Graduate Thesis Or Dissertation
 

The effect of the size and orientation of large wood on pool volume in two Oregon Coast Range streams

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https://ir.library.oregonstate.edu/concern/graduate_thesis_or_dissertations/r781wj03t

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  • This study was conducted to determine how the size and orientation of large wood placed in streams in combination with peak flows, substrate and channel gradient affect pool volume, surface area and maximum depth in two coastal Oregon streams. Eighteen Douglas-fir (Pseudotsuga menziesii) logs were placed in each of two streams, J-Line Creek and Preacher Creek, in the summer of 1989. Surveys were conducted annually from 1989-1996 at summer low flow using a total station electronic theodolite. The orientation of the introduced wood and the parameters of residual pools associated with the wood were determined from high resolution topographic maps made from the surveys. Residual pool volume associated with the introduced wood increased 2,500 percent over the seven years for J-Line Creek and 30 percent for Preacher Creek. Large spanners, logs placed perpendicular to the stream flow and flush with the stream bottom, had the greatest pool volume associated with them, however horizontal orientations shifted downstream over time. Large ramps, logs placed at a downstream orientation and angled up onto the bank, were the most stable treatment. Differences between the two watersheds and an interaction variable between the diameter of the introduced wood and the horizontal orientation of the introduced wood were the significant variables which entered the multiple linear regression model for residual pool volume. These variables, as well as the vertical orientation of the introduced wood, were significantly correlated to both residual pool surface area and maximum depth. The recurrence interval of the annual maximum instantaneous peak flow was not significantly associated with residual pool volume, surface area nor maximum depth. Multiple regression models explained, at most, twenty-eight percent of the variability in residual pool volume, maximum depth and surface area. Estimates of pool volume obtained with aquatic habitat inventories (Bisson et al., 1982) were compared with residual pool calculations determined from the topographic maps. Pool volume in a reach determined by aquatic habitat inventories explained 96 percent of the variability of residual pool volume in a reach, however estimates of individual pool volume explained only 40 percent of the variability in residual pool volume.
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