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Controlling the flow of water through the Okanagan Lake system an imperfect science

The Okanagan River dam at the outflow of Okanagan Lake in Penticton on Monday, May 8, 2017. Authorities had to reduce outflow slightly on the weekend to reduce the chance of flooding downstream, but flows should return to maximum later today.
May 08, 2017 - 8:00 PM

OKANAGAN - It’s shaping up to be a high water year in the Okanagan, but time, and the weather, will tell if it gets higher.

Kalamalka Lake and Okanagan Lake are going to be “above our comfort level” as far as high water goes this year, according to Ministry of Forests, Lands and Natural Resource Operations section head for public safety and protection Shaun Reimer.

“We have pretty high water for this time of year, especially in Kalamalka and Okanagan Lakes, which are hardest to manage because of volume,” Reimer says.

The Ministry controls a series of dams in the Okanagan Valley, including structures at the outflow of Kalamalka Lake, Okanagan Lake, Skaha Lake and Vaseux Lake. The Oroville-Tonasket Irrigation District in Washington state controls the Zosel dam at the outflow of Osoyoos Lake.

Reimer says its difficult to say whether we’ll have impactful flooding from high water levels this year, as so much of the flooding issue has to do with how quickly the water comes down.

“We’re seeing it coming down quickly now. I’m thinking we could be 30 centimetres higher than our operating target on Okanagan Lake, higher than 2012 levels by about 23 cm,” Reimer says.

The Ministry is trying to get away from using the term full pool when it comes to the level of Okanagan Lake, he says.

“We’d rather call it our operating target. That’s more accurate. People will hear full pool and say, ‘the lake is full, don’t let it go any higher,' but it’s not always within our control," Reimer says.

He feels this year’s target will likely not exceed lake levels in 1990 or 1997 when the lake was 42 cm above target.

Okanagan Lake is currently about 20 cm below the ministry's target level.

Reimer says the problem is the limited capacity to send water downstream because of the size of the Okanagan River Channel.

All through last week the Okanagan Lake dam was discharging at the designed maximum, but over the weekend, Reimer says he was forced to back off a bit on the flow rate.

“Downstream in the Oliver area, the tributaries increased so much we were getting too high down there and creating problems," he says. "I always tell people, if you have to choose between lake flooding or river and creek flooding, you chose a lake, because it’s safer.”

Reimer expects to be back up to maximum flows out of Okanagan Lake later today, May 8, or tomorrow.

“It’s an imperfect science, like forecasting the weather. Time will tell how far above our targets we’ll get. We’re probably weeks away from real impacts, though, and I’m always hopeful the weather will improve.”


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