Tracking Growth and Movement of the Slave River Log Jam

• Main Author: Hess-Homeier, Brooke E.
• Format: Text
• Language: unknown
• Published: ScholarWorks at University of Montana 2016
• Subjects: Great Slave Lake; Northwest Territories; Slave Lake; Slave River
• Online Access: https://scholarworks.umt.edu/umcur/2016/pmposters/32

Large wood accumulations in rivers, called log jams, influence channel morphology and flow processes. My research investigates a large log jam on a side channel of the Slave River. The Slave River flows north through northern Alberta and the Northwest Territories where it empties into the Great Slave Lake. The Slave River is 3km wide, and has average peak summer flows of 6,000m3/s. The objective of my research is to map the growth of the log jam in the upstream direction as logs float downstream from their origin and get trapped in the log jam on the upstream end. I am using field data including tree cores, log lengths and diameters, vegetation data, and aerial imagery spanning from 1930-2015. Through aerial imagery analysis using ArcGIS, I have determined an average rate of upstream log jam growth of 2.4 meters per year. However, this growth does not happen at an average rate, but rater through yearly episodic influxes of wood. I have observed morphological changes in the channel meanders downstream of the log jam including the formation of new islands and channel banks from vegetation growing out of decaying log jam materials. I have collected tree cores from Spruce trees growing out of decaying log jam material at the downstream end of the log jam, as well as one from the upstream end of the log jam. The Spruce at the downstream end average 40 years old, while the Spruce at the upstream end is 3 years old. Since it takes roughly three years for vegetation to sprout in deposited logs, this indicates at least a 43 year timespan for the deposition of 103 meters of log jam between the downstream tree cores and the upstream tree core, confirming the rate of episodic log jam growth of roughly 2.4 meters per year.