Terror Lake

On a rugged Alaskan island accessible only by air or sea, Kodiak Electric Association (KEA) is a cooperative utility that generates, transmits, and distributes electricity to 5,800+ members. Schnabel helped KEA implement the final component of its Upper Hidden Basin Diversion project – increasing water supply to its Terror Lake Hydroelectric Facility, the cornerstone of its renewable wind-hydro energy generation system.

The Terror Lake facility is the primary source of KEA’s energy supply. We assisted KEA with capturing and conveying as much water as is practical from the adjacent Upper Hidden Basin watershed to supplement water supply to the facility. Our initial involvement in the project started in 2014 with preliminary planning and conceptual design. KEA expanded our role, asking us to provide a geotechnical field investigation, final design, and construction services all the way through to the project’s completion in 2019.

Diverting the water supply will help provide an additional 33 million kilowatt hours of energy annually – the equivalent of 2.2 million gallons of diesel fuel. Getting the utility closer to its goal of 100% sustainable energy, this outcome will allow KEA to continue to meet growing loads, spearhead a shift in energy consumption from diesel to renewable electricity, and support Kodiak’s waterfront as the regional processing hub for Alaska’s seafood industry.

The $70 million endeavor encompassed two 30-foot-tall rockfill diversion dams, a 4-mile-long gravel access road, a 3,000-foot-long diversion pipe and access road, and a 1.2-mile conveyance tunnel to the reservoir. Contractor Kiewit used the drill-and-blast method to construct the tunnel, with headings driven from both portals. The two dams are composed of zoned rockfill components including an upstream welded PVC geocomposite liner. The remote location and tricky weather conditions were a major influence on both the design and construction of the project.