Diversion tunnels top priority as Site C construction heads into winter

Construction crews at Site C will be working around the clock through fall and winter to complete two tunnels needed to divert the Peace River next fall and allow workers to begin building the kilometre-long dam.

BC Hydro toured Fort St. John media through the construction site Tuesday for an update on the building of the estimated $10.7-billion project.

"With the diversion, there's other items tied to it. Coffer dams have to be built to a certain point, there's a temporary fishway that has to be functioning," said Ross Turner, director of construction.

Crews have already punched the two tunnels through the north bank of the river, though much work remains to be done.

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Gate construction at the Site C diversion tunnel inlet, Sept. 17, 2019. - Matt Preprost

As crews pour concrete liner in small, slipform segments at the start of the inlet portal and work their way inward, heavy machinery is still chewing up the rest of the earth needed to be dug up and moved at the outlet portals more than 700 metres away.

The tunnels, coffer dams, and fish passage need to be complete and ready by Sept. 1. That's the key deadline contractors need to hit in order to divert the Peace River and get the actual dam building underway. Missing that deadline would push construction back by at least a year. The project remains on time, Turner said.

Work will continue 24 hours a day, seven days a week throughout winter to get the tunnels finished by the end of spring. An estimated crew of 400 will work throughout the winter. "We allow time for commissioning," Turner said.

Once operational, the tunnels will move 3,000 cubic metres of the Peace River per second.

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Shotcrete inspections above the Site C diversion tunnel outlet portal. - Matt Preprost

A facility is being built to collect fish that will be unable to swim upstream through the strong flows of the diversion. Those fish will need to be taken from the facility and trucked to the other side of the dam to be returned to the river. A permanent fish passage is being built on the south bank of the river, near the powerhouse, though they will still need to be transported after the dam is completed.

In between the two diversion portals, crews have excavated the core trench for the earth filled dam, which will stand 60 metres tall. Crews will conduct trial placement of core materials this year, with work starting in earnest next year. The dam will measure 400 metres at its base, and will be filled with impervious materials from BC Hydro's industrial lands on 85th Avenue, shipped to site by conveyor belt.

A team of between 70 to 80 construction managers and engineers are co-ordinating work at the tunnels while another team co-ordinates work at the spillways and generating station under construction on the south bank of the river. With safety and other personnel, the teams total more than 200 staff combined.

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The core trench of the Site C dam is seen in the foreground and will be built against the buttress seen in the background. - Matt Preprost

"We tell all of our folks that you have the right to do a safety stop. In other words, if you're walking by something and you see something that could cause a serious injury, or worse, they have every right to call a safety stop, whether they're right or wrong," Turner said.

"We give everybody the right to do a safety stop. We actually had one on the weekend. Some workers were inside an area where another worker thought they wouldn't be able to get rescued out of because they weren't properly geared up. So, they called a safety stop and we got it sorted out. It's a really good culture these days."

On the south bank of the river, crews continue to piece together penstock segments while others build water intake gates. These will channel the Peace River through to the turbines that will produce power when the dam is put into operation.

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Penstock assembly at Site C, Sept. 17, 2019. - Matt Preprost

The Fort St. John area saw 224 millimetres of rain over the summer, up from an average of 192 mm. That slowed construction and caused some surface erosion, but didn't put work to a stop, Turner said.

"It lets us test out our care of water," he said.

"What the care of water is how we deal with runoff and high flows. So there's a lot of infrastructure put in around that. These last high water flows, a lot of our infrastructure we put in, if not most of it, has proven to be handling the high flows for what it was designed for."

The Peace River through the Site C construction zone will be closed to the public in spring. 

Email Managing Editor Matt Preprost at editor@ahnfsj.ca. 

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Construction at the Site C diversion tunnel outlets, Sept. 17, 2019. - Matt Preprost
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A temporary fish passage under construction at the Site C diversion tunnel outlet, Sept. 17, 2019. - Matt Preprost
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Spillway and powerhouse construction at Site C, Sept. 17, 2019. - Matt Preprost
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Tailrace construction at Site C, Sept. 17, 2019. - Matt Preprost
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Construction underway on the 500 kilovolt transmission line that will tie back into the Peace Canyon substation and join the existing 500kv line heading south to Prince George. - Matt Preprost
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Site C water intake gate construction, Sept. 17, 2019. - Matt Preprost
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A penstock segment is offloaded at Site C, Sept. 17, 2019. - Matt Preprost
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Site C powerhouse and generating station construction, Sept. 17, 2019 - Matt Preprost
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Site C spillway buttress construction, Sept. 17, 2019. - Matt Preprost
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Site C powerhouse buttress construction, Sept. 17, 2019. - Matt Preprost
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