Vertical Sorting of Bed Material in Gravel-Bed Streams-- Insights From Long-Term Observations in East Creek, British Columbia

The vertical sorting of streambed grains is a key control on river channel stability and sediment transport rates. In this study, we report on burial depths and mobility characteristics of coarse sediment in a small gravel-bed stream using an extensive data set of nearly 1,500 magnetically tagged tracer grains, deployed and annually surveyed between 2004 and 2018. We observe that sediment burial correlates with grain size and event magnitude, and we identify correlations between the burial depths of coarse grains and their mobility, residence time, and travel distance characteristics. A particularly large event in 2007 produced significant vertical sorting which affected tracer mobility and travel distance for the remaining study duration, despite numerous subsequent sediment-mobilizing events. These insights into the linkages between grain size, event magnitude, sediment burial, and sediment transport have potential to improve our ability to predict sediment transport rates and channel stability characteristics using tracer studies.