INITIATION OF MOTION TO ANTIDUNES: NEW VIDEOS OF THE STANDARD BEDFORM PROGRESSION FOR EDUCATORS

Since G.K. Gilbert (1914) ran sediment through his flume at Berkeley, there has been a rich tradition in sedimentology, geomorphology, and engineering of flume experiments on bedforms. These experiments reached their pinnacle in those conducted at M.I.T. in John Southard’s lab during the 1970s, where a wide range of sediment sizes, velocities, and flow depths were carefully analyzed to create bedform phase diagrams. It would be fair to say that nearly every geology student is introduced to bedforms and their sedimentary products at some point in their undergraduate career and that bedforms and bedform phase diagrams support a fundamental understanding of sediment transport in just about every sedimentology course. Most of these students, however, lack access to a flume to conduct these types of experiments. Video of sediment transport, bedforms and their motion are available through online resources, but they are piecemeal at best. The geoscience community lacks a set of quality videos that show the entire bedform progression from initiation of motion through antidunes under well-controlled conditions. We captured video of bedform dynamics using a large (L=9.1, W=0.5, D=0.7m) non-recirculating flume at the St. Anthony Falls Laboratory at the University of Minnesota. Normal speed, high speed, and slow motion video were shot for each bed state: initiation of motion, small ripples, large ripples/dunes, upper plane bed. In addition, we used an acoustic Doppler velocimeter to capture velocity profiles at each bed state and used precise measurements of discharge and flow depth to derive mean flow velocity. The large flume was not capable of producing antidunes. Hence, we used a smaller, tilting bed flume to capture examples of sediment transport in the super-critical flow regime. We ran experiments using two different grain sizes to capture the full range of bed states. These video and velocity data have been compiled into a single, well-documented dataset that we plan to make available to the geoscience community for teaching purposes. As part of this presentation, we would like to solicit feedback from the community on ways to improve or modify this dataset to make it most effective for wide adoption and use.