The lead engineer examining the feasibility of a 900-MW dam in northeastern British Columbia says the proposal holds enormous promise for additional power generation for the province. The Site C Dam would be the third dam along the Peace River.

Source: BC Hydro
The third impoundment on northeastern British Columbia’s Peace River would provide 900 MW of electricity, but cause a significant loss of habitat, opponents claim.

According to John Nunn, technical project director of Vancouver-based engineering consultant Klohn Crippen Berger Ltd., the provincial government is not putting pressure on his company to validate the government’s decision to end a 20-year moratorium on construction of the controversial $6.6-billion project.

Controversy has dogged the hydroelectric impoundment since it was first proposed nearly 40 years ago, but Nunn says the hydraulic engineering principles and electicity generating potential are sound. “This project gets a lot of generation from the storage that’s behind W.A.C. Bennett Dam and Williston Reservoir upstream and, in the modern context, is a very good project,” he says. “From a technical point of view, it can go forward.”

Klohn Crippen Berger, which expects to bill “a couple of million dollars” for project work, Nunn says, first became involved in 1989 during an overview of earlier studies. The company returned in 1997 to conduct a detailed technical review.

That task was complicated by design choices of the late 1970s and 1980s and eventually led engineers to conclude that BC Hydro needed an updated design more in keeping with current technical standards for dam construction.

A case in point is increased seismic activity. A magnitude-5.4 earthquake in 2001 near Dawson Creek 40 miles southeast of the site persuaded engineers to refine the proposed Site C design to accommodate maximum design earthquake (MDE) loads. The suggested sitework included contouring the north-bank slope above the earthfill dam to a flatter slope and reinforcing the foundation of the spillway headworks.

A larger problem, however, is the area’s geology and the susceptibility of foundation rock to rebound. Nunn says short-term swelling can be addressed during construction with careful foundation treatment and construction planning. Long-term swelling depends upon how the structures are configured and how the excavation for those structures isconducted.

“If you do a deep excavation and put a light structure in it, then you get significant rebound. So we’re trying to see if there are ways we can rearrange structures and foundations to mitigate that.”

The greatest challenge to the project continuing is local opposition.

The reservoir for the 3,600-ft-long, 984-ft- wide earthfill dam would be more than 50 miles long.

The resulting partial flooding of the Moberly and Halfway rivers and the Cache and Lynx creeks has sparked angry objections from local First Nations communities over the potential destruction of wildlife habitat and ancestral gravesites. One of the most vociferous opponents is Chief Roland Willson of the West Moberly First Nations.

“There’s going to be huge habitat loss along the river. The low-lying areas are abundant calving grounds for all ungulates—moose, elk, deer. If you flood that, they can’t come across anymore.”

Those concerns will be weighed during the much-anticipated environmental and regulatory assessment expected in early 2011, after Klohn Crippen Berger files a detailed project description. If the environmental hurdles are overcome and construction begins, the dam is expected to be complete by 2020.