UBC Theses and Dissertations

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UBC Theses and Dissertations

A stream in transition : short term morphodynamics of Fishtrap Creek following wildfire Andrews, Christie


In August 2003, a wildfire burned through Fishtrap Creek Watershed north of Kamloops British Columbia. This high intensity fire killed almost all the trees within the burned area, including 90% of the riparian vegetation in the vicinity of our study site. The fire did not significantly alter the duration or magnitude of the peak flows within this creek, nor did it have substantial effects on the total suspended sediment concentrations. Changes in channel morphology during the first two years after the fire were minor. The first evidence of morphologic adjustment occurred in 2006 when the channel began to widen and develop very distinct channel bars - adopting a characteristically riffle pool morphology by the end of the 2006 freshet. The most dramatic channel reconfiguration occurred during the 2007 freshet, when the channel widened by as much as 15 m in places. Approximately 82% of the total volume of large wood (LW) recruited to the channel following the fire entered the channel as a result of bank erosion, and the majority of the bank erosion occurred during the 2007 flood season. The post-fire wood load in Fishtrap Creek is slightly higher than other disturbed systems, but is comparable to wood load in undisturbed rivers. LW has had significant influence on channel morphology and bed surface texture distribution. The number of LW pieces of wood in the channel is related to the channel morphology, and 80% of the pools are a result of LW. Most of the post-fire wood is suspended above the channel bed and is not currently functioning in the channel as effectively as pre-fire wood. Estimates of net erosion and deposition were made based on Digital Elevation Models (DEMs) and cross-sections located at regular intervals: a comparison of the two methods shows that cross-sectional analysis results in biased estimates of net erosion and deposition in various, identifiable circumstances, while revealing the same general pattern of channel change within the study reach.

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