Washington State to maintain Osoyoos Lake summer level below the maximum allowed

By on April 16, 2014

 

The Zosel Dam at Oroville, WA is operated to control the level of Osoyoos Lake during the summer. During flooding season, however, all its gates are pulled out of the water and the dam doesn’t affect lake levels. When the Similkameen River is high, water can actually back up at the dam. (Richard McGuire file photo)

The Zosel Dam at Oroville, WA is operated to control the level of Osoyoos Lake during the summer. During flooding season, however, all its gates are pulled out of the water and the dam doesn’t affect lake levels. When the Similkameen River is high, water can actually back up at the dam. (Richard McGuire file photo)

Water levels on Osoyoos Lake will be maintained below the maximum allowed, but higher than usual snowpack in the Similkameen River watershed could cause some spring flooding in certain areas in this region.

The State of Washington has the authority to maintain the lake at 912 feet above sea level under new orders implemented early in 2013, said Al Josephy, of Washington’s Department of Ecology. The plan, however, is to keep it about six inches below that level through the summer.

“Over the years it’s been clear from local folks up there [on Osoyoos Lake] that in general people prefer 911.5 to 912,” said Josephy, from the state’s water resources program. “So to keep to that spirit, we intend to go to 911.5 once the floods (potential) are done and stay there through the summer and not raise it to 912. This is all based on what we consider the continuing good relationship with the folks on both sides of the border.”

The extra half foot, he said, is handy for Washington in case of a late-summer emergency, and the state has obligations to downstream irrigators, especially in the Oroville-Tonasket irrigation district, he said.

“We need to protect water in the lake for them, while at the same time try to honour our relationships, which are not in writing anywhere, with the folks who live along the lakes,” Josephy said.

Snowpack is slightly below average this year in the Okanagan and Kettle River basins, according to a survey released April 8 by the River Forecast Centre of the B.C. Ministry of Forests, Lands and Natural Resources (FLNRO).

In the Similkameen River basin, however, snowpack this year is at 124 per cent of normal, a sharp increase over last year when it was 82 per cent of normal.

Although the Similkameen River joins the Okanogan River below the Zosel Dam at Oroville, high water levels in the Similkameen can cause water to back up over the dam, increasing the level of Osoyoos Lake.

Josephy said a higher flow on the Similkameen could influence lake levels, but ultimately it is the weather and rate of snowmelt that have the biggest impact.

Last year, for example, a heat wave in May caused rapid melt and flooding, followed by a second spike in June.

Flow is also determined by the volume of water coming through the dam on the Okanagan River at Penticton, he said.

“We try to keep the lake level within the boundaries of the existing orders, which we are doing right now,” he said. “We were supposed to have the lake at 910 [feet above sea level] on April 1 and 911 on June 1. This gives us quite a lot of latitude to raise the lake that last foot over 60 days.”

Currently the Zosel Dam gates are partially in the water, but when flooding occurs, the gates are out of the water and the dam can’t control water levels, he said.

Asked about the large difference in snowpack between the Similkameen and Okanagan River basins, a provincial government spokesperson said there is higher than normal snowpack at mid elevations in the Similkameen.

“The storm systems that brought substantial increases in snowpack to B.C. through March had the greatest effect along the coast and western interior of the province and less so in the Okanagan region,” said Greig Bethel, of FLNRO.

As for the impact of the Similkameen’s flow below the Zosel Dam, Bethel said discharge is a function of both the amount of snow in the watershed and weather conditions during the snowmelt period.

“At this time, the ministry is not forecasting an elevated flood risk for Osoyoos Lake,” said Bethel. “However, we will continue to monitor conditions through the freshet period and update our forecast should conditions warrant.”

RICHARD McGUIRE

Osoyoos Times

 

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