Woodworth Dam Optimization

The City of Prince Rupert needed to replace the aging Woodworth Dam on British Columbia’s northwest coast, along with water supply lines. This 100-year-old critical piece of infrastructure has served as a reservoir and primary freshwater source for the community.

The municipal government turned to Austin Engineering, now part of BBA, to optimize the dam’s redesign, help secure the multi-year project and develop a state-of-theart freshwater distribution facility.

Prince Rupert had been under boil-water advisories in recent years, due to turbidity in the water system pumping from Shawatlan Lake. The completion and commissioning of the Woodworth Dam were celebrated on Oct. 14, 2022. Beginning in February 2023, for the first time in seven years, drinking water could be taken directly from the city’s original supply in Woodworth Lake and transported—via high-density polyethylene (HDPE) pipeline—down and across the harbour, entering the city’s water system. This has been a life-changing project for the community.

Getting the green light

In the initial stages of the project, there were successes; however, the challenges and costs associated with building a new dam in a remote region, with limited road access, tested its future. The firm’s team undertook a comprehensive value engineering review, optimized the initial design for the new dam and reduced the project budget by nearly 17%.

T he budgetary reduction was achieved by using multiple three-dimensional (3-D) printed dam and C NC-routed riverbed models, which were tested in hydraulic flumes to confirm their flow characteristics. This analytic approach allowed the team to optimize the design to meet the specific project goals, a process which reduced rock anchor quantity by 40%, concrete volume by 25% and rock excavation volume by 18%. This was also a more sustainable solution.

Reducing costs would help get the ‘green light’ for the project, but the team’s goal was also to incorporate the interests of the environment and of local communities. By way of example, reusing foundation rock saved 500 trips on the remote service road; the reduction in rock excavation limited the amount of debris entering the stream; and the team ensured special attention and care by protecting Indigenous ceremonial trees, traditional wetlands and other culturally significant features.

I mplementing industry best practices ensured climate resilience and dam safety. Prince Rupert is known for significantly hea vy rainfall, so a focus was placed on predicting and allowing for future changes to ‘flow regimes’ within the river system as a result of climate change. The spillway capacity w as oversized to allow for future flood flows and demand.

Site challenges

The site is located 7 km from a tidal barge landing. All equipment, concrete, rock, aggregate and other items for the project needed to be delivered by barge to this landing, which could only be accessed to load and unload equipment during high tide—a three-hour window each day. From there, the items needed to be trucked the 7 km up a single-lane forestry service road. The discovery of weak shale rock above the north abutment meant slope stabilization was required before the team could fully access the dam site. Additional measures were taken to ensure safety during mudslides; while these are considered one -in-75-years to one-in-50-years rainfall events, they did indeed occur during the project!

Collaboration with First Nations

The project is located on Indigenous land. Local communities were involved throughout the project, in a collaborative effort that ensured special attention was given to respect their culture.

These communities hold traditional ceremonies using sections of cedar trees. So, the project team carefully relocated the identified trees and returned them to their communities.

The project also included a joint venture (JV) partnership with an Indigenous community as the environmental consultant.

An investment in the future

The City of Prince Rupert’s main priority was to provide access to safe water for its residents and ensure future generations would also enjoy a secure water supply. Replacing the 100-year-old infrastructure was both a priority and a major investment.

Not only did the team redce costs to make the project possible, but it also successfully transformed the site into a state-of-the-art facility.

“The Woodworth Dam optimization project is an example of how we can successfully balance economic benefits with environmental and local community interests through innovation and collaboration,” says Guneet Uppal, the city’s engineering services manager. “It is an achievement we can all be proud of.”

Woodworth Dam Optimization, Prince Rupert, B.C.

Award-winning firm (prime consultant): BBA, Mont-Saint-Hilaire, Que. (Roger Austin, P.Eng.; Tanzim Alam, P.Eng.; Ruth Keyes, P.Eng.; Matt Pommer, Field Inspector Tech).

Owner: City of Prince Rupert.

Other key players: L&M Engineering, Eiffage Canada.