Cascade Creek Hydroelectric Project
The Cascade Creek Project is located approximately 15 miles north of Petersburg, Alaska, on Swan Lake. The Project utilizes the natural impoundment of Swan Lake with a surface area of 579 acres and usable stored capacity of 2,895 acre ft. “af”, assuming a 5 ft operational draw down. A lake siphon will be used to draw water from below existing minimum Swan Lake low water level to the power conduit. The power conduit consists of an approximately 16,000 ft long, 12 ft diameter tunnel bored portal to portal from the intake siphon to the powerhouse. The last 1,400 ft of tunnel before the powerhouse will be lined with an 9 ft diameter steel penstock. Tunnel gradient will be approximately one percent and include a 1,300 ft vertical shaft located approximately 2,200 ft from the powerhouse.
The powerhouse location is approximately 1⁄4 mile south of the mouth of Cascade Creek on Thomas Bay at approximately El 45. The powerhouse building is approximately 140 ft by 80 ft. It will house three impulse type turbines, each with a total rated head of 1,500 ft and a flow capacity of 225 cubic feet per second (cfs). The installed plant capacity plan is 70 MW. Discharge from these units will be directed by a short tailrace into Thomas Bay. The primary transmission line is approximately 19 miles long, consisting of an overhead/submarine 138 kilovolt (kV) segment running south from the Cascade Creek Project powerhouse to the existing Scow Bay substation located southwest of Petersburg. This substation is the northern terminus of an existing 138 kV transmission line connecting Petersburg, Wrangell and Ketchikan to the Tyee Lake Hydro Project.