For the first time ever, TransAlta was forced to open its spillway at Lake Minnewanka as huge volumes of water continued to build up in the reservoir near Banff.
Most other dams in the region, including Barrier Dam, Kananaskis Dam and Seebe’s Horseshoe Dam, are seeing stable or decreasing water levels, though video footage shows dramatic images of water roaring over some spillways.
At press time, the Minnewanka reservoir was continuing to rise slowly, according to TransAlta’s wesbite, and officials were expecting releases into the Cascade River to continue for at least the next 10 days.
TransAlta officials say they have been working around the clock to ensure safe operations of their hydro facilities, including the Cascade-Minnewanka plant, since torrential rains and widespread flooding began Thursday (June 20).
“The release is obviously being controlled, co-ordinated and timed with volumes, and we’re trying really hard to manage volumes in increments,” said Stacey Hatcher, a spokesperson for TransAlta.
“We’re balancing a whole bunch of things, including weather reports, and then there’s infrastructure, like the train tracks and highway that we have to take into consideration,” she added.
“The southern part of the province has been dealing in water volumes probably not seen in the last 100 years. Thank goodness all these teams are working together to deal with everything.”
TransAlta’s Cascade hydro power plant on the Cascade River is the only power development in a Canadian national park. It is part of the Bow River electric system and generates an average of 52,000 megawatt hours a year.
TransAlta bought the Cascade plant from the federal government in 1941. The following year, TransAlta built a new dam and power plant to replace the original.
Trouble occurred at the Cascade plant Saturday night (June 22) when water that needed to be released from the facility backed up and flowed over the Trans-Canada Highway, shutting down the roadway between Banff and Canmore.
This water also flooded a transformer at the facility, which in turn failed, knocking out power to Banff and Lake Louise for almost eight hours that night. The plant remains out of operation.
CP Rail built a larger culvert under the train tracks earlier this week to allow water through, while additional water is also reportedly being diverted from the north side of the highway under a wildlife underpass.
“Given the once in 100 years weather event, the lake is unusually high. Parks Canada is working in close co-operation with TransAlta and Canadian Pacific,” said Banff National Park spokesperson Michelle Macullo.
“A controlled release of the additional water is underway to mitigate the situation, and we are preparing all infrastructure for this controlled event.”
According to Environment Canada, Banff got hit with 91 millimetres of rain and the Bow Valley weather station east of Canmore recorded 240 mm in the downpours.
“There was lots of rain and it fell very quickly. The rate at which the rain occurred essentially created flash floods, like in Canmore,” said Bill McMurtry, a meteorologist with Environment Canada.
“The freezing level was very high and most areas received almost all of their precipitation in the form or rain, not snow, and it was all entering the watershed in a hurry.”
McMurtry said the big question is whether the heavy rain melted the snowpack.
“There is a strong possibility the significant rain falling on the snow then melted the snow, and it all headed into the watershed in a very short period of time,” he said.
“If the freezing levels were higher, that would have delayed the onslaught of all that precipitation coming into the watershed, particularly in the Bow River watershed.”