Water levels in Osoyoos Lake are currently rising in anticipation of the changing seasons.
“We’ve been coming up between a quarter and a half an inch a day for some weeks now,” said Al Josephy at Washington State Department of Ecology. “We’re trying to come up, as we always do, as gradually and as slowly as we can, especially in a normal year where we’re not concerned about getting water stored before it’s gone. In a year like this we don’t want to disrupt peoples’ lifestyle.”
The lake will be gradually raised to summer operational levels and then maintained between 911.5 and 912 feet above sea level until the end of October.
In most years, however, there is a period during spring runoff when actual water levels rise above these levels and the Zosel Dam in Oroville has no control over the lake level.
“In any normal or above year, you can pretty much figure that it will rise above 912 feet for a period of time,” said Josephy, who is contracts and grants manager for the state’s water resources program. “It usually continues quite strongly through most of June. It can be a five-to six-week period in which it’s above its operating level.”
This year snow levels in the basins that influence drainage are above normal, however there hasn’t been a lot of moisture in the last few weeks, Josephy said.
As a result, water levels are predicted to be about normal this year and drought is not anticipated.
Raising lake levels in the spring provides additional water storage for irrigation of summer crops and for recreational activities on the lake. It also improves stream flows throughout the season downstream on the Okanogan River in Washington State.
In the fall, dam operators lower the lake level to protect property along the lake from freezing water surfaces and wind erosion.
Lake levels are established under orders from the International Joint Commission (IJC), a board with representatives from both Canada and the United States.
In February, new orders were implemented, replacing the 25-year-old orders that expired that month.
Among changes in the new orders, a longer period for filling the lake in the spring is allowed.
Water flows from the Similkameen Valley watercourse systems also effects the levels in Osoyoos Lake, but that water isn’t controlled by operators at the Zosel Dam.
Josephy said that at public hearings held in recent years he has heard misunderstandings about the role of the Zosel Dam in maintaining lake levels, especially during runoff.
A public hearing in Osoyoos last July attracted a packed house as residents asked questions about the new orders and the signing of the new agreement by the IJC.
“The main effect of the dam is to maintain the lake levels after the runoff has taken place and subsided,” he said.
For most of the spring, the gates of the dam are completely out of the water and the dam ceases to be a dam, he said.
In high water years, the water actually flows uphill into the lake from the Similkameen River, which joins the Okanogan River just below the dam.
Josephy said officials from Washington State, which owns the dam, have a good working relationship with their counterparts in Canada, and they meet each spring to discuss water level management.
In particular, he works closely with the management that controls the level of Okanagan Lake, which impacts the entire river system.
Water levels in Osoyoos Lake have been controlled by the Zosel Dam dating back more than 60 years, when the first agreement was signed by the IJC, which has its directors appointed by the President of the United States.