OKANOGAN — Water levels in Osoyoos Lake are rising as the over-abundance of late- season snows begin to run off in Canada, causing flood warnings along the Okanogan and Similkameen rivers in the United States.
With much greater than 100 percent of average snow levels reported in all watersheds in the region, gates are wide open at Zosel Dam in Oroville, according to the state Department of Ecology, which operates the dam on the U.S. side of the border.
“We are at 914.04 feet, up by a foot and a half since Friday,” said Al Josephy with the state Department of Ecology’s water resources program. “Last year, which was the highest we recorded in more than a decade, we reached 914.87 on June 2.”
Ecology’s target is to maintain a level of between 911.5 and 912 feet from May 1 to Sept. 15.
Lake Osoyoos is fed from Okanagan Lake and is governed by operations in British Columbia. Making room for snow runoff in the upper watershed puts pressure on smaller Lake Osoyoos.
There is twice as much water coming into Lake Osoyoos than can exit, as the high flows in the Similkameen act as a dam at the confluence with the Okanogan, Josephy said.
“Once Zosel Dam gates are wide open as they have been since late March, the lake must seek its own level, when runoff is high throughout the system,” Josephy said. “This can mean people may see some flooding to property along the lake and down to the site of the dam itself.”
Lake levels are mandated by the International Joint Commission (IJC), a board made up of representatives from the United States and Canada. Osoyoos Lake is a source of irrigation water and summer recreation in both the U.S. and Canada.
Last week the Spokane office of the National Weather Service has issued a flood warning for the Okanogan River near Tonasket.
Officials said the river is expected to continue to rise to major flood stage by this weekend.
As of Monday afternoon, the river was at 16.34 feet. Flood stage is 15 feet. Officials said the river will continue to rise toward 19 feet by Saturday.
Comparatively, the Okanogan River crested at 22.54 feet at Janis Bridge in 1972, and 21.79 feet in 1948.
• At 15 feet — Minor flooding of low-lying areas is likely between Oroville and Tonasket.
• At 16 feet — Pasture land between Rodeo Trail and Benton Street, on the east side of the river near Omak, will begin to flood.
• At 17 feet — Low-lying fields and pasture land in the flood plain along the Okanogan River valley, from Oroville to Okanogan, will be flooded. Some homes near the river in Okanogan may experience some basement flooding from seepage. Water will be between the railroad and Highway 97 near Cordell, south of Oroville. Water will be against the shoulder of Omak River Road across from Wanacut Creek.
• At 17.5 feet — Water will be behind the levee due to seepage, with flooding the motocross track downstream of the City of Okanogan.
• At 18 feet — Major flooding of surrounding cropland is likely. Some homes and buildings adjacent to the river will experience some basement and first floor flooding.
It’s a similar situation with the Kettle River in Ferry County.
A flood watch was issued last week for the river near Curlew, where waters reached 19.39 feet as of Monday afternoon.
Flood stage for the Kettle River is 18.50 feet.
• At 18.3 feet — Minor flooding will occur in the Ol’ Swimming Hole County Park in Curlew
• At 18.5 feet — Flooding begins on Customs Road near milepost 6.
• At 19 feet — Flooding at Beal Park on West Kettle River Road, west of Curlew. Ol’ Swimming Hole Park in Curlew will be inundated. Flooding of yards and outbuildings along the river from the international border through Curlew on both sides of the river. Some driveways on Kettle River Road will be flooded. Water will be over Customs Road near Riverview Lane.