Circuit 5L063, built in 1978 is a 500 kV radial transmission system between Telkwa and Skeena substations. As a radial feed, the reliability of this line is essential for a large region in northwest BC. The circuit crosses the Telkwa Landslide, also known as the ‘Bulbous Toe Landslide’, on the north side of the Telkwa River, approximately 20 km west of Telkwa. The Landslide is a large, deep slide 3 km long and 1.5 km wide at its widest point. Approximately 2.4 km of the line had towers in this highly unstable area which has been moving 15 cm to 44 cm per year. The movement was creating a safety risk to crews performing maintenance on the towers and was leading to a growing risk of a potential line failure.

Mitigating the geotechnical risk was the driver for the project. Due to the urgency to contain the cascade failure of the line, the project was implemented in two phases. The first phase was to install two anti-cascading dead-end towers to contain the line section affected. The second phase was to construct a new line bypass north of the existing route, reconnect the existing line via the new dead-end towers and decommission the bypassed portion of the existing line.

During planning and implementation of the project, Wood provided Project Management; Civil, Structural, Transmission and Geotechnical Engineering; Scheduling and Cost Control; Estimating, Procurement; Materials Management; and Environmental Management services.

Construction was challenging due to the steep terrain, the short summer construction window, and working in a remote area in close proximity to an energized transmission line. The success of this unique and challenging project is attributed to a dedicated collaborative team effort from Wood, BC Hydro, Indigenous communities, and contractors. The project team successfully completed the project on time and on budget. The new line bypass increased reliability and reduced safety risks for a line that serves a large region in northwest BC.

Wood developed nine route options to relocate the line which were assessed from cost, environmental, Indigenous, reliability, safety, schedule, and stakeholder perspectives. Environmental and archaeological desktop reviews and field visits were completed to identify potential habitat loss/fragmentation and archaeologically sensitive areas. Wood conducted geotechnical investigations and a geohazard assessment to identify slide retrogression and movement. The results were used to refine the alignment and select site-specific towers and foundations and to upgrade10 km of existing access roads and construct 7 km of new access roads.

Wood used standard towers and foundations for all new structures and reinforced them to meet structural loading requirements of current BC Hydro standards and geotechnical conditions. We developed a minimum Right of Way clearing width requirement which was used to clear 58 ha of forested land for the new line bypass and associated roads.

During construction, we were onsite to support the contractors with foundation installation, tower assembly, erection, stringing and dismantling. Wood also provided environmental oversight and auditing of contractors.

The team consulted with the Office of the Wet’suwet’en (OW), the Wet’suwet’en First Nation, and the Witset First Nation by information sharing, providing opportunities for input into environmental deliverables, site visits, accommodation for OW and substantial procurement opportunities.

After 7 years of design and construction, we moved 2.4 km of a radial transmission line out of the path of the Bulbous Toe Landslide. The project increased reliability and reduced safety risks of a line that serves a large region in northwest BC and delivered benefits to local Indigenous communities by investing in infrastructure crucial for their cultural practices and offered substantial procurement opportunities. The new line came into service in August 2023 on time and on budget.