Culmback Dam Water Temperature Conditioning Phase 2

Project Summary

This remote project enhanced and improved the fish habitat in the Sultan River to increase the productivity and survivability for local and anadromous fish species. Work involved tunneling into solid rock on the side of Culmback Dam and building a 700-foot water conveyance tunnel to tie into the existing power water tunnel. Four hundred feet of the tunnel conveys water to the concrete tunnel plug. Beyond the plug, pipe ranging from 24- to 72-inches in diameter conveys water through the remaining 300 feet of tunnel and into the creek. The new conveyance pipeline connects into this system and sends water from the power water tunnel to the creek to increase the water temperature. The new waterline transports water from varying levels of the lake above, to the stream below. 

Limited access influenced every aspect of the project. The work was located at the bottom of the dam, 200 vertical feet down a 450-foot long 26-degree slope. Crews used cranes to transport all materials and equipment to the base of the dam. The technical tunneling scope required an experienced hard rock tunneling subcontractor partner. The extremely tight worksite accommodated steel pipe installation, portal improvement, complicated material and personnel logistics, and operations by multiple subcontractors. 



Sultan, Washington


Snohomish County PUD

Contract Amount

$7.9 million


August 2017 - October 2018

Project Highlights

Working down the steep slope of the dam required outside engineering to develop a safe and efficient access route to transport equipment and materials down the face of the dam. The team's commitment, transparency, and positive attitude in the face of difficult logistics and limitations were key to success. The project had 24,137 labor-hours with zero time-loss incidents.