to build twin 4.4-mile-long tunnels was required.

That project nears the final moments, as the tunnels will wrap yet this year and the overall project will come online in 2015.

Each of the twin tunnels run 12.4 ft in diameter for the length of the 4.4 miles, ranging from 525 ft to as much as 2,100 ft below ground. The massive tunnels, including the shafts, took six years to excavate, one year to install the permanent support and two years to line, according to Metro Vancouver officials.

Since the Seymour-Capilano Filtration Plant is higher in elevation than the Capilano Reservoir, excess pressure gets generated when treated water is returned through the treated water tunnel. Using a new energy recovery facility and its turbine, energy will be harnessed from the excess pressure. This energy will be used to partially offset the power requirements of the brand-new Capilano Pump Station, which sits ready for the completion of the remainder of the project.

In order to treat the Capilano source, untreated water from the Capilano Reservoir gets conveyed through one tunnel to the filtration plant. Once filtered, the treated water will return to the Capilano water distribution system using the second twin tunnel.

As part of the larger project, a new 1.3-mile, 6.9-ft diameter water main will replace an existing aging and seismically vulnerable water main along Capilano Road and the drainage works around Cleveland Dam are being enhanced to control groundwater seepage and slope stability. 

Tim Newcomb is Engineering News-Record’s Pacific Northwest contributor. He also writes for Popular MechanicsSports Illustrated and more. You can follow him on Twitter at @tdnewcomb or visit his website here.