Cordova Electric Cooperative


Humpback Creek Hydroelectric Plant

Humpback Creek Hydroelectric Project Features

General: The primary project features include a dam diversion structure that ponds water at 174 feet elevation above the power plant floor and develops a 12 foot deep pond of water that reaches approximately 500 feet upstream. A tunnel-and-pipeline power conduit conveys water 1,900 feet to a power house. A 17,000 foot underground and submarine transmission line delivers power from the project to a landing near Orca Adventure Lodge at the northern limit of the Cordova road system.

Diversion Dam and Intake Structure: The diversion dam is a 35 foot high concrete structure from bedrock to top. The dam features a 10 foot stoplog bay, a 3 ton jib crane, and a 10 foot x 10 foot Obermeyer gate for passing gravel and debris during high flows. A 3 foot x 8 foot sluice gate exterior to the trash racks sluices gravel and leafy-woody debris downstream, while an interior 2 foot x 2 foot sluice gate passes sand and debris downstream and away from the 7 foot x 7 foot penstock inlet gate. The intake features remote control lighting and video cameras. A concrete control building houses the electrical and mechanical equipment that operates the gates, SCADA, and tunnel ventilation. The plant is remotely operable over secure communications.

Power Conduit: The power conduit from the intake structure enters 113 feet of 54 inch diameter HDPE pipe, reducing to 3/8 inch thick 42 inch diameter pipe for the remaining 1,500 feet across a deep canyon bridge to a trifurcation (three pipes) entering the power house.

Powerhouse: The Powerhouse contains two 500 kW Francis turbines and one 250 kW Turgo turbine rated for 76 psi water pressure. A concrete tailrace returns water to Humpback Creek upstream of the pink salmon spawning beds.

Transmission Line: 17,000 feet of 25 kV rated Okonite solid conductor 1/0 aluminum EPR insulated wire energized at 12.47 kV is trenched down the beach to a submarine cable delivering power at Orca Lodge to the northern limit of the Cordova road system.

Access Roads: One 4,400 foot Eyak Corporation permanent access road runs from tidewater to upstream of the intake and diversion structures.