Tyee Lake set to power Wrangell through winter

PETERSBURG – The water level at Tyee Lake was at 1,380.6 feet as of Nov. 18, which will allow the hydro plant to produce power for over seven months should all inflows to the lake stop.

As part of the Southeast Alaska Power Agency, Tyee Lake dedicates its power to Petersburg and Wrangell, while Swan Lake produces power for Ketchikan. The 1,380.6 foot water level is about even with normal water levels for this time of the year, and is above the approximately 1,300 foot water level in November 2018, according to SEAPA.

The current lake level can provide enough hydropower to sustain both Wrangell and Petersburg for about 249.4 days. If all water inflows to Tyee and Swan Lakes stopped, then there would be enough water in both lakes to power the three communities for 213.9 days, according to SEAPA. The current water level in Tyee Lake means the hydro plant will still be able to provide power to Wrangell and Petersburg through the winter as inflows to the lake freeze.

"We're going to be making it through the wintertime, barring any catastrophic failure of a pipe or something like that," said Petersburg Borough Utility Director Karl Hagerman, as he knocked on his wooden desk. "We're sitting pretty good."

At the start of 2019, Tyee Lake's water level was at 1,280. In February, the lake level dropped to about 1,261 feet, causing the borough to run diesel generators as water levels approached the 1,258 draft level set by SEAPA. When Tyee Lake reaches its draft limit, the hydro plant no longer continues to provide power to Petersburg and Wrangell.

Petersburg also receives power from its own hydroelectric project at Blind Slough that draws water from Crystal Lake. It provides about 25 percent of the borough's electricity. Last Monday, the water level at Crystal Lake was at 1,291.5 feet. The Blind Slough Hydroelectric project operates between 1,274 and 1,294 feet.

If water in Tyee Lake reaches 1,400 feet, then water will begin to spill out. The same thing happens when Crystal Lake reaches 1,294 feet.

"Any water that spills over the spillway is lost energy," said Hagerman. "It's water we could have used to produce power."

In September, a bear gnawed on a fiber optic cable that carries data from the Blind Slough Hydroelectric project to a control room, causing the cable to fail. The cable has since been mended, but Hagerman said the borough may replace the cable because of its age and the condition it's in. The new cable would be 5,000 feet long and take about six months to produce. The project has an estimated cost of $10,000, according to Hagerman. The new cable would also be stronger than the current one.

"It looks pretty tough, but a full grown black bear or brown bear that wants to chew up a cable is probably going to be able to chew up that cable," said Hagerman.


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