Large volumes of water continue to be released from Banff’s Lake Minnewanka through the spillway – the first time in the dam’s 72-year history the spillway has been used.
TransAlta says water levels in the reservoir are going down and spillway releases started being reduced on July 15 to accommodate natural water inflow until the Cascade power plant is operational again.
TransAlta was forced to release water into the spillway as high volumes of water built up in the Lake Minnewanka reservoir in the wake of heavy rainstorms and widespread flooding June 19-21. Just days before, the levels were as low as they had been in at least 20 years.
“The controlled released is down to 15 cubic metres per second, but at the peak I heard it was anywhere between 100 and 400 at different intervals,” said Stacey Hatcher, a spokesperson for TransAlta.
“The amount of the controlled release would depend on rain and inflows and what was happening in terms of melt from the mountains. Even that 15 cubic metres per second could change if there’s more rain or snowmelt.”
The raging water coming out of the spillway more or less followed the historic route of the Cascade River – once a mighty tributary of the Bow River. The force of the water has destroyed a portion of the Lake Minnewanka loop.
The river is racing through the Cascade Pond area, beneath the Legacy Trail underpass on the Trans-Canada Highway and along the south side of the highway between the road and the train tracks. CP Rail has built larger culverts to allow water through.
The power plant went down June 22 when water that needed to be released from the facility backed up along the highway and flowed over the 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 is still not operational.
“We’re still working on getting the plant back up,” said Hatcher.
With the spillway open, the boat harbour and launch at the west end of Lake Minnewanka remain closed as currents from the open spillway pose a threat to the safety of recreational watercraft and the public.
Brewster continues to offer its commercial boat tours.
Hatcher said additional safety booms will be installed by July 19, which, along with the reduced spill release, will provide improved safety in the area of the spillway.
“The current there is pretty strong and there’s still lots of debris,” she said. “Some of that debris remains below the water surface and is not visible.”
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 each year.
TransAlta bought the Cascade Plant from the federal government in 1941 and built a new dam and power plant the following year to replace the original. They added a second generating unit in 1957.
When the Cascade plant was built, Lake Minnewanka was created as a storage reservoir. A four kilometre canal carries water from the lake to the Cascade plant.
Meanwhile, TransAlta has stopped spilling water out of Barrier Dam in Kananaskis Country to inspect the spillway.
Spillways at Horseshoe dam at Seebe and the Kananaskis dam continue to be used to release water, with inflow and reservoir levels now stable. The Three Sisters, Spray and Rundle systems are reported to be operating normally.
