The research team installs the Distributed Temperature Sensing (DTS) cable at one of the study sites. This was a difficult and physically intensive process due to the size of the equipment. (Credit: Erin Leahy)
Researchers and graduate students from Portland State University (PSU) and U.S. Geological Survey (USGS) scientists investigated how beaver dams influence stream temperature in three sub-basins of the Tualatin River basin. Principal Investigators Heejun Chang, a PSU professor of geography, and Erin Leahy, a USGS Hydrologist, sat down to discuss this collaborative study, its use of Distributed Temperature Sensing (DTS) to capture stream thermal dynamics, and offer insights into the effectiveness of restoration and beaver activities.
Q: Could you describe the scope and significance of this research project?
Heejun: The project is a collaboration between USGS and PSU researchers, focusing on collecting stream temperature data using DTS cables, provided by the Center for Transformative Environmental Monitoring Programs (CTEMPS). This research is significant because we are facing many climate change issues, and stream temperature is responding to changes in air temperature and stream flow. We’ve thought about how nature-based solutions, such as the beaver dams, can potentially help mitigate changes in stream temperature while providing other water-related ecosystem services, such as flood regulation and sediment retention. In this study, we focus on temperature regulation.
Erin: We also took into consideration the restoration work done in these areas. Some restoration projects were conducted a decade or so ago and others were more recent, like right before the studies started.
Q: How did you select the study sites?
Heejun: The restoration work influenced the sites we chose. We studied Fanno Creek, Springville, and Chicken Creek, and each site has a different history of restoration and urban development: Fanno Creek (most developed, oldest restoration), Springville (semi-urban), and Chicken Creek (semi-natural/wildlife refuge site, newer restoration site).
Erin: Each location also represented varying degrees of beaver establishment. At Chicken Creek, the restoration work was done in hopes that the beavers would start to populate the area. And that's definitely what was happening as we were doing the research. The cable actually became kind of intertwined in one of the dams at one point. For Fanno Creek - the beavers have been there for a while.
Q: Could you describe your research process? How did the DTS cable play into the data collection process?
Heejun: We did a lot of field data collection, measuring stream temperatures above, within, and below beaver dams. We were especially interested in how pond size, depth, and exposure to sunlight versus shade affected stream temperature.
We found that stream depth is a strong indicator of stream temperature, especially in well-established beaver systems like Fanno Creek. That relationship didn’t hold as strongly in less developed sites like Chicken Creek, where depth and temperature were more uniform. This led us to focus more on micro-scale temperature variations. For example, how temperatures change just upstream, inside, and downstream of beaver ponds, and how far those changes persist downstream. We also explored whether temperature patterns shift when water flows through a series of beaver dams.
Finally, we looked at how stream temperature is influenced by surrounding factors like vegetation cover, stream width, and depth, and using those geomorphic features as potential predictors.
Erin: Data collection was definitely tricky at times, especially when working with the DTS cable. It’s a long, heavy fiber optic cable that had to be lifted and rolled out across the reaches, often going over and around the beaver dams. We had to deal with thick sediment, muddy conditions, and a lot of downed logs. It took a full team and we all agreed it was some of the toughest fieldwork we’ve done.
I, personally, think that DTS is best suited for detecting things like groundwater inputs. I learned that taking synoptic snapshots on various days might’ve been a simpler approach with much less effort and less power intensive. We were constantly changing out batteries, and the sheer size and weight of the cable made things even harder. It’s tough to describe how massive the cable really is.
Heejun: The nice thing about the DTS is its ability to measure stream temperature at very high resolution - every 15 minutes and at intervals as fine as one meter or five meters, depending on how it's programmed. The more precise the data you want, the more power it requires, since higher resolution uses more energy.
In the second year, we realized that collecting data every 30 minutes, or even every hour, might still meet our needs. Similarly, we could space measurements out a bit farther than one meter to reduce power demands while still capturing the key trends.
We had the students going out to the field and constantly checking because one of the sites had a power failure, so we lost some of the data. And particularly in the urban site, we were super cautious about any vandalism. But luckily that didn't happen. At one point, I think a beaver chewed on a cable.
