Linking sediment supply, channel morphology, and aquatic habitat in forested, gravel-bed streams : spatial and temporal considerations

Gravel-bed streams in mountain environments are complex systems which respond unpredictably to episodic inputs of sediment from hillslopes. Stream channel response to episodic sediment supply has implications for channel morphology, stability, and aquatic habitat. While insight into the behaviour of these systems can be gained from numerical models and physical experiments, a paucity of long-term, comprehensive, and multi-scale field data has limited researchers’ ability to describe channel response to episodic sediment supply, and to situate this response in a broader landscape context. This thesis aims to overcome these limitations by examining long-term channel dynamics in response to episodic sediment supply and variable wood loading and then linking this variability to modeled aquatic habitat for juvenile salmonids. A 45 year field dataset from Carnation Creek, a small forested, gravel-bed stream located in a deglaciated catchment on coastal British Columbia, is used for analysis. Results indicate that temporal patterns of sediment storage are governed by the sediment conditions and local erosional and depositional processes, while spatial patterns are associated with sediment travel distance statistics. A conceptual model is proposed which presents channel response to episodic supply as a function of channel position downstream relative to colluvial input. In-stream wood is also found to influence channel morphology: logjams impact sediment throughput and lead to locations of elevated sediment storage, which decay exponentially over a 10-20 year period. A wood budget model indicates that wood loads will take up to 200 years to recover following riparian timber harvesting, with long-lasting implications for channel morphology. Modeled habitat for juvenile salmonids, simulated using Carnation Creek topographic and wood data, is found to vary through time by up to a factor of ten as a function of variable channel morphology and wood abundance. These results are found to support a conceptual model which links the contribution to habitat variability from channel morphology to a watershed’s sediment supply regime. Collectively, this work has improved our understanding of how episodic sediment supply and wood impact channel morphology, sediment storage, and aquatic habitat in a forested, gravel-bed stream over the long term.Arts, Faculty ofGeography, Department ofGraduat