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Columbia River system pretty full, but floods not likely — officials

Water flows swiftly over the horseshoe dam at Bonnington Falls. The Nelson Daily photo

BC Hydro officials say they’re not forecasting flooding along the Columbia River system in the Kootenays this year- but admit it could come pretty close as they try to manage “unprecedented” runoff.

While Nelson, Castlegar and Trail are unlikely to see any floods from high water levels on the river system, Kootenay Lake itself may peak at a point where flooding becomes possible, officials told reporters at a briefing on Tuesday.

“We already putting out as much as we can since the beginning of March… resulting in fairly high levels” on Kootenay Lake, said BC Hydro planner Gillian Wong.

“[Levels] are today continuing to climb on the lake, we are sitting at 1749 feet, just three feet below the onset of flood concerns,” Wong said.

The forecast is for Kootenay lake water levels to peak at 1752 feet on 31 May- the point at which flooding could begin. In the meantime, BC Hydro will continue to maximize the flow of water to reduce that danger.

Hydro officials say earlier this year precipitation levels in the Columbia watershed- which straddles the US-Canada border- were not a concern. But after a winter of normal or even below-normal snowfall, things changed quickly in March. Precipitation created a lot of new snowpack, and the water supply went from below-normal to as much as 138% of normal in some areas. 

“All that rain went to building snow in the higher elevations,” says Wong. That snow is now melting, pushing river and lake levels to new highs.

The water flow into  Kootenay Lake is the highest it’s been in nearly 60 years- running at about 128% of normal. While the lake is still below flood levels, heavy rains in the coming weeks or fast runoff could change the situation. In July 2012, rain and runoff brought the lake to 1753.4 feet.

Officials are doing what they can to reduce the danger of flooding, says Wong.

 “The entire time we expect to be running as much as we can and as soon as the lake turns around…  we will reduce discharge,” she says. “But for the time begin we expect to be running pretty hard to manage the lake levels.”

BC Hydro co-ordinates runoff with the US Army Corps of Engineers, to both control flooding and maintain the system’s capacity to produce electric power. The Libby Dam, south of Cranbrook in Montana, directly affects flows into Kootenay Lake.

“We’re co-ordinating with the Corps of Engineers on the operation of Libby (Dam) and we have calls each week as to what operations maybe Libby can do with the intention to reduce flows during the period when Kootenay Lake is at its highest.”

Wong says BC Hydro will also reduce outflows at Duncan Dam, at the north end of Kootenay Lake, prior to the lake hitting its peak.

She says water levels on the Columbia downstream at Trail and Castlegar will remain high as long as the push is on to empty Kootenay Lake as quickly as possible.

Wong says BC Hydro may also have to fill Arrow Lake, another major reservoir on the system, to its capacity to help manage water levels downstream. Currently the lake is about 24 feet below capacity, and projections indicate it should peak about two feet below full pool. However, runoff is 108% of normal in the area, and if necessary, the lake could be filled two feet above full capacity.

Arrow Lake was last filled to over-capacity in the high-water year of 2012.

Water flows and storage in the watershed are governed by the Columbia River Treaty, an international agreement between Canada and the US.

Water levels along the Kootenay River, which also has a series of dams and control structures is controlled by Fortis BC.