Culmback Dam Water Temperature Conditioning Phase 2

Project Summary

The purpose of the project was to enhance the environment and improve habitat in the Sultan River to improve the productivity and survivability for local and anadromous species of fish. This remote project 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 in size from 24 to 72 inches 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. This new water line takes water from varying levels of the lake above, down to the stream below. 

The work was located 200 vertical feet down a 450-foot long 26-degree slope, at the bottom of the dam. Limited access influenced every aspect of the project. The concrete plug, which was constructed as part of the construction, was remotely accessible 400 feet from the bottom of the dam. The work included building a new 700-foot-long water conveyance tunnel connecting to the dam’s existing power tunnel, requiring an experienced hard-rock tunneling subcontractor for this technical scope of work. Crews used cranes to assist in transporting materials to the base of the dam. It was an extremely tight work-site where activity included steel pipe installation, portal improvement, and complicated material and personnel logistics around multiple other subcontractors.  



Sultan, WA


Snohomish County PUD

Contract Amount



August 2017 - October 2018

Project Highlights

The work was located at the bottom of the dam, with limited access, and 450 feet down a 28 degree slope. IMCO safety personnel and the management teams worked with outside engineers to develop a safe and efficient access route down the slope. The team showed great commitment and positive attitudes in the face of difficult logistics and limitations. They kept safety as a high priority throughout the life of the project and managed safety incidents with transparency and a proactive approach. The project had 24,137 labor-hours with zero time-loss incidents.