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Power from rain

Sitka expands dam to wean itself from diesel

Posted: June 17, 2014 - 11:07pm
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The raised dam, in progress, as seen from a metal walkway above the project. The existing Blue Lake dam, completed in the early 1960s, is being raised 83 feet.   Mary Catharine Martin | Capital City Weekly
Mary Catharine Martin | Capital City Weekly
The raised dam, in progress, as seen from a metal walkway above the project. The existing Blue Lake dam, completed in the early 1960s, is being raised 83 feet.

Sitka is raising its bet on something it and other Southeast Alaska towns know well: water.

The city-owned electric company is raising Blue Lake Dam by 83 feet and adding three new turbines in a bid to keep its power local, clean and separate from the fluctuating cost of diesel. So far, that hydropower project appears to be on schedule.

Increases in some costs have been offset by decreases in others, project leaders say.

Though they’ve sought federal state, and other funding — everything including “a coin collection in the office,” utility director Christopher Brewton joked during a recent tour — the project is still $18.6 million short.

They met with the Alaska Energy Authority early last week to seek a loan; if they don’t receive it, that money will be raised through bonding, which will fund the project but will be more expensive for Sitka residents.

The visit went well and the loan is looking promising, said project engineer Dean Orbison.

Regardless of where the money comes from, raising the dam is a project Brewton and others say will pay for itself in the long run: Sitka’s diesel generators need 24,000 gallons of fuel each day. A hydroelectric turbine, in contrast, uses 387 million gallons of water, he said.

Though that sounds like a lot of water, it’s the equivalent of only a quarter-inch of rain.

Hydropower in Sitka

Sitka has two sources of hydropower: Green Lake and Blue Lake.

Green Lake produces 11 megawatts of electricity, said Jessica Stockel, a project assistant with McMillen LLC, the construction manager for the dam-raising project.

Blue Lake has a “nameplate capacity” of 6.7 megawatts and can generate 62,500 megawatt-hours per year with average water flow, Orbison said. The raising of the dam will increase energy capacity to 16.9 megawatts and generate 94,500 megawatt-hours per year, he said.

The rising water levels created by the dam produce more power, Orbison explained during a tour of the project. Imagine a rock rolling down a hill: A rock rolling down a short hill won’t gain much speed, but a rock rolling down a steep, tall hill will plunge rapidly.

In a dam, a tunnel or pipe carries water “downhill” to a turbine, which converts the energy of the falling water into electricity.

“The higher the water level, the faster the turbine, and the more electricity,” he said.

As long as the dam’s reservoir contains water, the turbines can operate.

In an average year, Blue Lake’s existing turbines are so small they use less water than falls into the reservoir as rain. That means water is released each year by the dam’s spillway and isn’t used to generate electricity..

The new turbines will allow more water to be used for electricity instead of simply being dumped downstream, Orbison said. “How much power you can generate is a function of how much water you have in the lake.”

Sitka’s homes and businesses can use 24 megawatts at peak usage, Stockel said. Sitka’s hydroelectric power plants can produce only 19 megawatts at its current capacity “if we’re really pushing it.”

If the city needs more than 19 megawatts, the power company turns on its diesel generators and passes the cost of fuel onto the consumer, she said.

The new project will keep the diesel generators quiet and eliminate the surcharge.

Progress

Orbison said the dam is about 75 percent complete and the powerhouse is 70 percent complete. On the tour, three turbines sat partially assembled, looking like huge blue snails.

Workers have constructed a new intake tunnel, where water for drinking and energy will exit the lake — the old one will be too deep for divers to maintain once the lake is raised. The new location will also provide cleaner drinking water, as, on a rocky cliff, the tunnel is more likely to avoid the turbidity raised by mudslides.

“We lucked out when it came to rock (for tunneling),” Orbison said.

The dryer than usual summer in 2013 also helped the dam’s construction, as did the warmer than usual winter.

Higher water levels will add 362 acres to the lake, which will be 1,646 acres. It’s 3.5 miles from one end to another, and the bottom of the lake is 100 feet below sea level.

Trees that will be swallowed by the growing lake are being left standing. Cutting them beforehand would cause mud and other material to fall into the reservoir, creating turbidity, they said. That’s a problem, since the Environmental Protection Agency regulates turbidity in drinking water. Too much turbidity, and Sitka would have to buy a $50 million filter.

“We have to pay very close attention to how we go about keeping the water clean,” he said.

When the Blue Lake dam was designed in the 1950s, its engineers planned for it to eventually be raised 23 feet, Orbison said. Engineers on the recent expansion “pushed the envelope” by raising the dam 83 feet. The dam’s canyon and improvements in technology since the 1950s have allowed the increase.

The dam’s current elevation is 342 feet above sea level; it stands at 140 feet above ground, with 70 additional feet underground. Including those 70 feet, once an additional 83 feet are added, the dam will be 425 feet above sea level at its top.

The project will be one-third operational by the end of September, two-thirds operational by the end of November, substantially complete by December of this year, and finally completed February 2015, Stockel said; the powerhouse will also be fully functional by the end of this year.

The city will install a temporary filtration plant so residents can drink out of Indian River during a generation outage, which will take place in September and October. That’s when the water level of the lake will rise at what Orbison expects to be an average of at least a foot a day.

During that outage, Green Lake will be providing the community’s hydropower.

Price tag

The cost of the Blue Lake project is $142 million, but the town is also spending millions more on a backup diesel generator, raising the total cost to $158 million.

Included in that bill is mitigation for the 362 acres of Forest Service land the water will cover. Sitka will fund a summer campground host for Blue Lake campground for the life of the dam’s license, which is 50 years, Stockel said.

They’ll pay the Forest Service $100,000 — $10,000 per year, over 10 years — to restock Redoubt Lake with fish, and they’ll give the Forest Service 48 acres of city land on Chichigof Island; that land is currently surrounded by a wilderness area, Stockel said.

Some speculated that some of the funding shortage may be due to a perception of hydropower as harmful to fish. The Blue Lake dam, however, comes after a natural waterfall and salmon barrier, meaning it doesn’t affect fish’s passage and is “fish friendly,” said Stockel.

Cost for Sitka residents

Sitka’s energy rates will rise to around 12 cents per kilowatt-hour for homeowners on July 1.

Stockel said Sitka’s rates haven’t changed in 20 years.

“Really we probably should have been raising them incrementally, with inflation,” she said. “The jumps aren’t just to handle Blue Lake, but to put us where we need to be.”

Many people in Sitka have been purchasing heat pumps, which are more efficient than baseboard heating, to heat their homes. Sitka, said Stockel, leads the pack in Alaska for heat pump installation, thanks in part to the city’s recent heat pump rebate program.

Even though fuel costs and average costs per kilowatt-hour for Sitka’s hydropower are currently comparable, hydro is important because diesel prices are always going to rise, Stockel said.

In a separate venture, Orbison hopes Sitka can eventually begin exporting drinking water, which is far more profitable than using it for hydropower.

Drinking water is a hundred times more valuable than water used for hydroelectricity.

“The problem is that tankers don’t show up to buy the water. So until we have someone with a boat for us to fill up, we can’t sell anything,” he said.

The dam will take about 30 years to pay off, Brewton said, but be in use for 100 years.

“It’s a lot cheaper than burning 24,000 gallons of fuel a day,” he said.

Find out more about the project at www.bluelakeexpansion.com.

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