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UBC Theses and Dissertations

Quantifying the variability in forest stream channel morphology Trainor, Kristie Marie

Abstract

Within forests, large variability exists in stream channel morphology. Recognizing this variability is important when attempting to characterize, quantify and/or compare stream channels. This point becomes extremely significant when considering the idea of "restoring" streams, a concept which seems to imply an ideal or "target" state. The idea of target states is intricately connected to stream channel variability, and it is this variability which is explored in this project. The study design incorporates comparison of stream channels, the drainage basins of which have similar biophysical, morphometric, and hydroclimatic characteristics. These characteristics are all known to affect or exert considerable influence on the processes which occur in forest streams. Numerous contingencies may also affect channel morphology locally. The key research objective is to determine the range of variability that these streams (under similar basic governing conditions and theoretically similar channel morphologies) possess. Nine stream channel characteristics (channel unit frequency, channel unit length, pool spacing, depth variability, width variability, LWD jam spacing, LWD volume, relative roughness, and average bankfull width [used as a surrogate for scale]) are measured in 12 old growth reaches and 6 managed reaches in the Queen Charlotte Islands and Vancouver Island. The data are split into six groups: all old-growth, uncoupled old-growth (stream is buffered from hillslopes by floodplain), coupled old-growth (stream receives material directly from adjacent hillslopes), selected old-growth, managed, and 'old-growth vs. managed'. Within each group, the stream channel characteristics can be analyzed by calculating the dissimilarity (a form of Euclidean distance measure) for all possible reach pair combinations. Frequency distributions based on the resulting dissimilarity values are constructed for each group. These distributions express the range of variability present in the streams analyzed. The resulting range of dissimilarity values precludes the definition of a single, ideal target state. However, the dissimilarity method of comparing stream channel reaches does enable definition of ranges of desirable or undesirable states and quantification of impact. Dissimilarity values for the 'all old-growth' reach pair group ranged from 2.73 to 10.92. For this reach pair group high dissimilarity was judged to be greater than or equal to 8.56. This value does not by any means constitute a regional reference dissimilarity value, as the sample size is simply too small. Reach pairs exhibiting high dissimilarity values tend to have significant differences in several key stream channel characteristics. These key stream channel characteristics vary between reach pairs. Those reaches consistently appearing in reach pairs with high dissimilarity values are considered 'severely impacted' (within this system of comparison).

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