It’s no longer a question of whether Okanagan Lake will flood this year, but by how much.
Those managing the outflow of water from the series of lakes that dot the floor of the Okanagan Valley into Washington State in the U.S. tried to release enough water downstream to leave space in the mainstem lakes for a deeper-than-normal amount of winter snow.
However, the delicate balancing act was complicated by heavy rainstorms that raised the water levels in tributaries emptying into the lake system, dumping even more water into the valley bottom than was expected from melting snow.
Plus, that snow has stayed at high elevations around the valley much longer than usual this spring, and now that it’s warmed, it is all coming down at once.
Des Anderson, head of public safety and protection for the forests, lands and natural resource operations ministry, explained that high inflows from tributaries have limited the amount that can be released south.
That includes inflows from the Similkameen River, which enters the Okanagan system south of the international border, but which impacts the amount of water that can be released from Osoyoos Lake.
American authorities have had the Zosel Dam on Osoyoos Lake in Washington State full open for some time, but with high flows from the Similkameen River, Osoyoos Lake still rose.
However, Anderson reported Friday that flows from the Similkameen peaked at midnight and the level in Osoyoos lake also peaked on Friday morning.
That will permit them to release a little more water down the system from Okanagan Lake now, he said.
A heavy rainstorm Tuesday is to blame for raising the lake’s level beyond what’s called ‘full pool,’ although that hadn’t happened yet Friday afternoon. It is forecast to occur over the weekend.
“Without rainfall we will only go over a few centimetres,” noted Anderson, “But that will all change it if rains.”
He’s just hoping there won’t be much rain for the next 10 to 15 days, to allow high-elevation snow to melt and run into Okanagan Lake, without the addition of runoff from rainfall in the watershed as well.
Environment Canada meteorologist David Jones is reassuring on that point. He forecasts there will be no significant rainfall in the next week.
“No major storms or widespread rain is expected over the weekend,” he said, and, although a weak system is expected to go through early next week, he doesn’t predict there’ll be much rain with it.
It’s also expected to move through pretty quickly.