EUGENE, Ore. (Feb. 11, 2013) -- A study of the Umpqua River basin in the Oregon Coast Range helps explain natural processes behind the width of valleys and provides potentially useful details for river restoration efforts designed to improve habitats for coho salmon (Oncorhynchus kisutch).
Coho salmon thrive in broad, flat valleys that contain multiple auxiliary channels to the main river. These valleys formed after large landslides altered the landscape, said study co-author Joshua J. Roering, professor of geological sciences at the University of Oregon. The network of secondary channels, while often devoid of water in the dry season, fill and provide a calm, safe haven away from swiftly running currents for the fish during periods of heavy rain and storms. They now have been identified as a critical component of salmon habitat.
While geologists and hydrologists long ago documented how river-channel width and depth varies, little had been done to understand how valleys beyond the channels form, and why they may be narrow or wide, Roering said. The study -- appearing online ahead of print in the journal Geology -- combined on-the-ground observations and a remote-sensing technology known as airborne Light Detection and Ranging (LiDAR).
"There are two things that this research tells us," Roering said. "Valleys are things we can see from airplanes or from maps, and they behave, if you let them, in a very simple way. They get wider as the river gets bigger. We've all seen that. What we've learned here is that if you introduce variable geology and geomorphology -- big landslides, messiness that happens in the world -- the valleys tend to narrow and widen, and fish appear to love that. They seem to respond to the heterogeneity that is so inherent in most real landscapes. Nature is messy, and the fish have adapted to that."
Roering used LiDAR in previous research, including a project in which he and colleagues disc
|Contact: Jim Barlow|
University of Oregon