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Near-record Okanagan snowpack raises flooding concerns

The third largest snowpack in the past 35 years is sitting in the Okanagan watershed just waiting for warm weather, and perhaps a little rain, to melt it and send it rushing down into the valley bottom.

And, creeks are powerful erosion machines, adds Black Mountain Irrigation District manager Bob Hrasko.

That utility is busy doing whatever it can to prevent damage from snags or trees that could be washed downstream and get caught on bridges, buildings or reservoirs as the water in creeks rises.

However, he says 90 per cent of the force of Mission Creek is completely unregulated, so there are no dams buffering the full onslaught of water from melting snow.

Because the sponge of the watershed is already full from wet weather last fall, all of the snowpack is expected to run off rather than some being absorbed by the ground first.

He warns people to stay away from the edges of creeks, particularly Mission Creek, in the next few weeks because adults or children who slip into the creek won’t be able to get out.

Since it’s melting snow, the water temperature will only be about 4 C to 6 C, so hypothermia will set in very quickly and the force of the current will make it impossible to get out of the water.

Youngsters and pets should be kept under control anywhere near streams.

That concern is echoed by Jason Brolund, assistant chief with the Kelowna Fire Department, who says they are keeping an eye on the flows in Mission and the height of Okanagan Lake and ensuring a sufficient inventory of sandbags is available in case there’s a threat of flooding.

“The weather is key. If there’s a slow warming trend without much moisture we could be fine, but rapid warming with rain will accelerate the freshet,” he explained.

Flooding is not entirely unpredictable, so property owners who are at risk should keep watch and be prepared to protect their lands.

The province’s River Forecast Centre now reports there is 45 per cent more than the normal amount of snow in the Okanagan’s watershed for May 1, with 34 per cent more in the Mission Creek watershed, which provides the largest single inflow to Okanagan Lake.

Because spring is late and the weather was cooler than normal through April, less of the snowpack has melted, even from low elevations, so there’s more still up there to run off.

So, lower elevation snowpack measurement stations like McCulloch still have all of winter’s snow, meaning there’s 373 per cent more than the normal amount for this time of year at that snowcourse.

At Postill Lake, there’s 67 per cent more than normal, while across the lake, at Brenda Mine, there’s twice the normal amount and at Whiterocks and Esperon there just slightly more than normal.

The RFC bulletin for May reports that La Nina is responsible for cooler and wetter than normal weather in B.C. and that’s forecast to persist through freshet this year, but neutralize in June.

Environment Canada is forecasting warmer than normal temperatures for the summer, it reports.

Weather in the coming weeks will dictate just what the flood risk is for the Okanagan. Rain and warmer temperatures are forecast for the next five days, except for Friday, when a warm, sunny day is in the cards.

 

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