On the wall of my office is a photo of one of my co-workers, Joe Puhn taken during a habitat survey on the Deschutes River. He’s standing in a few feet of water, hanging on to his float tube. What’s interesting about the picture is the width, depth, and curviness (sinuosity) of the river.
We were doing the survey in the summer when most of the Deschutes runs wide and straight, shallow and hot. Someone, probably kids looking for a better inner tubing experience, piled up rocks and gravel to narrow, deepen and add sinuosity to the channel to speed the river.
What is good for inner tubing is also good for fish — faster water makes more interesting tubing and sweeps out the fine sediment in spawning gravel (fine sediment can choke salmon before they ever emerge from the gravel). Added sinuosity lengthens the river and allows the water to interact more with the cool, underlying gravel.
The state Department of Ecology recently released a draft report that outlines the various reasons behind the declining health of the Deschutes River. One of the major obstacles faced by fish is high temperatures. If water is too warm for fish, they can die from heat stress.
Most of the discussion around this particular aspect of the Deschutes has focused on the need to plant more trees and better manage riparian vegetation to shade the river from the heating effects of the summer sun. But buried in the report is data that suggests planting trees is not enough to eliminate water temperatures lethal to fish (> 22 oC or 72 oF). Much more has to be done to approach the overall natural background condition where the summer, system-wide 7-day average maximum water temperature can potentially be as low as 16.6 oC (~62 oF).
The current summer condition is about 23.7 oC (~75 oF) due to the influence of human activities. Mature vegetation in a healthy riparian zone will lower that temperature by 4.5 oC (~8 oF), but improvements to channel conditions and microclimate can provide an additional 2 oC (~3.5 oF) of cooling. Only with improvements to channel conditions can water temperatures lethal to fish be completely eliminated from the Deschutes River system.
One way to improve channel conditions and cool water temperatures is with large woody debris. Planted trees will eventually fall into the river and create logjams. These structures will vary the river, digging out deep, cool pools for fish to rest and creating fine sediment-free riffles for fish to spawn.
But that sort of solution is too far down the road. We can get into the river today and build logjams that will start helping fish now, rather than a wait century or more for the trees to grow and fall.
The Squaxin Island Tribe recently built a series of logjams along Skookum Creek, and we’re already seeing the results. Juvenile salmonids prefer the cover of the logs and arrived in large numbers the day after we completed the jams and they continue to seek refuge there.
The logjams that we built will bridge the gap until a few thousand trees we planted around the creek grow large enough to naturally build logjams. This is the same sort of thing that we should do on the Deschutes.