Large- and Small-Scale Controls on Sediment Transport Processes

Rebecca Hodge

Bio: Rebecca Hodge completed her first degree in Geography and Earth Sciences at Durham University and received a PhD from the University of Cambridge. She then completed a post-doc position at the University of Glasgow, before returning to Durham in 2011 where she is now a professor in the Department of Geography. She is interested in developing new approaches for understanding flow and sediment transport in river systems, and uses methods including field data, physical and numerical modelling.

Dr. Hodge will address smaller-scale controls on sediment transport processes. Predicting rates of sediment transport in rivers is a long established problem in geomorphology. However, the complexities of the interactions between channel morphology, flow and sediment transport mean that our predictions still contain a considerable degree of uncertainty. In this talk I will outline how we have used novel approaches to get new insights into sediment transport processes, specifically critical shear stress. These approaches include using 3D printing to take rivers into the laboratory and using CT scanning to quantify the 3D structure of gravel beds. From this work we have demonstrated the importance of protrusion in controlling critical shear stress, evaluated different methods for measuring protrusion, and quantified how bedrock topography affects critical shear stress.

Desiree Tullos, Ph.D., P.E. (OR)

Bio: Desiree Tullos is a Professor in the Biological and Ecological Engineering Department at Oregon State University. Her research emphasizes the sustainable engineering and management of rivers by examining the intersections of hydraulics, infrastructure, ecology, and society. Projects include a) river responses to dam removal; b) analysis of reservoir operations in systems undergoing change; c) Ecohydraulics, and d) Sustainable flood risk management and nature-based solutions. Her research program heavily emphasizes engaging and mentoring undergraduate students in research with societal relevance. She also serves on multiple boards and science and engineering advisory panels to help translate science into practice and policy.

Drawdown operations at reservoirs involve draining a reservoir to let a river act like a river again, and can be critically important for maintaining ecosystems and addressing aging infrastructure. They also provide a unique opportunity to study the complex and coupled sediment transport processes that occur with base level lowering. The design of drawdowns and the resulting flushing of sediments has important implications for ecosystems and reservoir sustainability, but the science on these coupled erosional processes is still in its early stages. This talk will summarize the context for drawdown operations, the various sediment transport processes involved, what we’ve learned so far, with emphasis on lateral retrogression during drawdown, and what scientific questions remain.