EAR-PF: Quantifying the effects of flow transience on sediment transport

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Dr. Colin Phillips has been awarded an NSF Earth Sciences Postdoctoral Fellowship to carry out a research and educational outreach plan at the University of Minnesota. He will investigate the process of gravel transport in response to transient and intermittent flooding. Gravel rivers represent the rate limiting step in the incision of mountains and also provide critical habitat and breeding grounds to numerous aquatic species. These experiments will form the basis for understanding how potential changes in climate and land use will affect gravel streams. In addition these experiments will provide a quantitative framework for stream managers regulating flow releases below dams and stream restoration projects. The results from these experiments will be turned into interactive online tools for stream restoration practitioners. Furthermore, the knowledge gained from this project will be transferred to young scientists through classes and experiments during the National Center for Earth Surface Dynamics 2 (NCED2) Summer Institute, and to future young scientists by collaborating with NCED2 REU students.A large majority of our understanding of gravel river dynamics comes from flume experiments under constant or slowly varying floods. Many of the theories developed under steady flow provide reasonable predictions of the dynamics of gravel rivers when averaged over numerous floods, however due to the stochastic nature of sediment transport it remains unclear whether these predictions break down due to flow unsteadiness or granular phenomena. Through the use of laboratory experiments he will test the relative importance of flood shape and sequence to determine how an unsteady flow drives sediment transport. This project will compare the dynamics of gravel transport at the particle level through the tracking of several populations of marked particles under a variety of single and sequences of flows of varying magnitude and duration, but equivalent impulse (time-integrated momentum above the threshold of particle motion).