Hydro generation at the Whitehorse Rapids Dam was completely shut down by ice Saturday evening, says Yukon Energy spokeswoman Janet Patterson.

Patterson said diesel generators at the dam and in Dawson City and Faro – up to 10 at one time – were brought on line to replace the loss of all four hydro units, including the 20-megawatt number four turbine, the largest unit in the Yukon.

The Aishihik and Mayo hydro plants were also brought up to near capacity to help compensate for the loss, she explained.

Patterson said divers from Vancouver are continuing their underwater work today to steam away the ice, though the number four unit was brought back on line Monday afternoon.

With the return of number four, diesel generation was shut down at 9 p.m. Monday following the period of peak demand, though some was required to get through this morning’s peak, she said.

Patterson said the icing problem cost Yukon Energy nearly $200,000 in diesel fuel.

“Over the weekend, we had some mild temperatures and strong winds, and a combination of those two things caused some ice to break away from the shoreline of Schwatka Lake,” she said.

“The best way to describe the ice was slushy sheet ice, just like a slushy.”

The slush moved north to the dam and when it contacted the cold steel of the underwater debris grates protecting the intake pipes for the hydro units, it turned to solid ice, she said.

Patterson said the penstocks for units one, two and three were completely blocked and the intake pipe for number four was partially blocked.

Hydro generation was replaced with diesel generation at 6 p.m. Saturday, she said.

“So we contacted divers from Vancouver because there is no company here that does this type of work and we flew them in Sunday,” she said.

“They spent yesterday working on one, two and three with a steam wand, putting steam to the ice and melting it.

“They were able to completely clear number three and partially clear number two and they are going to be back working today on one and two.”

Patterson said because the penstock feeding the Fourth Wheel was only partially blocked, it ended up clearing itself.

The divers installed underwater cameras so that ongoing work could be monitored for both operational and safety reasons, she explained.

She said only one diver at a time goes in, and only stays in for an hour so as not to get too cold, but the work is being watched from the surface at all times.

Patterson said this is the type of emergency situation that clearly demonstrates the need for some type of immediate backup generation, whether it’s powered by diesel fuel or natural gas.

“If you think about it, we lost our whole hydro generation in Whitehorse, and nobody lost power,” she said.

Patterson said Yukon Energy is estimating it burned 159,000 litres of diesel fuel as result of the icing, at a total cost of $197,000.

Just as matter of fact, she pointed out, had Yukon Energy’s two new natural gas units been up and running, the publicly owned utility would have saved $34,000 in fuel costs.

Patterson said while problems with frazzle ice occur occasionally at the dam facility, nobody can remember an incident this serious, when the entire hydro capacity was lost.

Environment Canada meteorologist Doug Lundquist said this morning the average daily temperature for Whitehorse has been two degrees above normal over the last 30 days.

Overall, however, the weather so far this fall has not been that unusual, he said.