Erin: I’d toss equipment in and secure it with a rope, and if I placed it near spots where the beavers were coming in and out of the water or close to their dams, they’d definitely start gnawing on it.
Another photo of the research team installing the Distributed Temperature Sensing (DTS) cable at one of the study sites. (Credit: Erin Leahy)
Q: How did the community respond to the research process and beaver presence?
Heejun: We had quite a few volunteers from town that helped deploy the cables in both years. I think it shows there’s a lot of interest in beavers - not just from people focused on conservation or the environment. When we were out deploying equipment, we talked with some neighbors, including one who had lived there for over 20 years. He was really curious about what we were doing and seemed very supportive once we explained we were collecting stream data associated with beaver dams.
He was actually the one who let us know that someone had destroyed the beaver dam, which we later confirmed. He really knew the area well. That experience led us to do a separate social survey with Matt Guziejka, supported by the UPP, to better understand how people perceive beavers and how willing they are to live alongside them.
We found some really interesting patterns. For example, people who live near the beaver dams tended to have different views compared to folks just using the trails. Some were more receptive, while others were frustrated because the dams might flood their yards or beavers were chewing on fences. Some even added metal sheeting to stop them from chewing the wood. So it’s clear that more public education could help, especially around how people and beavers can coexist.
Q: What were some key findings? How do you hope these observations will impact local water management efforts?
Heejun: This is part of my hypothesis, and one of the key findings relates to what we’re calling ‘restoration age.’ It turns out that the site at Fanno Creek shows the lowest thermal sensitivity, which means how much stream temperature increases in response to a rise in air temperature. So, a highly sensitive stream will have a steep increase in temperature when air temperature rises, while a less sensitive stream will show a gentler slope.
We found that Fanno Creek, with its well-established beaver dams and mature vegetation, has the lowest thermal sensitivity. In contrast, Chicken Creek, which lacks much vegetation and where the beaver dams aren’t very established, shows the highest thermal sensitivity. That makes sense because without those natural features, the stream is more exposed to sunlight and reactive to changes in air temperature.
This has important implications for restoration. It suggests that long-term restoration efforts, including beaver activity, can help buffer streams from rising air temperatures, which could be really valuable as the climate warms.
But when we zoom in to the microscale and look at stream temperatures just above and below individual beaver dams, the picture gets more complicated. At Springville, we consistently saw higher stream temperatures upstream of the dam and cooler, more stable temperatures downstream. The downstream temperatures also fluctuated less, showing a muted response over time, while the upstream data followed a more pronounced daily cycle.
While the broader patterns are promising for restoration, the fine-scale dynamics around individual beaver structures are more nuanced and depend on a lot of local factors.
Q: What are the next steps?
Heejun: The project ended without additional funding, but I think there’s so much more we could do with additional resources, especially around data collection and monitoring. For example, understanding where water is coming from, how stream temperature changes, how much groundwater is surfacing, and whether there’s input from surrounding areas are key. In a complex urban environment, there can be contributions from residential runoff or even industrial sites. Being able to monitor those inputs, alongside the effects of climate variability and human impact, would give us a much fuller picture.
Right now, we’ve only done two summer snapshots, which is a great start, but not enough. Long-term monitoring is really needed to understand how these systems change over time, especially at sites with active beaver populations. Beavers don’t stay in one place, so we need to understand how that movement and their dam-building affect stream temperature and geomorphology along different parts of a stream.
Erin: I think it would also be valuable to look at temperature at various depths because we were just looking at temperature on the stream bottom, which is the least impacted by thermal input.
Heejun: And beyond just the science, there’s also a huge need for community engagement. If we want to coexist with beavers in urban or suburban areas, we need to educate people on the benefits beavers provide, like habitat creation, water retention, and cooling effects, and find ways to support coexistence.
At the same time, we have to acknowledge that not everyone feels that way. Some people are concerned about property damage, such as flooded yards or trees being gnawed down. So we need to think about creative, fair solutions, like compensation or better infrastructure that allow people and beavers to share space. It’s not just a biological or physical issue; it’s really a human-environment challenge that needs broad, thoughtful engagement.
To learn more about this study, visit the project website or contact Heejun Chang (changh@pdx.edu) and Erin Leahy (eleahy@usgs.gov).