On Sept. 8, the Federal Energy Regulatory Commission approved a May 2014 application from Juneau Hydropower Inc. for an original license to construct and operate the proposed Sweetheart Lake Hydroelectric Project, to be located on Sweetheart Creek in the Tongass National Forest, approximately 30 miles south of the City and Borough of Juneau, Alaska.
The project will occupy 2,058.24 acres of federal land administered by the U.S. Forest Service as part of the Tongass National Forest. The project’s authorized capacity being licensed is 19.8 MW.
A draft Environmental Impact Statement (EIS), analyzing the impacts of the proposed project and alternatives to it, was issued in October 2015. On May 31, 2016, commission staff issued a final EIS.
Sweetheart Lake is a 5.4-mile-long, 0.6-mile-wide, glacially-formed lake with a surface area of 1,414 acres at a normal elevation of 551 feet. Sweetheart Creek flows approximately 2.2 miles from the outlet of Sweetheart Lake to tidewater at Gilbert Bay.
The proposed project will consist of: a new dam constructed at the natural outlet of Sweetheart Lake; a reservoir outlet tunnel; an intake, power tunnel, and penstock; a powerhouse and switchyard; a tailrace; a transmission line and switchyard; and an access road. The new 280-foot-long, 111-foot-high roller-compacted concrete dam will raise Sweetheart Lake from a water surface elevation of 551 feet and a surface area of 1,414 acres to a new maximum water surface elevation of 636 feet and surface area of 1,702 acres, impounding 128,019-acre-feet of water.
Flows entering an intake will pass through a 9,612-foot-long, 15-foot-wide, 15- foot-high unlined underground power tunnel that will transition to an 896-foot-long, 9- foot-diameter steel penstock. The penstock will divide into three 160-foot-long, 7- to 9-foot-diameter buried steel penstocks connected to each of three 7.1-MW Francis turbines with 6.6-MW generators located within the 160-foot-long, 60-foot-wide, 30-foot-high concrete and steel powerhouse. The powerhouse will be located on Sweetheart Creek two miles downstream from the project dam on Sweetheart Lake.
Flows exiting the powerhouse will return to Sweetheart Creek about 1,300 feet upstream from the creek mouth on Gilbert Bay, through a 541-foot-long, 30- to 90-footwide rock tailrace.
The project’s transmission facilities will include: a 22,000-square-foot switchyard containing a step-up transformer located adjacent to the powerhouse; an 8.69-mile-long, 138-kV over-head transmission line and marine cable traversing Gilbert Bay, the Snettisham Peninsula, and Port Snettisham; and a 60-foot by 60-foot switchyard at the end of the transmission line on the north shore of Port Snettisham where it interconnects with the existing Snettisham transmission line. A 4,400-foot-long, 12.47-kV service transmission line and communication cable will extend from the powerhouse to a dock and caretaker’s facility, and a similar 10,000-foot-long, 12.47-kV service transmission line and communication cable will extend from the powerhouse to the dam.
The project will operate to provide continuous year-round flow to the powerhouse sufficient to meet a firm base-load for two units (13.2 MW) and a variable minimum instream flow in Sweetheart Creek below the project tailrace. The project’s third unit will operate when excess water is available. The project will draw on available storage during the low-flow winter months to reach a normal minimum pool level of 576 feet by April or May and capture flows between June and October to refill the reservoir to the maximum reservoir level of 636 feet, resulting in an annual reservoir fluctuation of about 60 feet.
Applicant contact information is: Juneau Hydropower, P.O. Box 22775, Juneau, AK 99802; (907) 789-2775.