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May 17, 2019
Culmback Dam Water-Temp Conditioning Tunnel
General contractor: IMCO General Construction
The purpose of this project was to provide optimal water temperature to the Sultan River downstream of Culmback Dam to enhance the productivity and survivability of local fish. This was accomplished by diverting water from the existing power tunnel through the newly constructed water temperature conditioning tunnel to the river. One challenge was ensuring that ESA-listed Marbled Murrelets and their old-growth habitat was not disturbed during construction. This 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 tunnel. Four hundred feet of tunnel conveys water to the concrete tunnel plug. Beyond the plug, pipe ranging from 24 to 72 inches conveys water through the remaining 300 feet of tunnel, into the creek. The new conveyance pipeline connects into this system and sends water from the power tunnel to the creek to increase water temperatures.