1F1: Tazimina River Hydroplant Example: Proving that hydropower is viable in subarctic environments, with desirable adaptations necessary for year-round operation to accommodate severe winter climate
July 13, 2022
Operations and Maintenance
By George Hornberger (INNEC General Manager), Paul Berkshire, P.E. (HDR), Mark Dalton (HDR), and Ed Zapel, P.E. (NHC) The Tazimina River hydropower project in southwestern Alaska has been successfully operating to displace diesel generation for the native communities of Iliamna, Newhalen, and Nondalton since the early 1990’s. The local electric cooperative utility serving the community of several hundred households, school, and businesses in this spectacularly beautiful region of Alaska serves as a critical element in the sustainable future for the area’s residents. The climate in this part of southwestern Alaska is at the edge of the subarctic region, with winter temperatures regularly plunging well below zero and at times remaining there for weeks at a time, three to four months of continuous ice cover on rivers, streams, and lakes, and considerable snowfall. INNEC, the local electric cooperative, engaged HDR Alaska in the early 1990’s to design a hydropower project that takes advantage of the natural Tazimina Falls of the Tazimina River, about 20 miles northeast of Iliamna. Mr. Paul Berkshire of HDR was one of the two principal designers of the Tazimina hydroelectric project, and has continued to support INNEC on the project throughout its long history, as well as more than a dozen small to medium hydropower projects he has designed for multiple electric cooperatives and utilities throughout southwest and southeast Alaska. HDR staff, including Mr. Dalton and Mr. Zapel and others, continue to support INNEC and the local communities with critical engineering and environmental expertise. The Tazimina project incorporates many features that help to isolate its operations from the otherwise very difficult climate in winter. An intake submerged in the Tazimina River above the falls delivers up to 120 cfs flow through a buried penstock and vertical shaft to an underground powerhouse to produce up to 800 kW of clean renewable hydroelectric power through two turbine/generator units, which then discharge through a short tunnel back to the river below the falls. The Tazimina River ices over in late fall in November or December and remains under ice and snow until April or May each year, even though river flows continue from Tazimina Lake upstream. The project is run-of-river, using only a low submerged partial sill of large concrete blocks to direct part of the flow of the river toward the intake. These sill blocks occasionally are thrust out of alignment by large ice floes, and small changes in river channel alignment require periodic adjustment of their alignment. During freeze-up and any time open leads form in the river during winter, frazil ice and anchor ice forms, and this has caused intake clogging problems many times in the past, requiring INNEC staff to remove ice from the intake until the lead closes or ice cover returns. In 2017, HDR designed a new robust, heavy duty flush-mounted counterflow hollow aluminum trashrack system for each of the four submerged intake openings that is heated with an antifreeze solution to a few degrees above freezing to minimize frazil and anchor ice clogging of the intake opening. The original trashracks were destoyed during a particularly harsh spring ice breakup season a number of years ago. The new fabricated hollow-core trashracks were installed in March of 2018 while river flows were at their lowest under the ice. The ice cover was excavated using construction equipment to expose the intake for the work. This paper discusses the various features of the project that ensure that it provides sustainable, carbon-free electric power to the three isolated communities despite the harsh environment, effectively displacing hundreds of thousands of gallons of diesel fuel that would otherwise be used by the diesel generators that now are reserved to provide emergency back up power. INNEC has been nearly 100% powered by hydropower since the Tazimina River project was constructed.