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Floods due to snow melt no longer likely
With the level of Osoyoos Lake falling close to its target, volume dropping on the Similkameen River and with mid-elevation snow mostly melted, the chance of flooding this spring has receded.
“Flood risk due to rapid snow melt is unlikely at this point, but is possible if areas receive extreme rainfall,” the B.C. River Forecast Centre said in its most recent Snow Survey and Water Supply Bulletin released last week.
Hotter weather in May led to rapid snowmelt, particularly in mid-elevation snow packs, the bulletin said.
Meanwhile, the snow basin index is still higher than normal in the Okanagan-Kettle river basins at 123 per cent of normal and significantly higher in the Similkameen River basin at 167 per cent of normal.
The level of Osoyoos Lake fell to below 912 feet above sea level last week. The State of Washington is permitted to maintain the lake level at 912 feet through the summer, although Washington officials have said they will try to keep it below 911.5 feet once the flood season ends.
In the summer, the lake level is controlled by raising or lowering the gates at the Zosel Dam just down river from Oroville, WA.
During spring runoff, however, the gates are out of the water and the dam doesn’t control the lake level.
A high volume of water on the Similkameen River can affect the level of Osoyoos Lake when water backs up the Okanogan River at the dam.
That volume, however, has dropped in recent weeks and was just over 8,000 cubic feet per second last week – down from a high of 17,700 cubic feet per second on May 18.