The mouth of Mission Creek flowing into Okanagan Lake. Image Credit: Kevin Parnell/Capital News

Snowmelt impact diminishing

Rain remains wildcard factor in Okanagan Lake flood risk.

Rainfall over the next two to three weeks will determine the ongoing flood risk level for Okanagan Lake, says the head of the BC River Forecast Centre.

Dave Campbell says the impact from the melting higher elevation snowpack is beginning to diminish across the Southern Interior, but rainfall in the 25 to 30 mm range can still have a damaging and immediate flood impact.

“The positive thing at this point is projecting for the month of June, we are not looking to have that kind of extreme rainfall occurring,” Campbell said.

“Everyone needs to remain vigilant but there are signs now that the flood risk is beginning to diminish.”

Campbell said the combination of rain and intense heat spells during May has contributed to a reduction of the alpine level snowpack, to the point where it is a limiting factor in driving up river and creek levels feeding into the Okanagan Lake system.

“The one thing that will have the single biggest impact at this point remains the rain,” Campbell stressed.

At its peak earlier this spring, Mission Creek was flowing at 80 cubic metres per second, which now has dropped down to the 25 to 30 cubic metre range level.

“It’s been three to four weeks since we’ve seen those levels at 80, which indicates in terms of risk the snowmelt impact on the creek is playing less of a flood risk role,” Campbell said.

Shawn Reimer, head of the water stewardship branch of the provincial ministry of forests, lands and natural resources, said the historic high water intake levels draining into Okanagan Lake may have peaked, again depending on the rainfall in the weeks ahead.

For the last five weeks, Reimer said the Okanagan Lake water release dam at Penticton maximum discharge level is 55 centimetres depth daily while the lake intake rate was 169 cm.

“As the snowmelt becomes less of a factor, we won’t see the lake continue to rise at significant levels. That fact alone is encouraging but that’s as long as we don’t see significant rainfall through this weekend or over the next few weeks,” Reimer noted.

Reimer said the water level for Kalamalka Lake, which feeds into the Okanagan Valley lake system, has also shown signs of remaining flat or dropping a little in recent days.

“There is no longer snow to feed the Kalamalka Lake and Wood Lake system so we should start to see some dramatic decline in those lake levels fairly soon, depending on precipitation,” Reimer said.

For people living along the Okanagan Lake shoreline living behind sandbag and other dam barriers, Campbell said while they might tentatively breathe a sigh of relief for the moment, the peak level for the lake could still rise.

“We still need a bit of time to create some (downward) space in the lake level before you start sending the message we are through with the flooding. The situation is still very sensitive to rainfall particularly over these next few weeks. It’s a situation we will continue to watch closely,” Campbell said.

Reimer said the water release balance at the Penticton dam needs to see the water release levels higher than the lake intake levels.

“I’m not sure that catch up in terms of water release is the right word with the lake level showing signs of at least stabilizing, but it is a better situation if that is to continue,” Reimer said. “The longer the lake levels remain flat or rise slowly, the more time it allows us to discharge water from (Okanagan Lake).”

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