VICTORIA – After an unseasonably cold April and cool temperatures in early May, snowmelt accelerated over the Victoria Day weekend.
Five days of above normal temperatures beginning May 16 triggered rapid snowmelt and produced rapidly rising water levels in rivers throughout B.C. High water levels and flooding occurred on many rivers and streams, particularly in the south and central Interior, in the Mt. Currie-Pemberton area. May’s normal-to-above-normal temperatures and light rains have kept river levels high.
Following two weeks of melt, all basin snow water indices have now declined. Snow water indices in a number of river basins are near normal for June 1 (South Thompson, Columbia, Kootenay, South Coast). Other basins remain above normal (Upper Fraser, North Thompson, Peace, Vancouver Island) while some are below normal (Nechako, Mid Fraser, Okanagan, Similkameen, Skeena/Nass).
All areas have experienced substantial snowmelt, runoff and reduced snowpacks from their peak levels of three weeks ago.
Present snow conditions are highly variable. In general, low elevation snow has melted, and mid-elevation snow is either largely depleted or entirely melted. Substantial high-elevation snow remains, and will continue to melt through June and into July. In some basins (Okanagan, Similkameen, Nicola, mid Fraser) high elevation snow is all that remains. In others (upper Fraser, lower Fraser, Peace, West Kootenay, and Vancouver Island) significant mid- and high-elevation snow remains.
High river levels and flooding occurred during late May, principally in the south and central interior, but also in Mt. Currie-Pemberton area, the Fraser River at Prince George and elsewhere. For Prince George, the flooding this spring was their third flooding in the past 12 months. The Fraser River through the Lower Mainland reached a peak on May 26, with a discharge near 10,200 cubic metres per second at Hope, and a water level of 5.75 metres at Mission. Since then, the Fraser has been receding slowly. Given the current snow conditions, there is little likelihood it will rise enough to surpass the late May peak.
The Skeena, Nass, and Bulkley rivers have also receded substantially from their late May peaks, and are unlikely to threaten those peaks again this spring. The Thompson River at Kamloops is expected to peak this week. Weather forecasts from now until mid-June are favourable with respect to flood risk. Periods of only light and/or scattered rain are expected throughout the Interior. Major rivers (Fraser, Skeena, Nass, etc.) should continue to recede during next week and into mid-June.
Water Supply Outlook:
The spring 2008 snow conditions provide a favourable outlook for summer water-supply conditions for most of the province, for community water-supply, instream flows, groundwater and aquifers. Near normal or slightly above normal volumes are expected in major rivers as the snow melts from now to July. The Peace River basin, along with rivers on Vancouver Island and other coastal areas, will likely experience above normal spring and summer volumes.
The forecast for the Okanagan and Similkameen continues to be for below normal spring and summer runoff (85 to 90 per cent). These arid basins could experience water-supply challenges this year, particularly if late spring and summer weather becomes hot and dry.
Environment Minister Barry Penner released Living Water Smart: A Plan for Water Sustainability on June 3. The Plan highlights the need for new water conservation measures to ensure adequate supplies of fresh water for British Columbia’s future. Details can be found at: www.livingwatersmart.ca
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