Al Josephy, of the Washington State Department of Ecology, says gates at the Zosel Dam in Oroville are now wide open. Despite this, the level of Osoyoos Lake is rising because water is being released by B.C. authorities in Penticton to lower the level of Okanagan Lake in preparation for anticipated high inflows from snowmelt. (Richard McGuire file photo)
The level of Osoyoos Lake is rising, but it’s because of what’s happening upriver rather than at the Zosel Dam in Oroville.
As of Monday afternoon, the lake level was at 910.8 feet above sea level as measured near Oroville by the U.S. Geographical Survey.
The water levels are rising as B.C. government water managers in Penticton release water from Okanagan Lake to prepare for expected high inflows into the lake from snowmelt, the Washington State Department of Ecology says in a news release.
“Once the Zosel Dam gates are wide open, as they are right now, Osoyoos Lake must seek its own level when runoff is high throughout the system,” said Al Josephy with Ecology’s water resources program.
The wide-open dam gates in Oroville mean there’s nothing U.S. authorities can do to slow the rising waters.
On March 1, snowpack levels in the Okanagan and Similkameen basins were exceptionally high – at 141 per cent of normal and 144 per cent of normal respectively.
While snowpack measurements are taken at the start of April and should provide new information on the current situation, those results aren’t made public until April 9.
Given the high snowpack levels at the beginning of March, the B.C. River Forecast Centre warned that there is a possibility of increased seasonal flooding.
Snowpack, however, is only one element in assessing seasonal flood risk. Intense or prolonged rainfall in the spring and high temperatures causing rapid melting are also important factors.
Washington State’s Ecology Department says it intends to manage to the usual summer target level on Osoyoos Lake at between 911.5 and 912 feet from May 1 to Sept. 15.
“We’ll continue to coordinate with our Canadian partners in managing our end of the system as the spring weather progresses,” Josephy said. “This can cause inconvenience and occasional flooding to property owners along the lake and down the [Okanogan] River itself.”
Lake levels are mandated by the International Joint Commission (IJC), a board made up of representatives from Canada and the U.S. Osoyoos Lake is a source of irrigation water and summer recreation in both countries.
Lake levels may exceed the targets when inflows into Osoyoos Lake are greater than water leaving the lake, notably when dam gates are fully open in Oroville.
RICHARD McGUIRE
Osoyoos Times
