Studying the impacts of drought on salmon habitat in the Nicola watershed

The first time I drove over the Coquihalla from the coast to the interior I was struck by how quickly the landscape changed. In a matter of minutes the moist, dense, green forests I’m used to were replaced by open grasslands, rolling hills, and towering Ponderosa Pines. As I descended into the Nicola Valley it quickly became apparent that this was cow country. Emerald hay fields dotted the valley bottom and cattle guards rumbled underneath. At first glance it was hard to believe that this landscape had anything to do with salmon.

The Nicola valley is situated in BC’s semi-arid southern interior, in Nlaka’pamux and Sylix territory. Since early summer I’ve been co-leading a project in the Nicola with Nathan Lustig, the fisheries biologist at Scw’exmx Tribal Council. Our goal is to monitor changes in salmon habitat throughout the summer low flow period and collect data that will inform drought management measures and habitat restoration. 

The Nicola watershed is a naturally semi-arid environment, receiving an average of 25 millimeters of rain each month in the summer. The region is facing worsening droughts due to a combination of climate change and a legacy of land use practices that alter local hydrology. 

The watershed also contains important spawning and rearing habitat for interior Fraser coho, Lower Thompson Chinook, and interior Fraser steelhead. Juveniles of these populations must spend at least one year in freshwater before they leave for the ocean. In addition, Lower Thompson Chinook are spring-run, spawning in late-summer when drought risk is at its highest.

These traits make these salmon extremely vulnerable to drought impacts, namely low flows, high water temperatures, and loss of rearing habitat. 

This year, our project focused on the Coldwater River, a major tributary of the Nicola River. From its headwaters near the Coquihalla summit, the river runs adjacent to the highway to its confluence with the Nicola in the town of Merritt. 

During the November 2021 floods, the Coldwater experienced record flows which flooded Merritt and dramatically altered the morphology of the river. 

Severe wildfire damage to riparian areas earlier that year also resulted in numerous washouts and landslides when the rains came. This loss of riparian vegetation, decrease in bank stability, and channel downcutting has profoundly changed the flow regime of the river. 

Understanding the current state of flows in the Coldwater, and how salmon habitat is impacted during low flow periods, is critical to inform ongoing habitat restoration and drought mitigation efforts.

Field days on the Coldwater

Our field days are very straightforward. 

We selected nine study sites along the entire course of the Coldwater, from its headwaters to Merritt. Each site was visited once a week in July and bi-weekly in August and September. At each site we collected data on flow, water temperature, stream width, water depth, and other habitat metrics, allowing us to observe the timing and extent of low flows over the summer. 

Using habitat suitability curves, we can then calculate the probability that a juvenile or adult salmon will use a specific stretch of habitat at a specific flow or depth. 

Ultimately, these data will allow us to set optimal flow targets for the Coldwater River that inform habitat restoration, water storage, and drought mitigation measures. 

My favourite part about this project is how collaborative it is. The project began at a meeting in Merritt early in the spring of this year, where I met with members of the Scw’exmx Tribal Council fisheries team, Title & Rights team, and Nicola Watershed Governance Project. 

We spent a day brainstorming in a lecture hall at the Nicola Valley Institute of Technology, talking about the community’s priorities for salmon, what responding to drought will look like, and how Raincoast can support their restoration goals. 

As the project developed, we also partnered with the nłeʔképmx (NLX) Guardians program from Citxw Nlaka’pamux Assembly. Over the course of the field season, NLX Guardians Crystal, Meghan, Jess, Bret, and Eagle contributed greatly to the project through their knowledge, experience, and great vibes. 

We hope this project will help people and salmon in the Nicola watershed adapt in the face of worsening drought. As our fieldwork wraps up for the year, I leave the Nicola valley with fond memories of friendly people, beautiful natural spaces, and an impatience for the start of the next field season.

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