Susitna-Watana Hydro is a large hydro project that would provide long-term stable power for generations of Alaskans. The project will generate 50 percent of the current Railbelt’s electric demand, or 2,800,000 megawatt hours (MWh) of annual energy, once it comes online.
As proposed, Susitna-Watana Hydro would include construction of a dam, reservoir and related facilities in a remote part of the Susitna River, 184 river miles from Cook Inlet, 87 river miles beyond Talkeetna and 22 to 32 river miles above Devils Canyon which acts as a natural impediment to salmon migration. Transmission lines connecting into the existing Railbelt transmission system and an access road would also be constructed.
The Alaska Energy Authority is in the mid stages of a long, complex permitting process with the Federal Energy Regulatory Commission (FERC) and hopes to file an actual license application in the near future.
The anticipated cost is $5.19 billion, including licensing and construction. The type and level of financing has not yet been determined. Initial models show Susitna-Watana Hydro rates will be competitive with other fuel sources at start-up.
Dam and Reservoir
As currently envisioned, Susitna-Watana Hydro would include a 705-foot dam built into the steep-sided Susitna River Canyon. The nearly 23,500-acre reservoir would stretch about 42 miles long with an average width of 1-mile, at normal maximum reservoir operating level, providing the water storage necessary to generate the electrical capacity to meet 50 percent of current Railbelt electrical demand, especially during critical winter months.
The reservoir fills during the spring and fall months when rainfall and snow melt is the greatest. It is expected Susitna-Watana Hydro will include three turbines, which will generate electricity when water is released to meet Railbelt demand. The maximum reservoir drawdown is anticipated to be 200 feet.
The height of the dam is measured from bedrock, which could be approximately 100 feet below the natural water surface. For perspective, about 605 feet of the dam will be visible above the downstream water surface. Thick alluvial deposits will be removed from the river bed in order to found the dam on sound bedrock.
The type of dam construction will be a roller-compacted concrete structure. Construction materials for the dam and appurtenant structures will use, as much as possible, rock from the structure excavations to minimize the quarry development.
Some additional stats:
- Maximum elevation of the dam: 2,065 feet (NAVD 88)
- Maximum elevation of reservoir water surface: 2,050 feet
- Minimum operating level of reservoir: 1,850 feet
- Approximate existing water surface at dam site: 1,460 feet
- Elevation difference between top of dam and existing water surface at the dam site: 605 feet
- Approximate distance to sound bedrock from existing water surface at the dam site: 100 feet