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Undercut streambanks in forested headwater streams of the Oregon coast range

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dc.contributor.advisor Beschta, Robert L.
dc.creator Salminen, Edward M.
dc.date.accessioned 2008-11-14T21:09:45Z
dc.date.available 2008-11-14T21:09:45Z
dc.date.issued 1990-09-19
dc.identifier.uri http://hdl.handle.net/1957/9758
dc.description Graduation date: 1991 en_US
dc.description.abstract This study was undertaken to evaluate the occurrence and characteristics of undercut streambanks in forested headwater streams of the Oregon Coast Range. Undercut streambanks and associated reach characteristics were surveyed along 46 sample reaches (each 152 m in length) in 8 streams; all sample reaches occurred in unmanaged forested riparian areas. Drainage areas ranged from 0.3 to 16.6 km^2. At each undercut location length, surface area, volume, low-flow (summertime) volume, and maximum horizontal depth were measured. Individual undercuts had surface areas ranging from 0.3 to 27.7 m^2 with a mean value of 2.6 m^2, and lengths ranging from 1.2 to 15.2 m with a mean value of 5.0 m. The area undercut streambanks ranged from 0.0 to 27.4 m^2 / 100 m of stream, with an average value of 6.5 m^2 / 100 m. The proportion of bankfull channel area undercut ranged from 0.0 to 4.5%, with an average value of 1.1%. Reach length undercut ranged from 0.0 to 23.6%, with an average value of 6.2%. The values reported in this study are approximately mid-range in comparison to characteristics of undercut banks reported in studies from Alaska, Montana, and Wisconsin. The % of reach area covered by undercut streambanks in this study is approximately half of that provided by large woody debris. Outside channel bends had approximately 6 times more undercut streambanks than inside bends or straight sections. Streams having a sinuosity index greater than 1.15 averaged approximately twice as much % surface area undercut than streams having a sinuosity index less than 1.15. Number of undercuts and undercut characteristics were inversely correlated with channel gradient; significant differences occurring among 1%, 2-4%, and 5+% channel gradient classes. Streambanks ranging in height from 1-2 m had a higher occurrence of undercut streambanks than either lower or higher streambanks. Undercut streambanks were 4 times more common in "composite" than "non-composite" streambanks. Undercut characteristics appear to be correlated with valley segment type. Channel widths were, on average, significantly narrower at undercut sites when compared to reach average channel widths. However, it does not appear than width characteristics are a cause of undercutting. Based on field observations it appears that flow obstructions (gravel bars, boulders, large woody debris) have little impact on undercut characteristics. Both at-a-site and reach-level comparisons of undercut bank characteristics showed relatively strong correlations with streamside tree densities. Red alder (Alnus rubra) is the most prevalent species found in Coast Range riparian areas, and the most significant species in explaining reach-level differences in undercut characteristics. Sitka spruce (Picea sitchensis) is less common in riparian zones, but appears to be positively correlated with the proportion of reach area undercut. en_US
dc.language.iso en_US en_US
dc.relation Explorer Site -- Oregon Explorer en_US
dc.subject.lcsh Rivers -- Oregon en_US
dc.subject.lcsh Rivers -- Coast Ranges en_US
dc.subject.lcsh Embankments en_US
dc.title Undercut streambanks in forested headwater streams of the Oregon coast range en_US
dc.type Thesis en_US
dc.degree.name Master of Science (M.S.) in Forest Engineering en_US
dc.degree.level Master's en_US
dc.degree.discipline Forestry en_US
dc.degree.grantor Oregon State University en_US

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