Parks Canada is rebuilding a dam at Johnson Lake that was damaged by raging floods in June.
Work is currently underway to replace the damaged earthen dam at the east end of the lake with a concrete seepage wall and spillway channel, a move officials say is necessary to protect infrastructure in future high water events.
Parks Canada officials say water levels at Banff’s popular recreational lake dropped by 28 inches after flooding damaged the dam at the east end of the lake, sending water rushing towards the Trans-Canada Highway.
“More flooding events in future could totally release and empty the lake, and have catastrophic effects on the highway,” said John Rose, Parks Canada’s asset manager.
“We’re putting in a new structure identical to the one at the west end of the lake. Rather than risk the dam blowing out again, we can release water out of there in high water events. We will be able to release water out both ends.”
The floods at the end of June turned small mountain streams into raging muddy torrents and, with heavy rainfall, a deluge of water came rushing down towards Johnson Lake from the Inglismaldie catchment to the north.
Bill Hunt, Banff’s resource conservation manager, said the force and volume of water from the lake just about washed out a wildlife underpass near the base of Seven Mile Hill, and started to erode the abutments of the structure.
“If that whole lake had gone, if that entire earthen dam had washed away, you’d get a big wall of water heading towards the highway and it could close down the highway,” he said.
Johnson Lake is a former wetland that was dammed at both the west and east ends decades ago in order to create a lake for recreational purposes, such as fishing, paddling and swimming. Historically, the wetland area drained to the east, feeding a series of smaller wetland areas downstream.
Parks Canada did not seriously consider returning the lake to more of a natural wetland state.
Hunt said a decision like that would need to go through a park management planning process.
“This decision to rebuild the dam was made for a combination of reasons, including public safety and the level of human use there,” he said.
“It’s a popular boating, fishing and swimming area, and we would need clear direction to take advantage of a natural opportunity to restore a wetland.”
Banff’s aquatics team wanted to see the Johnson Lake outflow continue east to restore the wetlands to the east, providing improved rearing habitat for fish, as well as better habitat for birds and amphibians.
Because there is no connectivity to the Bow River downstream of the east spillway, a two-way fish ladder is to be incorporated into the spillway design so that fish will be able to return to the lake from the downstream rearing habitat.
About 150 fish, including rainbow, brook and brown trout and suckers, were removed from the area around the construction site and returned to the reservoir.
A temporary U-shaped aqua-dam was installed above the construction site to allow dry working conditions, so fish were removed in those areas that were drained.
The price tag to replace the east end dam at Johnson Lake is around $70,000.
