Graduate Thesis Or Dissertation
 

Reach scale sampling metrics and longitudinal pattern adjustments of small streams

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https://ir.library.oregonstate.edu/concern/graduate_thesis_or_dissertations/z603r052b

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  • Several types of channel morphology measurement parameters used to characterize fish habitat of small streams are refined, developed and evaluated in terms of their accuracy, precision, and sensitivity to disturbance. Data for 74 stream reaches in Oregon and Alaska are used in analysis. Over half the reaches are from a pre-pilot study funded by EPA's Environmental Monitoring and Assessment Program (EMAP). A new methodology for determining residual pools is developed (termed the Longitudinal Streambed Simulation Method). This new method and an older method are compared with a more rigorous time consuming method for determining residual pools. Results indicate a generally close correspondence. For instance, the absolute percent departure of longitudinal residual pool area was typically within 10% and always less than 25% for streams with wetted widths greater than 3.5 meters. Precision is evaluated for three data sets containing replicated stream reach measurements. Directly measured parameters like standard deviation depth are demonstrated as precise and repeatable. In contrast, visual scoring systems and visual determinations of riffles versus pools have low precision. Adequate reach length for determining various channel characteristics is evaluated by using classic sample size statistics, time series, and short versus long reach comparisons. Results suggest that reach lengths of 30-40 channel widths with 2-3 measurements per wetted channel width seem to provide adequate coverage to determine residual pools. However, simple determinations of mean depth or width can be spaced as wide as two channel widths apart without significant accuracy loss. While many relationships regarding pool formation versus riparian and watershed characteristics are evaluated, probably the most intriguing result is the influence roughness (large woody debris) has on the formation of residual pools and in increasing variation in systematically placed depth measurements along the stream. The results also suggest a range of channel slope in which variability in these depth measurements is maximized (0.5-6.0% slope). These results provide valuable information for anyone attempting to develop, implement, or analyze data from a monitoring protocol that evaluates channel morphology or morphological fish habitat. Information on the residual pool concept and how to use it in monitoring is also provided.
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