Seymour-Capilano Twin Tunnels

Delivering clean drinking water to Vancouver residents

Metro Vancouver | Canada | 2002-2015

7.1-km-long twin tunnels
bored under Mount Fromme and Grouse Mountain

predominantly unlined tunnels in rock

Welded steel watermain pipe in tunnels under high hydrostatic pressure

2 raise-bore shafts 275 m deep and one drill and blast shaft 180 m deep.


  • Metro Vancouver required an efficient solution to the challenge of treating drinking water from two reservoirs separated by a mountain range.
  • Tunnel design accommodated up to 650 metres of rock cover.
  • Tunneling avoided disruptive open-cut pipelines in North Vancouver streets.
  • Protecting the overlying groundwater table from the pressurized tunnel was critical to a successful design.


  • The twin tunnels link the Capilano Reservoir with the new, state-of-the-art Seymour-Capilano Filtration Plant, which has a 1.8 billion litres/day capacity.
  • Tunnel depth, alignment, and shaft locations were chosen to minimize tunneling in fractured rock and avoid glacial soil-filled valleys.
  • Tunnel depth required an optimized permanent rock-support design in the unlined sections of the tunnels.
  • Steel liners designed for up to 300 metres of head pressure were installed where tunnel watermain pressures exceeded groundwater levels.
  • Boring unlined tunnels in natural granite saved CAD$40 million and 10 kilometres of pipeline.
  • Infrared technology provided quality assurance for grout backfill behind the steel tunnel liners. Computational fluid dynamics (CFD) aided the design of sand traps and ensured any loose material from the unlined tunnel will be intercepted.


  • Metro Vancouver’s first treated water tunnel to include unlined sections.
  • Temporary caverns at shaft and tunnel junctions enabled tunnel-boring machine (TBM) operations and steel pipe installation.
  • Innovative design approaches produced a resilient tunnel and employed new technology.
  • Recipient of the 2016 Award of Merit, BC Association of Consulting Engineering Companies.

Project Numbers

Capital cost of CAD$250 million
14.2 km of 3.8-metre-diameter, main-beam TBM-driven tunnel
Shafts of 180m and 275m depths
Tunnel depths of up to 650 m.
Approximately 5.5 km of 3.0-metre-diameter pipe installed in tunnels and shafts