UPDATE: As temperatures climb, risk of snowmelt and flooding increases

By on May 18, 2017

Water is high and strong at a weir on the Okanagan Channel north of Osoyoos Lake. (Richard McGuire photo)

As temperatures climb into the high 20s this weekend, melting snow is expected to put added pressure on Okanagan waterways, increasing the risk of floods.

The biggest threat continues to be in the Central Okanagan, where the level of Okanagan Lake as of Thursday morning had risen two centimetres since Wednesday to 342.75 metres above sea level.

These conditions are expected to last well into June due to record water levels in area lakes and the amount of snow at higher elevations, Central Okanagan Emergency Operations said in a news release Thursday morning.

But water in Okanagan Lake must still make its way down the valley into Osoyoos Lake, which currently hovers around 915.5 feet above sea level as recorded by the U.S. Geological Survey at Oroville, WA.

“Even though some rivers and lakes appear ‘stabilized,’ it is still important for property owners in flood-prone areas to remain alert and prepared,” the Regional District of Okanagan-Similkameen (RDOS) Emergency Operations Centre said in a news release late Tuesday.

The RDOS advised those with sandbags in place not to remove them because warmer weather is predicted.

“Environment Canada and the provincial authorities expect water levels to slowly begin rising again over the next few days and to continue for the next few weeks,” the RDOS advised.

Sandbagging is being done at some low-lying residences in rural Osoyoos.

Sandbags in Osoyoos are available at the Public Works yard in the industrial park at 11500 – 115th Street. They will be stacked outside the gates for pick-up over the long weekend.

Sand has been placed across the street from Dairy Queen on Highway 3.

The Department of Ecology in Washington State warned on Wednesday that during runoff season, the level of Osoyoos Lake can rise sharply and cause downstream rivers to flow more swiftly.

The level of Osoyoos Lake is regulated by the Department of Ecology at the Zosel Dam in Oroville, and currently the dam’s gates are wide open to allow the runoff to go down the Okanogan River.

“When runoff is high throughout the system and the Zosel Dam gates are wide open, the lake must seek its own level,” said Al Josephy, who oversees the dam for Ecology. “When lake levels return to normal, we can regulate flows at the dam through the summer and into the fall and winter.”

With snowpack levels much higher than normal for this time of year in all watersheds in the region, Ecology intents to manage the lake level to its usual summer target of between 911.5 and 912 feet from May 1 to Sept. 15.

“During spring runoff, the lake often rises beyond 913 feet and has reached as high as 915 feet, though rarely,” Josephy said. “This can cause inconvenience and occasional flooding to property owners along the lake and down to the site of the dam itself.”

Water can back up to the Zosel Dam where the much larger Similkameen River joins the Okanogan River south of Oroville. This makes it difficult to rapidly release water from Osoyoos Lake at the dam, Josephy said.

The discharge of the Similkameen, as measured at Nighthawk, WA, fell to 8,540 cubic feet per second early Thursday morning, but had risen again to 8,780 cubic feet per second by 2:30 p.m. Thursday.

This is well below its level of 14,500 cubic feet per second reached last Saturday.

As of Thursday afternoon, there are no Environment Canada weather alerts in effect for the South Okanagan.

The forecast for Saturday calls for a 60 per cent chance of showers, and temperatures will rise into the high 20s from Sunday into next week.

RICHARD McGUIRE

Osoyoos Times

 

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