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A model of the proposed Site C dam is on display at the Community Consultation Office in Fort St. John, B.C., on Jan. 16, 2013.DEBORAH BAIC/The Globe and Mail

Some 400 kilometres downstream from where BC Hydro proposes to build the Site C dam, Elaine Manzer is reminded daily of how the flow of the Peace River is controlled by a power company in another province.

"It affects our river right here," said Ms. Manzer, deputy mayor of the Town of Peace River in northwest Alberta. "The river levels go up and down. We see it because we look at the river every day."

Sometimes, the river drops so low that two rural ferries in the region have to stop running and towns and industries have to stop pumping water to protect intake pumps.

Ms. Manzer said residents of her small community have grown used to the way BC Hydro manipulates the river, which for more than 40 years has had two dams operating near Hudson's Hope in northeast B.C.

But that doesn't mean people in northwest Alberta aren't concerned by the possible addition of a third dam.

In submissions to a joint federal-provincial review panel that has just begun hearings into Site C, the governments of both Alberta and the Northwest Territories have raised concerns about the cumulative impact of adding the dam.

"The operations of the current W.A.C. Bennett Dam and Peace Canyon Dam by BC Hydro have significantly altered the natural flow regime of the Peace River," states Alberta in its submission. "Peace River flows are now much lower than natural during May to late July and much higher than natural from mid-October to mid-April. … This altered flow regime has had both positive and negative impacts in Alberta. Alberta is concerned that Site C will further exacerbate the negative impacts."

Since the W.A.C. Bennett Dam was built nearly 50 years ago, the flow of the Peace River has been controlled to generate power. The basic change is that the natural high-water events of spring have been greatly reduced, because water is being held back to charge reservoirs, and winter flows have been increased, because of the need to generate power when it is demanded.

Alberta states that during periods of low flows, water levels can drop so dramatically that infrastructure is affected.

"When flows are low, water levels can be too low, thereby preventing ferries from operating. This leaves both the public and businesses stranded without the ability to conveniently cross the Peace River," the Alberta submission states.

The government says that when water levels dropped in October, the La Crete Ferry stopped operating, Shell Canada had to turn off a water-intake pump just downstream from the Town of Peace River, and the Town of Fort Vermilion had to reduce its water intake to protect pumps.

"That specific event highlighted the fact that low-flow releases, even when they are higher than the licensed minimum flow, can still pose a challenge to Alberta's infrastructure," stated the province.

Alberta said higher minimum-flow standards are needed if Site C is approved, and the province called for measures to ensure enough water continues to flow both during construction of the dam, and while the new reservoir is being filled.

Alberta also raised environmental concerns, saying the dam would block the upstream migration of some fish and the creation of a reservoir would lead to release of mercury into the water, which would accumulate in fish.

The government of the Northwest Territories said it is important that the joint review panel look at the impacts of Site C and the two existing dams, far beyond the borders of B.C.

"The W.A.C. Bennett Dam has altered the flow regime of the Peace and Slave Rivers," stated the NWT. "A cumulative-effects assessment of the Site C hydro project should include the entire Peace River Basin."

Both the NWT and Alberta governments asked to be involved in the planning and development of any mitigation measures BC Hydro might propose.

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