Explaining Variations in the Onset of Sediment Motion
A Warren Distinguished Lecture with
Elowyn Yager
Civil and Environmental Engineering, University of Idaho
"Finding a Signal in the Noise: Using Turbulence, Bed Structure, and AI to Explain Variations in the Onset of Sediment Motion"
Abstract
Thresholds of sediment motion are integral to bedload transport estimates, which inform calculations of aquatic habitat, bridge pier scour, reservoir sedimentation, channel stability, and landscape evolution. Despite often being assumed constant, the critical Shields stress (stress needed to cause sediment motion), can vary by an order of magnitude between different gravel-bedded streams and even within the same river over time. This noise in critical Shields stresses obscures the mechanics of grain motion including the spatial and temporal variation of key processes that affect particle mobility. Using a combination of laboratory experiments, field measurements, and numerical modeling, Yager quantifies some of the key controls on particle motion. She specifically highlights the influence of flow turbulence and bed structure in controlling particle transport and incorporates aspects of these controls into a mechanistic theory. The theory is combined with simple photogrammetry and AI particle detection techniques to have an informed estimate of the onset of motion in any gravel bedded river. Her results demonstrate that much of the noise in critical Shields stresses can be explained by including grain-scale mechanics in reach-scale estimates of sediment motion.
Speaker
Elowyn Yager is a Professor in the Department of Civil and Environmental Engineering and the co-director of the Center for Ecohydraulics Research at the University of Idaho. Yager obtained her BS in Geology at SUNY Buffalo and her Ph.D. in Geology at the University of California at Berkeley. Yager’s research is focused on understanding the mechanics of geomorphic processes from the grain- to landscape scale including sediment and nutrient transport, post-fire hillslope erosion, bedrock erosion, and interactions between physical and ecological processes. She has received several awards for her research, teaching, and outreach including a National Science Foundation Career Award and a Fulbright Fellowship.
