Restoring rivers, restoring fish: How studying river hydraulics can bring back salmon populations

A WaterLeadership Snapshot

WaterLeadership Snapshots feature articles written by graduate students participating in the Water Institute’s WaterLeadership training program, which focuses on skills development in knowledge mobilization, leadership, and research communication. Here, students describe the value of their research and its potential for ‘real world’ impact.
 

By Michael Chislett

Have you ever been on a “skunked” fishing trip—one where you don’t catch a single fish? Sometimes, it’s the weather. Other times, it’s faulty gear. But if you’ve been fishing in rivers for a while, you may have noticed more and more skunked trips. The problem might not be your technique—it could be the river itself.

Michael Chislett, a PhD student in the River Hydraulics Research Group under the supervision of Dr. Bruce MacVicar in the Department of Civil and Environmental Engineering, is studying how the shape of riverbeds develops over time. Specifically, he is investigating river bedform morphologies—the undulations and patterns along the bottom of a river caused by hydraulics and sediment supply. His goal is to determine if there is a predictable way to induce the formation of specific morphologies using a process-based approach to river restoration.

As Chislett describes it, process-based river restoration works a bit like putting an airplane on autopilot; you can step back and let the journey take its course, but the pilot can intervene when turbulence gets rough. River engineers should prioritize letting rivers do the work of hydraulics on their own, but also need to recognize when it’s necessary to supplement the river’s function. This can happen when human activities threaten the stability of the channel.

What does this have to do with fishing?

One morphological feature—riffles—is crucial for fish spawning habitat. With climate change and urbanization amplifying river flow, many channels are losing their riffles. If experts can develop reliable methods to encourage the consistent formation of riffles, they can help restore habitat in many rivers that are experiencing dwindling fish populations, including salmon.

Salmon fishing is not just a recreational activity, it also holds cultural significance. For example, Mowachaht/Muchalaht First Nation has relied on the Muchalat Lake outlet, located on their unceded territory spanning part of Vancouver Island, for generations of fishing customs and heritage. Megan Iun, an alumna of the River Hydraulics Research Group, published a thesis exploring how to design the restoration of salmon spawning habitat using increased gravel supply to the river.

Chislett’s research further advances the ideas of process-based restoration. His recent research review suggests that pool-riffles—where riffles are coupled with depressions in the riverbed called pools—could likely exist on a spectrum of formation conditions, rather than a strict set of development criteria. He and MacVicar refer to this phenomenon as the “pool-riffle formation gradient.” By studying this gradient in the field, they hope to inform habitat rehabilitation strategies that account for diverse, local river conditions rather than a one-size-fits-all approach to developing healthy pool-riffles.

The bigger picture

The River Hydraulics Research Group’s projects on Muchalat Lake have been conducted in collaboration with Ecofish Research Ltd. (a consultant engaged by local Indigenous community partners) and Fisheries and Oceans Canada. Funding for M. Chislett’s research is supported by the Natural Sciences and Engineering Research Council of Canada (NSERC) Discovery Grants program.