At a time when large dams are being taken down, not put up, the state of Alaska is proposing to construct one of the tallest and most expensive hydroelectric dams ever built in North America.
The Alaska Energy Authority is planning to build a 735-foot, $5.2 billion structure on the Susitna River in a largely empty south-central part of the state, which is watered by runoff from the arc of the Alaska Range. The dam, designed to generate up to 600 megawatts of electricity, would create a new power supply for more than two-thirds of the state's population.
But in Alaska, where natural energy resources and wildlife are both foundations of the economy, the proposed dam presents twin conundrums.
One is economic: which is better, creating a reliable source of hydroelectricity and weaning some of the state off natural gas, or building a spur off a proposed pipeline to bring gas from the North Slope to the populated region from Fairbanks to the Kenai Peninsula? Or both? The other is environmental: what serves the environment best, replacing natural gas-fired electricity with hydroelectricity, which is free of greenhouse gas emissions, or keeping the Susitna watershed untrammeled and avoiding the risks involved in changing the dynamics of a major salmon stream?
For environmentalists, the choice is uncomfortable. "It is a bit of a hard choice for the environmental community to have to make. Do we choose a big natural gas project or do we choose a big dam?" said Corinne Smith, a Nature Conservancy official in Alaska responsible for the study of the Matanuska-Susitna Valley where the dam would be located.
While energy is a foundation of the Alaskan economy, it is most visible in the federal arena. The big political fights over energy have involved federal lands, like the Arctic National Wildlife Refuge or the National Petroleum Reserve. Discussions over how Alaskans should generate their own energy are less frequent and lower-key.
But now, the prospect of building the new dam is being drawn into a debate in the Legislature over a proposal much more familiar to environmental groups: the plan to build a $45 billion natural gas pipeline from the North Slope to the Midwest, perhaps including a spur that would carry some gas to south-central Alaska, where regional power plants are already fueled by gas.
Having this gas provide reliable electricity at stable and affordable prices, said an analyst of both projects, would make the dam superfluous and avoid its environmental impacts. But of course, there are significant environmental impacts associated with the 800-mile proposed pipeline.
Can the state afford both? Key legislative leaders think so, even though the oil revenues that made Alaska rich are inexorably dwindling along with the oil bounty of the North Slope.
"We're lucky we're financially healthy," said Representative Charisse Millett, co-chairwoman of the special Energy Committee in Alaska's House of Representatives. "We don't want to pick one project -- we want to go down parallel paths."
Moreover, the decades-old dam proposal, dusted off by the Legislature and Gov. Sean Parnell in 2010, would help the state abide by its policy that Alaska obtain half its energy from renewable sources by 2025. The dam legislation passed without a single dissenting vote.
Both the dam and the pipeline appeal to the state's appetite for supersize ventures, said Steve Colt, an environmental economist at the University of Alaska Anchorage.
"We're always looking for the next boom and we've been remarkably lucky in coming across one thing after another," he added. "People were thinking the gas pipeline would be the next big thing. Now, it's the most expensive hydroelectric project ever built in North America."
Construction of the dam, according to Emily Ford, a spokeswoman for the Alaska Energy Authority, would provide an essential new source of electricity and a hedge against a surge in energy prices. Oil price increases, of course, benefit the state in its role as an exporter of North Slope oil, but hurt regions in the state dependent on oil-fueled electricity and heating.
"We were looking for solutions to provide an affordable and stable power source" for more than 500,000 people in the Railbelt, the south-central region from Fairbanks to the Kenai Peninsula, Ms. Ford said.
Opponents of the dam, however, say that the declining supply of natural gas feeding most of the power plants in the Railbelt could be replaced with supplies form the North Slope, or from untapped resources in the gas-rich areas of the Cook Inlet.
Cook Inlet, at the mouth of the Susitna River, is one of the world's richest salmon fishing grounds. Susitna is among the four biggest state rivers used by salmon species when spawning.
As Chris Wood, president of the environmental group Trout Unlimited, said, "The fact is that this dam, in ways we don't know, would change the flow of the Susitna." In late July last year, for the first time, a reduced population of Chinook salmon resulted in the partial closure of the area for fishing.
The impact of large dams on salmon runs and the riverine environment has kept large hydroelectric projects elsewhere in the country off the federal list of renewable energy sources -- but not off Alaska's.
The concern for Mr. Wood and local opponents is not that the dam will block salmon runs, as large dams in the West have. The site of the Susitna project is far upriver, beyond the reach of all but the hardiest fish.
Instead, the issue is the way the dam will alter the river's rates of flow. Richard Leo, president of Susitna Dam Alternatives, argued that "in the wintertime, the dam is going to be releasing flow many times greater than normal." Juvenile salmon, he said, "will no longer be able to hover near the edge of the river, they will literally have to swim for their lives."
Ms. Ford, the spokeswoman for the energy agency, said that all the major issues, from stream flows to fish behavior, are being studied in an extensive review process that will take at least two more years. In 2015, if things go as planned, the state will ask federal regulators for a license, she said, and construction could start in 2017.
This article originally appeared in The New York Times.