Salmon Suffer from Flow Changes below Power Plant

By Francesca Knight, M.Sc., R.P. Bio. 

President, Squamish River Watershed Society 

The Cheakamus River is negatively affected by BC Hydro’s 66-year-old Cheakamus Generating System (CGS) and that is not unexpected. 

Many hydroelectric power plants impact fish and aquatic life as a result of plant operations, including drawing fish through the turbines, disrupting access to spawning grounds, stranding when water levels drop too fast, and displacement when water levels rise too fast. 

But the Cheakamus plant is unusual in one regard. 

The CGS is an inter-basin transfer facility, where water for power generation is taken from the Cheakamus and discharged into the Squamish River. In today’s regulatory environment, this arrangement likely would not be approved, as it permanently reduces flows in the Cheakamus below the dam. 

A Water Use Planning (WUP) process was completed for the GCS in 2006 to identify potential impacts to fish and aquatic life in the Cheakamus, and to develop plant operational constraints to mitigate these impacts. The Cheakamus WUP specifies minimum seasonal instream flows, as well as ramping rates. BC Hydro conducted WUP processes at all of their 23 generating facilities, but consensus was not reached for the Cheakamus plant. 

Ramping is one of the key technical issues, which resulted in a failure to reach an agreement on the Cheakamus station’s plan. Ramping can be defined as the rate of flow change or stage change per unit time. Streamflow and water surface elevation variability occur both naturally and because of hydro plant operations, but the rate and frequency at which streamflow changes is much more extreme in a flow-regulated river compared to an unregulated river.  

Juvenile salmonids are particularly vulnerable to stranding, which occurs either along gravel bar margins when water levels drop quickly or in rearing pools that become isolated when the water level or flow drops.  

In 2018, a scheduled drop in water levels, or rampdown, stranded thousands of juvenile steelhead and coho salmon. Multiple ramp downs with similar effects have been identified since. As a result of the stranding and the public pressure it attracted, BC Hydro has been studying the issue and created a stakeholder committee to review their findings.  

I believe even BC Hydro was surprised at the severity of effects as a result of CGS ramping operations. BC Hydro continued to execute ramping tests between 2019 and 2021, evaluating different ramping rates under different flows. Most of the tests showed that both ramping rates and the total amount of flow reduction on a test day can result in significant fish kills. With more than 17 kilometres of salmon and steelhead habitat in the Cheakamus, stranding events can kill thousands of fish. 

Adult fish are also vulnerable to stranding.  In 2019 and 2021, ramping events during the pink salmon run resulted in the death of thousands of fish before they could spawn.  

The Squamish River Watershed Society undertook a technical review of several years of Cheakamus River flow data and concluded that a slower ramping rate, coupled with higher seasonal minimum flows, would benefit fish populations. The society made a recommendation to BC Hydro, and many current stakeholders supported it. The CGS WUP and accompanying flow order are under review by the provincial Comptroller of Water.  

This review may result in changes to the CGS flow order intended to reduce the impacts to salmonids and other species, but changes are unlikely if public pressure is not maintained on both BC Hydro and regulatory authorities. I urge you to contact your local MLA and let them know that the protection of salmon should be balanced equally with power generation, and that BC Hydro needs to do a better job of protecting fish affected by their facilities. 

Read more about our call for BC Hydro to fulfil their legal requirement to compensate for the massive ecological impact of its hydroelectric dams. 

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