Canada’s Highway 37 stretches through British Columbia, giving drivers a very scenic and, at times, remote trip as they travel through rugged mountains to the Yukon border.

The northwest offers up vast wilderness and snow-capped peaks, but offers little by way of infrastructure.

It is here among the dense pines that the Iskut River drops in elevation and forms a confluence with the Forrest Kerr River.

To this location, approximately 1,000km north of Vancouver, equipment for a new hydroelectric facility, as well as construction equipment and man-power for the associated tunnels, must travel.

AltaGas, an energy infrastructure company headquartered out of Calgary is constructing the 195MW run-of-river hydroelectric project, which includes 4,500m of tunnelling.

The project will deliver power to the grid at Bob Quinn Lake via BC Hydro’s proposed 287kV Northwest Transmission Line (NTL), which is designed to provide an interconnection point for future industrial development and clean power projects in northwest British Columbia.

Among other infrastructure, the CAN 700M (USD 707M) project includes three tunnels ranging in length and diameter, but all excavated by drill and blast in the same depth and stable rock.

AltaGas came to own the project in 2008 with its acquisition of NovaGreen Power, a subsidiary of precious metals company NovaGold. David Harris, president of the power division at AltaGas, explains the subsidiary was really only made up of a few hydroelectric projects, which is specifically why AltaGas purchased NovaGreen. At that point only conceptual engineering work had been done. AltaGas moved forward with detailed design and bid the project’s construction contracts. Hatch, headquartered in Mississauga, Ontario, is engineer and Procon, based in Burnaby, British Columbia, is the tunnel contractor.

The Forrest Kerr project—and others purchased in the acquisition—is located solely within Tahltan First Nation traditional territory. AltaGas in May 2010 signed an Impacts and Benefits Agreement (IBA) with the Tahltan Nation to provide structure to their relationship during construction and long-term operations of the completed hydroelectric facility.

Site setup
Due to the location’s remoteness, infrastructure upgrades and construction were required before the tunneling operations could mobilize, such as building roads, bridges and the camp. TNDC, a First Nations company based in northwest British Columbia, has been responsible for road work, cutting trees and spoils trucking among other work for the project.

“Even though it’s remote we have a fairly decent transportation capability in the area,” Harris says. He explains there is an access road to site, which is off the existing Eskay Creek Mine road, which was built a long time ago for mining operations in the area, off of Highway 37. The Forrest Kerr project required an expansion of its access road last fall before the site was accessible for construction of the camp and the Eskay Creek Mine road is undergoing upgrades to the bridges along it, as well as the road itself. Occupancy began in March and tunnelling started in April on the Construction Access Tunnel (CAT) and Main Access Tunnel (MAT).

The project makes use of the Prince Rupert Port and the Vancouver Port. All equipment comes into site by truck. A small airport, located at Bob Quinn Lake, some 30 to 40 minutes’ drive from the site, is being used to transport personnel to the project. Logistics support has also factored in necessities such as on-site nursing and ambulance capabilities.

With the underground construction underway—and minimal work above ground—the project is in good stead for the upcoming winter, during which the area, sees plenty of snow and inclement weather. Though that is not anticipated to impact the construction schedule.

The bigger, longer power tunnel will connect the headworks and intake area to the power house. The alignment for this nearly 3km tunnel was dictated by finding the optimum point for taking water off of the confluence of the Iskut and Forrest Kerr Rivers, and at the other end, the best place to release discharge back to the river (see figure 1). This was based off of geography and environmental considerations, as well as making sure the appropriate amount of water could be used to get the required 195MW, explains Harris.

“Those criteria, the megawatt criteria and the head and flow that was needed dictated the location of the headworks intake and power house and subsequently the alignment of the Power Tunnel that connected the two,” he says.

There will be no access shafts along the alignment, and excavations on the Power Tunnel are being undertaken from an access portal roughly 8 by 8m, large enough to handle rock coming from both directions once the work begins on two faces. Contractor Procon began construction on the power tunnel in late August.

The tail race at the end of the tunnel is still in design, but is likely to be 300m long, with a 3 per cent Slope and a 10 by 10m diameter.

