Award of Excellence: Arrow Lakes Generating Station

CATEGORY: PROJECT MANAGEMENT

KLOHN CRIPPEN CONSULTANTS AND SNC-LAVALIN

When Keenleyside Dam was constructed in 1968 on the Columbia River near Castlegar, in southern British Columbia, no provisions were made for future generation. At that time it was not economic to construct a power plant given the project’s low head and the large annual variation in the reservoir levels.

By the early 1990s, however, BC Hydro had developed a preliminary design for a 220 MW power plant located at the north abutment of the existing dam. This design, however, would have required building two large cofferdams and special reservoir operations that would have affected generation at the upstream Mica and Revelstoke projects, so the utility terminated the work in 1992.

In 1995, the Columbia Power Corporation revived the design and submitted it for regulatory approvals, but environmental concerns were identified and the project was abandoned. However, the company subsequently engaged Klohn Crippen and SNC-Lavalin to assess whether the economics of the project could be improved and the potential environmental effects reduced. The firms developed the conceptual design and did a feasibility assessment that showed the Arrow Lakes generating station could be built economically and in an environmentally sound way. They co-ordinated and conducted studies for the environmental assessment and administered the proposal competition that led to the award of a design-build contract. They also provided project management, contract administration and monitoring services during the construction, commissioning and testing of the plant.

Bypass and powerhouse

KC-SNC proposed a 1,500-metre long approach channel to bypass the Keenleyside Dam and convey flow to a two-unit, 150 MW (+/- 20 MW) powerhouse located in a bedrock outcrop about 400 metres downstream of the dam. Instead of cofferdams, plugs of in-situ material would be left in place to isolate the works during construction.

The fundamental advantage of this design was that the entire project could be constructed dry on the shore of the reservoir. The changes to the layout and capacity of the power plant lowered the construction risk and reduced the construction schedule from seven to four years. The scheme also cut the unit cost of energy by over 25% compared to the 1990s 220-MW design, and it overcome many environmental hurdles faced by the project.

The design, licensing and construction of the generating station were very complex. Location and scheduling were the greatest challenges, as the project was subjected to the physical constraints of the existing dam, and scheduling challenges posed by maintaining Columbia River Treaty reservoir operations and aligning construction activities with sensitive fisheries windows. Complex modelling was needed to demonstrate the impact on downstream flow patterns, downstream temperatures, fish entrainment and silting during construction. As well, the engineers had to quantify the reduction in total gas pressure (TGP) supersaturation as a result of shifting discharge from the spillway to the power plant, a factor which environmental agencies saw as a major benefit of the project (TGP can lead to gas bubble trauma in fish, similar to the bends in human divers). The project was finally authorized under the Fisheries Act in the spring of 1999.

Comprehensive achievement

Few projects of this size and complexity have been undertaken in British Columbia using a design-build contract. The owner adopted a “design-evaluate-build” approach, which incorporated an “evaluate” phase into the traditional design-build process and allowed KC-SNC’s feasibility assessment to be confirmed.

The KC-SNC team integrated a broad range of technical and non-technical fields and wrote the owner’s requirements, specifying general design considerations as well as defining the technical requirements for specific components such as turbines and generators. KC-SNC helped the owner to qualify the design-build teams, set bid evaluation criteria, advised on the technical proposals and helped finalize a contract.

The project was completed in December 2002 on budget and ahead of schedule. The cost and generation estimates in the KC-SNC feasibility study were proven to be reasonably accurate:

Not only did the project develop the energy potential of an existing dam in an environmentally sound manner, it also created an estimated 1,000 person-years of direct and indirect employment, with residents of the region making up 85% of site employees. The project won two Consulting Engineers of B.C. Lieutenant-Government awards of excellence in 2003.

Name of project: Arrow Lakes Generating Station, Columbia River, Castlegar, B.C.

Design-build contractor: Peter Kiewit Sons (Harza Engineering, GE Hydro)