A new Report from Wildlife Conservation Society Canada (WCS Canada) warns of the potential for major negative impacts on fish and fish habitat caused by large hydroelectric dams, like that currently under evaluation through the Next Generation Hydro initiative. The Report, which focuses on north-western Canada, notes that substantial destruction of fish habitats caused by such a dam, along with additional threats and effects will be either very expensive or impossible to mitigate.
"Potential Impacts and Risks of Proposed Next Generation Hydroelectric Dams to Fish and Fish Habitats in Yukon Waters," is co-written by Yukon fish habitat specialist, Al von Finster, and Dr. Donald Reid, of WCSCanada's Whitehorse office.
Next Generation Hydro is a Yukon Territorial government initiative to find a for site a large (greater than 10 MW) hydroelectric dam on a tributary of the Yukon or Liard Rivers, in Yukon. Government contractors have been evaluating ten potential sites -- on the Stewart, Pelly, Teslin and Frances Rivers.
"The Territorial government decided that a dam should be built somewhere," says Dr Reid. "But it didn't start with the more important question of whether such a large dam should be built at all. The government's decision was based on economic considerations, but it is not clear that the economic incentives for a dam outweigh the likely negative effects on fish, wildlife and other resources. That's a question for a wider debate in society."
WCS Canada commissioned this Report to provide communities close to the potential dam sites with a better understanding of how their fish populations might be affected. Hydroelectric power generation is considered by some as an attractive source of energy, especially with society's need to reduce the burning of fossil fuels. Hydro power is "renewable," a term which suggests environmental compatibility. However, as von Finster points out, "Large-scale hydroelectric dams have degraded and even destroyed fish habitat with dramatic impacts to numerous fish populations in western Canada and the United States. Hydroelectric power might be renewable, but it isn't really "green."
As the result of a career spent working on fish habitat issues in Yukon, von Finster has a good understanding of what we know. "We know quite a bit about Chinook salmon. All the proposed dam sites on tributaries to the Yukon River would flood some Chinook spawning habitat" he says. "But we know little about the movements and habitats of most species, because they haven't been studied."
As the Report points out, a dam on a substantial river will almost certainly block movements of some freshwater species, perhaps leading to the destruction of populations. So, that natural capital could be lost without our knowledge unless some detailed survey and inventory work is done.
In the long history of hydroelectric dam building and operation on western North American rivers, biologists and managers have learned a lot about possible ways to avoid or mitigate impacts to fish. Dams block fish movements up and downstream. Some species will use fish-ways (fish ladders) to climb past a dam, others will not. Special turbine and spillway designs can reduce the numbers of fish injured or killed in trying to go downstream past a dam.
All mitigation measures are only partly effective, are expensive, and would have to be used throughout the long life of a dam to sustain the fish in question. However, many impacts cannot be mitigated. These include: the loss of stable shallow water habitats in a reservoir that fluctuates by many metres throughout the year; the extensive erosion around the edges of reservoirs and on newly flooded land; and changes to water quality and flow rates downstream of a dam.
"WCS Canada does not object to hydroelectric power generation in principle," says Reid. "But it's a scale issue. Building a large dam on a large river looks like it will have large impacts because the river is a water highway and home for lots of fish species. Large areas get flooded. But we have learned that small-scale hydro on headwater tributary streams can work with much fewer impacts. That's because these streams may already be impassable to fish, or be used by such a small proportion of species or so few fish that the overall impact is much less."
WCS Canada maintains that substantial electricity generation can happen in Yukon with small-scale hydroelectric projects that are much friendlier to the environment than a large dam on a major river.
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