Some Like It Cold: Is River Restoration Helping Cool Stream Temperatures?

Researchers inspect a length of fiber-optic cable in the Middle Fork John Day River. To find the cable, look for the the long, white object lying on the river bottom

The Middle Fork John Day River, one of the last core strongholds for mid-Columbia steelhead and spring Chinook, is much warmer these days than it used to be, due to historic removal of shading streamside vegetation and straightening of the river channel. This can translate to lethally warm water, as biologists saw first-hand during the devastating summer fish kills of 2007, 2013 and 2015. Salmon and steelhead are cold-water fish: Warm water stresses these fish’s immune systems, putting them at higher risk of infection and disease. One urgent goal of restoration activities in the Middle Fork is to cool water temperatures to improve this crucial salmon habitat.

But how do we know that our stream restoration strategies are working to cool down the river?

To answer this question, the Selker Water Resources Lab at Oregon State University’s Department of Biological and Ecological Engineering has studied stream temperature in the Middle Fork since 2008. Their goal: to learn what factors, such as shade, stream channel shape, groundwater, and weather, influence stream temperature, and how we can leverage that information to get the most water-cooling bang for our buck out of our restoration projects. Their strategy? A futuristically high-tech approach involving—no joke— lasers.

For many years, the only option for monitoring water temperatures was just to stick a waterproof data logger in the river at just one place, in order to record temperatures at that single place over a time period. But these point measurements don’t give us all the information, because stream temperatures also change continuously over space as a river channel changes shape, as water moves faster or slower, and as vegetation cools the water by shading.

To solve this problem, the OSU scientists are looking at how temperatures change continuously along the stream length. They do this by laying fiber-optic cables along the riverbed. Fiber-optic cables, normally used for long-distance telecommunications, have now been adapted for all kinds of applications, including sensing water temperature. By using the cables—also called Distributed Temperature Sensing, or DTS— the Selker Lab can get very high-resolution temperature data. DTS works by shooting a laser down the length of the fiber optic cable. The laser’s light behaves slightly differently depending on the temperature of the water, and the researchers use this information to translate into temperature data. Starting in 2013, large-scale installations of these cables have gathered data in the Middle Fork of the John Day River, collecting temperatures over about 8 miles of river.

The Selker Lab has focused much of their effort on stream sections within two major restoration project sites (Phase 2 and Phase 3*) on the Confederated Tribes of Warm Springs’ Oxbow Conservation Area. In 2012, the Phase 2 project consolidated the river channel from two channels back into its single, historic channel, while plugging the old, man-made channel. Whereas before the water ran through two shallower channels, with roughly twice the surface area, the current single channel means a deeper stream with less exposed surface area, reducing the ability of the sun to warm up the water. The lab found that within and downstream of the Phase 2 project site, temperatures swung less wildly from one extreme to the other between day and night. This means that during the make-or-break time of day when it really matters for salmon—the hottest hours, between 2 and 5 pm— the restored channel is doing its job by keeping the water cooler. Meanwhile, at night, the temperatures in the new channel cool off less dramatically than they would have in the old channels. The ability of the restored channel to buffer dramatic swings in temperature and keep the stream cooled during the day is a potential win for fish.

By contrast, Oxbow’s Phase 3 project, completed in 2014, is projected to actually increase stream surface area. That’s because it took an artificially straightened channel and added bends and meanders. Re-meandering the river does a number of beneficial things: it slows down the water during high flows, decreasing bank erosion; allows the river to flood its banks and exchange sediment and nutrients with its floodplain; and creates more pools and alcoves for fish to rest and feed. In the short term, the increased stream surface area is predicted to actually warm the water slightly—at least until the thousands of newly planted willows and alders get taller and provide some shade. The team predicts that if restoration changes the river channel by making it wider, it will need taller vegetation to shade it effectively than a narrow channel would. These predictions help determine if and where planting vegetation is most effective for achieving cooler water temperatures. In the long term, the Selker team predicts that the taller and denser the riparian canopy gets, the more shaded the channel will be, and the cooler the water.

But just because Phase 3 is predicted to slightly warm temperatures in the short term does not mean this restoration project won’t be successful. These results illustrate the challenging trade-offs that large-scale, comprehensive river restoration poses. Though warm temperatures are one of the most limiting factors for salmon in the Middle Fork, another obstacle is the lack of space for juvenile fish to thrive and survive so they can successfully return as adults to spawn. Even if all of the Middle Fork were shaded and cooled off, helping more adult salmon survive the summer and spawn in the fall, there still wouldn’t be enough space to support increased numbers of juvenile fish—the very problem that much of the Oxbow restoration is designed to address.

What’s next for DTS in the Middle Fork? As global climate change continues to heat up our summers, DTS data is being used to “virtually” compare pre- and post-restoration stream temperatures under potential future climate scenarios, to predict which restoration efforts might work best in the future.

And meanwhile, salmon and steelhead are cooling off from the hot summer sun in the restored river channels.

* A multi-year, multi-phase restoration effort on the Oxbow Conservation Area has been split into five phases. Three phases are completed; Phase IV is currently underway.

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Before restoration (top photo), the river was split into two channels (North and South)
and Granite Boulder Creek (top middle of both photos) flowed into the North channel

After restoration (bottom photo), flow was redirected to the historic South channel and Granite Boulder Creek was once again able to contribute its cold water and effectively cool down the river

- Emily Davis
Monitoring Coordinator, Oxbow & Forrest Conservation Areas
Confederated Tribes of the Warm Springs Reservation of Oregon