The Zosel Dam in Oroville controls the level of Osoyoos Lake. (Richard McGuire file photo)
The level of Osoyoos Lake is being raised for the spring season and as of Monday was almost a foot higher than at the start of March.
At this point the rise is the result of lowering the gates at the Zosel Dam at Oroville, WA, said Al Josephy, an official with Washington’s Department of Ecology.
Josephy pointed out that the rising lake levels are also affected by water flowing into Osoyoos Lake from the Okanagan River, which is controlled upstream at Penticton.
The lake level is raised slowly from its winter operating level to the summer level until about June 1.
Sudden rises from snowmelt can cause temporary flooding along shoreline properties and often this cannot be controlled at the Zosel Dam.
“Our challenge is to keep lake levels from rising too quickly during this period,” said Josephy. “This time of year we must co-ordinate lake levels with other lake management operations in Canada as well as respond to snowmelt and rain or snow events.”
As of Monday morning, the lake level was at 910.32 feet above sea level – up from 909.59 feet on March 1.
The Department of Ecology’s target is to maintain a level between 911.5 and 912 feet from May 1 to Sept. 15.
Meanwhile, snow pack at higher elevations in the Okanagan and Similkameen basins is slightly below normal this year. While this reduces the likelihood of flooding, a rapid melt could still cause flooding.
Snow pack in the Okanagan basin is at 85 per cent of normal and in the Similkameen it is at 89 per cent of normal, according to the March 1 Snow Survey and Water Supply Bulletin released by the B.C. River Forecast Centre on March 9.
“Flooding is always possible during the snowmelt freshet season, even in years with normal or lower than normal snow packs,” said the bulletin. “Given the snow conditions this year, extreme weather, such as extreme precipitation or combined hot and wet weather, would be required to produce flooding or higher than expected flows.”
Temperatures across B.C. were well above normal through February, said the bulletin. The Okanagan also saw above normal precipitation.
As a result of warmer temperatures, an increased proportion of precipitation fell as rain rather than snow. Combined with melting at low and mid elevations, this has meant above normal flows during the winter.
In the Okanagan basin, flows were 115 per cent of normal between Oct. 1, 2014 and Feb. 28, 2015.
The next Snow Survey and Water Supply Bulletin will be released on April 8.
Josephy said the lake levels this year will be maintained according to the same schedule as last year.
The International Joint Commission (IJC), a board made up of representatives from Canada and the United States, mandates levels.
In 2013, the IJC revised the orders affecting the schedule for increasing the lake’s level.
“It didn’t really change operations that much,” said Josephy. “It just gave us a little more flexibility in terms of how quickly we needed to raise the lake. We have more of a shoulder season and we’re able to be more gradual about it, to work within a bit of a wider range. Really nothing has changed from last year. The only thing at this point of the year is we have to respond to the weather.”
Although there have been complaints in the past about the rapid rise of the lake level, Josephy said he didn’t recall receiving any complaints last year.
The higher summer levels support irrigation and summer recreation in Canada and the U.S.
RICHARD McGUIRE
Osoyoos Times
