Susitna Hydro

Summary

The proposed Susitna hydro project is a 600 MW facility to be constructed about halfway between Fairbanks and Anchorage on the Susitna River.   The total cost of the project is currently estimated at $4.5 billion, not including an additional $900 million for transmission and integration into the Railbelt.  The state legislature approved $66 million in 2011 to begin permitting and feasibility studies, with a target date of producing power by 2023.  Environmental concerns include the impact on fisheries and earthquake risk.  However, the facility would also displace a large amount of electricity currently generated from fossil fuels, reduce the need for other generation projects, and provide base load to supplement renewable sources like wind and tidal energy that have variable power output.

History

The hydroelectric potential of the Susitna River was first examined by the US Bureau of Reclamation in 1948.  Additional studies took place throughout the next 40 years, culminating in a series of major feasibility studies in the early 1980's.  In 1983, the Alaska Power Administration (APA) applied for a hydroelectric permit from the Federal Energy Regulatory Commission (FERC), but the overall price of energy was in decline in the early 1980's and eventually the application was withdrawn, ending all of the ongoing studies.  The project gained new life in 2008, when the Alaska Energy Authority (AEA) commissioned a comprehensive review and update of the previous work.

The 1983 FERC application called for two dams, one at Watana and one at High Devil Canyon, that would have provided a combined 1800 MW of electricity.  The application was later amended to a "staged" plan to spread out the costs over a longer time period, and estimated to cost $5.9 billion ($11.8 billion in 2010 dollars).

The AEA-commissioned reassessment of the Susitna project examined potential for placing a dam at Watana ($6.6 billion in 2008 dollars) or at High Devil Canyon ($5.4 billion in 2008 dollars).  Either alternative was projected to produce around 1200 MW of electricity.  Improvements in technology, most notably the option of a roller compacted concrete (RCC) dam instead of a traditional embankment dam, reduced costs per MW relative to the 1980’s estimate.

During the summer of 2011, the Alaska state legislature appropriated $66 million in funds to move the Susitna project forward following two important events in 2010: the passage of a bill requiring that 50% of Alaska's electricity come from renewables by 2025, and the stated strong preference of the AEA for the Susitna project over the Chakachamna hydro project. 

Location, Economics, and Capacity

The current project plan calls for a single dam at Watana capable of generating 600 MW (2600 GWhrs annually) of power at an estimated cost of $4.5 billion. The site is about 50 miles northeast of Talkeetna, which puts it about halfway between Anchorage and Fairbanks.  It could be accessed by a new road from the Denali Highway and/or a new rail line from Gold Creek.  The dam would be around 700 feet tall and create a reservoir of 39 miles long, up to 2 miles in width at the widest point.  One issue that has yet to be resolved is the question of land ownership.  Much of the land to be flooded as well as the dam site itself are owned by Native corporations and no access agreements have yet been established.

Costs to construct transmission lines and substations have been estimated 14 MB at an additional $889 million to fully integrate the project into the Railbelt grid.  Electricity from Susitna has been estimated to cost as little as 6.3 cents per kWh, much lower than the state average.  However, this amount is dependent on a large amount of state support for the project.  Around half of the total costs would be paid by the state, and the remainder would be financed by the Railbelt utilities through grants and loans.

Environmental Concerns

The most significant environmental concerns with the Susitna hydro project relate seismic risk and the impact on fisheries.  Other concerns, more general to all hydropower projects, are destruction of wildlife habitat, aesthetic losses, and the production of methane as a greenhouse gas.  Opposition to the project has focused mostly on the impacts on fisheries and the cost of the project, with natural gas most often proposed as an alternative.

Fisheries

The proposed dam would have a complex, but relatively small, impact on fisheries.   In the Susitna River, most salmon don't spawn upstream of the proposed dam site, and so are not expected to be heavily impacted overall.  A small number of Chinook salmon spawn in a pair of creeks that enter the Susitna upstream of the dam site, and which would be flooded when the dam closed. 

Several miles of Arctic grayling spawning habitat are expected to be negatively impacted by the reservoir.  The presence of the dam would also change the downstream temperatures, flow rates, and sediment levels in the river, and the combination would likely help some fish species and hurt others.  The reservoir itself would provide new fish habitat.  Downstream effects on the salmon population are difficult to predict in detail.  For example, the lower summer flow rates may reduce the amount of salmon spawning habitat, but the increased winter flow and temperature may increase overwinter survival rates.

Seismic hazards

The Susitna hydro project is in a seismically active area, with major faults north and south of it.  Construction of a large dam in this region would need to take into account the probability of a large earthquake in the area and designing the dam to be safe would require extensive, careful work.  Building dams to withstand earthquakes is a difficult, but well-studied, engineering problem. In its 2010 report "Railbelt Large Hydro Evaluation," the AEA states:

"The design earthquake for the Susitna Project would likely be a based on consideration of a Denali fault event somewhere in the range of magnitude 8.0, a local crustal earthquake and a subduction zone earthquake with a magnitude of roughly 8.5."

The AEA also notes that good seismic data for the area exists as a result of the magnitude 7.9 Denali Fault earthquake in 2002, and that subsurface conditions at the site are well understood due to extensive drilling in the 1980's.

Current Status

During the summer of 2011, the Alaska state legislature appropriated $66 million for feasibility studies and to begin preparing for a FERC application.   AK Governor Parnell suggested that the project could be complete in 2023.   This timeline allows around six years for permitting and five years for construction.

The governor also announced in July 2011 that the (AEA) is actively preparing to file the FERC application, detailed mapping of the project site is underway, and the Department of Fish and Game is assessing fish populations in the area.  The official pre-application to FERC was submitted in January 2012.  Public meetings were held throughout March 2012.

Date Created: Wed, 28 Sep 2011 10:08:08 -0800

Last Modified: Thu, 5 Apr 2012 00:16:11 -0800