All three of the tunnels have been designed with a D-shape, which was the optimum design based on constructability, schedule cost and performance, Harris explains. He adds, “We looked at resistance and loss, and the fact that you wanted the ability to drive down there.”

Working in the wilderness
Excavations are being done with drill and blast, using three automated jumbos, procured by Procon. The Atlas Copco jumbo used on the power tunnel is the largest currently operating in North America, as far as project members are aware. The area’s geology consists of good, stable volcanic rock. Drill and blast is the most cost effective and efficient way to do excavations, Harris says, adding, “The length of the tunnels, they’re not that long, so economically, we couldn’t justify bringing in and trying to design for a TBM.”

The design team also felt this method of excavation would be much less complex and would leave less potential for something to go wrong.

“We felt we would be dealing with a consistent, stable rock formation so it made drilling and blasting fairly consistent and easy. These are decent sized tunnels, but nothing that’s too overbearing,” Harris says. “That turned out to be the right thing. Tunneling is going very well.

“We haven’t seen any abnormal rock conditions that we weren’t expecting and progress is going as planned if not better than scheduled.”

Procon is averaging two to two-and-a-half drill and blast cycles per 12 hour shift, and is working seven days a week. Crews are drilling roughly 4m at a time before loading ammonium nitrate for the blasts. There have been no problems with water, only minimal to no seepage reported. Anchor bolts and shotcrete are being used to support excavations where necessary, but the tunnels will remain largely unlined. “The rock quality has been consistent with the project geotechnical analysis and we have not run into any unexpected rock formations,” Harris says.

“A small portion of the CAT may have a concrete lining,” he explains, “to make it act a little bit like a surge tunnel.” There are concerns that with the region’s climate, water in the tunnel may freeze and later expand, potentially shattering the rock.

As T&TNA goes to press, the MAT has seen 235m excavated out of total 930m, and the CAT is 470m out of 580m. Procon is working on three faces and when the CAT finishes, expected in September, that third jumbo will be used to start the tail race or work from two faces on the power tunnel, once the access portal is complete.

This next step will be determined by the construction schedule, but so far everything is going well and the excavations haven’t reached anything unexpected, Harris reports, cautiously optimistic. “Based off of the depths we’re at with the Construction Access Tunnel, and the fact that we can see the full face of the gorge over the riverside, we’re pretty confident the rock formation should stay consistent.”

Most muck removal is being done by heavy machinery and trucked out of the tunnel to be dumped on a debris pile on-site. Because it’s good quality rock and environmentally compliant, some of the spoil is being reused on the project for road bedding material and other civil prep work, Harris explains.

“The rest is being stored on a spoils pile on-site with no plans to send it off site. It’s in a pretty remote area and so it’s expensive to ship it.”

One of the biggest issues in designing the project is dealing with such a high silt concentration in the rivers that at times during the year both the Iskut and the Forrest Kerr slow down.

The intake structure needed to be designed to handle the sediment loads so water is clean before it is sent down the power tunnel, avoiding any premature erosion to equipment. The design team worked with the turbine supplier, on protective measures against the silt, such as hard and soft coatings on the equipment to prevent wear.

In terms of power supply, the slowing water and silt are not a concern. “There is more than enough water and more than enough hydraulics to support the output,” Harris says. “As a matter of fact we’ll use less than 50 per cent of our capacity of the river to achieve our output.

“So we’re in very good shape with respect to water supply and flow.”

The construction schedule estimates excavations on the power tunnel will be completed by Q1 of 2013, and the entire facility should be operational by mid-2014. One of the main influences on the schedule is being able to tie into BC Hydro’s 344km NTL, which is anticipated to be in service by late 2013.

On a larger scale, British Columbia is currently working toward a goal to achieve energy self-sufficiency by 2016.

In addition to the Forrest Kerr Project, AltaGas expects to build two more run-of-river power generation facilities in the area, those being the McLymont Creek with a capactiy of 50-70MW and Volcano Creek with a capacity of 15-18MW).


Equipment is trucked in to the remote work site Three Atlas Copco jumbos are being used to excavate the tunnels Figure 1, the layout of the work site and tunnel alignments Figure 2, the remote location of the Forrest Kerr project in British Columbia Figure 3 – Dimensions of the tunnels