Innovative use of a well-known landscaping product is helping spawning fish avoid construction areas for the Trans Mountain Expansion Project.

Trans Mountain fisheries biologist Calum Bonnington and his team are temporarily installing snow fencing flat down onto some sections of streambed that are intersected by the pipeline construction right-of-way and sections immediately downstream.

Fish such as chinook, coho, rainbow and bull trout look for suitable gravel sections of stream bed when they’re ready to build their redds, or nests. The snow fencing serves as a “deterrent mat” atop gravel beds they might otherwise choose to lay their eggs in.

“By excluding fish from spawning in specific areas of a stream that may be within our proposed construction footprint, or immediately downstream within the zone-of-influence during construction activity, we then know we will not be disturbing redds or incubating eggs at the time of construction, if our construction timing will overlap with incubating eggs,” Bonnington explained.

Once the spawning season is complete, the mats are removed. This means when Trans Mountain construction teams arrive a few months later they won’t be disturbing critical fish nurseries when digging trenches and setting pipe in the proposed construction footprint at stream crossings.

Trans Mountain began field studies of streams along the Project right-of-way in 2012. Reflecting the results of those studies, Trans Mountain has identified 26 streams in British Columbia and Alberta where the mats will be used prior to a spawning season to mitigate the effects of subsequent construction activity. Through mid-August 2017, mats have already been placed in five streams in preparation for in-stream construction in early 2018.

“This is a relatively new mitigative method that’s gaining favour within the fish community,” Bonnington explained. “We’re not necessarily pioneering this — but it’s a new approach to mitigating construction impacts. Our initial evidence shows it’s working beautifully. Fish are not being spooked by it. They’re moving upstream past it to available spawning areas.”

Not all creeks and rivers crossed by the right of way are candidates for this low-impact, low-tech solution, Bonnington noted. “You wouldn’t bother about putting this mat down unless there was potential for spawning right where we are going to be working or directly downstream in what we call the immediate zone of influence.”

If the streambed section at the right-of-way crossing is covered with large cobbles or boulders and there is no suitable spawning substrate, the deterrent mat is not necessary, Bonnington added.

“Within Alberta and BC combined, we’re proposing to use this method at 26 locations. We are only using it at locations where we know we need to construct outside the least-risk windows and there is a potential for spawning to occur within or immediately adjacent to our construction footprint.

“On many streams, the construction time with the least risk to fish is summer — but that can coincide with freshet and peak high water flows which make construction very difficult.

“The challenge is that along certain sections of the pipeline, the seasonal timing for low stream flow occurs most often in the fall or winter — and that happens to be outside the least-risk window. It’s a time when fish are spawning or eggs may still be incubating.”

“So the deterrent mats allow us to construct the pipeline outside those least-risk windows and avoid serious harm.”

One of the five streams where Bonnington’s team has already installed a spawning deterrent mat is Swift Creek, a stream near Valemount that’s noted for a population of chinook.

“Already, they’re proving to be working incredibly well. At Swift Creek it’s working beautifully, just as we had hoped, with fishes continuing to spawn elsewhere within the channel.

“The mat doesn’t necessarily stay in place in the stream for a long time. It can be removed as soon as the spawning season is complete. In the case of Swift Creek where there is only one species of concern, chinook, we could go in and remove the mat in literally a month’s time — and it will have done its job.

“There are some locations where we have multiple species overlapping in which case we will leave it in longer — for example, it may be a stream where chinook turn up first, then perhaps coho later on.”

Bonnington has been carrying out in-stream studies along the Project right-of-way since 2012, and said work has provided Trans Mountain with the knowledge it needs to make effective, environmentally responsible decisions about the timing of in-stream construction activity.

The snow fence is weighted down with material, such as boulders or sandbags filled with substrate material from the immediate area of each stream. It can also be easily pinned down with sections of rebar driven into the streambed.

“You call it a low tech solution but it’s a low tech solution that requires really precise and good understanding of each of these environments.”

Bonnington added that the Department of Fisheries and Oceans Canada (DFO) is “pretty interested” in Trans Mountain’s use of deterrent mats since the technology is relatively new.

“The use of spawning deterrent mats was part of the site-specific mitigation we proposed to the National Energy Board and DFO to help avoid serious harm to fish during pipeline construction. This is a relatively new science, without a body of supporting evidence for its success. Recent applications of its use have shown it to be very successful under the right conditions.”