The level of Osoyoos Lake has come down considerably since it peaked two weeks ago, but more flooding is still possible.
On Monday afternoon, the lake level was 912.58 ft. after two weeks of steady decline.
The lake level peaked at 914.19 ft. on May 15, but has been declining since then.
The State of Washington, which owns the Zosel Dam in Oroville, aims to maintain the lake level between 911.5 and 912 ft. between May 1 and Sept. 15 – a level mandated by the International Joint Commission (IJC). However, when water levels are high on the Similkameen River, gates at the dam are raised completely from the water and the dam cannot control lake levels.
Levels on the Similkameen River had dropped considerably since they peaked May 13 when discharge was at 20,600 cubic feet per second. Discharge on Monday afternoon was down to 8,080 cubic feet per second – its lowest rate since May 6.
On May 22, the B.C. River Forecast Centre ended its high stream flow advisory for the Similkameen River, and two days later it ended a similar advisory for the Okanagan River.
Those advisories were put in place due to heavy rainfall, which caused the Similkameen flow to increase briefly on May 22 and 23.
“Snow packs have seen significant melt over the past three weeks,” the River Forecast Centre reported on May 24. The centre is operated by the B.C. Ministry of Forests, Lands and Natural Resource Operations (FLNRO).
“In smaller rivers and tributaries through the Interior, lower Thompson River, Okanagan and Similkameen, snow packs have now been depleted enough that flood risk from snow melt alone has eased,” the centre reported.
Flooding is still possible, but would require significant rainfall, the centre said.
Snow packs at higher elevations, however, are still sufficient to pose on-going flood risk, the centre said, pointing specifically to the Fraser, Thompson, Skeena, Columbia and Kootenay River systems.
Al Josephy, with Washington State’s Department of Ecology Office of Columbia River, said we aren’t out of the woods for future flooding of Osoyoos Lake.
While snow and lower and middle levels melted with the hot weather earlier in May, Josephy said there is still snow pack higher up. Combined with rain, that could still cause problems.
“I don’t think there’s any reason that we wouldn’t see a second peak in June,” said Josephy. “So I would not be at all surprised to see the lake rise again.”
This second peak could come in around two weeks depending on how quickly temperatures warm up again, Josephy said.
Although this year’s flooding came much earlier in the year than normal, it wasn’t especially severe, he said. The lake level surpassed 914 ft., but it wasn’t at that level for very long, he added.
Nonetheless, all gates at the Zosel Dam have continued to remain out of the water as the lake level continues to fall.
“Spring is still evolving,” said Josephy.
The B.C. River Forecast Centre and Washington State’s Department of Ecology will continue to keep a very close eye on the flooding situation in this region and will be issuing regular updates.
