A worker prepares to lay concrete for the intake building watertight parapet and bulkhead, during modernizations made at SEAPA's Swan Lake facility over the summer.
A crew at the Swan Lake hydroelectric facility prepare to slot the upper half of the dam's new vertical gate into place earlier in the fall. Work to raise the structure just wrapped up last week, and should boost the reservoir's capacity by about 25 percent.
Primary construction work at Swan Lake wrapped up last week, leaving full capacity for its hydroelectric dam 15 feet higher than it was at the year's start.
The $10,000,000 project was undertaken by Southeast Alaska Power Agency, a utility covering the communities of Ketchikan, Wrangell and Petersburg. Starting about two weeks behind schedule earlier in the summer, workers finished with time to spare with the barge platform used for the project's crane departing last week with general contractors moving off site this week.
"We still have some electrical items that we're working through," SEAPA power systems specialist Ed Schofield explained, which should be completed before the month's end.
An end date of October 28 was projected, with actual work concluding two days early. Due to the probability of rain, forecasting at the start of October had even projected a November 11 finish. Instead, it was one of the driest months on record, perfect for what workers were trying to accomplish.
"You can't get luckier than that," said Schofield. But on the main, he felt the weather had been fortuitous throughout the project's duration. "The whole summer was rather exceptional."
A large part of the work involved laying concrete, about 200 cubic yards' worth. This had to be laid in one-yard batches, which Schofield explained could on average be set at a pace of 12 segments per day. With the weather's help, crews at times were able to lay 20 yards at a time, speeding progress.
Additionally, due to the use of barges in the construction, water levels had to be maintained while work went on to prevent unwanted spillover. Additional water could be drawn out through the turbines instead of the spillway, which would have required a load bank to use that additional power as needed.
Concerns arose when in June the rented device experienced a problem with its cooling circuit, which ended up tripping the system's failsafe and causing a power outage to the grid.
The project also saw the addition of 78 feet of flashboards and a vertical gate. The spillway is in all 105 feet across at the crest and 14 feet deep, while the new water path will be 23 feet across for the vertical gate. The flashboards are designed to collapse to protect the dam's integrity during extremely large flood events.
As of Monday, Schofield reported five feet of flow through the dam's fixed wheel gate already. The emergency flash gates are also appearing to be doing their job, holding up under pressure.
"The flash gates are holding beautifully, not a drop of water through them," he said.
With main components of the addition wrapped up, all that will remain to be installed is the dam's debris boom, which prevents logs and other materials from impeding operations. For instance, on Tuesday a portion of the reservoir had to be dewatered to remove debris from the spillway.
"I think that they have that pretty much wrapped up now," reported Clay Hammer, Wrangell's electrical superintendent and alternate member on the SEAPA board.
The boom will be built from a high-density polyethylene, which Schofield estimated should hold up for half a century with regular maintenance. Work on that part of the project should wrap up either in December or early January depending on the weather.
The dam is already taking on extra water, and should now add 25-percent boost to capacity, yielding between 6,000 and 12,000 Megawatt hours annually. According to SEAPA's calculations, power generated by the added capacity will help offset up to 12,000 megawatt-hours of diesel generation annually, or about 800,000 gallons of fuel. This in turn is estimated to save nearly 18,000,000 pounds of carbon dioxide emissions from using diesel.
While the hydro facility at Tyee Lake is the main source of power for Wrangell, Hammer explained reserve gains at Ketchikan's Swan Lake dam would be a gain for all communities within the SEAPA network.
"In the long term we have more energy to be distributed between all the communities," he commented. In the past, shortcomings for the grid have not been a lack of generation, but rather having enough water in reserve to keep up with demand.
"This takes care of that," Hammer said of the raising.
End costs have not been tallied up yet, but the project is anticipated to hit at around its budget target of $10 million. At first the project was looking at costs of over $13 million but were reduced with design simplifications using a new flashboard and gate design. $3.9 million in direct legislative appropriations have gone toward the project, with the SEAPA board last year approving the sale of bonds to cover the difference.
A documentary covering the project's progress is expected to be edited and ready for viewing by mid-December, available on the SEAPA webpage at http://www.seapahydro.org.
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