Temperature has kept snow around longer

By Judie Steeves - Kelowna Capital News - May 07, 2008

NewS.113.20080506201828.07_SC_FloodWaters_20080506.jpg

A spike in the level of Mission Creek has already occurred with concerns registered by environment ministry officials about how high it might rise this spring.

Sean Connor/Capital News

A delayed snow melt due to cold weather in April has set the scene for possible flooding around waterways such as Mission Creek this year if a spell of warm weather causes sudden runoff, or if there’s a typical May rainstorm.

There’s about 30 per cent more snow than normal in the Mission Creek watershed right now, not because of a higher than normal snow level, but because there has not been much snow melting in the past month.

Allan Chapman, head of the river forecast centre in Victoria, says warmer weather in the past couple of days has resulted in some of that snowpack beginning to melt at the higher elevations, while mid-elevation snow began melting during the daytime a week or so ago.

“Clearly, as we move into May and retain snow in the watershed, the flooding risk increases because the cool weather keeps the snow water in the mountains,” Chapman said.

“It stays there into the season when there’s usually prolonged heat, and a time when there can be convective rainstorms, which, when added to a melting snowpack, can cause rapid runoff.”

At this point, the critical flood potential factor is sustained heat, hot weather for more than a few days at a time, he said.

Although there have been a few warm days, that spell has been interrupted by cooler weather, which will slow the melt.

One of the most dramatic illustrations is in the Trout Creek watershed where there is still 141 mm of snow water equivalent, half again over the normal for this point in the year, of 93 mm.

However, Chapman said that’s entirely due to the lateness of the melt, rather than a deeper than usual amount of snow in that watershed for the whole winter.

Elsewhere on the west side of Okanagan Lake there is still 270 mm of snow water equivalent at the Brenda snowcourse, near Brenda Mine, compared to the normal of 236 for May 1; 272 mm at Islaht Lake in the Westbank Irrigation District’s watershed, compared to the normal of 282 mm for this time of year; and 358 at Esperon Creek in Lakeview Irrigation District’s watershed, compared to the normal of 391 mm.

At Silver Star near Vernon, there is still 860 mm, compared to the normal for May 1 of 765.

Water flows past the gauge on Mission Creek began to rise on Saturday, he reported, and it was up to 4.5 cubic metres per second on Tuesday.

The level of Okanagan Lake has been controlled this winter with the expectation that there will be normal or less than normal inflows this spring, said Des Anderson, a section head in the environment ministry’s water stewardship division.

The lake didn’t reach full pool last year, and the management of its level is intended to allow it to fill this year in June.

Because it’s being managed in conservation mode, outflows down the Okanagan River channel are below normal this year.

But a fish-water management tool helps managers to balance the needs of downstream sockeye salmon and irrigation users with the needs of irrigation districts and shore spawning kokanee upstream

May 5 the lake was at an elevation of 341.686 metres. Full pool is 342.54 metres.

The lake level is controlled by a dam at Penticton, at the outlook of Okanagan Lake, while Skaha Lake is controlled by a dam at Okanagan Falls. Flows from Vaseux Lake are controlled at McIntyre Dam.

jsteeves@kelownacapnews.com

Email | Print | Letter to Editor | Share on Facebook

Temperature has kept snow around longer

Most read in your Region

Most read across BC