British Columbia

BC Hydro completes construction on cavern for new billion-dollar generating station

BC Hydro has finished blasting and excavating a giant cavern that will house a new generating station at the John Hart Dam near Campbell River.

Giant powerhouse cavern blasted 10 stories deep in solid rock

The completed powerhouse cavern for the John Hart Generating Station Replacement Project. (BC Hydro)

After 13 months of excavation and nearly 500 rock-blasting detonations, BC Hydro has completed a giant cavern that will house a new power plant near Campbell River.

It is the biggest component of the $1-billion John Hart Generating Station Replacement Project, which broke ground in 2014.

When completed in fall 2018, according to Hydro spokesman Stephen Watson, the facility will provide 132 megawatts of electricity, which is about six per cent of Vancouver Island's peak electricity demand — enough to power up to 80,000 homes.

May 2016: The excavation of the powerhouse cavern for the John Hart Generating Station Project is completed. (BC Hydro)

About 350 workers have been employed on the project. 

"This project is dealing with seismic concerns and reliability issues," Watson said in an interview with CBC Radio On the Island host Gregor Craigie. 

"It's all in bedrock and it's very impressive to see." 

BC Hydro blasted the new powerhouse cavern through solid rock after discovering the original dam, built in 1947, would not withstand even a moderate earthquake.

Power tunnel for the John Hart Generating Station Replacement Project. (BC Hydro)

Another benefit of the new facility is protecting fish habitat in the Campbell River from "unplanned flow events," Watson said.

"With the water bypass facility in place there, if the turbines do go offline you can quickly divert that water flow and maintain fish flows downstream," he said. 

An incident during construction in fall 2015 underlined the need for improvements. BC Hydro says blasting unexpectedly caused one generator to shut down and reduced water flows in the river below the minimum level of 80 cubic metres per second. 

The Crown corporation stated that the generator was restarted within 30 minutes and flows restored, with "minimal to no impacts to fish."

Aerial view of John Hart Generating Station Replacement Project. (BC Hydro)

Hydro's original plan was to replace the wood-stave-and-steel penstocks, which control the release of water from the dam, with steel and ring girders, but Watson said seismic concerns meant it would have been expensive. 

"It became just as cost-effective to put it underground in rock," he said.

Project managers SNC-Lavalin also came up with the plan to move the generating station, currently located along the river, below ground as well.

The excavation is eight metres wide, as deep as a 10-storey building, and 93 metres long — the length of an NFL football field, Watson said.

"It's kind of like the project of a career. Even on Vancouver Island, it's rare to see a project of this size."

Above ground, Watson said the new facility will blend better with the adjoining Elk Falls Provincial Park. 

Once the generating station is completed, BC Hydro expects to move on to upgrading the John Hart Dam itself, starting as early as 2019. 

With files from On the Island.

To hear the interview, click on the link labelled: Billion-dollar Hydro project reaches milestone