Canadian hydroelectric megaproject completes earthfill dam

Canadian electric utility BC Hydro announced the completion of the Site C earthfill dam at the end of last month. The 60m tall structure is 500m wide at its base and stretches more than 1km across Peace River in north east British Columbia.

Site C will form a third dam and hydroelectric generating station on the river. Once completed in 2025, it will provide 1,100MW of capacity and produce about 5,100GWh of electricity each year. Construction on the project began in 2015.

Peace River Hydro Partners, a partnership between Acciona Infrastructure Canada and Samsung C&T Canada, is the main civil works contractor on the scheme.

In 2021, it was announced that the project cost had risen to C$16bn (£9.3bn), from the preliminary estimate of C$6.6bn (£3.8bn). This was partly due to geotechnical issues related to the permanent structures on the project’s right bank, which needed to be stabilised with a large roller-compacted concrete buttress.

Geotechnical investigations and analysis of geological mapping and monitoring activities completed during construction identified that foundation enhancements would be required to increase the stability below the powerhouse, spillways and future dam core areas.

This involved installing large piles beneath the buttress to improve the stability and limit possible future movements, even under extreme loading conditions, and enhancing drainage within the right bank.

The Site C project is being built and designed in accordance with international and Canadian safety practices to withstand a one in 10,000 year earthquake.

The placement of material for the Site C earthfill dam began in 2021. Most of the 16M.m³ of earthfill material was taken directly from the dam site, while other material was sourced locally offsite and transported to the dam on a 5km long conveyor belt.

With the earthfill dam complete, the next steps involve capping it and building roads across it for crews to travel on once the project comes into operation. BC Hydro is targeting to begin reservoir filling this autumn.

Other key project areas that need to be completed include the approach channel, spillways, tailrace area, dam intake structures and certain components of the powerhouse.

Another key component for reservoir filling is the conversion of one of the tunnels that currently diverts the Peace River around the project site. This process, which is currently underway, requires the installation of constrictions inside one of the tunnels to restrict the flow of water.

In related news, earlier this month, Peace River Hydro Partners pleaded guilty in the Provincial Court of British Columbia to the discharge of 3,300m³ of contaminated drainage water into the Peace River in 2018.

As part of its investigation, Environment and Climate Change Canada enforcement officers determined that, during a high rainfall event, the water management infrastructure at the Site C project site had insufficient available capacity to treat the additional drainage, and a mix of treated and untreated drainage was released into the Peace River.

Peace River Hydro Partners has been fined C$1.1M (£638,000), which will be directed to the Government of Canada’s Environmental Damages Fund.