Barnard Snoqualmie Falls 2015 derik olsen 2968 reduced

After more than 100 years in operation, the century-old diversion dam and power plants located 25 miles east of Seattle needed an upgrade, an effort that included rehabilitating the world’s first underground powerhouse.

The Snoqualmie Falls Hydroelectric Operations are situated on a pristine river above Snoqualmie Falls. In the original design, an underground powerhouse was carved out of bedrock at the base of the falls, complete with a hand-mined 270-ft. shaft for access and the penstock. In 1910, an additional penstock and powerhouse was built, tunneling under a cliff for a flowline that fed external penstocks to a second powerhouse on the riverbank.

More than 100 years later, Barnard contributed to the design for the operation's redevelopment and expansion as PSE began the relicensing process with the Federal Energy Regulatory Commission (FERC). Our work included updating an underground 11.98 MW powerhouse by refurbishing four generators and replacing a fifth, while also enlarging the plant’s cavern and 270-ft.-deep shaft and updating other works. We also constructed a new second powerhouse to house a 12.5 MW turbine generator while preserving the 23 MW turbine generator and updating controls for both units. We completed this project while working around the roughly 2 million tourists who visit the falls and keeping the protection of the environment as an utmost priority.


Location: Snoqualmie, Washington

Owner: Puget Sound Energy

Engineer: Klohn Crippen Berger

Contract Type: Design-Assist; Guaranteed Maximum Price

Status: Completed


  • 2014 USSD Award of Excellence in the Constructed Project
  • 2012 American Council of Engineering Companies Washington Silver Award
  • Enlargement of a 270-ft.-deep shaft from 12. ft by 26 ft. to 12 ft. by 38 ft.
  • Upsizing and relining of a 1,200-ft.-long, 12-ft.-dia. flowline tunnel
  • New river intakes
  • Long-term cofferdams
  • Turbine replacement and refurbishment
  • Eight gates weighing up to 33 tons, fabricated and installed to +/- 0.03-in. tolerances
  • 20- to 30-ft. grouted and tensioned rock anchors for pier supports

1,620 LF of new penstocks

New Powerhouse to house 12.5 MW generator

>400 rock bolts

Barnard Snoqualmie Falls 2015 derik olsen 2937 reduced